全文获取类型
收费全文 | 4424篇 |
免费 | 348篇 |
国内免费 | 2篇 |
出版年
2021年 | 39篇 |
2019年 | 37篇 |
2018年 | 46篇 |
2017年 | 34篇 |
2016年 | 73篇 |
2015年 | 111篇 |
2014年 | 126篇 |
2013年 | 183篇 |
2012年 | 225篇 |
2011年 | 206篇 |
2010年 | 137篇 |
2009年 | 120篇 |
2008年 | 215篇 |
2007年 | 209篇 |
2006年 | 197篇 |
2005年 | 168篇 |
2004年 | 176篇 |
2003年 | 179篇 |
2002年 | 166篇 |
2001年 | 76篇 |
2000年 | 77篇 |
1999年 | 60篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 51篇 |
1995年 | 67篇 |
1994年 | 43篇 |
1993年 | 57篇 |
1992年 | 51篇 |
1991年 | 49篇 |
1990年 | 42篇 |
1989年 | 41篇 |
1988年 | 42篇 |
1987年 | 32篇 |
1986年 | 30篇 |
1985年 | 35篇 |
1984年 | 41篇 |
1983年 | 39篇 |
1982年 | 29篇 |
1981年 | 43篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1978年 | 50篇 |
1977年 | 25篇 |
1975年 | 28篇 |
1974年 | 28篇 |
1973年 | 32篇 |
1971年 | 25篇 |
1966年 | 30篇 |
1956年 | 24篇 |
排序方式: 共有4774条查询结果,搜索用时 15 毫秒
1.
2.
A comparison of the antimuscarinic effects of pirenzepine and N-methylatropine on ganglionic and vascular muscarinic receptors in the rat 总被引:2,自引:0,他引:2
The antimuscarinic properties of pirenzepine and N-methylatropine were evaluated in two intact preparations by measuring A) the inhibition of increase in mean arterial pressure evoked by McN-A-343 in pithed rats through activation of ganglionic muscarinic receptors and B) the inhibition of fall in arterial pressure evoked by methacholine in anaesthetized rats through activation of vascular muscarinic receptors. To characterize the antimuscarinic potencies of pirenzepine and N-methylatropine, for both antagonists doses were calculated that produce a 10-fold shift to the right of the dose-response curves for A) the pressor response to McN-A-343 (i.v. administration) in pithed rats (D10-p.r.) and B) for the depressor effect to methacholine (i.v. administration) in anaesthetized rats (D10-an.r.), respectively. Whereas N-methylatropine was virtually equieffective in blocking both muscarinic responses (D10-an.r./D10-p.r. approximately equal to 1), pirenzepine, however, was considerably more potent at ganglionic than at vascular muscarinic receptors (D10-an.r./D10-p.r. approximately equal to 16). These data confirm the existence of excitatory ganglionic muscarinic receptors with high affinity for pirenzepine (M1) and provide evidence for the presence of M2 receptors - receptors which show a low sensitivity to pirenzepine - on vascular smooth muscle cells. To further characterize the anticholinergic properties of pirenzepine, its effect on the pressor response to DMPP, a nicotinic ganglionic stimulant, was investigated in pithed rats. A high dose of pirenzepine (1.13 mumol/kg), given i.v., did not affect nicotinic ganglionic transmission. 相似文献
3.
Regina M. Santella Dezider Grunberger Alfred Nordheim Alexander Rich 《Biochemical and biophysical research communications》1982,106(4):1226-1232
Poly(dG-m5dC)·poly(dG-m5dC) was modified by treatment with N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF) and its conformation examined by circular dichroism (CD) and susceptibility to S1 nuclease digestion. A sample with a modification level of 10% shows a CD spectrum characteristic of the Z form and is resistant to digestion by S1 nuclease. The relative reactivity of several polymers with N-Aco-AAF was shown to follow the order of ease of formation of Z DNA: poly(dG-m5dC)·poly(dG-m5dC) > poly(dG-dC)·poly(dG-dC) > poly(dG)·poly(dC). This suggests that AAF reacts more readily with Z DNA than B DNA. 相似文献
4.
The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H+ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation. 相似文献
5.
6.
Alfred Fischel 《Development genes and evolution》1915,41(2):312-322
Ohne Zusammenfassung 相似文献
7.
8.
9.
10.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献