全文获取类型
收费全文 | 67917篇 |
免费 | 5789篇 |
国内免费 | 4860篇 |
专业分类
化学 | 7644篇 |
晶体学 | 126篇 |
力学 | 5376篇 |
综合类 | 562篇 |
数学 | 13397篇 |
物理学 | 13174篇 |
综合类 | 38287篇 |
出版年
2024年 | 272篇 |
2023年 | 792篇 |
2022年 | 1439篇 |
2021年 | 1574篇 |
2020年 | 1704篇 |
2019年 | 1529篇 |
2018年 | 1520篇 |
2017年 | 1906篇 |
2016年 | 2153篇 |
2015年 | 2168篇 |
2014年 | 3403篇 |
2013年 | 4017篇 |
2012年 | 3922篇 |
2011年 | 4251篇 |
2010年 | 3367篇 |
2009年 | 4046篇 |
2008年 | 3767篇 |
2007年 | 4534篇 |
2006年 | 4047篇 |
2005年 | 3573篇 |
2004年 | 3211篇 |
2003年 | 2856篇 |
2002年 | 2590篇 |
2001年 | 2094篇 |
2000年 | 2003篇 |
1999年 | 1701篇 |
1998年 | 1436篇 |
1997年 | 1249篇 |
1996年 | 1093篇 |
1995年 | 963篇 |
1994年 | 866篇 |
1993年 | 744篇 |
1992年 | 664篇 |
1991年 | 570篇 |
1990年 | 527篇 |
1989年 | 373篇 |
1988年 | 354篇 |
1987年 | 282篇 |
1986年 | 191篇 |
1985年 | 167篇 |
1984年 | 151篇 |
1983年 | 77篇 |
1982年 | 100篇 |
1981年 | 68篇 |
1980年 | 37篇 |
1979年 | 46篇 |
1978年 | 36篇 |
1977年 | 29篇 |
1976年 | 20篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
在时序数据库中,有许多成熟的技术和方法用来对布尔型属性之间的关系进行挖掘,但对于数值型属性变化趋势关联关系的研究却不是很多.本文提出了一种数值型属性变化趋势的研究模型QMP(QuantityMovementPattern),依据该模型可利用数据挖掘算法发现不同数值型属性之间变化趋势之间的关系.文中分析了该模型的几种实现算法,并给出了一种快速实现算法及实验数据. 相似文献
103.
104.
王胜奎 《数学的实践与认识》2006,36(5):5-10
根据松纵坑切梢小蠹的主要生物学特征,通过分析抚育间伐持续控制松纵坑切梢小蠹虫害的机理,应用复杂适应系统(CA S)理论,建立了模拟松纵坑切梢小蠹虫害的一种动态演化数学模型,并讨论了模型的收敛性.然后选用昆明小哨林场为背景,进行了各种抚育间伐决策的仿真,从中优选抚育间伐决策.结果表明:模拟优化方案与实际调查统计分析结果一致:均为弱度间伐与中弱度间伐控制蠹害效果最好.最后通过森林积材量与虫害程度之间的优化,给出了抚育间伐的优化策略. 相似文献
105.
臧忠卿 《数学的实践与认识》2006,36(10):132-136
运用中学生男性性别角色期望调查表和因子分析方法对贵阳市中学生进行男性性别角色期望调查和定性与定量分析,为中学生树立适宜的性别角色观,促进其心理健康发展提供量化依据.分析显示:传统的男性角色并不被现代中学生完全接受,无论是男中学生还是女中学生都在力图探求一种新的男性性别角色模式,且两性中学生对这一新的男性性别角色模式的期望和把握是有一定差异的. 相似文献
106.
In this paper, we report that the phase transformation of Ni-B, Ni-P diffusion barriers deposited electrolessly on Cu, for the reason that the Ni-P layer is a more effective diffusion barrier than the Ni-B layer. The Ni3B crystallized was decomposed to Ni and B2O3 above 400 °C and the Ni3P crystallized was decomposed to Ni and P2O5 above 600 °C respectively in Ar atmosphere. Also, the Ni3B was decomposed to Ni and free B above 400 °C and the Ni3P was decomposed to Ni and free P above 600 °C respectively in H2 atmosphere. The decomposed Ni formed a solid solution with Cu. The Cu diffusion occurred above 400 °C for Ni-B layer and above 600 °C for Ni-P layer, respectively. Because the decomposition temperature of Ni-P layer is about 200 °C higher than that of Ni-B layer, the Ni-P layer is a more effective barrier for Cu than the Ni-B layer. 相似文献
107.
M. A. Posypkin I. Kh. Sigal 《Computational Mathematics and Mathematical Physics》2006,46(12):2187-2202
The efficiency of parallel implementations of the branch-and-bound method in discrete optimization problems is considered. A theoretical analysis and comparison of two parallel implementations of this method is performed. A mathematical model of the computation process is constructed and used to obtain estimates of the maximum possible speedup. Examples of problems in which none of these two parallel implementations can speed up the computations are considered. 相似文献
108.
Within the framework of fractal analysis and percolation theory, an alternative model of reinforcement of filled polymers
is offered. Practically, this model can be used only to describe the reinforcement of nanocomposites, because, according to
the treatment considered, a pronounced reinforcement can be reached only at ratios of filler particle diameter to the statistical
segment length of about 10 and less. A theoretical calculation showed a good qualitative and quantitative agreement with experiments.
The type of reinforcement mechanism of composites is determined by the type of the space (fractal or Euclidean) in which the
structure of the polymeric matrix is formed.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 797–802, November–Decem ber, 2006. 相似文献
109.
A two-dimensional model for the simulation of a binary dendritic growth with convection has been developed in order to investigate the effects of convection on dendritic morphologies. The model is based on a cellular automaton (CA) technique for the calculation of the evolution of solid/liquid (s/l) interface. The dynamics of the interface controlled by temperature, solute diffusion and Gibbs–Thomson effects, is coupled with the continuum model for energy, solute and momentum transfer with liquid convection. The solid fraction is calculated by a governing equation, instead of some approximate methods such as lever rule method [A. Jacot, M. Rappaz, Acta Mater. 50 (2002) 1909–1926.] or interface velocity method [L. Nastac, Acta Mater. 47 (1999) 4253; L. Beltran-Sanchez, D.M. Stefanescu, Mat. and Mat. Trans. A 26 (2003) 367.]. For the dendritic growth without convection, mesh independency of simulation results is achieved. The simulated steady-state tip velocity are compared with the predicted values of LGK theory [Lipton, M.E. Glicksmanm, W. Kurz, Metall. Trans. 18(A) (1987) 341.] as a function of melt undercooling, which shows good agreement. The growth of dendrite arms in a forced convection has been investigated. It was found that the dendritic growth in the upstream direction was amplified, due to larger solute gradient in the liquid ahead of the s/l interface caused by melt convection. In the isothermal environment, the calculated results under very fine mesh are in good agreement with the Oseen–Ivanstov solution for the concentration-driven growth in a forced flow. 相似文献
110.
A nanoscale
multivalent platinum drug based on a poly(amidoamine) [PAMAM] dendrimer (generation
4.5, carboxylate surface) has been synthesized and fully characterized using
a variety of spectroscopic, chromatographic and thermal methods. Treatment
of the dendrimer with an aqueous solution containing an excess diaquo(cis-1,2-diaminocyclohexane)platinum(II) produces
a conjugate containing approximately forty (diaminocyclohexane)platinum(II)
moieties at the surface of the dendrimer. This material undergoes smooth two-stage
thermal decomposition to provide residual platinum oxide reflecting the platinum
loading in the drug. 相似文献