全文获取类型
收费全文 | 41246篇 |
免费 | 1453篇 |
国内免费 | 139篇 |
专业分类
化学 | 21733篇 |
晶体学 | 224篇 |
力学 | 1130篇 |
综合类 | 5篇 |
数学 | 7050篇 |
物理学 | 12696篇 |
出版年
2023年 | 266篇 |
2021年 | 357篇 |
2020年 | 535篇 |
2019年 | 440篇 |
2018年 | 569篇 |
2017年 | 549篇 |
2016年 | 1134篇 |
2015年 | 876篇 |
2014年 | 992篇 |
2013年 | 2174篇 |
2012年 | 1871篇 |
2011年 | 2029篇 |
2010年 | 1379篇 |
2009年 | 1163篇 |
2008年 | 1880篇 |
2007年 | 1749篇 |
2006年 | 1673篇 |
2005年 | 1493篇 |
2004年 | 1316篇 |
2003年 | 1055篇 |
2002年 | 950篇 |
2001年 | 879篇 |
2000年 | 721篇 |
1999年 | 513篇 |
1998年 | 443篇 |
1997年 | 441篇 |
1996年 | 539篇 |
1995年 | 488篇 |
1994年 | 512篇 |
1993年 | 516篇 |
1992年 | 572篇 |
1991年 | 385篇 |
1990年 | 399篇 |
1989年 | 368篇 |
1988年 | 338篇 |
1987年 | 360篇 |
1986年 | 322篇 |
1985年 | 521篇 |
1984年 | 496篇 |
1983年 | 419篇 |
1982年 | 436篇 |
1981年 | 438篇 |
1980年 | 430篇 |
1979年 | 415篇 |
1978年 | 404篇 |
1977年 | 403篇 |
1976年 | 368篇 |
1975年 | 366篇 |
1974年 | 353篇 |
1973年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
It is known that every conformai embedding of the disk into the extended complex plane possesses a r2-quasiconformal extension across eachr-level line (the r2-property of a domain). We show here that this is a characteristic property of the disk: any simply connected domain which
is not a disk does not admit ther
2-property.
Supported by the RiP-program of the Volkswagen-Stiftung in the Mathematisches Forschungsinstitut Oberwolfach. 相似文献
105.
106.
V. M. Baev J. Eschner E. Paeth R. Schüler P. E. Toschek 《Applied physics. B, Lasers and optics》1992,55(6):463-477
A multi-mode diode laser with an external cavity is studied experimentally and theoretically for its application to intra-cavity spectroscopy. One facet of a typical Ga0.89Al0.11As laser diode was antireflection-coated by deposition of HfO2 such that 10–3 residual reflectivity was left over. This diode was placed in an external optical cavity. The emission spectrum of this diode laser is highly sensitive to any frequency-dependent loss in the cavity, and the detectivity of such a loss grows with the pump rate. Even close to threshold, the absorption at 780 nm of Rb atoms with a density of 5×1010 cm–3 has been detected. An adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation is developed and applied to the calculations of output spectra. The sensitivity of these spectra to intra-cavity absorption is determined by the overall cavity loss — which is rather high — and the fraction of spontaneous emission in the total emission, in contrast with dye lasers where it is limited by nonlinear mode coupling. Various criteria for the sensitivity are suggested. The smallest detectable absorption with a perfectly antireflection-coated laser is 10–6 cm–1. Improvement of the characteristics of the laser diode would increase the sensitivity. 相似文献
107.
Örn Helgason Haraldur P. Gunnlaugsson Siguröur Steinthorsson Steen Mørup 《Hyperfine Interactions》1992,70(1-4):981-984
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (JS-T) curves with Curie temperatures of about 580°C, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability, of maghemite at temperatures above 350°C, this reversibility is rather surprising. Here we report Mössbauer studies on heated lava samples, showing high content of maghemite. The samples were kept at 600°C in oxidizing, reducing, and inactive atmospheres, respectively, for different lengths of time, and then analyzed with Mössbauer spectroscopy at room temperature. The Mössbauer spectra showed that maghemite is stable in the oxidizing atmosphere for at least several hours. In the inactive atmosphere a considerable amount of maghemite still exists after two hours heating. In the reducing atmosphere maghemite had transformed to magnetite after only 30 minutes. 相似文献
108.
Georg Süss-Fink Ulf Bodensieck Lisa Hoferkamp Gerd Rheinwald Helen Stoeckli-Evans 《Journal of Cluster Science》1992,3(4):469-478
The reaction of trirutheniumdodecacarbonyl with various thioureas was found to give, depending upon the substituents and the reaction conditions, a large variety of tri-, tetra-, penta-, and hexanuclear ruthenium clusters. The ligand systems observed in the products are derived from the thioureas employed; the fragmentation of the thiourea molecules involve N-H, C-S, C-H, and C-N activation processes. 相似文献
109.
Julie Clutterbuck Oliver C. Schnürer Felix Schulze 《Calculus of Variations and Partial Differential Equations》2007,29(3):281-293
We prove stability of rotationally symmetric translating solutions to mean curvature flow. For initial data that converge
spatially at infinity to such a soliton, we obtain convergence for large times to that soliton without imposing any decay
rates.
The authors are members of SFB 647/B3 “Raum – Zeit – Materie: Singularity Structure, Long-time Behaviour and Dynamics of Solutions
of Non-linear Evolution Equations”. 相似文献
110.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献