全文获取类型
收费全文 | 5204篇 |
免费 | 372篇 |
国内免费 | 195篇 |
专业分类
化学 | 4924篇 |
晶体学 | 2篇 |
力学 | 150篇 |
综合类 | 5篇 |
数学 | 31篇 |
物理学 | 659篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 31篇 |
2021年 | 70篇 |
2020年 | 71篇 |
2019年 | 80篇 |
2018年 | 62篇 |
2017年 | 75篇 |
2016年 | 127篇 |
2015年 | 131篇 |
2014年 | 133篇 |
2013年 | 158篇 |
2012年 | 211篇 |
2011年 | 238篇 |
2010年 | 234篇 |
2009年 | 289篇 |
2008年 | 234篇 |
2007年 | 228篇 |
2006年 | 310篇 |
2005年 | 445篇 |
2004年 | 294篇 |
2003年 | 237篇 |
2002年 | 136篇 |
2001年 | 97篇 |
2000年 | 135篇 |
1999年 | 121篇 |
1998年 | 90篇 |
1997年 | 135篇 |
1996年 | 110篇 |
1995年 | 109篇 |
1994年 | 97篇 |
1993年 | 76篇 |
1992年 | 89篇 |
1991年 | 82篇 |
1990年 | 93篇 |
1989年 | 69篇 |
1988年 | 91篇 |
1987年 | 65篇 |
1986年 | 60篇 |
1985年 | 49篇 |
1984年 | 71篇 |
1983年 | 51篇 |
1982年 | 80篇 |
1981年 | 59篇 |
1980年 | 37篇 |
1979年 | 59篇 |
1978年 | 28篇 |
1971年 | 1篇 |
排序方式: 共有5771条查询结果,搜索用时 0 毫秒
101.
T. Bücherl M. Eschler A. Gruner N. Palibroda E. Wolff 《Journal of separation science》1994,17(11):765-769
An integral restrictor interface with jet separator for coupling capillary column supercritical fluid extraction – supercritical fluid chromatography with high resolution mass spectrometry (SFE-SFC-MS) has been built and used for the analysis of a fatty acid ester, and of polymer additives with a wide range of masses. The mobile phase used was supercritical carbon dioxide; a flame ionization detector (FID) was used in parallel with the mass spectrometer. Different SFC-MS interface operating conditions, e.g. temperature, restrictor position, flow rate, and sample transfer conditions were optimized to obtain good sensitivity and separation for these applications. In addition, the sensitivity of measurements performed with the direct insertion probe and by SFC-MS interface have been compared. 相似文献
102.
关于Liesegang环形成机理的研究 总被引:1,自引:0,他引:1
本文研究了Liesegang环的形成,受到两扩散电解质溶液的浓度比、离子浓度积及光照等条件影响。侧重对成环的微观汇聚过程进行了探讨。 相似文献
103.
A capillary zone electrophoresis (CZE) method with ultraviolet-visible detection has been established and validated for the determination of five phenothiazines: thiazinamium methylsulfate, promazine hydrochloride, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride in human urine. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 150 mM tris(hydroxymethyl)aminomethane and 25% acetonitrile at pH 8.2, with temperature and voltage of 25 degrees C and 20 kV, respectively. Naphazoline hydrochloride was used as an internal standard. Field-amplified sample injection (FASI) has been applied to improve the sensitivity of the detection. Considering the influence of parameters affecting the on-line preconcentration (nature of preinjection plug, sample solvent composition, injection times, and injection voltage) and due to the significant interactions among them, in this paper we propose for the first time the application of a multivariate approach to carry out the study. The optimized conditions were as follows: preinjection plug of water for 7 s at 50 mbar, electrokinetic injection for 40 s at 6.2 kV, and 32 microm of H3PO4 in the sample solvent. Also, a solid-phase extraction (SPE) procedure is developed to obtain low detection limits and an adequate selectivity for urine samples. The combination of SPE and FASI-CZE-UV allows adequate linearities and recoveries, low detection limits (from 2 to 5 ng/mL), and satisfactory precisions (3.0-7.2% for an intermediate RSD %). 相似文献
104.
This paper details the analysis of the enantiomers of omeprazole, using aqueous CE coupled with MS detection. Following our
previously published work: where a non-aqueous CE–UV method was developed for omeprazole and 5-hydroxy-omeprazole; coupling
to electro-spray ionization (ESI) MS detection has now been investigated, using a sheath-flow interface for introduction.
An aqueous CE method was developed and designed to afford increased compatibility with ESI–MS detection, employing an ammonium
acetate buffer system (pH 5.8). Common partial filling methods could not be utilized to avoid the entrance of cyclodextrin
into the MS, and therefore a modified method of non-continuous-flow CE–MS was applied, with the CE separation carried out
without applied ESI voltage, before reapplying and allowing flow into the MS for data collection. A chiral CE separation of
omeprazole and 5-hydroxyomeprazole was achieved, and chiral CE resolution of omeprazole has been demonstrated using MS detection. 相似文献
105.
106.
Summary A rapid and sensitive capillary electrophoretic immunoassay is described for determination of estradiol in women's serum.
Addition of thermally reversible hydrogel in the buffer, serving as a replaceable packing material, improved the reproducibility
of the method. Using a laser-induced fluorescence detector this method can be applied to the determination of estradiol at
concentrations as low as 30.6 pg mL1. Estradiol levels in 16 normal women's serum were measured at the range 115≈370 pg mL1. The results of this method have been found to correlate well with those of chemiluminescent immunoassay. 相似文献
107.
V. G. Berezkin T. P. Popova A. A. Korolev V. E. Shiryaeva L. S. Vasin V. N. Lipavskii 《Journal of separation science》1988,11(1):42-46
The peculiarities of the flow splitting technique for sample injection into a capillary column have been discussed. A comparative investigation of reproducibility of the analytical results obtained for two gas chromatographic systems using flow splitting [1) sample injector-packed predolumn-splitter-open tubular capillary column and (2) sample injector-splitter-open tubular capillary column] has been carried out. It was experimentally shown that the first system ensures considerably better reproducibility for the results concerning the composition of the analyzed mixtures. Other advantages of the first system are also discussed. 相似文献
108.
109.
The CGC analysis of 25 organophosphorus and organonitrogen pesticides was optimized on two different stationary phases, namely a 5% diphenyl dimethyl silicone (SE-54 type) and a 50% diphenyl dimethyl silicone (OV-17 type) by selecting the best temperature program conditions, using computer simulation. 相似文献
110.
Stationary phase crosslinking conditions for fused silica capillary columns were optimized with the use of a factorial design experiment. This experimental strategy was chosen because it provided for the determination of two-factor interactions. A predictive model was developed for the desired chromatographic performance parameters as a function of the variables of the crosslinking reaction. Confirmatory experiments proved the usefulness of the mathematical model which resulted in the production of capillary columns of superior performance with significant improvements in reproducibility. 相似文献