全文获取类型
收费全文 | 2828篇 |
免费 | 71篇 |
国内免费 | 9篇 |
专业分类
化学 | 2125篇 |
晶体学 | 41篇 |
力学 | 34篇 |
数学 | 125篇 |
物理学 | 583篇 |
出版年
2021年 | 25篇 |
2020年 | 23篇 |
2019年 | 27篇 |
2018年 | 30篇 |
2017年 | 25篇 |
2016年 | 56篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 137篇 |
2012年 | 113篇 |
2011年 | 144篇 |
2010年 | 95篇 |
2009年 | 74篇 |
2008年 | 159篇 |
2007年 | 177篇 |
2006年 | 162篇 |
2005年 | 195篇 |
2004年 | 160篇 |
2003年 | 121篇 |
2002年 | 109篇 |
2001年 | 74篇 |
2000年 | 59篇 |
1999年 | 48篇 |
1998年 | 24篇 |
1997年 | 38篇 |
1996年 | 46篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 22篇 |
1992年 | 36篇 |
1991年 | 33篇 |
1990年 | 26篇 |
1989年 | 19篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 25篇 |
1985年 | 48篇 |
1984年 | 47篇 |
1983年 | 38篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 21篇 |
1979年 | 31篇 |
1978年 | 22篇 |
1977年 | 23篇 |
1976年 | 26篇 |
1975年 | 20篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1967年 | 12篇 |
排序方式: 共有2908条查询结果,搜索用时 15 毫秒
31.
Summary {\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}}
\viewkind4\uc1\pard\f0\fs20 New explanations are given for two types of irregular thermogravimetric (TG) data. A TG relationship between mass and temperature is derived on the basis of migration behavior of bubbles generated in bulk of sample system, and superposed on that derived on the basis of kinetics of the 4\super th\nosupersub order event, which is superposed on the experimental TG data obtained from three reference papers. This suggests that these TG data are reflecting migration of bubbles. A dependence of TG behavior on heating rate, which is contrary to usual that, is shown and is explained in terms of event-rate determination by boiling.
\par } 相似文献
32.
Masatoshi Oue Akira Ishigaki Keiichi Kimura Yousuke Matsui Toshiyuki Shono 《Journal of polymer science. Part A, Polymer chemistry》1985,23(7):2033-2042
Poly- and bis(thiacrown ether) derivatives in which some oxygen atoms of benzocrown ether moiety are replaced by sulfur atoms have been synthesized. Their cation-binding abilities were investigated by using the solvent extraction method. The poly- and bis(benzothiacrown ether)s showed great affinity for silver ion, being more excellent in the affinity than the corresponding monocyclic analogs. They, however, possess very poor cation-binding ability for alkali and alkaline-earth metal ions. The poly- and bis(thiacrown ether)s also bind mercuric ions effectively, whereas the corresponding monomeric analogs do not at all. 相似文献
33.
34.
35.
36.
Kondo T Kaneko Y Taguchi Y Nakamura A Okada T Shiotsuki M Ura Y Wada K Mitsudo TA 《Journal of the American Chemical Society》2002,124(24):6824-6825
Pyranopyrandiones were prepared by a novel ruthenium-catalyzed carbonylative dimerization of cyclopropenones via C-C bond cleavage. For example, treatment of dipropylcyclopropenone with a catalytic amount of Ru3(CO)12 and NEt3 in THF under 15 atm of carbon monoxide at 140 degrees C for 20 h gave a novel functional monomer, 3,4,7,8-tetrapropylpyrano[6,5-e]pyran-2,6-dione, in an isolated yield of 81%. Unsymmetrically substituted pyranopyrandiones were also obtained by ruthenium-catalyzed carbonylative coupling of cyclopropenones with alkynes under similar reaction conditions. 相似文献
37.
H
0 and S
0 values of the complex formation in water of benzo-18-crown-6 (B18C6) with K+, Tl+, and Pb2+ were determined and compared with those of 18-crown-6. The H0 values of B18C6 are negative. The stability in water of the B18C6-metal ion complex at 25°C is governed largely by the magnitude of the H
0 value. The B18C6-metal ion complex is less stable in water than the corresponding 18C6-metal ion complex. This is due largely to a less favorable enthalpic contribution of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex. The two aromatic ether oxygen atoms of B18C6 are responsible for the larger H
0 value of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex. 相似文献
38.
The enantioselective Reformatsky reaction of PhCHO was achieved by the use of trifluoromethylated amino alcohols as chiral ligands to afford the corresponding optically active β-hydroxy ester with up to 90% ee. 相似文献
39.
Palladium-diethylzinc or palladium-triethylborane catalytically promotes self-allylation of 2-(allyloxy)tetrahydrofurans, 2-(allyloxy)tetrahydropyrans, and their hydroxy derivatives on the rings (ribose, glucose, mannose, deoxyribose, deoxyglucose). All the reactions proceed at room temperature and provide polyhydroxyl products, sharing a structural motif of a homoallyl alcohol, in good to excellent yields with high levels of stereoselectivity. Useful C3-unit elongation, which makes the best use of an allyl ether as a protecting group and a nucleophilic allylation agent, is demonstrated. Mechanisms for the umpolung reaction (of an allyl ether into an allylic anion) and stereoselectivity associated with allylation of aldehydes are discussed. 相似文献
40.
The gas chromatographic separation of 22 carbonyl compounds as their 2,4-dinitrophenylhydrazones was investigated using glass capillary columns. Complete separation of the 2,4-dinitrophenylhydrazones of ten aliphatic aldehydes, eight aliphatic ketones and four aromatic aldehydes was obtained, except for the derivatives of n-valeraldehyde and isobutyl methyl ketone, whose peaks overlapped, and the o- and m-tolualdehyde derivatives, which were poorly separated. The optimum conditions were as follows: stationary phase, SF-96; column size, 20 m × 0.25 mm I.D. ; column temperature, 200-240°; injection and detector temperatures, 280-290°; carrier gas flow-rate, helium 1.0-1.2 ml/min or nitrogen 1.1-1.2 ml/min. The method was applied to the analysis of aliphatic carbonyl compounds in car exhaust fumes and cigarette smoke. 相似文献