全文获取类型
收费全文 | 4659篇 |
免费 | 431篇 |
国内免费 | 2篇 |
出版年
2021年 | 56篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2018年 | 54篇 |
2017年 | 48篇 |
2016年 | 89篇 |
2015年 | 154篇 |
2014年 | 148篇 |
2013年 | 203篇 |
2012年 | 271篇 |
2011年 | 241篇 |
2010年 | 160篇 |
2009年 | 148篇 |
2008年 | 200篇 |
2007年 | 219篇 |
2006年 | 213篇 |
2005年 | 227篇 |
2004年 | 221篇 |
2003年 | 196篇 |
2002年 | 199篇 |
2001年 | 69篇 |
2000年 | 48篇 |
1999年 | 62篇 |
1998年 | 64篇 |
1997年 | 48篇 |
1996年 | 47篇 |
1995年 | 55篇 |
1994年 | 58篇 |
1993年 | 51篇 |
1992年 | 48篇 |
1991年 | 35篇 |
1990年 | 44篇 |
1989年 | 37篇 |
1987年 | 42篇 |
1986年 | 34篇 |
1985年 | 33篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1982年 | 53篇 |
1981年 | 46篇 |
1980年 | 45篇 |
1979年 | 28篇 |
1978年 | 41篇 |
1977年 | 32篇 |
1976年 | 36篇 |
1975年 | 31篇 |
1974年 | 42篇 |
1973年 | 41篇 |
1972年 | 32篇 |
1967年 | 28篇 |
排序方式: 共有5092条查询结果,搜索用时 0 毫秒
1.
2.
3.
Simon Rosenstein Harry D. Brown 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,629(1):195-198
Comparative assays were made in a spectrophotometer and a microcalorimeter for the reaction between acetylcholinesterase (EC 3.1.1.7) and acetylthiocholine. The rate of light absorbance change and the rate of heat flow were measured from similar and simultaneous reactions in spectrophotometer and microcalorimeter, respectively. At the enzyme activity levels studied, i.e., 0.05–0.15 I.U. in calorimetry and 1–4 I.U. in spectrophotometry, the reaction rates were linear and showed first-order kinetics. A highly significant positive correlation was seen between the two methods (r = 0.997). More importantly, spectrophotometric assay with acetylthiocholine (which utilized a secondary reaction with chromagen, dithiobisnitrobenzoic acid) stood in highly significant positive correlation with calorimetric assays (which did not require a chromagen) either with the same substrate (r = 0.976) or with acetylcholine (r = 0.900). It appears that microcalorimetry can be used in preference to spectrophotometry for enzyme kinetic studies to overcome the complexity of reaction mixture and interference problems and with the advantage of using natural substrates. 相似文献
4.
5.
Valuable biological information can be obtained by monitoring the movement of organisms. However, the choice of monitoring
method becomes highly restricted when following small organisms (<100 mm), especially in aquatic ecosystems. Stable isotopes
are being increasingly used in this respect but rarely at the local spatial scale, i.e. 10–1000 s of metres. We sought to
identify movement of small fishes between a main river channel and its tributary. Little overlap in isotope baseline was detected
between the two channels despite some temporal variability in δ15N of baseline indicator organisms in the main river. The individuals of two small cyprinid fish species (Leuciscus souffia and Alburnoides bipunctatus) of all the size classes (40–100 mm) caught within the tributary showed considerable heterogeneity in δ15N values. Classification and discriminant analysis on isotope-derived data distinguished two significantly different groups.
Moreover, this result was supported by further sampling of fish caught in the main river (in May and December 2006). Alternative
hypotheses, such as dietary differences, biological factors, temporal shifts and spatial differences in diet, did not explain
δ15N variability. This application of stable isotopes at a relatively small spatial and temporal scales further demonstrates
its potential as a tool for ecologists. 相似文献
6.
Hydrobiologia - The taxonomic composition and biomass of phytoplankton in the San Joaquin River, California, were examined in relation to water depth, flow regime, and water chemistry. Without... 相似文献
7.
8.
Harry Le Vine Pedro Cuatrecasas 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,672(3):248-261
A cytosolic, macromolecular factor required for the cholera toxin-dependent activation of pigeon erythrocyte adenylate cyclase and cholera toxin-dependent ADP-ribosylation of a membrane-bound 43 000 dalton polypeptide has been purified 1100-fold from horse erythrocyte cytosol using organic solvent precipitation and heat treatment. This factor, 13 000 daltons, does not absorb to anionic or cationic exchange resins, is sensitive to trypsin or 10% trichloroacetic acid and is not extractable by diethyl ether. Activation of adenylate cyclase by cholera toxin requires the simultaneous presence of ATP (including possible trace GTP), NAD+, dithiothreitol, cholera toxin, membranes and the cytosolic macromolecular factor. Reversal of cholera toxin activation of adenylate cyclase, and of the toxin-dependent ADP-ribosylation, requires the presence of the cytosolic factor. The ability of the purified cytosolic factor to influence the hormonal sensitivity of liver membrane adenylate cyclase may provide clues to its physiological functions. 相似文献
9.
10.
Miranda Kleijn Harry O. Voorma Adri A. M. Thomas 《Journal of cellular biochemistry》1995,59(4):443-452
Mitogenic stimulation of protein synthesis is accompanied by an increase in elF-4E phosphorylation. The effect on protein synthesis by induction of differentiation is less well known. We treated P19 embryonal carcinoma cells with the differentiating agent retinoic acid and found that protein synthesis increased during the first hour of addition. However, the phosphorylation state, as well as the turnover of phosphate on elF-4E, remained unchanged. Apparently, the change in protein synthesis after RA addition is regulated by another mechanism than elF-4E phosphorylation. By using P19 cells overexpressing the EGF receptor, we show that the signal transduction pathway that leads to phosphorylation of elF-4E is present in P19 cells; the EGF-induced change in phosphorylation of elF-4E in these cells is likely to be regulated by a change in elF-4E phosphatase activity. These results suggest that the onset of retinoic acid-induced differentiation is triggered by a signal transduction pathway which involves changes in protein synthesis, but not elF-4E phosphorylation. © 1995 Wiley-Liss, Inc. 相似文献