全文获取类型
收费全文 | 40824篇 |
免费 | 3357篇 |
国内免费 | 3079篇 |
出版年
2024年 | 14篇 |
2023年 | 502篇 |
2022年 | 640篇 |
2021年 | 2010篇 |
2020年 | 1464篇 |
2019年 | 1844篇 |
2018年 | 1750篇 |
2017年 | 1265篇 |
2016年 | 1854篇 |
2015年 | 2490篇 |
2014年 | 3043篇 |
2013年 | 3269篇 |
2012年 | 3904篇 |
2011年 | 3372篇 |
2010年 | 2090篇 |
2009年 | 1808篇 |
2008年 | 2074篇 |
2007年 | 1818篇 |
2006年 | 1537篇 |
2005年 | 1357篇 |
2004年 | 1155篇 |
2003年 | 1045篇 |
2002年 | 909篇 |
2001年 | 751篇 |
2000年 | 695篇 |
1999年 | 688篇 |
1998年 | 436篇 |
1997年 | 445篇 |
1996年 | 427篇 |
1995年 | 384篇 |
1994年 | 349篇 |
1993年 | 230篇 |
1992年 | 340篇 |
1991年 | 258篇 |
1990年 | 225篇 |
1989年 | 184篇 |
1988年 | 124篇 |
1987年 | 124篇 |
1986年 | 81篇 |
1985年 | 96篇 |
1984年 | 61篇 |
1983年 | 53篇 |
1982年 | 42篇 |
1981年 | 26篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
23.
Chao Chen Xiaoli Sun Huizi Duanmu Dan Zhu Yang Yu Lei Cao Ailin Liu Bowei Jia Jialei Xiao Yanming Zhu 《PloS one》2015,10(11)
Calcium, as the most widely accepted messenger, plays an important role in plant stress responses through calcium-dependent signaling pathways. The calmodulin-like family genes (CMLs) encode Ca2+ sensors and function in signaling transduction in response to environmental stimuli. However, until now, the function of plant CML proteins, especially soybean CMLs, is largely unknown. Here, we isolated a Glycine soja CML protein GsCML27, with four conserved EF-hands domains, and identified it as a calcium-binding protein through far-UV CD spectroscopy. We further found that expression of GsCML27 was induced by bicarbonate, salt and osmotic stresses. Interestingly, ectopic expression of GsCML27 in Arabidopsis enhanced plant tolerance to bicarbonate stress, but decreased the salt and osmotic tolerance during the seed germination and early growth stages. Furthermore, we found that ectopic expression of GsCML27 decreases salt tolerance through modifying both the cellular ionic (Na+, K+) content and the osmotic stress regulation. GsCML27 ectopic expression also decreased the expression levels of osmotic stress-responsive genes. Moreover, we also showed that GsCML27 localized in the whole cell, including cytoplasm, plasma membrane and nucleus in Arabidopsis protoplasts and onion epidermal cells, and displayed high expression in roots and embryos. Together, these data present evidence that GsCML27 as a Ca2+-binding EF-hand protein plays a role in plant responses to bicarbonate, salt and osmotic stresses. 相似文献
24.
Hydroxyacid dehydrogenases are responsible for the conversion of 2-keto acids to 2-hydroxyacids and have a wide range of biotechnological applications. In this study, a D-lactate dehydrogenase (D-LDH) from a Sporolactobacillus inulinus strain was experimentally verified to have both the D-LDH and glutamate dehydrogenase (GDH) activities (reversible deamination). The catalytic mechanism was demonstrated by identification of key residues from the crystal structure analysis and site-directed mutagenesis. The Arg234 and Gly79 residues of this enzyme play a significant role in both D-LDH and GDH activities. His295 and Phe298 in DLDH744 were identified to be key residues for lactate dehydrogenase (LDH) activity only whereas Tyr101 is a unique residue that is critical for GDH activity. Characterization of the biochemical properties contributes to understanding of the catalytic mechanism of this novel D-lactate dehydrogenase enzyme. 相似文献
25.
The surface-exposed tyrosine residue Tyr83 of pea plastocyanin is involved in both binding and electron transfer reactions with cytochrome f. 总被引:5,自引:1,他引:4 下载免费PDF全文
Site-directed mutants of the pea plastocyanin gene in which the codon for the surface-exposed Tyr83 has been changed to codons for Phe83 and Leu83 have been expressed in transgenic tobacco plants. The mutant proteins have been purified to homogeneity and their conformations shown not to differ significantly from the wild-type plastocyanin by 1H-NMR and CD. Overall rate constants for electron transfer (k2) from cytochrome f to plastocyanin have been measured by stopped-flow spectrophotometry and rate constants for binding (ka) and association constants (KA) have been measured from the enhanced Soret absorption of cytochrome f on binding plastocyanin. These measurements allow the calculation of the intrinsic rate of electron transfer in the binary complex. An 8-fold decrease in the overall rate of electron transfer to the Phe83 mutant is due entirely to a decreased association constant for cytochrome f, whereas the 40-fold decrease in the overall rate of electron transfer to the Leu83 mutant is due to weaker binding and a lower intrinsic rate of electron transfer. This indicates that Tyr83 is involved in binding to cytochrome f and forms part of the main route of electron transfer. 相似文献
26.
27.
28.
Fei Mi Ying Zhang Dan Yang Xiaozhao Tang Pengfei Wang Xiaoxia He Yunrun Zhang Jianyong Dong Yang Cao Chunli Liu Ke-Qin Zhang Jianping Xu 《PloS one》2016,11(2)
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China. 相似文献
29.
30.
Mo Hui-Juan Sun Yan-Xiang Zhu Xiao-Li Wang Xing-Fen Zhang Yan Yang Jun Yan Gui-Jun Ma Zhi-Ying 《Planta》2016,243(4):1023-1039
Planta - Cotton S-adenosylmethionine decarboxylase-, rather than spermine synthase-, mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense... 相似文献