全文获取类型
收费全文 | 3150篇 |
免费 | 293篇 |
国内免费 | 487篇 |
专业分类
化学 | 2903篇 |
晶体学 | 26篇 |
力学 | 161篇 |
综合类 | 40篇 |
数学 | 564篇 |
物理学 | 236篇 |
出版年
2023年 | 69篇 |
2022年 | 72篇 |
2021年 | 135篇 |
2020年 | 148篇 |
2019年 | 143篇 |
2018年 | 99篇 |
2017年 | 123篇 |
2016年 | 145篇 |
2015年 | 101篇 |
2014年 | 146篇 |
2013年 | 229篇 |
2012年 | 149篇 |
2011年 | 153篇 |
2010年 | 141篇 |
2009年 | 157篇 |
2008年 | 154篇 |
2007年 | 192篇 |
2006年 | 185篇 |
2005年 | 181篇 |
2004年 | 169篇 |
2003年 | 191篇 |
2002年 | 118篇 |
2001年 | 105篇 |
2000年 | 88篇 |
1999年 | 83篇 |
1998年 | 70篇 |
1997年 | 66篇 |
1996年 | 41篇 |
1995年 | 66篇 |
1994年 | 44篇 |
1993年 | 29篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1972年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有3930条查询结果,搜索用时 15 毫秒
31.
32.
《Electroanalysis》2006,18(10):947-954
In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for Penicillin G in a flow‐injection system. A special computer‐based numerical calculation method (using Fast Fourier Transformation) is introduced here for enhancing the analyte signal and noise reduction. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on an Au disk microelectrode (with a radius 12.5 μm in radius). The stripping time was less than 200 ms. Effects of rest potential, sweep rate, and delay time on the sensitivity of the method were investigated. The limit of detection of the method was 1.0 × 10?11 M. The detection limit of the method is 660 times lower than the most sensitive reported method. The relative standard deviation of the method at 1.0×10?7 M of Penicillin G was 2.7% for 10 runs. 相似文献
33.
34.
Yu. A. Dyadin F. V. Zhurko I. V. Bondaryuk G. O. Zhurko 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):39-56
Experimental data on the investigation of the water-trimethyleneoxide system,P, t, x phase diagram (up to 6 kbar) are presented. The results are compared with those on water systems with ethyleneoxide, 1,3- and 1,4-dioxane, 1,3-dioxolane and tetrahydrofuran, on the basis of which a summarizedP, t, x diagram is plotted for water-cyclic ether systems. It is shown that in all the systems in which a cubic structure II hydrate forms at 1 bar, it eventually turns to cubic structure I under pressure. The nature of high pressure hydrates is discussed.Dedicated to the memory of D. W. Davidson. 相似文献
35.
D. G. Mazhakin V. K. Khlestkin A. Ya. Tikhonov L. B. Volodarsky 《Russian Chemical Bulletin》1996,45(4):880-884
Derivatives of 1,4-dihydroxypiperazine-2,3-dione were obtained by reaction of cis-1,2-bis(hydroxyamino)cycloalkanes with diethyl oxalate. Their alkylation with CH2N2 or Mel afforded 1,4-dimethoxypiperazine-2,3-diones. Hydrolysis of the latter gave 1,2-bis(methoxyamino)cycloalkanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–929, April, 1996. 相似文献
36.
37.
纳米金修饰玻碳电极在抗坏血酸共存下选择性测定去甲肾上腺素 总被引:16,自引:0,他引:16
利用电沉积的方法制得纳米金修饰玻碳电极 ,该修饰电极对去甲肾上腺素 (NE)氧化反应有催化作用。去甲肾上腺素在纳米金修饰玻碳电极上有很强的吸附作用。研究了磷酸缓冲溶液的pH值和浓度对NE的电化学行为的影响。从去甲肾上腺素和抗坏血酸在纳米金修饰电极的循环伏安图上可观察到两个明显分开的氧化峰 ,峰电位差达到 1 3 1mV ,因此 ,可利用该修饰电极在抗坏血酸存在下选择性测定去甲肾上腺素 ,线性范围为 1× 1 0 - 4 ~5× 1 0 - 6 mol L。 相似文献
38.
Nicole Fietkau Fran?ois G Chevallier Li Jiang Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(10):2162-2167
The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate. 相似文献
39.
1,1'-Diacetoacetylferrocene 1 reacted with phenylene-1,3-dioxyactyl hydrazine 2 in absolute ethanol to give the macrocyclic ferrocenyl dipyrazole compound in moderate yield. Determined by X-ray structure analysis, it crystallizes in monoclinic system, space group P21/c with a = 13.7509(4), b = 8.1277(2), c = 21.7472(6) , β = 103.1030(10)°, V = 2367.25(11) 3, Z = 4, Dc = 1.505 g/cm3, R = 0.0353 and wR = 0.0811. The electrochemical studies reveal that redox of Fe+/Fe in ferrocene is a reversible one-electron process. 相似文献
40.