全文获取类型
收费全文 | 23073篇 |
免费 | 2696篇 |
国内免费 | 653篇 |
专业分类
化学 | 2083篇 |
晶体学 | 44篇 |
力学 | 1764篇 |
综合类 | 219篇 |
数学 | 5282篇 |
物理学 | 3428篇 |
无线电 | 13602篇 |
出版年
2024年 | 35篇 |
2023年 | 247篇 |
2022年 | 377篇 |
2021年 | 538篇 |
2020年 | 555篇 |
2019年 | 374篇 |
2018年 | 388篇 |
2017年 | 763篇 |
2016年 | 929篇 |
2015年 | 1010篇 |
2014年 | 1682篇 |
2013年 | 1568篇 |
2012年 | 1657篇 |
2011年 | 1594篇 |
2010年 | 1229篇 |
2009年 | 1320篇 |
2008年 | 1485篇 |
2007年 | 1424篇 |
2006年 | 1304篇 |
2005年 | 1120篇 |
2004年 | 952篇 |
2003年 | 1048篇 |
2002年 | 725篇 |
2001年 | 575篇 |
2000年 | 519篇 |
1999年 | 448篇 |
1998年 | 374篇 |
1997年 | 297篇 |
1996年 | 272篇 |
1995年 | 251篇 |
1994年 | 201篇 |
1993年 | 166篇 |
1992年 | 119篇 |
1991年 | 116篇 |
1990年 | 85篇 |
1989年 | 65篇 |
1988年 | 62篇 |
1987年 | 52篇 |
1986年 | 48篇 |
1985年 | 70篇 |
1984年 | 40篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 48篇 |
1979年 | 48篇 |
1978年 | 26篇 |
1977年 | 36篇 |
1976年 | 37篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
分布在弱电介质溶液中的电磁力(Lorentz力),可以有效地控制边界层的流动.利用以转动水槽为主的实验系统和基于双时间步Roe格式的数值方法,对翼型绕流的电磁控制进行了实验和数值研究.结果表明,对于一定攻角的翼型,电磁力可以控制其绕流形态.当电磁力方向与流动方向相同时,可以抑制分离,消除涡街,其效果与减小攻角类似.当电磁力的方向与流动方向相反时,可在流场中形成大涡组成的涡街,增强流体的混合能力,其效果与增大攻角类似. 相似文献
952.
953.
Pu Zhou Zilun Chen Xiaolin Wang Xiao Li Zejin Liu Xiaojun Xu Jing Hou Zongfu Jiang 《中国光学快报(英文版)》2008,6(7)
We demonstrate a scalable architecture for coherent combining of pulsed fiber lasers.A new method for generating synchronous pulsed fiber lasers by direct phase modulation is proposed and investigated.It is shown that phase modulated mutually coupled laser array can be a steady synchronous pulsed fiber laser source.The synchronous pulsed fiber lasers are coherently combined with an invariable phase difference of π in adjacent lasers.Neither active phase control nor polarization control is taken in our experiment. 相似文献
954.
We carry out a systematic study of the different contributions to the deviations of the elliptic flows from the quark number scaling in high energy heavy ion collision in a quark combination model.The effects that we considered are:the resonance decay,the flavor dependence of the quark elliptic flow and the combination of quarks/antiquarks with slightly different transverse momenta.Our results show that the deviations observed in experiments can be well reproduced within the combination framework if all the three effects are considered. We make a detailed analysis of the different contributions using a Monte-Carlo program and suggest measuring the quark number scaling in intermediate pT range more precisely. 相似文献
955.
Xie Lihua Du Chunling Soh Yeng Chai Zhang Cishen 《Multidimensional Systems and Signal Processing》2002,13(3):265-287
This paper deals with output feedback stabilization and H
control problems for two-dimensional (2-D) discrete linear systems without or with parameter uncertainty. The class of systems under investigation is described by the 2-D local state space Fornasini-Marchesini second model. We aim at designing a dynamical output feedback controller to achieve asymptotic stability and H
performance for the 2-D system. It is shown that the design of output feedback controller can be recast into a convex optimization problem characterized by linear matrix inequalities (LMIs). The LMI solution is further extended to solve the robust stabilization problem for 2-D systems subject to norm-bounded uncertainty. The solutions for the H
control and robust stabilization are applied to two application examples: thermal process control and robust stabilization of processes in Darboux equation. 相似文献
956.
957.
Martin V. Day J. Hall J. Menendez D. Potter I. Rothstein 《Computational Optimization and Applications》2002,22(2):261-302
We generalize the analysis of J.A. Ball, M.V. Day, and P. Kachroo (Mathematics of Control, Signals, and Systems, vol. 12, pp. 307–345, 1999) to a fluid model of a single server re-entrant queue. The approach is to solve the Hamilton-Jacobi-Isaacs equation associated with optimal robust control of the system. The method of staged characteristics is generalized from Ball et al. (1999) to construct the solution explicitly. Formulas are developed allowing explicit calculations for the Skorokhod problem involved in the system equations. Such formulas are particularly important for numerical verification of conditions on the boundary of the nonnegative orthant. The optimal control (server) strategy is shown to be of linear-index type. Dai-type stability properties are discussed. A modification of the model in which new customers are allowed only at a specified entry queue is considered in 2 dimensions. The same optimal strategy is found in that case as well. 相似文献
958.
Z. Dostál A. Friedlander S.A. Santos K. Alesawi 《Computational Optimization and Applications》2002,23(1):127-133
In this paper we give corrections to our paper on an augmented Lagrangian type algorithm for strictly convex quadratic programming problems with equality constraints. 相似文献
959.
W.H. Enright 《Numerical Algorithms》2002,31(1-4):125-137
In the last decade it has become standard for students and researchers to be introduced to state-of-the-art numerical software through a problem solving environment (PSE) rather than through the use of scientific libraries callable from a high level language such as Fortran or C. In this paper we will identify the constraints and implications that this imposes on the ODE software we investigate and develop. In particular, the way a numerical solution is displayed and viewed by a user dictates that new measures of performance and quality must be adopted. We will use the MATLAB environment and ODE software for initial value problems, boundary value problems and delay problems to illustrate the issues that arise and the progress that has been made. One of the major implications is the expectation that accurate approximations at off-mesh points must be provided. Traditional numerical methods for ODEs have produced approximations to the underlying solution on an associated discrete, adaptively chosen mesh. In recent years it has become common for the ODE software to also deliver approximations at off-mesh values of the independent variable. Such a feature can be extremely valuable in applications and leads to new measures of quality and performance which are more meaningful to users and more consistently interpreted and implemented in contemporary ODE software. Numerical examples of the robust and reliable behaviour of such software will be presented and the cost/reliability trade-offs that arise will be quantified. 相似文献
960.
Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions
Garcia P Popot MA Fournier F Bonnaire Y Tabet JC 《Journal of mass spectrometry : JMS》2002,37(9):940-953
A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control. 相似文献