全文获取类型
收费全文 | 1911篇 |
免费 | 54篇 |
国内免费 | 7篇 |
专业分类
化学 | 1489篇 |
晶体学 | 9篇 |
力学 | 21篇 |
数学 | 164篇 |
物理学 | 289篇 |
出版年
2023年 | 9篇 |
2022年 | 25篇 |
2021年 | 109篇 |
2020年 | 42篇 |
2019年 | 63篇 |
2018年 | 79篇 |
2017年 | 53篇 |
2016年 | 76篇 |
2015年 | 85篇 |
2014年 | 66篇 |
2013年 | 166篇 |
2012年 | 91篇 |
2011年 | 114篇 |
2010年 | 98篇 |
2009年 | 81篇 |
2008年 | 116篇 |
2007年 | 129篇 |
2006年 | 87篇 |
2005年 | 93篇 |
2004年 | 58篇 |
2003年 | 66篇 |
2002年 | 51篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 10篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1965年 | 2篇 |
1963年 | 2篇 |
排序方式: 共有1972条查询结果,搜索用时 656 毫秒
61.
Tippmann EM Platz MS Svir IB Klymenko OV 《Journal of the American Chemical Society》2004,126(18):5750-5762
Laser flash photolysis (LFP, 308 nm) of endo-10-halo-10'-N,N-dimethylcarboxamidetricyclo[4.3.1.0]-deca-2,4-diene (1Cl and 1F) releases indan and halocarbene amide (2Cl and 2F). Although the carbenes are not UV-vis active, they react rapidly with pyridine to form ylides (4Cl, 4F), which are readily detected in LFP experiments (lambda(max) = 450 nm). Dioxane decreases the observed rate of carbene reaction with pyridine in CF(2)ClCFCl(2). Small amounts of THF decrease the observed rate of reaction of carbene 2F with pyridine but increase the rate of reaction of carbene 2Cl with pyridine. LFP (266 nm) of dienes 1Cl and 1F in CF(2)ClCFCl(2) with IR detection produces carbenes 2Cl and 2F with carbonyl vibrations at 1635 and 1650 cm(-1), respectively. In dioxane or THF solvent, LFP produces the corresponding ether ylides (5Cl, 5F) by capture of carbenes 2Cl and 2F. The ylides have broad carbonyl vibrations between 1560 and 1610 cm(-1). The addition of a small amount of dioxane in CFCl(2)CF(2)Cl extends the lifetime of the carbene. This observation, together with the ether-induced retardation of the rates of carbene capture by tetramethylethylene and pyridine, is evidence for solvation of the carbene by dioxane. 相似文献
62.
63.
4-Alkynyl-3,4-dihydropyrimidin-2-(1H)-ones were synthesized by a one-pot reaction of propynals, ethyl acetoacetate, and urea. The yields of acetylenic dihydropyrimidinones depend significantly upon the propynal structure and catalyst type. A comparative study of the catalysts revealed an important advantage of polyphosphate ester in tetrahydrofuran in comparison with hydrochloric acid in methanol or trimethylchlorosilane in dimethylformamide, allowing the preparation of target compounds in good or moderate yields. 相似文献
64.
Russian Physics Journal - Experimental data are presented on measuring the complex dielectric permittivity (CDP) of clays completely moistened with distilled water in the frequency range from 1 kHz... 相似文献
65.
C.M. da Fonseca Dan A. Mazilu Irina Mazilu H. Thomas Williams 《Applied Mathematics Letters》2013,26(12):1206-1211
A straightforward model for deposition and evaporation on discrete cells of a finite array of any dimension leads to a matrix equation involving a Sylvester–Kac type matrix. The eigenvalues and eigenvectors of the general matrix are determined for an arbitrary number of cells. A variety of models to which this solution may be applied are discussed. 相似文献
66.
67.
Andreea Irina Barzic Iuliana Stoica Dana-Ortansa Dorohoi 《Journal of Macromolecular Science: Physics》2016,55(6):575-590
New drug delivery systems based on hydroxypropyl cellulose (HPC) and different percents of glucose were prepared and characterized to check their suitability as UV resistant patches. The spectral absorption properties of the HPC and HPC-glucose blends before and after UV irradiation were analyzed. The surface polarity and hydrophilicity were correlated with the morphology of the films and analyzed with respect to the UV exposure time and the embedded amount of glucose. The effects of UV radiation on in vitro evaluation of glucose release from the HPC films are reported. The mechanism involved in the drug release process, evaluated using the Korsmeyer-Peppas equation, was dependent on the introduced amount of glucose and less on the UV exposure time. A more polar, smoother, and less dense surface releases the glucose over larger periods of time, making the system with lower percents of glucose more adequate for the pursued purpose. 相似文献
68.
69.
70.
Yury Yu. Rusakov Irina L. Rusakova Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2014,52(5):214-221
Four‐component relativistic calculations of 77Se–13C spin–spin coupling constants have been performed in the series of selenium heterocycles and their parent open‐chain selenides. It has been found that relativistic effects play an essential role in the selenium–carbon coupling mechanism and could result in a contribution of as much as 15–25% of the total values of the one‐bond selenium–carbon spin‐spin coupling constants. In the overall contribution of the relativistic effects to the total values of 1J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin‐orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second‐order polarization propagator approach (CC2) with the four‐component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of 1J(Se,C). Solvent effects in the values of 1J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2–78.4) are next to negligible decreasing negative 1J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of 77Se–13C spin‐spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1–0.2‐Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献