全文获取类型
收费全文 | 4948篇 |
免费 | 131篇 |
国内免费 | 19篇 |
专业分类
化学 | 3198篇 |
晶体学 | 38篇 |
力学 | 63篇 |
数学 | 825篇 |
物理学 | 974篇 |
出版年
2022年 | 48篇 |
2021年 | 78篇 |
2020年 | 75篇 |
2019年 | 96篇 |
2018年 | 83篇 |
2017年 | 58篇 |
2016年 | 124篇 |
2015年 | 86篇 |
2014年 | 122篇 |
2013年 | 234篇 |
2012年 | 224篇 |
2011年 | 256篇 |
2010年 | 142篇 |
2009年 | 160篇 |
2008年 | 225篇 |
2007年 | 193篇 |
2006年 | 182篇 |
2005年 | 221篇 |
2004年 | 154篇 |
2003年 | 148篇 |
2002年 | 150篇 |
2001年 | 71篇 |
2000年 | 64篇 |
1999年 | 66篇 |
1998年 | 59篇 |
1997年 | 50篇 |
1996年 | 71篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 66篇 |
1992年 | 55篇 |
1991年 | 47篇 |
1990年 | 44篇 |
1989年 | 46篇 |
1988年 | 44篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 34篇 |
1984年 | 51篇 |
1983年 | 27篇 |
1982年 | 36篇 |
1981年 | 50篇 |
1980年 | 45篇 |
1979年 | 52篇 |
1978年 | 37篇 |
1977年 | 43篇 |
1976年 | 43篇 |
1975年 | 44篇 |
1974年 | 34篇 |
1973年 | 33篇 |
排序方式: 共有5098条查询结果,搜索用时 15 毫秒
1.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
2.
3.
Anton M. Zeitlin 《Letters in Mathematical Physics》2015,105(2):149-167
4.
Galia Pozina Elizaveta I. Girshova Konstantin M. Morozov Konstantin A. Ivanov Anton Yu. Egorov Mikhail A. Kaliteevski 《Annalen der Physik》2019,531(6)
Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures. 相似文献
5.
6.
Jean Bellissard Anton Bovier Jean-Michel Ghez 《Communications in Mathematical Physics》1991,135(2):379-399
We study a one dimensional tight binding hamiltonian with a potential given by the period doubling sequence. We prove that its spectrum is purely singular continuous and supported on a Cantor set of zero Lebesgue measure, for all nonzero values of the potential strength. Moreover, we obtain the exact labelling of all spectral gaps and compute their widths asymptotically for small potential strength. 相似文献
7.
The Sample Average Approximation Method Applied to Stochastic Routing Problems: A Computational Study 总被引:1,自引:0,他引:1
Bram Verweij Shabbir Ahmed Anton J. Kleywegt George Nemhauser Alexander Shapiro 《Computational Optimization and Applications》2003,24(2-3):289-333
The sample average approximation (SAA) method is an approach for solving stochastic optimization problems by using Monte Carlo simulation. In this technique the expected objective function of the stochastic problem is approximated by a sample average estimate derived from a random sample. The resulting sample average approximating problem is then solved by deterministic optimization techniques. The process is repeated with different samples to obtain candidate solutions along with statistical estimates of their optimality gaps.We present a detailed computational study of the application of the SAA method to solve three classes of stochastic routing problems. These stochastic problems involve an extremely large number of scenarios and first-stage integer variables. For each of the three problem classes, we use decomposition and branch-and-cut to solve the approximating problem within the SAA scheme. Our computational results indicate that the proposed method is successful in solving problems with up to 21694 scenarios to within an estimated 1.0% of optimality. Furthermore, a surprising observation is that the number of optimality cuts required to solve the approximating problem to optimality does not significantly increase with the size of the sample. Therefore, the observed computation times needed to find optimal solutions to the approximating problems grow only linearly with the sample size. As a result, we are able to find provably near-optimal solutions to these difficult stochastic programs using only a moderate amount of computation time. 相似文献
8.
Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 1016 m−3, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 1021 m−3 for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy. 相似文献
9.
10.
Arnold Neumaier 《Journal of Global Optimization》2003,25(2):175-181
A family of multivariate rational functions is constructed. It has strong local minimizers with prescribed function values at prescribed positions. While there might be additional local minima, such minima cannot be global. A second family of multivariate rational functions is given, having prescribed global minimizers and prescribed interpolating data. 相似文献