全文获取类型
收费全文 | 5389篇 |
免费 | 173篇 |
国内免费 | 156篇 |
专业分类
化学 | 655篇 |
晶体学 | 83篇 |
力学 | 52篇 |
综合类 | 21篇 |
数学 | 3332篇 |
物理学 | 1035篇 |
无线电 | 540篇 |
出版年
2023年 | 19篇 |
2022年 | 47篇 |
2021年 | 88篇 |
2020年 | 52篇 |
2019年 | 126篇 |
2018年 | 100篇 |
2017年 | 89篇 |
2016年 | 57篇 |
2015年 | 71篇 |
2014年 | 151篇 |
2013年 | 246篇 |
2012年 | 210篇 |
2011年 | 293篇 |
2010年 | 255篇 |
2009年 | 355篇 |
2008年 | 375篇 |
2007年 | 379篇 |
2006年 | 378篇 |
2005年 | 305篇 |
2004年 | 238篇 |
2003年 | 184篇 |
2002年 | 198篇 |
2001年 | 179篇 |
2000年 | 151篇 |
1999年 | 157篇 |
1998年 | 109篇 |
1997年 | 103篇 |
1996年 | 113篇 |
1995年 | 71篇 |
1994年 | 82篇 |
1993年 | 57篇 |
1992年 | 50篇 |
1991年 | 43篇 |
1990年 | 22篇 |
1989年 | 43篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 38篇 |
1984年 | 25篇 |
1983年 | 28篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有5718条查询结果,搜索用时 15 毫秒
1.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
2.
A Volterra type integral equation in a Hilbert space with an additional linear operator L and a spectral parameter depending
on time is considered. If the parameter does not belong to the spectrum of L unconditional solvability of the considered problem
is proved. In the case where the initial value of the parameter coincides with some isolated point of the spectrum of the
operator L sufficient conditions for solvability are established. The obtained results are applied to the partial integral
equations associated with a contact problem of the theory of elasticity. 相似文献
3.
M.F. Al-Kuhaili 《Journal of luminescence》2006,117(2):209-216
Thin films of sodium salicylate were deposited by spin coating from a solution prepared by dissolving sodium salicylate in methanol. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, UV-visible spectroscopy and spectrofluorometry. The films were crystalline with a strong blue fluorescence peak at an emission wavelength of 419.3 nm. The influence of solution concentration, spin speed and annealing temperature on the fluorescence intensity was studied. Optimum results were obtained with a solution whose concentration was 2.5 M. It was found that lower spin speed resulted in higher fluorescence intensity. Moreover, the fluorescence intensity decreased as the annealing temperature was increased. The durability of the films over a period of 30 days was also investigated, and films annealed at higher temperatures were found to be less degraded with time. 相似文献
4.
LB11820M是日本SANYO(三洋)公司开发的三相直流无刷电机驱动芯片。它具备开环三相电机控制所需的全部有效功能,并且具有比较完善的保护电路。文中介绍了LB11820M的特点、功能和工作原理,给出了其典型应用电路。 相似文献
5.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
6.
Dedushenko S. K. Makhina I. B. Mar'in A. A. Mukhanov V. A. Perfiliev Yu. D. 《Hyperfine Interactions》2004,158(1-4):417-421
A colourless quartz crystal doped with 57Fe3+ was obtained by hydrothermal synthesis in an NH4F solution. The crystal was transformed into violet amethyst by gamma-irradiation. The change in colour was accompanied by changes in the Mössbauer spectrum that can be interpreted as the conversion of trivalent iron into the tetravalent state: Fe3+→Fe4+.
相似文献7.
8.
Walter Benz 《Monatshefte für Mathematik》2004,141(1):1-10
The lines of euclidean and hyperbolic geometries are characterized as metric lines in the sense of Blumenthal–Menger, and the lines of spherical and elliptic geometry as periodic ones. In euclidean geometries there do not exist periodic lines. 相似文献
9.
10.
A Pair of Dimeric Stilbene Epimers from Gnetum Montanum 总被引:1,自引:0,他引:1
GnetummontanumofgnetaceaisdistributedinsouthernChina.AsaChinesefOlkmedicine,itslianasareusedtotreatbronchitisandarthritis'.Previousinvestigationofthisspeciesledtotheisolationofsomealkaloidsanddibenzyletherde,i.ati.es2.lnourstudies,tenknowncomponentsincludingresveratrol,isohapontigenin,daucosterol,6-sitosterol,stearicacid,gnetifolinE,gnetol,isorhapontigenin-3-O-6-glucopyra(-)E-viniferinandgnetifolinCwereisolatedfromthesameresource.Atthesametime,apairoftraceepimerswereobtained.Thisisthefirste… 相似文献