全文获取类型
收费全文 | 15475篇 |
免费 | 486篇 |
国内免费 | 328篇 |
专业分类
化学 | 9807篇 |
晶体学 | 105篇 |
力学 | 424篇 |
综合类 | 30篇 |
数学 | 2004篇 |
物理学 | 3919篇 |
出版年
2022年 | 170篇 |
2021年 | 193篇 |
2020年 | 190篇 |
2019年 | 187篇 |
2018年 | 179篇 |
2017年 | 145篇 |
2016年 | 359篇 |
2015年 | 314篇 |
2014年 | 394篇 |
2013年 | 812篇 |
2012年 | 679篇 |
2011年 | 789篇 |
2010年 | 558篇 |
2009年 | 533篇 |
2008年 | 714篇 |
2007年 | 754篇 |
2006年 | 619篇 |
2005年 | 628篇 |
2004年 | 644篇 |
2003年 | 621篇 |
2002年 | 645篇 |
2001年 | 453篇 |
2000年 | 407篇 |
1999年 | 316篇 |
1998年 | 240篇 |
1997年 | 212篇 |
1996年 | 235篇 |
1995年 | 245篇 |
1994年 | 236篇 |
1993年 | 185篇 |
1992年 | 178篇 |
1991年 | 179篇 |
1990年 | 199篇 |
1989年 | 159篇 |
1988年 | 144篇 |
1987年 | 137篇 |
1986年 | 126篇 |
1985年 | 217篇 |
1984年 | 235篇 |
1983年 | 166篇 |
1982年 | 185篇 |
1981年 | 149篇 |
1980年 | 157篇 |
1979年 | 149篇 |
1978年 | 122篇 |
1977年 | 166篇 |
1976年 | 149篇 |
1975年 | 121篇 |
1974年 | 113篇 |
1973年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
M. De Falco F. De Giovanni C. Musella R. Schmidt 《Rendiconti del Circolo Matematico di Palermo》2003,52(1):70-76
A subgroupH of a groupG is said to bepermutable ifHX=XH for every subgroupX ofG. In this paper the structure of groups in which every subgroup either is abelian or permutable is investigated.
This work was done while the last author was visiting the University of Napoli Federico II. He thanks the “Dipartimento di
Matematica e Applicazioni” for its financial support. 相似文献
32.
Franca M. Cordero Francesco De Sarlo Alberto Brandi 《Monatshefte für Chemie / Chemical Monthly》2004,40(2):649-669
The review outlines the various different azaheterocycles available from 5-spirocyclopropane isoxazolidines. These compounds can be regarded as versatile direct precursors of tetrahydro-, dihydropyridone and azetidinone derivatives. The current scope and limitations, and the selectivity aspects of the different processes are discussed therein. 相似文献
33.
34.
A. M. Yakunin A. Yu. Silov P. M. Koenraad W. Van Roy J. De Boeck J. H. Wolter 《Superlattices and Microstructures》2003,34(3-6):539
An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn2+3d5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state. 相似文献
35.
The synthesis of several analogues of (±)-semivioxanthin including five thiophene analogues, using directed metalation are reported. The strategy consisted of the synthesis of functionalized naphthalene or benzo[b]thiophene as building blocks followed by annelation of the pyrone. 相似文献
36.
P. Schuurmans J. Wouters P. De Moor N. Severijns W. Vanderpoorten J. Vanhaverbeke L. Vanneste 《Hyperfine Interactions》1992,75(1-4):423-430
Anisotropic α-emission from nuclei in the decay chain from223Ra to207Tl has been observed using low temperature nuclear orientation in combination with high resolution α-detection at 4.2 K. Information
on partial wave amplitudes as well as hyperfine interactions has been extracted. 相似文献
37.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
38.
D. Kast A. Jungclaus K.P. Lieb M. Górska G. de Angelis P.G. Bizzeti A. Dewald C. Fahlander H. Grawe R. Peusquens M. De Poli H. Tiesler 《The European Physical Journal A - Hadrons and Nuclei》1998,3(2):115-128
In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler
shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the
problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model
calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and
still fair agreement for most measured B(M1) and B(E2) values.
Received: 30 June 1998 相似文献
39.
40.
Carlos E. Alciaturi Thais Montero Carlos De La Cruz Marcos E. Escobar 《Analytica chimica acta》1997,340(1-3):233-240
Reduction of the representation of infrared spectra from coal samples by osculating polynomials of degree nine is discussed. The reduced representation contains polynomial coefficients of order zero to four. Mathematical models of the original spectra are obtained by linear combination of the coefficients. These compressed models are statistically correlated to coal properties, namely, volatile matter, fixed carbon, ash content, heating value, hydrogen, carbon, sulphur, nitrogen, and maximum vitrinite reflectance, and the results are compared with those previously obtained from second derivatives of the same spectra. The use of compressed data, while giving slightly better correlations for some of the properties, has the advantage of requiring less computational time. 相似文献