全文获取类型
收费全文 | 133010篇 |
免费 | 8106篇 |
国内免费 | 7141篇 |
专业分类
化学 | 64588篇 |
晶体学 | 1484篇 |
力学 | 9630篇 |
综合类 | 530篇 |
数学 | 37911篇 |
物理学 | 34114篇 |
出版年
2024年 | 160篇 |
2023年 | 940篇 |
2022年 | 1669篇 |
2021年 | 1822篇 |
2020年 | 1984篇 |
2019年 | 1973篇 |
2018年 | 11785篇 |
2017年 | 11561篇 |
2016年 | 8272篇 |
2015年 | 3275篇 |
2014年 | 3222篇 |
2013年 | 4280篇 |
2012年 | 8285篇 |
2011年 | 15144篇 |
2010年 | 8909篇 |
2009年 | 9237篇 |
2008年 | 10222篇 |
2007年 | 11962篇 |
2006年 | 3336篇 |
2005年 | 3946篇 |
2004年 | 3706篇 |
2003年 | 3732篇 |
2002年 | 2813篇 |
2001年 | 1693篇 |
2000年 | 1570篇 |
1999年 | 1362篇 |
1998年 | 1209篇 |
1997年 | 1061篇 |
1996年 | 1186篇 |
1995年 | 922篇 |
1994年 | 847篇 |
1993年 | 728篇 |
1992年 | 647篇 |
1991年 | 586篇 |
1990年 | 459篇 |
1989年 | 379篇 |
1988年 | 342篇 |
1987年 | 284篇 |
1986年 | 292篇 |
1985年 | 288篇 |
1984年 | 202篇 |
1983年 | 149篇 |
1982年 | 149篇 |
1981年 | 120篇 |
1980年 | 129篇 |
1979年 | 120篇 |
1978年 | 83篇 |
1977年 | 58篇 |
1976年 | 58篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
2.
Yoshiaki Murata Cheng-Huang Lin Totaro Imasaka 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):543-544
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
3.
固体力学有限元体系的结构拓扑变化理论 总被引:2,自引:1,他引:1
本文是文[1]的继续.文[1]提出了杆件系统的结构拓扑变化理论和拓扑变化法本文将这一理论和方法推进到连续体有限元体系;且在此基础上揭示出有限元体系的一个新性质,称为基本位移之梯度的正交性定理,从而给出一套设计敏度的显式表达式,可直接用于计算. 相似文献
4.
Ma Jiangle Yang Hong-shen Zhang Zhongxi Lu Zhong-zuo 《International Journal of Infrared and Millimeter Waves》1993,14(5):1069-1076
A simple method is introduced to improve the analysing accuracy of circular groove guide. With this method, the characteristic equation of circular groove guide is derived and its solution is given and discussed.The Project Supported by National Natural Science Foundation of P.R.China 相似文献
5.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献
6.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
7.
8.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models. 相似文献
9.
设函数f(w)为凸区域D内的单叶解析函数,对于2≤n≤8和所有w∈D,本文得到估计式|f(n)(w)/f'(w)|的精确上界.这个结果推广了一些已知的结论. 相似文献
10.