全文获取类型
收费全文 | 670篇 |
免费 | 38篇 |
国内免费 | 50篇 |
专业分类
化学 | 476篇 |
晶体学 | 8篇 |
力学 | 19篇 |
综合类 | 8篇 |
数学 | 112篇 |
物理学 | 135篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 22篇 |
2021年 | 23篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 29篇 |
2016年 | 35篇 |
2015年 | 25篇 |
2014年 | 22篇 |
2013年 | 42篇 |
2012年 | 39篇 |
2011年 | 20篇 |
2010年 | 20篇 |
2009年 | 25篇 |
2008年 | 56篇 |
2007年 | 54篇 |
2006年 | 35篇 |
2005年 | 38篇 |
2004年 | 25篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 9篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有758条查询结果,搜索用时 0 毫秒
1.
U. Goginava 《分析论及其应用》2007,23(3):255-265
In this paper we prove that iff ∈ C([-π,π]2) and the function f is bounded partial p-variation for some p ∈ [1, ∞), then the double trigonometric Fourier series of a function f is uniformly (C;-α,-β) summable (α β< 1/p,α,β> 0) in the sense of Pringsheim. If α β≥ 1/p, then there exists a continuous function f0 of bounded partial double trigonometric Fourier series of fo diverge over cubes. 相似文献
2.
Dirk Lützenkirchen‐Hecht Kay Rohrmann Thomas Stöcker Wolfgang Thiel 《Surface and interface analysis : SIA》2007,39(11):845-851
Different ink‐jet printed paper materials were investigated using X‐ray photoelectron spectroscopy (XPS) yielding the elemental composition of the near‐surface region of the papers. We found significant differences with respect to the detected elements and their atomic concentrations in the different inks studied here. Two different groups of inks could be identified by means of a lower ratio of the O and C atomic concentrations and lower concentrations in specific trace elements like Mg, Na and Si. High‐resolution spectra of C 1s and O 1s core levels allowed a detailed determination of the chemical state of the respective elements. On the basis of a detailed deconvolution of these XPS signals, significant differences between all the investigated ink‐jet printed papers were found, thereby allowing their discrimination. The applicability of the measurements and, more generally, the XPS technique for forensic investigations of paper are discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
3.
Jocelyn Jalbert Roland Gilbert Pierre Tétreault Brigitte Morin Denise Lessard-Déziel 《Cellulose (London, England)》2007,14(4):295-309
In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by
the ageing of oil-impregnated paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative
conditions 0.5-g specimens of insulating paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture
of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the
number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of paper (ordinary Kraft or thermally-upgraded
(TU) Kraft paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft paper
constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the
system. Furthermore, additional 130 °C-tests with six different papers and pressboard samples under a tight control of initial
moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular
chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing
transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of
equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and
TU-nitrogenous agents modify the methanol partitioning coefficients in the paper/oil/air system, which makes their study essential
over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with
2-furfuraldehyde, which is the current reference in the domain. 相似文献
4.
The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes. 相似文献
5.
6.
Cheanyeh Cheng 《中国化学会会志》1998,45(5):679-688
The activity of cellulase has traditionally been described by pH and temperature; however, the buffering medium is also an important factor, Taking plain water as a reference medium, three kinds of buffer including KH2PO4/K5HPO4, citric acid/sodium citrate, and acetic acid/sodium acetate were adopted to survey their effects on the activity of cellulase. Chromatographic assays indicated that xylose, glucose, and cellobiose were the major products and that minor products such as cellotriose and cellotetraose were present in some cases. The activities of cellulase based on glucose production showed that the phosphate buffer acted as a deactivator for cellulase and each of the two organic acid buffers acted as activators for cellulase. The concentration of activation buffer should be high to reach a high cellulase activity; however, this effect would be compensated for by the product inhibition of cellulase. The highest activity obtained was 4.16 ± 0.08 (× 10?3) IU mg?1 for the citric acid/sodium citrate buffer under pH 4.80, 40 °C and an agitation speed of 150 rpm. 相似文献
7.
Behaviour of organic pollutants in paper and board samples intended to be in contact with food 总被引:1,自引:0,他引:1
This paper deals with the study of volatile compounds present in a set of three paper and board (P&B) samples of different composition, surface treatment, grammage and thickness. The volatile compounds released by the packaging material (P&B) can be trapped on the food and may then affect the safety and health of consumers. To evaluate if the recycled P&B could be used as food packaging material, adsorption studies have been performed with a selection of chemical substances. The adsorption isotherms are provided. Partition coefficients between paper and air have been calculated for a series of volatile compounds used as model compounds to represent different families of contaminants commonly present in P&B. Values from 4 to 3243 were obtained at different temperatures. The analysis of volatile compounds have been carried out by automatic headspace coupled on-line with GC/MS in SIM mode. The results obtained are shown and discussed. 相似文献
8.
M. Costa-Ferreira A. Dias C. Maximo M. J. Morgado G. Sena-Martins J. Cardoso Duarte 《Applied biochemistry and biotechnology》1994,44(3):231-242
Production of xylanolytic enzymes by anAspergillus niger CCMI 850 isolate was investigated in batch cultures. The effect of the composition of a fermentation medium that did not
include chemical inducers, on β-xylanase, β-xylosidase, α-l-arabinofuranosidase, and total cellulase activity was studied. With 4% xylan as the carbon source, about 65 U/mL of β-xylanase
was obtained, whereas the total cellulase activity was undetectable, under the specified conditions. This β-xylanase activity
represents the highest reported for a wild-type strain ofA. niger. The effect of pH and temperature on the activity of β-xylanase was studied. Partial characterization of the β-xylanase showed
that with insoluble birchwood as substrate theK
m
andV
max were 0.3 mM and 19 μmol/min, respectively. Aspects of using the crude β-xylanase preparation for applications in the pulp and paper industry
were discussed. 相似文献
9.
表面活性剂对铽—钛铁试剂体系纸上荧光的增敏作用及其应用 总被引:4,自引:0,他引:4
本文研究了9种表面活性剂对钛铁试剂体系纸上荧光法中Tb~(3+)特征荧光的增敏作用,并探讨了钛铁试剂-溴化十六烷基三甲胺体系纸上荧光法测定Tb~(3+)的最佳条件,Tb~(3+)的检测限为0.7ng。应用本方法成功地测定了中稀土分离富集物中Tb_4O_7的含量。 相似文献
10.
一种新的滤纸基质固体表面低温荧光(燐光)测定装置 总被引:1,自引:0,他引:1
对自行研制的铜制滤纸基质低温荧光(燐光)测定的样品支架,进行了滤纸基质固体表面低温荧光测定的可行性研究。与同类冷冻装置和室温装置比较,本装置用于滤纸基质固体表面低温荧光(燐光)测定具有以下优点;样品的分析周期大大地缩短,由45min缩短为5-6min;装置简单、便宜耐用;操作简便,简化了室温测定时的滤纸干燥程序,应用范围广,方法的重现性好,检样分析结果的相对标准偏差RSD%小于10%,荧光(燐光)分析灵敏度高,检出限低,线性范围宽。 相似文献