全文获取类型
收费全文 | 7118篇 |
免费 | 316篇 |
国内免费 | 79篇 |
专业分类
化学 | 4325篇 |
晶体学 | 99篇 |
力学 | 193篇 |
综合类 | 4篇 |
数学 | 1049篇 |
物理学 | 1843篇 |
出版年
2022年 | 56篇 |
2021年 | 70篇 |
2020年 | 96篇 |
2019年 | 144篇 |
2018年 | 103篇 |
2017年 | 101篇 |
2016年 | 143篇 |
2015年 | 122篇 |
2014年 | 191篇 |
2013年 | 564篇 |
2012年 | 319篇 |
2011年 | 360篇 |
2010年 | 244篇 |
2009年 | 213篇 |
2008年 | 250篇 |
2007年 | 256篇 |
2006年 | 222篇 |
2005年 | 178篇 |
2004年 | 179篇 |
2003年 | 203篇 |
2002年 | 173篇 |
2001年 | 103篇 |
2000年 | 98篇 |
1999年 | 67篇 |
1997年 | 71篇 |
1996年 | 79篇 |
1995年 | 82篇 |
1994年 | 78篇 |
1993年 | 77篇 |
1992年 | 91篇 |
1991年 | 78篇 |
1990年 | 66篇 |
1989年 | 94篇 |
1988年 | 70篇 |
1987年 | 67篇 |
1986年 | 71篇 |
1985年 | 121篇 |
1984年 | 104篇 |
1983年 | 81篇 |
1982年 | 96篇 |
1981年 | 100篇 |
1980年 | 83篇 |
1979年 | 98篇 |
1978年 | 74篇 |
1977年 | 103篇 |
1976年 | 80篇 |
1975年 | 86篇 |
1974年 | 92篇 |
1973年 | 98篇 |
1972年 | 57篇 |
排序方式: 共有7513条查询结果,搜索用时 15 毫秒
71.
Rao CN Kulkarni GU Thomas PJ Edwards PP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):28-35
Properties of materials determined by their size are indeed fascinating and form the basis of the emerging area of nanoscience. In this article, we examine the size dependent electronic structure and properties of nanocrystals of semiconductors and metals to illustrate this aspect. We then discuss the chemical reactivity of metal nanocrystals which is strongly dependent on the size not only because of the large surface area but also a result of the significantly different electronic structure of the small nanocrystals. Nanoscale catalysis of gold exemplifies this feature. Size also plays a role in the assembly of nanocrystals into crystalline arrays. While we owe the beginnings of size-dependent chemistry to the early studies of colloids, recent findings have added a new dimension to the subject. 相似文献
72.
H. Surya Prakash Rao S. Senthilkumar K. Gopu Shaik Rafi 《Chemistry of Heterocyclic Compounds》2007,43(3):292-297
The microwave-mediated reaction of 4-aryl-4-oxobutanoic acids with benzylamines furnished 1-arylmethyl-3-[(E)-1-arylmethylidene]-5-phenyl-2,3-dihydro-1H-pyrrolones.
This result is in contract to the earlier report on this reaction conducted under neat conditions. Structures for the products
were assigned on the basis of spectral data and confirmed by independent synthesis.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 368–373, March, 2007. 相似文献
73.
The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin. 相似文献
74.
T.?L.?Shanker Rao K.?N.?Lad A.?PratapEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):769-774
The crystallization kinetics of amorphous Cu50Ti50 has been studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The curves at different linear heating rates (2, 4, 8 and 16 K min–1) show sharp crystallization peaks. The crystallization peak shifts to higher temperatures with increasing heating rate. The Kissingers method of analysis of the shift in the transformation peak is applied to evaluate the activation energy (E
c). The KJMA formalism, which is basically developed for isothermal experiments, is also used to obtain E
c and the Avrami parameter (n).The DSC data have been analysed in terms of kinetic parameters, viz. activation energy (E
c), Avrami exponent (n) and frequency factor K
0 using three different theoretical models. It is observed that the activation energy values derived from KJMA approach and modified Kissinger equation agree fairly well with each other. The activation energy values obtained from normal Kissinger method, and Gao and Wang expression underestimate the activation energy.The financial support provided by All India Council for Technical Education (AICTE), New Delhi (Govt. of India) is gratefully acknowledged. 相似文献
75.
V. Bhagavathy M. L. P. Reddy T. Prasada Rao A. D. Damodaran 《Journal of Radioanalytical and Nuclear Chemistry》1991,149(1):35-40
A method is described for the simultaneous multielement determination of yttrium and lanthanides at microgram level. This is based on the preconcentration of these lanthanides on to 1-(2-pyridylazo)-2-naphthol (PAN) modified naphthalene. The optimal conditions for quantitative preconcentration viz., pH, amount of PAN modified naphthalene, time of stirring and aqueous phase volume were systematically evaluated. The quantitation of lanthanides was carried out by energy dispersive X-ray fluorescence analyzer, employing241Am annular source, via their characteristic K X-rays. The developed procedure gave reliable results in the analysis of xenotime samples. 相似文献
76.
J. C. Evans K. R. N. Rao S. K. Jackson C. C. Rowlands M. D. Barratt 《Journal of separation science》1985,8(12):829-830
Radicals generated in linoleic acid and deuterated linoleic acid have been trapped by the spin trap 2-methyl-2-nitroso-propane (MNP) and identified by electron spin resonance (ESR) and ENDOR spectroscopy. The formation of two distinct secondary alkyl radical adducts (one conjugated, the other non-conjugated, as shown by their UV absorption spectra) was demonstrated by 11, 11-dideuterio-9-cis-12-cis-linoleic acid using HPLC and ESR spectroscopy. 相似文献
77.
Experimental conditions have been developed for the titration of uraniumIV with ironIII alum solution, using Rhodamine 6G as a fluorescent indicator. The titration is best carried out at 98–100° in a 2–3N hydrochloric acid medium, under filtered ultraviolet light, using 2.0 ml of 0.05% Rhodamine 6G solution for 30 ml of the titration mixture. A slight excess of ironIII solution quenches the greenish-yellow fluorescence of the dye through inner filter action. With the titration assembly described here, it is possible to determine uraniumIV with an accuracy of about 0.4%. This method appears to be more convenient than the potentiometric titration or the method employing potassium thiocyanate as internal indicator.
Evidence is also presented to show that the reaction between uraniumIV and ironIII is slow at room temperature. 相似文献
78.
The application of Bacillus subtilis as a flocculant for fine coal has been reported here. Zeta-potential measurements showed that both the coal and bacteria had similar surface charge as a function of pH. Surface free energy calculations showed that the coal was hydrophobic while the bacterium was hydrophilic. The adhesion of the bacteria to coal and subsequent settling was studied in detail. Adhesion of bacteria to coal surface and subsequent settling of coal was found to be quick. Both adhesion and settling were found to be independent of pH, which makes the process very attractive for field applications. The presence of an electrolyte along with the bacterium was found to not only enhance adhesion of bacteria, but also produce a clear supernatant. Further, the settled fraction was more compact than with bacteria alone. Interaction energy calculations using the extended DLVO theory showed that the electrical forces along with the acid–base interaction energy play a dominant role in the lower pH range. Above pH 7, the acid–base interaction energy is the predominant attractive force and is sufficient enough to overcome the repulsive forces due to electrical charges to bring about adhesion and thus settling of fine coal. With increase in electrolyte concentration, the change in total interaction energy with pH is minimal which probably leads to better adhesion and hence settling. 相似文献
79.
Three simple and sensitive spectrophotometric methods for the determination of tamoxifen citrate have been developed. They are based on the formation of an ion-association complex between the drug and a dye, Erioglaucine A, which is extractable into chloroform and has an absorption maximum at 625 nm (method A), oxidation with excess potassium permanganate and the determination of unconsumed permanganate using Fast Green FCF (method B), or by the formation of a coloured cobalt thiocyante coordination complex which is extracted into benzene and measured at 635 nm (method C). Beer's law limits for methods A, B, and C are 0.5-3.0 mug ml(-1), 1.0-6.0 mug ml(-1) and 100-500 mug ml(-1), respectively. No interference was observed from tableting additives and the applicability of the methods was examined by analysing tablets containing tamoxifen. The quantities determined were 99.0-100.03% of the exptected values. 相似文献
80.
A. S. R. Anjaneyulu A. Madhusudhana Rao V. Kameswara Rao L. Ramachandra Row 《Tetrahedron letters》1975,16(52):4697-4700
A new lignan from is shown to be 1, 2a-dihydroxy-2e-piperonyl-6e-(6″-bromopiperonyl)-3, 7-dioxabicyclo-[3,3,0]-octane, the first example of a bromine containing lignan. 相似文献