全文获取类型
收费全文 | 176337篇 |
免费 | 17344篇 |
国内免费 | 12158篇 |
专业分类
化学 | 94293篇 |
晶体学 | 1850篇 |
力学 | 12064篇 |
综合类 | 666篇 |
数学 | 43457篇 |
物理学 | 53509篇 |
出版年
2024年 | 351篇 |
2023年 | 2068篇 |
2022年 | 3670篇 |
2021年 | 3826篇 |
2020年 | 4177篇 |
2019年 | 3964篇 |
2018年 | 13236篇 |
2017年 | 12767篇 |
2016年 | 10562篇 |
2015年 | 5703篇 |
2014年 | 6325篇 |
2013年 | 8066篇 |
2012年 | 12837篇 |
2011年 | 19329篇 |
2010年 | 11920篇 |
2009年 | 11964篇 |
2008年 | 12903篇 |
2007年 | 14259篇 |
2006年 | 5772篇 |
2005年 | 5888篇 |
2004年 | 5096篇 |
2003年 | 4819篇 |
2002年 | 3624篇 |
2001年 | 2458篇 |
2000年 | 2227篇 |
1999年 | 2199篇 |
1998年 | 1922篇 |
1997年 | 1700篇 |
1996年 | 1748篇 |
1995年 | 1481篇 |
1994年 | 1313篇 |
1993年 | 1095篇 |
1992年 | 953篇 |
1991年 | 838篇 |
1990年 | 701篇 |
1989年 | 560篇 |
1988年 | 436篇 |
1987年 | 395篇 |
1986年 | 392篇 |
1985年 | 308篇 |
1984年 | 230篇 |
1983年 | 189篇 |
1982年 | 166篇 |
1981年 | 116篇 |
1980年 | 105篇 |
1979年 | 70篇 |
1978年 | 56篇 |
1973年 | 42篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
The Al2O3−CdSe interface of a thin-film transistor is investigated in the frequency range 30 Hz-30 kHz under weak depletion and accumulation.
The surface states are, most likely, located in the insulator Al2O3 with a concentration varying from 4·1018 to 1019 cm−3 eV−1. The surface states have a negligible influence on the thin-film transistor operation. 相似文献
63.
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
64.
Li Boyu 《数学学报(英文版)》1991,7(3):247-251
H. Crapo raised in 1982 the following problem: IfP is a complete lattice, is Retr (P) a complete lattice? here Retr (P) denotes the set of all retraction operators onP with the pointwise order, that is,f≤g in Retr (P) ifff(x)≤g(x) for everyx inP. An affirmative answer will be given in the present paper. 相似文献
65.
Zi-Cai Li 《Numerical Methods for Partial Differential Equations》1989,5(4):279-295
The nonconforming combination of Ritz-Galerkin and finite difference methods is presented for solving elliptic boundary value problems with singularities. The Ritz-Galerkin method is used in the subdomains including singularities, the finite difference method is used in the rest of the solution domain. Moreover, on the common boundary of two regions where two different methods are used, the continuity conditions are constrained only on the nodes of difference grids. Theoretical analysis and numerical experiments have shown that average errors of numerical solutions and their generalized derivatives can reach the convergence rate O(h2-δ), where h is the mesh spacing of uniform difference grids, and δ is an arbitrarily small, positive number. This convergence rate is better than O(h), obtained by the nonconforming combination of the Ritz-Galerkin and finite element methods. 相似文献
66.
This paper reports that the growth of RuOx(110) thin layer growth on Ru(0001)
has been investigated by means of scanning tunnelling microscope (STM). The STM
images showed a domain structure with three rotational domains of RuOx(110)
rotated by an angle of 120℃.
The as-grown RuOx(110) thin layer is expanded from the bulk-truncated
RuOx(110) due to the large mismatch between RuOx(110) and the
Ru(0001) substrate. The results also indicate that growth of RuOx(110)
thin layer on the Ru(0001) substrate by oxidation tends first to formation
of the Ru-O (oxygen) chains in the [001] direction of RuOx(110). 相似文献
67.
68.
69.
70.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献