全文获取类型
收费全文 | 1080篇 |
免费 | 53篇 |
国内免费 | 16篇 |
专业分类
化学 | 695篇 |
晶体学 | 2篇 |
力学 | 16篇 |
数学 | 198篇 |
物理学 | 238篇 |
出版年
2024年 | 1篇 |
2023年 | 16篇 |
2022年 | 8篇 |
2021年 | 46篇 |
2020年 | 31篇 |
2019年 | 49篇 |
2018年 | 59篇 |
2017年 | 36篇 |
2016年 | 55篇 |
2015年 | 41篇 |
2014年 | 34篇 |
2013年 | 35篇 |
2012年 | 97篇 |
2011年 | 109篇 |
2010年 | 48篇 |
2009年 | 58篇 |
2008年 | 60篇 |
2007年 | 65篇 |
2006年 | 64篇 |
2005年 | 68篇 |
2004年 | 35篇 |
2003年 | 37篇 |
2002年 | 29篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1983年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 31 毫秒
991.
The Sr deficient perovskite Sr0.92NbO3 was synthesized from Sr5Nb4O15 and Nb and its crystal structure was determined using powder neutron diffraction. At room temperature the structure is orthorhombic in space group Pnma with both in-phase and out-of-phase tilting of the NbO6 octahedra. High temperature measurements have shown that the oxide undergoes a sequence of phase transitions with increasing temperature: Pnma→P4/mbm→Pm3¯m. The intermediate tetragonal phase has only in-phase tilts of the NbO6 octahedra, rather than the out-of-phase tilts present in the more commonly observed I4/mcm structure, due to initial softening at the M point rather than R point. The tetragonal phase exists only over a very narrow temperature range. The importance of M-M and M-O bonding in controlling the transition temperatures in SrMO3 perovskites is discussed. 相似文献
992.
This study evaluates the accuracy of estimating data in the series of systems carbon dioxide (1)–fatty acids (2) by two cubic equations of state, namely the EOS of Peng and Robinson in its original form and the recently proposed cubic EOS. The classical mixing rules are implemented in entirely predictive manner, i.e. without binary adjustable parameters. It is demonstrated that both models may yield reliable predictions of the data. However the EOS of Peng and Robinson fails in predicting the topology of phase behavior of the heavy homologues. The second cubic EOS predicts the Global Phase Behavior in the homologous series under consideration satisfactorily accurate, which in particular means qualitatively correct estimation of the liquid–liquid equilibria. The recently proposed EOS has no significant advantage over the EOS of Peng and Robinson in predicting the vapour–liquid equilibria data under consideration. 相似文献
993.
Artem L. Gushchin Maxim N. Sokolov Pavel A. Abramov Nina F. Zakharchuk Vladimir P. Fedin 《Journal of Cluster Science》2009,20(1):241-248
Single crystals of Ta4S1.5Se7.5I8 are obtained by heating Ta, S, Se and I2 at 300 °C in 4.0:1.0:8.0:4.4 molar ratio. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(μ4-S)(μ2-QaxSeeq)4I8] (Q ≈ Se0.87S0.13). The tantalum atoms form a square with long Ta…Ta distances (3.26–3.32 Å), with four dichalcogenide ligands bridging the Ta–Ta edges and a sulfur atom capping the square. Each Ta atom has two terminal iodine atoms. Raman spectroscopy study shows the presence of the characteristic absorption band at 396 cm?1 which is due to the Ta4–μ4-S vibrations. Cyclic voltammetry shows that Ta4S1.5Se7.5I8 in solid state undergoes quasi-reversible one-electron oxidation which is metal-centered. 相似文献
994.
995.
Artem L. Gushchin Maxim N. Sokolov Cristian Vicent Alexander V. Virovets Eugenia V. Peresypkina Vladimir P. Fedin 《Polyhedron》2009,28(16):3479-3484
Reactions of triangular telluride-bridged Mo and W clusters [M3(μ3-Te)(μ2-Te2)3(dtp)3]+ (M = Mo, W; dtp = (EtO)2PS2) with S2Cl2 or Br2 lead to Te/S exchange in the Te2 ligands, with the formation of complexes with a novel TeS2− ligand. Reaction of [W3(μ3-Te)(μ2-Te2)3(dtp)3]+ with Br2 or S2Cl2 gives a mixture of complexes formulated as [W3Te4.25S2.75(dtp)3]+ and [W3Te4.30S2.70(dtp)3]+, respectively, on the basis of X-ray structural analysis. Reaction of the Mo homolog, namely [Mo3(μ3-Te)(μ2-Te2)3(dtp)3]+, with S2Cl2 gives rise to [Мо3Te4.74S2.26((EtO)2PS2)3]+. Electrospray ionization mass spectrometry (ESI-MS) complements the information gathered from X-ray analysis regarding the degree of Te by S substitution; moreover, detailed insights on the regioselectivity of such replacement are also obtained from ESI-MS analysis. These experimental evidences indicate that Te by S replacement in W complexes display high regioselectivity (as evidenced by the exclusive formation of a W3Te4S34+ core), the equatorial Te ligands being preferentially replaced over the Teax and μ3-Te ligands. Conversely, for the Mo homologs, a broad distribution of Mo3Te7−xSx4+ cluster species ranging from x = 0 to 6 is observed. Bond distance analysis as well as crystal packing trends as a function of the cluster core M3Te7−xSx4+ (M = Mo, W; x = 0–6) composition are also reported. 相似文献
996.
Francisco Guerra Vázquez Hubertus Th. Jongen Vladimir Shikhman Maxim Ivanov Todorov 《Mathematical Methods of Operations Research》2009,70(1):35-46
We consider unconstrained finite dimensional multi-criteria optimization problems, where the objective functions are continuously
differentiable. Motivated by previous work of Brosowski and da Silva (1994), we suggest a number of tests (TEST 1–4) to detect,
whether a certain point is a locally (weakly) efficient solution for the underlying vector optimization problem or not. Our
aim is to show: the points, at which none of the TESTs 1–4 can be applied, form a nowhere dense set in the state space. TESTs
1 and 2 are exactly those proposed by Brosowski and da Silva. TEST 3 deals with a local constant behavior of at least one
of the objective functions. TEST 4 includes some conditions on the gradients of objective functions satisfied locally around
the point of interest. It is formulated as a Conjecture. It is proven under additional assumptions on the objective functions,
such as linear independence of the gradients, convexity or directional monotonicity.
This work was partially supported by grant 55681 of the CONACyT. 相似文献
997.
Maxim Kontsevich 《Japanese Journal of Mathematics》2009,4(1):1-25
We discuss a hypothetical correspondence between holonomic -modules on an algebraic variety X defined over a field of zero characteristic, and certain families of Lagrangian subvarieties in the cotangent bundle to X. The correspondence is based on the reduction to positive characteristic.
This article is based on the 5th Takagi Lectures that the author delivered at the University of Tokyo on October 4 and 5,
2008. 相似文献
998.
Avdeev M Thorogood GJ Carter ML Kennedy BJ Ting J Singh DJ Wallwork KS 《Journal of the American Chemical Society》2011,133(6):1654-1657
The technetium perovskite CaTcO(3) has been synthesized. Combining synchrotron X-ray and neutron diffraction, we found that CaTcO(3) is an antiferromagnetic with a surprisingly high Neel temperature of ~800 K. The transition to the magnetic state does not involve a structural change, but there is obvious magnetostriction. Electronic structure calculations confirm the experimental results. 相似文献
999.
Rusakov DA Belik AA Kamba S Savinov M Nuzhnyy D Kolodiazhnyi T Yamaura K Takayama-Muromachi E Borodavka F Kroupa J 《Inorganic chemistry》2011,50(8):3559-3566
Solid solutions InMn(1-x)Ga(x)O(3) (0 ≤ x ≤ 1) have been investigated using magnetic, dielectric, specific heat, differential scanning calorimetry (DSC), and high-temperature powder synchrotron X-ray diffraction (HT-SXRD) measurements. It was found that samples with 0.5 ≤ x ≤ 1 crystallize in space group P6(3)/mmc with a ~ 3.32 ? and c ~ 11.9 ?, and samples with 0.0 ≤ x ≤ 0.4 crystallize in space group P6(3)cm with a ~ 5.8 ? and c ~ 11.6 ? at room temperature. HT-SXRD data revealed the existence of a P6(3)cm-to-P6(3)/mmc phase transition at about 480 K in InMn(0.6)Ga(0.4)O(3) and at 950 K in InMn(0.7)Ga(0.3)O(3). However, no dielectric, phonon, second-harmonic-generation, or DSC anomalies were found to be associated with these phase transitions. The phase transition should be improper ferroelectric from the symmetry point of view, but the above-mentioned experimental facts, together with the absence of ferroelectric hysteresis loops, revealed no evidence for ferroelectricity in the low-temperature P6(3)cm structure. We suggest that InMn(1-x)Ga(x)O(3) corresponds to a nonferroelectric phase of hexagonal RMnO(3) with P6(3)cm symmetry. The antiferromagnetic phase-transition temperature decreases from 118 K for x = 0 to 105 K for x = 0.1 and 73 K for x = 0.2, and no long-range magnetic ordering could be found for x ≥ 0.3. Specific heat anomalies associated with short-range magnetic ordering were observed for 0.0 ≤ x ≤ 0.5. InMn(1-x)Ga(x)O(3) with small Mn contents (0.8 ≤ x ≤ 0.98) has a bright-blue color. 相似文献
1000.
Freydin Maxim Dowell Earl H. Spottswood S. Michael Perez Ricardo A. 《Nonlinear dynamics》2021,103(4):3019-3036
Nonlinear Dynamics - The transient response of a plate and a cavity is investigated in a supersonic wind tunnel start experiment where the freestream flow inside the test section reaches turbulent... 相似文献