全文获取类型
收费全文 | 206383篇 |
免费 | 11240篇 |
国内免费 | 115篇 |
专业分类
林业 | 8737篇 |
农学 | 6610篇 |
基础科学 | 1390篇 |
25381篇 | |
综合类 | 34962篇 |
农作物 | 8066篇 |
水产渔业 | 10079篇 |
畜牧兽医 | 106744篇 |
园艺 | 2653篇 |
植物保护 | 13116篇 |
出版年
2019年 | 1891篇 |
2018年 | 2891篇 |
2017年 | 3201篇 |
2016年 | 2977篇 |
2015年 | 2594篇 |
2014年 | 3140篇 |
2013年 | 8150篇 |
2012年 | 5793篇 |
2011年 | 7019篇 |
2010年 | 4756篇 |
2009年 | 4761篇 |
2008年 | 6971篇 |
2007年 | 6605篇 |
2006年 | 6314篇 |
2005年 | 5858篇 |
2004年 | 5825篇 |
2003年 | 5811篇 |
2002年 | 5427篇 |
2001年 | 6666篇 |
2000年 | 6533篇 |
1999年 | 5166篇 |
1998年 | 2137篇 |
1997年 | 2153篇 |
1996年 | 1994篇 |
1995年 | 2422篇 |
1994年 | 2167篇 |
1993年 | 2117篇 |
1992年 | 4323篇 |
1991年 | 4584篇 |
1990年 | 4543篇 |
1989年 | 4596篇 |
1988年 | 4171篇 |
1987年 | 4212篇 |
1986年 | 4302篇 |
1985年 | 4120篇 |
1984年 | 3353篇 |
1983年 | 3013篇 |
1982年 | 2055篇 |
1981年 | 1909篇 |
1979年 | 2940篇 |
1978年 | 2372篇 |
1977年 | 2006篇 |
1976年 | 1970篇 |
1975年 | 2050篇 |
1974年 | 2556篇 |
1973年 | 2640篇 |
1972年 | 2558篇 |
1971年 | 2371篇 |
1970年 | 2307篇 |
1969年 | 2138篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
The histomorphologic and immunohistochemical features of chordoma in 20 ferrets were evaluated. The mean age was 3.4 years, and, in the cases for which sex was known, females (n = 10) outnumbered males (n = 5) two to one. All 20 tumors occurred on the tip of the tail. Nineteen of 20 tumors (95%) were composed of three tissue components, often arranged concentrically with lobules of physaliferous cells at the periphery, trabecular bone in the center, and cartilage in between. The bone often contained marrow and hematopoietic cells. One tumor lacked chondromatous or osseous tissue. Immunohistochemical results were consistent with previous studies of chordoma. All 20 tumors (100%) were positive for keratin and vimentin intermediate filaments; 15 (75%) were positive for S-100 protein; and 17 (85%) were positive for neuron specific enolase. This neoplasm shares morphologic and immunohistochemical features with "classic," as well as chondroid chordoma, of human beings, making it a potential animal model. 相似文献
944.
The synthesis and secretion of trypsin (trypsin model serine protease) inhibitors are regulated in ovarian follicles by gonadotropins. The superovulation stimulations with 400 IU FSH, 1000 IU PMSG, 1000 IU HCG, 750 IIU PMSG + 750 IU HCG influence in a different way the trypsin inhibiting activities (TIA) of blood plasma (BP) (Figs 1 and 2) and follicular fluid (fig. 3); this points to a possibility of local effects. An increase in the average values of TIA in BP was statistically significant during the whole experiment: P less than 0.05 to P less than 0.001 (following the administration of PMSG+HCG, or PMSG, and HCG); Antisergon administered in 68 hours after PMSG reduced this increase. The changes in the fraction of low-molecular TIA in BP (after BP treatment with perchloric acid) were of converse nature; a decrease in the average values ranged from P less than 0.02 to P less than 0.001 (following PMSG or other stimulations). Antisergon did not influence this decrease. The changes observed on particular days of the trial (Figs. 1 and 2) also indicate different effects of the preparations, mainly of the component LH, which resulted in the occurrence of large nonovulating follicles (greater than 10 mm--"cystic" ones). No such follicles were observed in nonstimulated ewes and after FSH stimulation. The administration of antisergon (goat's antiserum against PMSG) 68 hours after PMSG administration did not prevent their creation. The TIA of follicular fluid (FF) of antral follicles was on average tenfold in comparison with that of blood plasma; and the TIA FF of follicles greater than 10 mm was higher (up to P less than 0.001) than the TIA FF of follicles less than 10 mm. The administration of Antisergon in shorter intervals following PMSG administration (12, 24, 48 and 58 hours) influenced the average values of TIA BP in 120 hours (since PMSG administration) in dependence on time (Tab. I). The effects of Antisergon administered in 12 and 24 hours after PMSG administration on the TIA BP were insignificant if it was administered in 48 and 58 hours the TIA BP increased (P less than 0.02; P less than 0.001) in comparison with the interval of 12 hours. The TIA FF of follicles less than 5 mm, 5-10 mm and greater than 10 mm varied in dependence on the time intervals of Antisergon administration (Fig. 4). The statistical significance of these changes in shown in Tab. II.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
945.
946.
Evaluation of a guarded bronchoscopic method for microbial sampling of the lower airways in foals. 下载免费PDF全文
A M Hoffman L Viel C A Muckle D B Tesarowski 《Canadian journal of veterinary research》1991,55(4):325-331
A novel method to reduce contamination of the bronchoscope during microbial sampling of the lower airways of foals was evaluated. Methylene blue (MB) was used as a nasopharyngeal dye marker to assess the relative contamination from the upper airways of bronchoalveolar lavage (BAL) specimens obtained by standard bronchoscopy (SB) and a "guarded" bronchoscopic method (GB). For GB, a clear sterile cellulose sheath was fitted over the bronchoscope in an effort to protect the endoscope tip and channel from contamination. Methylene blue was detected visually in seven of eight BAL samples from foals following SB, but in none of the samples recovered by GB (p less than 0.001). Significantly less MB was detected in BAL by spectrophotometry in the GB group as well (p less than 0.02). The GB was next employed to study the microbial flora in the lower airways of healthy weaned foals (n = 30). Bacteria were isolated from 29 of 30 (97%) BAL samples, and in moderate or large numbers from 26 of 30 (87%) of the foals. Potential pathogens, including Bordetella bronchiseptica, Streptococcus zooepidemicus, Staphylococcus aureus, Mycoplasma felis and Streptococcus pneumoniae, were cultured from the lower airways of foals. In conclusion, the bronchoscope and bronchoalveolar lavage specimens were readily contaminated by a dye marker placed in the nasopharynx of foals, and the degree of contamination was significantly reduced by sheathing the endoscope. This contamination during bronchoscopy may obscure the interpretation of isolates from BAL specimens from foals, which may possess a bacterial flora in the lower airways without cytological evidence of inflammation. 相似文献
947.
J M Aynaud S Bernard E Bottreau I Lantier H Salmon P Vannier 《Veterinary microbiology》1991,26(3):227-239
A transmissible gastroenteritis (TGE) coronavirus mutant (188-SG), selected as attenuated and resistant to acidity and proteases of the digestive tract of adult pigs, was used as vaccine ("Nouzilly strain") in sows to protect suckling piglets against a challenge exposure carried out with a highly virulent TGEV strain. The pregnant sows were immunized once (42-49 days before farrowing) or twice (42-49 and 7-15 days before farrowing) by the oral, intramuscular or conjunctival route with the 188-SG strain. Sows exposed to virulent TGEV in the field and experimentally infected sows (two oral inoculations during pregnancy) were used as positive controls leading to high protection. The neutralizing antibody response to vaccination and/or infection was studied in serum and milk. No protection against mortality was observed in the litters of (1) the nine seronegative, susceptible sows, with piglet mortality of 65/70, (2) the seven once orally vaccinated sows, with mortality of 44/54, (3) the seven sows vaccinated twice by the conjunctival route, with mortality of 55/76. Moderate protection was observed in (1) the eight sows vaccinated intramuscularly twice with piglet mortality of 36/90, (2) the seven orally and intramuscularly vaccinated sows with piglet mortality of 31/51. In of 3 contrast, improved protection was observed in (1) the 10 sows vaccinated twice orally, with piglet mortality of 23/95, (2) the four naturally infected sows with piglet mortality of 6/41, (3) the six sows experimentally infected with virulent TGEV with piglet mortality of 1/59. No correlation was found between neutralizing antibodies titers in serum and milk and protection rate of the piglets. The results indicate that relative protective lactogenic immunity against TGEV is induced only by repeated ingestion of the attenuated 188-SG strain of TGEV. 相似文献
948.
SHARON L. ULLMAN DVM MS MICHAEL M. PAVLETIC DVM Dipiomate ACVS GEOFFREY N. CLARK DVM 《Veterinary surgery : VS》1991,20(6):385-391
Surgical stapling equipment was used to perform open antiperistaltic side-to-side ("functional end-to-end") entero-anastomoses in 20 dogs and 4 cats. Twenty-one anastomoses healed uneventfully. Seven animals with severe bacterial peritonitis required open peritoneal drainage and delayed abdominal closure. There was postoperative leakage at the anastomotic site in two dogs and a localized abscess at the staple line in one cat. No long-term complications occurred in follow-up periods of 3 to 29 months. 相似文献
949.
N. J. M. Roozen J. W. L. Van Vuurde 《European journal of plant pathology / European Foundation for Plant Pathology》1991,97(5):321-334
Various compounds and basal media were tested for their suitability to create a semi-selective medium for isolation ofClavibacter michiganensis subsp.sepedonicus (Cms) from cattle manure slurry containing c. 108 colony forming units (cfu) per ml.Plating efficiency of Cms in yeast glucose mineral medium (YGM) was 104% compared with yeast peptone glucose medium. Nalidixic acid, polymyxin B sulphate and the experimental disinfectant S-0208 inhibited colony growth of cattle slurry bacteria as compared with Cms in YGM. The optimal concentration of these inhibitors in combination was determined by modified agar diffusion tests and by pour plating in 24-well tissue culture plates. The semi-selective medium YGMI consisted of YGM supplemented with nalidixic acid (2 mg/l), polymyxin B sulphate (30 mg/l) and S-0208 (125 mg/l). Plating efficiency varied for Cms between 50.9 and 69.6%, for cattle slurry bacteria between 1.8 and 2.5% and for saprophytes from potato heel end extracts between 11.5 and 27.4%.Differentiation of Cms colonies from other colonies was based on their small and bluish colony morphology in pour plates and on immunofluorescence colony-staining (IFC). IFC of a pure culture of micro colonies of Cms in YGM was possible after one day incubation (colonies c. 5 cells). Green background fluorescence in the agar gels was prevented by addition of Tween 20 (0.1%) to the washing buffer and the use of 1% agar gels. IFC of macro colonies of Cms in YGMI, visible with 4x objective magnification, was possible after 4 days. The detection level of the target organism in artificially inoculated cattle slurry in YGMI based on colony morphology varied between 1.4×103 and 2.3×104 cfu per ml of cattle slurry. Miniaturized plating combined with IFC, using wells in tissue culture plates (=16 mm), proved suitable for detection, but was c. 30 times les sensitive. The recovery of Cms was negatively correlated with the number of saprophytic colonies in the agar plates (R
2=0.74). 相似文献
950.
C. Soria M. L. Gomez-Guillamon J. E. Duffus 《European journal of plant pathology / European Foundation for Plant Pathology》1991,97(5):289-296
The agent causing a yellowing disease of melon (Cucumis melo), which results in severe losses in crops under plastic on the coastal plains of southeast Spain, was shown to be transmitted in a semipersistent manner by the greenhouse whitefly (Trialeurodes vaporariorum Westwood). The agent was transmitted by grafting, but not by mechanical inoculation or through seeds. The agent was acquired in the minimum period tested (2 h) and could infect plants in an infection feeding interval of 6 h.
Capsella bursa-pastoris, Cucumis melo, C. sativus, Cucurbita moschata, Cichorium endivia, Lactuca sativa andTaraxacum officinale were found susceptible.Results suggest that the yellowing disease affecting melon crops in the southeast of Spain is due to a pathogen similar to beet pseudo yellows virus, but this has to be confirmed by serology. 相似文献