全文获取类型
收费全文 | 154439篇 |
免费 | 9224篇 |
国内免费 | 815篇 |
专业分类
林业 | 6465篇 |
农学 | 5431篇 |
基础科学 | 1212篇 |
19214篇 | |
综合类 | 27383篇 |
农作物 | 5790篇 |
水产渔业 | 7784篇 |
畜牧兽医 | 79559篇 |
园艺 | 2140篇 |
植物保护 | 9500篇 |
出版年
2020年 | 1395篇 |
2019年 | 1743篇 |
2018年 | 2550篇 |
2017年 | 2923篇 |
2016年 | 2650篇 |
2015年 | 2402篇 |
2014年 | 2817篇 |
2013年 | 6011篇 |
2012年 | 5087篇 |
2011年 | 6244篇 |
2010年 | 4178篇 |
2009年 | 4019篇 |
2008年 | 5782篇 |
2007年 | 5461篇 |
2006年 | 5176篇 |
2005年 | 4654篇 |
2004年 | 4308篇 |
2003年 | 4412篇 |
2002年 | 4072篇 |
2001年 | 5086篇 |
2000年 | 4991篇 |
1999年 | 3897篇 |
1998年 | 1596篇 |
1997年 | 1592篇 |
1996年 | 1379篇 |
1995年 | 1575篇 |
1994年 | 1434篇 |
1993年 | 1417篇 |
1992年 | 2992篇 |
1991年 | 3250篇 |
1990年 | 3083篇 |
1989年 | 3080篇 |
1988年 | 2741篇 |
1987年 | 2797篇 |
1986年 | 2840篇 |
1985年 | 2607篇 |
1984年 | 2211篇 |
1983年 | 1876篇 |
1982年 | 1296篇 |
1979年 | 1926篇 |
1978年 | 1535篇 |
1976年 | 1297篇 |
1975年 | 1477篇 |
1974年 | 1771篇 |
1973年 | 1721篇 |
1972年 | 1627篇 |
1971年 | 1560篇 |
1970年 | 1549篇 |
1969年 | 1479篇 |
1967年 | 1331篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Reasons for performing study: Infundibular changes are frequently encountered computed tomographic studies of the equine maxillary cheek teeth but the possible importance of this finding is not known. Infundibular caries is a possible cause for pulpitis and apical infection in some horses. Objectives: To study the relationship between the 2 pathologies and the frequency of changes. Methods: The maxillary cheek teeth 108‐ 208 , 109–209 and 110–210 of 25 horses were evaluated using computed tomography and both the prevalence of infundibular and apical infection changes as the possible link with apical infection evaluated statistically. Results: The prevalence of infundibular changes was high in both normal and diseased teeth. Both apical infection and the occurrence of infundibular changes were more prevalent in 109–209 and 110–210. In spite of this, the 2 processes could not be linked to one another. No differences were noted between the left and right sides. Conclusions: A direct relationship between the 2 processes was not established statistically and other underlying causes for the high occurrence of both apical infection and infundibular changes in diseased and normal 108‐ 208 , 109–209 and 110210 are considered. 相似文献
992.
The objectives of the present study were to quantify the amount of nucleic acids, to examine the nucleobase composition and to determine the digestibility of individual nucleobases in diets containing various products from bacterial biomass grown on natural gas, including autolytic and hydrolytic fractions, using mink (Mustela vison) as a model animal. The diets consisted of cod fillet (control), commercial basic BioProtein, and five experimentally produced autolytic and hydrolytic fractions of the bacterial protein meal as protein sources. Each diet was assigned to four adult male mink, housed individually in cages equipped for controlled feeding and quantitative collection of faeces. Faeces were collected for 4 days, and the individual nucleobases in diet and faeces were analysed by HPLC after hydrolysis using HClO(4). The content of nucleobases in the diets containing bacterial protein meal was 37% to 205% higher than in the control diet. The nucleobase-nitrogen in the control diet amounted to 4.3% of the total nitrogen content, whereas the experimental bacterial protein diets contained from 7.4% to 17.4% of the total N content in the form of nucleic acids. The various methods used to produce the bacterial protein fractions clearly affected both the amount of nucleic acids and the molar proportions of the individual nucleobases. The average digestibility of the nucleobases was 95%, and all the individual nucleobases were highly digestible. Uracil showed the highest digestibility (on average 96.8%), whereas thymine showed the lowest digestibility (on average 93.6%). 相似文献
993.
T. C. Hall O. M. Mahony L. M. Freeman E. A. Rozanski 《Journal of animal physiology and animal nutrition》2008,92(2):219-220
The goal of this randomized, double‐blind study was to compare the effects of feeding a low carbohydrate, high protein diet versus a maintenance diet in a group of cats with diabetes mellitus treated with insulin glargine twice daily. All cats with naturally occurring diabetes mellitus not currently treated with insulin glargine or diabetogenic drugs or being fed a low carbohydrate, high protein diet were eligible for inclusion. Baseline testing included a physical examination, complete blood count, serum biochemistry profile, urinalysis and urine culture, serum thyroxine concentration, and serum fructosamine concentration. All cats were treated with insulin glargine (starting dose of 0.25 U/kg) twice daily. Insulin was adjusted as needed for glucose regulation. Cats were randomized to receive either a low carbohydrate, high protein diet or a feline maintenance diet. Re‐evaluations were performed on all cats at weeks 1, 2, 4, 6 and 10, and included an assessment of clinical signs, physical examination, 12‐h blood glucose curve, and serum fructosamine concentrations. Changes in continuous variables over the course of the study were analyzed using analysis of variance with repeated measures. p < 0.05 was considered statistically significant. Ten cats have completed the study. There were no significant differences between diet groups at baseline for age, gender, weight, body condition score, serum glucose or fructosamine concentrations. Although there was not a significant difference over time in clinical signs, insulin doses, or peak or nadir glucose concentrations between diet groups, diet did have a significant effect on serum fructosamine concentrations (p = 0.01). Six of the 10 cats that have completed the study achieved complete remission by the end of the study period, with no statistical difference between diets. The study's results indicate that diet can have significant effects on glucose regulation in cats receiving insulin glargine for treatment of feline diabetes mellitus. 相似文献
994.
A critical analysis of the results of research in the function of the endometrium was carried out and a view point presented. The role of the endometrium in endocrine regulation of the oestrus cycle can be summarized as follows: 1. The transfer of prostaglandin F2α (PGF2α) from the uterus to an ovary, which causes luteolysis, occurs mainly via the lymphatic pathways. 2. The system of retrograde transfer of PGs enables PGF2α and PGE2 to reach the myometrium and endometrium with arterial blood at high concentration. In the luteal phase, PGF2α, together with the increasing concentration of progesterone, constricts the arterial vessels of the uterus; in the follicular phase and in early pregnancy, PGE2 together with oestrogen and embryonic signals, relaxes the arterial vessels. In addition, this system protects the corpus luteum from premature luteolysis during the cycle and luteolysis during early pregnancy. 3. In days 10–12 of the cycle, the blood flow in the uterus decreases by 60–70% in pigs and around 90% in sheep. This causes ischaemia and local hypoxia confirmed by the presence of hypoxia inducible factor and thus remodelling of the endometrium commences. 4. The pulsatile elevations in PGF2α concentration occurring in the blood flowing out of the uterus during the period of luteolysis and the next few days, do not result from increased PGF2α synthesis as suggested in numerous studies. They are the effect of excretion of PGF2α and its metabolites together with lymph and venous blood and tissue fluids in which prostaglandin accumulates. 相似文献
995.
This study was undertaken to investigate the effects of storage of stallion semen in a defined milk protein extender at 5 and 15°C under either anaerobic or aerobic conditions, with or without addition of the antibiotic gentamicin. Semen samples were collected from eight fertile stallions and stored for 96 h (day 0–4) and assessed daily for motility, velocity and membrane integrity (viability) using a CASA system. Samples for bacteriology assessment were taken on day 2 of storage. No significant (p > 0.05) differences in motility, velocity or viability were observed between treatments on days 0–2. On days 3 and 4, semen stored without gentamicin at 5°C had a significantly (p < 0.05) better semen quality compared with storage at 15°C without gentamicin, irrespective of oxygen exposure. On days 3 and 4, motility and velocity were greater in samples stored at 15°C with gentamicin, compared with the corresponding treatments without antibiotic (p < 0.05). This effect was also evident for viability on day 4. The decline in semen quality observed at 15°C most likely resulted from the effect of bacterial growth. Bacterial growth was the greatest in samples stored at 15°C without gentamicin, under both anaerobic and aerobic conditions (p < 0.05). Bacterial growth was inhibited by adding of gentamicin at 15°C, which accordingly reduced the decline in semen quality. Addition of antibiotic to samples stored at 5°C had no significant effect on any parameter analysed. In conclusion, storage at 15°C can be achieved by using an extender containing the antibiotic gentamicin. Storage at 5°C tended to maintain better semen quality irrespective of oxygen exposure, and did not necessitate an antibiotic treatment. 相似文献
996.
De Britto Mari R Clebis NK Gagliardo KM Guimarães JP Stabille SR De Mello Germano R De Souza RR 《Anatomia, histologia, embryologia》2008,37(4):289-295
This study aimed to evaluate the effects of regular physical activity on the morphology of the myenteric plexus of the duodenum in rats during the ageing process. To this end, 45 Wistar rats were divided into three groups: C (sedentary – 6 months old), S (sedentary – 12 months old) and T (trained – 12 months old). The animals of group S were given with a physical activity programme consisting of a 10-min-treadmill workout once a week. The animals of group T were submitted to the physical activity programme five times a week. Their duodenums were collected and submitted to the techniques of nicotinamide adenine dinucleotide (NADH)-diaphorase enzyme histochemistry for whole-mount preparations and transmission electron microscopy. No differences in the constitution of the myenteric plexuses were found when the sedentary and trained groups were compared with the control group. The ultrastructural features were similar for the three groups. However, it was verified that the physical activity of the trained animals resulted in a similar myenteric neuron morphology to that of the adult animals (6 months old), thereby confirming its beneficial effect, as the sedentary animals had larger alterations in the collagen fibrils and the basal membrane that occur through ageing. The quantitative analysis showed that the NADH-diaphorase positive neurons decreased with ageing and increased with physical activity ( P > 0.05). No significant alteration ( P > 0.05) in the neuronal profile area of the NADH-diaphorase positive neurons has been observed with ageing. 相似文献
997.
J.M. Snyder L. Lipitz K.A. Skorupski F.S. Shofer T.J. Van Winkle 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2008,22(1):172-177
Background: This study investigates the frequency, location, and clinical findings associated with 177 secondary brain tumors in dogs.
Hypothesis: Secondary intracranial neoplasia is more common than primary intracranial neoplasia in dogs during the time period studied, and hemangiosarcoma (HSA) is the most common secondary intracranial tumor.
Animals: One hundred and seventy-seven client-owned dogs presented to the Matthew J. Ryan Veterinary Hospital between 1986 and 2003.
Methods: Medical records were searched for a diagnosis of intracranial neoplasia in dogs who underwent complete postmortem examination. Of these dogs, those with a diagnosis of primary intracranial neoplasia were excluded.
Results: Of the 177 secondary brain tumors, 51 (29%) were HSAs, 44 (25%) were pituitary tumors, 21 (12%) were lymphosarcomas, and 21 (12%) were metastatic carcinomas. The average age at diagnosis was 9.6 ± 3.0 years. Most tumors were located in the cerebrum, and a mentation change was the most common presenting clinical sign. On postmortem examination, the same tumor that was in the brain was also present in the lung in 84 cases (47%), in the kidney in 62 cases (35%), and in the heart in 55 cases (31%).
Conclusions and Clinical Importance: Secondary intracranial neoplasia in dogs was more common than primary intracranial neoplasia during the time period studied. Many of these dogs had related disease in other body systems that was apparent on diagnostic tests such as thoracic radiography. 相似文献
Hypothesis: Secondary intracranial neoplasia is more common than primary intracranial neoplasia in dogs during the time period studied, and hemangiosarcoma (HSA) is the most common secondary intracranial tumor.
Animals: One hundred and seventy-seven client-owned dogs presented to the Matthew J. Ryan Veterinary Hospital between 1986 and 2003.
Methods: Medical records were searched for a diagnosis of intracranial neoplasia in dogs who underwent complete postmortem examination. Of these dogs, those with a diagnosis of primary intracranial neoplasia were excluded.
Results: Of the 177 secondary brain tumors, 51 (29%) were HSAs, 44 (25%) were pituitary tumors, 21 (12%) were lymphosarcomas, and 21 (12%) were metastatic carcinomas. The average age at diagnosis was 9.6 ± 3.0 years. Most tumors were located in the cerebrum, and a mentation change was the most common presenting clinical sign. On postmortem examination, the same tumor that was in the brain was also present in the lung in 84 cases (47%), in the kidney in 62 cases (35%), and in the heart in 55 cases (31%).
Conclusions and Clinical Importance: Secondary intracranial neoplasia in dogs was more common than primary intracranial neoplasia during the time period studied. Many of these dogs had related disease in other body systems that was apparent on diagnostic tests such as thoracic radiography. 相似文献
998.
999.
Elizabeth A. Giuliano Ian MacDonald† Dudley L. McCaw‡ Thomas J. Dougherty† Gia Klauss§ Juri Ota Jacqueline W. Pearce Philip J. Johnson 《Veterinary ophthalmology》2008,11(S1):27-34
Objective Local photodynamic therapy (PDT) is a novel cancer therapy in veterinary ophthalmology. A prospective pilot study seeking to demonstrate proof of principle and safety for the treatment of equine periocular squamous cell carcinoma (PSCC) was therefore conducted. We hypothesized that surgical excision with adjunctive local PDT is an effective and safe treatment for equine PSCC.
Procedures Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength diode laser. Regular follow-up ophthalmic examinations were performed.
Results Surgical resection and PDT yielded disease-free intervals of 25–68 months in our study horses as of January, 2008. These results were obtained following a single treatment in seven horses and two treatments in one horse. In one horse, carcinoma in situ developed 2.5 months after partial surgical excision and PDT, requiring local excision under standing sedation.
Conclusions Preliminary results suggest that surgical resection and adjunctive local PDT is a safe and effective novel treatment for PSCC in horses. More research is needed before PDT for the treatment of equine PSCC can be adequately compared with other current modalities. Important to future investigations regarding PDT, tumor recurrence rate, length of hospitalization, number of treatment episodes required to effect tumor remission, and total treatment costs should be examined in a controlled manner. Our present results and experiences suggest that this treatment may be useful in the treatment of equine PSCC. 相似文献
Procedures Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength diode laser. Regular follow-up ophthalmic examinations were performed.
Results Surgical resection and PDT yielded disease-free intervals of 25–68 months in our study horses as of January, 2008. These results were obtained following a single treatment in seven horses and two treatments in one horse. In one horse, carcinoma in situ developed 2.5 months after partial surgical excision and PDT, requiring local excision under standing sedation.
Conclusions Preliminary results suggest that surgical resection and adjunctive local PDT is a safe and effective novel treatment for PSCC in horses. More research is needed before PDT for the treatment of equine PSCC can be adequately compared with other current modalities. Important to future investigations regarding PDT, tumor recurrence rate, length of hospitalization, number of treatment episodes required to effect tumor remission, and total treatment costs should be examined in a controlled manner. Our present results and experiences suggest that this treatment may be useful in the treatment of equine PSCC. 相似文献
1000.
Barbato O Sousa NM Klisch K Clerget E Debenedetti A Barile VL Malfatti A Beckers JF 《Research in veterinary science》2008,85(3):457-466
The present study describes the isolation and characterization of new pregnancy-associated glycoprotein molecules (PAG) from midpregnancy and late-pregnancy placentas in the water buffalo (Bubalus bubalis). After extraction, the homogenates are subjected to acid and ammonium sulfate precipitations followed by DEAE chromatography. Subsequently, the water buffalo PAG (wbPAG) from these solutions are enriched by Vicia villosa agarose (VVA) affinity chromatography. As determined by western blotting with anti-PAG sera, the apparent molecular masses of the immunoreactive bands from the VVA peaks range from 59.5 to 75.8 kDa and from 57.8 to 73.3 kDa in the midpregnancy and late-pregnancy placentas, respectively. Amino-terminal microsequencing of the immunoreactive proteins has allowed the identification of three distinct wbPAG sequences, which have been deposited in the SwissProt database: RGSXLTIHPLRNIRDFFYVG (acc. no. P85048), RGSXLTILPLRNIID (acc. no. P85049), and RGSXLTHLPLRNI (acc. no. P85050). Their comparison to previously identified proteins has shown that two of them are new because they have not been described before. Our results confirm the suitability of VVA chromatography for the enrichment of the multiple PAG molecules expressed in buffalo placenta. 相似文献