全文获取类型
收费全文 | 52430篇 |
免费 | 17783篇 |
国内免费 | 1212篇 |
出版年
2023年 | 219篇 |
2022年 | 364篇 |
2021年 | 1192篇 |
2020年 | 2652篇 |
2019年 | 4322篇 |
2018年 | 4470篇 |
2017年 | 4593篇 |
2016年 | 4859篇 |
2015年 | 5246篇 |
2014年 | 5070篇 |
2013年 | 5774篇 |
2012年 | 3795篇 |
2011年 | 3471篇 |
2010年 | 4208篇 |
2009年 | 2749篇 |
2008年 | 2070篇 |
2007年 | 1541篇 |
2006年 | 1460篇 |
2005年 | 1378篇 |
2004年 | 1248篇 |
2003年 | 1204篇 |
2002年 | 1110篇 |
2001年 | 975篇 |
2000年 | 851篇 |
1999年 | 731篇 |
1998年 | 316篇 |
1997年 | 265篇 |
1996年 | 251篇 |
1995年 | 219篇 |
1994年 | 212篇 |
1993年 | 164篇 |
1992年 | 340篇 |
1991年 | 346篇 |
1990年 | 283篇 |
1989年 | 297篇 |
1988年 | 246篇 |
1987年 | 221篇 |
1986年 | 211篇 |
1985年 | 230篇 |
1984年 | 187篇 |
1983年 | 160篇 |
1982年 | 135篇 |
1981年 | 142篇 |
1979年 | 155篇 |
1978年 | 140篇 |
1977年 | 111篇 |
1976年 | 109篇 |
1975年 | 124篇 |
1974年 | 128篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Madeleine St Clair Yewers Devi Stuart‐Fox Claire Alice McLean 《Ecology and evolution》2019,9(1):295-306
Space use including territoriality and spatial arrangement within a population can reveal important information on the nature, dynamics, and evolutionary maintenance of alternative strategies in color polymorphic species. Despite the prevalence of color polymorphic species as model systems in evolutionary biology, the interaction between space use and genetic structuring of morphs within populations has rarely been examined. Here, we assess the spatial and genetic structure of male throat color morphs within a population of the tawny dragon lizard, Ctenophorus decresii. Male color morphs do not differ in morphology but differ in aggressive and antipredator behaviors as well as androgen levels. Despite these behavioral and endocrine differences, we find that color morphs do not differ in territory size, with their spatial arrangement being essentially random with respect to each other. There were no differences in genetic diversity or relatedness between morphs; however, there was significant, albeit weak, genetic differentiation between morphs, which was unrelated to geographic distance between individuals. Our results indicate potential weak barriers to gene flow between some morphs, potentially due to nonrandom pre‐ or postcopulatory mate choice or postzygotic genetic incompatibilities. However, space use, spatial structure, and nonrandom mating do not appear to be primary mechanisms maintaining color polymorphism in this system, highlighting the complexity and variation in alternative strategies associated with color polymorphism. 相似文献
142.
Sarkar Avipsha Sen Shampa 《International journal of peptide research and therapeutics》2020,26(1):209-223
International Journal of Peptide Research and Therapeutics - Computer Aided Drug Discovery (CADD) has become a vital tool for the rapid identification of new candidate molecules prior to their... 相似文献
143.
144.
145.
146.
Interspecific transformation in Azotobacter 总被引:8,自引:0,他引:8
147.
148.
149.
Murine histocompatibility antigens were solubilized from the spleens and lungs of C57BL/6 (H-2b) animals with hypertonic salt (3 M KC1). Aggregate-free soluble antigens were incubated with nonadherent lymph node cells from BALB/c (H-2d) mice for 18 hr prior to their use as responder cells in the mixed-lymphocyte reaction (MLR). It was found that the generation of cytotoxic cells was suppressed while the proliferative response was not affected. The observed suppression was not due to a shift in the kinetics of the generation of cytotoxicity as determined throughout a 10-day culture period. The suppression was specific in that the response in MLR to unrelated H-2f stimulator cells and the subsequent generation of cytotoxic cells were unchanged. Using various H-2 recombinant strains as target cells in the assay of cell-mediated lympholysis, suppression of cytotoxicity was observed when the D end, but not the K end, was shared with the C57BL/6 strain from which the antigens were derived. 相似文献
150.
Pirjo Rajaniemi‐Wacklin Anne Rantala Maria. A. Mugnai Silvia Turicchia Stefano Ventura Jarka Komrkov Liisa Lepist Kaarina Sivonen 《Journal of phycology》2006,42(1):226-232
In this study, the first reported isolates of the genera Snowella and Woronichinia were characterized by 16S rRNA gene sequencing and morphological analysis. Phylogenetic studies and sequences for these genera were not available previously. By botanical criteria, the five isolated strains were identified as Snowella litoralis (Häyrén) Komárek et Hindák Snowella rosea (Snow) Elenkin and Woronichinia naegeliana (Unger) Elenkin. This study underlines the identification of freshly isolated cultures, since the Snowella strains lost the colony structure and were not identifiable after extended laboratory cultivation. In the 16S rRNA gene analysis, the Snowella strains formed a monophyletic cluster, which was most closely related to the Woronichinia strain. Thus, our results show that the morphology of the genera Snowella and Woronichinia was in congruence with their phylogeny, and their phylogeny seems to support the traditional botanical classification of these genera. Furthermore, the genera Snowella and Woronichinia occurred commonly and might occasionally be the most abundant cyanobacterial taxa in mainly oligotrophic and mesotrophic Finnish lakes. Woronichinia occurred frequently and also formed blooms in eutrophic Czech reservoirs. 相似文献