全文获取类型
收费全文 | 633篇 |
免费 | 13篇 |
国内免费 | 9篇 |
专业分类
化学 | 276篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 271篇 |
物理学 | 92篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 22篇 |
2020年 | 8篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 16篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 15篇 |
2013年 | 48篇 |
2012年 | 39篇 |
2011年 | 37篇 |
2010年 | 32篇 |
2009年 | 43篇 |
2008年 | 37篇 |
2007年 | 48篇 |
2006年 | 33篇 |
2005年 | 34篇 |
2004年 | 19篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1961年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有655条查询结果,搜索用时 15 毫秒
1.
Mihai V. Putz 《International journal of quantum chemistry》2006,106(2):361-389
A unified Mulliken valence with Parr ground‐state electronegativity picture is presented. It provides a useful analytical tool on which the absolute hardness as well ionization potential and electron affinity functionals are based. For all these chemical reactivity indices, systematic approximate density functionals are formulated within density functional softness theory and are applied to atomic systems. For the absolute hardness, a special relationship with the new electronegativity ansatz and a particular atomic trend paralleling the absolute electron affinity are established that should complement and augment the earlier finite‐difference energetic approach. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
2.
New Schiff bases of 2,4‐dihydroxybenzaldehyde with siloxane‐α,ω‐diamines having different numbers of siloxane units in the chain have been synthesized and characterized by spectroscopy, elemental and thermal analyses. These azomethines were found to form complexes readily with copper(II), nickel(II), cobalt(II), cadmium(II) and zinc(II). From IR and UV–Vis studies, the phenolic oxygen and imine nitrogen of the ligand were found to be the coordination sites. Thermogravimetric analysis (TGA) data indicate the chelates to be more stable than the corresponding ligands. The melting points increase with shortening of the siloxane segment from azomethine, as well as the result of complexation. The chelates obtained were covalently inserted in polymeric linear structures by polycondensation through the OH‐difunctionalized ligand with 1,3‐bis(carboxypropyl)tetramethyldisiloxane. Direct polycondensation, assisted either by acetic anhydride or N,N′‐dicyclohexylcarbodiimide as dehydrating agent and the complex 4‐(dimethylamino)pyridinium 4‐toluenesulfonate as catalyst, was used for the synthesis of these compound types. The structures of the polymers obtained were confirmed by IR, UV and 1H NMR. Characterization was undertaken by TGA, solubility tests and viscosity measurements. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
Mihai Tib?r 《Topology》2003,42(3):629-639
We show that the complex link of a large class of space germs (X,x0) is characterized by its “simplicity”, among the Milnor fibres of functions with isolated singularity on X. This amounts to the minimality of the Milnor number, whenever this number is defined. Such a phenomenon has been first pointed out in case (X,x0) is an isolated hypersurface singularity, by Teissier (Cycles évanescents, sections planes et conditions de Whitney, in: Singularités à Cargèse 1972, Asterisque, Nos. 7 et 8, Soc. Math. France, Paris, 1973, pp. 285-362). 相似文献
4.
Ecaterina Stela Dragan Marcela Mihai Anton Airinei 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5898-5908
The thermochemical transformation of electrostatically formed complexes of methyl orange (MO) with polycations containing primary amine groups such as ammonium salts afforded new polymers with a high concentration of covalently bound 4‐N,N‐dimethylaminoazobenzene groups in the side chain. Poly(allylamine hydrochloride) and poly(β‐aminoethylene acrylamide hydrochloride) were employed as support polycations for MO. The transformation of sulfonate–ammonium ion pairs into sulfonamide bonds, via heating at an elevated temperature, was supported by the polymer properties before and after the thermal treatment. The polymer structure changes were monitored with elemental analysis, Fourier transform infrared, 1H NMR, and ultraviolet–visible absorption spectroscopy, and thermogravimetric analysis. The spacer length between the backbone and azobenzene structures used as side chains strongly influenced the polymer properties before and after the heat‐induced reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5898–5908, 2006 相似文献
5.
Mihai Putinar 《Archiv der Mathematik》2006,87(1):41-51
We compare three levels of algebraic certificates for evaluating the maximum modulus of a complex analytic polynomial, on
a compact semi-algebraic set. They are obtained as translations of some recently discovered inequalities in operator theory.
Although they can be stated in purely algebraic terms, the only known proofs for these decompositions have a transcendental
character.
Received: 27 June 2005 相似文献
6.
Recently B.Y. CHEN initiated the study of the tensor product immersion of two immersions of a given Riemannian manifold [3]. In [6] the particular case of tensor product of two Euclidean plane curves was studied. The minimal one were classified, and necessary and sufficient conditions for such a tensor product to be totally real or complex or slant were established. In the present paper we study for tensor product of Euclidean plane curves the problem of B.Y. CHEN: to what extent do the properties of the tensor product immersion f ? h of two immersions f, h determines the immersions f, h ? [3] 相似文献
7.
8.
The concentrations of238Pu,239,240Pu and241Am were determined in eight sediment samples, collected from the bed of the Romanian sector of the Danube river and the Black Sea coast during 1994 and 1995. Fusion with potassium carbonate was used to achieve complete dissolution of the samples. Tracers,242Pu and243Am, were added and the separation of plutonium from americium, uranium and thorium was performed by anion exchange. Americium was separated from uranium in two steps, using a conventional anion exchange resin and an extraction chromatographic resin for transuranics. After electrodeposition on stainless steel discs the nuclides were counted with -spectrometry with -PIPS detectors. The total plutonium concentrations obtained by this method were compared with the acid leachable plutonium concentrations reported for the same samples in a previous paper. 相似文献
9.
Silvia-Angela Mihai G. Shaw Iulia I. Georgescu 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(6):461-469
The concentrations of238Pu and239, 240Pu were determined in 12 sediment samples collected from the bed of the Romanian Danube river and Black Sea coast during June–September 1994. After the sample material has been properly prepared and242Pu tracer added, plutonium was separated from americium and curium by anion exchange. After electrodeposition on stainless steel discs the elements were counted with an -spectrometry system with silicon surface-barrier detectors. The239, 240Pu concentrations range between 150 and 800 mBq kg–1 dry, while the238Pu concentrations rise up to max 150 mBq kg–1 dry. Although the chemical yields are rather low (51%) we appreciate the results as valuable since they report for the first time the distribution of the plutonium contamination along the Danube river and the Black Sea coast-Romanian sector. 相似文献
10.
The current work presents an objective overview of the impact of one important heterocyclic structure, the pyrazole ring, in the development of anti-proliferative drugs. A set of 1551 pyrazole derivatives were extracted from the National Cancer Institute (NCI) database, together with their growth inhibition effects (GI%) on the NCI’s panel of 60 cancer cell lines. The structures of these derivatives were analyzed based on the compounds’ averages of GI% values across NCI-60 cell lines and the averages of the values for the outlier cells. The distribution and the architecture of the Bemis–Murcko skeletons were analyzed, highlighting the impact of certain scaffold structures on the anti-proliferative effect’s potency and selectivity. The drug-likeness, chemical reactivity and promiscuity risks of the compounds were predicted using AMDETlab. The pyrazole ring proved to be a versatile scaffold for the design of anticancer drugs if properly substituted and if connected with other cyclic structures. The 1,3-diphenyl-pyrazole emerged as a useful scaffold for potent and targeted anticancer candidates. 相似文献