全文获取类型
收费全文 | 21081篇 |
免费 | 794篇 |
国内免费 | 354篇 |
专业分类
化学 | 13928篇 |
晶体学 | 120篇 |
力学 | 583篇 |
综合类 | 30篇 |
数学 | 2893篇 |
物理学 | 4675篇 |
出版年
2023年 | 145篇 |
2022年 | 363篇 |
2021年 | 459篇 |
2020年 | 373篇 |
2019年 | 373篇 |
2018年 | 293篇 |
2017年 | 237篇 |
2016年 | 605篇 |
2015年 | 568篇 |
2014年 | 627篇 |
2013年 | 1170篇 |
2012年 | 1145篇 |
2011年 | 1285篇 |
2010年 | 845篇 |
2009年 | 757篇 |
2008年 | 1110篇 |
2007年 | 1084篇 |
2006年 | 944篇 |
2005年 | 889篇 |
2004年 | 851篇 |
2003年 | 806篇 |
2002年 | 813篇 |
2001年 | 493篇 |
2000年 | 454篇 |
1999年 | 356篇 |
1998年 | 253篇 |
1997年 | 246篇 |
1996年 | 262篇 |
1995年 | 269篇 |
1994年 | 255篇 |
1993年 | 191篇 |
1992年 | 172篇 |
1991年 | 182篇 |
1990年 | 204篇 |
1989年 | 169篇 |
1988年 | 143篇 |
1987年 | 143篇 |
1986年 | 136篇 |
1985年 | 240篇 |
1984年 | 256篇 |
1983年 | 179篇 |
1982年 | 197篇 |
1981年 | 168篇 |
1980年 | 165篇 |
1979年 | 149篇 |
1978年 | 124篇 |
1977年 | 176篇 |
1976年 | 149篇 |
1975年 | 125篇 |
1973年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Normal human dermal fibroblasts: proteomic analysis of cell layer and culture medium. 总被引:7,自引:0,他引:7
Federica Boraldi Luca Bini Sabrina Liberatori Alessandro Armini Vitaliano Pallini Roberta Tiozzo Ivonne Pasquali Ronchetti Daniela Quaglino 《Electrophoresis》2003,24(7-8):1292-1310
Proteins present within the cell layer and those released in the cell medium from in vitro cultured normal human dermal fibroblasts were separated and characterized in terms of their isoelectric point and molecular weight, by two-dimensional (2-D) gel electrophoresis. All spots in the synthetic gel were firstly analyzed by the Melanie 3 software and compared with those of breast cancer cells, colorectal epithelial cells, HL60, lymphoma cells, and platelets, already available on-line. From the identification of 144 spots from both the cell layer and the medium, we were able to recognize 89 different proteins, since a certain number of spots represented different isoforms of the same molecule. Identifications were performed by matching with on-line 2-D databases, and by matrix assisted laser-desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), in order to confirm the identification by matching, or to identify new proteins. The procedure we used allows (i) to design a highly reproducible reference map of the proteome of adult human normal fibroblasts in culture, (ii) to evaluate protein species produced in the cell layer as well as those released in the culture medium, and (iii) to compare data from gel matching with those obtained by MS. This work represents an essential step for a better knowledge of mesenchymal cells, given the widespread use of this cell type in both clinical and experimental investigations. 相似文献
62.
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
63.
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
64.
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
65.
66.
67.
Laura R. Novick 《Mathematical Thinking and Learning》2004,6(3):307-342
According to the National Council of Teachers of Mathematics (2000), children need to learn how to create and use mathematical diagrams to represent and reason about phenomena in the world. The author proposes a model of diagram literacy that includes six types of knowledge required for diagrammatic competence - implicit, construction, similarity, structural, metacognitive, and translational. A study is reported that examined college students' diagram literacy for three interrelated mathematical diagrams - matrices, networks, and hierarchies. Three groups of students participated: preservice, secondary-level, math teachers; computer science majors; and typical undergraduates. The results of the study are reassuring in some ways concerning the level of diagram literacy possessed by students at the culmination of current K through 12 instruction and by teachers of future secondary students. However, the results also point to areas in which preservice math teachers should be better prepared if the goals for students' diagram literacy are to be met. 相似文献
68.
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
69.
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
70.
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