全文获取类型
收费全文 | 1061篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 559篇 |
晶体学 | 2篇 |
力学 | 44篇 |
数学 | 84篇 |
物理学 | 388篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 50篇 |
2012年 | 35篇 |
2011年 | 60篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 53篇 |
2007年 | 48篇 |
2006年 | 45篇 |
2005年 | 46篇 |
2004年 | 52篇 |
2003年 | 35篇 |
2002年 | 30篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 22篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 16篇 |
1972年 | 7篇 |
1968年 | 7篇 |
排序方式: 共有1077条查询结果,搜索用时 62 毫秒
21.
22.
23.
24.
The construction of immunochemical inhibition assays for beta-agonist and hormone residues have previously been described. In the present work the beta-agonist assay was further optimised for application to biological samples, using urine as the main model matrix. Matrix interferences with the antigen-antibody interaction and non-specific binding (NSB) of matrix components to the sensor surface were systematically studied. A full factorial design experiment was employed for evaluating the effects of assay buffer composition. In addition, the influence of antibody concentration and sample dilution on the matrix background was investigated. NSB from urine was highly affected by buffer pH and salt concentration, while buffer composition had little effect on matrix interferences with the antigen-antibody interaction. Ultra-filtration efficiently prevented NSB from urine and serum samples. Increased antibody dilution reduced the matrix background while sample dilution had an opposite effect. 相似文献
25.
Nordqvist Y Melin J Nilsson U Johansson R Colmsjo A 《Fresenius' Journal of Analytical Chemistry》2001,371(1):39-43
An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed. 相似文献
26.
An ab initio molecular orbital calculation has been carried out for three different conformations of 1,3 propanediol, one of which permits intramolecular H-bond studied by ab initio quantum mechanical methods. The ΔE for H-bonding formation is compated to be 0.9 kcal/mole and the charge redistributions and molecular orbital energy changes are compared to those found in intermolecular H-bonds. 相似文献
27.
A flow-through voltammetric cell with a hanging mercury drop electrode has been developed to fit the static mercury drop electrode (PAR 303). The design has resulted in a linear increase of sensitivity with flow rate and an enhancement of sensitivity by the wall-jet effect. The cell is used in a flow injection system in which samples are introduced with a R??i?ka—Hansen injector. The mercury drop is held at plating potentials while the sample peak passes through the cell. Stripping is done under stopped flow conditions, to reduce noise, after the sample has been washed completely from the cell. The stripping thus takes place into the carrier electrolyte which always has a constant composition independent of sample constituents. Film-forming interfering species will, however, remain on the surface of the mercury drop. The effect of medium exchange on films produced by l-cysteine is reported. The flow-through medium exchange simplifies deaeration, speeds up analysis and reduces contamination. 相似文献
28.
Kessel L Kalinin S Nagaraj RH Larsen M Johansson LB 《Photochemistry and photobiology》2002,76(5):549-554
The intrinsic fluorescence from the human lens on excitation in the UV region, referred to as blue lens autofluorescence, increases with age or in the presence of diabetes. The present study reveals that the relative contribution of compounds responsible for the blue autofluorescence appears to be a constant with age. Three potential candidates for the blue fluorescence were also studied with respect to fluorescence spectroscopic properties. These were argpyrimidine and pentosidine, both advanced glycation end products, and 3-hydroxykynurenine (3-OH-kynurenine), a photooxidative derivative of tryptophan. It was shown that the spectral properties of argpyrimidine and pentosidine are compatible with the observed blue fluorescence of the human lens, whereas the fluorescence from 3-OH-kynurenine is negligible. 相似文献
29.
Choytun DD Langlois LD Johansson TP Macdonald CL Leach GW Weinberg N Clyburne JA 《Chemical communications (Cambridge, England)》2004,(16):1842-1843
Azines (R(2)C[double bond, length as m-dash]N-N[double bond, length as m-dash]CR(2)) are 2,3-diaza analogues of 1,3-butadiene. In this report we show that strong polarisation of the azine imparts structural features consistent with delocalization within the azine fragment; NLO properties for the azines are also reported. 相似文献
30.
Johansson C 《Talanta》1972,19(11):1349-1354
Fluoride is determined by an integration technique with a flow calorimeter. All samples are absorbed on an anion-exchange resin before being brought into the calorimetric system. The reaction between hydrofluoric add and sodium hydroxide is used in the determinations. The method is applied to samples with between 7 mug and 5 mg of fluoride. The confidence limit is +/-2-5 mug for small samples and +/-25 mug for large samples. The enthalpy of the reaction H(+) + F(-) --> HF((aq)) was found to be 13.77 +/- 0.08 kJ mole . 相似文献