全文获取类型
收费全文 | 179219篇 |
免费 | 1813篇 |
国内免费 | 476篇 |
专业分类
化学 | 83995篇 |
晶体学 | 2444篇 |
力学 | 6123篇 |
综合类 | 4篇 |
数学 | 13805篇 |
物理学 | 47496篇 |
无线电 | 27641篇 |
出版年
2021年 | 1213篇 |
2020年 | 1372篇 |
2019年 | 1451篇 |
2018年 | 1834篇 |
2017年 | 1850篇 |
2016年 | 2844篇 |
2015年 | 1732篇 |
2014年 | 2661篇 |
2013年 | 6655篇 |
2012年 | 5332篇 |
2011年 | 6554篇 |
2010年 | 4710篇 |
2009年 | 5081篇 |
2008年 | 6889篇 |
2007年 | 6963篇 |
2006年 | 6786篇 |
2005年 | 6430篇 |
2004年 | 5905篇 |
2003年 | 5432篇 |
2002年 | 5303篇 |
2001年 | 6752篇 |
2000年 | 5215篇 |
1999年 | 4127篇 |
1998年 | 3112篇 |
1997年 | 3122篇 |
1996年 | 3042篇 |
1995年 | 2878篇 |
1994年 | 2879篇 |
1993年 | 2677篇 |
1992年 | 3232篇 |
1991年 | 3262篇 |
1990年 | 3003篇 |
1989年 | 2915篇 |
1988年 | 2764篇 |
1987年 | 2457篇 |
1986年 | 2250篇 |
1985年 | 2791篇 |
1984年 | 2764篇 |
1983年 | 2216篇 |
1982年 | 2201篇 |
1981年 | 2021篇 |
1980年 | 2003篇 |
1979年 | 2253篇 |
1978年 | 2318篇 |
1977年 | 2239篇 |
1976年 | 2163篇 |
1975年 | 2011篇 |
1974年 | 2004篇 |
1973年 | 2035篇 |
1972年 | 1351篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Tajiri A. Minakuchi K. Komeda K. Bessho Y. Inoue Y. Yodoshi K. Yamaguchi T. 《Electronics letters》1993,29(4):369-370
A highly reliable 200 mW AlGaAs laser diode with a fundamental transverse mode has been developed, by optimising its structure with a 0.8 mu m thick p-cladding layer, a 1200 mu m long cavity length, and a front facet coating with a low reflectivity of 2%. The maximum output power was 500 mW, and stable fundamental transverse mode operation was obtained up to 350 mW. Stable operation under 200 mW and 50 degrees C was confirmed for more than 1200 h. Optical feedback noise was below 3*10/sup -14/ Hz/sup -1/.<> 相似文献
92.
T. A. Beu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):263-266
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented. 相似文献
93.
94.
Partially supported by NSF Grants. 相似文献
95.
96.
A narrow linewidth has been obtained in a new 1.5 ?m distributed feedback laser integrated monolithically with a tunable external cavity. The linewidth of 18 MHz has been achieved by tuning the current in the external cavity, and the FM response was flat from 100 kHz to 500 MHz. 相似文献
97.
A novel typed of hybrid-mode feed horn is presented. It comprises a hollow conical dielectric waveguide whose outer surface is metallized, and whose inner surface is coated with circumferentially oriented conducting strips. It may be designed to have mimimal cross polarization at two arbitrarily separated frequencies, as for a dual depth corrugated horn. Compared to the corrugated horn, it has the potential of lower weight and lower price. Small horns will have some cross polarization due to undesired radiation from the fields transmitted within the dielectric. 相似文献
98.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
99.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this
addendum is to present a correct argument for it. 相似文献
100.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献