全文获取类型
收费全文 | 19890篇 |
免费 | 1954篇 |
国内免费 | 1695篇 |
出版年
2024年 | 46篇 |
2023年 | 451篇 |
2022年 | 543篇 |
2021年 | 865篇 |
2020年 | 944篇 |
2019年 | 1180篇 |
2018年 | 833篇 |
2017年 | 757篇 |
2016年 | 790篇 |
2015年 | 824篇 |
2014年 | 1037篇 |
2013年 | 1307篇 |
2012年 | 959篇 |
2011年 | 955篇 |
2010年 | 754篇 |
2009年 | 931篇 |
2008年 | 957篇 |
2007年 | 1044篇 |
2006年 | 974篇 |
2005年 | 936篇 |
2004年 | 826篇 |
2003年 | 701篇 |
2002年 | 710篇 |
2001年 | 530篇 |
2000年 | 511篇 |
1999年 | 400篇 |
1998年 | 319篇 |
1997年 | 315篇 |
1996年 | 273篇 |
1995年 | 214篇 |
1994年 | 221篇 |
1993年 | 207篇 |
1992年 | 156篇 |
1991年 | 144篇 |
1990年 | 103篇 |
1989年 | 100篇 |
1988年 | 77篇 |
1987年 | 74篇 |
1986年 | 70篇 |
1985年 | 77篇 |
1984年 | 69篇 |
1983年 | 50篇 |
1982年 | 55篇 |
1981年 | 48篇 |
1980年 | 63篇 |
1979年 | 34篇 |
1978年 | 34篇 |
1977年 | 17篇 |
1976年 | 21篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
11.
12.
13.
14.
Genomic DNA isolated from 20 horses was digested with up to six restriction endonucleases and subjected to southern blot hybridization analysis using various human class II alpha- and beta-chain cDNA probes. A high degree of restriction fragment length polymorphism (RFLP) was found for the DQ alpha, DP beta, DQ beta and DR beta probes, about 20 polymorphic bands being detected for each. DR alpha showed 2-4 polymorphic bands, whereas no evidence for DP alpha-like genes was found. A number of correlations of RFLPs with individual alloantisera were apparent. 相似文献
15.
Roberta L. Millstein 《Journal of the history of biology》2008,41(2):339-367
Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature,
particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case
– Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature
for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for
a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population,
but it is not (always) impossible. 相似文献
16.
17.
18.
FRAUKE M. MUENZEL MATTHIAS SANETRA WALTER SALZBURGER AXEL MEYER 《Molecular ecology resources》2007,7(6):1048-1050
Eleven microsatellites were isolated from the vairone Leuciscus souffia (Risso 1826), an endangered fish that inhabits river systems in and around the Alps in Europe. The level of genetic diversity was assessed in 29 individuals of the subspecies L. s. souffia, and their variability was further estimated in seven individuals of a different subspecies, L. s. muticellus. Eight of these microsatellite loci were also applied to seven closely related cyprinid species. Availability of the reported microsatellite loci will facilitate the investigation of population genetic structure of these species with applications for the development of conservation strategies and phylogeographical approaches. 相似文献
19.
D. F. Roberts 《International Journal of Anthropology》1996,11(2-4):185-191
As a conclusion, this paper reviews briefly the content of the volume. The wealth of demographic data has not been adequately
exploited in anthropology; this is why this publication is valuable in showing attempts to apply demographic data in a variety
of anthropological problems. This symposium has explored many interesting points which we recall here. Yet it has also opened
up a whole range of further questions on the material presented as well as in this broad field. Several directions of research
could be developed, for instance, testing among human populations, over long periods, the ecological thoughts of ecosystems
evolving as a cascade of instabilities, rather than a succession of equilibrium states. Let us also recall the pervasive nature
of demographic facts in topics such as the energy cycle or the genetic structure and evolution of human populations. 相似文献
20.
Robert A. Krebs 《Journal of Insect Behavior》1991,4(2):221-233
Variation in copulation duration of Drosophila mojavensisstrains was influenced by both sexes. Males maintained predominant control, as copulation duration of pairs from different strains was more similar to that of the strain from which the male was derived, but female origin also contributed significantly to the duration of copulation. Variation among strains was controlled by genes acting additively in both sexes. The size of both males and females also affected copulation duration. Small males copulated longer on average than large males, while males paired with large females copulated longer than those paired with small females. The importance of copulation duration to fitness was tested by correlation analyses with male size, female size, female remating latency, and number of eggs laid prior to female remating. Longer copulations stimulated earlier oviposition, possibly by increasing accessory gland secretions that are passed by males during copulation. 相似文献