全文获取类型
收费全文 | 8033篇 |
免费 | 676篇 |
国内免费 | 433篇 |
专业分类
化学 | 5468篇 |
晶体学 | 15篇 |
力学 | 1032篇 |
综合类 | 31篇 |
数学 | 235篇 |
物理学 | 2361篇 |
出版年
2023年 | 101篇 |
2022年 | 95篇 |
2021年 | 76篇 |
2020年 | 135篇 |
2019年 | 108篇 |
2018年 | 107篇 |
2017年 | 165篇 |
2016年 | 225篇 |
2015年 | 269篇 |
2014年 | 265篇 |
2013年 | 345篇 |
2012年 | 441篇 |
2011年 | 526篇 |
2010年 | 427篇 |
2009年 | 486篇 |
2008年 | 404篇 |
2007年 | 437篇 |
2006年 | 354篇 |
2005年 | 351篇 |
2004年 | 291篇 |
2003年 | 266篇 |
2002年 | 189篇 |
2001年 | 176篇 |
2000年 | 184篇 |
1999年 | 162篇 |
1998年 | 147篇 |
1997年 | 155篇 |
1996年 | 152篇 |
1995年 | 152篇 |
1994年 | 139篇 |
1993年 | 137篇 |
1992年 | 82篇 |
1991年 | 102篇 |
1990年 | 80篇 |
1989年 | 97篇 |
1988年 | 129篇 |
1987年 | 112篇 |
1986年 | 106篇 |
1985年 | 132篇 |
1984年 | 125篇 |
1983年 | 76篇 |
1982年 | 124篇 |
1981年 | 120篇 |
1980年 | 103篇 |
1979年 | 118篇 |
1978年 | 75篇 |
1977年 | 14篇 |
1976年 | 30篇 |
1973年 | 20篇 |
1972年 | 17篇 |
排序方式: 共有9142条查询结果,搜索用时 31 毫秒
121.
尿中3种苯氧羧酸类除草剂的气相色谱分析法 总被引:3,自引:1,他引:3
本文研究了2,4-滴、2,4-滴丙酸和2甲4氯3种苯氧羧酸类除草剂用硫酸、三氯化硼、氯化氢和三氟乙酸等4种催化剂的甲醇、乙醇、丙醇、丁醇、戊醇、苯甲醇、三氟乙醇、五氟丙醇、二氯丙醇和五氟苯甲醇等10种醇的酯化衍生反应条件,在此基础上建立了尿中3种苯氧羧酸类除草剂的各种衍生化气相色谱电子俘获检测方法,其中较灵敏的方法2,4-滴和2,4-滴丙酸的检出限低于10 ng/mL,2甲4氯的检出限低于20ng/mL,适于职业接触者和中毒者的尿分析。 相似文献
122.
The binding of sodium dodecyl benzene sulphonate (SDBS) with poly(N-vinyl-2-pyrrolidone) (PVP) has been investigated at 303.15 and 313.15 K using equilibrium dialysis, surface tension, viscosity, ultrasound velocity and ultrasound absorption techniques. From each of these studies four distinct regions of SDBS-PVP interactions were observed. Interaction of SDBS with PVP was found to involve the binding of surfactant dimers with the polymer molecule followed by usual micellization. The binding data has been analyzed in terms of various models of polymer-surfactant interaction. 相似文献
123.
K. Grob 《Journal of separation science》1978,1(5):263-267
During one year continuous use of on-column injection, the typical advantages described in our first report have fully been confirmed. In addition the analysis of large sample volumes has proved promising. Only minor modifications have been applied to the on-column injector device. Broad evidence has been gathered showing that full separation efficiency of the capillary columns after on-column injection is attained only when cold trapping or the solvent effect, as band shortening mechanisms, are working- While, under the conditions of on-column injection, cold trapping is less efficient than with other injection techniques, the opposite holds true for the solvent effect. Compared with splitless injection, the danger of excessive solvent condensation on the column is increased. A working rule is presented for establishing the optimal chromatographic conditions for handling large sample volumes while ensuring full separation efficiency yet avoiding harm to the column. 相似文献
124.
Summary The gas chromatographic analysis of the acetonyl esters of aromatic, dicarboxylic and higher fatty acids is reported and discussed together with their electron impact and chemical ionisation mass spectra. An improved method for the preparation of acetonyl esters is discussed. 相似文献
125.
The Gas Complex MnAlF5 and its Influence on the Purification of AlF3 by Sublimation The gas complex MnAlF5 has been determined mass spectroscopically by the ions MnAlF5+ and MnAlF4+. The gas complex MnAlF5 is formed above 973 K by heating up mixtures of AlF3/MnF2 or AlF3 · 3 H2O endowed with Mn2+ or by heating up solid MnAlF5 too. At 1 008 K the enthalpie of dissociation is 197 kJ/mole. The equilibrium structures of the high spin molecule MnAlF5 (S = 5/2) were examined with ab initio calculations at the HF-level by comlete gradient optimizing. Two minimum structures were found on the potential energy surface. A bidentate fluorine bridged structure was found to be the most stable at the HF-level. Vibrational frequencies and thermodynamic functions of complex formation were estimated for both minimum structures. The importance of the formation of the gas complex for the separation of MnF2 and AlF3 by sublimation is discussed. 相似文献
126.
H. Brtell G. Rietz S. Sandqvist M. Berg H. Ehrsson 《Journal of separation science》1982,5(11):596-603
A two- dimensional gas chromatograph based on the Deans switching principle is described. The unit comprises two separate ovens, each containing a fused silica capillary column. The columns are joined in a specially designed manifold permitting heart cuts to be performed without significant decrease in efficiency. The switching speed and the retention time stability of the system made it possible to perform heart cuts of only a few seconds' duration. The system has been used under isothermal conditions for the determination of an amino alcohol (KABI 2128) in the low ng/ml range after trifluoroacetylation and with electron capture detection. A much shorter clean-up procedure could be used in combination with the two-dimensional gas chromatograph as compared to a method using a single glass capillary column. 相似文献
127.
Analysis of earthy and musty odors in water samples by solid-phase microextraction coupled with gas chromatography/ion trap mass spectrometry 总被引:2,自引:0,他引:2
A method for the determination of the earthy and musty odors geosmin, 2-methylisoborneol (2-MIB), 2-isobutyl-3-methoxy pyrazine (IBMP), 2-isopropyl-3-methoxy pyrazine (IPMP) and 2,4,6-trichloroanisole (2,4,6-TCA) in water by headspace solid-phase microextraction (HSSPME) combined with gas chromatography-ion trap mass spectrometry (GC-ITMS) is described. Several parameters of the extraction and desorption procedure were studied and optimized (such as types of fibers, extraction temperature, extraction time, desorption temperature, desorption time, ionic strength and elutropic strength and pH of samples). The method shows good linearity over the concentration range 1-500 ng l−1 and gives detection limits of sub-part per trillion levels for all compounds. Good precision (5.9-9.8%) is obtained using IBMP as internal standard. Finally, the method was successfully applied to analyze earthy and musty odors in tap water and lake water. 相似文献
128.
Ali Liazid Gerardo F. Barbero Miguel Palma Jamal Brigui Carmelo G. Barroso 《Chromatographia》2007,66(7-8):571-575
Results from a systematic study of the factors affecting extraction of cis-verbenol and verbenone from pine seeds are presented. Five extraction conditions were investigated: extraction solvent, method
of extraction, extraction temperature, volume of solvent, and the ratio of the mass of sample to the amount of extraction
solvent. The resulting optimized method uses magnetic-stirring-assisted extraction of pine seeds (5 g) with ethyl acetate
(75 mL) for 20 min, at room temperature. RSDs were less than 5% for both compounds. GC–FID was used for quantification of
cis-verbenol and verbenone in the extracts. 相似文献
129.
A carbon-coated fiber for solid-phase microextraction (SPME) has been prepared from powdered activated carbon (PAC) and a
fused-silica fiber. Scanning electron microscopy of the coating revealed the carbon particles were uniformly distributed on
the surface of the fiber substrate. Efficient extraction of BTEX (benzene, toluene, ethylbenzene, p-xylene, and o-xylene) and halocarbons (chloroform, trichloroethylene, and carbon tetrachloride), with short extraction and desorption times,
was achieved by use of the coated fiber. The maximum working temperature of the coated fiber was 300 °C and the lifetime was
over 140 desorption operations at 260 °C. Limits of quantification (LOQ) of the SPME method for the eight analytes ranged
from 0.01 to 0.94 μg L−1, and relative standard deviations (RSD) were below 7.2% (n=6). Recoveries were 87.9–113.4% when the method was applied to the analysis of BTEX and the halocarbons in real aqueous samples.
An erratum to this article is available at . 相似文献
130.
A. Ono 《Chromatographia》1980,13(12):752-754
Summary Xylenol isomers can be resolved on most polyols (sugars or sugar alcohols) and polyethers (polyethylene glycol or polypropylene glycol) with hydrogen-bonding interaction. They are separated on vinical polyols which have more hydroxy hydrogen than tetrol, and even on vicinal triol when its hydroxy hydrogen is acidic (stronger proton donor). The stronger is the hydrogen bonding interaction between xylenols and the liquid phase, the better is the separation of 2,4- and 2,5-xylenol, and the poorer the separation of 2,4-and 2,3-xylenol. 相似文献