全文获取类型
收费全文 | 53748篇 |
免费 | 10052篇 |
国内免费 | 7314篇 |
专业分类
化学 | 38882篇 |
晶体学 | 745篇 |
力学 | 3305篇 |
综合类 | 458篇 |
数学 | 5988篇 |
物理学 | 21736篇 |
出版年
2024年 | 163篇 |
2023年 | 1015篇 |
2022年 | 1933篇 |
2021年 | 2009篇 |
2020年 | 2136篇 |
2019年 | 2205篇 |
2018年 | 1981篇 |
2017年 | 1902篇 |
2016年 | 2689篇 |
2015年 | 2767篇 |
2014年 | 3375篇 |
2013年 | 4305篇 |
2012年 | 5096篇 |
2011年 | 5144篇 |
2010年 | 3682篇 |
2009年 | 3680篇 |
2008年 | 4022篇 |
2007年 | 3388篇 |
2006年 | 3154篇 |
2005年 | 2537篇 |
2004年 | 1910篇 |
2003年 | 1530篇 |
2002年 | 1559篇 |
2001年 | 1244篇 |
2000年 | 1010篇 |
1999年 | 993篇 |
1998年 | 715篇 |
1997年 | 683篇 |
1996年 | 633篇 |
1995年 | 523篇 |
1994年 | 496篇 |
1993年 | 434篇 |
1992年 | 316篇 |
1991年 | 298篇 |
1990年 | 261篇 |
1989年 | 186篇 |
1988年 | 168篇 |
1987年 | 131篇 |
1986年 | 138篇 |
1985年 | 101篇 |
1984年 | 81篇 |
1983年 | 58篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 29篇 |
1977年 | 23篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers. 相似文献
132.
汪巍 《数学的实践与认识》2004,34(3):103-109
首先引入了差分系统基于两种度量的极端稳定性概念 ,然后建立了一些关于差分系统 ( h0 ,h)极端稳定性 (极端一致稳定性 ,极端渐近稳定性 ,极端一致渐近稳定性 )的判定准则 .在所得到的定理中 ,对△ V的限制较弱 ,特别地 ,△V甚至可以恒为正 ,从而便于实际应用 . 相似文献
133.
134.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
135.
魏嵬 《数学的实践与认识》2007,37(16):76-83
为给转炉设计提供依据,需要计算炉液倾动的重心.利用数学方法将实际问题进行简化,通过分析炉液倾动过程中变量间的相互关系,来确定每个倾动角度对应情况下的液面位置.利用数学中三重积分的有关应用,进一步得出转炉在每个倾动角度为α∈(0,π2)时的重心计算方法及相关结论,在理论上为工程计算重心的方法提供参考. 相似文献
136.
For one‐dimensional simple symmetric random walk, the Hausdorff and packing dimensions of sets of sample paths with prescribed rate of returns to the origin are determined. This gives a multifractal decomposition of the underlying sample space. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
137.
Diane L. Levesque Eng-Chi Wang Dau-Chang Wei Cherng-Chyi Tzeng Raymond P. Panzica Fardos N. M. Naguib Mahmoud H. El Kouni 《Journal of heterocyclic chemistry》1993,30(5):1399-1404
A new series of potent uridine phosphorylase inhibitors have been prepared from barbituric acid. Among them, 1-[(2-hydroxyethoxy)methyl]-5-)(m--benzyloxy)benzylbarbituric acid ( 37 , BBBA) is the most promising having a Ki value of 1.1 ± 0.2 nM with uridine phosphorylase from human liver. The new inhibitors are easily synthesized and are better inhibitors of human uridine phosphorylase than their uracil counterparts. 相似文献
138.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. 相似文献
139.
In this paper, we propose and analyze an SQP-type method for solving linearly constrained convex minimization problems where the objective functions are too complex to be evaluated exactly. Some basic results for global convergence and local superlinear convergence are obtained according to the properties of the approximation sequence. We illustrate the applicability of our approach by proposing a new method for solving two-stage stochastic programs with fixed recourse. 相似文献
140.