全文获取类型
收费全文 | 34144篇 |
免费 | 1268篇 |
国内免费 | 1616篇 |
专业分类
化学 | 15920篇 |
晶体学 | 370篇 |
力学 | 683篇 |
综合类 | 81篇 |
数学 | 10638篇 |
物理学 | 9336篇 |
出版年
2023年 | 230篇 |
2022年 | 373篇 |
2021年 | 336篇 |
2020年 | 491篇 |
2019年 | 779篇 |
2018年 | 574篇 |
2017年 | 630篇 |
2016年 | 461篇 |
2015年 | 422篇 |
2014年 | 717篇 |
2013年 | 2175篇 |
2012年 | 968篇 |
2011年 | 1538篇 |
2010年 | 1015篇 |
2009年 | 1383篇 |
2008年 | 1636篇 |
2007年 | 1681篇 |
2006年 | 1593篇 |
2005年 | 1253篇 |
2004年 | 1605篇 |
2003年 | 1624篇 |
2002年 | 2051篇 |
2001年 | 2059篇 |
2000年 | 1883篇 |
1999年 | 2032篇 |
1998年 | 1704篇 |
1997年 | 1048篇 |
1996年 | 597篇 |
1995年 | 355篇 |
1994年 | 375篇 |
1993年 | 225篇 |
1992年 | 202篇 |
1991年 | 154篇 |
1990年 | 213篇 |
1989年 | 206篇 |
1988年 | 149篇 |
1987年 | 129篇 |
1986年 | 168篇 |
1985年 | 222篇 |
1984年 | 219篇 |
1983年 | 90篇 |
1982年 | 180篇 |
1981年 | 264篇 |
1980年 | 248篇 |
1979年 | 129篇 |
1978年 | 179篇 |
1977年 | 113篇 |
1976年 | 76篇 |
1975年 | 81篇 |
1974年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
91.
92.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献
93.
Summary. We introduce linear semi-implicit complementary volume numerical scheme for solving level set like nonlinear degenerate diffusion
equations arising in image processing and curve evolution problems. We study discretization of image selective smoothing equation
of mean curvature flow type given by Alvarez, Lions and Morel ([3]). Solution of the level set equation of Osher and Sethian
([26], \[30]) is also included in the study. We prove and estimates for the proposed scheme and give existence of its (generalized) solution in every discrete time-scale step. Efficiency
of the scheme is given by its linearity and stability. Preconditioned iterative solvers are used for computing arising linear
systems. We present computational results related to image processing and plane curve evolution.
Received April 25, 2000 / Revised version received June 11, 2001 / Published online November 15, 2001 相似文献
94.
For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of
the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of
this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an
example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a
C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat
ambient metric in the sense of Fefferman and Graham.
Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse
9, 1090 Vienna, Austria
Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany 相似文献
95.
O. N. Karpenkov 《Monatshefte für Mathematik》2007,152(3):217-249
In this paper we develop an integer-affine classification of three-dimensional multistory, completely empty convex marked
pyramids. We apply it to obtain the complete lists of compact two-dimensional faces of multidimensional continued fractions
lying in planes at integer distances 2, 3, 4, … to the origin. The faces are considered up to the action of the group of
integer-linear transformations. 相似文献
96.
Various types of LU-factorizations for nonsingular matrices, where L is a lower triangular matrix and U is an upper triangular matrix, are defined and characterized. These types of LU-factorizations are extended to the general m × n case. The more general conditions are considered in the light of the structures of [C.R. Johnson, D.D. Olesky, P. Van den Driessche, Inherited matrix entries: LU factorizations, SIAM J. Matrix Anal. Appl. 10 (1989) 99-104]. Applications to graphs and adjacency matrices are investigated. Conditions for the product of a lower and an upper triangular matrix to be the zero matrix are also obtained. 相似文献
97.
98.
Gerhard Starke 《Numerische Mathematik》1997,78(1):103-117
Summary. The convergence rate of Krylov subspace methods for the solution of nonsymmetric systems of linear equations, such as GMRES
or FOM, is studied. Bounds on the convergence rate are presented which are based on the smallest real part of the field of
values of the coefficient matrix and of its inverse. Estimates for these quantities are available during the iteration from
the underlying Arnoldi process. It is shown how these bounds can be used to study the convergence properties, in particular,
the dependence on the mesh-size and on the size of the skew-symmetric part, for preconditioners for finite element discretizations
of nonsymmetric elliptic boundary value problems. This is illustrated for the hierarchical basis and multilevel preconditioners
which constitute popular preconditioning strategies for such problems.
Received May 3, 1996 相似文献
99.
100.