全文获取类型
收费全文 | 8978篇 |
免费 | 439篇 |
国内免费 | 846篇 |
出版年
2024年 | 11篇 |
2023年 | 92篇 |
2022年 | 118篇 |
2021年 | 145篇 |
2020年 | 146篇 |
2019年 | 158篇 |
2018年 | 179篇 |
2017年 | 124篇 |
2016年 | 180篇 |
2015年 | 189篇 |
2014年 | 442篇 |
2013年 | 526篇 |
2012年 | 348篇 |
2011年 | 360篇 |
2010年 | 303篇 |
2009年 | 410篇 |
2008年 | 446篇 |
2007年 | 453篇 |
2006年 | 453篇 |
2005年 | 452篇 |
2004年 | 395篇 |
2003年 | 410篇 |
2002年 | 395篇 |
2001年 | 303篇 |
2000年 | 255篇 |
1999年 | 270篇 |
1998年 | 240篇 |
1997年 | 234篇 |
1996年 | 197篇 |
1995年 | 219篇 |
1994年 | 202篇 |
1993年 | 187篇 |
1992年 | 212篇 |
1991年 | 156篇 |
1990年 | 142篇 |
1989年 | 124篇 |
1988年 | 138篇 |
1987年 | 105篇 |
1986年 | 99篇 |
1985年 | 98篇 |
1984年 | 110篇 |
1983年 | 58篇 |
1982年 | 69篇 |
1981年 | 33篇 |
1980年 | 17篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
131.
132.
133.
134.
Sequence of Guinea Pig Myelin Basic Protein 总被引:5,自引:5,他引:0
Gladys E. Deibler Russell E. Martenson Henry C. Krutzsch† Marian W. Kies 《Journal of neurochemistry》1984,43(1):100-105
This paper proposes a tentative amino acid sequence of guinea pig myelin basic protein obtained by comparison of peptide fragments of the guinea pig and bovine proteins. Analyses of the tryptic peptides confirmed the known sequence differences in the NH2-terminal half of the molecule and showed that in the COOH-terminal half of the guinea pig protein Ser131 was missing, Ala136 - His137 was deleted, Leu140 was replaced by Phe, and an extra Ala was inserted somewhere within sequence 142-151 (tryptic peptide T23 ). Sequence determination of guinea pig tryptic peptides corresponding to residues 130-134 ( T20 ), 135-138 ( T21 ), and 142-151 ( T23 ) of the bovine protein confirmed the above sequence changes and placed the extra Ala between Gly142 and His143 . The sequence of the region corresponding to bovine residues 130-143 is thus Ala-Asp-Tyr-Lys-Ser-Lys-Gly-Phe-Lys-Gly-Ala-His. No species differences were observed in the amino acid compositions of the remaining tryptic peptides obtained from the COOH-terminal half of the molecule. Based upon these results, the guinea pig basic protein contains 167 amino acid residues and has a molecular weight of 18,256. 相似文献
135.
Many studies have established a correlation of differences in the activities of various muscle types with differences in the expression of myosin isoforms. In this paper we report the sequence determination of myosin light chain-2 from rabbit slow skeletal (LC2s) and ventricular (LC2v) nmscles. We sequenced tryptic peptides from LC2v which account for all except a few terminal amino acid residues. The major part (87 residues) of the rabbit LC2s sequence, obtained from tryptic and cyanogen bromide (CNBr) peptides, was found to be identical to rabbit LC2v. Our results provide the first sequence information on LC2s from any species, and lend strong support to the hypothesis that LC2s and LC2v are identical. Comparisons of rabbit LC2v and LC2s with rabbit LC2f (from fast skeletal muscle), and also with chicken LC2f and LC2v, show clearly that LC2s and LC2v from mammalian and avian species are more closely related to each other than they are to LC2f isoforms from the same species. 相似文献
136.
Selenocysteine lyase activity was detected in crude extracts from a cysteine-requiring mutant ofEscherichia coli K-12. The level of activity was the same whether cells had been grown aerobically or anaerobically, with or without selenocysteine.
Selenocysteine lyase catalyzes the conversion of selenocysteine to alanine and elemental Se, a reaction that is followed by
a nonenzymatic reduction of the Se to hydrogen selenide. Both of these end products were identified in this study. With cysteine
as the substrate, alanine and H2S were formed, but only at levels 50% less than the products formed from selenocysteine. Selenocysteine lyase has been identified
in a number of mammals and bacteria; its presence in a cysK mutant ofE. coli K-12 suggests a common route whereby hydrogen selenide, derived from selenocysteine, can then be assimilated into selenoproteins. 相似文献
137.
The amino acid sequences of cytochrome c553 from the eukaryotic red alga Porphyridium cruentum and from the prokaryotic cyanobacterium Aphanizomenon flos-aquae have been determined from the tryptic and cyanogen bromide peptides. The results indicate that a charged region of these proteins has evolved with special rapidity to accomodate a rapid evolution of a binding site in the P700 electron acceptor complex. 相似文献
138.
Summary DNA sequences homologous to the T-DNA region of the octopine Ti plasmid from Agrobacterium tumefaciens are found in various fast-growing Rhizobium fredii strains. The largest fragment (BamHI fragment 2) at the right-boundary region of the core T-DNA hybridizes to more than one plasmid present in R. fredii. However, one smaller fragment (EcoRI fragment 19a) adjacent to the core T-DNA shows homology only with the plasmid carrying the symbiotic nitrogen-fixation genes (pSym). Hybridization data obtained with digested R. fredii USDA193 pSym DNA suggests that the homology is mainly with two HindIII fragments, 1.7 kb and 8.8 kb in size, of the plasmid. The 1.7 kb HindIII fragment also hybridizes to two regions of the virulence plasmid of A. tumefaciens, pAL1819, a deletion plasmid derived from the octopine Ti plasmid, pTiAch5. Hybridization studies with an insertion element IS66 from A. tumefaciens indicate that the 1.7 kb HindIII fragment of R. fredii plasmid, homologous to the T-DNA and the virulence region of Ti plasmid, is itself an IS66 homologue. 相似文献
139.
Summary An EcoRI 2.7 kbp fragment from Chlorella ellipsoidea chloroplast DNA (cpDNA) cloned in YIp5 was shown to promote autonomous replication in Saccharomyces cerevisiae. The fragment was localized in the small single copy region close to the inverted repeat. The ARS activity (autonomously replicating sequences in yeast) was found to be confined within a subclone of a ca. 300 bp HindIII fragment. Sequence analysis of this fragment revealed its high AT content and the presence of several direct and inverted repeats and a few elements that were related to the yeast ARS consensus sequence. Electron microscopic studies revealed that this sequence did not coincide with the primary replication origin of chloroplast DNA. The functioning of this sequence as a possible origin of plasmid replication in vivo is discussed. This is the first report on Chlorella cpDNA sequence. re]19850821 rv]19851211 ac]19851216 相似文献
140.
Robert A. MacLeod 《FEMS microbiology letters》1986,39(1-2):109-113
Abstract Many species of bacteria isolated from saline environments require Na+ specifically for membrane transport. Transport occurs by a Na+ symport process energized by an electrochemical gradient of Na+ ions. The gradient at neutral pH appears to be produced by a primary electrogenic extrusion of protons coupled to a secondary, outwardly directed Na+ pump, a Na+ /proton antiporter. At alkaline pH Vibrio alginolyticus may also produce the gradient by an energy-dependent primary extrusion of Na+ ions. Alteromonas haloplanktis and Vibrio costicola require salts in the medium to retain intracellular solutes. For A. haloplanktis the effects of the salts are primarily osmotic. For V. costicola , only NaCl is effective in retaining solutes and Na+ is required by this organism to maintain the membrane potential. In Escherichia coli a single substitution in the nucleotide sequence of the gene coding for the melibiose transport protein changed the cation specificity of the transport system. The possible ecological significance of this finding has been considered. 相似文献