全文获取类型
收费全文 | 786913篇 |
免费 | 95602篇 |
国内免费 | 429篇 |
专业分类
882944篇 |
出版年
2016年 | 8631篇 |
2015年 | 13160篇 |
2014年 | 15150篇 |
2013年 | 21051篇 |
2012年 | 24029篇 |
2011年 | 23994篇 |
2010年 | 16240篇 |
2009年 | 15467篇 |
2008年 | 21980篇 |
2007年 | 22580篇 |
2006年 | 21145篇 |
2005年 | 20382篇 |
2004年 | 20211篇 |
2003年 | 19546篇 |
2002年 | 18986篇 |
2001年 | 34392篇 |
2000年 | 34832篇 |
1999年 | 28104篇 |
1998年 | 10812篇 |
1997年 | 11449篇 |
1996年 | 10985篇 |
1995年 | 10383篇 |
1994年 | 10227篇 |
1993年 | 10057篇 |
1992年 | 23663篇 |
1991年 | 22926篇 |
1990年 | 22550篇 |
1989年 | 21860篇 |
1988年 | 20138篇 |
1987年 | 19799篇 |
1986年 | 18166篇 |
1985年 | 18244篇 |
1984年 | 15180篇 |
1983年 | 13257篇 |
1982年 | 10602篇 |
1981年 | 9460篇 |
1980年 | 8997篇 |
1979年 | 14591篇 |
1978年 | 11741篇 |
1977年 | 10608篇 |
1976年 | 10012篇 |
1975年 | 10839篇 |
1974年 | 11671篇 |
1973年 | 11456篇 |
1972年 | 10254篇 |
1971年 | 9513篇 |
1970年 | 8134篇 |
1969年 | 7686篇 |
1968年 | 6863篇 |
1967年 | 6201篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
992.
Decoupled evolution of display morphology and display behaviour in phrynosomatid lizards 总被引:1,自引:0,他引:1
JOHN J. WIENS 《Biological journal of the Linnean Society. Linnean Society of London》2000,70(4):597-612
A widespread trend in animals is the evolution of morphological ornaments and behaviours that are involved in aggressive and courtship displays. These display traits are important from the standpoint of communication, sexual selection, and speciation. Previous authors have suggested that the evolution of display morphology and display behaviour should be closely linked. In this study, I tested for this association with behavioural and morphological data for 59 taxa of phrynosomatid lizards using phylogenetic comparative methods (Mad-dison's concentrated changes test and Felsenstein's independent contrasts). The results showed little significant association between features of display morphology and behaviour, suggesting that the evolution of these traits is not tightly coupled. This decoupling is particularly evident in the genus Sceloporus , in which several species have lost the display coloration but retain unmodified display behaviour. The results also suggest that display morphology is more evolutionarily labile than display behaviour in this group. 相似文献
993.
Ecology of juvenile grouse during the transition to adulthood 总被引:1,自引:0,他引:1
994.
The first record of Misgurnus anguillicaudatus in Germany 总被引:1,自引:0,他引:1
Oriental weatherfish Misgurnus anguillicaudatus , from southern China, have been imported to Germany in large numbers for the garden pond trade. The first record of M. anguillicaudatus from Central Europe, a population that has been established for at least 14 years in a small nature reserve in Germany, is detailed. 相似文献
995.
We have isolated 18 polymorphic microsatellite loci for Cophixalus ornatus from genomic libraries enriched for (AAAG)n, (AACC)n and (AAGG)n repetitive elements. The number of alleles ranges from five to 22 per locus with the observed heterozygosity ranging from 0.10 to 0.92. These markers will be useful for the analysis of population structure in C. ornatus and testing alternative models of speciation. 相似文献
996.
M.A. Mena M.J. Casarejos J.A. Rodríguez-Navarro I. Rodal J.G. de Yebenes 《FEBS letters》2009,583(1):168-174
Parkin mutations produce Parkinson’s disease (PD) in humans and nigrostriatal dopamine lesions related to increased free radicals in mice. We examined the effects of NP7, a synthetic, marine derived, free radical scavenger which enters the brain, on H2O2 toxicity in cultured neurons and glia from wild-type (WT) and parkin null mice (PK-KO).NP7, 5-10 μM, prevented the H2O2 induced apoptosis and necrosis of midbrain neuronal and glial cultures from WT and PK-KO mice. NP7 suppressed microglial activation and the H2O2 induced drop-out of dopamine neurons. Furthermore, NP7 prevented the increased phosphorylation of ERK and AKT induced by H2O2. NP7 may be a promising neuroprotector against oxidative stress in PD. 相似文献
997.
The blue and the black wildebeest, Connochaetes taurinus and C. gnou, are currently classified as congeneric, but previous reports have placed C. taurinus in its own genus, Gorgon. To further clarify the evolutionary relationship between these two species, we examined and compared their mitotic chromosomes and mitochondrial DNA (mtDNA). No species-specific G-banded or C-banded chromosomal markers were found, and we conclude that the karyotypes are invariant at the level of resolution obtained. An evolutionary divergence time of approximately 1 million years was calculated from mtDNA restriction fragment data, indicating a close phylogenetic relationship for the two wildebeest species. The low nucleotide diversity detected within the black wildebeest (0.09%) is thought to reflect the recent population bottleneck to which the species has been subjected. In contrast, the limited heterogeneity (0.02%) within the South African blue wildebeest herds sampled in this study was surprising, and we argue that for many populations, especially those on smaller reserves, this may reflect common descent from a small number of animals through management-controlled translocations. 相似文献
998.
P Demol R Palma J J Bernier 《Archives internationales de physiologie et de biochimie》1980,88(3):237-240
In the conscious rat the increasing distension of the colon (from 2 to 6 ml) induced a slight decrease of exocrine pancreatic secretion which was more important for protein output than for volume. Nevertheless this inhibitory effect was never significant even with the important distension of 6 ml which induced a visible uneasiness in the animal. 相似文献
999.
1000.