全文获取类型
收费全文 | 170283篇 |
免费 | 15293篇 |
国内免费 | 22798篇 |
专业分类
化学 | 125305篇 |
晶体学 | 3243篇 |
力学 | 4243篇 |
综合类 | 1845篇 |
数学 | 23238篇 |
物理学 | 50500篇 |
出版年
2024年 | 140篇 |
2023年 | 1866篇 |
2022年 | 2514篇 |
2021年 | 4724篇 |
2020年 | 4843篇 |
2019年 | 4587篇 |
2018年 | 3865篇 |
2017年 | 5156篇 |
2016年 | 5617篇 |
2015年 | 4958篇 |
2014年 | 6841篇 |
2013年 | 12835篇 |
2012年 | 10426篇 |
2011年 | 10197篇 |
2010年 | 8551篇 |
2009年 | 11486篇 |
2008年 | 11740篇 |
2007年 | 11996篇 |
2006年 | 10526篇 |
2005年 | 8561篇 |
2004年 | 8033篇 |
2003年 | 6915篇 |
2002年 | 8965篇 |
2001年 | 5328篇 |
2000年 | 4859篇 |
1999年 | 4282篇 |
1998年 | 3776篇 |
1997年 | 2987篇 |
1996年 | 2362篇 |
1995年 | 2491篇 |
1994年 | 2216篇 |
1993年 | 1889篇 |
1992年 | 1806篇 |
1991年 | 1302篇 |
1990年 | 1023篇 |
1989年 | 934篇 |
1988年 | 783篇 |
1987年 | 614篇 |
1986年 | 575篇 |
1985年 | 624篇 |
1984年 | 534篇 |
1983年 | 305篇 |
1982年 | 533篇 |
1981年 | 693篇 |
1980年 | 614篇 |
1979年 | 632篇 |
1978年 | 520篇 |
1977年 | 389篇 |
1976年 | 333篇 |
1973年 | 219篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
131.
Masaaki Sugihara 《Numerische Mathematik》1997,75(3):379-395
Summary. In the light of the functional analysis theory we establish the optimality of the double exponential formula. The argument
consists of the following three ingredients: (1) introduction of a number of spaces of functions analytic in a strip region
about the real axis, each space being characterized by the decay rate of their elements (functions) in the neighborhood of
the infinity; (2) proof of the (near-) optimality of the trapezoidal formula in each space introduced in (1) by showing the
(near-) equality between an upper estimate for the error norm of the trapezoidal formula and a lower estimate for the minimum
error norm of quadratures; (3) nonexistence theorem for the spaces, the characterizing decay rate of which is more rapid than
the double exponential.
Received September 15, 1995 / Accepted December 14, 1995 相似文献
132.
We investigate congruence classes and direct congruence classes of m-tuples in the complex projective space ℂP
n
. For direct congruence one allows only isometries which are induced by linear (instead of semilinear) mappings. We establish
a canonical bijection between the set of direct congruence classes of m-tuples of points in ℂP
n
and the set of equivalence classes of positive semidefinite Hermitean m×m-matrices of rank at most n+1 with 1's on the diagonal. As a corollary we get that the direct congruence class of an m-tuple is uniquely determined by the direct congruence classes of all of its triangles, provided that no pair of points of
the m-tuple has distance π/2. Examples show that the situation changes drastically if one replaces direct congruence classes by
congruence classes or if distances π/2 are allowed. Finally we do the same
kind of investigation also for the complex hyperbolic space ℂH
n
. Most of the results are completely analogous, however, there are also some interesting differences.
Received: 15 January 1996 相似文献
133.
134.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
135.
136.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated
ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base
results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated
ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy.
For Part 3, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997. 相似文献
137.
138.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
139.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
140.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis. 相似文献