全文获取类型
收费全文 | 83633篇 |
免费 | 532篇 |
国内免费 | 379篇 |
专业分类
化学 | 27509篇 |
晶体学 | 813篇 |
力学 | 6879篇 |
数学 | 32681篇 |
物理学 | 16662篇 |
出版年
2021年 | 51篇 |
2020年 | 85篇 |
2019年 | 57篇 |
2018年 | 10475篇 |
2017年 | 10302篇 |
2016年 | 6185篇 |
2015年 | 967篇 |
2014年 | 434篇 |
2013年 | 564篇 |
2012年 | 4080篇 |
2011年 | 10834篇 |
2010年 | 5771篇 |
2009年 | 6157篇 |
2008年 | 6892篇 |
2007年 | 9052篇 |
2006年 | 526篇 |
2005年 | 1617篇 |
2004年 | 1758篇 |
2003年 | 2175篇 |
2002年 | 1190篇 |
2001年 | 391篇 |
2000年 | 395篇 |
1999年 | 216篇 |
1998年 | 237篇 |
1997年 | 213篇 |
1996年 | 241篇 |
1995年 | 178篇 |
1994年 | 127篇 |
1993年 | 157篇 |
1992年 | 114篇 |
1991年 | 105篇 |
1990年 | 92篇 |
1989年 | 101篇 |
1988年 | 98篇 |
1987年 | 97篇 |
1986年 | 111篇 |
1985年 | 108篇 |
1984年 | 110篇 |
1983年 | 94篇 |
1982年 | 127篇 |
1981年 | 111篇 |
1980年 | 111篇 |
1979年 | 108篇 |
1978年 | 107篇 |
1977年 | 82篇 |
1976年 | 73篇 |
1975年 | 58篇 |
1974年 | 65篇 |
1973年 | 84篇 |
1914年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
3.
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
4.
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
5.
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
6.
7.
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
8.
It is proved that biorthogonal polynomials obey two different kinds of Christoffel-Darboux-type formulae, one linking polynomials with a different parameter and one combining polynomials with different degrees. This is used to produce a mixed recurrence relation, which is valid for all biorthogonal polynomials. This recurrence relation establishes several results on interlacing property of zeros of successive biorthogonal polynomials and leads to a new result on the interlace of zeros of orthogonal polynomials (of equal degrees) with respect to two distributionsdψ(x) andx p dψ(x), 0<p≤1, with support in either [0, 1] or [1, ∞). 相似文献
9.
10.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献