全文获取类型
收费全文 | 110065篇 |
免费 | 1694篇 |
国内免费 | 2455篇 |
专业分类
114214篇 |
出版年
2024年 | 43篇 |
2023年 | 239篇 |
2022年 | 633篇 |
2021年 | 1021篇 |
2020年 | 668篇 |
2019年 | 805篇 |
2018年 | 12432篇 |
2017年 | 11055篇 |
2016年 | 8085篇 |
2015年 | 1703篇 |
2014年 | 1625篇 |
2013年 | 1678篇 |
2012年 | 5812篇 |
2011年 | 14127篇 |
2010年 | 12793篇 |
2009年 | 8965篇 |
2008年 | 10612篇 |
2007年 | 12091篇 |
2006年 | 970篇 |
2005年 | 1169篇 |
2004年 | 1470篇 |
2003年 | 1483篇 |
2002年 | 1142篇 |
2001年 | 549篇 |
2000年 | 435篇 |
1999年 | 295篇 |
1998年 | 177篇 |
1997年 | 181篇 |
1996年 | 190篇 |
1995年 | 136篇 |
1994年 | 160篇 |
1993年 | 127篇 |
1992年 | 133篇 |
1991年 | 145篇 |
1990年 | 86篇 |
1989年 | 79篇 |
1988年 | 65篇 |
1987年 | 68篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1972年 | 246篇 |
1971年 | 274篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
14.
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
15.
The abundance of an mRNA encoding an HMG1/2 protein from Pharbitis nil (HMG1) has been previously shown to be regulated by light and an endogenous rhythm in cotyledons. A second Pharbitis nil HMG cDNA (HMG2) was characterized. The sequence of HMG2 was 82% and 86% identical to HMG1 at the nucleotide and amino acid level, respectively. As with HMG1, HMG2 mRNA was detected in all vegetative tissues and was most abundant in roots. However, unlike HMG1, HMG2 mRNA abundance did not increase upon transfer of cotyledons to darkness and did not exhibit regulation by an endogenous circadian rhythm when maintained in continuous darkness over a 68 h period. Similarly, while the abundance of HMG1 mRNA during a dark period that induced photoperiodically controlled flowering was dramatically affected by brief light exposure (night break), this treatment had no effect on HMG2 mRNA abundance. Collectively, these data are consistent with a role of HMG1 in contributing to the circadian-regulated and/or dark-regulated gene expression with constitutive expression of HMG2 playing a housekeeping role in the general regulation of gene expression in Pharbitis nil cotyledons. 相似文献
16.
17.
山西省异爪蝗属二新种(直翅目:网翅蝗科) 总被引:4,自引:0,他引:4
本文记述在晋南地区采到的异爪蝗属二新种,黑条异爪蝗Euchorthippus nigiliineatus sp.nov.及曲线异爪蝗Eochorthippus sinucarinatus sp.nov. 相似文献
18.
19.
This paper describes a generic algorithm for finding restrictionsites within DNA sequences. The genericity ofthe algorithm is made possible through the use of set theory.Basic elements of DNA sequences, i.e. nucleotides (bases), arerepresented in sets, and DNA sequences, whether specific, ambiguousor even protein-coding, are represented as sequences of thosesets. The set intersection operation demonstrates its abilityto perform pattern-matching correctly on various DNA sequences.The performance analysis showed that the degree of complexityof the pattern matching is reduced from exponential to linear.An example is given to show the actual and potential restrictionsites, derived by the generic algorithm, in the DNA sequencetemplate coding for a synthetic calmodulin.
Received on October 2, 1990; accepted on December 18, 1990 相似文献
20.