全文获取类型
收费全文 | 10209篇 |
免费 | 1629篇 |
国内免费 | 1330篇 |
专业分类
化学 | 5675篇 |
晶体学 | 120篇 |
力学 | 442篇 |
综合类 | 53篇 |
数学 | 1136篇 |
物理学 | 2760篇 |
无线电 | 2982篇 |
出版年
2024年 | 25篇 |
2023年 | 248篇 |
2022年 | 305篇 |
2021年 | 380篇 |
2020年 | 381篇 |
2019年 | 357篇 |
2018年 | 313篇 |
2017年 | 325篇 |
2016年 | 480篇 |
2015年 | 530篇 |
2014年 | 662篇 |
2013年 | 736篇 |
2012年 | 942篇 |
2011年 | 939篇 |
2010年 | 658篇 |
2009年 | 595篇 |
2008年 | 671篇 |
2007年 | 543篇 |
2006年 | 549篇 |
2005年 | 492篇 |
2004年 | 402篇 |
2003年 | 331篇 |
2002年 | 313篇 |
2001年 | 246篇 |
2000年 | 167篇 |
1999年 | 245篇 |
1998年 | 179篇 |
1997年 | 132篇 |
1996年 | 155篇 |
1995年 | 163篇 |
1994年 | 137篇 |
1993年 | 88篇 |
1992年 | 80篇 |
1991年 | 78篇 |
1990年 | 84篇 |
1989年 | 54篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
51.
52.
53.
In this paper, a construction of optimal constant composition codes is developed, and used to derive some series of new optimal
constant composition codes meeting the upper bound given by [13]. 相似文献
54.
For given a graph H, a graphic sequence π = (d
1, d
2,..., d
n) is said to be potentially H-graphic if there is a realization of π containing H as a subgraph. In this paper, we characterize the potentially (K
5 − e)-positive graphic sequences and give two simple necessary and sufficient conditions for a positive graphic sequence π to
be potentially K
5-graphic, where K
r is a complete graph on r vertices and K
r-e is a graph obtained from K
r by deleting one edge. Moreover, we also give a simple necessary and sufficient condition for a positive graphic sequence
π to be potentially K
6-graphic.
Project supported by National Natural Science Foundation of China (No. 10401010). 相似文献
55.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
56.
Hao Yin Chuang Lin Berton Sebastien Bo Li Geyong Min 《International Journal of Communication Systems》2005,18(8):711-729
Fast and accurate methods for predicting traffic properties and trend are essential for dynamic network resource management and congestion control. With the aim of performing online and feasible prediction of network traffic, this paper proposes a novel time series model, named adaptive autoregressive (AAR). This model is built upon an adaptive memory‐shortening technique and an adaptive‐order selection method originally developed by this study. Compared to the conventional one‐step ahead prediction using traditional Box–Jenkins time series models (e.g. AR, MA, ARMA, ARIMA and ARFIMA), performance results obtained from actual Internet traffic traces have demonstrated that the proposed AAR model is able to support online prediction of dynamic network traffic with reasonable accuracy and relatively low computation complexity. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
57.
58.
In this paper, we discuss the viscosity solutions of the weakly coupled systems of fully nonlinear second-order degenerate parabolic equations and their Cauchy-Dirichlet problem. We prove the existence, uniqueness and continuity of viscosity solution by combining Perron's method with the technique of coupled solutions. The results here generalize those in Proc. London Math. Soc. 63 (1991) 212-240 and Comm. Partial Differential Equations 16 (1991) 1095-1128. 相似文献
59.
Canonical correlation analysis based on information theory 总被引:2,自引:0,他引:2
In this article, we propose a new canonical correlation method based on information theory. This method examines potential nonlinear relationships between p×1 vector Y-set and q×1 vector X-set. It finds canonical coefficient vectors a and b by maximizing a more general measure, the mutual information, between aTX and bTY. We use a permutation test to determine the pairs of the new canonical correlation variates, which requires no specific distributions for X and Y as long as one can estimate the densities of aTX and bTY nonparametrically. Examples illustrating the new method are presented. 相似文献
60.