全文获取类型
收费全文 | 11391篇 |
免费 | 741篇 |
国内免费 | 573篇 |
出版年
2024年 | 34篇 |
2023年 | 235篇 |
2022年 | 352篇 |
2021年 | 453篇 |
2020年 | 411篇 |
2019年 | 435篇 |
2018年 | 452篇 |
2017年 | 327篇 |
2016年 | 333篇 |
2015年 | 444篇 |
2014年 | 485篇 |
2013年 | 681篇 |
2012年 | 354篇 |
2011年 | 398篇 |
2010年 | 321篇 |
2009年 | 407篇 |
2008年 | 396篇 |
2007年 | 456篇 |
2006年 | 393篇 |
2005年 | 358篇 |
2004年 | 304篇 |
2003年 | 330篇 |
2002年 | 281篇 |
2001年 | 179篇 |
2000年 | 175篇 |
1999年 | 201篇 |
1998年 | 209篇 |
1997年 | 192篇 |
1996年 | 194篇 |
1995年 | 188篇 |
1994年 | 191篇 |
1993年 | 188篇 |
1992年 | 187篇 |
1991年 | 160篇 |
1990年 | 156篇 |
1989年 | 152篇 |
1988年 | 122篇 |
1987年 | 134篇 |
1986年 | 123篇 |
1985年 | 172篇 |
1984年 | 205篇 |
1983年 | 170篇 |
1982年 | 172篇 |
1981年 | 161篇 |
1980年 | 118篇 |
1979年 | 118篇 |
1978年 | 50篇 |
1977年 | 42篇 |
1976年 | 40篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
2.
C.J. Handley G. Speight K.M. Leyden D.A. Lowther 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,627(3):324-331
THe incorporation of [3H]glycine into acid-insoluble protein and of [3H]acetate into glysoaminoglycans by cultured chick chondrocytes was stimulated by the addition of L-glutamine to the incubation medium. The effect of exogenous L-glutamine on protein synthesis was studied further by examining changes in the sedimentation patterns on sucrose gardients of ribosomes isolated from chondrocytes incubated in presence and absence of L-glutamine. It was found that the absence of L-glutamine caused a disaggregation of poly-ribosomes that was reversed by the addition of this amino acid to the culture medium. No detectable glutamine synthetase activity could be measured in avian articular cartilage. These results indicate that L-glutamine is an essential amino acid for cartilage in that an extracellular supply of this amino acid is required for the maintenance of protein and glycosaminoglycan synthesis. A dependence on L-glutamine was also demonstrated for other avain connective tissues. 相似文献
3.
Using the fluorescent anion 8-anilino-1-naphthalenesulphonate (ANS) for determining the membrane surface potential necessitates that the intrinsic affinity constant Ki for the ANS sites be known. Two methods are presented which do not rely on a determination of Ki at high ionic strength. They are respectively applied to neutral membranes (egg phosphatidylcholine liposomes) and highly charged natural ones (horse bean microsomes and liposomes from their phospholipids). The value of Ki appears to be insensitive to the level of occupancy of the sites, the KCl concentration and the pH in large ranges. Furthermore, the classical Gouy-Chapman model seems to describe correctly the whole set of data, provided apparent mean molecular areas larger than the published crystallographic ones are admitted. 相似文献
4.
5.
6.
Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme·substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans. 相似文献
7.
《Developmental cell》2021,56(16):2329-2347.e6
8.
Thermoanaerobacter brockii 《Anaerobe》1997,3(6)
Thermoanaerobacter brockiifermented serine to acetate and ethanol. It oxidized leucine to isovalerate, isoleucine to 2-methylbutyrate, and valine to isobutyrate only in the presence of thiosulfate, or when co-cultured withMethanobacteriumsp. This oxidative deamination was rendered thermodynamically possible by the ability ofT. brockiito reduce thiosulfate to sulfide or the transfer of reducing equivalents to the hydrogenotrophic methanogen. The results suggest thatT. brockiimay be of ecological significance in thermal environments in the turnover of amino acids, especially with thiosulfate or H2-utilizing methanogens are present. 相似文献
9.
10.
Dehydration reduces the main phase transition pressure of phospholipids. An analysis based on the Gibbs-Duhem equation shows how the shift of the transition pressure is correlated to the hydration pressure.By using Fourier transform infrared (FT-IR) spectroscopy we determined the hydration-dependent phase transition pressure. The application of our new approach gives hydration pressure values which agree with the values obtained with the osmotic stress method. 相似文献