全文获取类型
收费全文 | 110528篇 |
免费 | 8457篇 |
国内免费 | 6965篇 |
专业分类
125950篇 |
出版年
2024年 | 215篇 |
2023年 | 1451篇 |
2022年 | 3239篇 |
2021年 | 5476篇 |
2020年 | 3576篇 |
2019年 | 4374篇 |
2018年 | 4353篇 |
2017年 | 3229篇 |
2016年 | 4599篇 |
2015年 | 6677篇 |
2014年 | 7863篇 |
2013年 | 8314篇 |
2012年 | 9960篇 |
2011年 | 8868篇 |
2010年 | 5444篇 |
2009年 | 4746篇 |
2008年 | 5585篇 |
2007年 | 4923篇 |
2006年 | 4370篇 |
2005年 | 3331篇 |
2004年 | 2933篇 |
2003年 | 2531篇 |
2002年 | 2205篇 |
2001年 | 2001篇 |
2000年 | 1860篇 |
1999年 | 1841篇 |
1998年 | 1017篇 |
1997年 | 1137篇 |
1996年 | 1017篇 |
1995年 | 919篇 |
1994年 | 942篇 |
1993年 | 666篇 |
1992年 | 993篇 |
1991年 | 838篇 |
1990年 | 613篇 |
1989年 | 559篇 |
1988年 | 485篇 |
1987年 | 411篇 |
1986年 | 388篇 |
1985年 | 390篇 |
1984年 | 211篇 |
1983年 | 197篇 |
1982年 | 137篇 |
1981年 | 114篇 |
1980年 | 107篇 |
1979年 | 115篇 |
1978年 | 78篇 |
1977年 | 60篇 |
1974年 | 74篇 |
1972年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Conformation of P22 tailspike folding and aggregation intermediates probed by monoclonal antibodies. 总被引:3,自引:2,他引:1 下载免费PDF全文
M. A. Speed T. Morshead D. I. Wang J. King 《Protein science : a publication of the Protein Society》1997,6(1):99-108
The partitioning of partially folded polypeptide chains between correctly folded native states and off-pathway inclusion bodies is a critical reaction in biotechnology. Multimeric partially folded intermediates, representing early stages of the aggregation pathway for the P22 tailspike protein, have been trapped in the cold and isolated by nondenaturing polyacrylamide gel electrophoresis (PAGE) (speed MA, Wang DIC, King J. 1995. Protein Sci 4:900-908). Monoclonal antibodies against tailspike chains discriminate between folding intermediates and native states (Friguet B, Djavadi-Ohaniance L, King J, Goldberg ME. 1994. J Biol Chem 269:15945-15949). Here we describe a nondenaturing Western blot procedure to probe the conformation of productive folding intermediates and off-pathway aggregation intermediates. The aggregation intermediates displayed epitopes in common with productive folding intermediates but were not recognized by antibodies against native epitopes. The nonnative epitope on the folding and aggregation intermediates was located on the partially folded N-terminus, indicating that the N-terminus remained accessible and nonnative in the aggregated state. Antibodies against native epitopes blocked folding, but the monoclonal directed against the N-terminal epitope did not, indicating that the conformation of the N-terminus is not a key determinant of the productive folding and chain association pathway. 相似文献
92.
Jin-Cherng Lien Li-Jiau Huang Jih-Pyang Wang Che-Ming Teng Kuo-Hsiung Lee Sheng-Chu Kuo 《Bioorganic & medicinal chemistry》1997,5(12):2111-2120
A series of 2-substituted 3-chloro-1,4-naphthoquinones was synthesized, and the antiplatelet, antiinflammatory, and antiallergic activities of these compounds were evaluated. The structure-activity relationships in this series were also examined. Most of the 2-alkyl/arylcarboxamido derivatives of 3-chloro-1,4-naphthoquinone showed potent activities with similar trends in each of the activities evaluated. 相似文献
93.
Activation of cAMP-dependent protein kinase (PKA) by cell-permeable analogs of cAMP causes early and mid-vitellogenic follicles of Hyalophora cecropia to terminate vitellogenin uptake [[Wang and Telfer, 1996], Insect Biochem. Mol. Biol. 26, 85-94 (1996)]. The response is shown here to entail the formation of an epithelial diffusion barrier. Follicle cells that have been loosely organized to provide intercellular pathways for the movement of vitellogenin to the oocyte surface transform into a tight epithelium within 1-2h of exposure to PKA activators. The follicle cells can now prevent the escape of Lucifer yellow CH that has been iontophoresed into the space surrounding the oocyte, and the entry of labeled vitellogenin from the medium. As they form this functional equivalent of a tight junction, the follicle cells further reduce the intercellular spaces by enlarging and pressing against each other, and by slowing the secretion of the sulfated glycosaminoglycan matrix that separates them during vitellogenesis. The activation of PKA in early and mid-vitellogenic follicles thus appears to trigger prematurely a set of changes that do not normally occur until the follicle has grown to a length of about 2.0mm. 相似文献
94.
95.
Structural basis for the RNA binding selectivity of oligonucleotide analogues containing alkylsulfide internucleoside linkages and 2'-substituted 3'-deoxyribonucleosides. 下载免费PDF全文
In this report we describe the synthesis of oligonucleotides containing sulfide-linked dinucleoside units, namely rT(2'OH)sdT, rT(2'OMe)sdT, dTsrU(2'OMe) and dT(2'OMe)srU(2'OMe). We also describe the interactions of such oligomers with complementary DNA and RNA targets, and provide the structural basis for their remarkable RNA binding selectivity. In all cases, the Tm values of the S/P-chimera duplexes were lower than those of the corresponding unmodified duplexes. We attribute this to steric interactions between the 5'sulfur and the atoms of the nearby base/sugar residues. The 2'-substituents (i.e., 2'OH or 2'OMe) vicinal to the alkylsulfide internucleoside linkage significantly perturb the structure and stability of the duplexes formed with DNA, and more so than with RNA. The introduction of three rT(2'OH)sdTp (or rT(2'OMe)sdTp) units into an oligodeoxynucleotide sequence was sufficient to abolish binding to complementary DNA but not RNA. The same three substitutions with dTsrU(2'OMe)p and dT(2'OMe)srU(2'OMe)p did not abolish binding to DNA but the resulting complexes had poor thermal stability. The RNA-binding 'selectivity' exhibited by these oligomers is attributed to the tendency of the 2'-substituted (branched) furanoses to adopt the C3'-endo pucker, a conformation that is inconsistent with the B-form structure of helical DNA. The preference of these sugars to exist often exclusively in the C3'-endo form is attributed to stereoelectronic effects, namely gauche and anomeric effects. Our findings support the hypothesis that nucleoside analogues puckered exclusively in the C3'-endo form may result in them being especially good binders of targeted mRNA [S.H. Kawai (1991), Ph.D. Thesis, McGill University; Kawasaki et al. (1993) J. Med. Chem. 36, 831-841]. 相似文献
96.
We detected the loss of a MspI restriction site by a C to T transition at +83 bp and a G to A transition at +84 bp of the 5-end non-coding region of the human apolipoprotein AI gene. This base change occurred at the hot spot (CCGG) for methylation, which may be important in the regulation of gene expression. The population frequency for the loss of the MspI site is 6.1%. 相似文献
97.
98.
鄂西南山地植被的基本特征 总被引:1,自引:0,他引:1
本文系湖北省区划办委托进行的湖北植被类型图、植被区划图过程中的一个阶段性小结。鄂西南山地位于中国亚热带东部(湿润)常绿阔叶林亚区域,为湖北植被区划中鄂西南山地植被区,所属范围包括整个鄂西自治州、宜昌地区的大部及神农架南坡。约当北纬29°05′—31°22′,东经108°30′—111°47′的地理位置。 相似文献
99.
100.