全文获取类型
收费全文 | 6289篇 |
免费 | 943篇 |
国内免费 | 733篇 |
专业分类
化学 | 4329篇 |
晶体学 | 55篇 |
力学 | 455篇 |
综合类 | 41篇 |
数学 | 864篇 |
物理学 | 2221篇 |
出版年
2024年 | 20篇 |
2023年 | 133篇 |
2022年 | 166篇 |
2021年 | 250篇 |
2020年 | 260篇 |
2019年 | 265篇 |
2018年 | 230篇 |
2017年 | 183篇 |
2016年 | 331篇 |
2015年 | 282篇 |
2014年 | 339篇 |
2013年 | 451篇 |
2012年 | 594篇 |
2011年 | 590篇 |
2010年 | 385篇 |
2009年 | 367篇 |
2008年 | 388篇 |
2007年 | 337篇 |
2006年 | 345篇 |
2005年 | 297篇 |
2004年 | 238篇 |
2003年 | 195篇 |
2002年 | 163篇 |
2001年 | 137篇 |
2000年 | 121篇 |
1999年 | 127篇 |
1998年 | 100篇 |
1997年 | 97篇 |
1996年 | 111篇 |
1995年 | 82篇 |
1994年 | 62篇 |
1993年 | 59篇 |
1992年 | 31篇 |
1991年 | 44篇 |
1990年 | 41篇 |
1989年 | 30篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1944年 | 4篇 |
1942年 | 3篇 |
1941年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有7965条查询结果,搜索用时 15 毫秒
41.
A new synthetic method for the manufacture of glutaric dialdehyde is investigated. Glutaric dialdehyde was prepared by the
addition-hydrolysis reaction of benzimidazolium salt with saturated dihalide as the di-Grignard reagent. The yield of glutaric
dialdehyde by this method can reach 73%. Both infrared spectra and melting point of the compound were consistent with those
reported earlier.
Translated from Journal of Northwest University (Natural Science Edition), 2005, 35(2) (in Chinese) 相似文献
42.
本证明了当(a,b)不属于{(1,8),(2,4),(3,6),(4,4),(2s^2-s,2s^2 s))时,L^m(Ka,b)以谱为特征,其中a≤b,s≥2. 相似文献
43.
44.
An algorithm for a time accurate incompressible Navier–Stokes solver on an unstructured grid is presented. The algorithm uses a second order, three‐point, backward difference formula for the physical time marching. For each time step, a divergence free flow field is obtained based on an artificial compressibility method. An implicit method with a local time step is used to accelerate the convergence for the pseudotime iteration. To validate the code, an unsteady laminar flow over a circular cylinder at a Reynolds number of 200 is calculated. The results are compared with available experimental and numerical data and good agreements are achieved. Using the developed unsteady code, an interaction of a Karman vortex street with an elliptical leading edge is simulated. The incident Karman vortex street is generated by a circular cylinder located upstream. A clustering to the path of the vortices is achieved easily due to flexibility of an unstructured grid. Details of the interaction mechanism are analysed by investigating evolutions of vortices. Characteristics of the interactions are compared for large‐ and small‐scale vortex streets. Different patterns of the interaction are observed for those two vortex streets and the observation is in agreement with experiment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
45.
The best-r-point-average (BRPA) estimator of the maximizer of a regression function, proposed in Changchien (in: M.T. Chao, P.E. Cheng (Eds.), Proceedings of the 1990 Taipei Symposium in Statistics, June 28–30, 1990, pp. 63–78) has certain merits over the estimators derived through the estimation of the regression function. Some of the properties of the BRPA estimator have been studied in Chen et al. (J. Multivariate Anal. 57 (1996) 191) and Bai and Huang (Sankhya: Indian J. Statist. Ser. A. 61 (Pt. 2) (1999) 208–217). In this article, we further study the properties of the BRPA estimator and give its convergence rate under some quite general conditions. Simulation results are presented for the illustration of the convergence rate. Some comparisons with existing estimators such as the Müller estimator are provided. 相似文献
46.
47.
With the help of the theorem of a fixed point index for A-proper semilinear operators established by Cremins, we get a existence theorem concerning the existence of positive solution for the second order ordinary differential equation of three-point boundary value problems at resonance. 相似文献
48.
The optical-limiting property of an optically active phthalocyanine derivative with different configuration in chloroform solution was measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex of the derivative was determined with the Z-scan technique. The results showed that the phthalocyanine derivative possesses larger σex than the ground state absorption cross-section σ0, indicating that it is a material for reverse saturable absorption. And it is specially noticed that the change in the optically active configuration affects its optical-limiting property significantly. 相似文献
49.
迄今未见任何稀土氨基酸络合物的ESR波谱报道,本文在合成Gd3+分别与甘氨酸、β-丙氨酸、谷氨酸、天冬氨酸和天冬酰胺五种氨基酸络合物的基础上,测定了不同温度下,水溶液、粉末及分子筛吸附样品的ESR谱,讨论了络合物中晶体场强,对称性及成键特性。 相似文献
50.
资源有限网络计划的PRWI启发式优化方法 总被引:1,自引:0,他引:1
本文在综合考虑了有资源约束的网络计划结构特征、资源强度、时间约束等方面因素的基础上,提出了一种新的资源优化的启发式优化方法—PRWI方法,并通过分析证明了该方法处理问题的效果较现有的其它方法好。 相似文献