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91.
The doped fiber amplifier has already emerged as the indispensable potential candidate for repeaterless transmission of information processed through single mode. Therefore the fundamental modal field in the doped single-mode fiber needs to be accurately prescribed both in the pump as well as the signal to facilitate further study of their variation with distance. Based on the novel approximation of the fundamental modal field in graded-index fiber, we formulate analytical expression as regards the variation of modal intensity with radial distance from the axis of the fiber both for the pump and the signal fields and estimate such variation for step-index fiber of some typical V values as example. We find that our estimation matches excellently with the available exact results in case of both the pump and the signal and is shown to be much superior to one-parameter Gaussian approximation. In addition, our methodology involves less computation compared to the exact analysis involving cumbersome computation. 相似文献
92.
The process of infrared multiple photon dissociation (IRMPD) of molecules is of great fundamental importance and has practical
significance, such as isotope separation etc. Unfortunately, a clear insight into the process has been hindered by the bewildering
array of important variables affecting MPD. The dissociation probability γ (φ) i.e. the yield has been found to be a sensitive
function of laser fluence φ along with numerous other parameters like laser frequency, gas pressure etc. We have shown that
in single frequency IRMPD, an accurate quantitative characterization of the dissociation probability can be adequately expressed
by a ‘power law’ model with two fitting parameters namely critical fluence, φc and multiphoton order,m. This model was exploited in analysing our MPD results on various systems. However, the small isotope shift encountered in
heavy elements and the sticking phenomenon observed in small light molecules restrict respectively the separation factor and
the dissociation yield. These problems can effectively be tackled by irradiation with multifrequency laser beams which can
be chosen appropriately on the basis of spectroscopic features. Based on our success in single frequency model, multifrequency
IRMPD is modelled by a functional form containing the product of power law terms for individual fluences on irradiation frequencies.
This model is successfully benchmarked with our experimental results on multifrequency LIS of tritium. Such knowledge can
be utilized for appropriate separation process design, evaluation and optimization. 相似文献
93.
94.
A. Chatterjee A. Sarkar Sourav Bhattacharya P. Mukherjee N. Gayathri P. Barat 《Physics letters. A》2008,372(22):4016-4020
Tensile tests were carried out by deforming polycrystalline samples of substitutional Al–2.5%Mg alloy at room temperature for a range of strain rates. The Portevin–Le Chatelier (PLC) effect was observed throughout the strain rate regime. The deformation bands in this region are found to be of type A in nature. From the analysis of the experimental stress time series data we could infer that the dynamics of type A dislocation band propagation is a Markov process. 相似文献
95.
Daniel C. Steigerwald Bardia Soltanzadeh Aritra Sarkar Cecilia C. Morgenstern Richard J. Staples Babak Borhan 《Chemical science》2021,12(5):1834
Intermolecular asymmetric haloamination reactions are challenging due to the inherently high halenium affinity (HalA) of the nitrogen atom, which often leads to N-halogenated products as a kinetic trap. To circumvent this issue, acetonitrile, possessing a low HalA, was used as the nucleophile in the catalytic asymmetric Ritter-type chloroamidation of allyl-amides. This method is compatible with Z and E alkenes with both alkyl and aromatic substitution. Mild acidic workup reveals the 1,2-chloroamide products with enantiomeric excess greater than 95% for many examples. We also report the successful use of the sulfonamide chlorenium reagent dichloramine-T in this chlorenium-initiated catalytic asymmetric Ritter-type reaction. Facile modifications lead to chiral imidazoline, guanidine, and orthogonally protected 1,2,3 chiral tri-amines.Intermolecular haloamination reactions are challenging due to the high halenium affinity of the nitrogen atom. This is circumvented by using acetonitrile as an attenuated nucleophile, resulting in an enantioselective halo-Ritter reaction. 相似文献
96.
S. Sarkar G. Erlebacher M. Y. Hussaini 《Theoretical and Computational Fluid Dynamics》1991,2(5-6):291-305
The purpose of this study is to investigate compressibility effects on the turbulence in homogeneous shear flow. We find that the growth of the turbulent kinetic energy decreases with increasing Mach number—a phenomenon which is similar to the reduction of turbulent velocity intensities observed in experiments on supersonic free shear layers. An examination of the turbulent energy budget shows that both the compressible dissipation and the pressure-dilatation contribute to the decrease in the growth of kinetic energy. The pressure-dilatation is predominantly negative in homogeneous shear flow, in contrast to its predominantly positive behavior in isotropic turbulence. The different signs of the pressure-dilatation are explained by theoretical consideration of the equations for the pressure variance and density variance. We previously obtained the following results for isotropic turbulence: first, the normalized compressible dissipation is of O(M
t
2
), and, second, there is approximate equipartition between the kinetic and potential energies associated with the fluctuating compressible mode. Both these results have now been substantiated in the case of homogeneous shear. The dilatation field is significantly more skewed and intermittent than the vorticity field. Strong compressions seem to be more likely than strong expansions.Dedicated to Professor J.L. Lumley on the occasion of his 60th birthday.This research was supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-18605 while the authors were in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 23665, U.S.A. 相似文献
97.
In this study, it is demonstrated that silver nanoparticles can be transferred from formamide to chloroform using oleic acid as a phase transfer agent with a transfer efficiency of 90–95%. The silver nanoparticles are initially formed as an organosol by the reduction of silver ions with formamide. On aging the complex, the particles self-assemble to form an ordered close-packed two-dimensional array of silver nanocrystals when dissolved in CHCl3. The size distribution of the colloidal silver particles after transfer in different solvents remains almost the same. On the basis of IR spectroscopy, we discuss the adsorption of oleic acid over the silver particles. 相似文献
98.
Sarkar M Aromí G Cano J Bertolasi V Ray D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(46):13825-13833
A high-spin Co(II) cluster with a rare pentagonal molecular structure and formula [Co(5)(CO(3))(2)(bpp)(5)]ClO(4) (1; Hbpp is 2,6-bis(phenyliminomethyl)-4-methylphenolate) has been synthesized and characterized by single-crystal X-ray diffraction. This topology arises from fusing five [Co(2)(bpp)] moieties in a cyclic manner around two CO(3)(2-) central ligands, resulting in propeller-like configuration. The irregular coordination of the carbonate ions to the metal centers results in a combination of coordination numbers (CNs) of the Co(II) ions of five and six. The bulk magnetization of this complicated magnetically exchanged system has been modeled successfully by employing a matrix diagonalization technique. For this, the combination of S=3/2 ions (CN=5) with ions exhibiting strong spin-orbit coupling (CN=6) has been considered and a perturbative approach to handle the data in the whole studied range of temperatures (2-300 K) yielding parameters of g and D (for the five-coordinate Co(II) ions), of A, κ, λ, and Δ (for the metals with spin-orbit coupling) and of the exchange constants J. The agreement with results from DFT calculations, also presented here, is remarkable. 相似文献
99.
Sengupta P Sarkar AK Bhaumik U Chatterjee B Roy B Chakraborty US Pal TK 《Biomedical chromatography : BMC》2010,24(12):1342-1349
A simple, high‐throughput and specific high‐performance liquid chromatography tandem mass spectrometry method has been developed and validated according to the FDA guidelines for simultaneous quantification of olmesartan and pioglitazone in rat plasma. The bioanalytical method consists of liquid–liquid extraction and quantitation by triple quadrupole mass spectrometry using electrospray ionization technique, operating in multiple reaction monitoring and positive ion modes. The compounds were eluted isocratically on a C18 column with a mobile phase consisting of a mixture of methanol and water (containing 0.5% formic acid) in a ratio of 9:1. The response to olmesartan and pioglitazone was linear over the range 0.01–10 µg/mL. The validation results demonstrated that the method had satisfactory precision and accuracy across the calibration range. Intra‐ and inter‐day precisions ranged from 0.66 to 3.32 and from 0.94 to 2.93% (%CV), respectively. The accuracy determined at three quality control levels was within 91.27–107.28%. There was no evidence of instability of the analytes in rat plasma following the stability studies. The method proved highly reproducible and sensitive and was successfully applied in a pharmacokinetic study after single dose oral administration of olmesartan and pioglitazone to the rat. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
100.