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131.
Abstract— The lowest-lying triplet states of a variety of aromatic molecules and complexes have been generated by the irradiation of these compounds in solvent glasses with plane-polarized light. Measurements of the allowed (Δ M=± 1) ESR transitions clearly demonstrate that the triplets so formed are oriented with respect to the external magnetic field. By this method the triplet zero-field splitting parameters, D and E , can be evaluated simply and reliably. Intramolecular energy transfer is postulated to explain the triplet spectra of Zn( o -phen)2 (NO3 )2 and Zn( o -phen)3 (NO3 )2 . It was observed that in triplet-triplet energy transfer from benzophenone to naphthalene there is no apparent orientation requirement between the donor and acceptor molecules. Further areas of significance and application of this technique are suggested. 相似文献
132.
Ben Yahia H Gaudin E Darriet J Banks M Kremer RK Villesuzanne A Whangbo MH 《Inorganic chemistry》2005,44(9):3087-3093
A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange. 相似文献
133.
Ben C. Freasier 《Chemical physics letters》1975,35(2):280-282
A monte-Carlo calculation has been made for 108 hard core dumbbells of the compressibility factor in the isotropic density range. These compressibility factors are compared to several approximate theories, and comments are made on the utility of these approximate theories. 相似文献
134.
The EPR spectrum of 17O? on partially reduced molybdenum oxide supported on silica-gel has been observed following adsorption of N2O at room temperature. The spectrum is chracterized by g⊥=2.019 and g|=2.002 with a|17O?=96±1 G and a|95MO,97MO=7.5±0.5 G. The O ?ion appears to undergo exchange with oxide ions at the surface. 相似文献
135.
L. G. Chalmet R. L. Francis J. F. Lawrence 《Journal of Optimization Theory and Applications》1980,32(2):135-149
An example of design might be a warehouse floor (represented by a setS) of areaA, with unspecified shape. Givenm warehouse users, we suppose that useri has a known disutility functionf
isuch thatH
i(S), the integral off
iover the setS (for example, total travel distance), defines the disutility of the designS to useri. For the vectorH(S) with entriesH
i(S), we study the vector minimization problem over the set {H(S) :S a design} and call a design efficient if and only if it solves this problem. Assuming a mild regularity condition, we give necessary and sufficient conditions for a design to be efficient, as well as verifiable conditions for the regularity condition to hold. For the case wheref
iis thel
p-distance from warehouse docki, with 1<p<, a design is efficient if and only if it is essentially the same as a contour set of some Steiner-Weber functionf
=1
f
1++
m
f
m
,when the
i
are nonnegative constants, not all zero.This research was supported in part by the Interuniversity College for PhD Studies in Management Sciences (CIM), Brussels, Belgium; by the Army Research Office, Triangle Park, North Carolina; by a National Academy of Sciences-National Research Council Postdoctorate Associateship; and by the Operations Research Division, National Bureau of Standards, Washington, D.C. The authors would like to thank R. E. Wendell for calling Ref. 16 to their attention. 相似文献
136.
Lawrence E. Thomas 《Communications in Mathematical Physics》1980,77(3):211-218
Let 1 and 2 be thermodynamic Gibbs measures on
m
and
n
, respectively. Diffusions are constructed having 1, and 2 as invariant measures. These diffusions are then coupled; inequalities between expectations of certain random variables on the two spaces result.Partially supported by NSF-MCS 74-07313-A03 相似文献
137.
Francis P. Gasparro Paola Gattolin Gerard A. Olack Lawrence I. Deckelbaum Bauer E. Sumpio 《Photochemistry and photobiology》1993,57(S1):1007-1009
Abstract— The formation of 8-methoxypsoralen-DNA monoadducts and cross-links is presumed to be responsible for the efficacy of photochemotherapies that employ 8-methoxypsoralen activated with long-wavelength ultraviolet radiation (UVA,320–400 nm). In this report it is shown that 8-methoxypsoralen can also be activated with visible light (419 nm). Bovine aorta smooth muscle cells were treated with 8-methoxypsoralen (1000 ng/mL) and 419 nm light (up to 12 J/cm2 ). Cellular DNA was isolated, hydrolyzed using nucleolytic enzymes and then analyzed by reversed-phase high-performance liquid chromatography. The primary effect of using visible light instead of long-wavelength ultraviolet radiation is a more than 10-fold reduction in the extent of cross-link formation. Because the extent of monoadduct and cross-link formation has not been routinely measured in experiments in which cellular assays have been performed, it is difficult to correlate cell response to the presence of a particular type of 8-methoxypsoralen photoadduct (monoadduct or cross-link). Thus, the use of visible light allows the study of cells containing nearly 100% monoadducts. In addition, the reduction in cross-link formation when visible light is used to activate the compound may also reduce the mutagenicity of 8-methoxypsoralen and hence enhance its therapeutic efficacy. 相似文献
138.
V. Pichon H. Rogniaux N. Fischer-Durand S. Ben Rejeb F. Le Goffic M. -C. Hennion 《Chromatographia》1997,45(1):289-295
Summary The trace-level determination of organic pollutants in complex matrices is difficult and often not reliable because theccurrent
extraction procedures are non-selective. New extraction sorbents involving antigen-antibody interactions, called immunosorbents
(ISs), have been synthesised in order to trap a group of structurally related pollutants. The IS capacity is always high for
the analyte-antigen used to make the antibodies, but can be low for some related compounds. In this work, we show the relationship
that exists between capacity, break-through volume and recovery of analytes because of the competition between the structurally
related compounds for antibody sites. Breakthrough due to the overloading of the column should be avoided because calibration
curves are no longer linear. The capacity of two ISs, one made for trapping the triazine pesticide group and the second for
the phenylurea, group, have been optimised by selecting silica with 50 nm pore size. Calibration curves are linear for all
the compounds in a mixture of ten phenylureas up to a concentration of 5 to 10 μg L−1 for each compound when handling 50 mL water samples through a precolumn packed with 0.22 g of IS. Under these conditions,
reliable quantitative results are obtained because calibration curves are similar when compounds are alone or in a mixture.
Application to the clean-up of soil extracts illustrates the high selectivity and the high potential of these new sorbents
in environmental analysis.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
139.
Ben Ghoulam M Moatadid N Graciaa A Lachaise J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2584-2589
Phase behaviors of water/nonionic surfactants/isooctane systems are determined experimentally in temperature-global surfactant concentration diagrams. The surfactants are monodistributed polyoxyethylene glycol n-dodecyl ether. They are used as model mixtures of two, three, or five compounds or as constituents of a commercial surfactant. It is found that the phase diagrams of these systems are bent gradually toward the highest temperatures as the global surfactant concentration decreases. Each phase diagram is well-characterized by the curve of the HLB (hydrophile-lipophile balance) temperature versus the global surfactant concentration. For any fixed global surfactant concentration, this temperature is the middle temperature of the three-phase region; it can be calculated from an additive rule of the HLB temperatures of the surfactants weighted by their mole fractions at the water/oil interface. These mole fractions are determined through the pseudophase model using surfactant partitioning. Calculations require the knowledge of the critical micelle concentration, the partition coefficient between water and oil, and the HLB temperature of each surfactant of the mixture. This treatment can be used to correctly predict the variation of the HLB temperatures of the surfactant mixtures studied versus the global surfactant concentration. Furthermore, these calculations show that the observed curvature of the phase diagrams at the lowest global concentrations is due to the most favorable partitioning toward the oil of the lowest ethoxylated surfactant molecules. 相似文献
140.
The neutral dimethyl pentamethylcyclopentadienylzirconium acetamidinate, (eta(5)-C(5)Me(5))ZrMe(2)[N(t-Bu)C(Me)N(Et)], can serve as a highly active initiator for the living Ziegler-Natta polymerization of alpha-olefins to produce polyolefins of narrow polydispersity (D < or = 1.05) when "activated" through mono demethylation by a substoichiometric amount of the borate, [PhNMe(2)H][B(C(6)F(5))(4)]. The mechanism by which this living polymerization proceeds is through a process of degenerative transfer involving rapid and reversible methyl group exchange between cationic (active) zirconium propagating centers and neutral (dormant) methyl, polymeryl zirconium end groups. Facile metal-centered epimerization of the dormant species is responsible for a loss of stereocontrol during propagation that produces iso-rich material in contrast to the pure isotactic polymer microstructure obtained when degenerative transfer is not present. By turning degenerative transfer "on" and "off" between successive monomer polymerizations, a successful strategy for the production of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length has been demonstrated. 相似文献