全文获取类型
收费全文 | 106646篇 |
免费 | 1369篇 |
国内免费 | 882篇 |
专业分类
108897篇 |
出版年
2022年 | 102篇 |
2021年 | 176篇 |
2020年 | 122篇 |
2019年 | 157篇 |
2018年 | 12009篇 |
2017年 | 10781篇 |
2016年 | 7745篇 |
2015年 | 1133篇 |
2014年 | 822篇 |
2013年 | 1090篇 |
2012年 | 5165篇 |
2011年 | 13664篇 |
2010年 | 12583篇 |
2009年 | 8693篇 |
2008年 | 10501篇 |
2007年 | 12139篇 |
2006年 | 1094篇 |
2005年 | 1314篇 |
2004年 | 1746篇 |
2003年 | 1740篇 |
2002年 | 1511篇 |
2001年 | 414篇 |
2000年 | 270篇 |
1999年 | 186篇 |
1998年 | 224篇 |
1997年 | 172篇 |
1996年 | 140篇 |
1995年 | 140篇 |
1994年 | 128篇 |
1993年 | 147篇 |
1992年 | 158篇 |
1991年 | 132篇 |
1990年 | 86篇 |
1989年 | 105篇 |
1988年 | 106篇 |
1987年 | 93篇 |
1986年 | 83篇 |
1985年 | 96篇 |
1984年 | 135篇 |
1983年 | 119篇 |
1982年 | 115篇 |
1981年 | 109篇 |
1980年 | 99篇 |
1979年 | 65篇 |
1978年 | 68篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1974年 | 57篇 |
1972年 | 289篇 |
1971年 | 316篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
21.
Membrane targeting of RecA during genetic transformation 总被引:2,自引:1,他引:1
H. Robert Masure Barbara J. Pearce Helen Shio & Barbara Spellerberg 《Molecular microbiology》1998,27(4):845-852
Recombination in prokaryotes and eukaryotes is mediated by the RecA family of proteins. Although the interactions between RecA and DNA are well studied, the cellular location of these interactions is not known. Using genetic transformation of Streptococcus pneumoniae as a model system, there was increased expression of a protein, colligrin, and RecA, products of the rec locus during genetic transfer. These proteins formed a complex and were found associated with the membranes of genetically competent cells. With immunoelectron microscopy and subcellular fractionation, we showed that the induction of competence led to the translocation of RecA and colligrin to the membrane and to the formation of clusters of RecA in a colligrin-dependent step. Based on the behaviour of colligrin and RecA during genetic exchange and the numerous proteins in prokaryotes and eukaryotes with domains similar to colligrin, we suggest that there may exist a family of proteins, which gathers macromolecules at specific sites in biological membranes. 相似文献
22.
Kondeti Subramanyam K. V. Sailaja Koona Subramanyam D. Muralidhara Rao K. Lakshmidevi 《Plant Cell, Tissue and Organ Culture》2011,105(2):181-192
Plants, when exposed to abiotic or biotic stress, produce several pathogenesis-related proteins to counteract the effects
of stress. Osmotin is one of the important pathogenesis-related proteins induced during several stress conditions. We have
developed improved salt stress tolerant transgenic chilli pepper plants (Capsicum annum L. var. Aiswarya 2103) by ectopic expression of the Nicotiana tabaccum osmotin gene using Agrobacterium
tumefaciens EHA105 as a vector. Four-week-old chilli pepper leaves were used as an explant and A. tumefaciens EHA105 harboring pBINASCOSM plasmid that contains osmotin gene under the control of CaMV 35S promoter and npt II as a selectable marker was used in co-cultivation. Transgene integration and expression were analyzed using molecular,
immunochemical, and biochemical assays. PCR and Southern blot analysis confirmed that osmotin gene has been successfully integrated
into the genome of chilli pepper plants. The osmotin gene was stably segregated and expressed in T2 generation transgenic chilli pepper plants, and it was confirmed by Western blot analysis. Biochemical assays of these putative
transgenic plants revealed enhanced levels of chlorophyll, proline, glycinebetaine, APX, SOD, DHAR, MDHAR, GR, and relative
water content. Yield potential of the putative transgenic chilli pepper plants was evaluated under salinity stress conditions
in a green house. The putative transgenic chilli pepper plants overexpressing the osmotin gene were morphologically similar
to wild-type plants and produced 3.32 kg chilli pepper fruits per plant at 300 mM NaCl concentration. 相似文献
23.
Andrew Leask 《Journal of cell communication and signaling》2010,4(1):71-72
Connective tissue growth factor (CTGF/CCN2) is overexpressed in diabetes. Diabetic rats possess myocardial and cardiomyocyte
hypertrophy. In a recent report, Wang and colleagues (Am J Physiol Cell Physiol. 2009 Jul 22. [Epub ahead of print]) show
that CCN2 directly mediates cardiomyocyte hypertrophy as well as that induced by high glucose and fatty acid. CCN2 acted via
the TrkA receptor. These data are the subject of this commentary, and emphasize that CCN2 may be an excellent target for therapy
in diabetes. 相似文献
24.
The ability of an invasive plant to occupy new areas is often attributed to both morphological and physiological plasticities
that allow them to remain viable over a wide range of environmental conditions. Studies addressing the ecological requirements
of Microstegium vimineum often consider soil moisture or soil moisture along with other factors as important explanatory components for the establishment
and persistence of this invasive monocot. However, controlled studies specifically targeting water relations in M. vimineum are needed. Therefore, the purpose of this study was to determine how different water availabilities influence the growth
and physiological performance of M. vimineum. This study utilized experimental microcosms to achieve different water availabilities including low soil moisture (<15%
water), moderate soil moisture (ca. 20–30%), and flooded conditions. While both flooded and low soil moisture resulted in
diminished growth, M. vimineum still survived under these conditions. Physiological processes including C4 metabolism, minimum stress under low water conditions, and the ability to increase tissue rigidity may confer some advantages
to M. vimineum during periods of limiting water conditions. Similarly, the proportionally low root biomass, shallow root structure, and
its ability to maintain stable water relations during flooding and/or soil waterlogging may facilitate M. vimineum’s ability to invade mesic habitats. It is likely, therefore, that the capacity to tolerate both low soil moistures and flooded
conditions has enhanced the ability of M. vimineum to populate disturbed systems in central North Carolina. 相似文献
25.
26.
27.
28.
David Skelly 《BMC biology》2010,8(1):136
A new study of divergence in freshwater fish provides strong evidence of rapid, temperature-mediated adaptation. This study
is particularly important in the ongoing debate over the extent and significance of evolutionary response to climate change
because divergence has occurred in relatively few generations in spite of ongoing gene flow and in the aftermath of a significant
genetic bottleneck, factors that have previously been considered obstacles to evolution. Climate change may thus be more likely
to foster contemporary evolutionary responses than has been anticipated, and I argue here for the importance of investigating
their possible occurrence. 相似文献
29.
Barbara A. Schaal 《American journal of botany》1980,67(5):703-709
The average number of ovules produced per individual of Lupinus texensis is much greater than the average number of seeds per plant. Each plant produces approximately 2,000 ovules but only 2.5% develop into seeds. One fourth of the seeds is lost due to abortion and 0.3% is lost due to predation on the plant. Mature seeds from this population exhibit a five-fold range in weight, from 10 to 56 mg. The distribution of seed weights in the field population is skewed and leptokurtic. Seed wt is positively correlated with both seed germination and seedling survivorship. Heritability of seed wt is 0.09. There is no correlation between average seed wt per plant and total number of seeds per plant, seeds per pod, or legumes per plant. 相似文献
30.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3