全文获取类型
收费全文 | 11607篇 |
免费 | 1204篇 |
国内免费 | 769篇 |
专业分类
化学 | 2108篇 |
晶体学 | 27篇 |
力学 | 800篇 |
综合类 | 262篇 |
数学 | 7774篇 |
物理学 | 2609篇 |
出版年
2024年 | 12篇 |
2023年 | 107篇 |
2022年 | 149篇 |
2021年 | 292篇 |
2020年 | 315篇 |
2019年 | 317篇 |
2018年 | 292篇 |
2017年 | 347篇 |
2016年 | 452篇 |
2015年 | 299篇 |
2014年 | 593篇 |
2013年 | 984篇 |
2012年 | 529篇 |
2011年 | 678篇 |
2010年 | 621篇 |
2009年 | 715篇 |
2008年 | 687篇 |
2007年 | 766篇 |
2006年 | 639篇 |
2005年 | 587篇 |
2004年 | 516篇 |
2003年 | 498篇 |
2002年 | 461篇 |
2001年 | 377篇 |
2000年 | 333篇 |
1999年 | 282篇 |
1998年 | 261篇 |
1997年 | 207篇 |
1996年 | 198篇 |
1995年 | 163篇 |
1994年 | 124篇 |
1993年 | 98篇 |
1992年 | 91篇 |
1991年 | 93篇 |
1990年 | 46篇 |
1989年 | 53篇 |
1988年 | 51篇 |
1987年 | 28篇 |
1986年 | 37篇 |
1985年 | 51篇 |
1984年 | 43篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
42.
周治修 《浙江大学学报(理学版)》2004,31(6):610-613
ZULLI L首先构造了一个用于计算纽结Kauffman尖括号多项式的模2矩阵,纽结的trip矩阵.为了构造链环的trip矩阵,引入了一个带标识的穿有m个孔的圆盘来取代纽结情形下的圆盘,其中m为链环的分支数.主要结果为:定理若状态S是从状态AA…A经过i1,i2,…,ip位置上的标记替换(A换成B)而得的状态.设Ts是将trip矩阵T的左上角的n×n子块中ai1i1,ai2i2,…,aipip之值进行替换(0→1或1→0)所得的矩阵,则#(L|S)=n+m-秩(Ts).因此计算链环Kauffman尖括号多项式就归结为计算一组模2矩阵的秩. 相似文献
43.
44.
45.
46.
47.
Based on the beam coherence-polarization (BCP) matrix, the polarization property of coherent and incoherent Gaussian beam combinations is studied in detail. The general expressions for the degree of polarization P of the resulting beam in case of incoherent and coherent combinations are derived. It is shown that P is dependent on the incoherent or coherent combination, propagation distance, separation, azimuth of the polarization plane and numbers of beamlets in general. The irradiance distribution of the resulting beam for the coherent cases depends on the azimuth of the polarization plane of beamlets. However, for the incoherent case it does not. 相似文献
48.
One of the most ignored, but urgent and vital challenges confronting society today is the vulnerability of urban areas to extreme events. Current organization of response systems, predominantly based on a command and control model, limits their effectiveness and efficiency. Particularly, in decision‐making processes where a large number of actors may be involved. In this article, a new distributed collaborative decision‐making model is proposed to overcome command and control limitations encountered in stressful, hostile, chaotic, and large‐scale settings. This model was derived by borrowing concepts from the collective decision making of honeybees foraging, a successful process in solving complex tasks within complex settings. The model introduced in this article was evaluated through differential equations, i.e., continuous analysis, and difference equations, i.e., discrete analysis. The most important result found is that the best available option in any large‐scale decision‐making problem can be configured as an attractor, in a distributed and timely manner. We suggest that the proposed model has the potential to facilitate decision‐making processes in large‐scale settings. © 2005 Wiley Periodicals, Inc. Complexity 11:28–38, 2005 相似文献
49.
A solution to the phase problem in optics is considered within the context of the analysis of signals changing in time and of the effect of an object under investigation on the probing radiation. The solution is based on the use of a twin-wave interferometer with phase modulation in one of the channels and a spectrometer. The analysis is concerned, in particular, with signals and processes of ultrashort duration. To shift the frequency in the interferometer channel, an electrooptical crystal of ferroelectric perovskite is used as the modulator. Errors of amplitude and phase structures determined are analyzed. 相似文献
50.