全文获取类型
收费全文 | 70139篇 |
免费 | 19304篇 |
国内免费 | 18篇 |
出版年
2022年 | 365篇 |
2021年 | 1003篇 |
2020年 | 2499篇 |
2019年 | 4145篇 |
2018年 | 4337篇 |
2017年 | 4553篇 |
2016年 | 4875篇 |
2015年 | 5340篇 |
2014年 | 5182篇 |
2013年 | 6153篇 |
2012年 | 4258篇 |
2011年 | 4047篇 |
2010年 | 4637篇 |
2009年 | 3313篇 |
2008年 | 2958篇 |
2007年 | 2645篇 |
2006年 | 2571篇 |
2005年 | 2711篇 |
2004年 | 2564篇 |
2003年 | 2600篇 |
2002年 | 2520篇 |
2001年 | 757篇 |
2000年 | 510篇 |
1999年 | 660篇 |
1998年 | 693篇 |
1997年 | 499篇 |
1996年 | 501篇 |
1995年 | 434篇 |
1994年 | 456篇 |
1993年 | 404篇 |
1992年 | 430篇 |
1991年 | 371篇 |
1990年 | 353篇 |
1989年 | 331篇 |
1988年 | 328篇 |
1987年 | 324篇 |
1986年 | 301篇 |
1985年 | 401篇 |
1984年 | 492篇 |
1983年 | 399篇 |
1982年 | 474篇 |
1981年 | 552篇 |
1980年 | 504篇 |
1979年 | 344篇 |
1978年 | 347篇 |
1977年 | 355篇 |
1976年 | 349篇 |
1975年 | 234篇 |
1974年 | 310篇 |
1973年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Juan Viruel Pilar Catalán José Gabriel Segarra‐Moragues 《Journal of Biogeography》2012,39(6):1073-1085
Aim The Chilean endemic Dioscorea biloba (Dioscoreaceae) is a dioecious geophyte that shows a remarkable 600 km north–south disjunction in the peripheral arid area of the Atacama Desert. Its restricted present‐day distribution and probable Neogene origin indicate that its populations have a history linked to that of the Atacama Desert, making this an ideal model species with which to investigate the biogeography of the region. Location Chile, Atacama Desert and peripheral arid area. Methods Two hundred and seventy‐five individuals from nine populations were genotyped for seven nuclear microsatellite loci, and plastid trnL–F and trnT–L sequences were obtained for a representative subset of these. Analyses included the estimation of genetic diversity and population structure through clustering, Bayesian and analysis of molecular variance analyses, and statistical parsimony networks of chloroplast haplotypes. Isolation by distance was tested against alternative dispersal hypotheses. Results Microsatellite markers revealed moderate to high levels of genetic diversity within populations, with those from the southern Limarí Valley showing the highest values and northern populations showing less exclusive alleles. Bayesian analysis of microsatellite data identified three genetic groups that corresponded to geographical ranges. Chloroplast phylogeography revealed no haplotypes shared between northern and southern ranges, and little haplotype sharing between the two neighbouring southern valleys. Dispersal models suggested the presence of extinct hypothetical populations between the southern and northern ranges. Main conclusions Our results are consistent with prolonged isolation of the northern and southern groups, mediated by the life‐history traits of the species. Significant isolation was revealed at both large and moderate distances as gene flow was not evident even between neighbouring valleys. Bayesian analyses of microsatellite and chloroplast haplotype diversity identified the southern area of Limarí as the probable area of origin of the species. Our data do not support recent dispersal of D. biloba from the southern range into Antofagasta, but indicate the fragmentation of an earlier wider range, concomitant with the Pliocene–Pleistocene climatic oscillations, with subsequent extinctions of the Atacama Desert populations and the divergence of the peripheral ones as a consequence of genetic drift. 相似文献
2.
In vivo EMG biofeedback was found to be an effective pedagogical tool for removing unwanted left-hand tension in nine violin and viola players. Improvement occurred rapidly and persisted throughout a 5-month follow-up period. Further studies will be necessary to assess the effect of biofeedback independent of placebo effects. The brevity of the method and the magnitude of improvement warrant further investigation. 相似文献
3.
The ability to metabolically label proteins with 35S-methionine is critical for the analysis of protein synthesis and turnover. Despite the importance of this approach, however, efficient labeling of proteins in vivo is often limited by a low number of available methionine residues, or by deleterious side-effects associated with protein overexpression. To overcome these limitations, we have created a methionine-rich variant of the widely used HA tag, called HAM, for use with ectopically expressed proteins. Here we describe the development of a series of vectors, and corresponding antisera, for the expression and detection of HAM-tagged proteins in mammalian cells. We show that the HAM tag dramatically improves the sensitivity of 35S-methionine labeling, and permits the analysis of Myc oncoprotein turnover even when HAM-tagged Myc is expressed at levels comparable to that of the endogenous protein. Because of the improved sensitivity provided by the HAM tag, the vectors and antisera described here should be useful for the analysis of protein synthesis and destruction at physiological levels of protein expression. 相似文献
4.
5.
6.
7.
HIF-1 expression in healing wounds: HIF-1alpha induction in primary inflammatory cells by TNF-alpha 总被引:12,自引:0,他引:12
8.
9.
10.