全文获取类型
收费全文 | 77638篇 |
免费 | 560篇 |
国内免费 | 112篇 |
专业分类
化学 | 41208篇 |
晶体学 | 1260篇 |
力学 | 3277篇 |
综合类 | 1篇 |
数学 | 7830篇 |
物理学 | 24734篇 |
出版年
2022年 | 571篇 |
2021年 | 869篇 |
2020年 | 965篇 |
2019年 | 1103篇 |
2018年 | 1596篇 |
2017年 | 1687篇 |
2016年 | 2151篇 |
2015年 | 1025篇 |
2014年 | 1719篇 |
2013年 | 3270篇 |
2012年 | 2898篇 |
2011年 | 3279篇 |
2010年 | 2637篇 |
2009年 | 2634篇 |
2008年 | 2999篇 |
2007年 | 2872篇 |
2006年 | 2767篇 |
2005年 | 2435篇 |
2004年 | 2238篇 |
2003年 | 2073篇 |
2002年 | 2133篇 |
2001年 | 2233篇 |
2000年 | 1625篇 |
1999年 | 1252篇 |
1998年 | 1125篇 |
1997年 | 1037篇 |
1996年 | 893篇 |
1995年 | 831篇 |
1994年 | 817篇 |
1993年 | 814篇 |
1992年 | 875篇 |
1991年 | 934篇 |
1990年 | 879篇 |
1989年 | 905篇 |
1988年 | 817篇 |
1987年 | 767篇 |
1986年 | 739篇 |
1985年 | 865篇 |
1984年 | 961篇 |
1983年 | 818篇 |
1982年 | 834篇 |
1981年 | 747篇 |
1980年 | 704篇 |
1979年 | 768篇 |
1978年 | 894篇 |
1977年 | 914篇 |
1976年 | 808篇 |
1975年 | 776篇 |
1974年 | 793篇 |
1973年 | 762篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
261.
262.
R. Martínez-Snchez J. A. Matutes-Aquino O. Ayala-Valenzuela S. D. De la Torre 《Physica B: Condensed Matter》2002,320(1-4):285-287
An amorphous phase containing traces of non-transformed Co and Ti powders was obtained by mechanical alloying nominal compositions of Co67Ti33 and Co50Ti50 in a high-energy ball-mill. These alloys were prepared from elemental powders of Co and Ti. The heat treatment of Co67Ti33 at 573, 873 and 1173 K crystallized nanoparticles of Co2Ti and Co3Ti compounds, while the same treatments conducted on Co50Ti50 resulted in the formation of Co2Ti and CoTi nanoparticles. The saturation magnetizations reached a maximum value in the amorphous state and they decreased when the temperatures of the heat treatment rose. Demagnetizing interparticle interaction effects were estimated through hysteresis loops and initial magnetization curves using the Fourier technique. 相似文献
263.
T.M. Mishonov N. Chéenne D. Robbes J.O. Indekeu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):291-296
The generation of harmonics of the voltage response is considered when an AC current is applied through a superconducting
film above Tc. It is shown that almost at all temperatures the mechanism of the temperature oscillations created by the AC current and
the temperature dependence of the resistance dominates over the isothermal nonlinear electric conductivity. Only in a narrow
critical region close to Tc the latter is essential for the generation of the harmonics. A detailed investigation of harmonics generation provides an
accurate method for measuring the thermal boundary conductance between the film and the insulating substrate. The critical
behaviour of the third harmonic will give a new method for the determination of the lifetime of metastable Cooper pairs above
Tc. The comparison of the calculated fifth harmonics of the voltage with the experiment is proposed as an important test for
the applicability of the employed theoretical models.
Received 8 September 2001 相似文献
264.
Atomic-force microscopy was used to study the surface topography of SiGe structures grown by epitaxial deposition of Ge on profiled Si(111) substrates under electromigration conditions. Systems of highly ordered germanium nanosized islands with dimensions of 10–20 nm and a density of 6×1010 cm?2 were obtained. It is shown that the geometrical parameters of self-organizing nanoislands can be controlled by a proper choice of the growth and postgrowth annealing conditions for these structures. 相似文献
265.
It was found that a beta-fructofuranosidase produced by Microbacterium sp. H-1 has potent trans-beta-fructofuranosylation activity from sucrose (donor). By means of this enzyme system, rebaudioside A (RA), the second major sweet steviol glycoside of the leaves of Stevia rebaudiana, was subjected to transfructosylation, affording a mono-beta-fructofuranosylated product (RA-F) in a high yield. The structure of RA-F was elucidated as beta-D-fructofuranosyl-(2----6)-beta-D-glucopyranosyl ester of steviol-13-O-[beta-D-glucopyranosyl-(1----2)]- [beta-D-glucopyranosyl-(1----3)]-beta-D-glucopyranoside. Some improvement in the quality of sweetness was observed for RA-F. 相似文献
266.
Daniel FRANCO Gennaro INFANTE Donal O'REGAN 《数学学报(英文版)》2006,22(6):1745-1750
We establish new criteria for the existence of either positive or nonzero solutions of the Urysohn integral equation. We also discuss the existence of an interval of positive eigenvalues and sufficient conditions for the existence of at least a positive eigenvalue with a nonzero or positive eigenfunction for the Urysohn integral operator. Among others, we employ techniques based on fixed point index theory for compact maps, which are new for this type of equation. 相似文献
267.
M. G. Voronkov E. A. Grebneva O. M. Trofimova A. I. Albanov N. F. Chernov N. N. Chipanina 《Russian Journal of General Chemistry》2006,76(12):1851-1853
Reaction of tetrafluorosilane with tris(2-hydroxyethyl)-and tris(2-trimethylsiloxyethyl)amine results in formation of 1-fluorosilatrane and fluorosilatrane in 75 and 53% yield, respectively. Reaction of tetrafluorosilane with bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative leads to the hitherto unknown 1,1-difluoroquasisilatranes (N → Si) F2Si(OCH2CH2)2NR (R = H, Me) containing donor-acceptor bond N → Si and pentacoordinate silicon atom. The structure of the synthesized compounds was proved by 1H, 13C, 15N, 19F, 29Si NMR and IR spectroscopy. 相似文献
268.
S. V. Ivanov V. V. Trachevskii O. S. Titova L. A. Zozulya 《Russian Journal of Applied Chemistry》2006,79(10):1712-1714
Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations. 相似文献
269.
270.
V. A. Zayats A. N. Nikolaevskii T. A. Filippenko O. P. Kniga G. A. Tikhonova 《Russian Journal of Applied Chemistry》2006,79(10):1651-1654
Specific features of the initiated oxidation of polyethylene and its low-molecular-weight analogue tridecane, associated with the occurrence of the process in the short-chain mode, were studied. 相似文献