全文获取类型
收费全文 | 591篇 |
免费 | 9篇 |
国内免费 | 132篇 |
专业分类
化学 | 235篇 |
晶体学 | 7篇 |
力学 | 73篇 |
综合类 | 1篇 |
数学 | 206篇 |
物理学 | 210篇 |
出版年
2023年 | 8篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 22篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 11篇 |
2014年 | 38篇 |
2013年 | 18篇 |
2012年 | 15篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 28篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 20篇 |
2002年 | 32篇 |
2001年 | 76篇 |
2000年 | 60篇 |
1999年 | 60篇 |
1998年 | 39篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 26篇 |
1987年 | 15篇 |
排序方式: 共有732条查询结果,搜索用时 62 毫秒
661.
《European Journal of Mechanics - B/Fluids》2000,19(5):547-557
An account is given of the working life of the recently decommissioned axisymmetric turbulent-boundary-layer windtunnel in the Hermann-Föttinger-Institut of the Technische Universität Berlin, and some principal investigations conducted in it. 相似文献
662.
GuoZongming YangZuodong 《高校应用数学学报(英文版)》2000,15(1):15-20
Abstract. Uniqueness results are obtained for positive solutions of a class of quasilinear ordi-nary differential equations. The methods rely on the energy analysis and a scale argument. 相似文献
663.
Li Deming Liu YanpeiDept. of Math. Capital Normal Univ. Beijing . Email: lidm @ mail.cnu.edu.cn Dept. of Math. Northern Jiaotong Univ. Beijing . 《高校应用数学学报(英文版)》2000,(4)
§ 1 IntroductionThe maximum genusγM(G) of a graph G is the maximum among the genera,which Ghas a cellularembedding on a sphere with k handles.Since any embedding of G has atleastone face,by Euler polyhedral equation,itcan be obtained thatγM(G)≤β(G) / 2 ,whereβ(G) is the Betti number of G.A graph G is called up-embeddable ifγM(G) =β(G) / 2 .[1 ] has showed that thereare atleasttwo edge-disjointspanning trees in G if G is 4 -edge connected.Let T be a span-ning tree of G.An odd … 相似文献
664.
665.
666.
667.
Many experimental works have recently investigated the dynamics of crease formation during the swelling of long soft slabs attached to a rigid substrate. Mechanically, the spatially constrained growth provokes a residual strain distribution inside the material, and therefore the problem is equivalent to the uniaxial compression of an elastic layer.The aim of this work is to propose a semi-analytical approach to study the non-linear buckling behaviour of a growing soft layer. We consider the presence of a microstructural length, which describes the effect of a simple strain gradient correction in the growing hyperelastic layer, considered as a neo-Hookean material. By introducing a non-linear stream function for enforcing exactly the incompressibility constraint, we develop a variational formulation for performing a stability analysis of the basic homogeneous solution. At the linear order, we derive the corresponding dispersion relation, proving that even a small strain gradient effect allows the system to select a critical dimensionless wavenumber while giving a small correction to the Biot instability threshold. A weakly non-linear analysis is then performed by applying a multiple-scale expansion to the neutrally stable mode. By applying the global conservation of the mechanical energy, we derive the Ginzburg–Landau equation for the critical single mode, identifying a pitchfork bifurcation. Since the bifurcation is found to be subcritical for a small ratio between the microstructural length and the layer׳s thickness, we finally perform a sensitivity analysis to study the effect of the initial presence of a sinusoidal imperfection on the free surface of the layer. In this case, the incremental solution for the stream function is written as a Fourier series, so that the surface imperfection can have a cubic resonance with the linear modes. The solutions indicate the presence of a turning point close to the critical threshold for the perfect system. We also find that the inclusion of higher modes has a steepening effect on the surface profile, indicating the incipient formation of an elastic singularity, possibly a crease. 相似文献
668.
《Journal of magnetism and magnetic materials》1999,195(1):168-173
Two types of Gaussian distribution function (`θ type’ and `tan θ type') describing the degree of grain alignment in sintered NdFeB magnets have been compared in the distribution coefficient σ (or σg), the distribution probability P(θ) and the grain alignment dependence of coercivity. The results show that when the grain alignment is good (the ratio of remanence-to-saturation polarization Jr/Js⩾0.90), σ(σg) and P(θ) for the two types of Gaussian functions have similar variation tendencies, the calculated values of normalized coercivity based on the starting field theory are basically the same and are consistent with experiments. When the grain alignment is not good (Jr/Js⩾0.80), the variation tendencies of σ and P(θ) are different. In addition, according to `tan θ type’ Gaussian function, the theoretical values of the normalized coercivity based on the starting field theory are still consistent with the experiments, but according to `θ type’ Gaussian function, the theoretical values seriously deviate from the experiments. This means that the `tan θ type’ Gaussian function is a better texture function for describing the grain alignment. 相似文献
669.
§ 1 IntroductionIn[1 ] ,Karakostas and Tsamatos studied the existence of positive solutions for two-pointboundary value problemx″+ sign( 1 -c) q( t) f( x,x′) x′=0 ,( 1 .1 )x( 0 ) =0 ,x′( 1 ) =cx′( 0 ) ,( 1 .2 )where c∈ ( 0 ,1 )∪ ( 1 ,∞ ) .By using indices ofconvergence ofthe nonlinearity at0 and +∞and fixed point theorem in cones,they provided a priori upper and lower bounds for theslope of the solutions.The“c∈ ( 0 ,1 ) part”of their results has been extended to the fol-lowing … 相似文献
670.
《Solid State Ionics》2006,177(13-14):1149-1155
The Lu2+xTi2−xO7−x/2 (x = 0; 0.052; 0.096; 0.286; 0.44; 0.63; 33.3–49 mol% Lu2O3) nanoceramics with partly disordered pyrochlore-type structure are prepared by sintering freeze-dried powders obtained by a co-precipitation technique with 1600 °C annealing. Similar to pyrochlore-like compositions in the zirconate system, some of the new titanates are good oxide-ion conductors in air. The new solid-state electrolytes have oxide-ion conductivity in the interval of 1.0 × 10− 3 – 2.5 × 10− 3 S/cm at 740 °C in air. This value of conductivity is comparable with that of ZrO2/Y2O3 ceramics. The conductivity of Lu2+xTi2−xO7−x/2 depends on the chemical composition. The highest ionic conductivity is exhibited by nearly stoichiometric Lu2+xTi2−xO7−x/2 (x = 0.096; 35.5 mol% Lu2O3) material containing ∼ 4.8 at.% LuTi anti-site defects. 相似文献