全文获取类型
收费全文 | 7324篇 |
免费 | 265篇 |
国内免费 | 48篇 |
专业分类
化学 | 5272篇 |
晶体学 | 27篇 |
力学 | 252篇 |
数学 | 946篇 |
物理学 | 1140篇 |
出版年
2023年 | 69篇 |
2022年 | 90篇 |
2021年 | 129篇 |
2020年 | 122篇 |
2019年 | 152篇 |
2018年 | 94篇 |
2017年 | 87篇 |
2016年 | 211篇 |
2015年 | 172篇 |
2014年 | 213篇 |
2013年 | 403篇 |
2012年 | 477篇 |
2011年 | 527篇 |
2010年 | 291篇 |
2009年 | 256篇 |
2008年 | 457篇 |
2007年 | 477篇 |
2006年 | 430篇 |
2005年 | 393篇 |
2004年 | 370篇 |
2003年 | 336篇 |
2002年 | 281篇 |
2001年 | 103篇 |
2000年 | 104篇 |
1999年 | 83篇 |
1998年 | 67篇 |
1997年 | 73篇 |
1996年 | 88篇 |
1995年 | 62篇 |
1994年 | 48篇 |
1993年 | 44篇 |
1992年 | 49篇 |
1991年 | 48篇 |
1990年 | 53篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1986年 | 30篇 |
1985年 | 41篇 |
1984年 | 60篇 |
1983年 | 39篇 |
1982年 | 51篇 |
1981年 | 42篇 |
1980年 | 58篇 |
1979年 | 37篇 |
1978年 | 45篇 |
1977年 | 43篇 |
1976年 | 36篇 |
1975年 | 42篇 |
1974年 | 26篇 |
1973年 | 31篇 |
排序方式: 共有7637条查询结果,搜索用时 31 毫秒
41.
42.
The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH2O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH2O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k1a = 5.0 × 1015 exp(‐308 kJ mol?1/RT) cm3 mol?1 s?1. The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M → H2 + CO + M, and the branching fraction β = k1a/(kA1a + k1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH2O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH2O molecules. At high initial CH2O mole fractions the reverse of reaction (6), CH2OH + HCO ? CH2O + CH2O becomes noticeable. The rate of the forward reaction was roughly measured to be k6 = 1.5 × 1013 cm3 mol?1 s?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004 相似文献
43.
Christophe Rochais Vincent Lisowski Patrick Dallemagne Sylvain Rault 《Tetrahedron letters》2004,45(33):6353-6355
Novel arylpyrrolo- and pyrazolopyrrolizinones were prepared in three or four steps starting from aminoarylpyrrole and pyrazole carboxylates through the cyclisation of a Vilsmeier-Haack intermediate. This synthesis was enhanced by diverse N-protections of the aza-heterocycle and furnish new series with potential biological interest. 相似文献
44.
Paul A. Binding Patrick J. Browne Bruce A. Watson 《Journal of Mathematical Analysis and Applications》2004,291(1):246-261
Three inverse problems for a Sturm-Liouville boundary value problem −y″+qy=λy, y(0)cosα=y′(0)sinα and y′(1)=f(λ)y(1) are considered for rational f. It is shown that the Weyl m-function uniquely determines α, f, and q, and is in turn uniquely determined by either two spectra from different values of α or by the Prüfer angle. For this it is necessary to produce direct results, of independent interest, on asymptotics and oscillation. 相似文献
45.
Heinz H. Bauschke Patrick L. Combettes 《Proceedings of the American Mathematical Society》2003,131(12):3757-3766
An iterative method is proposed to construct the Bregman projection of a point onto a countable intersection of closed convex sets in a reflexive Banach space.
46.
Patrick Pruja Sauveur Bnet Bernard Claudet Olivier Faugeroux Jean-Jacques Serra 《Superlattices and Microstructures》2004,35(3-6):409
Modeling the behavior of a protective coating during a thermal shock not only requires the knowledge of its own thermophysical characteristics, but also those of the coating–substrate discontinuity. According to its nature, this discontinuity can be modeled as a zero-thickness interface (thermal contact resistance) or a finite thickness layer (thermal third body). This paper presents an experimental device and two associated thermal transfer models developed in view of the microscale characterization of such discontinuities. 相似文献
47.
We review the proof of a conjecture concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems, obtained via a connection between the theories of ordinary differential equations and integrable models. Spectral equivalences inspired by the correspondence are also discussed. 相似文献
48.
Recent successes in applying tabu search to a wide variety of classical optimization problems have motivated the investigation of applying tabu search to the well-known general fixed charge problem (GFCP). In this paper, an adaptation of tabu search to GFCP is described and computational results are given. In addition, the computational results are compared with those obtained from SWIFT-2, the most well-known and frequently used heuristic method for GFCP. As will be shown, the results are very encouraging. 相似文献
49.
50.