全文获取类型
收费全文 | 3083篇 |
免费 | 399篇 |
国内免费 | 6篇 |
出版年
2021年 | 41篇 |
2020年 | 29篇 |
2019年 | 25篇 |
2018年 | 50篇 |
2017年 | 39篇 |
2016年 | 61篇 |
2015年 | 96篇 |
2014年 | 104篇 |
2013年 | 146篇 |
2012年 | 183篇 |
2011年 | 142篇 |
2010年 | 95篇 |
2009年 | 83篇 |
2008年 | 122篇 |
2007年 | 125篇 |
2006年 | 99篇 |
2005年 | 97篇 |
2004年 | 91篇 |
2003年 | 85篇 |
2002年 | 79篇 |
2001年 | 90篇 |
2000年 | 93篇 |
1999年 | 66篇 |
1998年 | 44篇 |
1997年 | 31篇 |
1996年 | 31篇 |
1995年 | 43篇 |
1994年 | 38篇 |
1993年 | 47篇 |
1992年 | 65篇 |
1991年 | 68篇 |
1990年 | 53篇 |
1989年 | 55篇 |
1988年 | 61篇 |
1987年 | 59篇 |
1986年 | 51篇 |
1985年 | 68篇 |
1984年 | 49篇 |
1983年 | 38篇 |
1982年 | 36篇 |
1981年 | 40篇 |
1980年 | 37篇 |
1979年 | 50篇 |
1978年 | 36篇 |
1976年 | 39篇 |
1974年 | 27篇 |
1973年 | 33篇 |
1972年 | 27篇 |
1971年 | 30篇 |
1970年 | 23篇 |
排序方式: 共有3488条查询结果,搜索用时 15 毫秒
1.
L-myo-Inositol-1-phosphate synthase has been found to have at least a 5-fold preference for the beta-anomer of its natural substrate D-Glc-6-P. The alpha-anomer appears to be an inhibitor of the reaction and may be converted to product as well. As well as showing an enzymatic preference for the equatorial C-1 hydroxyl of D-Glc-6-P, our results suggest that it is the pyranose form of D-Glc-6-P that binds to the enzyme and that ring-opening is an enzymatic step. We have also found D-2-dGlc-6-P, D-2-F-2-dGlc-6-P, and D-Man-6-P each to be both competitive inhibitors and substrates that are converted to inositol phosphates by the synthase. D-Allose-6-P is a weak inhibitor of the enzyme, but not a substrate. D-Gal-6-P is neither substrate nor inhibitor. Thus the specificity of the synthase with respect to single position epimers of D-Glc-6-P increases in the order C1 less than C2 much less than C3 less than C4. 相似文献
2.
3.
4.
The existence of an optimal range of cytosolic free calcium for insulin-stimulated glucose transport in rat adipocytes 总被引:9,自引:0,他引:9
B Draznin K Sussman M Kao D Lewis N Sherman 《The Journal of biological chemistry》1987,262(30):14385-14388
We have examined the effects of extracellular and intracellular Ca2+ concentrations upon basal and insulin-stimulated 2-deoxyglucose uptake in isolated rat adipocytes. In the absence of extracellular Ca2+, both basal and insulin-stimulated glucose uptake were significantly reduced. Insulin-stimulated glucose transport was optimal at 1 and 2 mM Ca2+. Further increases in extracellular Ca2+ concentration (3 mM) significantly diminished insulin-stimulated glucose uptake. When intracellular Ca2+ concentrations were augmented by ionomycin (1 microM), insulin-stimulated glucose uptake was significantly reduced at extracellular Ca2+ concentrations of 2 and 3 mM. The levels of intracellular free Ca2+ concentrations were then measured with Ca2+ indicator fura-2. The correlation between the levels of intracellular free Ca2+ and the magnitude of insulin-stimulated glucose uptake revealed that the optimal effect of insulin is observed at Ca2+ levels between 140 and 370 nM. At both extremes outside of this window, both low and high levels of intracellular Ca2+ result in diminished cellular responsiveness to insulin. These data suggest that intracellular calcium concentrations may exert a dual role in the regulation of cellular sensitivity to insulin. First, there must exist a minimal concentration of intracellular calcium to promote insulin action. Second, increased levels of intracellular calcium may provide a critical signal for diminution of insulin action. 相似文献
5.
6.
J R Lakowicz J Ku?ba W Wiczk I Gryczynski H Szmacinski M L Johnson 《Biophysical chemistry》1991,39(1):79-84
We report the first resolution of both the conformational distribution and end-to-end diffusion coefficient of a flexible molecule. This molecular information was recovered using only the donor intensity decay in a single solvent at a single viscosity, as observed by the technique of frequency-domain fluorometry. This technique can be extended to measurements of structural fluctuations of biological macromolecules. 相似文献
7.
Our studies aimed at determining a loss of active heparin from the peritoneal cavity after its intraperitoneal administration (250 JU/l of dialysis fluid) in 16 patients treated because of the end-stage renal failure with intermittent peritoneal dialysis and at comparing heparin influx clearance with that of glucose. It has been shown that heparin used in this dose loses 60-70% of its activity after 20-minute equilibration of dialysis fluid in the peritoneal cavity. Heparin influx clearance is higher than that of glucose but it depends on utilization of heparin in peritoneal cavity rather than on its penetration to the blood circulation. 相似文献
8.
Katharine Y. Ku Fred R. Butcher 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,631(1):70-78
Calmodulin coupled to Sepharose has provided a rapid and sensitive means of isolating a cyclic nucleotide phosphodiesterase activity which is stimulated by the calmodulin-Ca2+ complex, from rat parotid gland. Initial experiments established that phosphodiesterase activity sensitive to calmodulin and Ca2+ could not be demonstrated in crude extracts of rat parotid gland or after partial purification of rat parotid phosphodiesterase over DEAE-cellulose. However, it was possible to readily demonstrate the presence of a cyclic nucleotide phosphodiesterase activity regulated by calmodulin if the extracts were first purified by batch ion-exchange chromatography over DEAE-cellulose followed by affinity chromatography with calmodulin coupled to Sepharose. The batch ion-exchange chromatography step removed the major portion of free parotid calmodulin which could compete with calmodulin-coupled Sepharose for the proteins regulated by calmodulin. Thus, by employing an initial chromatography step over DEAE-cellulose to separate phosphodiesterase activity from calmodulin, it was possible to increase the recovery of calmodulin-sensitive phosphodiesterase after affinity chromatography with calmodulin coupled to Sepharose. This approach should be useful for demonstrating the presence of and for purifying other parotid proteins regulated by calmodulin. 相似文献
9.
10.