全文获取类型
收费全文 | 128422篇 |
免费 | 7288篇 |
国内免费 | 14909篇 |
专业分类
化学 | 73134篇 |
晶体学 | 1201篇 |
力学 | 2559篇 |
综合类 | 910篇 |
数学 | 13471篇 |
物理学 | 20736篇 |
综合类 | 38608篇 |
出版年
2024年 | 217篇 |
2023年 | 973篇 |
2022年 | 2478篇 |
2021年 | 2530篇 |
2020年 | 2971篇 |
2019年 | 2839篇 |
2018年 | 2533篇 |
2017年 | 3540篇 |
2016年 | 3827篇 |
2015年 | 3698篇 |
2014年 | 4679篇 |
2013年 | 7935篇 |
2012年 | 8288篇 |
2011年 | 7164篇 |
2010年 | 5831篇 |
2009年 | 7424篇 |
2008年 | 7866篇 |
2007年 | 9179篇 |
2006年 | 8487篇 |
2005年 | 7375篇 |
2004年 | 6802篇 |
2003年 | 5666篇 |
2002年 | 6493篇 |
2001年 | 4170篇 |
2000年 | 3892篇 |
1999年 | 3511篇 |
1998年 | 2863篇 |
1997年 | 2405篇 |
1996年 | 2090篇 |
1995年 | 1914篇 |
1994年 | 1744篇 |
1993年 | 1473篇 |
1992年 | 1379篇 |
1991年 | 1048篇 |
1990年 | 899篇 |
1989年 | 853篇 |
1988年 | 632篇 |
1987年 | 465篇 |
1986年 | 355篇 |
1985年 | 263篇 |
1984年 | 253篇 |
1983年 | 143篇 |
1982年 | 224篇 |
1981年 | 187篇 |
1980年 | 206篇 |
1979年 | 186篇 |
1978年 | 173篇 |
1977年 | 125篇 |
1976年 | 110篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
伞花木染色体核型的研究 总被引:2,自引:0,他引:2
本文首次报道了国家二级保护植物伴花木(无患子科)的染色体数目,并对其核型进行了分析,结果表明:该种染色体的核型公式为:K(2n)=22=16m+6sm,染色体属较对称的“2B”型。 相似文献
72.
Peter Imkeller 《Probability Theory and Related Fields》1996,106(1):105-135
Summary. The analytic treatment of problems related to the asymptotic behaviour of random dynamical systems generated by stochastic
differential equations suffers from the presence of non-adapted random invariant measures. Semimartingale theory becomes accessible
if the underlying Wiener filtration is enlarged by the information carried by the orthogonal projectors on the Oseledets spaces
of the (linearized) system.
We study the corresponding problem of preservation of the semimartingale property and the validity of a priori inequalities
between the norms of stochastic integrals in the enlarged filtration and norms of their quadratic variations in case the random
element F enlarging the filtration is real valued and possesses an absolutely continuous law. Applying the tools of Malliavin’s calculus,
we give smoothness conditions on F under which the semimartingale property is preserved and a priori martingale inequalities are valid.
Received: 12 April 1995 / In revised form: 7 March 1996 相似文献
73.
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
74.
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
75.
76.
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
77.
78.
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
79.
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
80.
一种用于PLC的模拟量/开关量转换电路 总被引:1,自引:0,他引:1
本文以可编程逻辑控制器(PLC)在某大型远洋测量船上首次成功的应用为例,提出一种简便、实用、可靠的模拟量/开关量转换电路。 相似文献