全文获取类型
收费全文 | 33055篇 |
免费 | 2827篇 |
国内免费 | 3441篇 |
专业分类
化学 | 22133篇 |
晶体学 | 593篇 |
力学 | 1070篇 |
综合类 | 338篇 |
数学 | 5412篇 |
物理学 | 9777篇 |
出版年
2023年 | 234篇 |
2022年 | 528篇 |
2021年 | 563篇 |
2020年 | 711篇 |
2019年 | 665篇 |
2018年 | 857篇 |
2017年 | 926篇 |
2016年 | 1257篇 |
2015年 | 1127篇 |
2014年 | 1352篇 |
2013年 | 2374篇 |
2012年 | 2242篇 |
2011年 | 2331篇 |
2010年 | 1712篇 |
2009年 | 1698篇 |
2008年 | 2306篇 |
2007年 | 2182篇 |
2006年 | 2018篇 |
2005年 | 1753篇 |
2004年 | 1538篇 |
2003年 | 1220篇 |
2002年 | 1112篇 |
2001年 | 940篇 |
2000年 | 978篇 |
1999年 | 626篇 |
1998年 | 369篇 |
1997年 | 339篇 |
1996年 | 445篇 |
1995年 | 325篇 |
1994年 | 371篇 |
1993年 | 314篇 |
1992年 | 307篇 |
1991年 | 254篇 |
1990年 | 251篇 |
1989年 | 214篇 |
1988年 | 198篇 |
1987年 | 180篇 |
1986年 | 181篇 |
1985年 | 236篇 |
1984年 | 241篇 |
1983年 | 151篇 |
1982年 | 164篇 |
1981年 | 175篇 |
1980年 | 156篇 |
1979年 | 116篇 |
1978年 | 109篇 |
1977年 | 108篇 |
1976年 | 85篇 |
1975年 | 95篇 |
1973年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
本文进一步讨论了我们新近提出的等近邻数键球谐函数方法,并通过分子动力学模拟研究了熔融LiCl及其急冷过程。对计算机模拟各时间步产生的瞬态构型进行平均,计算了不同温度下键序Ql谱.将模拟Ql谱与线性组合模型Ql谱比较,观察到模拟Ql谱与含90%局部正四面体结构的组合模型十分相似,表明熔融Licl及其急冷非晶中局部键取向序明显倾向于正四面体序。急冷过程中不同温度下局部键取向序可用同一线性组合模型描述,但模型方差随模拟温度明显变化。方差随温度而降低,且在发生玻璃态转变时有一显著下降。不同温度下的键角分布也作了计算,观察到键角分布在109°(正四面体局部结构键角)附近且分布峰随温度升高而展宽,与键序Ql得到的结论一致。 相似文献
43.
In this paper we develop a Fourier pseudospectral method forsolving two-dimensional vorticity equations. We prove the generalizedstability of the schemes and give convergence estimations dependingon the smoothness of the solution of the vorticity equations. Spectral methods have been applied widely to the partial differentialequations of fluid dynamics [411]. Guo Ben-yu proposeda technique to estimate strictly the error of the spectral schemesfor the K.D.V.-Burgers equation, the two-dimensional vorticityequations, and the Navier-Stokes equations [5,6,8]. On the otherhand, the authors [7,10] developed a pseudospectral method byusing Riesz spherical means to get better results. In this paper,we generalize this method to two-dimensional vorticity equations.The generalized stability and the convergence are proved. Thenumerical results show the advantage of such a method. 相似文献
44.
45.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
46.
Bajdik J. Pintye-Hódi K. Novák Cs. Kelemen A. Regdon G. Erős I. 《Journal of Thermal Analysis and Calorimetry》2002,68(2):613-627
The extents of the protective effects of coating films on the surface of crystals were determined. Three different samples
were made with different quantities of coating fluid (Sepifilm LP 010 in 10% aqueous solution). Since the atomizing rate was
constant, the coating time increased in parallel with the volume of coating fluid applied. The direct measurement of film
thickness and smoothness is very difficult, and therefore indirect methods were used. Dimenhydrinate was chosen as model drug;
this is a heat-sensitive antihistamine with a low melting point. This temperature can be reached during the tableting process.
The behaviour of samples on exposure to heat was examined by differential scanning calorimetry. The water uptakes of the samples
were determined with an Enslin apparatus. Plasticity was studied with an instrumented tablet machine. These indirect methods
(thermal conductivity, water uptake and plasticity measurements) revealed connections between the results of the various experiments.
An overlong coating time decreased the protective effect of the coating film.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
47.
Sub(L)中的五边形格特征及其数量不等式 总被引:1,自引:0,他引:1
五边形结构在刻画格的特征方面具有十分重要作用,应用格论及组合数学的方法讨论了格L与其子格格Sub(L)中所含五边形格之间的数量关系,给出了有限格L的子格格中三个元生成五边形格的充要条件,同时给出了Sub(L)所含不同五边形格数量的一个下界。 相似文献
48.
49.
Jerónimo Rodríguez 《Comptes Rendus Mathematique》2004,339(6):445-450
In the present Note we introduce an extension of the conservative space–time mesh refinement method presented by Fouquet et al. We also propose a post-treatment of the solution that reduces the spurious phenomena due to the non-conformity between the time meshes. A reinterpretation of the equations in terms of new unknowns leads to a new scheme with second order consistent coupling equations. Numerical experiments in 2D and a plane wave analysis for the 1D model show that the method is second order accurate for an arbitrary refinement. To cite this article: J. Rodríguez, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
50.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the
groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even
if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set
system consisting of sufficiently many sets contains at least one of these structures with many sets. 相似文献