全文获取类型
收费全文 | 39944篇 |
免费 | 7087篇 |
国内免费 | 5744篇 |
专业分类
化学 | 29903篇 |
晶体学 | 608篇 |
力学 | 2350篇 |
综合类 | 396篇 |
数学 | 4455篇 |
物理学 | 15063篇 |
出版年
2024年 | 28篇 |
2023年 | 644篇 |
2022年 | 927篇 |
2021年 | 1315篇 |
2020年 | 1506篇 |
2019年 | 1585篇 |
2018年 | 1349篇 |
2017年 | 1374篇 |
2016年 | 1880篇 |
2015年 | 2032篇 |
2014年 | 2485篇 |
2013年 | 3198篇 |
2012年 | 3750篇 |
2011年 | 3900篇 |
2010年 | 2861篇 |
2009年 | 2899篇 |
2008年 | 3207篇 |
2007年 | 2665篇 |
2006年 | 2503篇 |
2005年 | 2068篇 |
2004年 | 1563篇 |
2003年 | 1333篇 |
2002年 | 1326篇 |
2001年 | 1043篇 |
2000年 | 850篇 |
1999年 | 670篇 |
1998年 | 483篇 |
1997年 | 446篇 |
1996年 | 396篇 |
1995年 | 326篇 |
1994年 | 323篇 |
1993年 | 274篇 |
1992年 | 220篇 |
1991年 | 181篇 |
1990年 | 177篇 |
1989年 | 134篇 |
1988年 | 106篇 |
1987年 | 87篇 |
1986年 | 100篇 |
1985年 | 75篇 |
1984年 | 44篇 |
1983年 | 44篇 |
1982年 | 30篇 |
1981年 | 39篇 |
1980年 | 24篇 |
1979年 | 37篇 |
1978年 | 18篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
103.
104.
This paper presents a multiobjective hybrid metaheuristic approach for an intelligent spatial zoning model in order to draw territory line for geographical or spatial zone for the purpose of space control. The model employs a Geographic Information System (GIS) and uses multiobjective combinatorial optimization techniques as its components. The proposed hybrid metaheuristic consists of the symbiosis between tabu search and scatter search method and it is used heuristically to generate non-dominated alternatives. The approach works with a set of current solution, which through manipulation of weights are optimized towards the non-dominated frontier while at the same time, seek to disperse over the frontier by a strategic oscillation concept. The general procedure and its algorithms are given as well as its implementation in the GIS environment. The computation has resulted in tremendous improvements in spatial zoning. 相似文献
105.
求线性规划初始可行基的新方法 总被引:9,自引:3,他引:6
本文提出一个求线性规划初始可行基的新算法,该算法不仅避免了人工变量,而且理论分析及初步的数值实验结果表明其效率更高。 相似文献
106.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
107.
108.
109.
110.
Dong‐Guk Yu Jeong Ho An 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5608-5616
Ultrafine black particles, ranging in diameter from 1 to 3 μm, were prepared by dispersion polymerization in a methanol/water mixture with vinyl monomers, nonpolymerizable Sudan black B dyes, and fluorescein isothiocyanate labeled charge control additives. Both the ratio of the methanol to the water dispersion medium and the polymeric stabilizer concentration had significant effects on the particle size. The important role of the stabilizer concentration lay in the particle formation step, during which it determined the particle stability and final particle size. These could affect the extent of the aggregation of nuclei by changing the adsorption rate of the stabilizer and the viscosity of the dispersion medium, resulting in smaller particles. The fluorescent‐labeled charge control additives strongly affected the electrophoretic mobility. A small concentration of fluorescent‐labeled charge control additives increased the electrophoretic mobility. However, a further addition reduced the electrophoretic mobility of the polymer particles. The concentration dependence of the fluorescent‐labeled charge control additives on the deposition behavior in the polymer particles was successfully imaged and thereafter quantified by image analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5608–5616, 2004 相似文献