全文获取类型
收费全文 | 36820篇 |
免费 | 3432篇 |
国内免费 | 3988篇 |
专业分类
化学 | 29137篇 |
晶体学 | 489篇 |
力学 | 1600篇 |
综合类 | 206篇 |
数学 | 4593篇 |
物理学 | 8215篇 |
出版年
2024年 | 67篇 |
2023年 | 408篇 |
2022年 | 1080篇 |
2021年 | 978篇 |
2020年 | 1251篇 |
2019年 | 1215篇 |
2018年 | 1032篇 |
2017年 | 1238篇 |
2016年 | 1369篇 |
2015年 | 1232篇 |
2014年 | 1585篇 |
2013年 | 2757篇 |
2012年 | 1887篇 |
2011年 | 2218篇 |
2010年 | 1853篇 |
2009年 | 2359篇 |
2008年 | 2193篇 |
2007年 | 2209篇 |
2006年 | 1982篇 |
2005年 | 1769篇 |
2004年 | 1843篇 |
2003年 | 1439篇 |
2002年 | 1708篇 |
2001年 | 1001篇 |
2000年 | 876篇 |
1999年 | 713篇 |
1998年 | 624篇 |
1997年 | 608篇 |
1996年 | 622篇 |
1995年 | 622篇 |
1994年 | 532篇 |
1993年 | 395篇 |
1992年 | 418篇 |
1991年 | 254篇 |
1990年 | 206篇 |
1989年 | 202篇 |
1988年 | 199篇 |
1987年 | 163篇 |
1986年 | 115篇 |
1985年 | 99篇 |
1984年 | 91篇 |
1983年 | 34篇 |
1982年 | 88篇 |
1981年 | 112篇 |
1980年 | 117篇 |
1979年 | 127篇 |
1978年 | 97篇 |
1977年 | 73篇 |
1976年 | 70篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
A. Salam 《Numerical Algorithms》1996,11(1):327-337
The vector -algorithm is obtained from the scalar -algorithm by taking the pseudo-inverse of a vector instead of the inverse of a scalar. Thus the vector -algorithm is known only through its rules contrarily to the scalar -algorithm and some other extrapolation algorithms.The aim of this paper is to provide an algebraic approach to the vector -algorithm. 相似文献
882.
In this short note we show that Stanley—Reisner rings of simplicial complexes, which have had a dramatic application in combinatorics [2, p. 41], possess a rigidity property in the sense that they determine their underlying simplicial complexes. 相似文献
883.
The Modified Barrier Functions (MBF) have elements of both Classical Lagrangians (CL) and Classical Barrier Functions (CBF). The MBF methods find an unconstrained minimizer of some smooth barrier function in primal space and then update the Lagrange multipliers, while the barrier parameter either remains fixed or can be updated at each step. The numerical realization of the MBF method leads to the Newton MBF method, where the primal minimizer is found by using Newton's method. This minimizer is then used to update the Lagrange multipliers. In this paper, we examine the Newton MBF method for the Quadratic Programming (QP) problem. It will be shown that under standard second-order optimality conditions, there is a ball around the primal solution and a cut cone in the dual space such that for a set of Lagrange multipliers in this cut cone, the method converges quadratically to the primal minimizer from any point in the aforementioned ball, and continues, to do so after each Lagrange multiplier update. The Lagrange multipliers remain within the cut cone and converge linearly to their optimal values. Any point in this ball will be called a hot start. Starting at such a hot start, at mostO(In In
-1) Newton steps are sufficient to perform the primal minimization which is necessary for the Lagrange multiplier update. Here, >0 is the desired accuracy. Because of the linear convergence of the Lagrange multipliers, this means that onlyO(In
-1)O(In In
-1) Newton steps are required to reach an -approximation to the solution from any hot start. In order to reach the hot start, one has to perform
Newton steps, wherem characterizes the size of the problem andC>0 is the condition number of the QP problem. This condition number will be characterized explicitly in terms of key parameters of the QP problem, which in turn depend on the input data and the size of the problem.Partially supported by NASA Grant NAG3-1397 and National Science Foundation Grant DMS-9403218. 相似文献
884.
Vsevolod F. Lev 《Combinatorica》1996,16(4):587-590
In this note the method of [5] and a result from [3] are combined to treat the following classical problem: Given a finite setA and an infinite sequenceS (both inZ), what is the minimal number of elements ofA whose sum lies inS? We obtain an upper bound depending only on the densities ofA andS (but not on their arithmetic nature). 相似文献
885.
Muhammad El-Taha 《Queueing Systems》1996,22(1-2):47-63
An input-output processZ = {Z(t), t 0} is said to be-rate stable ifZ(t) = o((t)) for some non-negative function(t). We prove that the processZ is -rate stable under weak conditions that include the assumption that input satisfies a linear burstiness condition and Z is asymptotically average stable. In many cases of interest, the conditions for-rate-stability can be verified from input data. For example, using input information, we establish-rate stability of the workload for multiserver queues, an ATM multiplexer, and-rate stability of queue-length processes for infinite server queues. 相似文献
886.
The analysis of 90° vortex-vortex scattering is extended to /n scattering in all head-on collisions ofn vortices in the Abelian Higgs model. A Cauchy problem with initial data that describe the scattering ofn vortices is formulated. It is shown that this Cauchy problem has a unique global finite-energy solution. The symmetry of the solution and the form of the local analytic solution then show that /n scattering is realized. 相似文献
887.
John C. Baez 《Letters in Mathematical Physics》1996,38(2):129-143
Starting from a Lie group G whose Lie algebra is equipped with an invariant nondegenerate symmetric bilinear form, we show that four-dimensional BF theory with cosmological term gives rise to a TQFT satisfying a generalization of Atiyah's axioms to manifolds equipped with principal G-bundle. The case G=GL(4,) is especially interesting because every 4-manifold is then naturally equipped with a principal G-bundle, namely its frame bundle. In this case, the partition function of a compact oriented 4-manifold is the exponential of its signature, and the resulting TQFT is isomorphic to that constructed by Crane and Yetter using a state sum model, or by Broda using a surgery presentation of four-manifolds. 相似文献
888.
A.K. Tashmukhamedova I.A. Stempnevskaya 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(2):91-98
The effect of the nature of the substituent in the monosubstituted derivatives of dibenzo-18-crown-6 on the reactivity and direction of the electrophilic substitution reaction of the unsubstituted benzene ring has been determined. This transfer is carried out via the macrocycle and therefore is called transannular transmission. The possible mechanism of this transmission is discussed. 相似文献
889.
Summary Electrostatic and structural properties of a set of -lactam, -lactam and nonlactam compounds have been analyzed and compared with those of a model of the natural substrate d-alanyl-d-alanine for the carboxy- and transpeptidase enzymes. This first comparison of the electrostatic properties has been based on a distributed multipole analysis of high-quality ab initio wave functions of the substrate and potential antibiotics. The electrostatic similarity of the substrate and active compounds is apparent, and contrasts with the electrostatic properties of the noninhibitors. This has been quantified to give a reasonable correlation with the MIC (Minimum Concentration for Inhibition) and with kinetic data (k2/K) in accordance with the model for interaction of the lactam compounds with dd-peptidase. These correlations provide a better prediction of antibacterial activity than purely structural criteria. 相似文献
890.
S. I. Kuzina A. I. Mikhailov G. N. Nesterenko A. A. Shteinman 《Russian Chemical Bulletin》1996,45(4):824-826
-Irradiation of -oxo-bridged binuclear iron complexes FeIII
2OL
n
in a glycerol or dimethylformamide matrix at 77 K affords unstable mixed-valence FeIIFIII forms resulting from the transfer of a mobile electron generated by the ionizing radiation. These nonequilibrium forms retain the ligand environment of the original complexes, and their ESR spectra at 77–200 K are characterized by an asymmetric signal with an axially anisotropicg-factor, which is in agreement with the spectra of the FeIIFe syu forms obtained by chemical reduction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 869–871, April, 1996. 相似文献