全文获取类型
收费全文 | 92987篇 |
免费 | 7805篇 |
国内免费 | 8935篇 |
专业分类
化学 | 33538篇 |
晶体学 | 624篇 |
力学 | 8766篇 |
综合类 | 1646篇 |
数学 | 40268篇 |
物理学 | 24885篇 |
出版年
2023年 | 773篇 |
2022年 | 1096篇 |
2021年 | 1591篇 |
2020年 | 1969篇 |
2019年 | 2211篇 |
2018年 | 1961篇 |
2017年 | 2360篇 |
2016年 | 2621篇 |
2015年 | 2235篇 |
2014年 | 3375篇 |
2013年 | 6548篇 |
2012年 | 3989篇 |
2011年 | 4537篇 |
2010年 | 3945篇 |
2009年 | 5224篇 |
2008年 | 5816篇 |
2007年 | 6101篇 |
2006年 | 5567篇 |
2005年 | 4874篇 |
2004年 | 4465篇 |
2003年 | 4476篇 |
2002年 | 3881篇 |
2001年 | 3372篇 |
2000年 | 3129篇 |
1999年 | 2798篇 |
1998年 | 2562篇 |
1997年 | 2155篇 |
1996年 | 1893篇 |
1995年 | 1800篇 |
1994年 | 1596篇 |
1993年 | 1339篇 |
1992年 | 1280篇 |
1991年 | 1017篇 |
1990年 | 809篇 |
1989年 | 700篇 |
1988年 | 660篇 |
1987年 | 517篇 |
1986年 | 446篇 |
1985年 | 532篇 |
1984年 | 507篇 |
1983年 | 250篇 |
1982年 | 418篇 |
1981年 | 450篇 |
1980年 | 357篇 |
1979年 | 330篇 |
1978年 | 256篇 |
1977年 | 229篇 |
1976年 | 169篇 |
1974年 | 118篇 |
1973年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
动量矩变量描述的陀螺体永久转动的分岔特性 总被引:2,自引:0,他引:2
本文建立以动量矩分量和Deprit正则变量为独立变量的陀螺体动力学方程,用以描述无力矩非对称陀螺体的姿态运动。在动量矩空间内讨论了陀螺体永久转动轴的数目和稳定性随转子转速变化的分岔特性。 相似文献
992.
一阶非线性项、四阶色散项的Boussinesq类方程 总被引:1,自引:0,他引:1
推导了由一阶色散项O(β2)表示的Bousinesq类方程,方程中保留了一阶非线性项O(α)及四阶色散项O(β8),其中α=A/h0,β=h0/L,A为特征波高,L为特征波长,h0为特征水深从理论上证明了Bousinesq改善型方程对色散性精度的提高,阐明了此类方程对色散项所保留的精度为O(β8),而并非是此类方程推导之初的假设为O(β2)这一点,将改变人们传统的认识 相似文献
993.
P.W. Doyle 《International Journal of Non》1998,33(6):83
Newton equations are dynamical systems on the space of fields. The solutions of a given equation which are curves of characteristic fields for its force are planar and have constant angular momentum. Separable solutions are characteristic with angular momentum equal to zero. A Newton equation is separable if and only if its characteristic equation is homogeneous. Separable equations correspond to invariants of homogeneous ordinary differential equations, and those associated with a given homogenous equation correspond to its generalized dilation symmetries. A Newton equation is compatible with the characteristic condition if and only if its characteristic equation is linear. Such equations correspond to invariants of linear ordinary differential equations. Those associated with a given linear equation correspond to the central force problems on its solution space. Regardless of compatibility, any Newton equation with a plane of characteristic fields has non-separable characteristic solutions. 相似文献
994.
本文根据横观各向同性弹性力学的通解获得了无限体的点力解,由它可以直接退化到各向同性情形的Kelvin解,利用这个点力解编制的边界元法程序,适用于横观各向同性材料也适用于各向同性材料,因此是真正的统一点力解。还用边界元法计算了两个数值例题。 相似文献
995.
Redistribution of a LNAPL lens (oil) at the phreatic surface is described using a multi-phase flow model, with emphasis on the effect of oil entrapment by water. The flow process is analyzed under the assumption that the vertical capillary and gravitational forces balance. Vertical integration leads to explicit functions which approximate the relations between the free oil volume per unit lateral area and the vertically averaged oil relative permeability on the one hand and the vertical position of the interface between zones with either two or three phases on the other hand. A linear relation between the trapped and free oil volume per unit lateral area approximates the vertically integrated nonlinear expression for the trapped oil saturation. The resulting differential equation admits a similarity solution describing the lateral spreading of free oil and the amount and location of trapped oil. Comparison with illustrative numerical computations, which are based on the nonreduced flow model in a two-dimensional planar or axisymmetric domain, shows that the analytical solution provides a good approximation of the free oil distribution at all later times. 相似文献
996.
旋涡与行进表面水波相互作用的实验研究 总被引:1,自引:0,他引:1
采用振动板式造波器在二维水槽中生成近似单色的行进表面水波,采用夹板式涡发生器生成稳定上浮的涡对,在Froude数约为0.5的条件下,得到了水下涡对与不同波长和振幅的行进表面水波相互作用时的干扰图象,以实验方法验证了理论分析和数值计算的结果,并为进一步研究旋涡与行进表面水波的相互作用提供了一种实验研究方法 相似文献
997.
Local fracture resistance (FR) of short (SGF) and discontinuous long glass fibre (LGF) reinforced polypropylene (PP) was predicted using the ‘microstructural efficiency concept’ together with a simulation program for fibre orientation in injection molding. The ‘microstructural efficiency concept’ describes the relation between microstructural parameters such as the fibre content, the fibre aspect ratio and the processing (injection molding) induced layer structure taking also into account the local fibre orientation. The local fibre orientation in injection molding was predicted with the MOLDFLOW®-software. The predicted local FR was compared with the measured one, which was determined by using compact tension samples and linear elastic fracture mechanics (LEFM). The comparison showed, that for SGF-PP good consistence between the predicted and measured FR existed, for LGF-PP the discrepancy was higher. Yet for both materials, the ‘microstructural efficiency concept’ together with the results obtained from the simulation of the fibre orientation can be used for FR prediction of an injection molded workpiece. 相似文献
998.
999.
1000.
The stress vector-based constitutive model for cohesionless soil, proposed by SHI Hong-yan et al., was applied to analyze
the deformation behaviors of materials subjected to various stress paths. The result of analysis shows that the constitutive
model can capture well the main deformation behavior of cohesionless soil, such as stress-strain nonlinearity, hardening property,
dilatancy, stress path dependency, non-coaxiality between the principal stress and the principal strain increment directions,
and the coupling of mean effective and deviatoric stress with deformation. In addition, the model can also take into account
the rotation of principal stress axes and the influence of intermediate principal stress on deformation and strength of soil
simultaneously. The excellent agreement between the predicted and measured behavior indicates the comprehensive applicability
of the model.
Biography: SHI Hong-yan (1962-), Associate Professor, Doctor 相似文献