全文获取类型
收费全文 | 9459篇 |
免费 | 1377篇 |
国内免费 | 507篇 |
专业分类
化学 | 4998篇 |
晶体学 | 35篇 |
力学 | 1149篇 |
综合类 | 202篇 |
数学 | 2340篇 |
物理学 | 2619篇 |
出版年
2024年 | 15篇 |
2023年 | 132篇 |
2022年 | 350篇 |
2021年 | 398篇 |
2020年 | 494篇 |
2019年 | 344篇 |
2018年 | 291篇 |
2017年 | 406篇 |
2016年 | 532篇 |
2015年 | 428篇 |
2014年 | 560篇 |
2013年 | 632篇 |
2012年 | 582篇 |
2011年 | 565篇 |
2010年 | 443篇 |
2009年 | 526篇 |
2008年 | 480篇 |
2007年 | 508篇 |
2006年 | 465篇 |
2005年 | 412篇 |
2004年 | 371篇 |
2003年 | 323篇 |
2002年 | 304篇 |
2001年 | 218篇 |
2000年 | 222篇 |
1999年 | 179篇 |
1998年 | 188篇 |
1997年 | 141篇 |
1996年 | 117篇 |
1995年 | 122篇 |
1994年 | 104篇 |
1993年 | 83篇 |
1992年 | 69篇 |
1991年 | 47篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 42篇 |
1984年 | 26篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
A. A. Bulatov 《Algebra and Logic》2006,45(6):371-388
A combinatorial constraint satisfaction problem aims at expressing in unified terms a wide spectrum of problems in various
branches of mathematics, computer science, and AI. The generalized satisfiability problem is NP-complete, but many of its
restricted versions can be solved in a polynomial time. It is known that the computational complexity of a restricted constraint
satisfaction problem depends only on a set of polymorphisms of relations which are admitted to be used in the problem. For
the case where a set of such relations is invariant under some Mal’tsev operation, we show that the corresponding constraint
satisfaction problem can be solved in a polynomial time.
__________
Translated from Algebra i Logika, Vol. 45, No. 6, pp. 655–686, November–December, 2006. 相似文献
102.
P. S. Szczepaniak 《Journal of Optimization Theory and Applications》1989,63(3):459-468
This paper deals with dynamic systems described by nonlinear differential-difference equations of retarded type. The problem considered is to determine the initial function and certain system parameters which minimize a given cost functional. A computational method is presented and some convergence results are given. Numerical examples of linear and nonlinear systems are also included. 相似文献
103.
Henryk Brzeskwiniewicz 《Annals of the Institute of Statistical Mathematics》1989,41(1):199-204
The necessary and sufficient conditions for m-associate partially balanced block (PBB) designs to be connected are given. This generalizes the criterion for m-associate partially balanced incomplete block (PBIB) designs, which has originally been established by Ogawa, Ikeda and Kageyama (1984, Proceedings of the Seminar on Combinatorics and Applications, 248–255, Statistical Publishing Society, Calcutta).This work was partially supported by the Polish Academy of Sciences Grant No. MR I.1-2/2. 相似文献
104.
A. Y. Lee 《Journal of Optimization Theory and Applications》1988,56(1):157-166
In this paper, we consider a particular approximation scheme which can be used to solve hereditary optimal control problems. These problems are characterized by variables with a time-delayed argumentx(t – ). In our approximation scheme, we first replace the variable with an augmented statey(t) x(t - ). The two-sided Laplace transform ofy(t) is a product of the Laplace transform ofx(t) and an exponential factor. This factor is approximated by a first-order Padé approximation, and a differential relation fory(t) can be found. The transformed problem, without any time-delayed argument, can then be solved using a gradient algorithm in the usual way. Four problems are solved to illustrate the validity and usefulness of this technique.This research was supported in part by the National Aeronautics and Space Administration under NASA Grant NCC-2-106. 相似文献
105.
热活化延迟荧光(TADF)聚合物,不仅具有小分子TADF材料高的激子利用效率特性,而且还具备分子多样性好、可溶液加工、低成本、以及易实现大面积柔性器件等诸多优势,在近几年受到广泛的关注并展现了良好的应用前景。本文从TADF聚合物分子设计原理、器件结构及发光机理出发,依据TADF聚合物的构筑方法不同,概括了其结构设计策略,详述了各种类型TADF聚合物的分子结构和光电性能及其在有机电致发光器件领域应用的研究进展,最后探讨了TADF聚合物存在的问题,并展望了其发展前景。 相似文献
106.
光诱导[2+2]环加成在有机合成中的应用 总被引:1,自引:0,他引:1
综述了烯烃、二烯、烯酮双键和烯烃的分子间或分子内光环加成,总结了过去二十五年在有机合成中的研究成果。 相似文献
107.
108.
109.
Brian D. Hudson Ashley R. George Martyn G. Ford David J. Livingstone 《Journal of computer-aided molecular design》1992,6(2):191-201
Summary Molecular dynamics simulations have been performed on a number of conformationally flexible pyrethroid insecticides. The results indicate that molecular dynamics is a suitable tool for conformational searching of small molecules given suitable simulation parameters. The structures derived from the simulations are compared with the static conformation used in a previous study. Various physicochemical parameters have been calculated for a set of conformations selected from the simulations using multivariate analysis. The averaged values of the parameters over the selected set (and the factors derived from them) are compared with the single conformation values used in the previous study. 相似文献
110.
Pappa A. Kyriakou S. Mikedi K. Tzamtzis N. Statheropoulos M. 《Journal of Thermal Analysis and Calorimetry》2004,78(2):415-426
The design, the abilities and a characteristic application of an in-house made interface for combining thermogravimetry (TG)
with mass spectrometry (MS) are presented. The TG-MS interface consists mainly of three co-axial tubes. The position of the
intermediate tube was determined after calculation of the temperature profile at the TG furnace exit tube. The inner tube
position was determined taking into consideration its protection against condensation of heavy molecules and the time delay
for the transfer of the evolved gases. This interface allows either continuous sampling and transferring of the evolved gases
from the TG to the MS or repetitive introduction of short sampling pulses of TG evolved gases to MS. The interface is capable
of coupling various commercial instruments. In the present work two configurations of this interface are demonstrated. Finally
an example of application of this interface on forest fuel pyrolysis is presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献