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121.
Mostafa Shazly Vikas Prakash Bradley A. Lerch 《International Journal of Solids and Structures》2009,46(6):1499-1515
In the present study, a modified split Hopkinson pressure bar (SHPB) is employed to investigate the dynamic response of ice under uniaxial compression in the range of strain rates from 60 to 1400 s?1 and at initial test temperatures of ?10 and ?30 °C. The compressive strength of ice shows positive strain-rate sensitivity over the range of strain rates employed; a slight influence of ice microstructure is observed, but it is much less than that reported previously for ice deformation under quasi-static loading conditions [Schulson, E.M., IIiescu, D., Frott, A., 2005. Characterization of ice for return-to-flight of the space shuttle. Part 1 – Hard ice. NASA CR-2005-213643-Part 1]. Specimen thickness, within the range studied, was found to have little or no effect on the peak (failure) strength of ice, while lowering the test temperature from ?10 to ?30 °C had a considerable effect, with ice behaving stronger at the lower test temperature. Moreover, unlike in the case of uniaxial quasi-static compression of ice, the effect of specimen end-constraint during the high rate compression was found to be negligible. One important result of these experiments, which may have important implications in modeling ice impacts, involves the post “peak-stress” behavior of the ice in that the ice samples do not catastrophically lose their load carrying capacity even after the attainment of peak stress during dynamic compression. This residual (tail) strength of the damaged/fragmented ice is sizable, and in some cases is larger than the quasi-static compression strength reported for ice. Moreover, this residual strength is observed to be dependent on sample thickness and the strain rate, being higher for thinner samples and at higher strain-rates during dynamic compression. 相似文献
122.
A p-adic modification of the split-LBG classification method is presented in which first clusterings and then cluster centers
are computed which locally minimize an energy function. The outcome for a fixed dataset is independent of the prime number
p with finitely many exceptions. The methods are applied to the construction of p-adic classifiers in the context of learning. 相似文献
123.
Stephen M. Lipson Ashley J. Cadby Paul A. Lane Diarmuid F. O’Brien Anna Drury Donald D. C. Bradley Werner J. Blau 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):151-158
Summary. We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer
poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert
atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces
polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption.
It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and
non-radiative quenching routes, thus resulting in increased PL efficiency.
Received June 23, 2000. Accepted (revised) August 3, 2000 相似文献
124.
125.
Lowell H. Hall Bradley J. Orchard Sukant K. Tripathy 《International journal of quantum chemistry》1987,31(2):195-216
Molecular orbital calculations (MINDO /3) using energy minimized molecular geometries were performed on oxidized and reduced lumiflavin and related methylated isoalloxazines, including cationic and anionic species. Close agreement with experimental geometry, photoelectron spectra, and NMR data supports the importance of optimized geometries for these molecular systems and provides the basis for interpretation of chemical and biological properties. Oxidized forms are shown to be most stable in the planar configuration but also highly flexible about the N(5)—N(10) axis; only 1 kcal/mol is required for a 10° bend. N(10) is generally out of the plane slightly; also, C(9)-methyl substitution introduces nonplanarity. The unsubstituted isoalloxazine is computed to be 0.76 kcal/mol (ΔH) less stable than its isomer, alloxazine. Calculations were also performed on enol as well as quinone-methide tautomeric forms. Reduced flavin geometry depends on methyl substitution pattern: N(10) substituted forms are bent with typical fold angles around 155°, whereas the unsubstituted reduced form is planar. Both oxidized and reduced forms are also flexible. Proton affinities were calculated for protonation and deprotonation of oxidized and reduced forms. Protonation of oxidized forms is favored at N(1) by 10–12 kcal/mol and produces somewhat nonplanar isoalloxazinium ions. In addition, ΔH for the two-electron reduction of lumiflavin is estimated to be ?19.7 kcal/mol. In this paper investigations of geometric aspects are presented along with introductory and background material. Orbital structure and electron distribution studies are presented in paper II. 相似文献
126.
127.
A.S. Al-Shahrany D. Bradley M. Lawes R. Woolley 《Proceedings of the Combustion Institute》2005,30(1):225-232
A new technique is reported for measuring burning velocities at high pressures in the final stages of two inwardly propagating flame kernels in an explosion bomb. The flames were initiated at diametrically opposite spark electrodes, close to the wall, in quiescent mixtures. Measurements of pressure and flame kernel propagation speeds by high-speed photography showed the burning velocities to be elevated above the corresponding laminar burning velocities as a result of the developing flame instabilities. The enhancement increased with increase in pressure and decreased with increase in Markstein number. When the Markstein number was negative, instabilities could be appreciable, as could the enhancement. For the iso-octane–air mixtures investigated, where the mixtures had well-characterised Markstein numbers or critical Peclet numbers at the relevant pressures and temperatures, it was possible to explain the enhancement quantitatively by the spherical explosion flame instability theory of Bechtold and Matalon, provided the critical Peclet number was that observed experimentally, and allowance was made for the changing pressure. With this theoretical procedure, it was possible to derive values of laminar burning velocity from the measured values of burning velocity over a wide range of equivalence ratios, pressures, and temperatures. The values became less reliable at the higher temperatures and pressures as the data on Markstein and critical Peclet numbers became less certain. It was found that with iso-octane as the fuel the laminar burning velocity decreased during isentropic compression. 相似文献
128.
D. I. Bradley J. P. White C. J. Ashworth J. Rikovska N. J. Stone 《Hyperfine Interactions》1987,35(1-4):1033-1036
The Oxford top-loading PrNi5 nuclear demagnetisation stage /1/ has been further developed to reach temperatures below 1 mK. The hyperfine field for71As in nickel has been measured by low temperature nuclear orientation as 14.61(36)T. Measurements on transitions in71Ge yield spin values 3/2 (1299 kev and 1139 kev) and 5/2 (1027 kev) and 5 E2/M1 mixing ratios are given. 相似文献
129.
Richard C. Bradley 《Probability Theory and Related Fields》1989,81(1):1-10
Summary A strictly stationary finite-state non-degenerate random sequence is constructed which satisfies pairwise independence and absolute regularity but fails to satisfy a central limit theorem. The mixing rate for absolute regularity is only slightly slower than that in a corresponding central limit theorem of Ibragimov.This work was partially supported by NSF grant DMS 86-00399 相似文献
130.
Bobby G. Poe III Ciarán F. Duffy Michael A. Greminger Bradley J. Nelson Edgar A. Arriaga 《Analytical and bioanalytical chemistry》2010,397(8):3397-3407
Mitochondrial DNA (mtDNA) mutations have been associated with disease and aging. Since each cell has thousands of mtDNA copies,
clustered into nucleoids of five to ten mtDNA molecules each, determining the effects of a given mtDNA mutation and their
connection with disease phenotype is not straightforward. It has been postulated that heteroplasmy (coexistence of mutated
and wild-type DNA) follows simple probability rules dictated by the random distribution of mtDNA molecules at the nucleoid
level. This model has been used to explain how mutation levels correlate with the onset of disease phenotype and loss of cellular
function. Nonetheless, experimental evidence of heteroplasmy at the nucleoid level is scarce. Here, we report a new method
to determine heteroplasmy of individual mitochondrial particles containing one or more nucleoids. The method uses capillary
cytometry with laser-induced fluorescence detection to detect individual mitochondrial particles stained with PicoGreen, which
makes it possible to quantify the mtDNA copy number of each particle. After detection, one or more particles are collected
into polymerase chain reaction (PCR) wells and then subjected to real-time multiplexed PCR amplification. This PCR strategy
is suitable to obtain the relative abundance of mutated and wild-type mtDNA. The results obtained here indicate that individual
mitochondrial particles and nucleoids contained within these particles are not heteroplasmic. The results presented here suggest
that current models of mtDNA segregation and distribution (i.e., heteroplasmic nucleoids) need further consideration. 相似文献