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11.
The title intermediate () is produced on photolysis of hexakis(2,6-diethyl-phenyl)cyclotrigermane () or bis(2,6-diethylphenyl)bis(trimethylsilyl)germane () as evidenced by trapping experiments, and thermally dimerizes to tetrakis(2,6-diethyl-phenyl)digermene (). Diarylgermylenes such as do not form stable triethylamine adducts (e.g. ) as has been previously reported. 相似文献
12.
J. D. Menczel G. L. Collins S. K. Saw 《Journal of Thermal Analysis and Calorimetry》1997,49(1):201-208
Vectra® liquid crystalline polymers (LCP's) were introduced as commercial products in the mid-1980's. The first of these (Vectra A130) was a wholly aromatic thermotropic copolyester ofp-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. Vectra A130 is a thermotropic LCP that can be melt spun into filaments that on heat treatment are characterized by high strength and high modulus. Vectra resin can also be extruded into films. In the fiber or film form this material is commercially known as Vectran®. Heat treatment enhances the tensile strength of Vectran fiber variants. Because of this, the elucidation of the physical transformations taking place in the internal structure of the material during heating has always been an important subject. Several thermal techniques are used to indicate clearly that what is observed as a glass transition is unlike the conventional glass transition in typical semicrystalline polymers. There is also an indication of the presence of multiple states of mesophase aggregation that collapse into a single state when taken to high enough temperatures. 相似文献
13.
Copolymerization of a monomer X with an existing polymer yields a copolymer contaminated by poly-X homopolymer and ungrafted polymer. Measurements on the pure copolymer can yield only the molecular weights of the cumulative backbone portion and of the cumulative graft portion. However, if the grafts can be isolated, then the molecular weights of their individual chains may be determined also. Since it is not isolatable, the backbone is not amenable to similar treatment. Equations are derived for the molecular weights (of any average) of individual backbone chains; they are expressed in terms of the following experimentally accessible quantities: (i) molecular weight of original polymer; (ii) molecular weight of ungrafted portion: and (iii) fraction by weight of the original polymer which remains ungrafted. The procedure is thus the analogue, applied to the backbone, of chemical isolation applied to the grafts. The treatment has been examined for copolymers prepared by grafting acrylic acid to nylon-6 by mutual irradiation. 相似文献
14.
P. A. Beeley J. M. Brushwood M. G. Henesy M. W. Collins C. A. Haywood 《Journal of Radioanalytical and Nuclear Chemistry》1997,215(1):135-139
The measurement of16N and18F activity in the primary coolant of the JASON Argonaut reactor has been used to monitor in-core reactor power. The16N is produced by the16O(n, p)16N reaction and the 6.1 MeV photopeak was measured on-line using a BGO detector adjacent to the primary coolant circuit. These data provided a relative measure of power stability during steady state operation and a measure of linearity at different power levels. The18F is produced in the primary coolant by the18O(p, n)18F reaction and aliquots of primary coolant were sampled from the reactor dump tank for off-line radiochemical analysis. The18F was separated as trimethylfluorosilane and the activity was determined by measurement of the 0.511 MeV annihilation photopeak using a NaI(TI) detector. The measured18F activity was used to determine actual in-core reactor power using both ab-initio calculations and by comparison of results with a calibrated power reactor. The18F data also provided a method of nomalising the16N data for direct monitoring of in-core reactor power in JASON. 相似文献
15.
Fry FH Holme AL Giles NM Giles GI Collins C Holt K Pariagh S Gelbrich T Hursthouse MB Gutowski NJ Jacob C 《Organic & biomolecular chemistry》2005,3(14):2579-2587
Certain cancer cells proliferate under conditions of oxidative stress (OS) and might therefore be selectively targeted by redox catalysts. Among these catalysts, compounds containing a chalcogen and a quinone redox centre are particularly well suited to respond to the presence of OS. These catalysts combine the specific electrochemical features of quinones and chalcogens. They exhibit high selectivity and efficiency against oxidatively stressed rat PC12, human Jurkat and human Daudi cells in cell culture, where their mode of action most likely involves the catalytic activation of existent and the generation of new reactive oxygen species. The high efficiency and selectivity shown by these catalysts makes them interesting for the development of anti-cancer drugs. 相似文献
16.
Michael A. Collins 《Theoretical chemistry accounts》2002,108(6):313-324
This paper reviews the construction of molecular potential-energy surfaces by an interpolation method which has been developed
over the last several years. The method uses ab initio quantum chemistry calculations of the molecular electronic energy in
an automated procedure to construct global potential- energy surfaces which can be used to simulate chemical reactions with
either classical or quantum dynamics. The methodology is explained and several applications are presented to illustrate the
approach.
Received: 22 February 2002 / Accepted: 2 May 2002 / Published online: 6 November 2002
Correspondence to: M. A. Collins e-mail: collins@rsc.anu.edu.au
Acknowledgements. The methods described in this overview are the result of collaborations with former members of my group, in particular with
Josef Ischtwan, Meredith Jordon, Keiran Thompson and Ryan Bettens. I am also indebted for inspiration gained from many discussions
with my colleagues Leo Radom and Donghui Zhang (National University of Singapore). This work has been supported by the Supercomputer
Facility of the Australian National University and the Australian Partnership for Advanced Computing. 相似文献
17.
Josef Ischtwan Peter Schwerdtfeger Sigrid D. Peyerimhoff Michael A. Collins Trygve Helgaker Poul Jørgensen Hans Jørgen Aa. Jensen 《Theoretical chemistry accounts》1994,89(2-3):157-168
Summary The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (3–)+H2 (1
g
+
) NH2 (2B1)+H (2S) involving the lowest triplet electronic state of NH3 were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol–1 agrees with the experimental value within 2 kcal mol–1. The barrier to reaction is 23.4 kcal mol–1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H2, whereas those of the reverse reaction are by a factor of 20 larger than those of OH2 with H. 相似文献
18.
K. E. Collins M. L. M. M. Granja R. G. Pereira Filho T. A. Anazawa I. C. S. F. Jardim 《Chromatographia》1997,45(1):99-103
Summary Poly(methyloctylsiloxane) (PMOS), sorbed into the pores of HPLC silica particles by solvent evaporation, can function as a
useful stationary phase for reversed-phase chromatography. The present work addresses the question of how the PMOS is distributed
in the pores. Measurements of the surface area (BET, N2) of a series of partially loaded samples (0–40% PMOS, m/m) using a typical batch of HPLC silica (10 μm irregular particles
with 6 nm pores) show that the specific surface area of the samples decreases linearly with the specific loading (mass of
PMOS per gram of silica). This result is not consistent with a “film” model in which the PMOS is deposited uniformly on the
pore walls, but is consistent with a model in which long segmented “plugs” of PMOS are deposited within the pore system.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
19.
A preconcentration procedure was established for sulphate determination in rain waters at the mg/l level, employing a small column packed with the AG1-X8 (200-400 mesh) anionic resin inserted into a flow injection system. Sulphate determination was performed by using the turbidimetric method based on reaction with barium. For concentrations within 0.10 and 2.0 MgSO(2-)(4)/l, a throughput of 50 determinations/hr was achieved, and the relative standard deviation of results was better than 2%. 相似文献
20.
Sibrina N. Collins Constance M. Brett Bruce E. Bursten 《Journal of Cluster Science》2004,15(4):469-487
The photochemical CO-loss products of the diruthenium complexes [CpRu(CO) 2]2 (5; Cp = 5-C5H5), [Cp*Ru(CO)2]2 (5*; Cp* = 5-C5(CH3)5) and CpCp*[Ru(CO)2]2 (5) have been studied experimentally in low-temperature (96 K) matrices in 3-methylpentane by using IR spectroscopy. It is proposed that all three complexes undergo single-CO-loss chemistry but that the products have different structures. The single-CO-loss product from 5 is proposed to have one bridging and two terminal carbonyl ligands, whereas 5* and 5 generate triply bridged CO-loss products similar to that observed from [CpFe(CO)2]2 and [Cp*Fe(CO)2]2. Double-CO-loss from 5* and 5*
9 is also apparently observed. Relativistic DFT calculations have been carried out on various isomers of the starting materials and on potential CO-loss products from 5. The calculations suggest that the triply bridged product Cp2Ru2(-CO)3 (6) might have a singlet ground state in contrast to the corresponding diiron complex Cp2Fe2(-CO)3 (3), which has a triplet ground state. 相似文献