全文获取类型
收费全文 | 75872篇 |
免费 | 5244篇 |
国内免费 | 3963篇 |
专业分类
85079篇 |
出版年
2024年 | 131篇 |
2023年 | 983篇 |
2022年 | 1661篇 |
2021年 | 1915篇 |
2020年 | 1841篇 |
2019年 | 2409篇 |
2018年 | 2376篇 |
2017年 | 1685篇 |
2016年 | 1875篇 |
2015年 | 2527篇 |
2014年 | 3947篇 |
2013年 | 5381篇 |
2012年 | 2942篇 |
2011年 | 4084篇 |
2010年 | 3159篇 |
2009年 | 3864篇 |
2008年 | 4094篇 |
2007年 | 4159篇 |
2006年 | 3764篇 |
2005年 | 3640篇 |
2004年 | 3193篇 |
2003年 | 2841篇 |
2002年 | 2573篇 |
2001年 | 1690篇 |
2000年 | 1472篇 |
1999年 | 1554篇 |
1998年 | 1512篇 |
1997年 | 1288篇 |
1996年 | 1072篇 |
1995年 | 1148篇 |
1994年 | 1066篇 |
1993年 | 962篇 |
1992年 | 844篇 |
1991年 | 642篇 |
1990年 | 532篇 |
1989年 | 478篇 |
1988年 | 484篇 |
1987年 | 430篇 |
1986年 | 371篇 |
1985年 | 516篇 |
1984年 | 792篇 |
1983年 | 585篇 |
1982年 | 564篇 |
1981年 | 396篇 |
1980年 | 362篇 |
1979年 | 306篇 |
1978年 | 217篇 |
1977年 | 179篇 |
1976年 | 165篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Prashanth Sirigeri Jois 《Biochemical and biophysical research communications》2010,394(4):1036-1041
Bovine BSP5 belongs to the Binder of SPerm (BSP) family. BSP5 plays a role in the bovine sperm capacitation by promoting cholesterol and phospholipid efflux. The variable N-terminal part in the BSP proteins is the uncharacterized region with no known function. Full-length, N-terminal part, and individual fibronectin type II domains of bovine BSP5 were cloned, expressed and purified from Escherichia coli. His-S tagged N-terminal part showed large variation in migration on SDS-PAGE in comparison to other constructs. Using mass spectrometry it was demonstrated that the His-S-N-terminal part has the expected molecular mass (13 kDa). The recombinant N-terminal part was sensitive to E. coli endogenous proteases during purification. Denaturing purification involving boiling lysis of cells was carried out, as the protein was thermostable. The His-S-N-terminal part lacked structure as determined by CD analysis. Bioinformatics analyses confirmed that the N-terminal part of bovine BSP5 is intrinsically disordered. In addition, bioinformatics analysis indicated that rabbit BSP and multiple forms of BSP proteins of bovine and equine species possess partially or completely disordered N-terminus. The conservation of disorder at the N-terminus in BSP members belonging to different species suggests a role in biological process such as sperm capacitation and/or sperm-egg interactions. 相似文献
92.
93.
Jerome S. Kaye Rachel McMaster-Kaye 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,696(1):44-51
Typical somatic cell type histones are lost from the nucleus during late spermiogenesis in the house cricket; they are replaced by unusual basic proteins specific to the spermatid. We wish to characterize these proteins because they appear to determine the unusual chromatin structures of the spermatid. Molecular weights of the unusual basic proteins were estimated by chromatographing them on Bio-Gel A 0.5 M agarose columns eluted with 6 M guanidine hydrochloride. Two proteins named TH1 and TH2 have molecular weights in the range spanned by the somatic histones. The molecular weight of TH1 is 17 500 and that of TH2 is 15 500. Three additional spermatid proteins were also analyzed by molecular weight determination. They are called here protamines A, B and C, and they have molecular weights in the range typical of protamines. That of A is 6200, of B is 5500 and of C is 3800. They span the range from the large protamines typical of mammalian sperm to the small protamines of salmonid fish. The molecular weights of the TH proteins were also examined by electrophoresis on SDS-polyacrylamide gels. Amino acid compositions determined for TH1 and TH2 show that both are basic proteins rich in arginine relative to lysine. Their compositions are histone-like, but they appear to be distinct histone types rather than variant forms of the somatic histones. 相似文献
94.
When expressed in Escherichia coli, a truncated form of phytochrome (oat PHYA AP3 residues 464-1129) self associates to form a series of products ranging in size from monomers to aggregates of greater than 20 subunits. When these same phytochrome sequences are coexpressed with the chaperonins GroEL and GroES, the truncated phytochrome migrates as a native-like dimer in size exclusion chromatography and no higher-order aggregates were detected. GroEL and GroES inhibition of phytochrome aggregation in E. coli presumably occurs via the suppression of folding pathways leading to incorrectly folded phytochrome. 相似文献
95.
96.
Miguel R. Lugo Ravikiran Ravulapalli Debajyoti Dutta 《Journal of biomolecular structure & dynamics》2016,34(12):2537-2560
C3larvin toxin is a new member of the C3 class of the mono-ADP-ribosyltransferase toxin family. The C3 toxins are known to covalently modify small G-proteins, e.g. RhoA, impairing their function, and serving as virulence factors for an offending pathogen. A full-length X-ray structure of C3larvin (2.3 Å) revealed that the characteristic mixed α/β fold consists of a central β-core flanked by two helical regions. Topologically, the protein can be separated into N and C lobes, each formed by a β-sheet and an α-motif, and connected by exposed loops involved in the recognition, binding, and catalysis of the toxin/enzyme, i.e. the ADP-ribosylation turn–turn and phosphate–nicotinamide PN loops. Herein, we provide two new C3larvin X-ray structures and present a systematic study of the toxin dynamics by first analyzing the experimental variability of the X-ray data-set followed by contrasting those results with theoretical predictions based on Elastic Network Models (GNM and ANM). We identify residues that participate in the stability of the N-lobe, putative hinges at loop residues, and energy-favored deformation vectors compatible with conformational changes of the key loops and 3D-subdomains (N/C-lobes), among the X-ray structures. We analyze a larger ensemble of known C3bot1 conformations and conclude that the characteristic ‘crab-claw’ movement may be driven by the main intrinsic modes of motion. Finally, via computational simulations, we identify harmonic and anharmonic fluctuations that might define the C3larvin ‘native state.’ Implications for docking protocols are derived. 相似文献
97.
The role of the polypeptide matrix in electron transfer processes in proteins has been studied in two distinct systems: first
in a protein where the induced ET is artificial, and second as part of the catalytic cycle of an enzyme. Azurins are structurally
well-characterized blue single-copper proteins consisting of a rigid β-sheet polypeptide matrix. We have determined rate constants
and activation parameters for intramolecular long-range electron transfer between the disulfide radical anions (generated
by pulse radiolysis) and the copper(II) centre as a function of driving force and nature of the intervening medium in a large
number of wild-type and single-site-mutated proteins. In ascorbate oxidase, for which the three-dimensional structure is equally
well characterized, the internal ET from the type-I Cu(I) to the trinuclear Cu(II) centre has been studied. We find that the
results correlate well with distance through well-defined pathways using a through-bond electron tunnelling mechanism.
Received: 2 January 1997 / Accepted: 6 February 1997 相似文献
98.
99.
100.
We investigated the synthesis and translocation of amino compounds in Parasponia, a genus of the Ulmaceae that represents the only non-legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap of P. andersonii we identified asparagine. aspartate. glutamine, glutamated significant quantities of a non-protein amino acid. 4-methylglutamte(2-amino-4-methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples from P. andersonii and P. parviflora we also identified the related compounds 4-methyleneglutamate and 4-methyleneglulamine. Using 15N2 labelling and GC-Ms analysis of root nodule extracts we followed N2 fixation and ammonia assimilation in P. andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2-oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of 15N into 4-methylglutamate in nodules, demonstrating the de nova synthesis of this non protein amino acid and suggesting a role in the translation of N in symbioticParasponia. 相似文献