全文获取类型
收费全文 | 3119篇 |
免费 | 92篇 |
国内免费 | 12篇 |
专业分类
化学 | 2364篇 |
晶体学 | 41篇 |
力学 | 35篇 |
数学 | 150篇 |
物理学 | 633篇 |
出版年
2023年 | 19篇 |
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 51篇 |
2019年 | 39篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 50篇 |
2015年 | 64篇 |
2014年 | 73篇 |
2013年 | 165篇 |
2012年 | 133篇 |
2011年 | 172篇 |
2010年 | 85篇 |
2009年 | 87篇 |
2008年 | 187篇 |
2007年 | 197篇 |
2006年 | 194篇 |
2005年 | 186篇 |
2004年 | 178篇 |
2003年 | 150篇 |
2002年 | 137篇 |
2001年 | 53篇 |
2000年 | 60篇 |
1999年 | 58篇 |
1998年 | 28篇 |
1997年 | 43篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 40篇 |
1993年 | 36篇 |
1992年 | 44篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 36篇 |
1984年 | 40篇 |
1983年 | 25篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1980年 | 18篇 |
1979年 | 31篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 24篇 |
1974年 | 21篇 |
1973年 | 17篇 |
排序方式: 共有3223条查询结果,搜索用时 15 毫秒
31.
32.
33.
The effect of solid particles on the flow structure of a round air jet in a stagnant surrounding was investigated experimentally. Information on the averaged two-component velocities, the kinetic energies, and the u′ v′-properties were obtained for both phases by means of a monochromatic three beam laser Doppler anemometer. The particle number density was also measured by this system. Glass beads of 64 μm and 132 μm diameter were used for a constant mass loading ratio of 0.3 in a jet with a Reynolds number of 20 000. The lateral mean velocity and number density profiles were expressed by best fitting functions and several invariable coefficients were found. The standard drag force coefficient C D for a single particle was applicable for a dilute particle cloud even in a non-uniform air velocity field. 相似文献
34.
35.
Lipophilic acyclic dibenzopolyether diamides, 12 kinds, have been designed to prepare solvent polymeric membrane ion-selective electrodes (ISEs) for Pb(2+). The ionophores include 1,5-bis[2-(N,N-dialkylcarbamoylmethoxy)phenoxy]-3-oxapentanes1-4, 1,5-bis[2-(N,N-dialkylcarbamoylpentadecyloxy)phenoxy]-3-oxapentanes 5-8, and 1,2-bis[2-(2'-N,N-dialkylcarbamoylpentadecyloxy)phenoxy]ethanes 9-12. Linear response concentration range of the ISE based on 9 is 3 x 10(-2) - 1 x 10(-6) M of Pb(2+) (average slope = 28.5 mV decade(-1)). Potentiometric selectivities of the ISEs based on 1-12 for Pb(2+) over other heavy metal cations, alkali metal cations, and alkaline earth metal cations have been assessed. These ISEs exhibit remarkably high selectivities for Pb(2+) relative to heavy metal cations, such as Cu(2+), Fe(2+), and Ni(2+), the selectivity coefficients (K(Pot)(Pb,Cu)) being 5 x 10(-5) - 6 x 10(-5) for 1-4 and ca. 6 x 10(-4) for 9. For the Pb(2+) selectivities over alkali metal cations, such as Na(+) and K(+), 9 which has an ethylene glycol spacer and a N,N-diethyl group is superior to other dibenzopolyether diamide ionophores 1-8 and 10-12. 相似文献
36.
The title compound a novel cyclophane containing p-tropoquinone, was synthesized starting from 5-methoxytropolone and its physical properties were discussed comparing with those of 3,7-dimethyl-p-tropoquinone and p-benzoquinonophane. The reduced quinone character exhibited by was ascribed to the intramolecular CT interaction and the deformation of the quinone ring. 相似文献
37.
Antioxidant activity of a series of hydroxybenzalacetones was determined against peroxynitrite-induced lipid peroxidation in red blood cell membrane and SOS response through DNA damage in bacterial cells. Hydroxybenzalacetone derivatives with hydroxy, methoxy, ethoxy or methyl substitution were analyzed and found to be more effective than the water-soluble vitamin E analogue Trolox. The inhibitory effect against lipid peroxidation correlated well to that against the SOS response, which is dependent on decomposition of peroxynitrite by hydroxybenzalacetones outside of the cell membrane. The antioxidant activity was shown to correlate well with the electric parameter sigma+. Electron-donating substituents with more negative sigma+ values increased the potencies. The result suggests that hydroxybenzalacetones with more electron-donating substituents will protect tissue more effectively against oxidative stress. 相似文献
38.
Evaluation of the disintegration time of rapidly disintegrating tablets via a novel method utilizing a CCD camera 总被引:6,自引:0,他引:6
Morita Y Tsushima Y Yasui M Termoz R Ajioka J Takayama K 《Chemical & pharmaceutical bulletin》2002,50(9):1181-1186
Many kinds of rapidly disintegrating or oral disintegrating tablets (RDT) have been developed to improve the ease of tablet administration, especially for elderly and pediatric patients. In these cases, knowledge regarding disintegration behavior appears important with respect to the development of such a novel tablet. Ordinary disintegration testing, such as the Japanese Pharmacopoeia (JP) method, faces limitations with respect to the evaluation of rapid disintegration due to strong agitation. Therefore, we have developed a novel apparatus and method to determine the dissolution of the RDT. The novel device consists of a disintegrating bath and CCD camera interfaced with a personal computer equipped with motion capture and image analysis software. A newly developed RDT containing various types of binder was evaluated with this protocol. In this method, disintegration occurs in a mildly agitated medium, which allows differentiation of minor distinctions among RDTs of different formulations. Simultaneously, we were also able to detect qualitative information, i.e., morphological changes in the tablet during disintegration. This method is useful for the evaluation of the disintegration of RDT during pharmaceutical development, and also for quality control during production. 相似文献
39.
A fluorescent-labeled oligopeptide (DACM-CLRRASLK-fluorescein), containing a consensus amino acid sequence (RRXSL) of cyclic AMP (cAMP) dependent protein kinase A (PKA) substrate-proteins, was designed. The fluorescent peptide was a good substrate of PKA, and the phosphorylation of its serin residue caused an intensive change in fluorescent intensity. We expect that the peptide will be useful as a fluorescent indicator for monitoring PKA activity in living cells. 相似文献
40.
Yoshitaka Gotoh Yutaka Kohno Wakichi Fukuda Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》1994,32(8):1543-1550
Soluble polystyrenes with crown ether structures and hydroxyl groups adjacent to the macrorings were prepared by the reaction of epoxide-containing polystyrenes with monoaza-15-crown-5 or monoaza-18-crown-6. Rate of formation of the polymer-bound alkali cation-crown alkoxide ion pair from the soluble polystyrenes and aqueous NaOH or KOH depended on the loading of crown ether and hydroxyl units and on the size of the macroring. The elimination of HCl from less reactive 2-chloroethylbenzene with aqueous NaOH or KOH in the presence of the soluble polystyrene catalysts under two-phase conditions was limited mainly by the intrinsic reaction rate. The elimination of HBr from more reactive 2-bromoethylbenzene in the presence of the less (11%) ring-substituted polymer catalyst with 18-crown unit was limited by the alkoxide formation rate. © 1994 John Wiley & Sons, Inc. 相似文献