全文获取类型
收费全文 | 2007篇 |
免费 | 76篇 |
国内免费 | 35篇 |
专业分类
化学 | 1235篇 |
晶体学 | 2篇 |
力学 | 149篇 |
综合类 | 5篇 |
数学 | 291篇 |
物理学 | 436篇 |
出版年
2024年 | 6篇 |
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 15篇 |
2020年 | 33篇 |
2019年 | 37篇 |
2018年 | 38篇 |
2017年 | 43篇 |
2016年 | 38篇 |
2015年 | 37篇 |
2014年 | 81篇 |
2013年 | 95篇 |
2012年 | 84篇 |
2011年 | 106篇 |
2010年 | 87篇 |
2009年 | 103篇 |
2008年 | 68篇 |
2007年 | 78篇 |
2006年 | 64篇 |
2005年 | 72篇 |
2004年 | 48篇 |
2003年 | 41篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 32篇 |
1999年 | 19篇 |
1998年 | 27篇 |
1997年 | 31篇 |
1996年 | 29篇 |
1995年 | 37篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 52篇 |
1987年 | 55篇 |
1986年 | 61篇 |
1985年 | 109篇 |
1984年 | 68篇 |
1983年 | 27篇 |
1982年 | 47篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1973年 | 1篇 |
排序方式: 共有2118条查询结果,搜索用时 15 毫秒
81.
Sameena Ashraf Keith D. Bartle Anthony A. Clifford Robert Moulder 《Journal of separation science》1992,15(8):535-538
Lubricating oil additives have been analyzed by supercritical fluid chromatography on open tubular and packed capillary columns. Carbon dioxide and modified carbon dioxide were used as mobile phases and detection was accomplished by flame ionization and micro UV. Rapid and efficient analysis of the lubricating oil additives was demonstrated. 相似文献
82.
The use of a low-temperature (0 degrees C) bath-assisted coupled capillary for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized dopamine and norepinephrine using the sweeping-micellar electrokinetic capillary chromatography (MEKC) mode is described. In this technique, a capillary consisting of two portions with different inside diameters is used. Therefore, the field strength inside the capillary is different. Hence, the electrophoretic migration velocities of the analytes and the electro-osmotic flow (EOF) also are different. Furthermore, when a portion of the capillary (wide portion, used for sweeping) is immersed in a low-temperature bath, the viscosity of the buffer and the retention factor of the analytes inside are increased. Thus, not only are the interactions between the SDS micelles and the analytes increased, but the SDS-analytes also move more slowly. As a result, a more complete separation can be achieved, even when the sample injection volume is large, up to approximately 2 microL. In general, when the volume of an injected sample is larger, the effects of sweeping and separation would become insufficient, especially when the retention values (k) of the analytes are quite different. However, this limitation can be improved when the low-temperature bath/coupled capillary/sweeping-MEKC mode is used. 相似文献
83.
HPLC-separation of cis and trans monounsaturated fatty acids 总被引:1,自引:0,他引:1
Summary The chromatography of monounsaturated fatty acids as their methyl esters on silver nitrate-loaded HPLC-columns has been studied. The separation of cis- and trans-isomers was easily achieved even with columns of low performance. High-performance small-particle-columns treated with silver nitrate separated a large variety of monounsaturated cis and trans positional isomers. The influence of variable silver-loads on the selectivity of the system was studied and a survey of the distribution of positional trans C181 isomers in commercial margarines is given. 相似文献
84.
Summary A miniaturized flow cell for an electrical conductivity detector has been made and applied to the ion chromatography of inorganic anions. It consisted of stainless steel tubes (0.13 mm ID×0.31 mm OD) and PTFE tubes (0.25 mm ID×2 mm OD). The detection limit for chloride at S/N=3 was 36 pg or 0.33 ppm for a 0.11 l injection. 相似文献
85.
K. E. Markides B. J. Tarbet C. M. Schregenberger J. S. Bradshaw M. L. Lee K. D. Bartle 《Journal of separation science》1985,8(11):741-747
A method is described for surface deactivation and modification of fused silica capillary columns with a cyanopropyl-containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropyl)methylhydropolysiloxane reagent and surface silanol groups at an optimum temperature of only 250°C. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases. 相似文献
86.
V. F. Ruban 《Journal of separation science》1990,13(2):112-115
The main characteristics of a dual-electrode amperometric detector with a cell of the “cylinder-in-flow” type with a working wire electrode have been investigated. The effective cell volume is 10–40 nl in a system with 0.2–0.4 mm i.d. packed fused-silica columns. Extra-column spreading at the optimum elution rate does not exceed 0.005 μl2. The linear range is 103 at a relative standard deviation of 0.009. The low noise level (2–3 pA) facilitates determination of electro-active substances. The detection limit for catecholamines is of the order of tenths of a femtomole. 相似文献
87.
A procedure for packing 15 cm × 1 mm id reverse-phase microbore columns with 3 μm silicas obtained from different manufacturers is described. The speed of analysis and detection limits are compared to those obtained with a 50 cm × 1 mm id column packed with 10 μm ODS. The effect of detector time constant on the system, and flow rates on column efficiency are also examined. 相似文献
88.
Summary An on-line combination of liquid chromatography, gas chromatography and mass spectrometry has been realized by coupling a quadrupole mass spectrometer to an LC-GC apparatus. Liquid chromatography was used for sample pretreatment of oil samples of different origin. The appropriate LC fraction, containing polycyclic aromatic hydrocarbons, was transferred to the gas chromatograph using a loop-type interface. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were introduced into the mass spectrometer for detection and identification. The GC column was connected to a short piece of deactivated fused silica that protruded into the ion source. The total analytical set-up allowed the direct analysis of oil samples after dilution in n-pentane without any sample clean-up. Detection limits are about 40 pg in the full scan mode and about 1 pg with selective ion monitoring, i.e. 20 ppb and 0.5 ppb respectively. 相似文献
89.
Due to their high polarity and unique selectivity, cyanopropyl silicones are basic stationary phases for high resolution capillary gas chromatography. Different OH-terminated cyanopropyl silicones, containing a high cyanopropyl content, were synthesized and chromatographically evaluated. Special attention was paid to the degree of immobilization of the phases in FSOT columns. Depending on the problem at hand, a choice has to be made between immobilization and maximum selectivity. 相似文献
90.
Norbert V. Fehringer Dalia M. Gilvydis Stephen M. Walters Colin F. Poole 《Journal of separation science》1992,15(2):124-127
The combination of open tubular column gas chromatography with electrolytic conductivity detection has been evaluated for the determination of nitrogen-containing pesticide residues in food extracts. Optimization of the column position at the column-detector interface was crucial to the successful operation of the detector. The signal-to-noise ratio and response stability of the detector are greatly influenced by the composition of the electrolyte solvent. Large volume splitless injections using retention gaps and optimized detector operating conditions enabled pesticide residues in food extracts to be determined at sub parts-per-million levels. Although the electrolytic conductivity detector is less sensitive than the thermionic ionization detector, its greater nitrogen selectivity can he crucial to the determination of nitrogen-containing contaminants in food extracts, particularly in complex mixtures where phosphorus-containing contaminants or matrix compounds are also present. 相似文献