全文获取类型
收费全文 | 49772篇 |
免费 | 3832篇 |
国内免费 | 3703篇 |
专业分类
化学 | 26919篇 |
晶体学 | 497篇 |
力学 | 2455篇 |
综合类 | 327篇 |
数学 | 11273篇 |
物理学 | 15836篇 |
出版年
2024年 | 40篇 |
2023年 | 389篇 |
2022年 | 601篇 |
2021年 | 702篇 |
2020年 | 890篇 |
2019年 | 894篇 |
2018年 | 1878篇 |
2017年 | 2108篇 |
2016年 | 1728篇 |
2015年 | 1649篇 |
2014年 | 1645篇 |
2013年 | 2216篇 |
2012年 | 4914篇 |
2011年 | 4300篇 |
2010年 | 3176篇 |
2009年 | 2924篇 |
2008年 | 2061篇 |
2007年 | 1926篇 |
2006年 | 1904篇 |
2005年 | 5612篇 |
2004年 | 4810篇 |
2003年 | 3081篇 |
2002年 | 1322篇 |
2001年 | 949篇 |
2000年 | 655篇 |
1999年 | 634篇 |
1998年 | 447篇 |
1997年 | 371篇 |
1996年 | 347篇 |
1995年 | 322篇 |
1994年 | 268篇 |
1993年 | 219篇 |
1992年 | 310篇 |
1991年 | 296篇 |
1990年 | 235篇 |
1989年 | 200篇 |
1988年 | 168篇 |
1987年 | 112篇 |
1986年 | 86篇 |
1985年 | 73篇 |
1984年 | 47篇 |
1983年 | 46篇 |
1976年 | 80篇 |
1975年 | 40篇 |
1974年 | 42篇 |
1973年 | 52篇 |
1972年 | 40篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
91.
92.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
93.
In this paper a half space problem for the one-dimensional Boltzmann equation with specular reflective boundary condition is investigated. It is shown that the solution of the Boltzmann equation time-asymptotically converges to a global Maxwellian under some initial conditions. Furthermore, a time-decay rate is also obtained. 相似文献
94.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
95.
Si衬底上ZnSe外延膜的低压MOCVD生长 总被引:2,自引:2,他引:0
以硒化氢(H2Se)和二甲基锌为源材料,生长温度是300℃时,用低压金属有机化学气相沉积(LP-MOCVD)系统在Si(111)衬底上外延生长了ZnSe薄膜。通过X射线衍射(XRD)、扫描电子显微镜的能量色散(EDS)以及光致发光(PL)实验验证ZnSe外延膜的质量,在X射线衍射谱中只有一个强的ZnSe(111)面衍射峰,这说明外延膜是(111)取向的单晶薄膜,在能量色散谱中除了Si,Zn和Se原子外,没有观测到其他原子,说明ZnSe外延膜中杂质含量较少。ZnSe外延膜中Zn/Se原子比接近1,有较好的化学配比。在ZnSe外延膜的77K光致发光谱中没有观测到与深中心发射相关的发光峰,表明ZnSe外延膜的晶格缺陷密度较小。77K时的近带边发射峰447nm在室温时移至465nm附近。 相似文献
96.
97.
Goran Pavi? 《Applied Acoustics》2006,67(9):864-881
A method is formulated for the identification of an unknown physical parameter of a fluid-filled pipe using the measurement of sound speed in the pipe. The method uses a simple formula which provides the relationship between the sound speed and a few physical parameters of the pipe: thickness, diameter, wall material constants and fluid constants. Once the sound speed in the pipe is measured, the simple formula can be used to extract one of the unknown parameters providing the remaining ones are known.The sound speed in the pipe is measured using a 3-transducer array. In order to demonstrate the potential of the technique the results of several measurements obtained in a water-filled steel pipe are presented.The required accuracy of the measurement of sound speed and of the specification of known parameters is analysed. The accuracy depends on the unknown parameter which is to be identified. For example, if the pipe thickness is the unknown parameter, the other parameters have to be known within a very narrow margin of error. On the contrary, if the fluid properties have to be identified the needed accuracy of known parameters gets much lower. 相似文献
98.
求解非线性方程的一个新方法 总被引:2,自引:0,他引:2
张艺 《宁波大学学报(理工版)》2002,15(3):55-57
提出了一种求解非线性方程的数值方法,此方法不需要导数的计算,其收敛阶与抛物线法相同,但计算量要比抛物线法小得多。 相似文献
99.
Laser driven shocks can lead to a dynamic failure, called film spallation. Here, we use a modified laser spallation set-up
to measure the dynamic adhesion of thin films and we propose a novel diagnostic technology. Based on correlation theory, new
spallation criteria for characterizing the progressive damage at the interface between the film and the substrate are established,
such as interface delamination, film spallation and film expulsion. With the help of the theory, the degree of damage and
the dimension of damage (i.e. fracture), such as the minimum width of delamination radius, the thickness of the film etc.,
are estimated. Experiments are carried out on epoxy/stainless steel and epoxy/Al, and the experimental results show that their
dynamic bonding strengths are about 25 MPa and 20 MPa, respectively. The detailed results, analyses and discussions are presented
in this paper.
Received: 6 February 2001 / Accepted: 3 December 2001 / Published online: 11 February 2002 相似文献
100.
对Sn-C60薄膜进行紫外可见光吸收,X-射线衍射和扫描电镜的测定结果显示,薄膜样品紫外可见光吸收的两个短波段吸收峰比纯C60薄膜的吸收峰显著下降,说明Sn-C60薄膜的电子光吸收跃迁为间接跃迁,能带中有杂质能级的存在;样品的X射线衍射峰则对应于面心立方结构;扫描电镜结果显示薄膜为纳米级颗粒组成。 相似文献