全文获取类型
收费全文 | 4926篇 |
免费 | 184篇 |
国内免费 | 12篇 |
专业分类
化学 | 2971篇 |
晶体学 | 86篇 |
力学 | 156篇 |
数学 | 387篇 |
物理学 | 1522篇 |
出版年
2023年 | 46篇 |
2022年 | 61篇 |
2021年 | 88篇 |
2020年 | 105篇 |
2019年 | 106篇 |
2018年 | 121篇 |
2017年 | 89篇 |
2016年 | 149篇 |
2015年 | 123篇 |
2014年 | 177篇 |
2013年 | 297篇 |
2012年 | 387篇 |
2011年 | 373篇 |
2010年 | 203篇 |
2009年 | 186篇 |
2008年 | 223篇 |
2007年 | 207篇 |
2006年 | 212篇 |
2005年 | 162篇 |
2004年 | 123篇 |
2003年 | 118篇 |
2002年 | 98篇 |
2001年 | 75篇 |
2000年 | 61篇 |
1999年 | 55篇 |
1998年 | 32篇 |
1997年 | 56篇 |
1996年 | 66篇 |
1995年 | 45篇 |
1994年 | 75篇 |
1993年 | 82篇 |
1992年 | 80篇 |
1991年 | 49篇 |
1990年 | 49篇 |
1989年 | 55篇 |
1988年 | 37篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 39篇 |
1982年 | 40篇 |
1981年 | 51篇 |
1980年 | 41篇 |
1979年 | 32篇 |
1978年 | 27篇 |
1977年 | 35篇 |
1975年 | 26篇 |
1974年 | 28篇 |
1973年 | 38篇 |
排序方式: 共有5122条查询结果,搜索用时 15 毫秒
991.
Debasis Das Mohuya B. Kar Arindam Roy Samarjit Kar 《Central European Journal of Operations Research》2012,20(2):251-280
This paper develops a production-inventory model for a deteriorating item with stock-dependent demand under two storage facilities
over a random planning horizon, which is assumed to follow exponential distribution with known parameter. The effects of learning
in set-up, production, selling and reduced selling is incorporated. Different inflation rates for various inventory costs
and time value of money are also considered. A hybrid genetic algorithm is designed to solve the optimization problem which
is hard to solve with existing algorithms due to the complexity of the decision variable. To illustrate the model and to show
the effectiveness of the proposed approach a numerical example is provided. A sensitivity analysis of the optimal solution
with respect to the parameters of the system is carried out. 相似文献
992.
Mixed convection flow in a two-sided lid-driven cavity filled with heat-generating porous medium is numerically investigated.
The top and bottom walls are moving in opposite directions at different temperatures, while the side vertical walls are considered
adiabatic. The governing equations are solved using the finite-volume method with the SIMPLE algorithm. The numerical procedure
adopted in this study yields a consistent performance over a wide range of parameters that were 10−4 ≤ Da ≤ 10−1 and 0 ≤ Ra
I
≤ 104. The effects of the parameters involved on the heat transfer characteristics are studied in detail. It is found that the
variation of the average Nusselt number is non-linear for increasing values of the Darcy number with uniform or non-uniform
heating condition. 相似文献
993.
The unsteady hydromagnetic flow due to non-coaxial rotations of a porous disk with slip condition and a fluid at infinity
has been studied on taking Hall currents into account. An exact solution of the governing equation has been obtained by the
Laplace transform technique. Asymptotic solution is obtained for large time. It is found that for large time there exists
a thin boundary layer near the disk. The thickness of this layer decreases with increase in either suction or magnetic parameter. 相似文献
994.
In this paper, change of flow patterns during the simultaneous flow of high viscous oil and water through the sudden contraction and expansion in a horizontal conduit has been studied. It is noted that these sudden changes in cross-section have a significant influence on the downstream phase distribution of lube oil–water flow. The observation suggests a simple technique to establish core flow as well as a way to prevent pipe wall fouling during the transportation of such oil. A number of interesting differences have been noted during low viscous oil–water flow through the same test rigs. While several types of core annular flow are observed for the former case, a wider variety of interfacial distribution characterizes kerosene–water systems. The pressure profiles during the simultaneous flow of lube oil and water through the sudden contraction and expansion are also studied and compared with low viscous oil–water flows. The pressure profiles are found to be independent of liquid viscosity and the loss coefficients are observed to be independent of flow patterns in both the cases. 相似文献
995.
B. Saha A.K. Das P.K. Mukherjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):33-37
Transition energies, oscillator strengths and transition probability values for radiative transitions have been calculated
for the highly ionised atoms of Si isoelectronic sequence from Mn11+ to Kr22+ for the singly excited states up to principal quantum number n = 7. Time-dependent coupled Hartree-Fock (TDCHF) theory has been used to estimate such transition properties. Most of the
results for the oscillator strengths and transition probabilities are new. Transition energies agree reasonably well with
available spectroscopic values.
Received 25 January 2000 and Received in final form 24 October 2000 相似文献
996.
We shall discuss about the scientific motivation and construction of a 7×7 BaF2 crystal array at Variable Energy Cyclotron Centre, Calcutta. This detector would be used to measure high energy γ-ray photons from GDR decay and proton-neutron bremsstrahlung reactions at the present 88″ cyclotron and upcoming superconducting
cyclotron at VECC, Calcutta. This detector can also be used to measure photons from quark-gluon plasma at the relativistic
heavy ion collider (RHIC) in USA. 相似文献
997.
P. K. Das 《International Journal of Theoretical Physics》2001,40(9):1631-1645
In this paper we study homodyne statistics of some vectors on a deformed Hilbert space. 相似文献
998.
Scheicher R. H. Cammarere D. Briere T. M. Sahoo N. Das T. P. Pratt F. L. Nagamine K. 《Hyperfine Interactions》2001,136(3-8):755-758
The microscopic details of the electron transfer in cytochrome c (cyt c) are being investigated by the Muon Spin Relaxation
(μSR) technique. We are using the Hartree–Fock Cluster Procedure to determine the most likely trapping sites for μ+ and muonium (Mu) in the protein chain, and have performed extensive calculations in single amino acid molecules of the protein
chain of cyt c. The double-bonded oxygen atom of the carboxyl group was identified as the trapping site for both μ+ and Mu. Utilizing the wave functions we obtained from the Hartree–Fock calculations, we have determined the hyperfine field
that the μ+ in Mu experiences while the latter is trapped at the oxygen.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
999.
Jeong Junho Briere Tina M. Sahoo N. Das T. P. Ohira Seiko Nishiyama K. Nagamine K. 《Hyperfine Interactions》2001,136(3-8):769-775
The trapping sites for muon and muonium in ferromagnetic p-Cl–Ph–CH=N–TEMPO [(4-(p-chlorobenzylideneamino)–TEMPO (TEMPO = 2,6,6-tetramethyl-piperidin-1-yloxyl)]
and the hyperfine interaction tensors for these sites are obtained using first-principles Unrestricted Hartree–Fock theory.
The calculated hyperfine interactions are used to compare the calculated zero field muon spin rotation (μSR) frequencies for
different choices for the easy axis and the observed frequency. It has been concluded that the two trapping centers that can
best explain the observed μSR frequency are a trapped singlet muonium near the radical oxygen and a trapped muon site near
the chlorine. The direction of the easy axis also is determined to be the b-axis of the monoclinic lattice. This direction for the easy axis is confirmed by determining the direction of the distributed
magnetization in the molecular solid which leads to a minimum dipole–dipole interaction energy. The consequences of this agreement
for the easy axis direction by two independent procedures are discussed.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
1000.
The paper deals with the interaction between three Griffith cracks propagating under antiplane shear stress at the interface of two dissimilar infinite elastic half-spaces. The Fourier transform technique is used to reduce the elastodynamic problem to the solution of a set of integral equations which has been solved by using the finite Hilbert transform technique and Cooke’s result. The analytical expressions for the stress intensity factors at the crack tips are obtained. Numerical values of the interaction effect have been computed for and results show that interaction effects are either shielding or amplification depending on the location of each crack with respect to other and crack tip spacing. 相似文献