全文获取类型
收费全文 | 1857篇 |
免费 | 30篇 |
国内免费 | 10篇 |
专业分类
化学 | 1513篇 |
晶体学 | 11篇 |
力学 | 22篇 |
数学 | 88篇 |
物理学 | 263篇 |
出版年
2020年 | 10篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 76篇 |
2012年 | 51篇 |
2011年 | 79篇 |
2010年 | 45篇 |
2009年 | 46篇 |
2008年 | 85篇 |
2007年 | 88篇 |
2006年 | 106篇 |
2005年 | 93篇 |
2004年 | 102篇 |
2003年 | 73篇 |
2002年 | 77篇 |
2001年 | 37篇 |
2000年 | 38篇 |
1999年 | 32篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 25篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 29篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 40篇 |
1984年 | 47篇 |
1983年 | 14篇 |
1982年 | 43篇 |
1981年 | 52篇 |
1980年 | 40篇 |
1979年 | 31篇 |
1978年 | 35篇 |
1977年 | 31篇 |
1976年 | 34篇 |
1975年 | 22篇 |
1974年 | 34篇 |
1973年 | 21篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1967年 | 13篇 |
排序方式: 共有1897条查询结果,搜索用时 218 毫秒
41.
Chiral beta-amino esters are synthesized in one-pot from three components, amines, aldehydes, and ethyl bromoacetate, under the rhodium-catalyzed Reformatsky-type reaction condition, where complete diastereoselection is achieved in the nucleophilic addition step of ethyl bromoacetate to the imines prepared in 相似文献
42.
James P. Kutney Toshio Honda Peter M. Kazmaier Norman J. Lewis Brian R. Worth 《Helvetica chimica acta》1980,63(2):366-374
The synthesis and conformational analysis of (3′R)-3-hydroxyleurosidine ( 5 ), (3′S)-3-hydroxyleurosidine ( 10 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 15 ), (3′R)-3-acetoxy-4′-deoxyleurosidine ( 23 ), (3′R)-3-acetoxy-4′-deoxyvinblastine ( 16 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 28 ) is discussed. 相似文献
43.
Hisahiro Hagiwara Fumihide TakeuchiTakashi Hoshi Toshio SuzukiToshihiro Hashimoto Yoshinori Asakawa 《Tetrahedron letters》2003,44(11):2305-2306
1,9-Dideoxyforskolin 2 has been synthesized starting from ptychantin A 3. 相似文献
44.
Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale. To date, the Hertzian theory was used for analyzing force-distance curves as the simplest model among several contact mechanics between elastic bodies. However, the preexisting methods based on this theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. A new analytical method was introduced to estimate the elasticity and the adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Poly(dimethylsiloxane) (PDMS) and isobutylene-co-isoprene rubber (IIR) were analyzed to verify the applicable limit of the JKR analysis. For elastic samples such as PDMS, the force-deformation plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the experimental plots revealed large deviations from JKR curves depending on scanning velocity and maximum loading force. Some nano-rheological arguments were employed based on the difference between these specimens. 相似文献
45.
46.
47.
Nakamura Y Asami A Ogawa T Inokuma S Nishimura J 《Journal of the American Chemical Society》2002,124(16):4329-4335
The reactions of [60]fullerene with bis-o-quinodimethane precursors 3, 4, and 5 containing a dibenzo-18-crown-6, 24-crown-8 and 30-crown-10 moiety, respectively, were investigated. Both 3 and 4 provided trans-4 bisadducts 6a and 7a, respectively, as major product, though the selectivity in the latter was lower than that in the former. As minor product, 6b (cis-2) was produced from 3, while 7c (e) as well as 7b (cis-2) were produced from 4. Precursor 5 exclusively afforded e bisadduct 8 without any other regioisomers. These bisadducts showed different ionophoric properties from one another; for instance, 6a and 7b exhibited a high complexing ability toward the K+ ion, while 6b hardly showed complexation with any alkali metal ions. The selectivity coefficients (K(Na,K)(pot)) of 6a and 7b toward K+ over Na+ ion, determined with an ion-selective electrode, were much higher than that of dibenzo-18-crown-6. 相似文献
48.
Toshio Fuchigami 《Journal of fluorine chemistry》2007,128(4):311-316
Recent studies on solvent effects on electrochemical partial fluorination are reviewed. At first, the historical background and some problems of electrochemical fluorination in organic solvents like acetonitrile (MeCN) are briefly mentioned. Ethereal solvents like dimethoxyethane (DME) and a mixture of DME and MeCN were found to improve both the yield and current efficiency for electrochemical fluorination since these solvent systems effectively suppress anode passivation and overoxidation of fluorinated products once formed during the electrolysis. It was also found that DME stabilizes radical cationic intermediates of 4-arylthio-1,3-dioxolan-2-ones and 3-phenylthiophthalide leading to α-fluorination while dichloromethane (CH2Cl2) destabilizes them leading to fluorodesulfurization. On the other hand, imidazolium ionic liquids and liquid fluoride salts like Et4NF·4HF and Et3N·5HF exhibited similar effects to CH2Cl2. Selective fluorination of hardly oxidizable phthalide was also achieved using a combination of two kinds of ionic liquids (imidazolium triflate and liquid fluoride salts). 相似文献
49.
Toshio Morikawa Osama Bashir Abdel-Halim Hisashi Matsuda Osamu Muraoka Masayuki Yoshikawa 《Tetrahedron》2006,62(26):6435-6442
Three new pseudoguaiane-type sesquiterpenes, dichrocepholides A-C, and two new pseudoguaiane-type sesquiterpene dimers, dichrocepholides D and E, were isolated from the aerial part of Dichrocephala integrifolia. Their stereostructures were determined on the basis of chemical and physicochemical evidence. In addition, the extract and its principal sesquiterpene constituent, parthenin, showed an inhibitory activity on nitric oxide (NO) production and on induction of inducible NO synthase. 相似文献
50.
Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms. 相似文献