全文获取类型
收费全文 | 247541篇 |
免费 | 3340篇 |
国内免费 | 1550篇 |
专业分类
化学 | 140505篇 |
晶体学 | 3340篇 |
力学 | 9521篇 |
综合类 | 62篇 |
数学 | 29673篇 |
物理学 | 69330篇 |
出版年
2020年 | 2070篇 |
2019年 | 2193篇 |
2018年 | 2751篇 |
2017年 | 2814篇 |
2016年 | 4219篇 |
2015年 | 3000篇 |
2014年 | 4141篇 |
2013年 | 10227篇 |
2012年 | 8994篇 |
2011年 | 10973篇 |
2010年 | 7529篇 |
2009年 | 7223篇 |
2008年 | 10127篇 |
2007年 | 10230篇 |
2006年 | 9796篇 |
2005年 | 8977篇 |
2004年 | 8081篇 |
2003年 | 7055篇 |
2002年 | 6945篇 |
2001年 | 7132篇 |
2000年 | 5457篇 |
1999年 | 4047篇 |
1998年 | 3402篇 |
1997年 | 3421篇 |
1996年 | 3380篇 |
1995年 | 2958篇 |
1994年 | 3088篇 |
1993年 | 2915篇 |
1992年 | 3136篇 |
1991年 | 3194篇 |
1990年 | 2971篇 |
1989年 | 2893篇 |
1988年 | 2803篇 |
1987年 | 2710篇 |
1986年 | 2761篇 |
1985年 | 3650篇 |
1984年 | 3719篇 |
1983年 | 3113篇 |
1982年 | 3380篇 |
1981年 | 3111篇 |
1980年 | 2930篇 |
1979年 | 3051篇 |
1978年 | 3286篇 |
1977年 | 3306篇 |
1976年 | 3279篇 |
1975年 | 2974篇 |
1974年 | 3092篇 |
1973年 | 3118篇 |
1972年 | 2425篇 |
1971年 | 1937篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
T. Geppert S.L. Schweizer U. Gösele R.B. Wehrspohn 《Applied Physics A: Materials Science & Processing》2006,84(3):237-242
We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. It also enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics. The limits of this new process are simulated using electrostatic models and are verified experimentally. PACS 82.45.Yz; 81.16.-c 相似文献
982.
Conclusion The reaction of 1-arylsulfamido-2-chloroethanes with diethylamine and aniline gives 1-arylsulfamido-2-aminoethanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 943–946, April, 1987. 相似文献
983.
It is demonstrated that the diffraction of a plane light wave by an acoustic wave of fundamental frequency in the Raman-Nath
mode with admixture of the second acoustic harmonic may be accompanied by a considerable change in the higher diffraction
orders with numbers ±2, ±3, etc. Conditions for the selective suppression of the orders are obtained in the weak and strong
interaction modes. Results of a numerical simulation are presented. 相似文献
984.
L. N. Luk’yanova V. A. Kutasov V. V. Popov P. P. Konstantinov 《Physics of the Solid State》2006,48(4):647-653
The galvanomagnetic and thermoelectric properties of n-Bi2-x SbxTe3-y-z SeySz multicomponent solid solutions with atomic substitutions (Sb → Bi; Se, S → Te) are studied. The principal components of the effective mass tensor (m 1, m 2, m 3) for the isotropic mechanism of charge carrier scattering are determined within a many-valley model of the energy spectrum for compositions 0.08 ≤ x ≤ 0.4 and 0.06 ≤ y = z ≤ 0.15. The effect of a variation in the parameters of the constant-energy surface on the thermoelectric efficiency is analyzed for different compositions and carrier concentrations in solid solutions. 相似文献
985.
J. Balogh D. Kaptás L. F. Kiss T. Kemény L. Bujdosó I. Vincze 《Hyperfine Interactions》2006,169(1-3):1343-1347
Magnetic multilayers of 57Fe with nominal thickness, T
nom, between 0.4 and 1.0 nm separated by 3.0 nm Al spacer layers were prepared by alternate deposition of the constituents in
high vacuum. The samples were investigated at 4.2 K in external magnetic field. A fraction of Fe atoms corresponding to about
0.3 nm equivalent Fe-thickness was found to mix into the Al spacer. The extremely strong magnetic anisotropy observed for
T
nom < 0.8 nm is attributed to Fe layers of approximately two atomic planes thick. The anisotropy decreases considerably after
the building up of the third Fe atomic layer starts at T
nom = 0.8 nm, but full saturation was not achieved even for T
nom = 1 nm and 3 T magnetic field applied perpendicularly to the sample plane. 相似文献
986.
The first twelve members of three new mesogenic homologous series have been characterized, each of which are composed of molecules possessing lateral alkyl chains. The n-alkyl 2,5-bis-(4-n-hexyloxy-benzoyloxy)-benzoates are purely nematic whereas both nematic and smectic behaviour is observed for the 4-cyano-4'-biphenylyl 3'-n-alkyloxybenzoates and the 4-cyano-4'-biphenylyl 3',4'-n-alkyloxybenzoates. The transitional properties of these series are similar to those of the analogous conventional mesogens and hence, can be rationalized without making any special assumptions concerning the conformational distribution of the lateral alkyl chain. 相似文献
987.
H. A. Levine R. Quintanilla L. E. Payne 《Mathematical Methods in the Applied Sciences》1989,11(1):71-77
We consider a three-dimensional hyperelastic cylinder in Ω = D × [0, ∞]. We study the asymptotic behaviour of the deformations of the cross-sections in an equilibrium state. In this case we show that the solutions either have exponential decay or exponential growth. We give some initial conditions such that the latter case occurs. 相似文献
988.
Beat Jaggi Peter Mani-Levitska Bernd Sturmfels Neil White 《Discrete and Computational Geometry》1989,4(1):97-100
We give an easy general construction for uniform oriented matroids with disconnected realization space. This disproves the longstanding isotopy conjecture for simple line arrangements or order types in the plane.The research of Bernd Sturmfels and Neil White was supported in part by the Institute for Mathematics and Its Applications with funds provided by the National Science Foundation. 相似文献
989.
The measurement of the inertial mass of the antiproton and proposed antihydrogen formation experiments require antiprotons
stored in ion traps, cooled to very low (4K) temperatures. Techniques to cool the trapped antiprotons from energies around
1 keV are discussed. Coupling to an external circuit produces cooling times of order 103 s, which may be reduced somewhat with negative feedback. Adiabatic reduction of the trapping potential produces significant
cooling when the particle energies are substantially less than the well depth. Most promising is cooling via energy-transferring
collisions to a cooled cloud of electrons simultaneously trapped with the antiprotons. Electron cooling times are of order
1 s, and strongly depend on electron number and density. 相似文献
990.
F. F. Dedus L. I. Kulikova S. A. Makhortykh N. N. Nazipova A. N. Pankratov R. K. Tetuev 《Moscow University Computational Mathematics and Cybernetics》2007,31(2):49-53
The analysis problem for genetic sequences is formulated from the viewpoint of modern mathematical and information approaches. Statistical, correlative, entropic, and spectral approaches are considered. A brief introduction into the background of the problem is given. Genesis of a new interdisciplinary subject area, bioinformatics, a science considering application of computer methods in biological studies, is analyzed. New approaches to studying macromolecular systems on the basis of combined spectral-analytic technologies are proposed. Estimates of the algorithmic complexity of implementation of the proposed approaches are presented. 相似文献