全文获取类型
收费全文 | 2785篇 |
免费 | 82篇 |
国内免费 | 11篇 |
专业分类
化学 | 2149篇 |
晶体学 | 38篇 |
力学 | 36篇 |
数学 | 167篇 |
物理学 | 488篇 |
出版年
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 32篇 |
2019年 | 55篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 46篇 |
2015年 | 33篇 |
2014年 | 38篇 |
2013年 | 130篇 |
2012年 | 149篇 |
2011年 | 149篇 |
2010年 | 73篇 |
2009年 | 95篇 |
2008年 | 146篇 |
2007年 | 146篇 |
2006年 | 153篇 |
2005年 | 126篇 |
2004年 | 89篇 |
2003年 | 101篇 |
2002年 | 115篇 |
2001年 | 61篇 |
2000年 | 47篇 |
1999年 | 33篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 33篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 32篇 |
1987年 | 27篇 |
1986年 | 36篇 |
1985年 | 43篇 |
1984年 | 54篇 |
1983年 | 32篇 |
1982年 | 44篇 |
1981年 | 40篇 |
1980年 | 42篇 |
1979年 | 35篇 |
1978年 | 42篇 |
1977年 | 36篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 27篇 |
1973年 | 24篇 |
排序方式: 共有2878条查询结果,搜索用时 19 毫秒
71.
Ohne Zusammenfassung 相似文献
72.
Yoshihiko Taguchi Yasuyuki Ishida Hajime Ohtani Hiroyuki Bekku Masaya Sera 《Analytical sciences》2004,20(3):495-499
A polymeric hindered amine light stabilizer (HALS), Tinuvin 622 (MW [symbol: see text] 4000), in PP materials formulated with a magnesium hydroxide flame retardant was determined by reactive thermal desorption (RTD) gas chromatography (GC). Two kinds of the HALS components that were formed through the RTD in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH] were clearly observed in the chromatograms of the PP samples, with negligible interference from the other additives and the PP substrate. Here, the coexisting flame retardant was proved to affect significantly the RTD process of the occluded HALS. As a result, the recovery of the HALS components in the RTD-GC chromatograms of the PP samples increased with increase in the content of the flame retardant. This enhancement of the HALS recovery is attributed mainly to the preferential exposure of the HALS on the surface of the ground PP sample through the interaction between the polymeric HALS and the flame retardant in the molten PP during kneading. In spite of such a considerable action of the flame retardant, the observed intensities of the characteristic peaks of HALS by RTD-GC showed a good linear relationship with the HALS content in the PP samples with constant content of the flame retardant (50 phr); this relationship could be used as the calibration line for the determination of the polymeric HALS in the PP materials containing the flame retardant. 相似文献
73.
74.
The synthetic procedures for spilanthol and trail-following pheromone for a southern subterranean termite were described. The syntheses heavily depend on the new diene synthesis using titanium reagent. 相似文献
75.
CuBr2-catalyzed three-component coupling of N-benzylallylamine, ethyl glyoxalate, and terminal alkynes afforded glycinate-tethered 1,6-enynes, which were further transformed into polycyclic pyrrole-2-carboxylates via iridium-catalyzed cycloisomerization/Diels-Alder cycloaddition/dehydrogenation sequence under conventional and microwave heating conditions. The corresponding β-amino acid analogues were obtained from the Ir-catalyzed reaction of enynes prepared from lithium amides of allylamines with methyl non-2-en-4-ynoate. The Cu-catalyzed Mannich-type condensation was further extended to the synthesis of the glycinate-tethered dienyne and cyclopropylenyne, which were subjected to Rh-catalyzed cycloisomerizations to furnish bicyclic amino acids. 相似文献
76.
A rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones has been developed under mild conditions. Considering the ease of preparation of these propargyl alcohols (terminal alkynes + aromatic aldehydes), this method provides a new way of constructing indanones with high efficiency. By the mechanistic investigations using deuterium-labeled substrates, it has also been demonstrated that the reaction goes through an unexpected cascade, with a 1,4-hydrogen shift being the turnover-limiting step of the catalytic cycle. 相似文献
77.
Five Ci-Se...O...Se-Ci atoms in anthraquinone and 9-(methoxy)anthracene bearing phenylselanyl groups at 1,8-positions align linearly, the origin of which is shown to be a nonbonded 5c-6e interaction of the five atoms. 相似文献
78.
Reaction of α-nitro olefins with secondary amines in the presence of palladium(O) catalyst affords allylic amines. 相似文献
79.
80.
New synthetic methods for the preparation of 1,3-dienes are described. 相似文献