全文获取类型
收费全文 | 235015篇 |
免费 | 40161篇 |
国内免费 | 47377篇 |
专业分类
化学 | 165425篇 |
晶体学 | 5033篇 |
力学 | 15470篇 |
综合类 | 4792篇 |
数学 | 34344篇 |
物理学 | 97489篇 |
出版年
2024年 | 686篇 |
2023年 | 3563篇 |
2022年 | 7795篇 |
2021年 | 8183篇 |
2020年 | 8523篇 |
2019年 | 8359篇 |
2018年 | 7608篇 |
2017年 | 8465篇 |
2016年 | 9945篇 |
2015年 | 11159篇 |
2014年 | 13531篇 |
2013年 | 17791篇 |
2012年 | 19807篇 |
2011年 | 20760篇 |
2010年 | 16678篇 |
2009年 | 16695篇 |
2008年 | 18110篇 |
2007年 | 16289篇 |
2006年 | 15646篇 |
2005年 | 13297篇 |
2004年 | 10655篇 |
2003年 | 8132篇 |
2002年 | 7943篇 |
2001年 | 7453篇 |
2000年 | 7318篇 |
1999年 | 5540篇 |
1998年 | 3899篇 |
1997年 | 3419篇 |
1996年 | 3412篇 |
1995年 | 2955篇 |
1994年 | 2778篇 |
1993年 | 2411篇 |
1992年 | 2133篇 |
1991年 | 1816篇 |
1990年 | 1591篇 |
1989年 | 1349篇 |
1988年 | 1157篇 |
1987年 | 966篇 |
1986年 | 837篇 |
1985年 | 671篇 |
1984年 | 617篇 |
1983年 | 546篇 |
1982年 | 409篇 |
1981年 | 323篇 |
1980年 | 258篇 |
1979年 | 193篇 |
1978年 | 124篇 |
1977年 | 77篇 |
1976年 | 84篇 |
1975年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
LIU Jixue ZHANG Sanguo & CHEN Xiru Department of Statistics Finance University of Science Technology of China Hefei China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,49(6):752-769
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article. 相似文献
22.
GAO Jing ZHOU Xiaohua CHEN Xun Chongqing University Chemical Engineering Department Chongqing China 《Chinese Journal of Reactive Polymers》2006,(2)
1. INTRODUCTION In the process of coking plant, about 30%~35% sulfur is transformed to H2S and some other sulfide, which form impurity in coal gas together with NH3 and HCN. Only 0.1% H2S containing in air can lead to die, so it is very important to carry on desulphurization and decyanation with coal gas [1~3]. Currently desulphurization and decyanation craft technique have Dry Oxidation Technology, Wet Oxidation Technology and Liquid Absorption Technology [2] three main kinds. The… 相似文献
23.
本文研究具有随机开参数集的随机场构造,获得了具有已知有穷维分布的随机场存在和唯一性条件。 相似文献
24.
Fractional factorial split-plot (FFSP) designs have an important value of investigation for their special structures. There are two types of factors in an FFSP design: the whole-plot (WP) factors and sub-plot (SP) factors, which can form three types of two-factor interactions: WP2fi, WS2fi and SP2fi. This paper considers FFSP designs with resolution III or IV under the clear effects criterion. It derives the upper and lower bounds on the maximum numbers of clear WP2fis and WS2fis for FFSP designs, and gives some methods for constructing the desired FFSP designs. It further examines the performance of the construction methods. 相似文献
25.
本文介绍一种用牛顿力学研究赛跑运动的物理模型,给出两种情形下跑步时间的最优化结果.这一结果与优秀运动员的实际比赛成绩很好地相符. 相似文献
26.
Chunguang Du Hongyi Chen Shiqun Li 《量子光学学报》2006,12(B08):70-71
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of metameterial which have negative permittivity and negative permeability, which lead to negative refractive index in a frequency range. The LHMs that have been available so far are in the microwave range and are usually composed of classical particles, such as split-ring resonators. Some quantum phenomena such as spontaneous emission of atoms in the LHMs which are considered to be 'classical background' have also been investigated. Many potential applications of LHMs have been proposed, such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. 相似文献
27.
Theoretical and experimental investigations on the performance of micro-perforated -panel absorbers are reviewed in this paper. By reviewing recent research work, this paper reveals a relationship between the maximum absorption coefficient and the limit of the absorption frequency bandwidth. It has been demonstrated that the absorption frequency bandwidth can be extended up to 3 or 4 octaves as the diameters of the micro-holes decrease. This has become possible with the development of the technologies for manufacturing micro-perforated panels, such as laser drilling, powder metallurgy, welded meshing and electro-etching to form micrometer order holes. In this paper, absorption characteristics of such absorbers in random fields and in high sound intensity are discussed both theoretically and experimentally. A new absorbing structure based on micro-perforated-panel absorbers demonstrate experimentally high sound absorption capability. This review shows that the micro-perforated-panel absorber has potentials to be one of ideal absorbing materials in the 21st century. 相似文献
28.
在保持非负定性不变的前提下,本文对矩阵每一元素容许多大的扰动作了进一步的研究, 将本文的结论和C.R.Johnson提出的部分正定阵的正定完备化进行比较,容易发现对已知的正定矩阵求扰动,本文的结论比用C.R.Johnson的正定完备化计算扰动形式上更简单,同时也给出了不同于C.R.Johnson的部分正定阵的正定完备化表示的另外一个公式,推出了这些正定完备化矩阵应具有的若干性质. 相似文献
29.
两种拔尿管方法对膀胱功能损伤的临床观察 总被引:2,自引:0,他引:2
为观察两种不同的拔尿管方法对膀胱功能损伤的差异,将80例患者随机分成两组,分别采用改良法(40例)和常规法(40例)拔除留置尿管,分析比较了两组患者排尿顺利率、逼尿肌功能恢复率及尿道刺激症、尿失禁、尿潴留。结果表明,两组患者拔管后上述指标与情况有显著性差异,P<0.05。提示改良组膀胱功能损伤明显低于对照组。改良的拔管方法是一种值得护理推广应用的好方法。 相似文献
30.
Chong-Guang Cao Zhong-Peng Yang Xian Zhang 《Journal of Applied Mathematics and Computing》2002,10(1-2):101-109
We extend two inequalities involving Hadamard products of positive definite Hermitian matrices to positive semi-definite Hermitian matrices. Simultaneously, we also show the sufficient conditions for equalities to hold. Moreover, some other matrix inequalities are also obtained. Our results and methods are different from those which are obtained by S. Liu in [J. Math. Anal. Appl. 243:458–463(2000)] and B.-Y. Wang et al. in [Lin. Alg. Appl. 302–303: 163–172(1999)]. 相似文献