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51.
52.
Basant Kumar Jha 《Heat and Mass Transfer》2005,41(8):675-679
This study addresses the Brinkman-extended Darcy model (Brinkman flow) of a laminar free-convective flow in an annular porous region. Closed form expressions for Velocity field, Temperature field, Skin-friction and Mass flow rate are given, under a thermal boundary condition of mixed kind at the outer surface of the inner cylinder while the inner surface of the outer cylinder is isothermal. The governing independent parameters are identified to be Darcy number (Da) and ratio of outer to inner radii (R). It is hoped that the study of such flows gives limiting conditions for developing flows and provides an analytical check on numerical solutions for more complex problems dealing with non-Darcian free-convection flow in an annular region. 相似文献
53.
N. Kumar S. K. Jha S. S. Chaturvedi 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(3):525-533
Radiation dose-risk assessment was carried out for cereal species Brassica compestris var. dichotoma, Oryza sativa var. Shalum1, Zea mays, Lactuca indica, Cumunis sativum, and Clocasia esculanta due to naturally available radionuclides 40K, 238U and 232Th in Domiasiat area. The activity in biota and corresponding soil was measured by precipitation method using NaI(TI) detector.
Transfer factor (TF) was for Oryza spp. (1.00E−01-40K, 8.76E−05-232Th, and 9.11E−05-238U), for Brassica spp. (5.39E−01-40K, 8.17E−04-232Th and 2.96E−04-238U) and for Zea spp. (3.41E−01-40K, 5.84E−05-232Th, 8.87E−05-238U) etc., respectively. A detailed physio-morphological study of the biota and extensive investigation of ecosystem was carried
out for assessment. The data was modeled using FASSET for dose estimation and obtained total dose was 1.58E−04
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1} in Oryza spp., 2.87E−04
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1}
Brassica spp. and 6.90E−03
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1} in Zea spp. etc. The dose was compared with the UNSCEAR dataset for screening level dose for biota. Zea spp. was more susceptible for the chronic radiation exposure. 相似文献
54.
It is well‐established that exposure of aqueous suspensions of titanium dioxide (TiO2) nanoparticles to ultraviolet A (UVA) light produces reactive oxygen species which leads to biological damage. However, there is disagreement in the literature as to the exact nature of these species and how they are formed. Using a number of different spin traps (i.e. PBN, POBN, DMPO, DEPMPO), we have shown that the primary damaging species produced on irradiation of an aqueous suspension of TiO2 is the hydroxyl radical, which is formed at the valence band hole under both aerobic and hypoxic conditions. Hydroxyl radical production is enhanced by the presence of oxygen which probably reacts with the conduction band electrons or resultant Ti3+, inhibiting hole‐electron recombination, although we find no evidence of reaction of oxygen to form free superoxide radical anions or of the formation of any other radical at that site. The present results suggest that the resulting O2 ?? species may not be as labile as previously thought and may possibly undergo further reduction to the O 2 2? dianion. Hydroxyl radicals formed at the surface of the TiO 2 readily react with substrates containing an abstractable hydrogen to produce secondary radicals that, in biological systems, could lead to cell damage. 相似文献
55.
Jha M Ramanujachary KV Lofland SE Gupta G Ganguli AK 《Dalton transactions (Cambridge, England : 2003)》2011,40(31):7879-7888
A new process has been developed for the synthesis of nanocrystalline niobium oxide and niobium diboride using an amorphous niobium precursor obtained via the solvothermal route. On varying the ratio of niobium precursor to boron and the reaction conditions, pure phases of nanostructured niobium oxides (Nb(2)O(5), NbO(2)), niobium diboride (NbB(2)) and core-shell nanostructures of NbB(2)@Nb(2)O(5) could be obtained at normal pressure and low temperature of 1300 °C compared to a temperature of 1650 °C normally used. The above borothermal process involves the in situ generation of B(2)O(2) to yield either oxide or diboride. The niobium oxides and borides have been characterized in detail by XRD, HRTEM and EDX studies. The core-shell structure has been investigated by XPS depth profiling, EFTEM and EELS (especially to characterize the presence of boron and the shell thickness). The niobium diboride nanorods (with high aspect ratio) show a superconducting transition with the T(c) of 6.4 K. In the core-shell of NbB(2)@Nb(2)O(5), the superconductivity of NbB(2) is masked by the niobium oxide shell and hence no superconductivity was observed. The above methodology has the benefits of realizing both oxides and borides of niobium in nanocrystalline form, in high purity and at much lower temperatures. 相似文献
56.
A numerical study is reported on the fully developed unsteady laminar fluid flow in microchannel parallel-plates partially filled with a uniform porous medium and partially filled with a clear fluid. The flow is induced by the movement of one of the plates and the pressure gradient. The Brinkman-extended Darcy model is utilized to model the flow in the porous region, while the Stokes equation is used in the clear fluid region. A theoretical analysis is also presented for the fully developed steady flow to find closedform expressions for the interfacial velocity and the velocity and skin frictions at the bounding plates. Numerical computations shows excellent agreement between the closedform solutions for fully developed steady flow and the numerical solution to unsteady flow at large values of time. 相似文献
57.
A classification is given of all translation planes of order q 2 that admit a collineation group G admitting a two-transitive orbit of q + 1 points on the line at infinity. 相似文献
58.
The phonon spectra of unstrained and strained quasiperiodic semiconductor superlattices (QSSL) have been calculated using
one-dimensional linear chain model. We consider two types of quasiperiodic systems, namely cantor triadic bar (CTB) and Fibonacci
sequences (FS), constituting of AlAs, GaAs and GaSb of which the latter two have a lattice mismatch of about 7%. The calculations
have been made using transfer matrix method and also with and without the inclusion of strain. We present the results on phonon
spectra of two component CTB and two as well as three component FS semiconductor superlattices (SSL), thickness and order
dependence on LO mode of GaAs, effect of strain on LO frequency of GaAs. The calculated results show that the strain generated
due to lattice mismatch reduces significantly the magnitudes of the confined optical phonon frequency of GaAs. 相似文献
59.
60.
Vikram Jha 《Discrete Mathematics》1982,41(1):43-51
Let πl∞ be an affine translation plane of order qr with GF(q) in its kern. Suppose G is a subgroup of the translation complement of πl∞ which leaves invariant a set Δ of q + 1 slopes and acts transitively on l∞?Δ. We study the situation when G≌SL(n, q) or PSL(n, q).We show that if G|Δ = identity, then πl∞ is a Hall plane, a Lorimer-Rahilly plane (LR-16) or a Johnson-Walker plane (JW-16). Moreover, if n?3, then G fixes Δ elementwise and πl∞ is LR-16 or JW-16. 相似文献