全文获取类型
收费全文 | 2695篇 |
免费 | 368篇 |
国内免费 | 214篇 |
专业分类
化学 | 1248篇 |
晶体学 | 35篇 |
力学 | 17篇 |
综合类 | 19篇 |
数学 | 243篇 |
物理学 | 1715篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 51篇 |
2021年 | 35篇 |
2020年 | 50篇 |
2019年 | 38篇 |
2018年 | 45篇 |
2017年 | 103篇 |
2016年 | 91篇 |
2015年 | 92篇 |
2014年 | 164篇 |
2013年 | 348篇 |
2012年 | 178篇 |
2011年 | 147篇 |
2010年 | 130篇 |
2009年 | 133篇 |
2008年 | 118篇 |
2007年 | 127篇 |
2006年 | 118篇 |
2005年 | 153篇 |
2004年 | 121篇 |
2003年 | 101篇 |
2002年 | 84篇 |
2001年 | 96篇 |
2000年 | 64篇 |
1999年 | 51篇 |
1998年 | 67篇 |
1997年 | 65篇 |
1996年 | 55篇 |
1995年 | 56篇 |
1994年 | 43篇 |
1993年 | 39篇 |
1992年 | 29篇 |
1991年 | 30篇 |
1990年 | 33篇 |
1989年 | 18篇 |
1988年 | 25篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有3277条查询结果,搜索用时 15 毫秒
61.
A detector for HPLC is based on suppression of chemiluminescence from the Cu(II)-luminol-peroxide reaction. Analytes which complex Cu(II) reduce the free Cu(II) concentration and thus the observed chemiluminescence intensity. The degree of chemiluminescence suppression is a measure of the analyte concentrations. Detection limits are in the range of 1 pmole-1 nmole for amino acids (both primary and secondary without derivatization), CN–, amines, catecholamines, catechol, and aminoglycoside antibiotics. The detection approach is demonstrated with an ion-exchange separation of amino acids, a reverse phase separation of catecholamines, and an ion-pair separation of the three components of gentamicin C in commercial gentamicin sulfate. 相似文献
62.
Isotachophoresis carried out in a 0.25 mm i.d. fused-silica capillary tube yielded high resolution, compared with that in a fluorinated ethylene-propylene polymer tube. The use of an ultraviolet-visible multichannel spectrophotometer with photodiode array as detector together with a cross flow cell (volume 0.01 μl) was investigated. The system was successfully applied to the analysis of cationic dyes such as neutral red, bismarck brown, and basic fuchsine. 相似文献
63.
Summary A flow-through two electrode wall-jet cell with a platinum measuring electrode and a cell volume of 20 nl has been designed and evaluated. It has been used to detect phenols by reversed phase liquid chromatography using short micro bore columns. The linear dynamic range between the measured current and the concentration is greater than 103 (1.5×10–7–5×10–4 mol/l) and the minimum analyzable amount was found to be 10 pg for pyrocatechol. A negligible broadening in the detector permits the use of micro columns down to 0.5 mm internal diameter, packed with 5 m particles, without any substantial distortion of eluted zones.Presented at the 14th International Symposium on Chromatography London, September, 1982 相似文献
64.
65.
Andreas Manz Elisabeth Verpoorte Carlo S. Effenhauser Norbert Burggraf Daniel E. Raymond D. Jed Harrison H. Michael Widmer 《Journal of separation science》1993,16(7):433-436
Miniaturization of separation columns implies equally reduced vol- umes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm. 相似文献
66.
A novel thin-layer amperometric detector (TLAD) based on chemically modified ring-disc electrode and its application for simultaneous measurements of nitric oxide (NO) and nitrite (NO2−) in rat brain were demonstrated in this work. The ring-disc electrode was simultaneously sensitive to nitric oxide (NO) and nitrite (NO2−) by modifying its inner disc with electropolymerized film of cobalt(II) tetraaminophthalocyanine (polyCoTAPc)/Nafion and its outer ring with poly(vinylpyridine) (PVP), respectively. The ring-disc electrode was used to constitute a novel TLAD in radial flow cell for simultaneous measurements of NO and NO2− in rat brain combined with techniques of high performance liquid chromatography (HPLC) and in vivo microdialysis. It was found that the basal concentration of NO in the caudate nucleus of rat brain is lower than 1.0×10−7 mol l−1, NO2− concentration is 5.0×10−7 mol l−1 and NO exists in brain maybe mainly in the form of its decomposed product. 相似文献
67.
The electron capture detector (ECD) response to numerous aromatic hydrocarbons of low electron affinity (EA) is shown to be detrimentally affected by two processes which compete with and typically overwhelm the electron capture reactions of these molecules. It is shown that the effects of these two undesired reactions can be eliminated by the permanent addition of trimethylamine and one of several alkyl monochlorides to the detector make-up gas. These modifications of the detector gas result in greatly increased sensitivity, increased linearity, and increased reproducibility of response. A kinetic model for the ECD responses of low EA resonance capture molecules is developed which appears to explain these improvements. 相似文献
68.
用二维色谱技术测定聚合反应气体组成 总被引:1,自引:1,他引:1
介绍一种无阀切换的二维气相色谱分析方法。采用两根不同性质的色谱柱并联连接,样品分别经两根色谱柱分离后汇合在一起进入同一检测器。一次进样可同时测定H2、O2、N2及C1~C3的组分。 相似文献
69.
Ursula Ehrmann Lante Carbognani Claudio Ceccarelli 《Journal of separation science》1992,15(7):467-471
Two methods have been developed for the determination of trace levels of acetonitrile and propionitrile in light naphthas. One involves clean-up and preconcentration by medium pressure liquid chromatography (MPLC) in which nitriles are concentrated ten-fold while the complex hydrocarbon matris is removed. The concentrated solution is then analyzed by high resolution GC with flame ionization detection. The second method involves direct injection of samples into a capillary GC equipped with chemiluminescence nitrogen detection. The results and repeatability obtained from both methods are comparable. Preconcentration enables identification by GC-MS and simultaneous analysis of other polar species, with no need for selective detectors. Direct analysis is, on the other hand, much less time-consuming and requires less sample. 相似文献
70.
Summary The separation of two families of plastics additives (phenolic antioxidants and UV absorbers) has been achieved by high performance liquid chromatography with a quaternary gradient. A methodology of separation based on a sequential optimization is described. After a preliminary study of the effects of solvents on retention of compounds, the mobile phase is first chosen for each class of additives (Irganox and Tinuvin), then for the mixture of all the compounds and the separation is finally optimized. The importance of the column phase ratio is also reported. The use of two detectors, UV absorbance and light-scattering, enables all the compounds to be detected. The performance of the detectors has been compared and the effects of the nebulization temperature on the detection of low molecular mass compounds is reported. 相似文献