全文获取类型
收费全文 | 493961篇 |
免费 | 6158篇 |
国内免费 | 1403篇 |
专业分类
化学 | 233294篇 |
晶体学 | 6489篇 |
力学 | 18763篇 |
综合类 | 13篇 |
数学 | 49928篇 |
物理学 | 133143篇 |
无线电 | 59892篇 |
出版年
2021年 | 4109篇 |
2020年 | 4644篇 |
2019年 | 4974篇 |
2018年 | 6394篇 |
2017年 | 6211篇 |
2016年 | 9532篇 |
2015年 | 5876篇 |
2014年 | 9293篇 |
2013年 | 21486篇 |
2012年 | 16447篇 |
2011年 | 20262篇 |
2010年 | 14590篇 |
2009年 | 15178篇 |
2008年 | 19939篇 |
2007年 | 20295篇 |
2006年 | 18986篇 |
2005年 | 17288篇 |
2004年 | 16078篇 |
2003年 | 14379篇 |
2002年 | 14049篇 |
2001年 | 15777篇 |
2000年 | 12391篇 |
1999年 | 10032篇 |
1998年 | 8613篇 |
1997年 | 8280篇 |
1996年 | 7962篇 |
1995年 | 7211篇 |
1994年 | 7100篇 |
1993年 | 6739篇 |
1992年 | 7380篇 |
1991年 | 7476篇 |
1990年 | 7116篇 |
1989年 | 6788篇 |
1988年 | 6615篇 |
1987年 | 6002篇 |
1986年 | 5649篇 |
1985年 | 7189篇 |
1984年 | 7264篇 |
1983年 | 5813篇 |
1982年 | 5809篇 |
1981年 | 5795篇 |
1980年 | 5340篇 |
1979年 | 5659篇 |
1978年 | 5786篇 |
1977年 | 5678篇 |
1976年 | 5568篇 |
1975年 | 5141篇 |
1974年 | 5108篇 |
1973年 | 5116篇 |
1972年 | 3626篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
871.
M. Schmöger E. O. Erdmann und Rindell 《Fresenius' Journal of Analytical Chemistry》1883,22(1):115-117
Ohne Zusammenfassung 相似文献
872.
A numerical analysis of an optical chaotic transmission system, based on the synchronization of two chaotic lasers, in a master-slave closed loop configuration is presented. At the transmitter, the master chaotic wave is superposed on the information message; at the receiver, the message is recovered by subtracting the synchronized slave chaotic wave from the received signal. The performances are analyzed in terms of the Q-factor, considering two different message modulation formats: the nonreturn-to-zero and the Manchester coding. The Manchester coding shows enhanced performances due to the shift of the signal spectrum to higher frequencies. 相似文献
873.
M. I. Makoviychuk 《Russian Microelectronics》2008,37(4):226-237
The solution proposed relates to flicker-noise gas sensors under development, which differ from conventional chemical sensors in offering exceptional selectivity for the analysis of a gaseous environment. The classification and analytical justification are given of low-frequency-noise spectroscopy techniques and measures that are proposed for investigation of disordered semiconductors. The feasibility is shown of patterning processes for flicker-noise gas sensors. Some methods are proposed for these processes and for measurement procedures of gaseous-environment monitoring. 相似文献
874.
V. N. Jmerik A. M. Mizerov T. V. Shubina A. V. Sakharov A. A. Sitnikova P. S. Kop’ev S. V. Ivanov E. V. Lutsenko A. V. Danilchyk N. V. Rzheutskii G. P. Yablonskii 《Semiconductors》2008,42(12):1420-1426
Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells. Structural and optical properties of the Al x Ga1 ? x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm. 相似文献
875.
Ohne Zusammenfassung 相似文献
876.
J. B. Lewis E. L. Baldeschwieler L. D. Tabern E. F. Shelberg D. Hillis S. Cromer I. F. Bingham S. Givaudon M. Aubert M. R. Moutte A. Andant P. Lambert J. Lecomte J. Tausz H. Wolf B. Gordon W. Dachnow I. Perrier M. Lobunetz M. O. Chaikin C. Engler D. Holde 《Analytical and bioanalytical chemistry》1940,119(7-8):307-310
877.
878.
879.
E. L. Kristallovich A. G. Eshimbetov N. D. Chuvylkin L. I. Belen'kii Kh. M. Shakhidoyatov 《Chemistry of Natural Compounds》2003,39(5):495-500
The principal types of electronic transitions in absorption spectra of deoxyvasicinone and its 6-amino- and 6-nitro-derivatives were determined by analyzing the electron-density distributions in excited states calculated using ZINDO/S. 相似文献
880.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献