全文获取类型
收费全文 | 12373篇 |
免费 | 397篇 |
国内免费 | 81篇 |
专业分类
化学 | 8150篇 |
晶体学 | 117篇 |
力学 | 358篇 |
综合类 | 1篇 |
数学 | 1865篇 |
物理学 | 2360篇 |
出版年
2023年 | 74篇 |
2022年 | 75篇 |
2021年 | 174篇 |
2020年 | 181篇 |
2019年 | 162篇 |
2018年 | 129篇 |
2017年 | 115篇 |
2016年 | 271篇 |
2015年 | 240篇 |
2014年 | 298篇 |
2013年 | 599篇 |
2012年 | 713篇 |
2011年 | 828篇 |
2010年 | 438篇 |
2009年 | 342篇 |
2008年 | 680篇 |
2007年 | 690篇 |
2006年 | 716篇 |
2005年 | 691篇 |
2004年 | 572篇 |
2003年 | 493篇 |
2002年 | 417篇 |
2001年 | 232篇 |
2000年 | 191篇 |
1999年 | 144篇 |
1998年 | 117篇 |
1997年 | 140篇 |
1996年 | 198篇 |
1995年 | 140篇 |
1994年 | 165篇 |
1993年 | 168篇 |
1992年 | 139篇 |
1991年 | 115篇 |
1990年 | 101篇 |
1989年 | 106篇 |
1988年 | 98篇 |
1987年 | 97篇 |
1986年 | 90篇 |
1985年 | 166篇 |
1984年 | 121篇 |
1982年 | 124篇 |
1981年 | 97篇 |
1980年 | 83篇 |
1979年 | 95篇 |
1978年 | 104篇 |
1977年 | 84篇 |
1976年 | 87篇 |
1975年 | 84篇 |
1974年 | 91篇 |
1973年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
991.
A new proof of the characterization of the Chinese postman polyhedra is given. In developing this proof, a theorem of Gomory about homomorphic lifting of facets for group polyhedra is generalized to subproblems. Some results for the Chinese postman problem are generalized to binary group problems. In addition, a connection is made between Fulkerson's blocking polyhedra and a blocking pair of binary group problems. A connection is also developed between minors and lifting of facets for group problems. 相似文献
992.
Ohne Zusammenfassung 相似文献
993.
Pseudo-Hermitian symmetries 总被引:1,自引:0,他引:1
In this paper, we study different types of symmetries for the Tanaka-Webster connection of contact strictly pseudo-convex
pseudo-Hermitian CR manifolds.
The second author was financially supported by Chonnam National University. 相似文献
994.
E. J. K. Nilsson M. S. Johnson O. J. Nielsen E. W. Kaiser T. J. Wallington 《国际化学动力学杂志》2009,41(6):401-406
Relative rate techniques were used to study the title reactions in 930–1200 mbar of N2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH2F2) = 1.19 × 10?17 T2 exp(?1023/T) cm3 molecule?1 s?1 (253–553 K), k(Cl + CH3CCl3) = 2.41 × 10?12 exp(?1630/T) cm3 molecule?1 s?1 (253–313 K), and k(Cl + CF3CFH2) = 1.27 × 10?12 exp(?2019/T) cm3 molecule?1 s?1 (253–313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401–406, 2009 相似文献
995.
Kai Jiang Andriy Zakutayev Jason Stowers Michael D. Anderson Janet Tate David H. McIntyre David C. Johnson Douglas A. Keszler 《Solid State Sciences》2009,11(9):1692-1699
High-quality TiO2 thin films have been deposited from aqueous titanium-peroxo solutions via spin coating. The effects of precursor solution pH on the crystallization behavior, morphology, density, and refractive index of the films are reported. From X-ray diffraction measurements, the amorphous as-deposited films are found to crystallize in the anatase phase at 250 °C. Surface and cross-section SEM images reveal that films deposited from an acidic precursor are more uniform and denser than those deposited from a basic precursor. X-ray reflectivity measurements show that films with smooth surfaces and high densities (up to 87% of single-crystal anatase) can be produced at temperatures as low as 300 °C. Measured densities are consistent with high refractive indices at 633 nm of 2.24 and 2.11 for films derived from acidic and basic precursors, respectively. The uniformity and dense nature of the films have allowed fabrication of multilayer dielectric optical elements with thermal processing at only 300 °C. The distributed Bragg reflector with four bilayers exhibits a reflectance of 92% and a stop band width of 150 nm. The optical microcavity has a quality factor of 20. The optical properties of all elements agree well with theoretical models, indicating good optical quality. Use of the precursor chemistry for direct photopatterning of TiO2 films without a polymer resist is also demonstrated. 相似文献
996.
Charles Eric Brown Charles A. Wilkie Jeffrey Smukalla Robert B. Cody James A. Kinsinger 《Journal of polymer science. Part A, Polymer chemistry》1986,24(6):1297-1311
The reaction of red phosphorus with poly(methyl methacrylate) under pyrolysis conditions was investigated with a number of physical techniques. A random methyl methacrylate/cyclic anhydride copolymer is formed from atatic PMMA, whereas a random methyl methacrylate/methacrylic acid copolymer is obtained with isotactic PMMA. The backbones of both these copolymers are more stable toward depolymerization than that of PMMA. The flame-retardant activity of red phosphorus with PMMA may arise in part from stabilization of the polymer toward depolymerization via modification of the sidechains. 相似文献
997.
998.
999.
E. Erlenmeyer H. Wattenberg Ernst Wein Ludwig Rösch Julius Lehmann S. W. Johnson und E. H. Jenkins 《Fresenius' Journal of Analytical Chemistry》1880,19(1):243-246
Ohne Zusammenfassung 相似文献
1000.
Russell A. Johnson 《Annali di Matematica Pura ed Applicata》1987,147(1):211-248
Sunto Si definisce un esponente di Floquet per certe equazioni differenziali lineari nonperiodiche, la parte immaginaria del quale rappresenta una «rotazione» delle soluzioni di dette equazioni. Inoltre si discute la relazione fra l'esponente di Floquet e le funzioni m di Weyl-Kodaira, e fra la rotazione e certi problemi spettrali.
The author would like to thank Dr. RichardCushman for stimulating conversations on the subjects considered in this paper. 相似文献
The author would like to thank Dr. RichardCushman for stimulating conversations on the subjects considered in this paper. 相似文献