全文获取类型
收费全文 | 5580篇 |
免费 | 129篇 |
国内免费 | 19篇 |
专业分类
化学 | 3414篇 |
晶体学 | 50篇 |
力学 | 122篇 |
数学 | 764篇 |
物理学 | 1378篇 |
出版年
2022年 | 36篇 |
2021年 | 51篇 |
2020年 | 71篇 |
2019年 | 52篇 |
2018年 | 39篇 |
2017年 | 45篇 |
2016年 | 112篇 |
2015年 | 98篇 |
2014年 | 124篇 |
2013年 | 265篇 |
2012年 | 233篇 |
2011年 | 279篇 |
2010年 | 160篇 |
2009年 | 149篇 |
2008年 | 213篇 |
2007年 | 238篇 |
2006年 | 235篇 |
2005年 | 221篇 |
2004年 | 212篇 |
2003年 | 172篇 |
2002年 | 160篇 |
2001年 | 77篇 |
2000年 | 95篇 |
1999年 | 86篇 |
1998年 | 64篇 |
1997年 | 61篇 |
1996年 | 82篇 |
1995年 | 80篇 |
1994年 | 86篇 |
1993年 | 90篇 |
1992年 | 94篇 |
1991年 | 80篇 |
1990年 | 66篇 |
1989年 | 70篇 |
1988年 | 58篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 98篇 |
1984年 | 84篇 |
1983年 | 81篇 |
1982年 | 77篇 |
1981年 | 76篇 |
1980年 | 82篇 |
1979年 | 73篇 |
1978年 | 61篇 |
1977年 | 72篇 |
1976年 | 55篇 |
1975年 | 53篇 |
1974年 | 60篇 |
1973年 | 70篇 |
排序方式: 共有5728条查询结果,搜索用时 0 毫秒
991.
Henning A. Hppe Guy C. Lloyd-Jones Martin Murray Torren M. Peakman Kenneth E. Walsh 《Angewandte Chemie (International ed. in English)》1998,37(11):1545-1547
Simply reversing the order of addition of aqueous acid and Et2O to the Barbier intermediate 1 of the known indium-mediated allylation leads to unprecedented deoxygenative rearrangements [Eq. (a)]. 相似文献
992.
Guy Even Oded Goldreich Michael Luby Noam Nisan Boban Veli
kovi 《Random Structures and Algorithms》1998,13(1):1-16
We describe efficient constructions of small probability spaces that approximate the joint distribution of general random variables. Previous work on efficient constructions concentrate on approximations of the joint distribution for the special case of identical, uniformly distributed random variables. © 1998 John Wiley & Sons, Inc. Random Struct. Alg., 13: 1–16, 1998 相似文献
993.
994.
AlfredP. Weber Martin Seipenbusch Joachim Binnig Gerhard Kasper 《Particle & Particle Systems Characterization》2002,19(5):300-305
For nanoparticle agglomerates, the catalytic activity may depend strongly on their structure. The influence of different parameters such as agglomerate structure, primary particle temperature history and surface preconditioning on the catalytic activity of nanoparticles was investigated. The fraction of agglomerate surface contributing to the reaction depends on the agglomerate structure and on the velocity of the reaction under investigation. For extremely fast reactions such as the oxidation of hydrogen on Pt nanoparticles, only the outermost surface (exposed surface) contributes substantially to the formation of water. For the system investigated here, the inner surface not substantially contributing to the reaction accounted for at least 70% of the total particle surface as determined from oxygen presaturation experiments of the agglomerate surface. A considerable activity loss of the platinum particles was observed on preheating the nanoparticle agglomerates. The preheating leads to an increase in the nanoparticle size by an order of magnitude due to sintering. It is unclear if this activity reduction is due to changes in the particle surface state or to a real size effect of the nanoparticles. 相似文献
995.
996.
997.
Anne Simon Yves Grohens Laurent Vandanjon Patrick Bourseau Eric Balnois Guy Levesque 《Macromolecular Symposia》2003,203(1):331-338
From a long time, the traditional source of collagen has been mammals wastes, mainly bovine and porcine skins and bones. This study undertakes a comparative analysis of the viscoelastic behaviour and the structural properties of gelatin gels from both mammalian and fish origins. All the rheological measurements were carried out within the linear viscoelastic region for gelatin gels and tentatively related to structural characteristics. At a given concentration the pig gelatine exhibits a high storage modulus, G′, which indicates that the gel is stiffer than the fish one. The helical structures content measured by the specific rotation, [α], is also higher for the pig gelatin. Moreover, the gel is denatured in the same range of temperature, namely, around 30°C but the transition is sharper for fish gelatine. These differences between the gelatins lie in the amino-acid composition and molecular weight distribution which may influence the nature of the interchain junctions yielding to various gel mesostruture. 相似文献
998.
999.
On the Reactivity of the Ferriophosphaalkene (Z)‐[Cp*(CO)2Fe‐P=C(tBu)NMe2] towards Propiolates HC≡C‐CO2R (R=Me, Et) and Acetylene Dicarboxylates RO 2C‐C≡C‐CO2R (R=Me, Et, tBu) The reaction of equimolar amounts of (Z)‐[Cp*(CO)2Fe‐P=C(tBu)NMe2] 3 and methyl‐ and ethyl‐propiolate ( 2a, b ) or of 3 and dialkyl acetylene dicarboxylates 1a (R=Me), 1b (Et), 1c (tBu) afforded the five‐membered metallaheterocycles [Cp*(CO) =C(tBu)NMe2] ( 4a, b ) and [Cp*(CO) =C(tBu)NMe2] ( 5a—c ). The molecular structures of 4b and 5a were elucidated by single crystal X‐ray analyses. Moreover, the reactivity of 4b towards ethereal HBF4 was investigated. 相似文献
1000.
Lothar Weber 《Angewandte Chemie (International ed. in English)》2002,41(4):563-572
Phosphabenzenes and phosphaferrocenes were among the first compounds with P−C multiple bonds. For nearly 30 years the chemistry of these molecules was essentially a domain left to basic researchers. Recently, however, it was reported that transition metal complexes with phosphabenzene and phosphaferrocene ligands exhibit remarkable potential as catalysts. Catalysts based on rhodium (I ) and various phosphabenzenes appear to be superior to classical systems in the hydroformylation of terminal and internal alkenes. In addition planar‐chiral phosphaferrocene species display an excellent performance as directing ligands in a series of enantioselective asymmetric syntheses. 相似文献