全文获取类型
收费全文 | 7989篇 |
免费 | 352篇 |
国内免费 | 64篇 |
专业分类
化学 | 5956篇 |
晶体学 | 88篇 |
力学 | 290篇 |
综合类 | 2篇 |
数学 | 982篇 |
物理学 | 1087篇 |
出版年
2024年 | 23篇 |
2023年 | 66篇 |
2022年 | 416篇 |
2021年 | 415篇 |
2020年 | 270篇 |
2019年 | 308篇 |
2018年 | 319篇 |
2017年 | 249篇 |
2016年 | 415篇 |
2015年 | 278篇 |
2014年 | 284篇 |
2013年 | 693篇 |
2012年 | 528篇 |
2011年 | 539篇 |
2010年 | 345篇 |
2009年 | 305篇 |
2008年 | 373篇 |
2007年 | 343篇 |
2006年 | 271篇 |
2005年 | 236篇 |
2004年 | 212篇 |
2003年 | 178篇 |
2002年 | 208篇 |
2001年 | 92篇 |
2000年 | 107篇 |
1999年 | 59篇 |
1998年 | 48篇 |
1997年 | 55篇 |
1996年 | 52篇 |
1995年 | 47篇 |
1994年 | 46篇 |
1993年 | 50篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 57篇 |
1989年 | 33篇 |
1988年 | 31篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 24篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 9篇 |
排序方式: 共有8405条查询结果,搜索用时 31 毫秒
21.
任胜兵 《武汉大学学报(理学版)》2006,52(5):644-648
针对基于Web的图书馆管理系统资源访问控制的动态性问题,提出了一种基于角色的访问控制策略描述方案.通过对基于Web的图书馆管理系统访问控制管理影响因素和访问控制需求的分析,结合NIST基于角色的访问控制统一模型标准,构造了一种基于角色的访问控制元模型.并在这一元模型的基础上,提出了一种紧凑的基于角色的访问控制XML策略描述语言框架.结果表明该访问控制策略描述语言框架适合表述动态环境下对图书馆资源的访问策略,提高了基于Web的图书馆管理系统资源访问的安全性. 相似文献
22.
In this paper, we introduce a new concept of semi-preemptive scheduling and we show how it can be used to derive a maximum-flow-based lower bound for the P|rj|Lmax which dominates the well-known preemptive lower bound. We show that, in some cases, the proposed bound strictly dominates the preemptive one while having the same complexity. 相似文献
23.
In this paper, we use parametric quintic splines to derive some consistency relations which are then used to develop a numerical method for computing the solution of a system of fourth-order boundary-value problems associated with obstacle, unilateral, and contact problems. It is known that a class of variational inequalities related to contact problems in elastostatics can be characterized by a sequence of variational inequations, which are solved using some numerical method. Numerical evidence is presented to show the applicability and superiority of the new method over other collocation, finite difference, and spline methods. 相似文献
24.
There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.
25.
We consider the rate of convergence for a class of perturbed hemivariational inequalities in reflexive Banach Spaces. Our results can be viewed as an extension and refinement of some previous known results in this area. 相似文献
26.
A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials. 相似文献
27.
Mohamed El-Gebeily Donal O'Regan 《Journal of Mathematical Analysis and Applications》2007,334(1):140-156
Existence theory is developed for the equation ?(u)=F(u), where ? is a formally self-adjoint singular second-order differential expression and F is nonlinear. The problem is treated in a Hilbert space and we do not require the operators induced by ? to have completely continuous resolvents. Nonlinear boundary conditions are allowed. Also, F is assumed to be weakly continuous and monotone at one point. Boundary behavior of functions associated with the domains of definitions of the operators associated with ? in the singular case is investigated. A special class of self-adjoint operators associated with ? is obtained. 相似文献
28.
Raed Ali Al-Khasawneh Fudziah Ismail Mohamed Suleiman 《Applied mathematics and computation》2007,190(2):1803-1814
In this paper, third-order 3-stage diagonally implicit Runge–Kutta–Nystrom method embedded in fourth-order 4-stage for solving special second-order initial value problems is constructed. The method has the property of minimized local truncation error as well as the last row of the coefficient matrix is equal to the vector output. The stability of the method is investigated and a standard set of test problems are tested upon and comparisons on the numerical results are made when the same set of test problems are reduced to first-order system and solved using existing Runge–Kutta method. The results clearly shown the advantage and the efficiency of the new method. 相似文献
29.
Effect of Deborah number and phase difference on peristaltic transport of a third-order fluid in an asymmetric channel 总被引:1,自引:0,他引:1
The effect of a third-order fluid on the peristaltic transport in an asymmetric channel is studied. The wavelength of the peristaltic waves is assumed to be large compared to the varying channel width, whereas the wave amplitudes need not be small compared to the varying channel width. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The flow is investigated in a wave frame of reference moving with velocity of the wave. The effects of Deborah number, phase difference, varying channel width and wave amplitudes on the pumping characteristics, streamline pattern and trapping phenomena are investigated. It is observed that the trapping regions increase as the channel becomes more and more symmetric and the trapped bolus volume decreases for increasing Deborah number, phase difference and varying channel width whereas it increases for increasing flow rate and wave amplitudes. Furthermore, the obtained results could also have applications to a range of peristaltic flows for a variety of non-Newtonian fluids such as aqueous solutions of high-molecular weight polyethylene oxide and polyacrylamide. 相似文献
30.
In this paper we establish a sharp result concerning integral mean estimates for self-reciprocal polynomials. 相似文献