全文获取类型
收费全文 | 457137篇 |
免费 | 2927篇 |
国内免费 | 882篇 |
专业分类
化学 | 218101篇 |
晶体学 | 7140篇 |
力学 | 24410篇 |
综合类 | 7篇 |
数学 | 61461篇 |
物理学 | 149827篇 |
出版年
2021年 | 4078篇 |
2020年 | 4527篇 |
2019年 | 5374篇 |
2018年 | 7677篇 |
2017年 | 7811篇 |
2016年 | 10253篇 |
2015年 | 5204篇 |
2014年 | 9335篇 |
2013年 | 19210篇 |
2012年 | 15544篇 |
2011年 | 18440篇 |
2010年 | 14324篇 |
2009年 | 14405篇 |
2008年 | 17403篇 |
2007年 | 17398篇 |
2006年 | 15991篇 |
2005年 | 14085篇 |
2004年 | 13416篇 |
2003年 | 12184篇 |
2002年 | 12321篇 |
2001年 | 12813篇 |
2000年 | 10053篇 |
1999年 | 7565篇 |
1998年 | 6717篇 |
1997年 | 6566篇 |
1996年 | 5999篇 |
1995年 | 5495篇 |
1994年 | 5410篇 |
1993年 | 5299篇 |
1992年 | 5658篇 |
1991年 | 6012篇 |
1990年 | 5921篇 |
1989年 | 5708篇 |
1988年 | 5556篇 |
1987年 | 5624篇 |
1986年 | 5187篇 |
1985年 | 6338篇 |
1984年 | 6783篇 |
1983年 | 5692篇 |
1982年 | 6082篇 |
1981年 | 5750篇 |
1980年 | 5408篇 |
1979年 | 5935篇 |
1978年 | 6103篇 |
1977年 | 6195篇 |
1976年 | 6351篇 |
1975年 | 5875篇 |
1974年 | 5716篇 |
1973年 | 6002篇 |
1972年 | 4578篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Stanley D. Rasberry 《Fresenius' Journal of Analytical Chemistry》1993,345(2-4):87-89
Summary Sales and use of analytical instruments have expanded in the United States over the past two years, despite the recessionary nature of the economy. Interest in increasing the quality of analytical measurements seems to be undiminished, if not growing. Trends in several measurement areas, including health, environment, manufacturing, and commerce, are described as they bear on this growth of interest in reliably accurate measurements. The paper also considers trends in the development of reference materials and accreditation of laboratories in the USA. United States of America participation in efforts of the International Organization for Standardization, and a study by the International Bureau of Weights and Measures of how to provide for international traceability for analytical chemical measurements are mentioned. 相似文献
922.
Weak-signal methods are used to study long-term changes in the electrophysical and photoelectric properties of Si-SiO2 systems of n- and p-type semiconductors after the action of a steady magnetic field of 102 Oe. It is found that the field electrode can produce regions characterized by the anomalous recombination, migration, and
transformation of nonequilibrium charge carriers, leading to a quasi-oscillating change in the recombination activity of the
semiconducting system. It is observed that the magnetically induced changes in the system depend on the impurity of composition
of the semiconductor. The results obtained are attributed to the decomposition of the growth structures of complexes and subsequent
clustering of the decomposition products at elastic stress sinks.
Tomsk State Academy of Control Systems and Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.
2, pp. 62–66, February, 1997. 相似文献
923.
Triorganotin(IV) and triorganolead(IV) derivatives of the types Me3Sn(SCZ) and Ph3Pb(SCZ) (where SCZ? is the anion of a semicarbanzone ligand) have been synthesized by substitution reactions of trimethyltin chloride and triphenyl-lead chloride with semicarbazones derived from heterocyclic ketones. The resulting complexes have been characterized by elemental analyses, molecualr weight determinations and conductivity measurements. The mode of bonding has been established on the basis of infrared and 1H, 13C and 119Sn NMR spectroscopic studies. Some respresentative complexes have also been evaluated for their antimicrobial effects on different species of pathogenic fungi and bacteria; the results of these investigations have been reported in the present paper. 相似文献
924.
V. S. Zayachkivs'kii 《Journal of Mathematical Sciences》1993,66(6):2552-2555
We study the variety of divisors of a polynomial operator bundle and the action of the natural symmetry group on it—the group of invertible operators that commute with the linearizer of the bundle. It is established that the orbits can be parametrized by standard Young tableaux whose form and weight depend on the spectral parameters of the bundle and its divisors. We consider the question of existence of factorizations with prescribed spectral characteristics. The correspondence is given in terms of the Littlewood-Richardson combinatorial rule.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 34, 1991, pp. 8–12. 相似文献
925.
926.
927.
G. M. Zharkova S. A. Streltsov V. M. Khachaturyan 《Journal of Structural Chemistry》1993,34(6):934-937
Light transmission of nematic liquid crystals dispersed in a polymeric matrix is investigated. The paper gives a theoretical analysis of light transmission by the liquid crystal-polymer and liquid crystaldye-polymer systems based on determination of the total cross section of extinction. The mathematical model is considered in the anomalous diffraction approximation. The theoretical calculations are in good agreement with experimental data obtained for films based on cyanodiphenyl dispersed into a polyvinyl acetate matrix.Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 118–122, November–December, 1993.Translated by L. Chernomorskaya 相似文献
928.
V. A. Osadchuk 《Journal of Mathematical Sciences》1993,67(2):2912-2916
A method is proposed for determining the technological residual stresses in glass shells of revolution based on the solution of inverse problems of shell theory with proper stresses and the use of experimental data obtained by the photoelastic method.
Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 35, 1992, pp. 100–105. 相似文献
929.
P. A. Bokhan T. Ya. Dubnishcheva D. E. Zakrevskii Yu. V. Nastaushev 《Journal of Russian Laser Research》1995,16(2):164-171
A gas-discharge gold-vapor laser on self-terminating transitions with operating wavelength λ=312.2 nm has been used to develop a highly efficient system for image transfer. An optical scheme and all its parameters have been chosen optimal for image quality. It has been found both theoretically and experimentally that the best results on micron-structure image transfer are obtained with 2–5-times image reduction. Various types of masks have been used. A 1-µm structure has been resolved due to the choice of optimal exposure time of 10 ms under a period of pulse repetition (0.6 – 0.8) ms; in this case, the minimal fringe dimension was ≈2 µm with an image dimension of 2 mm for a laser tube 1.8 cm in diameter. 相似文献
930.
Energy dispersive X-ray fluorescence spectrometry with radionuclide excitation has been applied to determine As, Cu, Fe, Pb, Rb, Sr, Ti, Zn and Zr in inorganic pollutants of gravitation dust sediments. Application of this technique required a complete optimization including sampling and their preparation for analysis and evaluation. This method has been finally used to analyze series of samples of dust sediments. 相似文献