全文获取类型
收费全文 | 12299篇 |
免费 | 1394篇 |
国内免费 | 1201篇 |
专业分类
化学 | 4496篇 |
晶体学 | 120篇 |
力学 | 1474篇 |
综合类 | 191篇 |
数学 | 5856篇 |
物理学 | 2757篇 |
出版年
2024年 | 14篇 |
2023年 | 106篇 |
2022年 | 193篇 |
2021年 | 256篇 |
2020年 | 355篇 |
2019年 | 380篇 |
2018年 | 378篇 |
2017年 | 434篇 |
2016年 | 456篇 |
2015年 | 408篇 |
2014年 | 598篇 |
2013年 | 1184篇 |
2012年 | 623篇 |
2011年 | 731篇 |
2010年 | 604篇 |
2009年 | 671篇 |
2008年 | 718篇 |
2007年 | 719篇 |
2006年 | 655篇 |
2005年 | 611篇 |
2004年 | 514篇 |
2003年 | 526篇 |
2002年 | 507篇 |
2001年 | 441篇 |
2000年 | 424篇 |
1999年 | 363篇 |
1998年 | 359篇 |
1997年 | 292篇 |
1996年 | 219篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 113篇 |
1992年 | 92篇 |
1991年 | 97篇 |
1990年 | 75篇 |
1989年 | 56篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 33篇 |
1985年 | 54篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 39篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1972年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Kai-li Xiang 《计算数学(英文版)》2002,(2)
1. IntroductionWe consider a class of direct hybrid methods proposed in [11 for solving the second orderinitial value problemy" = f(t,y), y(0),y'(0) given (1.1)The basic method has the formandHere t. = nh and we define t.l.. = t. I aih, i = 1, 2 and n=0,1… 相似文献
82.
R. Minami A. Kasugai K. Takahashi N. Kobayashi Y. Mitsunaka K. Sakamoto 《International Journal of Infrared and Millimeter Waves》2006,27(1):13-24
A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A
helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have
been optimized for the TE31.8 mode at 170 GHz and TE22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking
the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing
in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design.
High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the
thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of
high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons. 相似文献
83.
Bernardo Lafuerza-Guillén Donal O’regan Reza Saadati 《Proceedings Mathematical Sciences》2007,117(1):61-70
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness
of a quotient. 相似文献
84.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of simpler linear differentialoperators and a nonlinear term. 相似文献
85.
New Kamenev-type oscillation criteria for second-order nonlinear differential equations with damping 总被引:1,自引:0,他引:1
Yuan Gong Sun 《Journal of Mathematical Analysis and Applications》2004,291(1):341-351
Some new oscillation criteria are established for the nonlinear damped differential equation (r(t)y′)′+p(t)y′+q(t)f(y)=0 that are different from most known ones in the sense that they are based on a class of new functions Φ(t,s,r) defined in the sequel. Our results are sharper than some previous results which can be seen by the examples at the end of this paper. 相似文献
86.
J. T. Haslinger K. Kunisch G. Peichl 《Computational Optimization and Applications》2003,26(3):231-251
This contribution deals with an efficient method for the numerical realization of the exterior and interior Bernoulli free boundary problems. It is based on a shape optimization approach. The state problems are solved by a fictitious domain solver using boundary Lagrange multipliers. 相似文献
87.
88.
89.
Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings. 相似文献
90.
In this paper, we exhibit a unified treatment of the mixed initial boundary value problem for second order (in time) parabolic linear differential equations in Banach spaces, whose boundary conditions are of a dynamical nature. Results regarding existence, uniqueness, continuous dependence (on initial data) and regularity of classical and strict solutions are established. Moreover, several examples are given as samples for possible applications.