全文获取类型
收费全文 | 2428篇 |
免费 | 42篇 |
国内免费 | 5篇 |
专业分类
化学 | 1591篇 |
晶体学 | 5篇 |
力学 | 28篇 |
数学 | 504篇 |
物理学 | 347篇 |
出版年
2021年 | 15篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2016年 | 36篇 |
2015年 | 33篇 |
2014年 | 36篇 |
2013年 | 65篇 |
2012年 | 65篇 |
2011年 | 85篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 68篇 |
2007年 | 73篇 |
2006年 | 68篇 |
2005年 | 54篇 |
2004年 | 70篇 |
2003年 | 33篇 |
2002年 | 46篇 |
2001年 | 49篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 31篇 |
1996年 | 39篇 |
1995年 | 36篇 |
1994年 | 38篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 35篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 31篇 |
1986年 | 17篇 |
1985年 | 53篇 |
1984年 | 43篇 |
1983年 | 40篇 |
1982年 | 19篇 |
1981年 | 43篇 |
1980年 | 39篇 |
1979年 | 26篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 26篇 |
1975年 | 35篇 |
1974年 | 32篇 |
1973年 | 22篇 |
1972年 | 17篇 |
1960年 | 19篇 |
1885年 | 15篇 |
排序方式: 共有2475条查询结果,搜索用时 515 毫秒
101.
Vadim V. Ilyushin Zbigniew Kisiel Heinrich Mäder 《Journal of Molecular Spectroscopy》2010,259(1):26-12194
A new program is described for fitting rotation-torsion energy levels in molecules like toluene, in which the frame (C6H5) has C2v symmetry and the methyl top has C3v symmetry, i.e., for molecules where the internal rotation barrier is expanded in cos6nα, where α is the internal rotation angle and n = 1,2,…. The program is based on the theoretical framework developed by Sørensen and Pedersen in their application of the Longuet-Higgins permutation-inversion group G12 to the microwave spectrum of CH3NO2. It is specifically designed for sixfold barrier molecules, and allows the user to select almost any symmetry-allowed torsion-rotation term for inclusion in the fitting Hamiltonian. This program leads to a very successful fit of transitions in the microwave spectrum of toluene characterized by J ? 30, Ka ? 12, and by the free-rotor quantum number ∣m∣ ? 3. In these fits we included both published and rather extensive unpublished new measurements, for which fits using other torsion-rotation programs have not been very successful. The fit presented here uses 28 parameters to give an overall standard deviation of 7.4 kHz for 372 line frequencies, and results in a much improved value for the sixfold barrier for toluene, V6 = 13.832068(3) cal mol−1. 相似文献
102.
Francis R. Costa Sudip Pradhan Udo Wagenknecht Anil K. Bhowmick Gert Heinrich 《Journal of Polymer Science.Polymer Physics》2010,48(22):2302-2311
In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
103.
Hydroperoxides, olefins, and arenediazonium salts selectively combine to give azo compounds via an iron(II)-mediated three-component reaction. Starting with a fragmentation liberating acetic acid, the hydroperoxides act as radical source and the diazonium ions as nitrogen-centered radical scavengers. 相似文献
104.
105.
Johannes Tauer Heinrich Kofler Elisabeth Schwarz Ernst Wintner 《Central European Journal of Physics》2010,8(2):242-248
Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated. 相似文献
106.
Radiation measurements made onboard the MIR Orbital Station have spanned nearly a decade and covered two solar cycles, including one of the largest solar particle events, one of the largest magnetic storms, and a mean solar radio flux level reaching 250 x 10(4) Jansky that has been observed in the last 40 years. The cosmonaut absorbed dose rates varied from about 450 microGy day-1 during solar minimum to approximately half this value during the last solar maximum. There is a factor of about two in dose rate within a given module, and a similar variation from module to module. The average radiation quality factor during solar minimum, using the ICRP-26 definition, was about 2.4. The drift of the South Atlantic Anomaly was measured to be 6.0 +/- 0.5 degrees W, and 1.6 +/- 0.5 degrees N. These measurements are of direct applicability to the International Space Station. This paper represents a comprehensive review of Mir Space Station radiation data available from a variety of sources. 相似文献
107.
Felder D Heinrich B Guillon D Nicoud JF Nierengarten JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(19):3501-3507
Cyclotriveratrylene (CTV) derivatives substituted with 9 (1) or 18 (2) long alkyl chains have been prepared. Whereas no liquid crystalline behavior has been observed for 1, the CTV derivative 2 has mesomorphic properties. Indeed, at room temperature compound 2 exhibits a nematic phase characterized by cybotactic groups with a local lamello-columnar order. Both CTV derivatives 1 and 2 are able to form supramolecular complexes with C60 in the solid state. In both cases, the 2:1 host-guest species have been obtained as brown compounds. No liquid crystalline behavior was observed for the supramolecular complex [C60 is included in (1)2]. In contrast, observation of the brown product obtained from C60 and the CTV derivative 2 directly after preparation by polarized optical microscopy revealed a fluid birefringent phase at room temperature. When the sample is heated above 70 degrees C, the birefringence of the texture under the microscope disappears and the X-ray diffraction pattern is transformed into a pattern characteristic of a cubic phase. For the first time in thermotropic liquid crystals, the space group of this cubic phase can be assigned as I4(1)32. 相似文献
108.
Felder D Gallani JL Guillon D Heinrich B Nicoud JF Nierengarten JF 《Angewandte Chemie (International ed. in English)》2000,39(1):201-204
In spite of a molecular mass of 7704.6 g mol(-1), third-generation compound G3 (shown schematically; Z=C(8)H(17)) is able to form stable Langmuir films. In a systematic study, the amphiphilic properties of the corresponding dendrimers of first (G1) and second generation (G2), with one and two peripheral fullerene units, respectively, were investigated and a model could be proposed for the multilayer films obtained from G1. 相似文献
109.
Heinrich L Li Y Vaissermann J Chottard G Chottard JC 《Angewandte Chemie (International ed. in English)》1999,38(23):3526-3528
Postcoordination oxidation by dioxygen of one of the thiolate groups in a pentadentate N(2)S(3) ligand results in an iron(III) complex with two N-carboxamido, two thiolato, and one O-sulfinato ligands (see the CAMERON representation). This novel mixed coordination is similar to that determined for the inactive form of the nitrile hydratase from Rhodococcus sp. N-771, but differs by the O versus S binding of the sulfinato ligand. 相似文献
110.
In a review paper [H. M. Jaeger, S. R. Nagel, and R. P. Behringer, "Granular solids, liquids and gases," Rev. Mod. Phys. 68, 1259-1273 (1996)] a few years ago, we wrote about granular material as a distinctive form of matter that exhibits behavior rather different from that of ordinary solids, liquids, or gases. We traced this distinction to three characteristic properties. First, the individual particles making up a granular material are typically large so that thermal energy is irrelevant compared to gravitational energy. Consequently, concepts from equilibrium statistical mechanics are often not applicable. Second, the interactions between particles are frictional and can be mobilized to different degrees depending on the preparation history, giving rise to memory effects, i.e., a static pile will remember how it was formed. Third, when particles collide they do so inelastically so that a "gas" of particles will slow down and come to rest in clumps. In the intervening years, the research on granular matter has progressed rapidly and this may be a good time to ask what we have learned since that article was written. In this spirit, the present special issue of the journal Chaos assembles a spectrum of papers discussing recent developments in the field. (c) 1999 American Institute of Physics. 相似文献