全文获取类型
收费全文 | 2589篇 |
免费 | 119篇 |
国内免费 | 14篇 |
专业分类
化学 | 1436篇 |
晶体学 | 58篇 |
力学 | 98篇 |
综合类 | 3篇 |
数学 | 507篇 |
物理学 | 620篇 |
出版年
2023年 | 18篇 |
2022年 | 27篇 |
2021年 | 45篇 |
2020年 | 68篇 |
2019年 | 91篇 |
2018年 | 105篇 |
2017年 | 87篇 |
2016年 | 120篇 |
2015年 | 79篇 |
2014年 | 117篇 |
2013年 | 281篇 |
2012年 | 167篇 |
2011年 | 158篇 |
2010年 | 169篇 |
2009年 | 129篇 |
2008年 | 183篇 |
2007年 | 143篇 |
2006年 | 102篇 |
2005年 | 79篇 |
2004年 | 81篇 |
2003年 | 94篇 |
2002年 | 55篇 |
2001年 | 55篇 |
2000年 | 45篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 2篇 |
1970年 | 4篇 |
排序方式: 共有2722条查询结果,搜索用时 328 毫秒
71.
72.
The magnetic filtration theory was evaluated to intensify the filtration of industrial fluids by magnetic filters. Effects of filtration velocity and external magnetic field intensity on filter performance were investigated and the dependence of the logarithmic efficiency coefficient on filtration velocity was questioned. It was concluded that change in the magnetic susceptibility of the dispersion particles, caused by external magnetic field, and change in the flow rate properties of the liquid alongside the filter pores are the most essential factors to be considered in the design, development, and modeling of magnetic filtration systems in various industrial areas. 相似文献
73.
74.
75.
Oğuz Türünç Michael A. R. Meier 《Journal of polymer science. Part A, Polymer chemistry》2012,50(9):1689-1695
The ability of thiyl radicals to add to terminal unsaturations in an efficient way made them considered being one of the click reactions. Recently, thiol‐yne addition reactions have been used extensively for the synthesis of crosslinked networks and dendrimers and postpolymerization functionalization protocols. Herein, we report a novel step‐growth type reaction for highly functional linear polymers using a monoalkyne and dithiol compound. First, we investigated the model reaction between 1‐octyne and 1‐octanethiol as well as 1,4‐butanedithiol compounds, which were initiated via self‐, thermal‐, and UV‐initiation; the UV‐initiation was found to be the most efficient method and completed within 2‐h reaction time. The same conditions were applied for the polymerization of four different functional alkynes bearing different functional groups with two dithiol compounds. All polymerizations resulted in highly functional linear polymers with number averaged molecular weights ranging from 5 to 30 kDa, except for propargylic acid and its methyl ester, where only oligomers formed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
76.
A distance based measure of dependence is proposed for stable distributions that completely characterizes independence for a bivariate stable distribution. Properties of this measure are analyzed, and contrasted with the covariation and co-difference. A sample analog of the measure is defined and demonstrated on simulated and real data, including time series and distributions in the domain of attraction of a stable law. 相似文献
77.
Firstly, poly[phenyl thiadiazole methacrylamide-co-divinylbenzene-co-2-acrylamido-2-methylpropane sulfonic acid] (PTMAAm-co-DVB-co-AMPS), a new polymer resin was synthesized. This polymer resin was characterized by elemental analyzer, X-ray diffractometer, scanning electron microscope (SEM) and IR spectrometer. The glass column packed with the synthesized polymer resin was used for solid phase extraction (SPE). At the same time, the analytes were separated and preconcentrated from various water, dried vegetables samples and standard reference material (CRM) with SPE and determined by flame atomic absorption spectrometer (FAAS). The experimental conditions of this method such as pH, flow rates of sample, flow rates of eluent, type / concentration / volume of eluent, sample volume and matrix ions were examined. The limits of detection (µg L?1) were calculated (3s) 0.9 for Mn(II), 1.4 for Cd(II), Co(II) and Zn(II), 1.5 for Cr(III), 2.2. for Cu(II), 1.9 for Pb(II),1.5 for Ni(II) and 1.9 for Fe(III) (n = 21). The low relative standard deviation, ≤ 2% (n = 11) and preconcentration factor as 75 for analytes were obtained. 相似文献
78.
Bünyamin Ak Duygu Elma Nermin Meriç Cezmi Kayan Uğur Işık Murat Aydemir Feyyaz Durap Akın Baysal 《Tetrahedron: Asymmetry》2013,24(20):1257-1264
A new and versatile class of unsymmetrical ferrocenyl-phosphinite ligands possessing a stereogenic center has been prepared from commercially available, inexpensive aminoacids such as, d-, l-phenylglycine and d-, l-phenylalanine, through a concise synthetic procedure. These ligands are not very sensitive to air and moisture, and display good enantioselectivities in the ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives, in which up to 91% ee was obtained. A comparison of the catalytic properties of amino alcohols and other analogues based on a ferrocenyl backbone is also discussed briefly. The structures of these ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. 相似文献
79.
Ramoğlu Bahtışen Gümrükçüoğlu Abidin Çekirge Ender Ocak Miraç Ocak Ümmühan 《Journal of fluorescence》2021,31(6):1587-1598
Journal of Fluorescence - A simple microwave-assisted synthesis of nitrogen-doped carbon dots with high oxygen content (O-N-CDs) was carried out with citric acid as a carbon source and... 相似文献
80.
Semra Öztürk Kaptanoğlu 《Algebras and Representation Theory》2014,17(5):1437-1455
We introduce the class of restricted k[A]-modules and p t -Jordan types for a finite abelian p-group A of exponent at least p t and a field k of characteristic p. For these modules, we generalize several theorems by Benson, verify a generalization of conjectures stated by Suslin and Rickard giving constraints on Jordan types for modules of constant Jordan type when t is 1. We state conjectures giving constraints on p t -Jordan types and show that many p t -Jordan types are realizable. 相似文献