全文获取类型
收费全文 | 341541篇 |
免费 | 3860篇 |
国内免费 | 1246篇 |
专业分类
化学 | 172495篇 |
晶体学 | 5459篇 |
力学 | 15889篇 |
综合类 | 37篇 |
数学 | 40250篇 |
物理学 | 112517篇 |
出版年
2021年 | 3298篇 |
2020年 | 3493篇 |
2019年 | 3925篇 |
2018年 | 5344篇 |
2017年 | 5562篇 |
2016年 | 7663篇 |
2015年 | 4414篇 |
2014年 | 7359篇 |
2013年 | 16587篇 |
2012年 | 12923篇 |
2011年 | 15433篇 |
2010年 | 11456篇 |
2009年 | 11318篇 |
2008年 | 13796篇 |
2007年 | 13787篇 |
2006年 | 12607篇 |
2005年 | 11019篇 |
2004年 | 10317篇 |
2003年 | 9181篇 |
2002年 | 9205篇 |
2001年 | 10757篇 |
2000年 | 8003篇 |
1999年 | 6221篇 |
1998年 | 5153篇 |
1997年 | 4979篇 |
1996年 | 4666篇 |
1995年 | 4061篇 |
1994年 | 4011篇 |
1993年 | 3847篇 |
1992年 | 4235篇 |
1991年 | 4451篇 |
1990年 | 4256篇 |
1989年 | 4130篇 |
1988年 | 3896篇 |
1987年 | 4031篇 |
1986年 | 3775篇 |
1985年 | 4809篇 |
1984年 | 4865篇 |
1983年 | 4027篇 |
1982年 | 4118篇 |
1981年 | 3808篇 |
1980年 | 3775篇 |
1979年 | 4026篇 |
1978年 | 4001篇 |
1977年 | 4047篇 |
1976年 | 3999篇 |
1975年 | 3775篇 |
1974年 | 3718篇 |
1973年 | 3743篇 |
1972年 | 2663篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Electronic properties of model quantum-dot structures in zero and finite magnetic fields 总被引:1,自引:0,他引:1
H. Saarikoski E. Räsänen S. Siljamäki A. Harju M.J. Puska R.M. Nieminen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):241-252
We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral
dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional
theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method.
The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions
which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic
field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability
of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained
for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking
solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed.
Received 16 October 2001 and Received in final form 17 January 2002 相似文献
962.
R. A. Kotel’nikova G. N. Bogdanov G. V. Zotina V. S. Romanova Z. N. Parnes 《Physics of the Solid State》2002,44(3):576-577
Efficient quenching of eosin phosphorescence by amino-acid derivatives of fullerene (AADFs) such as C60-alanine and C60-glycine in aqueous solutions indicates the possibility of transferring electrons from eosin to fullerene upon collisions or in the exciplex state. To investigate electron transfer in the protein structure, we studied the process of incorporation of C60-alanine and C60-glycine into the heme pocket of myoglobin by controlling Förster quenching. The dissociation constant for the protein-AADF complex was estimated. 相似文献
963.
964.
Several variations of two-dimensional (workers x jobs) and three-dimensional (workers x jobs x machines) time- as well as cost-minimizing assignment problems, which arise owing to (i) precedence relations of some form among the jobs or (ii) capacity restrictions on workers/machines imposed by the requirement that the surplus resources have to be fully employed, have been considered in the literature. In this paper, an algorithm is presented for time-cost trade-off analysis which is applicable to any general pair of such constrained problems. The algorithm is also illustrated by a numerical example. 相似文献
965.
We present in this paper an efficient approach for solving the problem of planning the long-term (multiyear) operation of a multireservoir hydroelectric power system for the critical period with a monthly variable load. This load is equal to a certain percentage of the total generation at the end of the year, subject to satisfying a number of constraints on the hydrosystem, using the minimum norm formulation.The proposed method is efficient in computing time and in calculating the total expected benefits from the system during the critical period. Numerical results are reported for a real system in operation consisting of two rivers. Each river has two series reservoirs.This work was supported by the Natural Science and Engineering Research Council of Canada, Grant No. A4146. 相似文献
966.
967.
A. Noda S. Nakamura Y. Iwashita S. Sakabe M. Hashida T. Shirai S. Shimizu H. Tongu H. Ito H. Souda A. Yamazaki M. Tanabe H. Daido M. Mori M. Kado A. Sagisaka K. Ogura M. Nishiuchi S. Orimo Y. Hayashi A. Yogo S. Bulanov T. Esirkepov A. Nagashima T. Kimura T. Tajima T. Takeuchi K. Matsukado A. Fukumi Z. Li 《Laser Physics》2006,16(4):647-653
In order to widely spread out particle beams utilized in cancer therapy, laser-produced ions are developed as the injection beam for an ion synchrotron dedicated for cancer therapy. Such a laser ion source is expected to contribute largely to the realization of compactness of the size and low cost of the cancer therapy accelerator. The energy spectrum of the laser-produced ions, however, has no peak, but their intensities decrease exponentially according to the increase of the energy. For the purpose of modifying such a situation, we have proposed a scheme to rotate the beam in the longitudinal phase space with the use of the RF electric field, which is phase-adjusted with the pulse laser. We aim for a reduction of the energy spread of ± 5% selected by an energy analyzer and slits to ±1% by such phase rotation. For this purpose, a quarter wavelength resonator with two gaps with the same resonant frequency as the source laser has already been fabricated, together with its RF power source. The above phase rotation system and its recent experimental realization are presented. 相似文献
968.
Wei-Yan Shao Ying-Nan Cao Wen-Jie Pan Xian-Zhang Bu Lin-Kun An Lian-Quan Gu Albert S.C. Chan 《Tetrahedron letters》2006,47(24):4085-4089
Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy. 相似文献
969.
Regina S. Burachik Rafail N. Gasimov Nergiz A. Ismayilova C. Yalçin. Kaya 《Journal of Global Optimization》2006,34(1):55-78
We study convergence properties of a modified subgradient algorithm, applied to the dual problem defined by the sharp augmented
Lagrangian. The primal problem we consider is nonconvex and nondifferentiable, with equality constraints. We obtain primal
and dual convergence results, as well as a condition for existence of a dual solution. Using a practical selection of the
step-size parameters, we demonstrate the algorithm and its advantages on test problems, including an integer programming and
an optimal control problem.
*Partially Supported by 2003 UniSA ITEE Small Research Grant Ero2.
Supported by CAPES, Brazil, Grant No. 0664-02/2, during her visit to the School of Mathematics and Statistics, UniSA. 相似文献
970.