全文获取类型
收费全文 | 9680篇 |
免费 | 1001篇 |
国内免费 | 1166篇 |
专业分类
化学 | 4237篇 |
晶体学 | 105篇 |
力学 | 1306篇 |
综合类 | 195篇 |
数学 | 2536篇 |
物理学 | 3468篇 |
出版年
2024年 | 11篇 |
2023年 | 62篇 |
2022年 | 170篇 |
2021年 | 214篇 |
2020年 | 226篇 |
2019年 | 222篇 |
2018年 | 221篇 |
2017年 | 287篇 |
2016年 | 348篇 |
2015年 | 255篇 |
2014年 | 387篇 |
2013年 | 633篇 |
2012年 | 572篇 |
2011年 | 585篇 |
2010年 | 472篇 |
2009年 | 615篇 |
2008年 | 660篇 |
2007年 | 631篇 |
2006年 | 604篇 |
2005年 | 505篇 |
2004年 | 482篇 |
2003年 | 415篇 |
2002年 | 368篇 |
2001年 | 374篇 |
2000年 | 291篇 |
1999年 | 302篇 |
1998年 | 241篇 |
1997年 | 212篇 |
1996年 | 201篇 |
1995年 | 187篇 |
1994年 | 156篇 |
1993年 | 108篇 |
1992年 | 126篇 |
1991年 | 106篇 |
1990年 | 98篇 |
1989年 | 89篇 |
1988年 | 60篇 |
1987年 | 61篇 |
1986年 | 54篇 |
1985年 | 35篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 34篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
1.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange. 相似文献
2.
Sensitivity analysis is a mathematical tool, first developed for optimization methods, which aim is to characterize a system response through the variations of its output parameters following modifications imposed on the input parameters of the system. Such an analysis may quickly become laborious when the thermal model under consideration is complex or the number of input parameters is high. In this paper, we develop a mathematical model to analyse the heat exchanges in four different types of solar air collectors. When building this thermal model we show that for each collector, at quasi-steady state, the energy balance equations of the components of the collector cascade into a single first-order non-linear differential equation that is able to predict the thermal behaviour of the collector. Our heat transfer model clearly demonstrates the existence of an important dimensionless parameter, referred to as the thermal performance factor of the collector, that compares the useful thermal energy which can be extracted from the heater to the overall thermal losses of that collector for a given set of input parameters. A sensitivity analysis of our thermal model has been performed for the most significant input parameters such as the incident solar irradiation, the inlet fluid temperature, the air mass flow rate, the depth of the fluid channel, the number and nature of the transparent covers in order to measure the impact of each of these parameters on our model. An important result which can be drawn from this study is that the heat transfer model developed is robust enough to be used for thermal design studies of most known flat plate solar air heaters, but also of flat plate solar water collectors and linear solar concentrators. 相似文献
3.
In this paper we consider a wavelet algorithm for the piecewise constant collocation method applied to the boundary element solution of a first kind integral equation arising in acoustic scattering. The conventional stiffness matrix is transformed into the corresponding matrix with respect to wavelet bases, and it is approximated by a compressed matrix. Finally, the stiffness matrix is multiplied by diagonal preconditioners such that the resulting matrix of the system of linear equations is well conditioned and sparse. Using this matrix, the boundary integral equation can be solved effectively. 相似文献
4.
Nagendranath Mahata V. Vishwanathan 《Journal of molecular catalysis. A, Chemical》1997,120(1-3):267-270
Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (Ea) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed. 相似文献
5.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
6.
7.
8.
关于AOR迭代法的研究 总被引:5,自引:0,他引:5
陈恒新 《应用数学与计算数学学报》2002,16(1):40-46
本文论证了严格对角占优矩阵之AOR法的误差估计式中的误差估计常数hγ,ω(0≤γ≤ω0)的最小值是h1,1. 相似文献
9.
10.
关于惠斯登电桥测电阻倍率与检流计灵敏度关系的研究 总被引:1,自引:0,他引:1
在相同的设备条件下,电桥临近平衡时灵敏度最高的最佳倍率是:组成倍率的两个电阻的数量级与待测电阻数量级相等,且比值为1的倍率。 相似文献