全文获取类型
收费全文 | 49905篇 |
免费 | 3264篇 |
国内免费 | 2647篇 |
专业分类
化学 | 24275篇 |
晶体学 | 262篇 |
力学 | 4648篇 |
综合类 | 687篇 |
数学 | 14638篇 |
物理学 | 11306篇 |
出版年
2024年 | 86篇 |
2023年 | 500篇 |
2022年 | 1216篇 |
2021年 | 1253篇 |
2020年 | 1223篇 |
2019年 | 1185篇 |
2018年 | 1087篇 |
2017年 | 1420篇 |
2016年 | 1832篇 |
2015年 | 1359篇 |
2014年 | 2070篇 |
2013年 | 3513篇 |
2012年 | 2815篇 |
2011年 | 2572篇 |
2010年 | 2265篇 |
2009年 | 2856篇 |
2008年 | 2840篇 |
2007年 | 3159篇 |
2006年 | 2664篇 |
2005年 | 2413篇 |
2004年 | 2278篇 |
2003年 | 1904篇 |
2002年 | 1563篇 |
2001年 | 1338篇 |
2000年 | 1251篇 |
1999年 | 1158篇 |
1998年 | 1037篇 |
1997年 | 932篇 |
1996年 | 827篇 |
1995年 | 783篇 |
1994年 | 671篇 |
1993年 | 552篇 |
1992年 | 519篇 |
1991年 | 450篇 |
1990年 | 389篇 |
1989年 | 273篇 |
1988年 | 256篇 |
1987年 | 185篇 |
1986年 | 154篇 |
1985年 | 188篇 |
1984年 | 162篇 |
1983年 | 74篇 |
1982年 | 124篇 |
1981年 | 73篇 |
1980年 | 66篇 |
1979年 | 96篇 |
1978年 | 44篇 |
1977年 | 30篇 |
1976年 | 33篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
72.
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
73.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
74.
Eremenko L. T. Oreshko G. V. Nesterenko D. A. Lagodzinskaya G. V. Eremenko I. L. 《Russian Chemical Bulletin》2002,51(1):157-159
The reactions of ethylene glycol mononitrate and glycerol 1,3-dinitrate with methylphosphonic dichloride afforded new nitroxyalkyl methylphosphonates. 相似文献
75.
Michael Giudici 《Designs, Codes and Cryptography》2006,39(2):163-172
We determine all linear codes C containing the constant code E, for which there is a weight-preserving group of semilinear automorphisms which acts transitively on the set of nontrivial
cosets of E in C.
Michael Giudici - The author holds an Australian Postdoctoral Fellowship. 相似文献
76.
臧忠卿 《数学的实践与认识》2006,36(10):132-136
运用中学生男性性别角色期望调查表和因子分析方法对贵阳市中学生进行男性性别角色期望调查和定性与定量分析,为中学生树立适宜的性别角色观,促进其心理健康发展提供量化依据.分析显示:传统的男性角色并不被现代中学生完全接受,无论是男中学生还是女中学生都在力图探求一种新的男性性别角色模式,且两性中学生对这一新的男性性别角色模式的期望和把握是有一定差异的. 相似文献
77.
S. P. Popov 《Computational Mathematics and Mathematical Physics》2006,46(6):983-994
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined. 相似文献
78.
The prepared amorphous
γ-ZrP\SiO2 composite had a complicated composition,
since a part of γ-ZrP is converted to α-form during the exfoliation
of it. The γ-ZrP\SiO2 composite have specific surface
area of 421 m2g–1.
The acidic P–OH groups of the lamellae species placed on the surface
(it is ≈1.0 meq g–1), do not destroy until
the temperature of 1030 K. During the thermal treatment the total mass loss
of 7.79% was found. This value corresponds to 0.42 mole of H2O
per molecule unit. The water loss process was found very slow, because of
the placing of bilamellar species in the composite. 相似文献
79.
Qiu Hong WU He Xiang WANG Kun GAO State Key Laboratory of Applied Organic Chemistry College of Chemistry Chemical Engineering Lanzhou University Lanzhou 《中国化学快报》2006,17(2)
Many Ligularia species have long been used as traditional folk medicine for theirantibiotic, antiphlogistic and antitussive activities1, and were found to be an importantsource of eremophilane. In the course of our search for bioactive sesquiterpenoids, w… 相似文献
80.