全文获取类型
收费全文 | 7121篇 |
免费 | 1576篇 |
国内免费 | 600篇 |
专业分类
化学 | 1560篇 |
晶体学 | 104篇 |
力学 | 1572篇 |
综合类 | 64篇 |
数学 | 297篇 |
物理学 | 5700篇 |
出版年
2024年 | 23篇 |
2023年 | 65篇 |
2022年 | 170篇 |
2021年 | 206篇 |
2020年 | 183篇 |
2019年 | 154篇 |
2018年 | 180篇 |
2017年 | 218篇 |
2016年 | 286篇 |
2015年 | 219篇 |
2014年 | 343篇 |
2013年 | 904篇 |
2012年 | 368篇 |
2011年 | 489篇 |
2010年 | 398篇 |
2009年 | 464篇 |
2008年 | 474篇 |
2007年 | 472篇 |
2006年 | 447篇 |
2005年 | 427篇 |
2004年 | 344篇 |
2003年 | 295篇 |
2002年 | 305篇 |
2001年 | 228篇 |
2000年 | 223篇 |
1999年 | 195篇 |
1998年 | 213篇 |
1997年 | 148篇 |
1996年 | 122篇 |
1995年 | 109篇 |
1994年 | 102篇 |
1993年 | 108篇 |
1992年 | 85篇 |
1991年 | 66篇 |
1990年 | 51篇 |
1989年 | 42篇 |
1988年 | 30篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 19篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1971年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有9297条查询结果,搜索用时 15 毫秒
1.
用波导产生倍频波时,如果倍频波进入辐射模区,仍然有相匹配问题。契伦可夫辐射式倍频不是自动地实现相匹配的。相匹配要求导波基波模式场,倍频传输场(自由波),倍频触发场,以及经多次反射透射后的辐射场的迭加形成的总辐射场处于同步的相匹配状态。根据这个相匹配的分析,提出波导契伦可夫相匹配的特有的方法,那就是对波导的模色散进行设计,并指出非对称波导的特有优点,是改变一个边界上的反射相变,即选择不同色散的线性材料作包层,由此可得到相匹配的高效契伦可夫倍频辐射。 相似文献
2.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
3.
4.
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
5.
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
6.
7.
8.
Houman Borouchaki Abdelhakim Cherouat Patrick Laug Khemais Saanouni 《Comptes Rendus Mecanique》2002,330(10):709-716
The analysis of mechanical structures using the Finite Element Method in the framework of large elastoplastic strain, needs frequent remeshing of the deformed domain during computation. Indeed, the remeshing is due to the large geometrical distortion of finite elements and the adaptation to the physical behavior of the solution. This paper gives the necessary steps to remesh a mechanical structure during large elastoplastic deformations with damage. An important part of this process is constituted by geometrical and physical error estimates. The proposed method is integrated in a computational environment using the ABAQUS/Explicit solver and the BL2D-V2 adaptive mesher. To cite this article: H. Borouchaki et al., C. R. Mecanique 330 (2002) 709–716. 相似文献
9.
H.-J. Sue E. I. Garcia-Meitin N. A. Orchard 《Journal of Polymer Science.Polymer Physics》1993,31(5):595-608
The fracture behavior of a core-shell rubber (CSR) modified epoxy is investigated using both fracture mechanics and microscopy tools. The CSR-modified epoxy is found to be toughened via numerous line-array cavitations of the CSR particles, followed by plastic flow of the epoxy matrix. The toughening effect via the above craze-like damage process is found to be as effective as that of the well-known widespread rubber cavitation/matrix shear yielding mechanisms. The conditions for triggering the craze-like damage appear to be both stress state and rubber concentration dependent. The type of rubber tougheners utilized also plays a critical role in triggering this rather unusual craze-like damage in epoxy systems. © 1993 John Wiley & Sons, Inc. 相似文献
10.
I.IntroductionWhenastructurcvibratcs,itsvibratingsurfacewillmakesurroundingmediummovetogethcrwithit.Ifthernotionissofastthatthcmediumroundthestructureproduccaloca1contractionandcxpansionandthcypropagatefaraway,thesoundradiationisformed.Itispossiblctodcscribeanalytica11ytheradiationfic1dofsimplyandregularlyshapcdsourcessuchaspointsoundsourccs,spherica1soundsourccsandinflnite1engthllnearsoundsourccs,butitisa1mostimpossib1ctosolvetheradiationfiledbyanyanalyt-ica1methodforsourcesofvcrycomplicateds… 相似文献