全文获取类型
收费全文 | 42771篇 |
免费 | 6159篇 |
国内免费 | 5379篇 |
专业分类
化学 | 31499篇 |
晶体学 | 558篇 |
力学 | 2268篇 |
综合类 | 426篇 |
数学 | 5387篇 |
物理学 | 14171篇 |
出版年
2024年 | 89篇 |
2023年 | 703篇 |
2022年 | 1145篇 |
2021年 | 1324篇 |
2020年 | 1536篇 |
2019年 | 1525篇 |
2018年 | 1325篇 |
2017年 | 1265篇 |
2016年 | 1802篇 |
2015年 | 1852篇 |
2014年 | 2167篇 |
2013年 | 2929篇 |
2012年 | 3558篇 |
2011年 | 3917篇 |
2010年 | 2722篇 |
2009年 | 2608篇 |
2008年 | 2980篇 |
2007年 | 2656篇 |
2006年 | 2334篇 |
2005年 | 2069篇 |
2004年 | 1636篇 |
2003年 | 1377篇 |
2002年 | 1415篇 |
2001年 | 1173篇 |
2000年 | 909篇 |
1999年 | 859篇 |
1998年 | 712篇 |
1997年 | 631篇 |
1996年 | 669篇 |
1995年 | 577篇 |
1994年 | 527篇 |
1993年 | 455篇 |
1992年 | 437篇 |
1991年 | 374篇 |
1990年 | 313篇 |
1989年 | 248篇 |
1988年 | 208篇 |
1987年 | 165篇 |
1986年 | 162篇 |
1985年 | 188篇 |
1984年 | 115篇 |
1983年 | 76篇 |
1982年 | 76篇 |
1981年 | 61篇 |
1980年 | 53篇 |
1979年 | 58篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 41篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
林正炎 《数学物理学报(B辑英文版)》2003,23(3)
Let {X_n, n≥1} be a strictly stationary sequence of random variables, whichare either associated or negatively associated, f(·) be their common density. In this paper,the author shows a central limit theorem for a kernel estimate of f(·) under certain regularconditions. 相似文献
82.
83.
Random copolymers of poly{(methacrylamide)-co-(vinyl trimethoxysilane)} and poly{(methacrylic acid)-co-(vinyl trimethoxysilane)} were synthesized via a free radical polymerization reaction. Acid catalyzed sol-gel process of tetraethylorthosilicate (TEOS) with aforementioned polymers in the presence of methyl xanthine class of alkaloid like caffeine resulted in the formation of highly transparent monoliths. Solvent extraction of the template leaves behind the recognition sites intact with high selectivity towards the print molecule. The ionic and non-specific adsorptions, which are considered to be the main disadvantages of the molecularly imprinted polymers (MIP), are prevented to a considerable extent by the end capping of surface silanol groups. The template binding efficiencies of MIP were determined by HPLC analysis. 相似文献
84.
85.
86.
Xiao Qi ZHENG Yong Hui WANG Qing Xiang GUO* Li YANG You Cheng LIU Department of Chemistry University of Science Technology of China Hefei National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid… 相似文献
87.
近年来,决定椭圆型方程系数反问题在地磁、地球物理、冶金和生物等实际问题上有着广泛的应用.本文讨论了二维的决定椭圆型方程系数反问题的数值求解方法.由误差平方和最小原则,这个反问题可化为一个变分问题,并进一步离散化为一个最优化问题,其目标函数依赖于要决定的方程系数.本文着重考察非线性共轭梯度法在此最优化问题数值计算中的表现,并与拟牛顿法作为对比.为了提高算法的效率我们适当选择加快收敛速度的预处理矩阵.同时还考察了线搜索方法的不同对优化算法的影响.数值实验的结果表明,非线性共轭梯度法在这类大规模优化问题中相对于拟牛顿法更有效. 相似文献
88.
The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results. 相似文献
89.
A least‐squares meshfree method based on the first‐order velocity–pressure–vorticity formulation for two‐dimensional incompressible Navier–Stokes problem is presented. The convective term is linearized by successive substitution or Newton's method. The discretization of all governing equations is implemented by the least‐squares method. Equal‐order moving least‐squares approximation is employed with Gauss quadrature in the background cells. The boundary conditions are enforced by the penalty method. The matrix‐free element‐by‐element Jacobi preconditioned conjugate method is applied to solve the discretized linear systems. Cavity flow for steady Navier–Stokes problem and the flow over a square obstacle for time‐dependent Navier–Stokes problem are investigated for the presented least‐squares meshfree method. The effects of inaccurate integration on the accuracy of the solution are investigated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
90.
E. V. McCloskey A. Dey R. M. Parr N. Aras A. Balogh J. Bostock A. Borell S. Krishnan G. Lobo L. L. Qin Y. Zhang S. Cvijetic V. Zaichick M. Lim-Abraham K. Bose S. Wynchank G. V. Iyengar 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(2):341-345
In 1994, the International Atomic Energy Agency (IAEA) initiated a 5-year Co-ordinated Research Project (CRP) to determine
geographical and racial differences in peak bone mineral density (BMD) in men and women aged 15-49 years. The study demonstrates
that there are distinct global differences in BMD at the hip and spine in both men and women approximating to one population
standard deviation between populations with the highest and lowest BMD. These differences persist following adjustments for
age, sex and body size. Such information is valuable in understanding the reasons for global differences in fracture rate
and predicting future trends in fracture incidence.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献