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排序方式: 共有327条查询结果,搜索用时 15 毫秒
81.
1mThODUCT'ONSomecomPOundsofN--thionophosphonylandN,N'--his(thionophosphonyl)thiOSemicarbazideshaveattractedmuchattentionandbeenextensivelystudiedinrecentyears"~'i.ThiskindofcomPOundsareknowntohaveobviousantibacterialandantifungalactivitiest3}.TherearetwochiralphosphoratomsinthecomPOundsofN,N'--his(thionophosphonyl)thiosemicarbazide.Inordertostudyfurthertherelationshipbetweenthestructureandbiologicalactivities,hereinwerePOrtthecrystalstructureofakindofN,N'--his(thionophosphonyl)thiose… 相似文献
82.
83.
Olivier J.-C Nicaise 《Tetrahedron》2003,59(34):6433-6443
The temperature-dependent formation of a remarkably stable enol from the reaction of EtMgBr with a 1,2-diester was accidentally discovered. This compound was spectroscopically characterized (1H and 13C NMR, IR), and both methyl carbonate and trimethylsilyl ether derivatives were prepared. A mechanism for the selective formation of the stable enol ester and its corresponding keto form was suggested, and the kinetic stability of the enol was also documented. The generality of the observation of such a stable enol ester was demonstrated with the use of other Grignard reagents, and also other 1,2-diesters. The reaction of EtMgBr with a series of 1,2-amide esters also produced stable enol amides. The remarkable stability of the enol esters was attributed to the steric hindrance present in the aryl ester moiety of these compounds, and further studies will address the origin of this effect. 相似文献
84.
85.
With a polarized double‐zeta basis set, we carried out MP2 and density functional theory geometry optimization of bis(2,2′‐bipyridine) interacting either with Cu(I) or Ag(I). The computed gas‐phase geometries of both Cu and Ag complexes present tetrahedral distortions around the ions. However, geometry optimization on Cu or Ag ions complexing with ammonia molecules yield perfect tetrahedral coordination and interaction energies comparable to those of the bis(2,2′‐bipyridine) complexes. Solid‐state laboratory studies on complexes of the same metal ions with substituted bis(2,2′‐bipyridine) revealed tetrahedral distortions around the ions, even stronger than those computed in the gas phase. From our analysis of the potential interaction energies we conclude that the origin of the larger distortions in the solid state result from stacking interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 395–404, 2003 相似文献
86.
Preparation and Crystal Structure of BaLi[BO3] For the first time colourless lamellar single crystals of BaLi[BO3] have been prepared from intimate mixtures of BaO2, Li2O and B2O3. The structure determination from four-circle diffractometer data (MoKα , 882 independent reflections, R = 2.4%, Rw = 1.9%) confirms the space group P 21/c with Z = 4; a = 646.1(3), b = 710.7(2), c = 740.3(3) pm, β = 117.99(3)°. Characteristic units of the structure are layers {Li[BO3]} parallel to (100) consisting of trigonal planar [BO3] groups and distorted [LiO5] pyramids. Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR), the Madelung Part of Lattice Energy (MAPLE) and the Charge Distribution (CHARDI) are calculated and discussed. 相似文献
87.
《Indagationes Mathematicae》2017,28(2):601-611
We study qualitative properties of solutions of an integral equation associated the Benjamin–Ono–Zakharov–Kuznetsov operator. We establish the regularity of the positive solutions without the assumption of being in fractional Sobolev–Liouville spaces. Moreover we show that the solutions are axially symmetric. Furthermore we establish Lipschitz continuity and the decay rate of the solutions. 相似文献
88.
掺Nd3+的Sr3 Gd(BO3)3晶体的激光特性 总被引:1,自引:0,他引:1
介绍了一种新的硼酸盐激光晶体Nd^3+:Sr3Gd(BO3)3的激光特性.采用氙灯作为泵浦源,获得激光输出为17.84mJ,总效率ηo=0.092%,曲线的斜效率ηs=0.27%.实验表明Nd^3+:Sr3Gd(BO3)3晶体是一种新的有潜在应用价值的激光晶体. 相似文献
89.
Joydeep Choudhury Srinivasa Rao Karumuri Nirmal Kumar Sarkar Ramendu Bhattacharjee 《Pramana》2008,71(3):439-445
The stretching and bending vibrational energies of SnBr4 and CCl4 are calculated in the one-dimensional framework. The dynamical symmetry group of tetrahedral molecule was taken into consideration
to construct the model Hamiltonian in this framework. Casimir and Majorana invariant operators were also determined accordingly.
Using the model Hamiltonian so constructed, we reported the vibrational energy levels of SnBr4 and CCl4 molecules accurately.
相似文献
90.
In a recent paper by the first author, a simple proof was given of a result by Tutte on the validity of barycentric mappings,
recast in terms of the injectivity of piecewise linear mappings over triangulations. In this note, we make a short extension
to the proof to deal with arbitrary tilings. We also give a simple counterexample to show that convex combination mappings
over tetrahedral meshes are not necessarily one-to-one.
Mathematics subject classifications (2000) 05C10, 05C85, 65D17, 58E20 相似文献