全文获取类型
收费全文 | 5764篇 |
免费 | 425篇 |
国内免费 | 265篇 |
专业分类
化学 | 1658篇 |
晶体学 | 32篇 |
力学 | 2483篇 |
综合类 | 22篇 |
数学 | 923篇 |
物理学 | 1336篇 |
出版年
2024年 | 6篇 |
2023年 | 75篇 |
2022年 | 105篇 |
2021年 | 98篇 |
2020年 | 135篇 |
2019年 | 114篇 |
2018年 | 126篇 |
2017年 | 154篇 |
2016年 | 199篇 |
2015年 | 143篇 |
2014年 | 201篇 |
2013年 | 359篇 |
2012年 | 289篇 |
2011年 | 344篇 |
2010年 | 266篇 |
2009年 | 340篇 |
2008年 | 309篇 |
2007年 | 316篇 |
2006年 | 273篇 |
2005年 | 326篇 |
2004年 | 226篇 |
2003年 | 231篇 |
2002年 | 202篇 |
2001年 | 169篇 |
2000年 | 142篇 |
1999年 | 121篇 |
1998年 | 112篇 |
1997年 | 112篇 |
1996年 | 91篇 |
1995年 | 118篇 |
1994年 | 87篇 |
1993年 | 84篇 |
1992年 | 54篇 |
1991年 | 72篇 |
1990年 | 53篇 |
1989年 | 45篇 |
1988年 | 66篇 |
1987年 | 55篇 |
1986年 | 55篇 |
1985年 | 42篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 44篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有6454条查询结果,搜索用时 15 毫秒
71.
Robert J. Houben Hans-Gerd M. Janssen Piet A. Leclercq Jacques A. Rijks Carel A. Cramers 《Journal of separation science》1990,13(10):669-673
A simple and versatile system is described for the on-line coupling of SFE to capillary GC. The interfacing consists of a programmed temperature vaporizer (PTV) injector. With this injector it is possible to combine solute trapping, elimination of a high flow of extraction fluid, and quantitative transfer of solutes to the seperation column. The problems caused by impurities in the extraction fluid in on-line SFE-GC are discussed. Simple methods are described for the purification of commercially available carbon dioxide. The trapping efficiency of the PTV injector is studied. Applications of the SFE-PTV-GC system are given for the analysis of polymer anti-degradants, polar compounds, and samples with environmental relevance. 相似文献
72.
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
73.
Summary Methods for the determination of specific migration of polymer additives from polypropylene to aqueous acetic acid and isooctane have been studied. The migrants were extracted from aqueous acetic acid and characterized by supercritical fluid chromatography (SFC) with flame ionization detection (FID) and mass spectrometry (MS). The isooctane simulant was concentrated and injected directly into the SFC. Injection of extracts after incubation, using the solvent venting injection technique in the SFC, enabled additive concentrations as low as 10 ppb in 150 ml simulant to be determined, corresponding to a specific migration level of approximately 1 g additive/dm2 polymer. 相似文献
74.
在仅以碘化钾为重原子微扰剂、亚硫酸钠为除氧剂及无任何保护性介质存在的水溶液中 ,吲哚_3_丁酸 (IBA)能发射很强的室温光 (RTP) ;详细研究了分析测定条件及有机溶剂对RTP的影响 ;在最大光波长λex/λem =281/447nm处 ,光强度与IBA浓度在2.0×10 -7~1.0×10 -5mol/L范围内呈良好的线性关系 ,检出限4.3×10-8 mol/L ;方法直接用于强化水样和土壤中IBA的测定 ,回收率96 %~104 % ,相对标准偏差2.37 %~3.97 %。 相似文献
75.
A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, 1H NMR, 29Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography. 相似文献
76.
Daixin Tong Keith D. Bartle Anthony A. Clifford Robert E. Robinson 《Journal of separation science》1992,15(8):505-509
A unified approach to sequential gas and supercritical fluid Chromatography using 50 μm i.d. open tubular columns is described. Sample introduction is performed by means of a rotary injection valve. In order that linear velocities can be optimized independently, a second rotary valve in the chromatographic oven is used to direct the flow of column eluate to the flame ionization detector through either fused silica tubing in GC, or a frit restrictor in SFC. Applications of sequential GC-SFC on a 50 μm i.d. open tubular column are demonstrated, and comparisons made between sequential GC-SFC on 50 and 100 μm i.d. columns. 相似文献
77.
We have observed an unusual reduction of shear stress with increasing shear rate under direct current electric fields, for
an electrorheological fluid composed of sulfonated poly(styrene-co-divinylbenzene) particles dispersed in silicone oil. At all shear rates, the shear stress under the electric field is larger
than that in the absence of the field, indicating that there is still some field-induced agglomeration of the particles. In
contrast, the behavior under alternating current electric fields is the Bingham-fluid-type response commonly observed with
electrorheological fluids. It is suggested that the conventional dipole–dipole interaction approach based on simplified microstructural
models would be unable to explain these phenomena.
Received: 27 November 2000 Accepted: 22 May 2001 相似文献
78.
Summary This work describes the study of a degradation curve of Oxadixyl in field-treated potato and tomato samples. The residues
were extracted using classical and supercritical fluid (SFE) extraction methods and analyzed by HRGC/ECD. The extraction techniques
were compared and the results indicate the advantages of using SFE as an alternative method for pesticide analyses in these
samples. 相似文献
79.
In this paper, we present a rheological study of a compact layer of highly swollen gel beads. The flow regimes of these systems are modelled by an elastic sinusoid moving in a Newtonian fluid. This model predicts a yield stress varying with the square root of the elastic modulus of the gel bead. The slope at the origin (at zero velocity) of the flow curve is expected to depend only on geometrical parameters and on the solvent viscosity. The experimental data are in qualitative agreement with the theoretical predictions. 相似文献
80.