全文获取类型
收费全文 | 25721篇 |
免费 | 2203篇 |
国内免费 | 1737篇 |
专业分类
化学 | 11523篇 |
晶体学 | 252篇 |
力学 | 2072篇 |
综合类 | 285篇 |
数学 | 4129篇 |
物理学 | 11400篇 |
出版年
2023年 | 215篇 |
2022年 | 579篇 |
2021年 | 562篇 |
2020年 | 588篇 |
2019年 | 574篇 |
2018年 | 571篇 |
2017年 | 625篇 |
2016年 | 797篇 |
2015年 | 697篇 |
2014年 | 1015篇 |
2013年 | 1655篇 |
2012年 | 1611篇 |
2011年 | 1656篇 |
2010年 | 1316篇 |
2009年 | 1727篇 |
2008年 | 1584篇 |
2007年 | 1676篇 |
2006年 | 1367篇 |
2005年 | 1044篇 |
2004年 | 954篇 |
2003年 | 919篇 |
2002年 | 927篇 |
2001年 | 718篇 |
2000年 | 720篇 |
1999年 | 648篇 |
1998年 | 579篇 |
1997年 | 391篇 |
1996年 | 311篇 |
1995年 | 294篇 |
1994年 | 259篇 |
1993年 | 263篇 |
1992年 | 330篇 |
1991年 | 209篇 |
1990年 | 174篇 |
1989年 | 144篇 |
1988年 | 153篇 |
1987年 | 132篇 |
1986年 | 108篇 |
1985年 | 95篇 |
1984年 | 99篇 |
1983年 | 60篇 |
1982年 | 113篇 |
1981年 | 184篇 |
1980年 | 192篇 |
1979年 | 197篇 |
1978年 | 168篇 |
1977年 | 105篇 |
1976年 | 114篇 |
1974年 | 38篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
大学物理实验教学改革的实践与思索 总被引:10,自引:0,他引:10
本主要介绍了我校近年来在大学物理实验课程体系和教学内容改革的实践及下一步改革的思路。 相似文献
142.
魏嵬 《数学的实践与认识》2007,37(16):76-83
为给转炉设计提供依据,需要计算炉液倾动的重心.利用数学方法将实际问题进行简化,通过分析炉液倾动过程中变量间的相互关系,来确定每个倾动角度对应情况下的液面位置.利用数学中三重积分的有关应用,进一步得出转炉在每个倾动角度为α∈(0,π2)时的重心计算方法及相关结论,在理论上为工程计算重心的方法提供参考. 相似文献
143.
144.
145.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(6):571-588
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters
occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance
matrix is either unknown, or partially unknown, or known.
Supported by the grant of the Council of Czech Republic MSM 6 198 959 214. 相似文献
146.
Adam B. Levy 《Mathematical Programming》2007,110(3):615-639
Numerical methods for solving constrained optimization problems need to incorporate the constraints in a manner that satisfies
essentially competing interests; the incorporation needs to be simple enough that the solution method is tractable, yet complex
enough to ensure the validity of the ultimate solution. We introduce a framework for constraint incorporation that identifies
a minimal acceptable level of complexity and defines two basic types of constraint incorporation which (with combinations)
cover nearly all popular numerical methods for constrained optimization, including trust region methods, penalty methods,
barrier methods, penalty-multiplier methods, and sequential quadratic programming methods. The broad application of our framework
relies on addition and chain rules for constraint incorporation which we develop here. 相似文献
147.
Summary Assuming a completely disordered lattice it is shown that all the states are localized when the disorder parameterx=a
0/0 reachesthe value 0.31, wherea is the mean atomic separation anda
0 is the Bohr radius. 相似文献
148.
In this paper, we consider a queueing system in which there are two exponential servers, each having his own queue, and arriving
customers will join the shorter queue. Based on the results given in Flatto and McKean, we rewrite the formula for the probability
that there are exactlyk customers in each queue, wherek = 0, 1,…. This enables us to present an algorithm for computing these probabilities and then to find the joint distribution
of the queue lengths in the system. A program and numerical examples are given. 相似文献
149.
J. Seke 《Il Nuovo Cimento D》1993,15(7):1031-1034
Summary By using a self-consistent projection-operator method, developed recently by the present author, a gauge-invariant Markovian
treatment of the spontaneous decay of an unstable atomic state is presented. Without ignoring retardation and electron-spin
effects a gauge-invariant result for the probability amplitude of finding the atom in the unstable state is obtained. 相似文献
150.
The mucosal upheaval (MU), where the mucosal wave starts and propagates upward, appears only when the vocal fold vibrates. The location of the MU histologically and the effect of changes in mean air flow rate (MFR) and vocal fold length on occurrence of the MU were studied in twelve excised canine larynges. The lower surface of the vocal fold was marked to serve as a landmark for subsequent study. Cricothyroid approximation was performed to lengthen the vocal fold. After taking high-speed pictures or recording stroboscopic images from the tracheal side, a small cut wound was made at the mark. This wound served to compare the position of the MU with the histologically identified location of the mark. The larynx was then sectioned in the frontal plane. Before lengthening the vocal fold, the MU occurred on the area where the lamina propria became thinner and where the muscular layer neared the epithelial layer. After lengthening the vocal fold, the MU actually shifted medially compared with its original position. The subglottic area surrounded by the bilateral MUs became longer and thinner. Whether or not complete glottal closure during a vibratory cycle was achieved did not alter these findings. In contrast, with a fixed vocal fold length the MU appeared more laterally as MFR increased, but, based on the relation with the mark, its location on the vocal fold did not change from its original position before increase of MFR. 相似文献