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991.
Computational investigations are reported on the local flow and heat transfer characteristics from staggered, multiple circular
air jets impinging on a flat surface with effusion holes. The geometrical and flow parameters for the computational study
are chosen as per the experimental arrangement of Cho and Rhee J Turbomachinery 123:601–608, (14) so as to explain salient features observed in these experiments. The two peaks in the Nusselt number observed in the case
of H/D = 6 and three peaks in the case of H/D = 2 are attributed to the flow characteristics such as primary vortices forming
an up-wash region, followed by secondary vortices resulting in a secondary stagnation zone. The magnitude of local peak in
heat transfer increases up to 88% with increasing values of D/d from 0.5 to 1.5 at Re = 10,000. 相似文献
992.
Enantioselective formal synthesis of macrolactone palmerolide A, a polyketide marine natural product, is described. Key strategies in the synthesis include the oxidative furan ring-opening of a chiral furyl carbinol for the installation of the 1,4-dienol core and a Jung nonaldol-aldol reaction for the dienamide core. 相似文献
993.
A highly active catalytic system for the carbonylation of meso- and terminal epoxides to β-lactones is described. The active catalyst, analogous to Coates' catalyst, is generated in situ from commercially available (TPP)CrCl and Co(2)(CO)(8). This practical system circumvents the preparation of air sensitive cobaltate salts, operates at low catalyst loadings, and allows the carbonylation of functionalized, sterically demanding and heterocyclic meso-epoxides. 相似文献
994.
K. Vajravelu K. V. Prasad Robert A. Van Gorder Jinho Lee 《Transport in Porous Media》2011,90(3):977-992
Numerical solutions for the free convection heat transfer in a viscous fluid at a permeable surface embedded in a saturated
porous medium, in the presence of viscous dissipation with temperature-dependent variable fluid properties, are obtained.
The governing equations for the problem are derived using the Darcy model and the Boussinesq approximation (with nonlinear
density temperature variation in the buoyancy force term). The coupled non-linearities arising from the temperature-dependent
density, viscosity, thermal conductivity, and viscous dissipation are included. The partial differential equations of the
model are reduced to ordinary differential equations by a similarity transformation and the resulting coupled, nonlinear ordinary
differential equations are solved numerically by a second order finite difference scheme for several sets of values of the
parameters. Also, asymptotic results are obtained for large values of | f
w|. Moreover, the numerical results for the velocity, the temperature, and the wall-temperature gradient are presented through
graphs and tables, and are discussed. It is observed that by increasing the fluid variable viscosity parameter, one could
reduce the velocity and thermal boundary layer thickness. However, quite the opposite is true with the non-linear density
temperature variation parameter. 相似文献
995.
996.
B. RiscobS.K. Kushwaha Mohd. ShakirK. Nagarajan K.K. MauryaD. Haranath S.D.D. RoyG. Bhagavannarayana 《Physica B: Condensed Matter》2011,406(23):4440-4446
Single crystals of l-histidine nitrate (LHN), a recently investigated nonlinear optical material, were grown by conventional solution technique. Crystal structure and vibrational modes of the grown crystals were confirmed by powder X-ray diffractometry and FT-Raman spectrometry, respectively. Crystalline perfection of the grown crystals was evaluated by employing an in-house developed high-resolution X-ray diffractometer (HRXRD) and it was found that the grown crystals were free from structural grain boundaries and the perfection was reasonably good. However, HRXRD could reveal the fact that the crystals contain predominantly the interstitial point defects. The birefringence was measured over a range of wavelength between 5480 and 5630 Å and it was found that its value is nearly constant and 10 times higher than that of KDP. The optical band gap was found to be ∼3.73 eV. The photoluminescence excitation and emission spectra for single crystals were recorded. The SHG efficiencies of LHN samples of different particle sizes were measured by the Kurtz and Perry technique and they removed the ambiguity in the values reported differently in the literature. Dielectric properties were studied as a function of temperature over a wide range of frequency. The optical and dielectric studies along with the crystalline perfection reveal that the LHN crystal could be a good candidate for nonlinear optical devices. 相似文献
997.
Amodini MishraS.N. Choudhary K. Prasad R.N.P. Choudhary 《Physica B: Condensed Matter》2011,406(17):3279-3284
The polycrystalline sample of Ba(Pr1/2Ta1/2)O3 was prepared by a high-temperature solid-state reaction technique. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase tetragonal structure with the space group P4/mmm (1 2 3). Impedance and electric modulus analysis were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The impedance analysis of the compound indicated a typical negative temperature coefficient of resistance behavior, and dielectric relaxation was found to be of non-Debye type. The frequency dependent maximum of the imaginary part of the electric modulus follows the Arrhenius law with activation energy of 0.15 eV. The ac conductivity data obeys double power law. 相似文献
998.
Synthesis and characterization of di- and trivalent pyrazolylborate β-diketonates and cyanometalates
Tang M Li D Mallik UP Zhang YZ Clérac R Yee GT Whangbo MH Mungalimane A Holmes SM 《Inorganic chemistry》2011,50(11):5153-5164
The syntheses, structures, and magnetic properties of a series of di- and trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates are described. Treatment of tris(acetylacetonate)manganese(III) [Mn(acac)(3)] with KTp* and tetra(ethyl)ammonium cyanide affords [NEt(4)][(Tp*)Mn(II)(κ(2)-acac)(CN)] (1), as the first monocyanomanganate(II) complex; attempted oxidation of 1 with iodine affords {(Tp*)Mn(II)(κ(2)-acac(3-CN))}(n) (2) as a one-dimensional chain and bimetallic {[NEt(4)][(Tp*)Mn(II)(κ(2)-acac(3-CN))](2)(μ-CN) (3) as the major and minor products, respectively. A fourth complex, [NEt(4)][(Tp*)Mn(II)(η(2)-acac(3-CN))(η(1)-NC-acac)] (4), is obtained via treatment of Mn(acac(3-CN))(3) with KTp* and [NEt(4)]CN, while [NEt(4)](2)[Mn(II)(CN)(4)] (5) was prepared from manganese(II) trifluoromethanesulfonate and excess [NEt(4)]CN. Tricyanomanganate(III) complexes, [cat][(Tp*)Mn(III)(CN)(3)] [cat = NEt(4)(+), 7; PPN(+), 8], are prepared via sequential treatment of Mn(acac(3-CN))(3) with KTp*, followed by [NEt(4)]CN, or [cat](3)[Mn(III)(CN)(6)] with (Tp*)SnBu(2)Cl. Magnetic measurements indicate that 1, 2, and 4 contain isotropic Mn(II) (S = (5)/(2); g = 2.00) centers, and no long-range magnetic ordering is found above 1.8 K. Compounds 7 and 8 contain S = 1 Mn(III) centers that adopt singly degenerate spin ground states without orbital contributions to their magnetic moments. 相似文献
999.
Papia Datta Ambika Prasad Mukhopadhyay César J. Pastor 《Journal of organometallic chemistry》2011,696(2):488-166
Cr, Mo and W tetracarbonyl complexes of 2-(2-pyridyl)benzoxazole (PBO) and 2-(2-pyridyl)benzothiazole (PBT) are spectroscopically characterised. The confirmatory structure of [Mo(CO)4(PBO)] has been determined by X-ray crystallography. The complexes show negative solvatochromic effect, with increasing solvent polarity the MLCT band is shifted to longer wavelength region. Cyclic voltammetry shows M(I)/M(0) redox response and also exhibit fluorescence spectra at room temperature. The electronic structures of the complexes are calculated by density functional theory (DFT) and time dependent-DFT calculated results are used to explain redox property and electronic transitions. 相似文献
1000.
A convergent synthesis of the orally active renin inhibitor aliskiren (1) is described. The synthesis was accomplished in 12 steps starting from the known chloride 2. The key step involves the Curtius rearrangement of the advanced intermediate 15, which provides lactone/carbamate 17 containing the correct stereochemistry and all of the functionality required for the preparation of the drug substance. 相似文献