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991.
F.G. Fuchs A.D. McMurry S. Mishra N.H. Risebro K. Waagan 《Journal of computational physics》2010,229(11):4033-4058
Wave propagation in idealized stellar atmospheres is modeled by the equations of ideal MHD, together with the gravity source term. The waves are modeled as small perturbations of isothermal steady states of the system. We consider a formulation of ideal MHD based on the Godunov–Powell form, with an embedded potential magnetic field appearing as a parameter. The equations are discretized by finite volume schemes based on approximate Riemann solvers of the HLL type and upwind discretizations of the Godunov–Powell source terms. Local hydrostatic reconstructions and suitable discretization of the gravity source term lead to a well-balanced scheme, i.e., a scheme which exactly preserves a discrete version of the relevant steady states. Higher order of accuracy is obtained by employing suitable minmod, ENO and WENO reconstructions, based on the equilibrium variables, to construct a well-balanced scheme. The resulting high order well-balanced schemes are validated on a suite of numerical experiments involving complex magnetic fields. The schemes are observed to be robust and resolve the complex physics well. 相似文献
992.
Rupali Mishra Raghvendra S. Yadav Avinash C. Pandey Sharda. S. Sanjay 《Journal of luminescence》2010,130(3):365-198
We report the formation of highly stable and luminescent ZnO@Cd(OH)2 core-shell nanoparticles by simple introduction of cadmium salt in the initial precursor solution, used to synthesize ZnO nanoparticles by sol-gel route. The cadmium to zinc salt concentration ratio has been also varied to control the growth of ZnO nanoparticles at the smaller particle size. Formation of ZnO@Cd(OH)2 core-shell nanostructure has been confirmed by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). UV-vis absorption spectroscopy exhibits blue-shift in absorption edge on increasing cadmium concentrations. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO@Cd(OH)2 nanoparticles in comparison to bare ZnO nanoparticles. It is postulated that Cd(OH)2 layer at the surface of ZnO nanoparticles prevents the agglomeration of nanoparticles and efficiently assists the trapping of hole at the surface site, a first step necessary for visible emission. The Fourier transform infrared spectroscopy (FTIR) also supports our assumption about surface chemistry. 相似文献
993.
Anuj Soni M.S. Kulkarni D.R. Mishra S.K. Gupta D.N. Sharma 《Journal of luminescence》2010,130(7):1308-497
Single crystals of α-Al2O3 (10×10 mm2, 0.4 mm thick) were annealed in vacuum at about 1500 °C in the ambience of boron. The OA studies on these samples showed bands at 203, 232 and 258 nm signifying that such a treatment leads to the formation of F and F+ centers in significant concentrations, these bands, however, were not found in the Al2O3 crystals processed in the similar manner in the absence of boron. The Al2O3:B samples were irradiated to different absorbed doses of 90Sr/90Y β-source and the continuous wave OSL (CW-OSL) was recorded on the samples using 470 nm blue light stimulation. These samples have shown a linear TL and CW-OSL response in the dose range of 20 mGy to 15 Gy. The minimum detectable dose, corresponding to 3σ limit of the variation of the output of the unirradiated dosimeters, was found to be 100 μGy. Irradiated samples stored in dark at room temperature for a period of two months show negligible fading. The TL and OSL sensitivities of the samples were found to be strongly dependent on process temperature and time. The TL response is marked by the absence of low temperature peak (<100 °C), unlike the case of α-Al2O3:C, implying that the boron doping does not lead to formation of shallow traps. The Al2O3:B samples show faster photoionisation cross-section as compared to α-Al2O3:C. This approach of processing of single crystal Al2O3 in the boron ambience thus represents a potential way of introducing dosimetrically pertinent defects in Al2O3 single crystals. 相似文献
994.
Measurements of the local susceptibility and 3d spin relaxation rate for single Fe impurities embedded in a nanocrystalline Nb host indicates the emergence of a local moment on Fe at and below a critical size of 11?nm. Our ab?initio electronic structure calculations show that the moment formation occurs due to Stoner enhancement arising from a size dependent lattice expansion and a consequent shift in the Fermi level. We also show that a size-induced positive host spin polarization of the Nb-4d band electrons strongly influences the fluctuation rate of the Fe moment. 相似文献
995.
Green luminescence and degradation of Ce3+ doped CaS nanocrystalline phosphors were studied with a 2 keV, 10 μA electron beam in an O2 environment. The nanophosphors were synthesized by the co-precipitation method. The samples were characterized using X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy/electron dispersive X-ray spectroscopy and Photoluminescence (PL) spectroscopy. Cubic CaS with an average particle size of 42 ± 2 nm was obtained. PL emission was observed at 507 nm and a shoulder at 560 nm with an excitation wavelength of 460 nm. Auger electron spectroscopy and Cathodoluminescence (CL) were used to monitor the changes in the surface composition of the CaS:Ce3+ nanocrystalline phosphors during electron bombardment in an O2 environment. The effect of different oxygen pressures ranging from 1 × 10−8 to 1 × 10−6 Torr on the CL intensity was also investigated. A CaSO4 layer was observed on the surface after the electron beam degradation. The CL intensity was found to decrease up to 30% of its original intensity at 1 × 10−6 Torr oxygen pressure after an electron dose of 50 C/cm2. The formation of oxygen defects during electron bombardment may also be responsible for the decrease in CL intensity. 相似文献
996.
V. Pulhani S. Kayasth A. K. More U. C. Mishra 《Journal of Radioanalytical and Nuclear Chemistry》2000,243(3):625-629
Radioactive elements like 232Th and 238U along with their daughter products, form part of all environmental matrices and are getting transferred to living beings by different pathways, leading to a continuous radiation exposure and need to be monitored. This paper presents an analytical methodology, highlighting the need to separate interfering beta- and gamma-emitters from the analytes, when neutron activation analysis is employed for the determination of traces of uranium and thorium in soil and plant materials. The method has been applied to the soil and plant materials from selected regions of India, along with standard reference materials to verify the validity of the proposed separation scheme. The overall reproducibility of the procedure was 2–10%. The concentration values of uranium and thorium so obtained, have been used to calculate transfer factors from soil to various parts of wheat plant. 相似文献
997.
Cantilever steel beams of uniform strength are having various industrial applications. In particular when it is used as leaf
spring it undergoes very large deflection in comparison to beam of uniform cross section. The damage occurs in these beams
mainly due to fatigue loading. Early detection of damage in such type of beams is very essential to avoid a major failure
or accident. In this paper, firstly formulation of an objective function for the genetic search optimization procedure along
with the residual force method are presented for the identification of macroscopic structural damage in an uniform strength
beam. Two cases have been investigated here. In the first case the width is varied keeping the strength of beam uniform throughout
and in the second case both width and depth are varied to represent a special case of uniform strength beam. The developed
model require experimentally determined data as input and detect the location and extent of the damage in the beam. Here,
experimental data are simulated numerically by using finite element models of structures with inclusion of random noise on
the vibration characteristics. It has been shown that the damage may be identified for the said problems with a good accuracy. 相似文献
998.
Devdutt Chaturvedi Nisha Mishra Amit K. Chaturvedi Virendra Mishra 《Monatshefte für Chemie / Chemical Monthly》2008,139(12):1467-1470
A single-step novel protocol for the preparation of symmetrical trithiocarbonates from a corresponding variety of primary,
secondary, and tertiary alcoholic tosylates using the Cs2CO3/CS2 system, was developed. This protocol is mild and more efficient than the reported methods.
Correspondence: Devdutt Chaturvedi, Bio-Organic Chemistry Division, Indian Institute of Integrative Medicine, Canal Road,
Jammu-Tawi-18000, J&K, India. 相似文献
999.
Devdutt Chaturvedi Amit K. Chaturvedi Nisha Mishra Virendra Mishra 《Monatshefte für Chemie / Chemical Monthly》2008,139(12):1463-1466
A quick and efficient, one-pot synthesis of carbazates was accomplished in high yields by the reaction of various primary,
secondary, and tertiary alkyl halides with a variety of substituted hydrazines using the benzyltrimethylammonium hydroxide
(Triton-B)/CO2 system. The reaction conditions are mild with simpler work-up procedures than the reported methods.
Correspondence: Devdutt Chaturvedi, Bio-Organic Chemistry Division, Indian Institute of Integrative Medicine, Canal Road,
Jammu-Tawi 18000, J&K, India. 相似文献
1000.
O. N. Srivastava A. Srivastava D. Dash D. P. Singh R. M. Yadav P. R. Mishra J. Singh 《Pramana》2005,65(4):581-592
TiO2 nanostructured films have been synthesized by the hydrolysis of Ti[OCH(CH3)2]4 as the precursor. These films have been utilized for the dissociation of phenol contaminant in water. Free-standing nanostructured
film of silicon carbide (SiC) has been synthesized, employing a simple and new route of spray pyrolysis technique utilizing
a slurry of Si in hexane. Another study is done on organized carbon nanotube (CNT) structures. These are made in the form
of hollow cylinders (50 mm length, 4 mm diameter and 1.5 mm wall thickness). These CNT-based cylinders are made of conventional
CNT and bamboo-shaped CNT. The filtrations of heavy hydrocarbons andE. coli bacteria from water have been carried out. In addition to this, ZnO nanostructures have also been studied. Another study
concerns CNT-blood platelet clusters. 相似文献