全文获取类型
收费全文 | 3535篇 |
免费 | 547篇 |
国内免费 | 609篇 |
专业分类
化学 | 2953篇 |
晶体学 | 47篇 |
力学 | 149篇 |
综合类 | 74篇 |
数学 | 373篇 |
物理学 | 1095篇 |
出版年
2024年 | 10篇 |
2023年 | 63篇 |
2022年 | 122篇 |
2021年 | 130篇 |
2020年 | 145篇 |
2019年 | 180篇 |
2018年 | 126篇 |
2017年 | 142篇 |
2016年 | 192篇 |
2015年 | 174篇 |
2014年 | 214篇 |
2013年 | 235篇 |
2012年 | 305篇 |
2011年 | 323篇 |
2010年 | 240篇 |
2009年 | 224篇 |
2008年 | 253篇 |
2007年 | 226篇 |
2006年 | 192篇 |
2005年 | 172篇 |
2004年 | 159篇 |
2003年 | 114篇 |
2002年 | 136篇 |
2001年 | 119篇 |
2000年 | 89篇 |
1999年 | 68篇 |
1998年 | 45篇 |
1997年 | 35篇 |
1996年 | 42篇 |
1995年 | 44篇 |
1994年 | 30篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1961年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4691条查询结果,搜索用时 125 毫秒
991.
992.
Improvement of pulse amperometric detection (PAD) method is demonstrated in determination of ethylenethiourea (imidazolidine‐2‐thione, ETU). The anodic detection of ETU will produce polymeric film on an electrode leading to an inactive electrode surface. Here, the PAD method was used to remove the polymeric film formed on the electrode surface between ETU detection. Further, the scheme was integrated with automated flow injection analysis (AFIA) for determining ETU. The operational parameters of PAD in the AFIA system were discussed thoroughly. The analytical characteristics of the system were evaluated at optimum conditions. The linear range of calibration plot was between 20 to 300 μM (the correlative coefficient, r = 0.999) and the detection limit was 0.9 μM (S/N = 3). The relative standard deviations of detection of 50 μM ETU were 0.82% with and 9.07% without PAD scheme. The results indicate the system is a very promising tool for ETU determination. Finally, the matrix effects of two water samples that were collected from a campus and a farm show good recoveries of 92% and 96%. 相似文献
993.
Zhao Chu Hu Shan Gao Sheng Hong Hu Yong Sheng Liu Hai Hong Chen 《中国化学快报》2007,18(10):1297-1300
Isopropyl alcohol matrix effect was found to be element specific by using the defined matrix effect factor in ICP-MS,which could not be corrected by using the conventional internal reference method.Unlike the conventional internal reference method,the presented method allows for the analyte to behave differently from the internal reference under the influence of the matrix. 相似文献
994.
以离子液体1-十六烷基-3-甲基溴代咪唑为模板剂合成了Al-MSU-S-Y介孔分子筛,利用XRD、N2吸附-脱附对其进行结构表征,结果表明该方法合成的样品具有较大的孔径、孔容以及比表面积,而且孔径分布较窄.研究了Al-MSU-S-Y对乙二醇与环己酮、丁酮、丙酮、丙醛、丁醛、异丁醛、戊醛、异戊醛、正己醛、正辛醛、苯甲醛等十余种醛(酮)的缩合反应的催化性能,结果表明Al-MSU-S-Y介孔分子筛对醛(酮)与醇的缩合反应有较好的催化性能. 相似文献
995.
DaQingSHI JingCHEN QiYaZHUANG XiangShanWANG HongWenHU 《中国化学快报》2003,14(12):1242-1245
The condensation of aromatic aldehydes with acidic methylene compounds such as malononitrile, methyl cyanoacetate, cyanoacetamide, 5,5-dimethyl-1,3-cyclohexanedione,bartbituric acid and 2-thiobarbituric acid proceeded very efficiently in water in the presence of triethylbenzylammonium chloride (TEBA) and the products were isolated simply by filtration. 相似文献
996.
介稳态氧化钨超微粉体的水热合成与光致变色性质研究 总被引:5,自引:0,他引:5
Under hydrothermal conditions, the superfine powders of cubic pyrochlore-type of tungsten oxide and hexagonal tungsten bronze were obtained by using Na2WO4·2H2O as the starting material. The products were characterized by XRD, TG, IR, UV and EPMA, respectively. The effects of the pH value, the acid concentration, reaction temperature and time on the structure and particle size of products were investigated in detail. The conditions for the preparation of superfine powders of tungsten oxide were optimized. The pH 2.5~4.5 of the reaction system led to the formation of a pyrochlore phase and pH 0.5~2.0 gave the hexagonal tungsten bronze structure. The photochromism property of the hexagonal tungsten bronze was studied. The results show that pyrochlore and bronze phases are decomposed at 300 ℃ and 450 ℃, respectively. With the increasing of temperature, the structure of the two oxides changes. The pyrochlore-type powder changes completely into triclinic Na2W4O13 around 500 ℃, while the bronze phase into a mixture of Na2W6O19 and triclinic WO3 at 550 ℃. The powder of the hexagonal tungsten bronze showed better photochromism property. 相似文献
997.
Keggin结构的钨磷钒稀土四元杂多配合物的合成和物化性质 总被引:4,自引:0,他引:4
合成了9种具有Keggin结构特征的钨磷钒稀土四元杂多配合物,利用化学分析,IR,UV,XPS<ESR,TG-DTA<XRD等手段对配合物进行一表征。 相似文献
998.
Two New Steroidal Glycosides from Liriope muscari 总被引:4,自引:0,他引:4
Zhi Hong CHENG Tao WU Yin Long GUO Bo Yang YU Luo Shan XU 《中国化学快报》2006,17(1):31-34
Liriope muscari (Decn.) Bailey (Liliaceae) is a folk medicinal plant used as a substitute of Ophiopogon japonicus (Thunb.) Ker-Gawl., mainly distributing in Quanzhou, Fujian Province, China1. Previously, we reported the isolation and identification of two… 相似文献
999.
1000.
Through three stories about alcohol antiseptics, "hand" messengers, characters of the article find the best choice of alcohol, and method of application. This article introduces proper ways to use alcohol antiseptics in daily life from the following three aspects. The ethanol and propanol can be used, the best concentration for daily use is 70%, and the optimal use of alcohols is considered under different circumstances. 相似文献