全文获取类型
收费全文 | 5694篇 |
免费 | 535篇 |
出版年
2022年 | 40篇 |
2021年 | 73篇 |
2020年 | 43篇 |
2019年 | 37篇 |
2018年 | 69篇 |
2017年 | 62篇 |
2016年 | 113篇 |
2015年 | 192篇 |
2014年 | 199篇 |
2013年 | 260篇 |
2012年 | 341篇 |
2011年 | 295篇 |
2010年 | 193篇 |
2009年 | 181篇 |
2008年 | 226篇 |
2007年 | 259篇 |
2006年 | 239篇 |
2005年 | 242篇 |
2004年 | 244篇 |
2003年 | 228篇 |
2002年 | 223篇 |
2001年 | 110篇 |
2000年 | 85篇 |
1999年 | 89篇 |
1998年 | 72篇 |
1997年 | 58篇 |
1996年 | 66篇 |
1995年 | 66篇 |
1994年 | 81篇 |
1993年 | 72篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 74篇 |
1989年 | 58篇 |
1988年 | 51篇 |
1987年 | 63篇 |
1986年 | 51篇 |
1985年 | 54篇 |
1984年 | 65篇 |
1983年 | 52篇 |
1982年 | 64篇 |
1981年 | 61篇 |
1980年 | 56篇 |
1979年 | 44篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 38篇 |
1975年 | 37篇 |
1974年 | 45篇 |
1973年 | 50篇 |
排序方式: 共有6229条查询结果,搜索用时 15 毫秒
1.
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
2.
3.
4.
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
5.
6.
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
7.
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
8.
G. Matthew Hebdon Harry Le Vine Naji E. Sahyoun Claus J. Schmitges Pedro Cuatrecasas 《Life sciences》1980,26(17):1385-1396
3T3C2 mouse fibroblasts rendered permeable to (α?32P)NAD+ show cholera toxin-dependent labeling of a 45,000 m.w. protein and of a doublet of polypeptides around 52,000 m.w. These same bands are ADP-ribosylated in broken cells. Membranes prepared from pigeon erythrocytes pretreated with choleragen show a decrease in subsequent cholera toxin-specific ADP-ribosylation of a 43,000 m.w. polypeptide. Both whole cell and broken cell adenylate cyclase activation and toxin-specific ADP-ribosylation are reversed specifically by low pH and high concentrations of toxin and nicotinamide in all systems. Thus ADP-ribosylation appears to be relevant to the molecular action of choleragen in whole cells as well as in broken cells. 相似文献
9.
10.
Bart A. Nolet Abel Gyimesi Roderick R. D. van Krimpen Willem F. de Boer Richard A. Stillman 《PloS one》2016,11(2)
Predicting the environmental impact of a proposed development is notoriously difficult, especially when future conditions fall outside the current range of conditions. Individual-based approaches have been developed and applied to predict the impact of environmental changes on wintering and staging coastal bird populations. How many birds make use of staging sites is mostly determined by food availability and accessibility, which in the case of many waterbirds in turn is affected by water level. Many water systems are regulated and water levels are maintained at target levels, set by management authorities. We used an individual-based modelling framework (MORPH) to analyse how different target water levels affect the number of migratory Bewick’s swans Cygnus columbianus bewickii staging at a shallow freshwater lake (Lauwersmeer, the Netherlands) in autumn. As an emerging property of the model, we found strong non-linear responses of swan usage to changes in water level, with a sudden drop in peak numbers as well as bird-days with a 0.20 m rise above the current target water level. Such strong non-linear responses are probably common and should be taken into account in environmental impact assessments. 相似文献