全文获取类型
收费全文 | 108488篇 |
免费 | 5592篇 |
国内免费 | 46篇 |
专业分类
林业 | 7472篇 |
农学 | 4810篇 |
基础科学 | 780篇 |
14928篇 | |
综合类 | 15110篇 |
农作物 | 5474篇 |
水产渔业 | 6757篇 |
畜牧兽医 | 49000篇 |
园艺 | 2187篇 |
植物保护 | 7608篇 |
出版年
2020年 | 736篇 |
2019年 | 955篇 |
2018年 | 4408篇 |
2017年 | 4682篇 |
2016年 | 2869篇 |
2015年 | 1479篇 |
2014年 | 1733篇 |
2013年 | 3724篇 |
2012年 | 3781篇 |
2011年 | 5919篇 |
2010年 | 4685篇 |
2009年 | 3943篇 |
2008年 | 4996篇 |
2007年 | 5199篇 |
2006年 | 3182篇 |
2005年 | 2802篇 |
2004年 | 2699篇 |
2003年 | 2784篇 |
2002年 | 2466篇 |
2001年 | 3406篇 |
2000年 | 3362篇 |
1999年 | 2561篇 |
1998年 | 986篇 |
1997年 | 1054篇 |
1996年 | 885篇 |
1995年 | 1023篇 |
1994年 | 896篇 |
1993年 | 919篇 |
1992年 | 1883篇 |
1991年 | 1929篇 |
1990年 | 1871篇 |
1989年 | 1943篇 |
1988年 | 1669篇 |
1987年 | 1650篇 |
1986年 | 1672篇 |
1985年 | 1573篇 |
1984年 | 1228篇 |
1983年 | 1038篇 |
1982年 | 717篇 |
1979年 | 1062篇 |
1978年 | 820篇 |
1975年 | 816篇 |
1974年 | 900篇 |
1973年 | 868篇 |
1972年 | 811篇 |
1971年 | 797篇 |
1970年 | 802篇 |
1969年 | 783篇 |
1968年 | 732篇 |
1967年 | 742篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
R. Iori O. Leoni L. Lazzeri G. Mosca S. Palmieri 《Journal of Agronomy and Crop Science》1991,167(2):91-95
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype. 相似文献
182.
S E Sanford 《Journal of veterinary diagnostic investigation》1991,3(4):328-333
Segmented filamentous bacteria were seen attached to apical villous enterocytes of the terminal ileum in 15 of 2,766 live pigs submitted for necropsy over a 6-year period. Infected pigs ranged in age from 2 to 13 weeks. All pigs except 2, however, were greater than 4 weeks old and had been weaned. All infected pigs came from conventional commercial herds with intensive, all-indoor, confinement rearing management systems. The bacteria were gram negative or gram variable and were not associated with any clinical disease. Bacteria were more commonly attached to epithelium on the dome villi in the ileum. Electron microscopic examination revealed organisms composed of a cranial segment with a nipple-like appendage and several other segments making up elongated filaments of various lengths. Each filament was divided into segments by transverse septa. The nipple-like appendage served as an attachment apparatus by indenting the enterocyte surface without physically penetrating it. Occasionally, the colonizing bacterium was itself colonized by small rod-shaped bacteria that completely surrounded the filament. 相似文献
183.
J Sherrill T Schock J L Dunn D J St Aubin V V Burnley S E Poet 《Journal of zoo and wildlife medicine》2001,32(1):17-24
Humoral immune responses of black-footed penguins (Spheniscus demersus) to DNA-mediated immunization with a beta-galactosidase reporter gene expression plasmid were evaluated. Six male and 6 female adult penguins received either test plasmid, pCMV-beta, containing the beta-galactosidase gene or control plasmid, pCI, lacking a gene for expression. Three birds from each group were used previously in a diluent control group and given one injection of sterile saline. All samples were screened for anti-beta-galactosidase antibodies by indirect enzyme-linked immunosorbent assay with anti-chicken immunoglobulin G as secondary antibody. Antibodies to beta-galactosidase were detected in the sera of pCMV-beta-inoculated penguins, with a peak response on day 21. Antibody titers of the test plasmid group versus both control groups on days 21, 28, and 42 differed significantly. These results demonstrate that black-footed penguins can be safely transfected with the gene encoding beta-galactosidase and will mount a humoral response against the in vivo-expressed protein. Knowledge from this initial study can be applied to the development of DNA-mediated vaccines against specific infectious diseases of penguins. 相似文献
184.
AM Mwanza A Madej H Kindahl N Lundeheim & S Einarsson 《Reproduction in domestic animals》2001,36(3-4):157-161
The effects of lipopolysaccharide ( Escherichia coli , O55:B5), administered 18 h after ovulation in the second oestrus after weaning on the hormonal profiles in 14 Swedish cross-bred (Landrace × Yorkshire) multiparous sows were studied. The endotoxin group (E-group) sows were administered with 300 ng/kg of lipopolysaccharide (LPS) whereas the control group (C-group) sows were administered 5 ml of saline intravenously via an indwelling jugular cannula. Blood samples for hormonal analyses were collected from all sows until slaughter. In the E-group, progesterone, cortisol and prostaglandin F2α metabolite levels increased significantly (p < 0.05) following LPS compared with the C-group. It can be concluded from this study that apart from elevating cortisol and prostaglandin F2α metabolite, LPS also elevates progesterone levels. 相似文献
185.
186.
187.
Fluid accumulation in mouse ligated intestine inoculated with the vascular permeability factor produced by Bacillus cereus. 总被引:1,自引:0,他引:1
K Shinagawa K Sato H Konuma N Matsusaka S Sugii 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(2):167-171
Partially purified vascular permeability (VP) factor (VPF) of Bacillus cereus induced fluid accumulation in the ligated intestinal loops of mouse (MIL) and rabbit (RIL), suggesting that the VP activity may correlate with fluid accumulation in ligated intestinal loops of these animals. Fluid accumulation was observed at 6-8 hr in 55-67% of mouse intestinal loops inoculated with 40-50 immunodiffusion units (IDU) of partially purified VPF, whereas it was found at 2 hr in all loops with 400-600 IDU of partially purified VPF. In rabbit intestinal loops with 120-190 IDU of partially purified VPF, fluid accumulation was observed at 6 hr. From these findings, VPF produced by B. cereus can be easily detected in both MIL and RIL. The intestinal tissue of mouse intestinal loops was histopathologically damaged at different concentrations of the VPF to induce fluid accumulation. With 50 IDU of partially purified VPF, severe edema was found in the laminia proprial layer and submucosa. With 600 IDU of partially purified VPF, on the other hand, severe necrosis in the surface epithelium of villus and laminia proprial layer, and hyperemia in the submucosa were observed, suggesting that partially purified VPF may be cytotoxic and/or intestinecrotic. 相似文献
188.
189.
Intraperitoneal Circulation and Drainage in the Dog 总被引:1,自引:0,他引:1
GISELLE HOSGOOD BVSc MS FACVSc S. KATHLEEN SALISBURY DVM MS DiplomateACVS H. DAN CANTWELL DVM MS DiplomateACVR DENNIS B. DENICOLA DVM PhD DiplomateACVP 《Veterinary surgery : VS》1989,18(4):261-268
The patterns of dispersion and drainage of a low viscosity, oil-based contrast medium within the peritoneal cavity were examined in 12 normal dogs. Intraperitoneal injection of contrast medium was cranial or caudal and drainage was by the sump-Penrose or open peritoneal method. Radiographs were made over a 96 hour period, before and after peritoneal drainage was established. Each dog was euthanatized and necropsied. The contrast medium was dispersed throughout the peritoneal cavity 15 to 30 minutes after cranial injection and 1 to 2 hours after caudal injection. Most of the contrast medium drained within 6 hours after open peritoneal drainage and within 24 to 48 hours after sump-Penrose drainage. At necropsy, there was complete encasement of all sump-Penrose drains and partial occlusion of all open peritoneal incisions by omentum adhered to the abdominal wound edges. Peritonitis was not grossly evident, but all dogs showed histologic evidence of an acute inflammatory reaction associated with the drain or wound edge. 相似文献
190.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype. 相似文献