全文获取类型
收费全文 | 5464篇 |
免费 | 475篇 |
国内免费 | 447篇 |
专业分类
6386篇 |
出版年
2024年 | 12篇 |
2023年 | 82篇 |
2022年 | 191篇 |
2021年 | 321篇 |
2020年 | 206篇 |
2019年 | 232篇 |
2018年 | 261篇 |
2017年 | 175篇 |
2016年 | 206篇 |
2015年 | 360篇 |
2014年 | 354篇 |
2013年 | 459篇 |
2012年 | 515篇 |
2011年 | 469篇 |
2010年 | 251篇 |
2009年 | 248篇 |
2008年 | 281篇 |
2007年 | 246篇 |
2006年 | 188篇 |
2005年 | 179篇 |
2004年 | 136篇 |
2003年 | 137篇 |
2002年 | 107篇 |
2001年 | 121篇 |
2000年 | 85篇 |
1999年 | 106篇 |
1998年 | 60篇 |
1997年 | 47篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 35篇 |
1993年 | 25篇 |
1992年 | 40篇 |
1991年 | 25篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有6386条查询结果,搜索用时 0 毫秒
81.
Nostoc flagelliforme, which is distributed on arid and semi-arid steppes of northwestern parts of China, has attracted increasing interest for
its stress tolerance. In order to gain more insight into the genetic background of N. flagelliforme, we sequenced its partial genomic DNA for similarity analyses against current public databases, followed by phylogenetic
comparison of N. flagelliforme and the potentially related species deduced from the similarity analyses. Approximately 430 kb genomic sequence (~5% of genome
as a rough estimate) was determined from 106 distinct genomic clones. Nucleotide BLAST showed that ~23.1% of the partial genomic
sequence was similar to N. punctiforme genomic DNA and ~12.4% to its plasmid DNA. Similar protein search by online FASTA-protein program showed 46.2% of the similar
proteins had their corresponding orthologs in N. punctiforme genome. Furthermore, phylogenetic comparison based on 16S rRNA sequences showed N. flagelliforme and N. punctiforme clustered closer among the deduced related species. These results indicated that N. punctiforme might also be potentially close neighbor species of N. flagelliforme, in addition to the formerly regarded close neighbor species N. commune and N. sphaeroids. In general, these data enriched our recognition of the evolutionary relationship between N. flagelliforme and other Nostoc species, especially N. punctiforme. 相似文献
82.
Nan Zhang Zhentai Han Guiling Sun Angela Hoffman Iain W. Wilson Yanfang Yang Qian Gao Jianqiang Wu Dan Xie Jungui Dai Deyou Qiu 《Biochemical and biophysical research communications》2014
Taxol is a well-known effective anticancer compound. Due to the inability to synthesize sufficient quantities of taxol to satisfy commercial demand, a biotechnological approach for a large-scale cell or cell-free system for its production is highly desirable. Several important genes in taxol biosynthesis are currently still unknown and have been shown to be difficult to isolate directly from Taxus, including the gene encoding taxoid 9α-hydroxylase. Ginkgo biloba suspension cells exhibit taxoid hydroxylation activity and provides an alternate means of identifying genes encoding enzymes with taxoid 9α-hydroxylation activity. Through analysis of high throughput RNA sequencing data from G. biloba, we identified two candidate genes with high similarity to Taxus CYP450s. Using in vitro cell-free protein synthesis assays and LC–MS analysis, we show that one candidate that belongs to the CYP716B, a subfamily whose biochemical functions have not been previously studied, possessed 9α-hydroxylation activity. This work will aid future identification of the taxoid 9α-hydroxylase gene from Taxus sp. 相似文献
83.
84.
Adler A Park YD Larsen P Nagarajan V Wollenberg K Qiu J Myers TG Williamson PR 《The Journal of biological chemistry》2011,286(23):20977-20990
85.
Mark J. Ammirati Kim M. Andrews David D. Boyer Anne M. Brodeur Dennis E. Danley Shawn D. Doran Bernard Hulin Shenping Liu R. Kirk McPherson Stephen J. Orena Janice C. Parker Jana Polivkova Xiayang Qiu Carolyn B. Soglia Judith L. Treadway Maria A. VanVolkenburg Donald C. Wilder David W. Piotrowski 《Bioorganic & medicinal chemistry letters》2009,19(7):1991-1995
A series of 4-substituted proline amides was synthesized and evaluated as inhibitors of dipeptidyl pepdidase IV for the treatment of type 2 diabetes. (3,3-Difluoro-pyrrolidin-1-yl)-[(2S,4S)-(4-(4-pyrimidin-2-yl-piperazin-1-yl)-pyrrolidin-2-yl]-methanone (5) emerged as a potent (IC50 = 13 nM) and selective compound, with high oral bioavailability in preclinical species and low plasma protein binding. Compound 5, PF-00734200, was selected for development as a potential new treatment for type 2 diabetes. 相似文献
86.
本试验以206小麦为母本,二棱大麦旱燕3号和六棱大麦原早1号为父本进进杂交。结果表明,两个组合早期的胚胎发育基本上是正常的,前者成胚率为8.75%,后者为16.8%。胚乳核最早于授粉后3天开始形成细胞。当胚乳细胞充满囊后,很快就转入迅速解体,胚随即停止生长,没有能够进一步分化出器官来。胚乳于授粉15天后,几乎全部败育,胚亦相继夭亡。胚胎发育过程中的不正常现象普遍存在。主要是极核受精过程遭受破坏;合子和初生胚乳核发育停滞;原胚虽能正常发育而胚乳没有形成;胚乳细胞过早形成和迅速解体等。讨论了杂交不孕和胚乳败育的原因。同时,提出了幼胚离体培养的适宜时间。 相似文献
87.
RNA聚合酶Ⅱ最大亚基Rpb1的羧基端结构域(carboxyl-terminal repeat domain,CTD)是RNA聚合酶Ⅱ发挥转录延伸功能所必需的,对其执行精确的转录调节功能至关重要。酵母细胞周期蛋白依赖性激酶CTDK-I(carboxyl-terminal repeat domain kinase,CTDK-I)由CTK1、CTK2和CTK3组成,作用于RNA聚合酶Ⅱ羧基端结构域,动态磷酸化CTD的七肽重复序列(YSPTSPS)来调控转录和翻译。酵母中的特异性蛋白CTK3与特殊的细胞周期蛋白CTK2结合形成异二聚体,再与CTDK-I的催化亚基CTK1结合以调节其活性。CTK1作为细胞周期蛋白CDK(cyclin dependent kinase,CDK)的同源蛋白,其结构与功能的研究可拓展人们对CDK蛋白家族的认识;CTK2-CTK3复合物对CTK1调控机制的研究也可为细胞周期蛋白抑制剂的研发提供新的思路。本文简述了酵母CTDK-I的功能特点及其亚基的结构与功能以及亚基间的相互作用,并展望了CTDK-I复合物的研究前景。 相似文献
88.
89.
Sun X Qiu J Strong SA Green LS Wasley JW Colagiovanni DB Mutka SC Blonder JP Stout AM Richards JP Chun L Rosenthal GJ 《Bioorganic & medicinal chemistry letters》2011,21(12):3671-3675
S-Nitrosoglutathione reductase (GSNOR) is a member of the alcohol dehydrogenase family (ADH) that regulates the levels of S-nitrosothiols (SNOs) through catabolism of S-nitrosoglutathione (GSNO). GSNO and SNOs are implicated in the pathogenesis of many diseases including those in respiratory, cardiovascular, and gastrointestinal systems. The pyrrole based N6022 was recently identified as a potent, selective, reversible, and efficacious GSNOR inhibitor which is currently undergoing clinical development. We describe here the synthesis and structure-activity relationships (SAR) of novel pyrrole based analogues of N6022 focusing on scaffold modification and propionic acid replacement. We identified equally potent and novel GSNOR inhibitors having pyrrole regioisomers as scaffolds using a structure based approach. 相似文献
90.