全文获取类型
收费全文 | 1089篇 |
免费 | 43篇 |
专业分类
化学 | 696篇 |
晶体学 | 4篇 |
力学 | 27篇 |
数学 | 158篇 |
物理学 | 247篇 |
出版年
2023年 | 5篇 |
2022年 | 56篇 |
2021年 | 61篇 |
2020年 | 17篇 |
2019年 | 28篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 80篇 |
2015年 | 49篇 |
2014年 | 56篇 |
2013年 | 109篇 |
2012年 | 60篇 |
2011年 | 58篇 |
2010年 | 47篇 |
2009年 | 52篇 |
2008年 | 51篇 |
2007年 | 26篇 |
2006年 | 43篇 |
2005年 | 20篇 |
2004年 | 23篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1992年 | 3篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有1132条查询结果,搜索用时 15 毫秒
31.
Alina T. Dubis Piotr Stasiewicz Katarzyna Pogorzelec‐Glaser Andrzej Łapiński 《Journal of Physical Organic Chemistry》2015,28(10):652-662
The formation of intramolecular hydrogen bonding by certain N‐substituted 2‐acylpyrroles has been demonstrated by B3LYP/aug‐cc‐pVDZ calculations, the quantum theory of atoms in molecules, and the natural bond orbital method. Total electron energy densities HBCP at the bond critical point of the H?O bond were applied to analyze the strength of these interactions. The relations between quantum theory of atoms in molecules, carbonyl stretching vibrational modes νC = O, and natural bond orbital parameters associated with the formation of the C–H?O interaction have been established. The short contacts were found experimentally in the crystal structure of a new 2‐acylpyrrole derivative 5‐chloro‐2‐oxopentyl‐1‐(5‐chloro‐2‐oxopentyl)pyrrolo‐2‐carboxylate. The influence of 2‐ and N‐substitution of 2‐acylpyrroles on C‐H?O interaction energy is discussed. It was found that the methylene group may act as a proton donor leading to a red‐shift or blue‐shift phenomenon of the νC–H stretching mode. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
32.
Piotr Łyżwa Marian Mikołajczyk 《Phosphorus, sulfur, and silicon and the related elements》2014,189(7-8):1174-1192
AbstractAminophosphonic acids have become important in different fields of chemistry, medicine and agriculture. In this review article, we highlight a new strategy developed in the author's laboratory of asymmetric synthesis of enantiomeric aminophosphonic acid that users chiral sulfinimines as reagents. A key reaction in the synthesis of enantiopure α-, β- and γ-aminophosphonic acids is a highly or fully diastereoselective addition of trivalent phosphorus nucleophiles and α-phosphonate carbanions to enantiopure sulfinimines. The steric course of these addition reactions is rationalized. The usefulness of the sulfinimine methodology is demonstrated by the synthesis of biologically active enantiopure 2-amino-3-phosphonopropanoic acid (AP3), 2-amino-4-phosphonobutanoic acid (AP4) and phosphoemeriamine. 相似文献
33.
34.
ukasz Balewski Franciszek Sczewski Patrick J. Bednarski Lisa Wolff Anna Nadworska Maria Gdaniec Anita Kornicka 《Molecules (Basel, Switzerland)》2020,25(24)
The appropriate 1-arylhydrazinecarbonitriles 1a–c are subjected to the reaction with 2-chloro-4,5-dihydro-1H-imidazole (2), yielding 7-(4,5-dihydro-1H-imidazol-2-yl)-2-aryl-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-imines 3a–c, which are subsequently converted into the corresponding amides 4a–e, 8a–c, sulfonamides 5a–n, 9, ureas 6a–I, and thioureas 7a–d. The structures of the newly prepared derivatives 3a–c, 4a–e, 5a–n, 6a–i, 7a–d, 8a–c, and 9 are confirmed by IR, NMR spectroscopic data, as well as single-crystal X-ray analyses of 5e and 8c. The in vitro cytotoxic potency of these compounds is determined on a panel of human cancer cell lines, and the relationships between structure and antitumor activity are discussed. The most active 4-chloro-N-(2-(4-chlorophenyl)-7-(4,5-dihydro-1H-imidazol-2-yl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)benzamide (4e) and N-(7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)-[1,1′-biphenyl]-4-sulfonamide (5l) inhibits the growth of the cervical cancer SISO and bladder cancer RT-112 cell lines with IC50 values in the range of 2.38–3.77 μM. Moreover, N-(7-(4,5-dihydro-1H-imidazol-2-yl)-2-phenyl-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)-4-phenoxybenzenesulfonamide (5m) has the best selectivity towards the SISO cell line and induces apoptosis in this cell line. 相似文献
35.
The paper presents experimental investigations of the concrete covers’ protective ability to counteract rebar corrosion in reinforced concrete cubes. The concrete sample was subjected to a chloride-induced environment to get corroded and combined with an un-corroded sample. The chloride-accelerated technique can induce a high degree of corrosion within a controlled time. Moreover, detailed and thorough experimental measurements and analyses of reinforcement loss due to corrosion and its influence on concrete microstructure, were studied through 3D X-ray micro-computed tomography. The rebar outside the concrete was heavily corroded due to the chloride-accelerated test, whereas, only local surface corrosion products appeared inside the concrete. It turned out that the concrete cover showed protective ability to counteract the reinforcing-steel corrosion mechanism despite the accelerated corrosion environment. Moreover, the bond strength between the reinforcement rebar and concrete was not visibly affected since the failure force in the pull-out test and failure mechanisms, observed by 3D X-ray micro-CT, were similar for corroded and un-corroded samples. The failure occurred due to radial cracks with a maximum width equal to approximately 0.25 mm. 相似文献
36.
W. Łada A. DeptuŁa T. Olczak W. Torbicz D. Pijanowska A. Di Bartolomeo 《Journal of Sol-Gel Science and Technology》1994,2(1-3):551-554
SnO2 sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl4, (2) washing the precipitates with NH4NO3 solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO3, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO2 by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared. 相似文献
37.
This paper introduces the Independent Components Analysis (ICA) to voltammetry and extends possibility of the qualitative and quantitative analysis of binary mixtures of similar oxidation/reduction potentials. It was demonstrated that even in the case of distance between peaks potentials equal to 10 mV, determinations may be realized according to typical validation criteria. The methodology was presented using the simulated data and capabilities and limitations of the method were described. Further, the usefulness of ICA was presented for voltammograms registered during simultaneous determination of copper and antimony, and thallium and indium. The results of high practical importance for chemical analysis were achieved and documented. In the quantitative analysis a property was extensively used, that ICA is an unsupervised method. 相似文献
38.
39.
J. Łukasik G. Auger M. L. Begemann-Blaich N. Bellaize R. Bittiger F. Bocage B. Borderie R. Bougault B. Bouriquet J. L. Charvet A. Chbihi R. Dayras D. Durand J. D. Frankland E. Galichet D. Gourio D. Guinet S. Hudan P. Lautesse F. Lavaud A. Le Fèvre R. Legrain O. Lopez U. Lynen W. F. J. Müller L. Nalpas H. Orth E. Plagnol E. Rosato A. Saija C. Schwarz C. Sfienti B. Tamain W. Trautmann A. Trzciński K. Turzó E. Vient M. Vigilante C. Volant B. Zwiegliński 《Acta Physica Hungarica A》2006,25(2-4):229-239
Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies. 相似文献
40.
We introduce a method that allows the disclosure of correlations between particle positions in an arbitrary many‐body system. The method is based on a well‐known simulated annealing algorithm and the proposed artificial distribution technique. Additionally, we investigate correlations in quantum Hall liquids (we consider many‐body wave functions that have been recently determined via the cyclotron subgroup model) and present three‐dimensional plots of configuration probability distributions that have been established from numerical simulations. We demonstrate that the preferred simultaneous positions of particles (configurations of positions, which correspond to large values of a system's probability distribution, ) tend to form complicated geometric structures, which are equivalent to classical Wigner crystals only for Laughlin states. Furthermore, we claim that quantum Hall liquids attributed to non‐Laughlin fillings are correlated on subdomains rather than on a whole particle domain (due to a quantizing magnetic field, which modifies the topology of a system's dynamics). Finally, we characterize Hall‐like internal orders in terms of statistical correlations (one‐dimensional unitary representations of cyclotron subgroups). Our conclusions concerning the stability of many‐body states agree with transport measurements and various numerical studies. 相似文献