全文获取类型
收费全文 | 5190篇 |
免费 | 175篇 |
国内免费 | 32篇 |
专业分类
化学 | 2939篇 |
晶体学 | 56篇 |
力学 | 198篇 |
数学 | 1254篇 |
物理学 | 950篇 |
出版年
2023年 | 51篇 |
2022年 | 147篇 |
2021年 | 160篇 |
2020年 | 143篇 |
2019年 | 174篇 |
2018年 | 174篇 |
2017年 | 167篇 |
2016年 | 229篇 |
2015年 | 172篇 |
2014年 | 240篇 |
2013年 | 373篇 |
2012年 | 351篇 |
2011年 | 376篇 |
2010年 | 201篇 |
2009年 | 216篇 |
2008年 | 263篇 |
2007年 | 227篇 |
2006年 | 177篇 |
2005年 | 144篇 |
2004年 | 142篇 |
2003年 | 105篇 |
2002年 | 93篇 |
2001年 | 81篇 |
2000年 | 59篇 |
1999年 | 41篇 |
1998年 | 32篇 |
1997年 | 39篇 |
1996年 | 54篇 |
1995年 | 45篇 |
1994年 | 39篇 |
1993年 | 44篇 |
1992年 | 37篇 |
1991年 | 40篇 |
1990年 | 35篇 |
1989年 | 26篇 |
1988年 | 33篇 |
1987年 | 40篇 |
1986年 | 41篇 |
1985年 | 39篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 27篇 |
1979年 | 39篇 |
1978年 | 29篇 |
1977年 | 22篇 |
1976年 | 25篇 |
1975年 | 21篇 |
1974年 | 15篇 |
排序方式: 共有5397条查询结果,搜索用时 15 毫秒
101.
20-Deoxoluteone has been synthesized from sclareol. Sclareol was brominated with phosphorus tribromide to form a mixture of primary allyl bromides, from which, by the malonic synthesis, a mixture of bicyclogeranylgeranylacetic acids was obtained which was cyclized with fluorosulfonic acid to form a mixture of two diastereomeric -lactones. The predominating lactone was converted by successive reduction with lithium tetrahydroaluminate, oxidation with oxalyl chloride in dimethyl sulfoxide, reaction with methylmagnesium iodide, and oxidation by the chromium trioxide/pyridine complex into 20-deoxyluteone.Institute of Chemistry, Moldavian SSR Academy of Science, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 346–353, May–June, 1990. 相似文献
102.
Résumé Le thiocarbohydrazide est un réactif d'accès facile précipitant quantitativement les aldéhydes et quelques cétones. Les points de fusion sont nets. Les précipités formés se prêtent à la gravimétrie. Nous avons étudié avec la thermobalance leur domaine de stabilité et fourni la température à ne pas dépasser pour le séchage à poids constant.
Summary Thiocarbohydrazide is a readily available reagent which quantitatively precipitates aldehydes and some ketones. The melting points are sharp. The resulting precipitates are suitable for gravimetry. Their regions of stability have been investigated with the thermobalance and the temperatures which should not be exceeded in drying to a constant weight have been found.
Zusammenfassung Thiocarbohydrazid ist ein leicht zugängliches Reagens zur quantitativen Fällung der Aldehyde und mancher Ketone. Die Schmelzpunkte der Niederschläge sind scharf. Diese eignen sich zur gravimetrischen Auswertung. Ihre Stabilität wurde mit Hilfe der Thermowaage untersucht und die Höchsttemperaturen für ihre Trocknung bis zur Gewichtskonstanz bestimmt.相似文献
103.
Nguyen Ai Viet 《Czechoslovak Journal of Physics》1981,31(3):269-274
In this paper the analytical expression is derived for the third-order optical harmonic coefficients x
abcd
v
(,,) of the atomic hydrogen at very low frequencies 0 in many level of the discrete energy spectrum.The author expresses his thank to Prof. Nguyen Van Hieu for suggesting the problem and fruitful discussions. 相似文献
104.
Spin gapless semiconductor like Ti2MnAl film as a new candidate for spintronics application 下载免费PDF全文
Wuwei Feng Xiao Fu Caihua Wan Zhonghui Yuan Xiufeng Han Nguyen Van Quang Sunglae Cho 《固体物理学:研究快报》2015,9(11):641-645
A novel Heusler ferrimagnet Ti2MnAl film has been grown on Si(001) substrate using magnetron sputtering. Characteristics of its magnetic and transport properties reveal the spin‐gapless‐semiconductor (SGS) nature of the stoichiometric Ti2MnAl, in agreement with theoretical prediction. The as‐grown SGS‐like Ti2MnAl film demonstrated high Curie temperature, nearly compensated ferrimagnetic properties with small coercivity and low magnetization. It also showed semiconductor‐like behavior at room temperature allowing good compatibility with commercial Si‐based semiconductor. In this regards, Ti2MnAl film is a potential candidate material for spintronics application, especially for the minimization of energy consumption of device. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
105.
106.
107.
Manfred Meisel Hans-Uwe Steinberger Burkhard Ziemer Nguyen Huu Thong 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):291-293
Abstract A Guide to Organophosphorus Chemistry, by Louis D. Quin, an internationally recognized authority, published by John Wiley and Sons (http://www.wiley.com/chemistry) ISBN 0-471-31824-8, $94.95, 394pp. Aminophosphonic and Aminophosphinic Acids: Chemistry and Biological Activity. Editors: Valery P. Kukhar (Ukrainian Academy of Sciences) and Harry R Hudson (University of North London). Published by John Wiley and Sons Ltd., Chichester, UK, on 31 March, 2000. ISBN 0 471-89149-5, 175.00 Pounds sterling, 634 pages. Phosphorus Ylides. Chemistry and Application in Organic Synthesis, by Oleg I. Kolodiazhnyi. Published by Wiley-VCH, 1999, ISBN 3-527-29531-3, 220SF, 555 pages. 相似文献
108.
Martin Pomerantz Jiping Wang Seeyearl Seong Kyle P. Starkey Long Nguyen Dennis S. Marynick 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):507-508
Abstract Poly(benzo[1,2-b:4,5-b′]dithiophene-4,8-diyl vinylene) (1) has been prepared by the pyrolysis of the precursor polymer 2 and studied. Quantum mechanical calculations on the aromatic and quinoid monomers, oligomers and polymers indicate that 1 is a planar aromatic polymer. 相似文献
109.
Abstract Elevated plasma cholesterol is now well established as a major risk factor for cardiovascular diseases. It has also been shown that the oxidation of low density lipoproteins leads to the formation of foam cells which contribute to the deposition of cholesterol in arteries. 相似文献
110.
Lauren Tedmon Jeremy S. Barnes Hien P. Nguyen Kevin A. Schug 《Journal of the American Society for Mass Spectrometry》2013,24(3):399-409
Steroid hormones and their metabolites are currently undergoing clinical trials as potential therapeutics for traumatic brain injury (TBI). To support this work, it is necessary to develop improved procedures for differentiating isobaric species in this compound class. Equilin sulfate (E-S), estrone sulfate (E1-S), 17α-dihydroequilin sulfate (ADHE-S), and 17β-dihydroequilin sulfate (BDHE-S) are primary constituents in hormone replacement therapies, such as Premarin, which are among pharmaceuticals being investigated for TBI treatment. The latter three compounds are isomers and can be difficult to differentiate in trace analytical determinations. In this work, a systematic study of the fragmentation of ADHE-S, BDHE-S, E1-S, and E-S under different stages of higher order tandem mass spectrometry (MSn) and variation of collision energy, allowed optimization of conditions for distinguishing the isomeric structures. For epimeric variants (e.g., ADHE-S versus BDHE-S; α- versus β-stereoisomerization in the C-17 position), differentiation was achieved at MS4 and fragmentation was demonstrated through MS5. Computational analysis was performed to further explore differences in the fragmentation pathways due to changes in stereochemistry. 相似文献