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81.
Gottfried Lichti Brian S. Hawkett Robert G. Gilbert Donald H. Napper David F. Sangster 《Journal of polymer science. Part A, Polymer chemistry》1981,19(4):925-938
Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or γ-radiation. The unswollen PSDs at various times during interval II of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments. 相似文献
82.
The new methylidene trinickel cluster complexes, [RCNi3(η5-C5H53] (R CMe3 or SiMe3) and [Me3SiCNi3(η5-C5H5)2(η5-C5H4CH2SiMe3)] have been isolated in low yield from reactions between nickelocene and the corresponding alkyllithium reagents, RCH2Li. The compounds [RCNi3(η5-C5H5)3] (R Ph, CMe3 or SiMe3) have also been obtained by treatment of the σ-alkylnickel complexes [(η5-C5H5)Ni(CH2R)(PPh3)] with n-BuLi in the presence of an excess of nickelocene, but under similar conditions [(η5-C5H5)Ni(CH2C1OH7-2)-(PPh3)] (where C1OH7-2 2-naphthyl) failed to give [2-C1OH7CNi3(η5-C5H5)3]. The attempted synthesis of [(η5-C5H5)Ni(CH2CCH)(PPh3)] from [(η5-C5H5)-NiBr(PPh3)] and CHCCH2MgBr gave only [(η5-C5H5)Ni(CCMe)(PPh3)] by an unusual rearrangement reaction. 相似文献
83.
The dynamic behaviour of [Pt(/gh3-allyl){P(cyclohexyl)3}2]+[PF6]- has been reinvestigated, and the earlier interpretation of restricted rotation about the Pt—P endorsed. The activation parameters were obtained. [Pt(/gh3-allyl)(PPri3)2]+[PF6]- behaves similarly, while it has not prove possible to stop the rotation in [Pt(/gh3-allyl){P(CH2Ph)3}2]+[PF6]-. 相似文献
84.
The products of hydrolysis of C60F48 (which contains six isolated double bonds) by either aq. acetone or aq. THF show that no more than twelve fluorines are replaced through nucleophilic substitution, as predicted by the recently identified S(N)2' mechanism. Subsequent HF elimination gives fragments containing a maximum of six epoxide oxygens. Calculated heats of formation of models for the possible initial hydroxy derivatives indicate that there is little energetic discrimination between them, so that a complex mixture is likely to be formed. Overall the data show that hydrolytic degradation of fluorofullerenes is less severe than believed previously, requires a specific motif, and explains the low susceptibility of C60F18 towards hydrolysis and the high stability of trannulenes. 相似文献
85.
Fry B Silva SR Kendall C Anderson RK 《Rapid communications in mass spectrometry : RCM》2002,16(9):854-858
Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the delta(34)S isotopic composition of plants, animals and soils. We found that the online technology for automated delta(34)S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO(2) produced, and as a result calculated delta(34)S values were often 1-3 per thousand too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO(2)-SiO(2) buffering method that minimizes detrimental oxygen isotope variations in SO(2). 相似文献
86.
Dimitris K. Agrafiotis Brian Tansy Andrew Streitwieser 《Journal of computational chemistry》1990,11(9):1101-1110
Two new computational methods for the evaluation and partitioning of projected, planar, and averaged slab electron densities, implemented in the program PRODEN, are presented. The new algorithms for the projection, demarcation, and integration of electron densities are described and evaluated in terms of speed and numerical accuracy. Integrated Projected Populations are analyzed and some of the advantages and limitations of the methods are discussed. 相似文献
87.
The ab initio Neglect of Differential Diatomic Overlap (N.D.D.O.) method of Roby is tested numerically for an extensive series of molecules. Agreement with the full ab initio molecular orbital method is poor. Total energies are more negative and dipole moments are overestimated. The failings of the N.D.D.O. method are accounted for using multipole-multipole expansions. 相似文献
88.
-Methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside undergoes the Wadsworth- Emmons cyclopropanation with phosphonopropionate to give a cyclopropyl carboxylate which is processed to give the gem-dimethylcyclopropano pyranoside. The glycosylic acetal of this substance is readily hydrolyzed by boiling water, and the resulting cis-cyclopropane carboxaldehyde may be epimerized quantitatively to the trans-analog by treatment with sodium methoxide. These aldehydes are now converted into the (+)- and (-)-chrysanthemum dicarboxylic acids, respectively, by the same sequence of reactions involving (a) olefination with methyl 2-(triphenylphosphoranylidene)propionate, (b) hydro- lysis of the benzylidine ring and cleavage of the resulting triol with sodium metaperiodate, and (c) oxidation of the resulting aldehyde with silver I oxide. In the case of the (+)-enantiomer the last reaction is proceeded by epimerization. The overall yields from the D-allopyranoside are respectively 27%, in 10 steps for the (+)-enantiomer, and 24%, in 10 steps for the (-)-enantiomer, from the known epoxide 7. 相似文献
89.
The reactions of NaCo(CO)4 with MenSiCl4?n (n = 0–3) in diethylether (Et2O) and in tetrahydrofuran (THF) have been studied. Three distinct reaction pathways were recognised which depend on the acidity of the chlorosilane and basicity of solvent. Attack at the silicon centre via the Co atom of Co(CO)4? leads to formation of a SiCo bond; reaction involving a CO ligand of Co(CO)4? gives clusters R3SiOCCo3(CO)9; and chlorosilane induced attack of Co(CO)4? on the solvent gives products derived from THF molecules. 相似文献
90.
Five routes to stable chlorins bearing 0 or 1 meso substituents have been investigated, among which reaction of a 9-bromo-1-formyldipyrromethane and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin proved most effective. Application of this route afforded metallochlorins [Cu(II), Zn(II), and Pd(II)] including the chlorin lacking any β-pyrrole and meso substituents. 相似文献