全文获取类型
收费全文 | 7690篇 |
免费 | 236篇 |
国内免费 | 37篇 |
专业分类
化学 | 5224篇 |
晶体学 | 48篇 |
力学 | 178篇 |
数学 | 1335篇 |
物理学 | 1178篇 |
出版年
2024年 | 7篇 |
2023年 | 62篇 |
2022年 | 159篇 |
2021年 | 192篇 |
2020年 | 136篇 |
2019年 | 147篇 |
2018年 | 122篇 |
2017年 | 129篇 |
2016年 | 295篇 |
2015年 | 206篇 |
2014年 | 237篇 |
2013年 | 455篇 |
2012年 | 566篇 |
2011年 | 622篇 |
2010年 | 341篇 |
2009年 | 322篇 |
2008年 | 528篇 |
2007年 | 502篇 |
2006年 | 434篇 |
2005年 | 439篇 |
2004年 | 362篇 |
2003年 | 280篇 |
2002年 | 250篇 |
2001年 | 94篇 |
2000年 | 92篇 |
1999年 | 60篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 94篇 |
1995年 | 39篇 |
1994年 | 48篇 |
1993年 | 53篇 |
1992年 | 45篇 |
1991年 | 43篇 |
1990年 | 57篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 46篇 |
1984年 | 41篇 |
1983年 | 22篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 21篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1974年 | 13篇 |
1971年 | 7篇 |
排序方式: 共有7963条查询结果,搜索用时 0 毫秒
11.
The covering graph of a lattice which is contained in an ordered set with a planar covering graph is itself planar.Presented by R. W. Quackenbush. 相似文献
12.
In this article we prove a local existence and uniqueness theorem for the Kadomtsev-Petviashvili Equation (u
t
+u
xxx
+uu
x
)
x
−u
yy
=0) in the Sobolev spaces of orders≥3, with initial values in the same spaces, and periodic boundary conditions. This theorem improves previous results based
upon the application of singular perturbation techniques. 相似文献
13.
In this work we consider computing and continuing connecting orbits in parameter dependent dynamical systems. We give details
of algorithms for computing connections between equilibria and periodic orbits, and between periodic orbits. The theoretical
foundation for these techniques is given by the seminal work of Beyn in 1994, “On well-posed problems for connecting orbits
in dynamical systems”, where a numerical technique is also proposed. Our algorithms consist of splitting the computation of
the connection from that of the periodic orbit(s). To set up appropriate boundary conditions, we follow the algorithmic approach
used by Demmel, Dieci, and Friedman, for the case of connecting orbits between equilibria, and we construct and exploit the
smooth block Schur decomposition of the monodromy matrices associated to the periodic orbits. Numerical examples illustrate
the performance of the algorithms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Jorge Rivera-Noriega 《Proceedings of the American Mathematical Society》2004,132(5):1321-1331
An extension of an inequality of J. B. Garnett (1979), with improvements by B. E. J. Dahlberg (1980), on an approximation property of harmonic functions is proved. The weighted inequality proved here was suggested by the work of J. Pipher (1993) and it implies an extension of a result of S. Y. A. Chang, J. Wilson and T. Wolff (1985) and C. Sweezy (1991) on exponential square integrability of the boundary values of solutions to second-order linear differential equations in divergence form. This implies a solution of a problem left open by R. Bañuelos and C. N. Moore (1989) on sharp estimates for the area integral of harmonic functions in Lipschitz domains.
15.
Miguel A. Arcones 《Annals of the Institute of Statistical Mathematics》1998,50(1):87-117
We consider exact weak and strong Bahadur-Kiefer representations of the least absolute deviation estimator for the linear regression model. The precise behavior of these representations is obtained under minimal conditions. 相似文献
16.
Jorge F. J. Coelho Ana M. F. P. Silva Anatoliy V. Popov Virgil Percec Mariana V. Abreu Pedro M. O. F. Gonalves M. H. Gil 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):3001-3008
The synthesis of a block copolymer poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) is reported. This new material was synthesized by single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization (SET‐DTLRP) in two steps. First, a bifunctional macroinitiator of α,ω‐di(iodo)poly (butyl acrylate) [α,ω‐di(iodo)PBA] was synthesized by SET‐DTLRP in water at 25 °C. The macroinitiator was further reinitiated by SET‐DTLRP, leading to the formation of the desired product. This ABA block copolymer was synthesized with high initiator efficiency. The kinetics of the copolymerization reaction was studied for two PBA macroinitiators with number–average molecular weight of 10 k and 20 k. The relationship between the conversion and the number–average molecular weight was found to be linear. The dynamic mechanical thermal analysis suggests just one phase, indicating that copolymer behaves as a single material with no phase separation. This methodology provides the access to several block copolymers and other complex architectures that result from combinations of thermoplastics (PVC) and elastomers (PBA). From industrial standpoint, this process is attractive, because of easy experimental setup and the environmental friendly reaction medium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3001–3008, 2006 相似文献
17.
Jorge F. J. Coelho Ana M. F. P. Silva Anatoliy V. Popov Virgil Percec Mariana V. Abreu Pedro M. O. F Gonalves M. H. Gil 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2809-2825
Living radical polymerization of n‐butyl acrylate was achieved by single electron transfer/degenerative‐chain transfer mediated living radical polymerization in water catalyzed by sodium dithionate. The plots of number–average molecular weight versus conversion and ln[M]0/[M] versus time are linear, indicating a controlled polymerization. This methodology leads to the preparation of α,ω‐di(iodo) poly (butyl acrylate) (α,ω‐di(iodo)PBA) macroinitiators. The influence of polymerization degree ([monomer]/[initiator]), amount of catalyst, concentration of suspending agents and temperature were studied. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right‐angle light scattering (RALLS), a differential viscometer (DV), and refractive index (RI). The methodology studied in this work represents a possible route to prepare well‐tailored macromolecules made of butyl acrylate in an environmental friendly reaction medium. Moreover, such materials can be subsequently functionalized leading to the formation of different block copolymers of composition ABA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2809–2825, 2006 相似文献
18.
Miguel Angel Javaloyes Paolo Piccione 《Differential Geometry and its Applications》2006,24(5):521-541
We study the singularities of the exponential map in semi Riemannian locally symmetric manifolds. Conjugate points along geodesics depend only on real negative eigenvalues of the curvature tensor, and their contribution to the Maslov index of the geodesic is computed explicitly. We prove that degeneracy of conjugate points, which is a phenomenon that can only occur in semi-Riemannian geometry, is caused in the locally symmetric case by the lack of diagonalizability of the curvature tensor. The case of Lie groups endowed with a bi-invariant metric is studied in some detail, and conditions are given for the lack of local injectivity of the exponential map around its singularities. 相似文献
19.
Singularity patterns in a chemotaxis model 总被引:3,自引:0,他引:3
20.
We study the convergence properties of reduced Hessian successive quadratic programming for equality constrained optimization. The method uses a backtracking line search, and updates an approximation to the reduced Hessian of the Lagrangian by means of the BFGS formula. Two merit functions are considered for the line search: the
1 function and the Fletcher exact penalty function. We give conditions under which local and superlinear convergence is obtained, and also prove a global convergence result. The analysis allows the initial reduced Hessian approximation to be any positive definite matrix, and does not assume that the iterates converge, or that the matrices are bounded. The effects of a second order correction step, a watchdog procedure and of the choice of null space basis are considered. This work can be seen as an extension to reduced Hessian methods of the well known results of Powell (1976) for unconstrained optimization.This author was supported, in part, by National Science Foundation grant CCR-8702403, Air Force Office of Scientific Research grant AFOSR-85-0251, and Army Research Office contract DAAL03-88-K-0086.This author was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contracts W-31-109-Eng-38 and DE FG02-87ER25047, and by National Science Foundation Grant No. DCR-86-02071. 相似文献