全文获取类型
收费全文 | 32322篇 |
免费 | 192篇 |
国内免费 | 289篇 |
专业分类
化学 | 12706篇 |
晶体学 | 278篇 |
力学 | 1488篇 |
综合类 | 12篇 |
数学 | 9627篇 |
物理学 | 8692篇 |
出版年
2022年 | 57篇 |
2021年 | 96篇 |
2020年 | 93篇 |
2019年 | 91篇 |
2018年 | 1248篇 |
2017年 | 1484篇 |
2016年 | 796篇 |
2015年 | 632篇 |
2014年 | 558篇 |
2013年 | 786篇 |
2012年 | 3287篇 |
2011年 | 2558篇 |
2010年 | 1938篇 |
2009年 | 1681篇 |
2008年 | 737篇 |
2007年 | 785篇 |
2006年 | 777篇 |
2005年 | 4564篇 |
2004年 | 4026篇 |
2003年 | 2399篇 |
2002年 | 596篇 |
2001年 | 329篇 |
2000年 | 127篇 |
1999年 | 207篇 |
1998年 | 137篇 |
1997年 | 105篇 |
1996年 | 106篇 |
1995年 | 74篇 |
1994年 | 88篇 |
1993年 | 55篇 |
1992年 | 202篇 |
1991年 | 181篇 |
1990年 | 163篇 |
1989年 | 128篇 |
1988年 | 126篇 |
1987年 | 77篇 |
1986年 | 68篇 |
1985年 | 88篇 |
1984年 | 82篇 |
1983年 | 66篇 |
1982年 | 51篇 |
1981年 | 57篇 |
1980年 | 56篇 |
1979年 | 78篇 |
1976年 | 99篇 |
1975年 | 48篇 |
1974年 | 59篇 |
1973年 | 62篇 |
1970年 | 49篇 |
1968年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
Ekkehard Kr?tzel Werner Georg Nowak László Tóth 《Central European Journal of Mathematics》2012,10(2):761-774
The paper deals with asymptotics for a class of arithmetic functions which describe the value distribution of the greatest-common-divisor
function. Typically, they are generated by a Dirichlet series whose analytic behavior is determined by the factor ζ2(s)ζ(2s − 1). Furthermore, multivariate generalizations are considered. 相似文献
992.
A model of spring-block on a moving plate with a nonlinear periodic substrate potential whose shape can be varied continuously as a function of a shape parameter is investigated. The dynamical study of the system for different values of the shape parameter involves the analysis of phase space, the construction of bifurcation diagrams, and the computation of the largest Lyapunov exponent. A smart damper associated with drag coefficient is proposed to reduce stick-slip and chaotic motions. The domain of validity of the control method is derived. 相似文献
993.
Magaly A. M. Lyra José L. Soares-Sobrinho Regina C. B. Q. Figueiredo Jana M. Sandes ádley A. N. Lima R?mulo P. Tenório Danilo A. F. Fontes Fabiana L. A. Santos Larissa A. Rolim Pedro J. Rolim-Neto 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):397-404
The current chemotherapy for Chagas disease is still based on benznidazole, which has low solubility, but complexation with cyclodextrins provides a way of increasing the solubility. The objective of this work was to characterize the inclusion complexes formed between benznidazole (BNZ) and randomly 2-methyled-β-cyclodextrin (RM-β-CD) in aqueous solution and study cytotoxicity and trypanocidal. BNZ:RM-β-CD solution complex systems were prepared and characterized using the phase solubility diagram, nuclear magnetic resonance and a photostability assays, also to investigate the in vitro trypanocidal activity with epimastigote forms of Trypanossoma cruzi and the study of cytotoxicity against mammal cells. The phase-solubility diagram displayed an A L-type feature, providing evidence of the formation of soluble inclusion complexes. The continuous variation method showed the existence of a complex with 1:1 stoichiometry. Toxicity assays demonstrated that inclusion complexes were able to reduce the toxic effects caused by benznidazole alone and that this did not interfere with the trypanocidal activity of the benznidazole. The use of inclusion complexes benznidazole:cyclodextrin is thus a promising alternative for the development of a safe and stable liquid formulation and a new option for the treatment of Chagas disease. 相似文献
994.
A. Habibi H. S. Ghorbani G. Bruno H. A. Rudbari Y. Valizadeh 《Crystallography Reports》2013,58(7):1084-1087
The crystal structure of 1-Methyl-3-([2,2-dimethyl-4,6-dioxo-1,3-dioxane-5-ylidene]methyl)urea (C9H12N2O5) has been determined by single crystal X-ray diffraction analysis. The crystals are monoclinic, a = 5.3179(2), b = 18.6394(6), c =10.8124(3) Å, β = 100.015(2)°, Z = 4, sp. gr. P21/c, R = 0.0381 for 2537 reflections with I > 2σ(I). Except for C(CH3)2 group, the molecule is planar. The structure is stabilized by inter- and intramolecular N-H...O hydrogen bonds and weak C-H...O interactions. 相似文献
995.
996.
Vijayanand Chandrasekaran Eugen Johannes Hauke Kobarg Frank D S?nnichsen Thisbe K Lindhorst 《ChemistryOpen》2014,3(3):99-108
Spatial orientation of carbohydrates is a meaningful parameter in carbohydrate recognition processes. To vary orientation of sugars with temporal and spatial resolution, photosensitive glycoconjugates with favorable photochromic properties appear to be opportune. Here, a series of azobenzene glycosides were synthesized, employing glycoside synthesis and Mills reaction, to allow “switching” of carbohydrate orientation by reversible E/Z isomerization of the azobenzene N=N double bond. Their photochromic properties were tested and effects of azobenzene substitution as well as the effect of anomeric configuration and the orientation of the sugars 2-hydroxy group were evaluated. 相似文献
997.
998.
999.
P. Ko?cik A. Okopińska 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(3):93
We study systems of a few charged bosons contained within a strongly anisotropic harmonic
trap. A detailed examination of the ground-state correlation properties of two-, three-,
and four-particle systems is carried out within the framework of the single-mode
approximation of the transverse components. The linear correlation entropy of the quasi-1D
systems is discussed in dependence on the confinement anisotropy and compared with a
strictly 1D limit. Only at weak interaction the correlation properties depend strongly on
the anisotropy parameter. 相似文献
1000.
We give an elementary proof of a majorization inequality concerning Wright-convex functions. 相似文献