全文获取类型
收费全文 | 112920篇 |
免费 | 2232篇 |
国内免费 | 918篇 |
专业分类
116070篇 |
出版年
2023年 | 103篇 |
2022年 | 220篇 |
2021年 | 466篇 |
2020年 | 210篇 |
2019年 | 319篇 |
2018年 | 12126篇 |
2017年 | 10904篇 |
2016年 | 7965篇 |
2015年 | 1567篇 |
2014年 | 1353篇 |
2013年 | 1567篇 |
2012年 | 5889篇 |
2011年 | 14364篇 |
2010年 | 12998篇 |
2009年 | 9057篇 |
2008年 | 11063篇 |
2007年 | 12590篇 |
2006年 | 1468篇 |
2005年 | 1685篇 |
2004年 | 2106篇 |
2003年 | 2094篇 |
2002年 | 1791篇 |
2001年 | 425篇 |
2000年 | 258篇 |
1999年 | 228篇 |
1998年 | 264篇 |
1997年 | 180篇 |
1996年 | 146篇 |
1995年 | 124篇 |
1994年 | 122篇 |
1993年 | 141篇 |
1992年 | 112篇 |
1991年 | 129篇 |
1990年 | 89篇 |
1989年 | 72篇 |
1988年 | 71篇 |
1987年 | 73篇 |
1986年 | 47篇 |
1985年 | 65篇 |
1984年 | 72篇 |
1983年 | 86篇 |
1982年 | 79篇 |
1981年 | 74篇 |
1980年 | 76篇 |
1978年 | 65篇 |
1977年 | 44篇 |
1975年 | 42篇 |
1972年 | 258篇 |
1971年 | 280篇 |
1962年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Anne M. Berry Eric M. Glare David Hansman James C. Paton 《FEMS microbiology letters》1989,65(3):275-278
Twenty-four of 63 enteric Gram-negative organisms (38.1%) which were isolated from 35 apparently healthy Nigerian students were found to have low trimethoprim resistance (MIC less than 1000 mg/l). These isolates were also found to be resistant to several other antibiotics and trimethoprim resistance was found to be transferable from 15 (62.5%) of the trimethoprim resistant organisms into E. coli EC 1005. It is likely that the high percentage of trimethoprim resistance encountered in this study is related to the high rate of resistance transfer which was observed. 相似文献
23.
H Härtel S Nikunen E Neuvonen R Tanskanen S-L Kivelä P Aho T Soveri H Saloniemi 《Acta veterinaria Scandinavica》2004,45(4):193-200
Pathogens causing bovine respiratory tract disease in Finland were investigated. Eighteen cattle herds with bovine respiratory
disease were included. Five diseased calves from each farm were chosen for closer examination and tracheobronchial lavage.
Blood samples were taken from the calves at the time of the investigation and from 86 calves 3–4 weeks later. In addition,
6–10 blood samples from animals of different ages were collected from each herd, resulting in 169 samples. Serum samples were
tested for antibodies to bovine parainfluenza virus-3 (PIV-3), bovine respiratory syncytial virus (BRSV), bovine coronavirus
(BCV), bovine adenovirus-3 (BAV-3) and bovine adenovirus-7 (BAV-7). About one third of the samples were also tested for antibodies
to bovine virus diarrhoea virus (BVDV) with negative results. Bacteria were cultured from lavage fluid and in vitro susceptibility
to selected antimicrobials was tested. According to serological findings, PIV-3, BAV-7, BAV-3, BCV and BRSV are common pathogens
in Finnish cattle with respiratory problems. A titre rise especially for BAV-7 and BAV-3, the dual growth of Mycoplasma dispar and Pasteurella multocida, were typical findings in diseased calves. Pasteurella sp. strains showed no resistance to tested antimicrobials. Mycoplasma bovis and Mannheimia haemolytica were not found. 相似文献
24.
25.
Eric Guilbert 《Australian Journal of Entomology》1999,38(1):15-15
Cephalidiosus is proposed as a replacement name for Stenotrachelus Guilbert, a genus of Tingidae from New Caledonia. New combinations are Cephalidiosus megapharsus (Guilbert) and Cephalidiosus mesopharsus (Guilbert). 相似文献
26.
Comparing models and observations of shelf plankton 总被引:1,自引:0,他引:1
In a previous paper (Solow and Steele, J. Plankton Res., 17,1995), the differences between variability in zooplankton biomassand in copepod stage structure were demonstrated using datafrom the northern North Sea. Here, a model is used to describethe underlying demographic processes and the effects of interannualphysical variability. Comparison of output with observationscan test the theory and so help to reconcile the apparent contradictionbetween great variability and persistence in these populations. 相似文献
27.
28.
29.