全文获取类型
收费全文 | 18147篇 |
免费 | 1770篇 |
国内免费 | 1875篇 |
专业分类
化学 | 3838篇 |
晶体学 | 230篇 |
力学 | 2009篇 |
综合类 | 375篇 |
数学 | 12440篇 |
物理学 | 2900篇 |
出版年
2024年 | 39篇 |
2023年 | 177篇 |
2022年 | 223篇 |
2021年 | 290篇 |
2020年 | 439篇 |
2019年 | 434篇 |
2018年 | 431篇 |
2017年 | 483篇 |
2016年 | 535篇 |
2015年 | 391篇 |
2014年 | 729篇 |
2013年 | 1319篇 |
2012年 | 863篇 |
2011年 | 1034篇 |
2010年 | 1023篇 |
2009年 | 1122篇 |
2008年 | 1245篇 |
2007年 | 1313篇 |
2006年 | 1098篇 |
2005年 | 1015篇 |
2004年 | 926篇 |
2003年 | 970篇 |
2002年 | 858篇 |
2001年 | 656篇 |
2000年 | 606篇 |
1999年 | 551篇 |
1998年 | 507篇 |
1997年 | 413篇 |
1996年 | 330篇 |
1995年 | 275篇 |
1994年 | 234篇 |
1993年 | 171篇 |
1992年 | 165篇 |
1991年 | 119篇 |
1990年 | 100篇 |
1989年 | 83篇 |
1988年 | 78篇 |
1987年 | 59篇 |
1986年 | 64篇 |
1985年 | 73篇 |
1984年 | 56篇 |
1983年 | 27篇 |
1982年 | 63篇 |
1981年 | 48篇 |
1980年 | 32篇 |
1979年 | 37篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Mingxin Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):424-436
This paper deals with positive solutions of degenerate and quasilinear parabolic systems not in divergence form: ut=up(Δu+av), vt=vq(Δv+bu), with null Dirichlet boundary conditions and positive initial conditions, where p, q, a and b are all positive constants. The local existence and uniqueness of classical solution are proved. Moreover, it will be proved that all solutions exist globally if and only if ab?λ12, where λ1 is the first eigenvalue of −Δ in Ω with homogeneous Dirichlet boundary condition. 相似文献
32.
33.
A new method is presented for the determination of Ricci Collineations (RC) and Matter Collineations (MC) of a given spacetime, in the cases where the Ricci tensor and the energy momentum tensor are non-degenerate and have a similar form with the metric. This method reduces the problem of finding the RCs and the MCs to that of determining the KVs whereas at the same time uses already known results on the motions of the metric. We employ this method to determine all hypersurface homogeneous locally rotationally symmetric spacetimes, which admit proper RCs and MCs. We also give the corresponding collineation vectors. These results conclude a long due open problem, which has been considered many times partially in the literature. 相似文献
34.
During the course of our investigation of the electron transfer properties of some redox species through highly hydrophobic
long chain alkanethiol molecules on gold in aqueous and non-aqueous solvents, we obtained some intriguing results such as
unusually low interfacial capacitance, very high values of impedance and film resistance, all of which pointed to the possible
existence of a nanometer size interfacial gap between the hydrophobic monolayer and aqueous electrolyte. We explain this phenomenon
by a model for the alkanethiol monolayer—aqueous electrolyte interface, in which the extremely hydrophobic alkanethiol film
repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively
increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance.
This behaviour is very much akin to the ‘drying transition’ proposed by Lum, Chandler and Weeks in their theory of length
scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize
around them without sacrificing their hydrogen bonds. Since for an extended hydrophobic unit, the existence of hydrogen bonded
water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading
to the possible creation of a hydrophobic interfacial gap. 相似文献
35.
李治明 《新疆大学学报(理工版)》2004,21(2):135-141,146
研究了具有开发的单种群非自治周期系统.利用非自治微分方程理论.以及变分法理论和泛函极值的Euler方程方法,得到了该开发系统的持续生存性.周期解存在性,全局渐近稳定性.研究了在开发情况下的最大收获量问题,以及取得最大经济效益下的收获问题等. 相似文献
36.
37.
Vincenzo Santagada Ferdinando FiorinoElisa Perissutti Beatrice SeverinoSara Terracciano Giuseppe CirinoGiuseppe Caliendo 《Tetrahedron letters》2003,44(6):1145-1148
A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating. 相似文献
38.
Existence, Multiplicity and Infinite Solvability of Positive Solutions for One-Dimensional p-Laplacian 总被引:5,自引:0,他引:5
Qing Liu YAO 《数学学报(英文版)》2005,21(4):691-698
The existence, multiplicity and infinite solvability of positive solutions are established for some two-point boundary value problems of one-dimensional p-Laplacian. In this paper, by multiplicity we mean the existence of m solutions, where m is an arbitrary natural number. 相似文献
39.
LIN Chang ZHANG Xiu-Lian 《理论物理通讯》2005,44(2):247-251
The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation. 相似文献
40.
李永祥 《数学物理学报(A辑)》2003,23(2):245-252
该文讨论四阶常微分方程边值问题u^(4)(t)=f(t,u,u″), t∈[0,1],u(0)=u(1)=u″(0)=u″(1)=0解的存在性, 其中f(t,u,v):[0,1]×R×R→R为Carathéodory函数. 在不限制f关于u,v的增长阶, 不假定f关于u,v的单调性的一般情形下, 用上下解方法获得了解的存在性结果,并讨论了单调迭代求解的有效性. 相似文献