全文获取类型
收费全文 | 1161篇 |
免费 | 144篇 |
出版年
2021年 | 20篇 |
2017年 | 16篇 |
2016年 | 15篇 |
2015年 | 27篇 |
2014年 | 29篇 |
2013年 | 37篇 |
2012年 | 42篇 |
2011年 | 45篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 32篇 |
2007年 | 42篇 |
2006年 | 27篇 |
2005年 | 35篇 |
2004年 | 41篇 |
2003年 | 28篇 |
2002年 | 28篇 |
2001年 | 39篇 |
2000年 | 28篇 |
1999年 | 31篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1993年 | 15篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 34篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1982年 | 28篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 12篇 |
1972年 | 9篇 |
1971年 | 14篇 |
1970年 | 12篇 |
1969年 | 17篇 |
1968年 | 15篇 |
1966年 | 13篇 |
排序方式: 共有1305条查询结果,搜索用时 171 毫秒
91.
Xinghua?LuEmail author Chengxiang?Zhai Vanathi?Gopalakrishnan Bruce?G?Buchanan 《BMC bioinformatics》2004,5(1):122
Background
Conserved protein sequence motifs are short stretches of amino acid sequence patterns that potentially encode the function of proteins. Several sequence pattern searching algorithms and programs exist foridentifying candidate protein motifs at the whole genome level. However, amuch needed and importanttask is to determine the functions of the newly identified protein motifs. The Gene Ontology (GO) project is an endeavor to annotate the function of genes or protein sequences with terms from a dynamic, controlled vocabulary and these annotations serve well as a knowledge base. 相似文献92.
Spencer KA Buchanan KL Goldsmith AR Catchpole CK 《Proceedings. Biological sciences / The Royal Society》2004,271(Z3):S121-S123
Bird song is a sexually selected trait and females have been shown to prefer males that sing more complex songs. However, for repertoire size to be an honest signal of male quality it must be associated with some form of cost. This experiment investigates the effects of food restriction and social status during development on song complexity in the European starling (Sturnus vulgaris). Birds that experienced an unpredictable food supply early in life produced a significantly smaller repertoire of song phrases than those with a constant food supply. Social status during development was also significantly correlated with repertoire size, with dominant birds producing more phrase types. This study therefore provides novel evidence that social as well as nutritional history may be important in shaping the song signal in this species. 相似文献
93.
Genes are widely assumed to play a major role in the epidemiology of complex chronic diseases, yet attempts to characterize the genetic architecture of such traits have been frustrating. Understanding that evolution works by screening phenotypes rather than genotypes can help explain the source of this frustration. Complex traits are usually the result of long-term, often subtle, gene-environment interactions, such that individual life histories may be as important as population histories in predicting and explaining these traits. Recognizing that the problem is not due to technological limitations can help temper expectations and guide the design of future work in biomedical genetics, by allowing us to focus on better approaches where they exist and on those problems most likely to yield a genetic solution. We may even be forced to re-conceive complex biological causation. 相似文献
94.
The Escherichia coli Tat system serves to export folded proteins harbouring an N-terminal twin-arginine signal peptide across the cytoplasmic membrane. In this report we have studied the functions of conserved residues within the structurally related TatA and TatB proteins. Our results demonstrate that there are two regions within each protein of high sequence conservation that are critical for efficient Tat translocase function. The first region is the interdomain hinge between the transmembrane and the amphipathic alpha-helices of TatA and TatB proteins. The second region is within the amphipathic helices of TatA and TatB. In particular an invariant phenylalanine residue within TatA proteins is essential for activity, whereas a string of glutamic acid residues on the same face of the amphipathic helix of TatB is important for function. 相似文献
95.
The absolute configuration of the 2-substituted arabinitol 1-phosphate residue present in the repeating unit of the capsular polysaccharide (CPS) from Streptococcus pneumoniae Type 17F is confirmed as D, based on a comparison of proton and carbon chemical shifts in a synthetic oligosaccharide and in an oligosaccharide derived from the CPS by degradation. 相似文献
96.
97.
98.
Huang CY Buchanan DL Gordon RL Sherman MJ Razzaq J White K Buetow DE 《Cell biochemistry and function》2003,21(4):355-361
Chronic pressure overload leads to an increase in the size, i.e. hypertrophy, of cardiomyocytes in the heart. However, the molecular mechanisms underlying this hypertrophy are not understood. Insulin-like growth factor-I (IGF-I) synthesized locally in the heart is known to be associated with the hypertrophic process. So far, however, cardiac IGF-I gene expression in the widely used rat model system has only been shown to be increased when the hypertrophy induced by pressure-overload was already established. Therefore, the question of whether IGF-I serves as an initiating or early-enhancing factor for the cardiac hypertrophy remains unanswered. Here, cardiac hypertension and hypertrophy were rapidly induced in the rat by complete constriction of the abdominal aorta between the origins of the renal arteries. Carotid arterial systolic blood pressure remained unchanged in sham rats but increased rapidly in the pressure-overloaded constricted rats with a sustained hypertension established by 3 days. Hypertrophy of left ventricular (LV) cardiomyocytes in constricted rats also occurred by 3 days. However, this hypertrophy was preceded by increases in LV IGF-I mRNA and protein which occurred within 1 day. These results support the hypothesis that cardiac-synthesized IGF-I is an initiating or early-enhancing factor for hypertrophy of LV cardiomyocytes. 相似文献
99.
The mob genes of several bacteria have been implicated in the conversion of molybdopterin to molybdopterin guanine dinucleotide. The mob locus of Rhodobacter sphaeroides WS8 comprises three genes, mobABC. Chromosomal in-frame deletions in each of the mob genes have been constructed. The mobA mutant strain has inactive DMSO reductase and periplasmic nitrate reductase activities (both molybdopterin guanine dinucleotide-requiring enzymes), but the activity of xanthine dehydrogenase, a molybdopterin enzyme, is unaffected. The inability of a mobA mutant to synthesise molybdopterin guanine dinucleotide is confirmed by analysis of cell extracts of the mobA strain for molybdenum cofactor forms following iodine oxidation. Mutations in mobB and mobC are not impaired for molybdoenzyme activities and accumulate wild-type levels of molybdopterin and molybdopterin guanine dinucleotide, indicating they are not compromised in molybdenum cofactor synthesis. In the mobA mutant strain, the inactive DMSO reductase is found in the periplasm, suggesting that molybdenum cofactor insertion is not necessarily a pre-requisite for export. 相似文献
100.
3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the formation of mevalonate, the committed step in the biosynthesis of sterols and isoprenoids. The activity of HMGR is controlled through synthesis, degradation and phosphorylation to maintain the concentration of mevalonate-derived products. In addition to the physiological regulation of HMGR, the human enzyme has been targeted successfully by drugs in the clinical treatment of high serum cholesterol levels. Three crystal structures of the catalytic portion of human HMGR in complexes with HMG-CoA, with HMG and CoA, and with HMG, CoA and NADP(+), provide a detailed view of the enzyme active site. Catalytic portions of human HMGR form tight tetramers. The crystal structure explains the influence of the enzyme's oligomeric state on the activity and suggests a mechanism for cholesterol sensing. The active site architecture of human HMGR is different from that of bacterial HMGR; this may explain why binding of HMGR inhibitors to bacterial HMGRs has not been reported. 相似文献