全文获取类型
收费全文 | 511191篇 |
免费 | 3199篇 |
国内免费 | 936篇 |
专业分类
化学 | 240391篇 |
晶体学 | 7295篇 |
力学 | 28416篇 |
综合类 | 9篇 |
数学 | 79277篇 |
物理学 | 159938篇 |
出版年
2020年 | 4531篇 |
2019年 | 5396篇 |
2018年 | 12525篇 |
2017年 | 12919篇 |
2016年 | 12652篇 |
2015年 | 5508篇 |
2014年 | 9200篇 |
2013年 | 18910篇 |
2012年 | 17520篇 |
2011年 | 25114篇 |
2010年 | 17828篇 |
2009年 | 18096篇 |
2008年 | 23373篇 |
2007年 | 25516篇 |
2006年 | 15565篇 |
2005年 | 16861篇 |
2004年 | 14383篇 |
2003年 | 13841篇 |
2002年 | 12870篇 |
2001年 | 12065篇 |
2000年 | 9836篇 |
1999年 | 7175篇 |
1998年 | 6505篇 |
1997年 | 6414篇 |
1996年 | 6068篇 |
1995年 | 5212篇 |
1994年 | 5323篇 |
1993年 | 5312篇 |
1992年 | 5493篇 |
1991年 | 5883篇 |
1990年 | 5755篇 |
1989年 | 5788篇 |
1988年 | 5500篇 |
1987年 | 5517篇 |
1986年 | 5224篇 |
1985年 | 6372篇 |
1984年 | 6739篇 |
1983年 | 5621篇 |
1982年 | 6017篇 |
1981年 | 5602篇 |
1980年 | 5243篇 |
1979年 | 5867篇 |
1978年 | 6122篇 |
1977年 | 6171篇 |
1976年 | 6250篇 |
1975年 | 5861篇 |
1974年 | 5726篇 |
1973年 | 6046篇 |
1972年 | 4655篇 |
1971年 | 4175篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Martin E. Schimpf J. Calvin Giddings 《Journal of Polymer Science.Polymer Physics》1989,27(6):1317-1332
The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent. 相似文献
942.
In recent years there has been tremendous progress in lithium niobate-based photonic switches. The various switch configurations proposed and implemented, and their characteristics, are reviewed. A summary of the device technology is given. Performance analysis based on different architecture and the size of arrays that can be relalized are discussed.Indian Institute of Science, Bangalore, India 相似文献
943.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989. 相似文献
944.
G Padmaja A V Ravi Kumar V Vidyalal P Radhakrishnan V P N Nampoori C P G Vallabhan 《Pramana》1989,32(5):L693-L698
Laser induced plasma emission spectra from highT
c superconducting samples of YBa2Cu3O7 and GdBa2Cu3O7 obtained with 1.06μm radiation from a Q switched Nd:YAG laser beam has been analysed. The results clearly show the presence of diatomic oxides
in addition to ionized species of the constituent metals in the plasma thus produced. 相似文献
945.
946.
M. P. Nosov V. A. Smirnova Yu. F. Zabashta A. Ya. Fridman M. P. Mokhnach 《Mechanics of Composite Materials》1989,25(1):8-12
Conclusion A method was proposed which makes it possible to study the low-frequency internal friction of complex fibers. This method was used to study the internal friction of complex composite fibers based on PCA and PE. We observed a relaxation process which is typical of the composite and is absent in the pure materials.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 11–15, January–February, 1989. 相似文献
947.
P. P. Kirpichok N. B. Voronina A. F. Sitnikov V. Ya. Garmash 《Russian Physics Journal》1989,32(1):26-30
The effect of rare-earth oxides on the properties of anisotropic barium ferrites has been studied by x-ray structural and Mössbauer methods. Additions of SrCO3, as well as SrCO3 and La2O3, SrCO3 and Pr6O11, SrCO3 and Nd2O3, SrCO3 and Sm2O3 in amounts of 7.5 mole % Sr and 10 mole % rare-earth element to grade-A barium powder results in the substitution of barium ions by Sr and rare-earth ions; consequently, the energy of magnetic anisotropy changes and the technically important parameters Br and (BH)max increase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–39, January, 1989. 相似文献
948.
M. Faucher D. Garcia E. Antic-Fidancev M. Lemaitre-Blaise 《Journal of Physics and Chemistry of Solids》1989,50(12)
Some structural and spectroscopic features of rare earth orthoaluminates are examined.The trigonal→ orthorhombic transition is studied in a series of NdxSm1−xAlO3 compounds. The evolution of the crystal structure is followed by X-ray analysis and optical absorption. The free ion and crystal field parameters of Nd3+ (4f3 configuration) are determined in LuAlO3:Nd3+.The anomaly of the calculated splitting of the
levels is slight, but well characterized in NdAlO3. The spin correlated crystal field and orbitally correlated crystal field models are tested as well as an empirical correction which was proposed earlier. 相似文献
949.
The influence of an electrical field on the charge transfer in crystals with orbital degeneration is investigated. An expression is obtained for the current density in crystals with narrow d-conduction bands in transition metal compounds. As the electrical field intensity increases, a current density maximum is observed with a subsequent section of negative differential conductivity. The results of the investigation agree qualitatively with experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 14–18, February, 1989. 相似文献
950.
V. A. Popova I. V. Podgornaya V. G. Lundina L. I. Kurnikova A. I. Tarasov 《Russian Chemical Bulletin》1987,36(11):2361-2364
Conclusions Complex compounds of bisacyl derivatives of diaminodibenzo-18-crown-6 ether are active catalysts of the two stages of the synthesis of poly(ethylene terephthalate).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2544–2547, November. 1987. 相似文献