全文获取类型
收费全文 | 1272篇 |
免费 | 115篇 |
国内免费 | 53篇 |
专业分类
化学 | 58篇 |
晶体学 | 7篇 |
力学 | 767篇 |
综合类 | 13篇 |
数学 | 224篇 |
物理学 | 371篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 26篇 |
2020年 | 49篇 |
2019年 | 23篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 50篇 |
2015年 | 53篇 |
2014年 | 55篇 |
2013年 | 79篇 |
2012年 | 73篇 |
2011年 | 83篇 |
2010年 | 61篇 |
2009年 | 80篇 |
2008年 | 86篇 |
2007年 | 67篇 |
2006年 | 61篇 |
2005年 | 60篇 |
2004年 | 49篇 |
2003年 | 37篇 |
2002年 | 57篇 |
2001年 | 33篇 |
2000年 | 32篇 |
1999年 | 31篇 |
1998年 | 27篇 |
1997年 | 32篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 29篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1440条查询结果,搜索用时 15 毫秒
941.
A new approach to carrying out and interpreting hydrodynamic investigations of horizontal wells is proposed. The problem of determining the flow parameters of an inhomogeneous oil reservoir is considered. As the initial information, the pressure recovery curves recorded simultaneously in different sections of the horizontal well borehole are used. 相似文献
942.
Control of mean and fluctuating forces on a circular cylinder at high Reynolds numbers 总被引:2,自引:0,他引:2
A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 × 104 to 1.0 × 105. The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized
by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the
cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in
an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local
changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak
value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points
of view.
The project supported by the National Natural Science Foundation of China (10172087 and 10472124).
The English text was polished by Yunming Chen. 相似文献
943.
The salient features of the interaction between a free-surface flow and a cylinder of rectangular cross-section are investigated and discussed. Laboratory-scale experiments are performed in a water channel under various flow conditions and elevations of the cylinder above the channel floor. The flow field is characterized on the basis of time-averaged and fluctuating local velocity measurements. Dynamic loadings on the cylinder are measured by two water-insulated dynamometers placed inside the cylinder structure. Starting from frequency and spectral analyses of the force signals, insights on the relationship between force dominant frequencies and the Strouhal number of the vortex shedding phenomenon are provided. Experimental results highlight the strong influence of the asymmetric configuration imposed by the two different boundary conditions (free surface and channel floor) on (i) the mean force coefficients and (ii) the vortex shedding frequencies. We provide an analysis of the nature of the dependence of average force coefficients on relevant dimensionless groups, i.e., the Reynolds number, normalized flow depth and cylinder submersion. 相似文献
944.
The equation of stress intensity factors(SIF) of internally pressurized thick- walled cylinder was used as the reference case.SIF equation of rotating thick-walled cylinder containing a radial crack along the internal bore was presented in weight function method.The weight fumction formulas were worked out and can be used for all kinds of depth of cracks,rotating speed,material,size of thick-walled cylinder to calculate the stress intensity factors.The results indicated the validity and effectiveness of these formulas.Meanwhile,the rules of the stress intensity factors in rotating thick-walled cylinder with the change of crack depths and the ratio of outer radius to inner radius were studied.The studies are valuable to engineering application. 相似文献
945.
A novel method for measuring and characterizing dynamic fracture-initiation toughness of elastic-plastic materials 总被引:5,自引:0,他引:5
The characterization and testing methods of the dynamic fracture initiation toughness of elastic-plastic materials under tensile
impact are studied. By using the self-designed bar-bar tensile impact apparatus, a novel test method for studying dynamic
fracture-initiation has been proposed based on the one-dimensional test principle. The curve of average loadv. s. displacement
is smooth until unstable crack propagation, and the kinetic energy which does not contribute to the crack growth can be removed
from total work done by external-force to the specimen. The fracture-initiation point is determined by compliance-changing
rate method. The results show that these methods are feasible and effective. Through the analysis of the conversion between
work and energy of a fracture specimen, the dynamicJ-integral is adopted as a characteristic parameter for elastic-plastic materials under impact loading. TheJ-integral is calculated from
and
curves by using the formula proposed, by Rice. TheJ-integral at fracture initiation is employed to describe the dynamic fracture-initiation toughness of elastic-plastic materials
and the experimental results indicate thatJ
ID can be regarded as a material constant. 相似文献
946.
Summary The paper presents a three-dimensional approximate solution of a longitudinally vibrating cylinder. It is based on the frequency equation for free waves travelling along an infinitely long cylinder which follows from the radial boundary condition on the lateral surface of the cylinder. An equivalent longitudinal traction is calculated by integration of the normal stresses over the end cross section. The full solution of the longitudinally vibrating rod adapted to given axial boundary conditions is derived. The solution is compared to numerical results, and good agreement is obtained. 相似文献
947.
含有裂纹和夹杂的复合柱体的扭转 总被引:3,自引:0,他引:3
本文根据Saint-Venant扭转理论,提出了一种能用于扭转分析的线夹杂模型,并得到了它的基本解,进而将此解与的单层势函数解及单裂纹基本解结合,对同时带有裂纹和夹杂的复合柱体的扭转作了讨论,最后将问题归为解一组混合型积分方程,并建议了数值解法。文中通过问题的退化,证明本文提出的夹杂模型在数学和力学上都是正确的,最后作了若干数值例子的计算,其结果令人满意。 相似文献
948.
结合KHT、BKW、JWL状态方程和DYNA2D二维流体力学计算程序可以模拟分子间炸药的圆筒试验,并以EDD的标准圆筒试验结果进行修正,可计算EDD系列分子间炸药理想爆轰时加速金属最大能力。用KHT和BKW分别计算分子间炸药EA和EAR15,壳体膨胀6mm和19mm时,两种方程计算的圆筒壁速值相差在30m/s以内。经计算可得,在EA配方中加入约40%的RDX,可获得加速金属性能赶上B(64%RDX)炸药的配方。依据圆筒试验理论计算和实验结果可近似计算爆轰反应率。 相似文献
949.
Torsion problems for a cylinder with a rectangular hole and a rectangular cylinder with a crack 总被引:1,自引:0,他引:1
Using the method of singular integral equation and the crack-cutting technique, the rigorous solutions are obtained for a
cylinder with a rectangular hole and a rectangular cylinder with a crack, which exactly satisfy the boundary conditions and
the conditions at the corner points. After that the torsional rigidities and the stress intensity factors at the crack tip
are determined. Next, for the doubly connected circular cylinder with a rectangular hole the expressions for the singular
stresses around the concave corner points are derived and the generalized stress intensity factors are then defined. Since
the crack-cutting technique is used in this paper, the solution of the matching rectangular cylinder is also obtained and
its numerical results coincide with those in references. Thus the method proposed here is verified.
The project supported by National Natural Science Foundation of China 相似文献
950.
本文采用流场显示方法研究单圆柱在非定常流动中的涡旋脱落规律。实验结果表明:在不同的KC数(KC=U∞T/D)下,非常圆柱绕流的涡旋脱落特性是不相同的,一般随KC数值的增加,其涡旋脱落对数也增加,但有明显的阶梯性,同时圆柱分离点的周期变化后于流场的变化。 相似文献