全文获取类型
收费全文 | 179573篇 |
免费 | 873篇 |
国内免费 | 262篇 |
专业分类
化学 | 89654篇 |
晶体学 | 2635篇 |
力学 | 9377篇 |
综合类 | 7篇 |
数学 | 20911篇 |
物理学 | 58124篇 |
出版年
2020年 | 1848篇 |
2019年 | 2288篇 |
2018年 | 3395篇 |
2017年 | 3523篇 |
2016年 | 4157篇 |
2015年 | 1852篇 |
2014年 | 3587篇 |
2013年 | 7047篇 |
2012年 | 5532篇 |
2011年 | 6586篇 |
2010年 | 5510篇 |
2009年 | 5635篇 |
2008年 | 6360篇 |
2007年 | 6323篇 |
2006年 | 5617篇 |
2005年 | 4982篇 |
2004年 | 4821篇 |
2003年 | 4366篇 |
2002年 | 4523篇 |
2001年 | 4999篇 |
2000年 | 3690篇 |
1999年 | 2823篇 |
1998年 | 2603篇 |
1997年 | 2457篇 |
1996年 | 2253篇 |
1995年 | 2049篇 |
1994年 | 2005篇 |
1993年 | 2038篇 |
1992年 | 2073篇 |
1991年 | 2380篇 |
1990年 | 2314篇 |
1989年 | 2384篇 |
1988年 | 2264篇 |
1987年 | 2294篇 |
1986年 | 2125篇 |
1985年 | 2656篇 |
1984年 | 2670篇 |
1983年 | 2316篇 |
1982年 | 2371篇 |
1981年 | 2275篇 |
1980年 | 2076篇 |
1979年 | 2393篇 |
1978年 | 2547篇 |
1977年 | 2639篇 |
1976年 | 2729篇 |
1975年 | 2536篇 |
1974年 | 2467篇 |
1973年 | 2634篇 |
1972年 | 2152篇 |
1971年 | 1973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons
coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a
high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either
absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally
quantized levels can be up to 66%.
Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997) 相似文献
92.
L. K. Aminov I. N. Kurkin D. A. Lukoyanov K. P. Chernov 《Physics of the Solid State》1997,39(8):1184-1186
Results are reported for measurements of the spin-lattice relaxation times of E′1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz
over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of
the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency
dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation
of irradiation centers in crystalline quartz and quartz glass.
Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997) 相似文献
93.
The asymptotics of the necessary sample size is considered in testing close hypotheses when the error probabilities vanish.
Proceedings of the XVII Seminar on Stability Problems for Stochastic Models, Kazan, Russia, 1995, Part III. 相似文献
94.
I. M. Karnaukh A. S. Moskovkin G. V. Ponomarev 《Chemistry of Heterocyclic Compounds》1994,30(1):20-25
The mass spectral behavior of 1, 2-di (mesoetioporphyr inyl-1)- and 1, 2-di (mesooctaethylporphyrlnyl) ethanes and ethylenes, their Cu and Ni complexes, as well as Ni Schiff bases of 1, 2-di (mesooctaethylporphyrinyl)ethane complexes, under ionization by electron impact and bombardment by accelerated atoms, was studied. Peaks of molecular ions, for which the basic decomposition pathways were established on the basis of an analysis of the parent and daughter ions, were observed in the electron impact mass spectra of all these compounds.For Communication 29, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 24–29, January, 1994. 相似文献
95.
S. V. Litvinenko V. I. Savich L. D. Bobrovnik 《Chemistry of Heterocyclic Compounds》1994,30(3):340-344
We have developed a method for synthesis of N-(3-clzloro-2-quinoxalyl)sulfonamides by reaction of 2,3-dichloroquinoxaline with substituted arylsufonamides. Based on the IR spectra, we have established that in the solid state, the synthesized compounds exist in the form of amide tautomers. Alkylation of these compounds leads to N-metliyl-N-(3-chloro-2-quinoxalyl)arylsulfonamides. We demonstrate the possibility of nucleophilic substitution of the halogen upon treatment with O- and N-nucleophiles. The use of bifunctional nucleophiles leads to condensed quinoxalines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 3, pp. 387–392, March, 1994. 相似文献
96.
G. D. Krapivan N. I. Val'ter T. Ya. Kaklyugina V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1994,30(3):289-295
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994. 相似文献
97.
A. Sh. Isamukhamedov N. P. Goncharova A. I. Glushetskova 《Chemistry of Natural Compounds》1994,30(2):170-174
The influence of sunflowerseed and cottonseed oils and also of fractions of normal and oxidized triacylglycerols isolated from them on cytochrome P-450 from rat liver microsomes has been investigated. 相似文献
98.
N. I. Khamidov B. T. Kadyrov N. T. Ul'chenko A. Sh. Isamukhamedov A. I. Glushenkova 《Chemistry of Natural Compounds》1994,30(4):430-433
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed
oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis,
and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate
have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls.
The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations. 相似文献
99.
The qualitative and quantitative compositions of the carbohydrates of the leaf vegetables Lactuca sativa L., Spinacea oleracea L., and Rumex acetosa L. have been studied.M. V. Lomonosov Odessa Technological Institute of the Food Industry. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 349–351, May–June, 1993. 相似文献
100.
V. I. Storozhev 《Journal of Mathematical Sciences》1995,77(6):3514-3518
On the basis of the method of successive approximations in formal series we construct systems of particular solutions of the
equations of planar and flexural harmonic vibrations of thin rectilinear anisotropic plates with a plane of symmetry of elastic
properties parallel to the faces. The solutions constructed are classified as special sk-functions of generalized complex
variables.
Translated fromTeoreticheskaya i Prikladnaya Mekhanika No. 24, 1993, pp. 54–61. 相似文献