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991.
YAN Zi-Feng 《天然气化学杂志》1996,5(3):261-271
Introduction0ncofthcintriguingpr0blcmsinhctcrogcncouscatal}'sisisthcactit'ationanddircctconversionofmcthancintoliquidfucIanduscful.h..i..l,lllMcthancactivationisvcry'difficultbccauscn1cthancisathcrmod}'namicalI}'stablccompoundt`ithanoblcgas-likcconfigurati0nThcvcry'strongtctrahcdralC-Hbonds(435kJ/mol)offcrnofiJnctionalgroups,magncticm0mcnts'orpolardistortionstofacilitatcchcmicalattackThismakcsmcthanelcssrcactivcthanncarl}'allitsconvcrsionproducts.Rccentl}'oxidativccouplinghasbecnconsidcrcda… 相似文献
992.
Eiichi Kobayashi Shojiro Kaita Sadahito Aoshima Junji Furukawa 《Journal of polymer science. Part A, Polymer chemistry》1995,33(13):2175-2182
Homo- and copolymerizations of butadiene (BD) and styrene (St) were carried out by gadolinium catalysts having various tricarboxylate ligands [Gd(OCOR)3: R = CH3, CH2Cl, CHCl2, CCl3, and CF3], to investigate the effects of ligands and discuss the cis polymerization mechanism. Polymerization of BD with Gd(OCOR)3—(i—Bu)3Al—Et2AlCl catalysts was carried out in hexane at 50°C. By each catalyst, poly(BD) having a high cis content (cis = 97–99%) in 22–85% yields for 2–24 h were obtained. The ligands with low pKa values increased the polymerization activity as follows: R of Gd(OCOR)3: CF3 > CCl3 > CHCl2 > CH2Cl ~ CH3. On the other hand, in the polymerization of St or copolymerization of BD and St under similar conditions, the highest activity was attained by a Gd(OCOCCI3)3- based catalyst. The difference in the optimum ligand among the homo- and copolymerization of BD and St was discussed on the basis of energy levels of the catalysts. In the copolymers of BD and St, the cis-1,4 content of the BD unit decreased with increasing St content. Furthermore, according to the diad analysis of copolymers (St content ~ 14.5 mol %) by 13C NMR spectroscopy, the low cis value of the BD unit was observed in the St-BD diad (cis/trans/vinyl = 24/53/23), while the high cis value of the BD unit remained in the BD-BD diad (cis/trans/vinyl = 89/10/1). These results suggest that the terminal BD unit is controlled by the cis configuration by the coordination between the penultimate cis vinylene unit and the gadolinium metal catalyst, whereas the presence of the penultimate St unit interferes with cis polymerization of the terminal BD unit. The difference in the coordination mechanism in the course of polymerization between rare earth metal and transition metal catalysts such as the Ni(acac)2 and Co(acac)3-based catalyst was also discussed. © 1995 John Wiley & Sons, Inc. 相似文献
993.
100公里以上的大气分子离子主要为NO~+。它的辐射特点及它与电子、原子或分子的相互作用,对于理解大气的化学过程具有特别重要的意义。为了研究这些过程,确定NO~+分子离子基态及其各个激发态的分子势能函数是非常重要的。精确的X~1Σ~+,A~1Ⅱ和a~3∑~+势能曲线已发表;基于光电子谱的研究发现了NO~+的其它激发态,但对于这些激发态的研究尤其是势能函数的研究不多。本文研究并导出NO~+的基态和10个激发态的势能函数。 相似文献
994.
A method is described for the gas-chromatographic determination of the diastereomers of vitamin K1 (phylloquinone) in the form of their dihydro dimethyl ethers. The reported method of derivatization and chromatographic analysis in conjunction with optical rotation measurements are useful approaches for characterization of vitamin K1 samples with respect to their origin. 相似文献
995.
Bo Jiang Lixing Yang Yong Zhou Guanglin Huang Libin Lin 《Radiation Physics and Chemistry》2002,63(3-6):469-473
The radiation-induced hybrid polymerization in the presence of the N-alkoxypyridinium salt having relatively stable nonnucleophilic anion (PF6−) has been investigated in the paper. Based on the analysis of experimental data and the GPC spectrum, the onium salts not only oxidize -alkoxyalkyl radicals, produced from IBVE in dichloromethane by irradiation, to the corresponding cations, but also give nonnucleophilic anions PF6− for the polymerization system. The experimental results clearly demonstrate that free radical and cationic polymerization mechanisms occurred simultaneously in IBVE/EMP+PF6−/CH2Cl2 systems on irradiation with γ-ray. 相似文献
996.
The enthalpy of oxidation of SrFe1-xCoxO3-d with x=0.33 and 0.67 has been determined by adiabatic calorimetry; average values for x=0.33 and 0.67 are -67±11 and -49.5±9 kJ (mol O2)-1. These data and the previously reported value for SrFeO3-d suggest that the enthalpy of oxidation for pure (perovskite-type) SrCoO3-d is close to zero. Earlier reported composition - partial pressure data for SrFe0.67Co0.33O3-d are reproduced when preferential oxidation of iron is assumed for low partial pressures of oxygen.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
We present a method for computing classical Newtonian trajectories that minimize the path length or transit time from reactant
to product. Our approach is based on a generalization of the fast-marching method, which allows us to construct the solution
of the Hamilton-Jacobi equation for the action that optimizes the desired quantity. The resulting “reactive paths” can be
interpreted as reaction coordinates but, unlike more conventional choices, they contain dynamical information about the chemical
system of interest. 相似文献
998.
Tao Miao 《Tetrahedron letters》2007,48(1):95-99
The immobilization of copper in organic-inorganic hybrid materials catalyzing the Ullmann reaction has been described. Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl functionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-supported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials without loss of its reactivity. 相似文献
999.
Marti E. Kaisersberger E. Emmerich W.-D. 《Journal of Thermal Analysis and Calorimetry》2004,77(3):905-934
The definitions of the temperature resolution, the so-called resolution of DSC instruments given in literature are discussed.
A new definition of the resolution for DSC instruments is presented and outlined. The main characteristic introduced in this
new definition is a minimum between two caloric events as a prerequisite of an existing resolution. Possible candidates of
test substances have been evaluated. The oligomer n-hexatriacontane is revealing an interesting phenomenon, namely a lambda
transition which is in the peak temperature only 2 K lower than the melting temperature of 76°C. The substance was selected
as an ideal test substance for the quantification of the resolution of DSC instruments. The lambda transition is a second
order process which may reach under certain conditions the saturation of the occurring molecular dislocation within 0.2 K,
and after saturation the heat flow rate drops sharply down. Investigations concerning the main characteristics of n-hexatriacontane
in respect to the temperatures of transition (lambda transition and melting), to the involved enthalpies, and to the resolution
factors were performed as functions of the sample mass and the heating rate. The importance of relevant evaluation procedures
increasing the resolution factors of DSC curves are discussed and these procedures are integrated into the testing of the
resolution. The necessity for widening the experimental scope from instruments to evaluation procedures is forced by the existence
of instruments with built-in signal treatments based on electronic devices and software procedures. A comparison with literature
data is outlined for all of the mentioned characteristic values of n-hexatriacontane.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
1000.
Sung Woo Moon Gun-Dae Lee Seong Soo Park Seong-Soo Hong 《Reaction Kinetics and Catalysis Letters》2004,82(2):303-310
Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO2 was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared
by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VOx/TiO2catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However,
in the VOx/TiO2catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result
suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared
to the impregnation method.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献