全文获取类型
收费全文 | 27275篇 |
免费 | 769篇 |
国内免费 | 373篇 |
专业分类
化学 | 17166篇 |
晶体学 | 217篇 |
力学 | 798篇 |
综合类 | 30篇 |
数学 | 3736篇 |
物理学 | 6470篇 |
出版年
2022年 | 208篇 |
2021年 | 337篇 |
2020年 | 362篇 |
2019年 | 363篇 |
2018年 | 329篇 |
2017年 | 289篇 |
2016年 | 599篇 |
2015年 | 523篇 |
2014年 | 611篇 |
2013年 | 1465篇 |
2012年 | 1222篇 |
2011年 | 1447篇 |
2010年 | 933篇 |
2009年 | 852篇 |
2008年 | 1274篇 |
2007年 | 1292篇 |
2006年 | 1159篇 |
2005年 | 1105篇 |
2004年 | 1103篇 |
2003年 | 994篇 |
2002年 | 1021篇 |
2001年 | 628篇 |
2000年 | 593篇 |
1999年 | 462篇 |
1998年 | 376篇 |
1997年 | 373篇 |
1996年 | 408篇 |
1995年 | 360篇 |
1994年 | 380篇 |
1993年 | 354篇 |
1992年 | 332篇 |
1991年 | 332篇 |
1990年 | 308篇 |
1989年 | 279篇 |
1988年 | 273篇 |
1987年 | 302篇 |
1986年 | 276篇 |
1985年 | 412篇 |
1984年 | 418篇 |
1983年 | 295篇 |
1982年 | 351篇 |
1981年 | 322篇 |
1980年 | 321篇 |
1979年 | 298篇 |
1978年 | 271篇 |
1977年 | 313篇 |
1976年 | 274篇 |
1975年 | 267篇 |
1974年 | 226篇 |
1973年 | 234篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
82.
In this paper, we examine a variant of the uncapacitated lot-sizing model of Wagner–Whitin that includes fixed charges on the stocks. Such a model is natural in a production environment where stocking is a complex operation, and appears as a subproblem in more general network design problems.
Linear-programming formulations, a dynamic program, the convex hull of integer solutions and a separation algorithm are presented. All these turn out to be very natural extensions of the corresponding results of Barany et al. (Math. Programming Stud. 22 (1984) 32) for the uncapacitated lot-sizing problem. The convex hull proof is based on showing that an extended facility location formulation is tight and by projecting it onto the original space of variables. 相似文献
83.
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
84.
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
85.
Margherita De RosaMaria Rosaria Acocella Rosaria VillanoAnnunziata Soriente Arrigo Scettri 《Tetrahedron letters》2003,44(32):6087-6090
Initial concentration of enantioenriched or enantiopure catalysts proved to be an important factor for the achievement of a more pronounced amplification of ee's in the Ti(IV)/BINOL-catalyzed aldol reaction of an O-silyldienolate. 相似文献
86.
87.
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
88.
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
89.
90.
Deák L. Bottyán L. Major M. Nagy D. L. Spiering H. Szilágyi E. Tanczikó F. 《Hyperfine Interactions》2002,144(1-4):45-52
Hyperfine Interactions - Synchrotron Mössbauer Reflectometry (SMR), the grazing incidence nuclear resonant scattering of synchrotron radiation, can be applied to perform depth-selective phase... 相似文献