全文获取类型
收费全文 | 53482篇 |
免费 | 13152篇 |
国内免费 | 4851篇 |
专业分类
化学 | 54353篇 |
晶体学 | 678篇 |
力学 | 1492篇 |
综合类 | 370篇 |
数学 | 4203篇 |
物理学 | 10389篇 |
出版年
2024年 | 41篇 |
2023年 | 404篇 |
2022年 | 547篇 |
2021年 | 876篇 |
2020年 | 2067篇 |
2019年 | 3359篇 |
2018年 | 1748篇 |
2017年 | 1450篇 |
2016年 | 4320篇 |
2015年 | 4540篇 |
2014年 | 4572篇 |
2013年 | 5560篇 |
2012年 | 4757篇 |
2011年 | 4058篇 |
2010年 | 4209篇 |
2009年 | 4140篇 |
2008年 | 3718篇 |
2007年 | 2952篇 |
2006年 | 2602篇 |
2005年 | 2633篇 |
2004年 | 2191篇 |
2003年 | 1951篇 |
2002年 | 2668篇 |
2001年 | 1875篇 |
2000年 | 1719篇 |
1999年 | 747篇 |
1998年 | 285篇 |
1997年 | 265篇 |
1996年 | 235篇 |
1995年 | 193篇 |
1994年 | 148篇 |
1993年 | 127篇 |
1992年 | 100篇 |
1991年 | 72篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 29篇 |
1987年 | 39篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 13篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1957年 | 7篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
On Dirichlet Characters of Polynomials 总被引:1,自引:0,他引:1
The main purpose of this paper is to use the properties of Gaussiansums and the analytic method to study the problem of calculatingone kind of character sums modulo q, and to give an interestingidentity. 2000 Mathematics Subject Classification 11L10, 11L40. 相似文献
92.
Hongbo Zhang Rui Wang Kaixin Chen Han Yang Daming Zhang Maobin Yi Guoquan Wang Zhenchang Ma 《Optics & Laser Technology》2002,34(4):283-286
A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip. 相似文献
93.
Quiver Hopf algebras 总被引:1,自引:0,他引:1
In this paper we study subHopfalgebras of graded Hopf algebra structures on a path coalgebra kQc. We prove that a Hopf structure on some subHopfquivers can be lifted to a Hopf structure on the whole Hopf quiver. If Q is a Schurian Hopf quiver, then we classified all simple-pointed subHopfalgebras of a graded Hopf structure on kQc. We also prove a dual Gabriel theorem for pointed Hopf algebras. 相似文献
94.
95.
96.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
97.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
98.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
99.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
100.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献