全文获取类型
收费全文 | 56060篇 |
免费 | 3139篇 |
国内免费 | 35篇 |
专业分类
林业 | 3063篇 |
农学 | 1736篇 |
基础科学 | 243篇 |
7104篇 | |
综合类 | 10333篇 |
农作物 | 2256篇 |
水产渔业 | 2819篇 |
畜牧兽医 | 27400篇 |
园艺 | 664篇 |
植物保护 | 3616篇 |
出版年
2019年 | 541篇 |
2018年 | 1000篇 |
2017年 | 1078篇 |
2016年 | 956篇 |
2015年 | 823篇 |
2014年 | 1023篇 |
2013年 | 2129篇 |
2012年 | 1882篇 |
2011年 | 2084篇 |
2010年 | 1290篇 |
2009年 | 1336篇 |
2008年 | 1919篇 |
2007年 | 1947篇 |
2006年 | 1757篇 |
2005年 | 1666篇 |
2004年 | 1577篇 |
2003年 | 1537篇 |
2002年 | 1425篇 |
2001年 | 1647篇 |
2000年 | 1580篇 |
1999年 | 1295篇 |
1998年 | 484篇 |
1997年 | 490篇 |
1996年 | 485篇 |
1995年 | 537篇 |
1994年 | 481篇 |
1993年 | 492篇 |
1992年 | 940篇 |
1991年 | 939篇 |
1990年 | 926篇 |
1989年 | 948篇 |
1988年 | 877篇 |
1987年 | 920篇 |
1986年 | 903篇 |
1985年 | 908篇 |
1984年 | 734篇 |
1983年 | 662篇 |
1979年 | 654篇 |
1978年 | 544篇 |
1977年 | 465篇 |
1976年 | 470篇 |
1975年 | 508篇 |
1974年 | 693篇 |
1973年 | 611篇 |
1972年 | 681篇 |
1971年 | 673篇 |
1970年 | 602篇 |
1969年 | 595篇 |
1968年 | 457篇 |
1967年 | 521篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Lopes Júnior ES Cruz JF Teixeira DI Lima Verde JB Paula NR Rondina D Freitas VJ 《Veterinary research communications》2004,28(2):119-125
The prevalence of pseudopregnancy over 44 months was investigated in 23 Saanen goats raised in Northeast Brazil during continuous oestrous cycling (cyclic group) or after synchronization of oestrus (synchronized group). The goats were monitored by ultrasonography and their plasma progesterone profile. The overall prevalence of pseudopregnancy was 30.4% (7/23). In the cyclic group, 28.6% (4/14) of goats showed pseudopregnancy, while in the synchronized group the prevalence was 33.3% (3/9). There was no significant difference between the groups (p>0.05). The mean (+/- SD) length of pseudopregnancy, as shown by the progesterone profile, was 121.6 +/- 33.5 days, ranging from 70 to 155 days. The study defined the prevalence of pseudopregnancy in Saanen goats raised in Northeast Brazil for the first time. This finding identified a major problem for this breed, as without treatment such animals remain unproductive until the spontaneous resolution of the condition. More research seems desirable to ascertain the prevalence of this condition in other breeds in this region of Brazil. 相似文献
942.
An 11-year-old, male castrated, Labrador Retriever was evaluated for the presence of rapidly growing concurrent leg and intraocular masses. Metastasis was noted in the chest at time of initial presentation. Indium-111 labeled vitamin B12 imaging was performed, and there was significant uptake by both primary tumors and the lung metastases. Enucleation and amputation were performed for palliative relief. The leg mass was a grade 2 soft tissue sarcoma and the ocular mass a ciliary adenoma. The dog remained symptom-free for approximately 10 weeks before developing signs of respiratory distress. He was euthanized 12 weeks after initial presentation, and there was diffuse infiltration of the lungs with metastatic sarcoma. Indium-111 labeled vitamin B12 imaging identified a ciliary adenoma in this case and may provide a useful differentiation technique for evaluation of intraocular and retrobulbar masses if it can be demonstrated that there is differential uptake between inflammatory or infectious conditions and neoplasia. 相似文献
943.
The primary objective of this study was to demonstrate the utility of a hierarchical Bayes implementation of a multiple-breed animal model (MBAM) to estimate breed composition means and additive genetic variances as well as on variances due to the segregation between breeds. The MBAM and a conventional animal model (AM) were both applied to five simulated data sets derived from each of two different populations. Population I consisted of crosses between two breeds having a twofold difference in genetic variance and a nonzero segregation variance. Population II had the same population structure as Population I, except that the two breeds had the same genetic variance with no segregation variance; that is, Population II was essentially single breed in its genetic architecture. For Population I, posterior means of all variance components obtained by MBAM were unbiased, with 95% posterior probability intervals (PPI) having the expected coverage based on five replicates. The MBAM showed a slightly superior performance over the AM for genetic predictions in Population I, although there was no evidence that the use of the MBAM translated into greater genetic gains relative to the use of the AM. Nevertheless, the MBAM was clearly demonstrated to have superior fit to the data using pseudo-Bayes factors (PBF) as the basis for model choice. As expected, the MBAM and AM performed equally well in Population II. A data set consisting of 22,717 postweaning gain (PWG) records of a Nelore-Hereford population (40,082 animals in the pedigree) also was analyzed. The MBAM inference on Nelore and Hereford additive heritabilities (h2A) substantially differed. Herefords had a posterior mean h2A of 0.20 with a 95% PPI of 0.15 to 0.25, whereas the corresponding values for the Nelores were 0.07 and 0.04 to 0.11, respectively. The posterior mean genetic variance due to the segregation between these breeds was 8.4 kg2, with a 95% PPI of 2.3 to 24.8 kg2, and represented 35.4% of the Nelore but only 9.9% of the Hereford posterior mean genetic variance. The posterior mean h2A using the AM was 0.15, presumed common across the two breeds, with a 95% PPI of 0.11 to 0.19. The PBF heavily favored the MBAM over the AM for the PWG data. Accordingly, the MBAM represents a viable alternative to AM for multiple-breed genetic evaluations, providing the necessary flexibility in modeling heteroskedastic genetic variances of breed composition groups. 相似文献
944.
Mao J Smith MF Rucker EB Wu GM McCauley TC Cantley TC Prather RS Didion BA Day BN 《Journal of animal science》2004,82(7):1967-1975
The object of this study was to investigate the role of epidermal growth factor (EGF) and IGF-I in the regulation of preantral follicular growth, antrum formation, and granulosal cell proliferation/ apoptosis. Porcine preantral follicles were manually dissected and cultured for up to 8 d in Waymouth's (Exp. 1) or alpha-minimum Eagle's essential medium (Exp. 2 and 3) supplemented with 10 microg/mL of transferrin, 100 microg/mL of L-ascorbic acid, and 2 mU/mL of ovine FSH, in the presence (Exp. 1 and 3) or absence (Exp. 2) of 7.5% fetal calf serum. According to the experimental protocol, IGF-I (0, 1, 10, or 100 ng/mL; Exp. 1), or IGF-I (50 ng/mL), EGF (10 ng/mL) and EGF+IGF-I (Exp. 2 and 3) were added to the culture media. In Exp. 1, follicles exhibited a concentration-dependent response (P < 0.05) to IGF-I, with the highest rates of granulosal cell proliferation, follicular integrity, and recovery rate of cumulus cell-oocyte complexes and lowest incidence of apoptosis occurring at the highest IGF-I dose. In Exp. 2 serum-free medium, granulosal cell proliferation was low (1 to 5%), irrespective of whether EGF and/or IGF-I were present and cellular apoptosis was increased (P < 0.05) on d 4 and 8 in the EGF+IGF-I group compared with the addition of either factor alone. In Exp. 3, granulosal cell proliferation was high in all follicles cultured in serum-containing medium for the first 3 d, but fell sharply (P < 0.05) on d 4, except in media containing IGF-I. Collectively, EGF and IGF-I increased granulosal cell proliferation, decreased apoptosis, and promoted follicular antrum formation. These results may provide useful information for developing a preantral follicular culture system in which the oocytes are capable of fertilization and embryonic development. 相似文献
945.
Pasquali F De Cesare A Ricci A Kehrenberg C Schwarz S Manfreda G 《Veterinary microbiology》2004,103(1-2):71-76
The tetracycline resistance (tet) gene patterns of 52 tetracycline resistant Salmonella enterica subsp. enterica (S.) serovar Typhimurium isolates collected from animals, food of animal origin, and humans in Italy, were investigated to evaluate whether the tet gene patterns could be used for strain differentiation in addition to phage typing and ribotyping. The detection of tet genes was performed by specific PCR assays. Ribotyping was performed automatically using PvuII as restriction enzyme. Ten different ribotyping patterns were detected. All isolates were positive for at least one of the tet genes studied and six different tet gene patterns were observed. Ribotyping and tet gene patterns showed discriminatory indices of 0.741 and 0.812, respectively. Multiple tet genes were commonly found among tetracycline resistant S. typhimurium isolates from various sources. The resulting tet gene patterns allowed further discrimination of strains which were otherwise indistinguishable by their phage type, ribotype and origin. Thus, the analysis of tet gene patterns might represent an additional tool for the differentiation of S. typhimurium isolates. 相似文献
946.
Solymosi N Reiczigel J Berke O Harnos A Szigeti S Fodor L Szigeti G Bódis K 《Preventive veterinary medicine》2004,65(1-2):9-16
A Geographic Information System (VetEpiGIS) was used to analyze the ADV (Aujeszky's disease virus) sero-status in large-scale pig units regarding certain geographical features in a county of southern Hungary. The ADV sero-statuses were collected from all swine units in Csongrád county in 1998-2000. The units' coordinates were combined with a vector graphical digital map of the county, with a resolution of 1:100,000. Logistic regression tested the associations between sero-status of large-scale units and presence of topographical features, other units and villages in the neighborhood. "Neighborhood" was defined by circular zones with radius 1-10km around the unit (in 1km increments; one logistic regression for each radius). The following topographical features showed significant positive association with the ADV seropositivity: lake (3km OR: 5.7; 5km OR: 7.5; 6km OR: 6.1; 10km OR: 5.4) and highway (5km OR: 4.2; 6km OR: 5.3). Other features had negative association with ADV seropositivity: forest (3km OR: 0.13; 4km OR: 0.15; 5km OR: 0.15; 6km OR: 0.10; 7km OR: 0.10; 8km OR: 0.23) and uninfected large-scale unit (4km OR: 0.07; 5km OR: 0.27; 6km OR: 0.32; 7km OR: 0.31). 相似文献
947.
Effects of supplemental vitamin E during the laying period on the reproductive performance of Taiwan native chickens 总被引:1,自引:0,他引:1
1. One-day-old Taiwan Native Breeder female chicks were fed on maize/soybean growing diets without supplemental vitamin E from hatch to 17 weeks of age. After 17 weeks the birds (n = 300) were randomly assigned to 5 dietary treatments and fed on maize/soybean laying diets supplemented with 0, 40, 80, 120 and 160 mg/kg of vitamin E (dl-alpha-tocopherol acetate), respectively, until 46 weeks of age. The variates measured included: age at first egg, feed consumption (FC), feed efficiency (FE), egg production (EP), egg weight (EW), egg specific gravity (ESG), eggshell strength (ESS), fertility and hatchability. 2. The addition of 120mg/kg of vitamin E lowered the first EW (P<0.05); however, there was no significant difference in the age or body weight (BW) of pullets at first egg or mortality rate to 46 weeks of age among the treatments. FE and egg mass were improved (P<0.05) in pullets fed 80 mg/kg of supplemental vitamin E. A significant increase in EP was observed after peak EP in pullets given 80 mg/kg of supplemental vitamin E. However, this favourable effect decreased as supplemental vitamin E exceeded 80 mg/kg. 3. From 17 to 46 weeks of age, egg quality (ESG and ESS) decreased with age. However, there was no correlation between age and fertility or hatchability during the experimental period, suggesting that egg quality is more age-sensitive than reproductive performance for breeder pullets. 4. Compared with the control, fertility and hatchability of all eggs set for the treatment with 80 mg/kg supplemental vitamin E increased by 7.7 and 13.4%, respectively. There was no difference in the hatchability of fertile eggs. 5. These results suggest that using supplemental vitamin E during the laying period can improve the reproductive performance of breeder pullets. The addition of 80 mg/kg of vitamin E obtained the best performance in EP, egg mass, FE (feed/egg), hatchability and fertility. 相似文献
948.
Peek SF Borah S Semrad S McGuirk S Slack JA Patton E Coombs D Lien L Darien BJ 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2004,33(1):29-31
Background: Accurate determination of plasma endotoxin concentration is critical for ex vivo and in vitro cellular and molecular studies of endotoxemia in horses. However, reports are conflicting with respect to anticoagulant, handling, and sample preparation.
Objective: The purpose of this study was to determine the effect of blood sample fraction and handling time on measurement of endotoxin concentration in horses.
Methods: Whole blood, anticoagulated with 3.8% (0.12 M) sodium citrate (9:1), was collected from 5 healthy horses. Whole blood (WB), platelet-rich plasma (PRP), and platelet-poor plasma (PPP) were spiked with endotoxin (2 EU/mL). Endotoxin-spiked WB samples were centrifuged immediately to generate PRP for measurement. Endotoxin concentration was subsequently measured by Limulus amebocyte assay at 0, 15, 30, 45, and 60 minutes. Assays were performed in triplicate and results were analyzed using Student's t -test, with significance set at P < .05.
Results: Mean endotoxin concentrations in 2 EU/mL-spiked WB were significantly different from those in PPP at all time points tested. Recovery of endotoxin in PRP generated from WB was significantly diminished after just 15 minutes.
Conclusion: PRP generated from WB is significantly more reliable than PPP in determining endotoxin concentration ex vivo. Measurement of endotoxin in PRP generated from WB was significantly diminished after 15 min, identifying a time frame within which to process blood samples for endotoxin analysis. 相似文献
Objective:
Objective: The purpose of this study was to determine the effect of blood sample fraction and handling time on measurement of endotoxin concentration in horses.
Methods:
Methods: Whole blood, anticoagulated with 3.8% (0.12 M) sodium citrate (9:1), was collected from 5 healthy horses. Whole blood (WB), platelet-rich plasma (PRP), and platelet-poor plasma (PPP) were spiked with endotoxin (2 EU/mL). Endotoxin-spiked WB samples were centrifuged immediately to generate PRP for measurement. Endotoxin concentration was subsequently measured by Limulus amebocyte assay at 0, 15, 30, 45, and 60 minutes. Assays were performed in triplicate and results were analyzed using Student's t -test, with significance set at P < .05.
Results:
Results: Mean endotoxin concentrations in 2 EU/mL-spiked WB were significantly different from those in PPP at all time points tested. Recovery of endotoxin in PRP generated from WB was significantly diminished after just 15 minutes.
Conclusion:
Conclusion: PRP generated from WB is significantly more reliable than PPP in determining endotoxin concentration ex vivo. Measurement of endotoxin in PRP generated from WB was significantly diminished after 15 min, identifying a time frame within which to process blood samples for endotoxin analysis. 相似文献
949.
Chapman PS Green C Main JP Taylor PM Cunningham FM Cook AJ Marr CM 《The Veterinary record》2000,146(4):91-95
A total of 1235 tracheal aspirates taken from 724 thoroughbreds in race training, aged from two to 10 years, were examined cytologically and bacteriologically. An inflammation scoring system on a scale of 0 to 9 was devised to allow the severity of lower airway disease to be assessed from the cytological results. The inflammation scores were closely related to the isolation of bacteria (P<0.001), and the most common bacterial isolates were Streptococcus zooepidemicus, Streptococcus pneumoniae and Pasteurella/Actinobacillus-like species. Lower airway disease was less common in older horses (P = 0.031), and the groups at highest risk were the two- and four-year-olds. Lower airway inflammation was more common in the four-year-olds at National Hunt yards than in the four-year-olds at flat racing yards (P = 0.040, odds ratio = 3.80). 相似文献
950.