全文获取类型
收费全文 | 12316篇 |
免费 | 669篇 |
国内免费 | 661篇 |
专业分类
化学 | 963篇 |
晶体学 | 13篇 |
力学 | 1034篇 |
综合类 | 77篇 |
数学 | 1204篇 |
物理学 | 1164篇 |
综合类 | 9191篇 |
出版年
2024年 | 61篇 |
2023年 | 154篇 |
2022年 | 255篇 |
2021年 | 288篇 |
2020年 | 330篇 |
2019年 | 264篇 |
2018年 | 259篇 |
2017年 | 403篇 |
2016年 | 468篇 |
2015年 | 470篇 |
2014年 | 655篇 |
2013年 | 582篇 |
2012年 | 656篇 |
2011年 | 726篇 |
2010年 | 593篇 |
2009年 | 630篇 |
2008年 | 595篇 |
2007年 | 767篇 |
2006年 | 672篇 |
2005年 | 569篇 |
2004年 | 571篇 |
2003年 | 497篇 |
2002年 | 421篇 |
2001年 | 383篇 |
2000年 | 299篇 |
1999年 | 288篇 |
1998年 | 219篇 |
1997年 | 217篇 |
1996年 | 187篇 |
1995年 | 182篇 |
1994年 | 170篇 |
1993年 | 118篇 |
1992年 | 108篇 |
1991年 | 98篇 |
1990年 | 131篇 |
1989年 | 84篇 |
1988年 | 90篇 |
1987年 | 61篇 |
1986年 | 38篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
31.
Poisson回归模型广泛应用于分析计数型数据 ,Dean&Lawless(1989)和Dean(1992 )讨论了非重复测量得到的计数型数据的偏大离差存在性的检验问题 .本文分别利用随机系数模型和对数非线性模型讨论了基于重复测量得到的计数型数据的偏大离差的检验问题 ,得到了检验的score统计量 . 相似文献
32.
Dmitry I. Belov Ronald D. Armstrong 《Computational Optimization and Applications》2006,33(2-3):319-332
This paper introduces a novel approach for extracting the maximum number of non-overlapping test forms from a large collection
of overlapping test sections assembled from a given item bank. The approach involves solving maximum set packing problems
(MSPs). A branch-and-bound MSP algorithm is developed along with techniques adapted from constraint programming to estimate
lower and upper bounds on the optimal MSP solution. The algorithm is general and can be applied in other applications including
combinatorial auctions. The results of computer simulations and experiments with an operational item bank are presented.
An erratum to this article is available at . 相似文献
33.
34.
Two tests for multivariate conditional heteroscedastic models are proposed. One is based on the cross-correlations of standardized squared residuals and the other is a score (Lagrange multiplier) test. The cross-correlations test can be used to detect the presence of multivariate conditional heteroscedasticity whereas the other test can be used for diagnostic checking. Simulation studies on the size and power of the test statistics are reported. The application of the tests is illustrated by an example using the S & P 500 and Sydney All Ordinary Indexes. 相似文献
35.
Youssef Randjiou 《Journal of Theoretical Probability》2006,19(3):701-720
Let μ+(t) and μ−(t) be the locations of the maximum and minimum, respectively, of a standard Brownian motion in the interval [0,t]. We establish a joint integral test for the lower functions of μ+(t) and μ−(t), in the sense of Paul Lévy. In particular, it yields the law of the iterated logarithm for max(μ+(t),μ−(t)) as a straightforward consequence. Our result is in agreement with well-known theorems of Chung and Erdős [(1952) Trans. Amer. Math. Soc. 72, 179–186.], and Csáki, F?ldes and Révész [(1987) Prob. Theory Relat. Fields
76, 477–497].
相似文献
36.
Microstructure effect on chemical etching behavior of the annealed Ti-6Al-4V and Ti-3Al-2.5V titanium (Ti) alloys was compared with that of unalloyed commercially pure titanium. The microstructural evolution of structure phases after annealing the titanium and its alloys at temperature near and above β transus and followed by furnace cooling to room temperature was studied using optical microscope, scanning electron microscope and X-ray diffraction techniques. The microstructure study illustrates that the heat treatment enhanced partitioning effect allows extensive formation of hemispherical and near spherical pits roughened surface to be readily acquired by chemically etching the annealed α + β titanium alloys. The kinetics of the chemical etching reaction process show a linear dependence on time. The annealed α + β titanium alloys that exhibit relatively lower weight loss and thickness reduction rate illustrate less chemical activity than the annealed unalloyed titanium. 相似文献
37.
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
38.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
39.
40.
遥感器CCD驱动器热设计及其在摄像过程中的温度变化 总被引:3,自引:3,他引:0
CCD驱动器是航天成像遥感器摄像过程中的主要热源之一。防止CCD驱动器过热是保证其正常工作的重要方面。介绍了遥感器的工作模式和对CCD驱动器采取的热控制措施。通过热平衡试验,利用回归的方法,对CCD驱动器在摄像过程中的温度变化规律进行了分析,同时对热控制效果进行了评估。CCD驱动器工作时升温速率在0.85℃/min左右,整个摄像过程中最高温度约为26℃,所实施的热控制措施效果理想。 相似文献