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131.
132.
Stephan Jüngling Rolf Mülhaupt Udo Stehling Hans-Herbert Brintzinger David Fischer Franz Langhauser 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1305-1317
Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me2Si(Benz[e]Indenyl)2ZrCl2 ( BI ) and rac-Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2 ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H2-addition, which affords active metallocene hydrides. This effect of H2-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc. 相似文献
133.
The OH--catalysed hydrolysis of p-nitroacetanilide and p-nitroacetanilide-1-d3 has been studied between pH11·5 and 13·5 at 30°. The value of the secundary isotope effect is changed with respect to the OH--concentration. The inverse istope effects at high OH--concentrations (Hkkorr/Dkkorr = 0·87 ±0·05) and the opposite effects in the lower OH?-concentration ranges (Hkkorr/Dkkorr = 1·08 ± 0·04)are discussed on the basis of change in the rate limiting step. 相似文献
134.
From solutions of chromium(III) perchlorate and periodic acid, single crystals of γ‐HIO3 were obtained and characterized by single‐crystal X‐ray diffraction, Raman spectroscopy and thermal analysis. The compound crystallizes in the orthorhombic crystal system, space group Pbca (a = 563.92, b = 611.10, c = 1507.16 pm). The structure is built up by dimers (HIO3)2, which are formed by hydrogen bonds. The crystals are metastable and transform into the stable modification, α‐HIO3, within a couple of weeks. 相似文献
135.
Frank Herwig Köhler Hans Jürgen Kalder Ernst Otto Fischer 《Journal of organometallic chemistry》1975,85(2):C19-C22
Carbon-13 NMR data are reported for trimethyltin derivatives containing ERn groups where E C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ 2J(119SnE13C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ERn groups in the concentrated solutions studied. 相似文献
136.
The preparation, the spectroscopic characterization, the crystal structure and chemical reactions of the new six-membered heterocyclic betaine2 are reported; 2 is a representative of a possibly large group of yet unkonwn betaines of the general structure 8. 相似文献
137.
Palladium(II) bromide reacts with gallium(III) bromide in the presence of arenes yielding binuclear palladium(I) complexes [Pd2(GaBr4)2(arene)2], where arene=benzene (1), toluene (2) and p-xylene (3). Reaction of palladium(II) chloride with gallium(III) chloride in p-xylene leads to the analogous palladium(I) compound [Pd2(GaCl4)2(p-xylene)2] (4); the X-ray structures of 1-4 were determined. 相似文献
138.
Werner Marty Pramesh N. Kapoor Hans-Beat Bürgi Erwin Fischer 《Helvetica chimica acta》1987,70(1):158-170
The bidentate diphosphine ligand, 3,3′-oxybis[(dipenylphosphino)methylbenzene] ( 1 ) forms monomeric, trans-square-planar complexes MX2( 1 ) (M = Ni, Pd, Pt; X = Cl?, Br? I?, and, in part, N, NCS?, CN?, NO) as well as Pt(H)Cl( 1 ), Pt(H)Br( 1 ), and RhCl(CO)( 1 ). Polymeric species have been observed with substitutionally inert metal centres: trans-[PtCl2( 1 )]2 and cis-[PtCl2( 1 )]n (mean value of n ≈ 4–5) 31P-NMR, and selected IR and UV/VIS parameters are reported. Ligand 1 shows a marked preference for trans-spanning and monomeric chelate formation, despite its various degrees of freedom of internal rotation in the lignad backbone. The readily available ligand 1 as well as analogues with other donor atoms, therefore, appear useful in most potential applications of trans-spanning chelate ligands. The crystal structure of AgCl( 1 )·0.5 (CH3)2C?O·0.39 C6H12 (space group C2/c,a = 21.02 Å, b = 14.57 Å, c = 24.79 Å, β = 99.77°, V = 7531.4 Å3, Z = 8) confirms the presence of three-coordinate Ag( I ), with a coordination intermediate between a trigonal-planar and a T-shaped geometry (P-Ag-P = 145.61(8)°). 相似文献
139.
Fischer CJ Gafni A Steel DG Schauerte JA 《Journal of the American Chemical Society》2002,124(35):10359-10366
The interpretation of room temperature phosphorescence studies of proteins requires an understanding of the mechanisms governing the tryptophan triplet-state lifetimes of residues fully exposed to solvent and those deeply buried in the hydrophobic core of proteins. Since solvents exposed tryptophans are expected to behave similarly to indole free in solution, it is important to have an accurate measure of the triplet state lifetime of indole in aqueous solution. Using photon counting techniques and low optical fluence (J/cm(2)), we observed the triplet-state lifetime of aqueous, deoxygenated indole and several indole derivatives to be approximately 40 micros, closely matching the previous reports by Bent and Hayon based on flash photolysis (12 micros; Bent, D. V.; Hayon, E. J. Am. Chem. Soc. 1975, 97, 2612-2619) but much shorter than the 1.2 ms lifetime observed more recently (Strambini, G. B.; Gonnelli, M. J. Am. Chem. Soc. 1995, 117, 7646-7651). However, we have now been able to reproduce the long lifetime reported by the latter workers for aqueous indole solutions and show that it likely arises from geminate recombination of the indole radical cation and solvated electron, a conclusion based on studies of the indole radical cation in water (Bent and Hayon, 1975). The evidence for this comes from a fast rise in the phosphorescence emission and measurements of a corresponding enhanced quantum yield in unbuffered solutions. This species can be readily quenched, and the corresponding fast rise disappears, leaving a monoexponential 40 micros decay, which we argue is the true indole triplet lifetime. The work is put in the context of room temperature phosphorescence studies of proteins. 相似文献
140.
Dieter Naumann Prof. Dr. Wieland Tyrra Dr. Hendrik T. M. Fischer Silke Kremer 《无机化学与普通化学杂志》2007,633(4):527-528
Tetrakis(pentafluorophenyl)tellurium(IV), Te(C6F5)4, was prepared from the reaction of TeCl4 and Mg(C6F5)Br. Crystallization of the crude product from n‐pentane at ?25 °C gave suitable single crystals. The title compound crystallizes in the monoclinic space group P21/c (Z = 8) with two independent molecules per unit cell. 相似文献