全文获取类型
收费全文 | 41442篇 |
免费 | 6075篇 |
国内免费 | 4573篇 |
专业分类
化学 | 29472篇 |
晶体学 | 472篇 |
力学 | 2279篇 |
综合类 | 346篇 |
数学 | 5081篇 |
物理学 | 14440篇 |
出版年
2024年 | 120篇 |
2023年 | 701篇 |
2022年 | 1218篇 |
2021年 | 1302篇 |
2020年 | 1380篇 |
2019年 | 1414篇 |
2018年 | 1209篇 |
2017年 | 1174篇 |
2016年 | 1763篇 |
2015年 | 1773篇 |
2014年 | 2068篇 |
2013年 | 2835篇 |
2012年 | 3347篇 |
2011年 | 3664篇 |
2010年 | 2512篇 |
2009年 | 2543篇 |
2008年 | 2734篇 |
2007年 | 2468篇 |
2006年 | 2210篇 |
2005年 | 1944篇 |
2004年 | 1572篇 |
2003年 | 1322篇 |
2002年 | 1329篇 |
2001年 | 1117篇 |
2000年 | 923篇 |
1999年 | 845篇 |
1998年 | 764篇 |
1997年 | 653篇 |
1996年 | 636篇 |
1995年 | 584篇 |
1994年 | 559篇 |
1993年 | 478篇 |
1992年 | 428篇 |
1991年 | 376篇 |
1990年 | 326篇 |
1989年 | 257篇 |
1988年 | 212篇 |
1987年 | 166篇 |
1986年 | 175篇 |
1985年 | 177篇 |
1984年 | 120篇 |
1983年 | 86篇 |
1982年 | 84篇 |
1981年 | 59篇 |
1980年 | 61篇 |
1979年 | 60篇 |
1978年 | 44篇 |
1976年 | 38篇 |
1974年 | 42篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)
Zhou Dongmei Zheng Yongnan Du Enpeng Xu Yongjun Zhu Jiazheng Yuan Daqing Wang Zhiqiang Luo Hailong Zuo Yi Ma Ruigang Duan Xiao M. Mihara M. Fukuda K. Matsuta T. Minamisono Zhu Shengyun 《中国科学G辑(英文版)》2004,47(5):531-539
The spin polarized β-emitting nuclei12B (I
π=1+,T
1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment
of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift. 相似文献
72.
Wenbing Hu Alexander Buzin Jar‐Shyong Lin Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》2003,41(4):403-417
The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003 相似文献
73.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
74.
A detailed study of the generalized M2 factor of hard-edged diffracted beams based on the truncated second-order moments method, asymptotic analysis and self-convergent beam width approach is performed. The dependence of the generalized M2 factor on the parameters characterizing the spatial profile, and beam truncation, etc. is analyzed. 相似文献
75.
76.
用迈克耳逊干涉仪测量气体折射率的误差的研究 总被引:1,自引:0,他引:1
研究在用迈克尔逊干涉仪测量气体折射率时存在的系统和方法误差,提出了误差修正方法。 相似文献
77.
Jin Cheng Ching-Lung Lin Gen Nakamura 《Proceedings of the American Mathematical Society》2005,133(8):2359-2367
In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.
78.
Ming-Chieh Lin Der-San Chuu 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):421-428
A simple time-dependent model is presented to investigate lifetimes of the quasibound states in coupled quantum wells (CQWs). The transfer matrix approach is employed to discretize the conduction-band profile of the heterostructure and form a dispersion equation whose zeros correspond to the complex eigenenergies. Both the bound and quasibound states are extracted numerically in the complex plane by Newton's method. The lower and higher well subbands are found to have negative and positive energy shift, respectively, as following the no level crossing theorem. Besides, the decay rate of the quasibound state is approximately proportional to the absolute energy shift. The quasibound states, which have larger energy shift, have shorter lifetime and decay more quickly. Furthermore, the differences in lifetime between the quasibound states in CQWs can be easily realized as all the wave functions are specially adjusted to form the relative probability density distributions. 相似文献
79.
关于高阶中立型偏微分方程系统解的振动性 总被引:16,自引:0,他引:16
近年来,由于偏泛函微分方程(组)理论在人口动力学,生物遗传工程和化学反应过程等领域中有广泛的应用,因而很多学者在偏泛函微分方程(组)解的振动性理论的研究方面做了大量工作,取得了许多成果.本文将研究一类较广泛的高阶中立型偏微分方程组 相似文献
80.
林诒勋 《高校应用数学学报(英文版)》2003,18(3):361-369
§ 1 IntroductionThe cutwidth problem for graphs,as well as a class of optimal labeling and embed-ding problems,have significant applications in VLSI designs,network communicationsand other areas (see [2 ] ) .We shall follow the graph-theoretic terminology and notation of [1 ] .Let G=(V,E)be a simple graph with vertex set V,| V| =n,and edge set E.A labeling of G is a bijec-tion f:V→ { 1 ,2 ,...,n} ,which can by regarded as an embedding of G into a path Pn.Fora given labeling f of G,th… 相似文献