全文获取类型
收费全文 | 30235篇 |
免费 | 3591篇 |
国内免费 | 3922篇 |
专业分类
化学 | 13588篇 |
晶体学 | 118篇 |
力学 | 2201篇 |
综合类 | 349篇 |
数学 | 9650篇 |
物理学 | 11842篇 |
出版年
2024年 | 86篇 |
2023年 | 289篇 |
2022年 | 724篇 |
2021年 | 828篇 |
2020年 | 943篇 |
2019年 | 844篇 |
2018年 | 830篇 |
2017年 | 1001篇 |
2016年 | 1248篇 |
2015年 | 1068篇 |
2014年 | 1637篇 |
2013年 | 2451篇 |
2012年 | 1657篇 |
2011年 | 1933篇 |
2010年 | 1540篇 |
2009年 | 1977篇 |
2008年 | 1996篇 |
2007年 | 2063篇 |
2006年 | 1787篇 |
2005年 | 1561篇 |
2004年 | 1277篇 |
2003年 | 1249篇 |
2002年 | 1088篇 |
2001年 | 864篇 |
2000年 | 861篇 |
1999年 | 725篇 |
1998年 | 690篇 |
1997年 | 524篇 |
1996年 | 380篇 |
1995年 | 357篇 |
1994年 | 300篇 |
1993年 | 275篇 |
1992年 | 253篇 |
1991年 | 210篇 |
1990年 | 222篇 |
1989年 | 215篇 |
1988年 | 186篇 |
1987年 | 174篇 |
1986年 | 149篇 |
1985年 | 168篇 |
1984年 | 152篇 |
1983年 | 90篇 |
1982年 | 121篇 |
1981年 | 112篇 |
1980年 | 98篇 |
1979年 | 101篇 |
1978年 | 78篇 |
1977年 | 76篇 |
1976年 | 70篇 |
1973年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
171.
172.
Within the framework of free interaction theory numerical methods are used to investigate the occurrence of supersonic zones with shocks in the outer inviscid region for flow past roughness in the lower viscous sublayer, with and without the formation of local separation zones. 相似文献
173.
Eduardo Rissi Roberto Rivelino Sylvio Canuto 《International journal of quantum chemistry》2003,91(4):575-585
Density functional theory (DFT), using the most common functionals, and ab initio quantum chemistry methods are used to calculate the rotational constants and dipole moments of the astrophysically important molecules HCN, CH3CN, CH3CNH+, HCCCN, and HCCNC. As far as millimeter‐wave spectroscopy is of interest the DFT methods performed well with most functionals, giving results within ±1% of experiments for rotational constants and ±3% for dipole moments. Analyzing the results obtained with all theoretical models, it may be concluded that the Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP) and Becke's three‐parameter functional with Perdew–Wang correlational functional [B3PW91/6‐31G(d, p)] give the best performances. A detailed analysis of the electron correlation effects shows that HCCCN is more stable than is HCCNC, by 1.16 eV, with important contribution arising from triple excitations. This result is also compared with those obtained with DFT methods. Despite occasional difficulties, DFT with the currently available functionals are of great utility in quickly assessing spectroscopic parameters of astrophysical interest. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
174.
175.
176.
用庞小峰先生提出的生物能量传递的新理论和 Runge-Kutta数值模拟方法,研究了三通道α-螺旋蛋白质中激发的孤子的动力学特性,求出在0K和300K温度下该孤子稳定地沿蛋白质链传递.由此可见,它能担任在蛋白质分子中传递生物能量的功能.从而再次证实了新理论的可利用性. 相似文献
177.
本文针对单件小批量生产系统 ,建立了模糊优化的动态随机投入产出模型 ,同时给出了该模型的递推解法 ,并用此模型对某单件小批企业在生产计划期的商品量进行了规划 相似文献
178.
Jesús M. Velásquez Bermúdez 《Annals of Operations Research》2002,117(1-4):21-31
This document presents theoretical considerations about the solution of dynamic optimization problems integrating the Benders Theory, the Dynamic Programming approach and the concepts of Control Theory. The so called Generalized Dual Dynamic Programming Theory (GDDP) can be considered as an extension of two previous approaches known as Dual Dynamic Programming (DDP): The first is the work developed by Pereira and Pinto [3–5], which was revised by Velásquez and others [8,9]. The second is the work developed by Read and others [2,6,7]. 相似文献
179.
Masanori Asakura 《K-Theory》2002,27(3):273-280
We construct 0-cycles on a self-product of a curve whose cycle classes are linearly independent in the extension group of arithmetic Hodge structure. This is an extended version of Theorem 4.5 of Asakura's contribution to CMR Lecture Notes Ser. 24 ((2000), pp. 133–154). 相似文献
180.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献