全文获取类型
收费全文 | 9977篇 |
免费 | 343篇 |
国内免费 | 48篇 |
专业分类
化学 | 6287篇 |
晶体学 | 174篇 |
力学 | 201篇 |
综合类 | 2篇 |
数学 | 1648篇 |
物理学 | 2056篇 |
出版年
2023年 | 53篇 |
2022年 | 162篇 |
2021年 | 155篇 |
2020年 | 153篇 |
2019年 | 191篇 |
2018年 | 215篇 |
2017年 | 258篇 |
2016年 | 482篇 |
2015年 | 364篇 |
2014年 | 453篇 |
2013年 | 822篇 |
2012年 | 552篇 |
2011年 | 630篇 |
2010年 | 438篇 |
2009年 | 339篇 |
2008年 | 599篇 |
2007年 | 520篇 |
2006年 | 448篇 |
2005年 | 376篇 |
2004年 | 339篇 |
2003年 | 266篇 |
2002年 | 220篇 |
2001年 | 182篇 |
2000年 | 134篇 |
1999年 | 84篇 |
1998年 | 88篇 |
1997年 | 67篇 |
1996年 | 81篇 |
1995年 | 71篇 |
1994年 | 64篇 |
1993年 | 62篇 |
1992年 | 57篇 |
1991年 | 81篇 |
1990年 | 56篇 |
1989年 | 78篇 |
1988年 | 68篇 |
1987年 | 57篇 |
1986年 | 56篇 |
1985年 | 120篇 |
1984年 | 116篇 |
1983年 | 78篇 |
1982年 | 75篇 |
1981年 | 81篇 |
1980年 | 72篇 |
1979年 | 68篇 |
1978年 | 43篇 |
1977年 | 45篇 |
1976年 | 54篇 |
1975年 | 51篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
991.
研究了桂枝和桂皮醛对环丙沙星在小鼠体内分布的影响,并基于此探讨了桂枝作为引药使用的作用机制.实验中将小鼠分为三组,分别灌胃生理盐水、桂枝(50gkg-1)和桂皮醛(0.25mLkg-1),然后对三组小鼠尾静脉注射环丙沙星(20mgkg-1),并以荧光法测定不同时间点小鼠体内各组织中环丙沙星的浓度.结果显示桂枝、桂皮醛均促进了环丙沙星在四肢的分布,桂枝与桂皮醛组相对于生理盐水组可将环丙沙星在四肢的含量提高约40%~200%,证实了桂枝引药到达肢节的作用.桂枝与桂皮醛组对环丙沙星分布情况的影响没有显著性差异,说明桂皮醛很可能是发挥桂枝引药作用的主要物质. 相似文献
992.
Simone Manéglier-Lacordaire Pierre Besançon Jacques Rivet Jean Flahaut 《Journal of Non》1975,18(3):439-454
The glasses of the germanium-tellurium-sulphur ternary system were investigated in order to determine the formation and crystallization processes. Vitreous samples were prepared by quenching. The vitreous transition and crystallization temperatures, together with microhardnesses, were measured throughout the vitreous region. The latter was sub-divided into several zones, and the behaviour of the glasses in each of these zones was analyzed separately. 相似文献
993.
994.
Joanna Słowikowska Janusz Lipkowski 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(2):187-189
The structure of l -seryl-l -leucine, C9H18N2O4, has been determined and analysed in relation to the geometries of its amino acid constituents. The most important feature is the different conformational behaviour of the side chains at the Cβ atoms; a less pronounced discrepancy concerns the orientation of the C=O bond with respect to the Cα—N bond. The conformational preferences of these torsion angles are also established for related structures stored in the Cambridge Structural Database [Allen & Kennard (1993). Chem.Des.Autom. News, 8 , 1, 31–37]; the title structure compares well with these data. The molecules are organized in double layers, with the hydrophilic faces linked by an extensive hydrogen-bonding network, as in l -leucine. 相似文献
995.
We investigate quantum correlations in the ground state of the Moshinsky model formed by N harmonically interacting particles confined in a harmonic potential. The model is solvable which allows an exact determination of entanglement between the subset of p particles and the remaining N ? p particles. We study linear entropies and von Neumann entropies of the bipartitions and compare their behavior with that of the relative correlation energy and of the statistical Kutzelnigg coefficient. 相似文献
996.
997.
Marija Mirković Drina Janković Sanja Vranješ‐Đurić Magdalena Radović Dragana Stanković Dušan Mijin Nadežda Nikolić 《应用有机金属化学》2012,26(7):347-355
Two novel diamine dioxime ligands, 4,7‐diaza‐3,8‐diethyldecane‐2,9‐dione bis oxime (3) and 4,9‐diaza‐3,10‐diethyldodecane‐2,11‐dione bis oxime (5), were synthesized in order to develop new brain perfusion imaging agents, based on 99mTc(V)‐complexes. The synthesis involved condensation of 2‐hydroxyimino‐3‐pentanone with appropriate diamine in protic solvent which afforded the bis imine adducts. Subsequent reduction of imine functional groups yielded a diastereoisomeric mixture of 3 and 5. UV–visible, IR, 1H NMR, 13C NMR and elemental analysis were used to characterize the structures of the synthesized compounds. 99mTc‐complexes of both diamine dioximes were prepared and radiolabeling conditions optimized to give the maximum yield. Physicochemical parameters of the labeled complexes as well as and their biodistribution in rats were investigated. Both compounds (3 and 5) formed 99mTc‐complexes with a net charge of zero, determined by electrophoresis. The resultant lipophilic 99mTc‐complexes of 3 and 5 were readily formed at pH ~9.0 within 10 min at room temperature with yields of 90% and 95%, respectively. The 99mTc‐3 complex was found to be stable within 1 h, while 99mTc‐5 was stable for a few hours. A significant brain uptake of 99mTc‐3 (2.1% injected dose) and 99mTc‐5 (1.8% injected dose) complexes, 2 min after injection, is in accordance with their lipophilicity. The present study suggests that both ligands are promising candidates as new 99mTc‐based brain‐imaging agents. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
998.
999.
1000.
Włodzimierz Fechner 《Monatshefte für Mathematik》2011,46(4):383-392
In the spirit of some earlier studies of Jean Dhombres, Roman Ger and Ludwig Reich we discuss the alienation problem for quadratic
and multiplicative mappings. 相似文献