全文获取类型
收费全文 | 3025篇 |
免费 | 875篇 |
国内免费 | 289篇 |
专业分类
化学 | 688篇 |
晶体学 | 132篇 |
力学 | 37篇 |
综合类 | 22篇 |
数学 | 62篇 |
物理学 | 3248篇 |
出版年
2024年 | 9篇 |
2023年 | 16篇 |
2022年 | 84篇 |
2021年 | 72篇 |
2020年 | 77篇 |
2019年 | 58篇 |
2018年 | 72篇 |
2017年 | 113篇 |
2016年 | 120篇 |
2015年 | 109篇 |
2014年 | 190篇 |
2013年 | 220篇 |
2012年 | 217篇 |
2011年 | 235篇 |
2010年 | 214篇 |
2009年 | 198篇 |
2008年 | 244篇 |
2007年 | 228篇 |
2006年 | 211篇 |
2005年 | 156篇 |
2004年 | 139篇 |
2003年 | 118篇 |
2002年 | 174篇 |
2001年 | 101篇 |
2000年 | 109篇 |
1999年 | 100篇 |
1998年 | 60篇 |
1997年 | 74篇 |
1996年 | 72篇 |
1995年 | 62篇 |
1994年 | 39篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1957年 | 1篇 |
排序方式: 共有4189条查询结果,搜索用时 31 毫秒
991.
992.
抗坏血酸为还原剂制备Se纳米线(英) 总被引:2,自引:0,他引:2
0IntroductionOne鄄dimensionalnanostructuressuchasnanowires,nanorods,ornanotubeshavebeenthesub鄄jectofintensiveresearchduetotheirpotentialuseasactivecomponentsorinterconnectsinfabricatingnanoscaleelectronicorelectromechanicaldevices[1].Theyalsorepresentane… 相似文献
993.
Takeshi HiroseHiroyuki Imai Toshio NaitoTamotsu Inabe 《Journal of solid state chemistry》2002,168(2):535-546
Three kinds of the 1:1 Ni(dmit)2 salts with 4-(4-pyridyl)pyridinium (PP), 4-[2-(4-pyridyl)ethenyl]pyridinium (P=P), and 4-[2-(4-pyridyl)ethyl]pyridinium (P-P) cations have been prepared and structurally characterized. All of these crystals are composed of a multi-dimensional network of the Ni(dmit)2 anions and the hydrogen-bonding one-dimensional cation chains. Compared with tight hydrogen bonds in the P=P and P-P chains, that in the PP chain is rather loose. The P=P and P-P salts show semiconducting behavior with high resistivity and large activation energy, while the PP salt shows the op-posite temperature dependence with low resistivity at high temperature. The thermoelectric power indicates that the PP salt is an n-doped semiconductor. The proton defects may occur in the loosely bound PP chain which results in the carrier doping in the conduction band formed by the π-π interaction of the Ni(dmit)2 anion radicals. 相似文献
994.
Electronic nose based on metal oxide semiconductor sensors as a fast alternative for the detection of adulteration of virgin olive oils 总被引:4,自引:0,他引:4
《Analytica chimica acta》2002,459(2):219-228
An “electronic nose” has been used for the detection of adulterations of virgin olive oil. The system, comprising 12 metal oxide semiconductor sensors, was used to generate a pattern of the volatile compounds present in the samples. Prior to different supervised pattern recognition treatments, feature selection techniques were employed to choose a set of optimally discriminant variables. Linear discriminant analysis (LDA), quadratic discriminant analysis (QDA) and artificial neural networks (ANN) were applied. Excellent results were obtained in the differentiation of adulterated and non-adulterated olive oils and it was even possible to identify the type of oil used in the adulteration. Promising results were also obtained as regards quantification of the percentages of adulteration. 相似文献
995.
Djalma A. de Barros Filho Pompeu P. Abreu Filho U. Werner Michel A. Aegerter 《Journal of Sol-Gel Science and Technology》1997,8(1-3):735-742
Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb2O5 coatings have been determined. The coatings are n-type semiconductor with indirect allowed transition and present an overall low quantum efficiency ( < 4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb2O5 coatings can be made of 10–20 nm size nanoparticles. 相似文献
996.
采用表面改性法制备了负载型NiO-TiO2/SiO2复合半导体材料,用X射线衍射、比表面测定、透射电镜、红外光谱、拉曼光谱、紫外-可见漫反射等技术,研究了光催化材料的物相结构、微粒尺寸、光响应性能及其能带结构.结果表明:复合半导体材料具有较高的比表面积,NiO和TiO2在材料表面产生相互修饰作用,NiO的加入促进了TiO2在载体表面的分散程度,两者复合后部分地形成了Ni-O-Ti键联.复合后的NiO-TiO2/SiO2增强了对紫外光的吸收性能,而且NiO与TiO2间的n-p复合效应改变了原来TiO2单一的能带结构,有效的抑制了光生电子和空穴的复合,从而明显提高材料的光催化性能. 相似文献
997.
Ying-Wu Xu Jing-Ru Zhang Yu-Mei Deng Ling-Kai Hui Shou-Ping Jiang Shao-Hui Lian 《Journal of photochemistry and photobiology. B, Biology》1987,1(2)
At room temperature, the UV fluorescence of trypsin, thyroglobulin, hemoglobin and ablumin are observed; these molecules undergo two-photon absorption when they are excited with the radiation of a frequency-duplicated Q-switched Nd:YAG laser. It is shown that the fluorescence of these proteins comes from the tryptophan residues and that it has a red shift of about 20 nm relative to the one-photon fluorescence. We suggest that the weak emission from tyrosine arises from the forbidden two-photon transition. The influence of concentration on the fluorescence of hemoglobin and tryptophan is discussed. The two-photon absorption cross-sections are estimated. 相似文献
998.
Silicon (Si) is a prime candidate for manufacturing water-splitting photoelectrochemical cells, however, the stability of this material remains a serious bottleneck. This is particularly true for the photoanode, subject to severe deactivation mechanisms. So far, thin film homogeneity has been the paradigm in the quest for stable and efficient Si-based photoanodes, which involved the use of vapor deposition methods to produce conformal thin films ensuring Si protection and efficient catalysis during operation. Conversely, recent reports on n-Si/metal thin film junctions have highlighted the benefits of the junction heterogeneity, generated in situ. In addition, results obtained from n-Si photoanodes partially covered with discontinuous films of Co and Ni nanoparticles lately suggested that homogeneity is not a prerequisite to reach efficiency and stability. Such findings may open new protection routes for Si-based photoanodes, breaking with classical strategies and allowing the use of liquid phase modification methods such as electrodeposition. 相似文献
999.
采用水热法合成了Sn1-x-yMnxFeyO2(0≤x≤0.10, 0≤y≤0.10)稀磁半导体. 通过XRD, Raman, TEM, SQUID和Mössbeaur等技术对化合物进行了结构和性能的表征. 结果表明, XRD中没有出现第二相的沉积, Raman光谱中出现了Mn位于SnO2晶格中的局域模式. 磁性测试结果表明, 当x=0.10, y=0时, 样品在低温下具有较强的磁化强度, 但室温下其磁化强度急剧降低. 而y=0.10, x=0时, 样品的磁化强度和矫顽力都比较小, 但随温度的改变变化不大, Mössbeaur谱测试结果表明, 其中的Fe一部分是铁磁耦合的, 拟合得到超精细场和同质异能移等参数表明, 铁磁性来源于Fe替代SnO2本征性能. Mn和Fe共同掺杂的样品的磁化强度随x的减少和y的增加而减少, 矫顽力却相对于单一元素掺杂的样品大大增加. 相似文献
1000.
Sol–gel glass matrices in which organic laser dyes are embedded can be used as the gain medium in solid‐state, continuously tunable lasers. Such lasers are very simple to construct, and potentially very compact and efficient. Unlike the commonly used liquid dye laser systems, solid‐state dye lasers can be made mechanically robust and portable. In this article, the development of sol–gel/dye lasers, including the sol–gel technology, dye properties, and laser operation, is reviewed. In addition, new solid‐state hosts (such as polyurethane/silica ORMOSILs), additional organic dyes (cyanines), and new studies on the stability of the dyes are presented. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献