全文获取类型
收费全文 | 46455篇 |
免费 | 8496篇 |
国内免费 | 7118篇 |
专业分类
化学 | 34593篇 |
晶体学 | 737篇 |
力学 | 2844篇 |
综合类 | 509篇 |
数学 | 5182篇 |
物理学 | 18204篇 |
出版年
2024年 | 154篇 |
2023年 | 855篇 |
2022年 | 1683篇 |
2021年 | 1765篇 |
2020年 | 1942篇 |
2019年 | 2003篇 |
2018年 | 1674篇 |
2017年 | 1752篇 |
2016年 | 2263篇 |
2015年 | 2476篇 |
2014年 | 2971篇 |
2013年 | 3786篇 |
2012年 | 4305篇 |
2011年 | 4398篇 |
2010年 | 3230篇 |
2009年 | 3250篇 |
2008年 | 3549篇 |
2007年 | 2948篇 |
2006年 | 2706篇 |
2005年 | 2238篇 |
2004年 | 1720篇 |
2003年 | 1468篇 |
2002年 | 1543篇 |
2001年 | 1234篇 |
2000年 | 996篇 |
1999年 | 810篇 |
1998年 | 567篇 |
1997年 | 522篇 |
1996年 | 478篇 |
1995年 | 414篇 |
1994年 | 403篇 |
1993年 | 322篇 |
1992年 | 253篇 |
1991年 | 204篇 |
1990年 | 197篇 |
1989年 | 143篇 |
1988年 | 123篇 |
1987年 | 95篇 |
1986年 | 101篇 |
1985年 | 103篇 |
1984年 | 50篇 |
1983年 | 53篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 22篇 |
1979年 | 28篇 |
1977年 | 22篇 |
1976年 | 14篇 |
1974年 | 13篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献
93.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
94.
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
95.
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
96.
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
97.
98.
99.
100.
Jie Da Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2004,42(2):360-373
The synthesis is reported of copolymers of N,N‐dimethylacrylamide (DMA) and methacrylates containing 2,2′‐dihydroperfluorodecanoyl (RF) groups separated from the methacrylate by long polyethylene glycol (PEG) tether groups (between 1000 and 14,000 Da). At concentrations of between 1 and 8 wt % the copolymers with macromonomer contents of 1 mol % or less give gels in organic solvents such as dioxane, THF, or methanol, as well as in water. Given the low molecular weights, this indicates very efficient association of very low numbers of RF groups. Association and gel formation is enormously enhanced in the presence of longer PEG tethers. This is consistent with smaller poly(N,N,‐dimethylacrylamide) (PDMA) intermolecular excluded volume effects that are mediated by the longer PEG tethers and possibly by the incompatibility of PEG and PDMA that may lead to the formation of PEG microdomains. This increases the local concentrations of the RF groups in the PEO domains that are not diluted by the PDMA chains, as would be the case in the absence of PEG tethers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 360–373, 2004 相似文献