全文获取类型
收费全文 | 6609篇 |
免费 | 663篇 |
国内免费 | 561篇 |
专业分类
化学 | 2296篇 |
晶体学 | 115篇 |
力学 | 240篇 |
综合类 | 152篇 |
数学 | 2194篇 |
物理学 | 2836篇 |
出版年
2024年 | 17篇 |
2023年 | 60篇 |
2022年 | 148篇 |
2021年 | 145篇 |
2020年 | 142篇 |
2019年 | 175篇 |
2018年 | 176篇 |
2017年 | 197篇 |
2016年 | 246篇 |
2015年 | 187篇 |
2014年 | 378篇 |
2013年 | 574篇 |
2012年 | 363篇 |
2011年 | 396篇 |
2010年 | 339篇 |
2009年 | 398篇 |
2008年 | 448篇 |
2007年 | 442篇 |
2006年 | 363篇 |
2005年 | 333篇 |
2004年 | 301篇 |
2003年 | 301篇 |
2002年 | 241篇 |
2001年 | 192篇 |
2000年 | 184篇 |
1999年 | 170篇 |
1998年 | 143篇 |
1997年 | 139篇 |
1996年 | 134篇 |
1995年 | 96篇 |
1994年 | 66篇 |
1993年 | 51篇 |
1992年 | 40篇 |
1991年 | 36篇 |
1990年 | 33篇 |
1989年 | 19篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有7833条查询结果,搜索用时 10 毫秒
991.
叶大年 《中国科学B辑(英文版)》1989,(3)
The optical anisotropy index is a new conception which has been proposed by the author of this paper on the basis of the Gladstone refractivity (i.e. specific energy by Larsen). The conception is very useful for studying the structural-optical mineralogy. The polarizability ellipsoid of atom groups in minerals may be obtained from the optical anisotropy index; conversely, when the crystal structure, orientation, and the polarizability ellipsoid of atom groups are known, the optical anisotropy index of the minerals may be calculated, and then three principal refractive indices, and the optical axis angles may be calculated, too. The calculated values of optical properties are in very good agreement with the experimental values. This calculation method is much simpler thanBragg's for the carbonates, and the precision of calculated values is much higher than that of Bragg's. The principle of calculation method is suitable for all the minerals containing some strong anisotropic atom groups, besides carbonat 相似文献
992.
本文得到在L^2(Qn)上,共轭多重Fourier级数的临界阶Bochner-Riesz平均S^0R(f;x)几乎处处收敛的一个充分条件。 相似文献
993.
应用类比法求解介质光波导中场分布的几个实例 总被引:1,自引:1,他引:0
利用定态薛定锷方程和介质光波导中亥姆堆兹方程的相似性,分析了类比条件,给出了用类比法求解介质光波导中场分布的几个实例。 相似文献
994.
We compare vibrational, translational and rotational excitations of CO molecules desorbed by electron impact, and the yield of oxygen and carbon atoms from electron-induced fragmentation of CO molecules for: (1) CO monolayers on bare transition metals [Ru(001) and Pt(111)]; (2) CO monolayers coadsorbed with well-ordered oxygen atoms; (3) weakly bound CO monolayers on epitaxially grown silver films; and (4) CO monolayers decoupled from the metallic substrate by mono-atomic xenon spacer layers. For all but the last system, we find CO molecules which are vibrationally extremely hot. This is explained by the excitation of strongly antibonding multi-electron states which are quenched in the vicinity of the metal surface before enough translational energy is acquired by the nuclei to complete dissociation. For CO/Xe/Ag(111), vibrationally hot CO molecules are missing among the desorbing particles, whereas strong fragment signals persist. Because of the isolating Xe layer, the substrate-adsorbate coupling is too weak to terminate the dissociation reaction which is induced by the electron impact before the rupture of the molecular bond. 相似文献
995.
Shu Xiaobao Xu Yuantong 《Annals of Differential Equations》2005,21(3):397-402
By means of variational structure and Z2 group index theory, we obtain infinite periodic solutions to a class of second-order neutral differential equations. 相似文献
996.
Summary Retention indices or five 1-alkenes, seven branched alkenes and five cycloalkenes and the corresponding epoxides were determined
at two temperatures on a fused-silica capillary column coated with cyanopropyl methyl siloxane to interpret their chromatographic
behaviour. The standard deviation was 0.2 index units. 相似文献
997.
Summary The separation of the products obtained by the hydrogenation of 1,5,9-cyclododecatriene stereoisomers on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices of cyclododecatrienes, cyclododecadienes, cyclododecenes and cyclododecane were determined at three temperatures. The respective standard deviations were 0.3 and 0.6 i.u. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic hydrocarbones is discussed. 相似文献
998.
999.
This paper presents a newly developed resource-constrained project scheduling method in stochastic networks by merging the new and traditional resource management methods. In each project, the activities consume various types of resources with fixed capacities. The duration of each activity is a random variable with a given density function. Since the backward pass method is implemented for feeding-in resources. The problem is to determine the finish time of each activity instead of its start time. The objective of the presented model is defined as minimizing the multiplication of expected project duration and its variance. The values of activities finish times are determined at decision points when at least one activity is ready to be operated and there are available resources. If at a certain point of time, more than one activity is ready to be operated but available resources are lacking, a competition among ready activities is carried out in order to select the activities which must be operated first. This paper suggests a competition routine by implementing a policy to maximize the total contribution of selected activities in reducing the expected project duration and its variance. In this respect, a heuristic algorithm is developed and compared with the other existing methods. 相似文献
1000.
We report a technique to measure the value of the nonlinear refractive index of materials in presence of nonlinear absorption using a phase object at the entry of a 4f coherent imaging system. We show that it is possible to obtain a signal approximately due only to the induced nonlinear refraction in presence of two photon absorption. Experimental and simulated Z-scan transmittance profiles with and without phase object, as well as acquired and calculated images are presented here in order to validate our approach. We show also that the use of a reference material simplifies the measurement procedure avoiding computer fits. 相似文献