全文获取类型
收费全文 | 7655篇 |
免费 | 203篇 |
国内免费 | 24篇 |
专业分类
化学 | 5783篇 |
晶体学 | 45篇 |
力学 | 70篇 |
数学 | 1115篇 |
物理学 | 869篇 |
出版年
2020年 | 77篇 |
2019年 | 73篇 |
2016年 | 147篇 |
2015年 | 146篇 |
2014年 | 114篇 |
2013年 | 258篇 |
2012年 | 244篇 |
2011年 | 326篇 |
2010年 | 183篇 |
2009年 | 192篇 |
2008年 | 293篇 |
2007年 | 301篇 |
2006年 | 274篇 |
2005年 | 307篇 |
2004年 | 285篇 |
2003年 | 231篇 |
2002年 | 199篇 |
2001年 | 112篇 |
2000年 | 103篇 |
1999年 | 110篇 |
1998年 | 109篇 |
1997年 | 129篇 |
1996年 | 129篇 |
1995年 | 124篇 |
1994年 | 112篇 |
1993年 | 123篇 |
1992年 | 109篇 |
1991年 | 108篇 |
1990年 | 85篇 |
1989年 | 109篇 |
1988年 | 119篇 |
1987年 | 105篇 |
1986年 | 113篇 |
1985年 | 138篇 |
1984年 | 107篇 |
1983年 | 109篇 |
1982年 | 112篇 |
1981年 | 100篇 |
1980年 | 107篇 |
1979年 | 96篇 |
1978年 | 88篇 |
1977年 | 85篇 |
1976年 | 82篇 |
1974年 | 95篇 |
1973年 | 86篇 |
1971年 | 75篇 |
1961年 | 141篇 |
1960年 | 195篇 |
1959年 | 102篇 |
1958年 | 115篇 |
排序方式: 共有7882条查询结果,搜索用时 15 毫秒
51.
Pure-silica optical waveguides, fiber couplers, and high-aspect ratio submicrometer channels for electrokinetic separation devices 总被引:1,自引:0,他引:1
Mogensen KB Eriksson F Gustafsson O Nikolajsen RP Kutter JP 《Electrophoresis》2004,25(21-22):3788-3795
A new fabrication procedure for integration of ultraviolet transparent pure-silica planar waveguides, fiber couplers and high-aspect ratio submicrometer channels is presented. Only a single photolithographic mask step is required. The channels are 80-90 microm deep and the width can be reduced to about 0.5 microm, corresponding to a height-to-width ratio of more than 150. The core of the waveguides consists of pure silicon dioxide, which is favorable over doped silica, due to the absence of absorption centers associated with the dopants. This furthermore improves the long-term stability of the waveguides, because of an increased radiation resistance of the glass. The propagation loss decreases from 1.0 dB/cm at 200 nm to 0.2 dB/cm at 800 nm, which, to our knowledge, is the lowest propagation loss reported for integrated planar waveguides in the ultraviolet wavelength region to date. The effective optical path length is 1.2 mm for an absorbance cell with a nominal length of 1.0 mm, indicating effective suppression of stray light. The limit of detection for paracetamol when present in the entire channel network was determined to 3 microg/mL. Finally, the applicability of the fabricated devices for capillary electrophoresis was evaluated by separation of caffein, paracetamol and ketoprofone using absorbance detection at 254 nm. 相似文献
52.
53.
54.
55.
56.
57.
Klaus Weisskopf 《Journal of polymer science. Part A, Polymer chemistry》1988,26(7):1919-1935
The use of the solvent mixture chloroform/hexafluoroisopropanol (98 : 2 vol %) in the GPC-analysis of polyethylene terephthalate (PET) is described. PET-samples of different molecular weight have been prepared and characterized by light scattering, viscometry, and improved techniques of osmometry and end group titration. These well characterized samples were used in calibrating the GPC. The calibration with polydisperse standards was found superior to the universal calibration procedure in the solvent system chosen. 相似文献
58.
Klaus G. Heumann 《Trends in analytical chemistry : TRAC》1982,1(15):357-361
Isotope dilution mass spectrometry is an important method for accurate and precise determination of trace- and micro-amounts of the elements. Using different ionization techniques in the mass spectrometer most of the elements of the periodic table can be analysed. 相似文献
59.
Nelson Durán Klaus Zinner Roberto Casadei de Baptista Carmen C. C. Vidigal Giuseppe Cilento 《Photochemistry and photobiology》1976,24(4):383-388
Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
60.