全文获取类型
收费全文 | 41073篇 |
免费 | 1412篇 |
国内免费 | 271篇 |
专业分类
化学 | 28387篇 |
晶体学 | 361篇 |
力学 | 828篇 |
综合类 | 1篇 |
数学 | 6689篇 |
物理学 | 6490篇 |
出版年
2022年 | 295篇 |
2021年 | 479篇 |
2020年 | 676篇 |
2019年 | 653篇 |
2018年 | 468篇 |
2017年 | 426篇 |
2016年 | 1057篇 |
2015年 | 932篇 |
2014年 | 1106篇 |
2013年 | 1955篇 |
2012年 | 2413篇 |
2011年 | 2686篇 |
2010年 | 1462篇 |
2009年 | 1327篇 |
2008年 | 2475篇 |
2007年 | 2297篇 |
2006年 | 2320篇 |
2005年 | 2165篇 |
2004年 | 1839篇 |
2003年 | 1535篇 |
2002年 | 1491篇 |
2001年 | 628篇 |
2000年 | 602篇 |
1999年 | 502篇 |
1998年 | 490篇 |
1997年 | 515篇 |
1996年 | 559篇 |
1995年 | 418篇 |
1994年 | 451篇 |
1993年 | 434篇 |
1992年 | 391篇 |
1991年 | 358篇 |
1990年 | 302篇 |
1989年 | 291篇 |
1988年 | 296篇 |
1987年 | 298篇 |
1986年 | 251篇 |
1985年 | 491篇 |
1984年 | 427篇 |
1983年 | 358篇 |
1982年 | 428篇 |
1981年 | 374篇 |
1980年 | 344篇 |
1979年 | 321篇 |
1978年 | 303篇 |
1977年 | 299篇 |
1976年 | 281篇 |
1975年 | 265篇 |
1974年 | 213篇 |
1973年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
Convective heat transfer from an array of small, cylindrical bodies of arbitrary shape in an unbounded, two-dimensional domain is a singular perturbation problem involving an infinite logarithmic expansion in the small parameter ε, representing the order of magnitude of the size of the bodies. Using the method of matched asymptotic expansions, we formulate a hybrid asymptotic-numerical method to solve for the dimensionless, steady-state temperature. We assume that the velocity field of the fluid surrounding the bodies is arbitrary but known. From our asymptotic solution for an arbitrary velocity field, we present the results for two special cases: a uniform flow field and a simple shear flow field. We demonstrate the asymptotic results of the hybrid method through a number of examples and, in a particular case, we compare these results to an exact analytical solution. 相似文献
83.
84.
85.
86.
Using topological methods we give a proof that the free product of two strict subgroup separable groups with infinite cyclic amalgamation is subgroup separable. 相似文献
87.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
88.
Humberto Bustos Rodriguez Dagoberto Oyola Lozano Yebrayl A. Rojas Martínez Germán A. Pérez Alcázar Stefan Flege Adam G. Balogh Louis J. Cabri Michael Tubrett 《Hyperfine Interactions》2007,175(1-3):195-206
X-ray diffraction (XRD), Mössbauer spectrometry (MS), secondary ions mass spectroscopy (SIMS) and laser-ablation microprobe–inductively coupled plasma–mass spectrometry (LAM–ICP–MS) were used to study mineral samples of Colombian auriferous ores collected from the “El Diamante” mine, located in the municipality of Guachavez-Nariño, in Colombia. The samples were prepared as polished thin sections and polished sections. From XRD data, quartz, sphalerite and pyrite were detected and their respective cell parameters were estimated. From MS analyses, pyrite, arsenopyrite and chalcopyrite were identified; their respective hyperfine parameters and respective texture were deduced. Multiple regions of approximately 200 × 200 μm in each sample were analyzed with SIMS; the occurrence of “invisible gold” associated mainly with pyrite and secondarily with arsenopyrite could thus be assigned. It was also found that pyrite is of the arsenious type. Spots from 30 to 40 μm in diameter were analyzed with LAM–ICP–MS for pyrite, arsenopyrite and sphalerite; Au is “homogeneously” distributed inside the structure of the arsenious pyrite and the arsenopyrite (not as inclusions); the chemical composition indicates similarities of this “invisible gold”, forming a solid solution with arsenious pyrite and arsenopyrite. One hundred nineteen and 62 ppm of ‘invisible gold’ was quantified in 21 spots analyzed on pyrite and in 14 spots on arsenopyrite, respectively. 相似文献
89.
90.
Ohne ZusammenfassungDiese Arbeit wurde während eines Aufenthaltes von Schmidt in der Bundesrepublik Deutschland als Preisträger der Alexander von Humboldt-Stiftung geschrieben. 相似文献