全文获取类型
收费全文 | 8770篇 |
免费 | 1467篇 |
国内免费 | 785篇 |
专业分类
化学 | 1584篇 |
晶体学 | 69篇 |
力学 | 921篇 |
综合类 | 143篇 |
数学 | 3485篇 |
物理学 | 4820篇 |
出版年
2024年 | 13篇 |
2023年 | 92篇 |
2022年 | 118篇 |
2021年 | 162篇 |
2020年 | 215篇 |
2019年 | 198篇 |
2018年 | 241篇 |
2017年 | 265篇 |
2016年 | 313篇 |
2015年 | 241篇 |
2014年 | 399篇 |
2013年 | 1060篇 |
2012年 | 427篇 |
2011年 | 568篇 |
2010年 | 432篇 |
2009年 | 577篇 |
2008年 | 614篇 |
2007年 | 579篇 |
2006年 | 529篇 |
2005年 | 501篇 |
2004年 | 434篇 |
2003年 | 399篇 |
2002年 | 406篇 |
2001年 | 278篇 |
2000年 | 295篇 |
1999年 | 240篇 |
1998年 | 247篇 |
1997年 | 178篇 |
1996年 | 158篇 |
1995年 | 113篇 |
1994年 | 122篇 |
1993年 | 113篇 |
1992年 | 102篇 |
1991年 | 72篇 |
1990年 | 56篇 |
1989年 | 45篇 |
1988年 | 27篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
41.
The basic concepts about the active structures and some attributes of the modes were presented in paper "Liner Active Structures and Modes ( Ⅰ ) ". The characteristics of the active discrete systems and active beams were discussed, especially, the stability of the active structures and the orthogonality of the eigenvectors. The notes about modes were portrayed by a model of a seven-storeyed building with sensors and actuators. The concept of the adjoint active structure was extended from the discrete systems to the beams that were the representations of the continuous structures. Two types of beams with different placements of the measuring and actuating systems were discussed in detail. One is the beam with the discrete sensors and actuators, and the other is the beam with distributed sensor and actuator function. The orthogonality conditions were derived with the modal shapes of the active beam and its adjoint active beam. An example shows that the variation of eigenvalues with feedback amplitude for the homo-configuration and non-homo-configuration active structures. 相似文献
42.
A. N. Logunov 《Journal of Russian Laser Research》2004,25(4):331-348
A physical multidimensional local model of the propagation process of a laser pulse in air having no analogy to famous models in laser physics is constructed. It is based on the representations of classical wave mechanics characteristic of the theory of scalar wave fields. 相似文献
43.
Hans‐Peter Brack Denise Ruegg Heinrich Bührer Michal Slaski Selmiye Alkan Günther G. Scherer 《Journal of Polymer Science.Polymer Physics》2004,42(13):2612-2624
The influence of irradiation and grafting on the crystallinity of three base polymers has been investigated with differential scanning calorimetry. Grafting has the largest effect on the base polymer crystallinity and results in a reduction of the crystallinity. The thermal degradation of the base polymers and grafted films has been investigated with thermogravimetric analysis. The extent of the fluorination of the base polymer, the irradiation method, and the graft level all influence the thermal degradation and its activation energy. It is proposed that the variation of the chain lengths of the grafted polystyrene chains is actually a primary underlying factor responsible for the influence of these various parameters on the degradation process. The first results of a comparative thermal analysis of some fuel‐cell membranes are also presented, and the promise and shortcomings of this method are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2612–2624, 2004 相似文献
44.
45.
46.
半自由声场环境下的声源重建和声场预测研究对声全息技术走向实际应用具有非常重要的意义.在提出基于分布源边界点法的半自由声场全息重建和预测方法的基础上,对此展开了实验研究.并将重建和预测的结果与常规方法重建和预测的结果进行了比较和讨论,说明了重建预测过程中反射声压的影响和考虑反射声压的必要性,证明了所提出方法在解决半自由声场环境下存在地面反射时的声源重建和声场预测时的有效性和准确性.还提出了采用奇异值截断滤波和Tikhonov正则化方法来削弱测量误差的影响,从而进一步优化了重建结果,提高了全息成像的可信度.
关键词:
声全息
半自由场
边界点
声辐射
反射声 相似文献
47.
Takayuki Abe 《Mathematical Methods in the Applied Sciences》2004,27(9):1007-1048
This paper is concerned with the standard Lp estimate of solutions to the resolvent problem for the Stokes operator on an infinite layer with ‘Neumann–Dirichlet‐type’ boundary condition. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
48.
49.
50.