全文获取类型
收费全文 | 85003篇 |
免费 | 5674篇 |
国内免费 | 12篇 |
专业分类
90689篇 |
出版年
2023年 | 623篇 |
2022年 | 741篇 |
2021年 | 1507篇 |
2020年 | 1226篇 |
2019年 | 1400篇 |
2018年 | 2613篇 |
2017年 | 2361篇 |
2016年 | 3125篇 |
2015年 | 3948篇 |
2014年 | 4101篇 |
2013年 | 5560篇 |
2012年 | 6575篇 |
2011年 | 6110篇 |
2010年 | 3893篇 |
2009年 | 3107篇 |
2008年 | 4662篇 |
2007年 | 4413篇 |
2006年 | 4177篇 |
2005年 | 3504篇 |
2004年 | 3435篇 |
2003年 | 3132篇 |
2002年 | 2835篇 |
2001年 | 1942篇 |
2000年 | 1946篇 |
1999年 | 1448篇 |
1998年 | 755篇 |
1997年 | 560篇 |
1996年 | 552篇 |
1995年 | 517篇 |
1994年 | 408篇 |
1993年 | 388篇 |
1992年 | 710篇 |
1991年 | 610篇 |
1990年 | 529篇 |
1989年 | 515篇 |
1988年 | 506篇 |
1987年 | 456篇 |
1986年 | 422篇 |
1985年 | 435篇 |
1984年 | 428篇 |
1983年 | 302篇 |
1982年 | 290篇 |
1981年 | 236篇 |
1980年 | 229篇 |
1979年 | 280篇 |
1978年 | 260篇 |
1975年 | 231篇 |
1974年 | 264篇 |
1973年 | 266篇 |
1972年 | 216篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Jeremy D. Hogan Katharine M. Jack Fernando A. Campos Urs Kalbitzer Linda M. Fedigan 《American journal of primatology》2019,81(7)
Primates have long been used as indicator species for assessing overall ecosystem health. However, area‐wide census methods are time consuming, costly, and not always feasible under many field conditions. Therefore, it is important to establish whether monitoring a subset of a population accurately reflects demographic changes occurring in the population at large. Over the past 35 years, we have conducted 15 area‐wide censuses in Sector Santa Rosa, Costa Rica. These efforts have revealed important trends in population growth patterns of capuchin monkeys following the protection and subsequent regeneration of native forests. During this same period, we have also intensively studied a subset of the capuchin groups. Comparing these two datasets, we investigate whether the population structures of the closely monitored groups are reliable indicators of area‐wide demographic patterns. We compare the overall group size and the individual age/sex class compositions of study groups and nonstudy groups (i.e., those contacted during area‐wide censuses only). Our study groups contained more individuals overall with a larger proportion of infants, and there were indications that the proportion of adult and subadult males was lower. These differences can be ascribed either to sampling errors or real differences attributable to human presence and/or better habitat quality for the study groups. No other sex/age classes differed, and major demographic changes were simultaneously evident in both study and nonstudy groups. This study suggests that the Santa Rosa capuchin population is similarly impacted by large‐scale ecological patterns observable within our study groups. 相似文献
3.
Sacramento Doralice Rodrigues Coelho Rosalie Reed Rodrigues Wigg Márcia Dutra Toledo Luna Linhares Luiz Fernando de Matos dos Santos Marta Gonçalves Azevedo Soares Semêdo Luzia Teixeira de Ribeiro da Silva Antonio Jorge 《World journal of microbiology & biotechnology》2004,20(3):225-229
A promising producer of bioactive compounds isolated from a Brazilian tropical soil was tested for its range of antimicrobial
activities. Strain 606, classified as Streptomyces sp., could not be identified up to species level, suggesting a possible new taxon. The supernatant and 10 extracts and fractions,
obtained by extraction and chromatographic techniques, presented antimicrobial activity using antibiograms. The methanolic
fraction was highly active against pathogenic bacteria, phytopathogenic fungi and the human pathogenic yeast Candida albicans. It also possessed high antiviral activity inhibiting the propagation of an acyclovir-resistant herpes simplex virus type
1 strain on HEp-2 cells at non-cytotoxic concentration. The strong cytotoxic effect suggests an antitumour action.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
5.
Sebastián Moran Miguel Vizoso Anna Martinez-Cardús Antonio Gomez Xavier Matías-Guiu Sebastián M Chiavenna Andrés G Fernandez Manel Esteller 《Epigenetics》2014,9(6):829-833
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array. 相似文献
6.
7.
"Pertussis toxin induces tachycardia and impairs the increase in blood pressure produced by alpha 2-adrenergic agonists" 总被引:4,自引:0,他引:4
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested. 相似文献
8.
9.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献
10.