全文获取类型
收费全文 | 5353篇 |
免费 | 249篇 |
国内免费 | 52篇 |
专业分类
化学 | 3723篇 |
晶体学 | 68篇 |
力学 | 251篇 |
综合类 | 1篇 |
数学 | 616篇 |
物理学 | 995篇 |
出版年
2023年 | 43篇 |
2022年 | 202篇 |
2021年 | 324篇 |
2020年 | 239篇 |
2019年 | 240篇 |
2018年 | 207篇 |
2017年 | 173篇 |
2016年 | 275篇 |
2015年 | 152篇 |
2014年 | 209篇 |
2013年 | 456篇 |
2012年 | 327篇 |
2011年 | 325篇 |
2010年 | 204篇 |
2009年 | 176篇 |
2008年 | 220篇 |
2007年 | 230篇 |
2006年 | 188篇 |
2005年 | 143篇 |
2004年 | 145篇 |
2003年 | 124篇 |
2002年 | 139篇 |
2001年 | 63篇 |
2000年 | 46篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 38篇 |
1993年 | 31篇 |
1992年 | 38篇 |
1991年 | 36篇 |
1990年 | 29篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 29篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有5654条查询结果,搜索用时 15 毫秒
971.
Irfan Anjum Badruddin N. J. Salman Ahmed Abdullah A. A. A. Al-Rashed Jeevan Kanesan Sarfaraz Kamangar H. M. T. Khaleed 《Transport in Porous Media》2012,91(2):697-715
The present study is intended to study heat and mass transfer in a vertical annular cylinder embedded with saturated porous
medium. The inner surface of cylinder is maintained at uniform wall temperature and uniform wall concentration. The governing
partial differential equations are non-dimensionalised and solved by using finite element method (FEM). The porous medium
is discritised using triangular elements with uneven element size. Large number of smaller-sized elements are placed near
the walls of the annulus to capture the smallest variation in solution parameters. The results are reported for both aiding
and opposing flows. The effects of various non-dimensional numbers such as buoyancy ratio, Lewis number, Rayleigh number,
aspect ratio, etc on heat and mass transfer are discussed. The temperature and concentration profiles are presented. 相似文献
972.
973.
Mosayeb Naseri Mona Abdolmaleky Fariborz Parandin Negin Fatahi Ahmed Farouk Reza Nazari 《理论物理通讯》2018,69(2):215-226
In this paper, a new quantum images encoding scheme is proposed. The proposed scheme mainly consists of four different encoding algorithms. The idea behind of the scheme is a binary key generated randomly for each pixel of the original image. Afterwards, the employed encoding algorithm is selected corresponding to the qubit pair of the generated randomized binary key. The security analysis of the proposed scheme proved its enhancement through both randomization of the generated binary image key and altering the gray-scale value of the image pixels using the qubits of randomized binary key. The simulation of the proposed scheme assures that the final encoded image could not be recognized visually. Moreover, the histogram diagram of encoded image is flatter than the original one. The Shannon entropies of the final encoded images are significantly higher than the original one, which indicates that the attacker can not gain any information about the encoded images. 相似文献
974.
975.
Raghad Saeed Hasan Shelan Khasro Tawfeeq Nahla Qader Mohammed Ahmed Ismael Khaleel 《Chinese Journal of Physics (Taipei)》2018,56(1):385-391
True random number generators are essential components for communications to be confidentially secured. In this paper a new method is proposed to generate random sequences of numbers based on the difference of the arrival times of photons detected in a coincidence window between two single-photon counting modules. 相似文献
976.
Koji Nagata Tadao Nakamura Han Geurdes Josep Batle Soliman Abdalla Ahmed Farouk Do Ngoc Diep 《International Journal of Theoretical Physics》2018,57(4):973-980
An interpretation of quantum mechanics is discussed. It is assumed that quantum is energy. An algorithm by means of the energy interpretation is discussed. An algorithm, based on the energy interpretation, for fast determining a homogeneous linear function f(x) := s.x = s 1 x 1 + s 2 x 2 + ? + s N x N is proposed. Here x = (x 1, … , x N ), x j ∈ R and the coefficients s = (s 1, … , s N ), s j ∈ N. Given the interpolation values \((f(1), f(2),...,f(N))=\vec {y}\), the unknown coefficients \(s = (s_{1}(\vec {y}),\dots , s_{N}(\vec {y}))\) of the linear function shall be determined, simultaneously. The speed of determining the values is shown to outperform the classical case by a factor of N. Our method is based on the generalized Bernstein-Vazirani algorithm to qudit systems. Next, by using M parallel quantum systems, M homogeneous linear functions are determined, simultaneously. The speed of obtaining the set of M homogeneous linear functions is shown to outperform the classical case by a factor of N × M. 相似文献
977.
Koji Nagata Tadao Nakamura Han Geurdes Josep Batle Soliman Abdalla Ahmed Farouk 《International Journal of Theoretical Physics》2018,57(6):1605-1611
We present a new method of more speedily calculating a multiplication by using the generalized Bernstein-Vazirani algorithm and many parallel quantum systems. Given the set of real values \(\{a_{1},a_{2},a_{3},\ldots ,a_{N}\}\) and a function \(g:\textbf {R}\rightarrow \{0,1\}\), we shall determine the following values \(\{g(a_{1}),g(a_{2}),g(a_{3}),\ldots , g(a_{N})\}\) simultaneously. The speed of determining the values is shown to outperform the classical case by a factor of \(N\). Next, we consider it as a number in binary representation; M1 = (g(a1),g(a2),g(a3),…,g(a N )). By using \(M\) parallel quantum systems, we have \(M\) numbers in binary representation, simultaneously. The speed of obtaining the \(M\) numbers is shown to outperform the classical case by a factor of \(M\). Finally, we calculate the product; \( M_{1}\times M_{2}\times \cdots \times M_{M}. \) The speed of obtaining the product is shown to outperform the classical case by a factor of N × M. 相似文献
978.
This article examines a mathematical model to analyze the rotating flow of three-dimensional water based nanofluid over a convectively heated exponentially stretching sheet in the presence of transverse magnetic field with additional effects of thermal radiation,Joule heating and viscous dissipation.Silver(Ag),copper(Cu),copper oxide(Cu O),aluminum oxide(Al_2O_3)and titanium dioxide(Ti O_2)have been taken under consideration as the nanoparticles and water(H_2O)as the base fluid.Using suitable similarity transformations,the governing partial differential equations(PDEs)of the modeled problem are transformed to the ordinary differential equations(ODEs).These ODEs are then solved numerically by applying the shooting method.For the particular situation,the results are compared with the available literature.The effects of different nanoparticles on the temperature distribution are also discussed graphically and numerically.It is witnessed that the skin friction coefficient is maximum for silver based nanofluid.Also,the velocity profile is found to diminish for the increasing values of the magnetic parameter. 相似文献
979.
The current study focuses on the numerical investigation of the mixed convective peristaltic mechanism through a vertical tube for non-zero Reynolds and wave number. In the set of constitutional equations, energy equation contains the term representing heat generation parameter. The problem is formulated by dropping the assumption of lubrication theory that turns the model mathematically into a system of the nonlinear partial differential equations. The results of the long wavelength in a creeping flow are deduced from the present analysis. Thus, the current study explores the neglected features of peristaltic heat flow in the mixed convective model by considering moderate values of Reynolds and wave numbers. The finite element based on Galerkin's weighted residual scheme is applied to solve the governing equations. The computed solution is presented in the form of contours of streamlines and isothermal lines, velocity and temperature profiles for variation of different involved parameters. The investigation shows that the strength of circulation for stream function increases by increasing the wave number and Reynolds number. Symmetric isotherms are reported for small values of time-mean flow. Linear behavior of pressure is noticed by vanishing inertial forces while the increase in pressure is observed by amplifying the Reynolds number. 相似文献
980.
Ahmed Missaoui Jouda Jemaa Khabthani Nejm-Eddine Jaidane Didier Mayou Guy Trambly de Laissardière 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(4):75
We describe the electronic conductivity, as a function of the Fermi energy, in the Bernal bilayer graphene (BLG) in presence of a random distribution of vacancies that simulate resonant adsorbates. We compare it to monolayer (MLG) with the same defect concentrations. These transport properties are related to the values of fundamental length scales such as the elastic mean free path L e , the localization length ξ and the inelastic mean free path L i . Usually the later, which reflect the effect of inelastic scattering by phonons, strongly depends on temperature T. In BLG an additional characteristic distance l 1 exists which is the typical traveling distance between two interlayer hopping events. We find that when the concentration of defects is smaller than 1%–2%, one has l 1 ≤ L e ? ξ and the BLG has transport properties that differ from those of the MLG independently of L i (T). Whereas for larger concentration of defects L e <l 1 ? ξ, and depending on L i (T), the transport in the BLG can be equivalent (or not) to that of two decoupled MLG. We compare two tight-binding model Hamiltonians with and without hopping beyond the nearest neighbors. 相似文献