全文获取类型
收费全文 | 44780篇 |
免费 | 1205篇 |
国内免费 | 268篇 |
专业分类
化学 | 30827篇 |
晶体学 | 399篇 |
力学 | 1022篇 |
综合类 | 2篇 |
数学 | 7289篇 |
物理学 | 6714篇 |
出版年
2022年 | 244篇 |
2021年 | 368篇 |
2020年 | 498篇 |
2019年 | 563篇 |
2018年 | 406篇 |
2017年 | 383篇 |
2016年 | 839篇 |
2015年 | 694篇 |
2014年 | 890篇 |
2013年 | 2216篇 |
2012年 | 2109篇 |
2011年 | 2714篇 |
2010年 | 1374篇 |
2009年 | 1128篇 |
2008年 | 2324篇 |
2007年 | 2449篇 |
2006年 | 2406篇 |
2005年 | 2390篇 |
2004年 | 2088篇 |
2003年 | 1752篇 |
2002年 | 1714篇 |
2001年 | 613篇 |
2000年 | 539篇 |
1999年 | 467篇 |
1998年 | 494篇 |
1997年 | 557篇 |
1996年 | 664篇 |
1995年 | 515篇 |
1994年 | 480篇 |
1993年 | 524篇 |
1992年 | 470篇 |
1991年 | 418篇 |
1990年 | 380篇 |
1989年 | 374篇 |
1988年 | 400篇 |
1987年 | 399篇 |
1986年 | 374篇 |
1985年 | 577篇 |
1984年 | 676篇 |
1983年 | 489篇 |
1982年 | 631篇 |
1981年 | 626篇 |
1980年 | 512篇 |
1979年 | 506篇 |
1978年 | 549篇 |
1977年 | 481篇 |
1976年 | 427篇 |
1975年 | 411篇 |
1974年 | 420篇 |
1973年 | 374篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
43.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r
ϕ(z),B(r, ϕ)=sup|z|=r
ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics. 相似文献
44.
Azepane rings have been constructed diastereoselectively upon a carbohydrate derivative utilising reductive amination and RCM. The stereochemistry of the ring junctions was confirmed by X-ray crystallography and NMR. Diastereoselective dihydroxylation has also been employed to afford a tetrahydroxylated azepane carbohydrate derivative with potential biological activity. 相似文献
45.
This paper deals with the unsupervised classification of univariate observations. Given a set of observations originating from a K-component mixture, we focus on the estimation of the component expectations. We propose an algorithm based on the minimization of the “K-product” (KP) criterion we introduced in a previous work. We show that the global minimum of this criterion can be reached by first solving a linear system then calculating the roots of some polynomial of order K. The KP global minimum provides a first raw estimate of the component expectations, then a nearest-neighbour classification enables to refine this estimation. Our method’s relevance is finally illustrated through simulations of various mixtures. When the mixture components do not strongly overlap, the KP algorithm provides better estimates than the Expectation-Maximization algorithm. 相似文献
46.
Ricaurte Rodríguez Manuel Nogueras Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(7):o376-o378
Molecules of the title compound, C12H13ClN4, are linked by two independent N—H...N hydrogen bonds into a chain of edge‐fused R22(8) rings. The significance of this study lies in its attempt to rationalize the patterns of supramolecular aggregation in the title compound and in a range of analogous 4,6‐disubstituted 2‐aminopyrimidines. 相似文献
47.
Christopher E. Stuart Paul Abraham 《Journal of Mathematical Analysis and Applications》2004,300(2):224-361
Generalizations of the Nikodym boundedness and Vitali–Hahn–Saks theorems for scalar-valued measures on rings of sets that are in general not σ-rings are presented. As a consequence, the rings of subsets of N with density zero and uniform density zero are shown to have the Nikodym property. In addition, vector measure generalizations of the Vitali–Hahn–Saks theorem are given. 相似文献
48.
Right disfocality and criteria for right disfocality of linear difference equations are considered. The criteria require the positivity of appropriate minors of a Wronskian determinant and are analogues to criteria for the disconjugacy of linear ordinary differential equations and linear difference equations. 相似文献
49.
Volker John 《国际流体数值方法杂志》2004,44(7):777-788
This paper presents a numerical study of a two‐dimensional time‐dependent flow around a cylinder. Its main objective is to provide accurate reference values for the maximal drag and lift coefficient at the cylinder and for the pressure difference between the front and the back of the cylinder at the final time. In addition, the accuracy of these values obtained with different time stepping schemes and different finite element methods is studied. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
50.
John A. Ekaterinaris 《国际流体数值方法杂志》2004,45(11):1187-1207
A high‐order accurate, finite‐difference method for the numerical solution of incompressible flows is presented. This method is based on the artificial compressibility formulation of the incompressible Navier–Stokes equations. Fourth‐ or sixth‐order accurate discretizations of the metric terms and the convective fluxes are obtained using compact, centred schemes. The viscous terms are also discretized using fourth‐order accurate, centred finite differences. Implicit time marching is performed for both steady‐state and time‐accurate numerical solutions. High‐order, spectral‐type, low‐pass, compact filters are used to regularize the numerical solution and remove spurious modes arising from unresolved scales, non‐linearities, and inaccuracies in the application of boundary conditions. The accuracy and efficiency of the proposed method is demonstrated for test problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献