全文获取类型
收费全文 | 1281篇 |
免费 | 55篇 |
国内免费 | 4篇 |
专业分类
化学 | 1028篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 185篇 |
物理学 | 101篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2016年 | 23篇 |
2015年 | 44篇 |
2014年 | 29篇 |
2013年 | 77篇 |
2012年 | 73篇 |
2011年 | 70篇 |
2010年 | 33篇 |
2009年 | 35篇 |
2008年 | 60篇 |
2007年 | 45篇 |
2006年 | 33篇 |
2005年 | 49篇 |
2004年 | 51篇 |
2003年 | 26篇 |
2002年 | 33篇 |
2001年 | 15篇 |
2000年 | 22篇 |
1999年 | 19篇 |
1998年 | 23篇 |
1997年 | 32篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 27篇 |
1993年 | 38篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 22篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 33篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 15篇 |
1974年 | 11篇 |
1973年 | 18篇 |
1972年 | 10篇 |
排序方式: 共有1340条查询结果,搜索用时 953 毫秒
991.
In an approach to understand the influence of structural parameters of interfaces on calcification in biomineralisation, the distribution of COOH groups as active sites in an inert matrix was varied using two-component lipid model monolayers. Octadecanoic acid (ODA) and octadecyl succinic acid (OSA), respectively, were the active components, and methyl octadecanoate (MOD) the inactive matrix. Surface pressure-area isotherms provide evidence for a different distribution of the active components in the matrix. Formation of solid calcium carbonate (CaCO3) with two-component monolayers on subphases containing aqueous CaCO3 was observed in situ by Brewster angle microscopy, where CaCO3 domains appear bright. Striking differences in kinetics and extent of CaCO3 formation were observed between monolayers containing ODA and those containing OSA of the same average surface density of COOH groups. 相似文献
992.
993.
Sachslehner Alois Haltrich Dietmar Gübitz Georg Nidetzky Bernd Kulbe Klaus D. 《Applied biochemistry and biotechnology》1998,(1):939-953
Sclerotium rolfsii CBS 191.62 was cultivated on a number of carbon (C) sources, including mono- and disaccharides, as well as on polysaccharides,
to study the formation of different mannan-degrading enzyme activities. Highest levels of mannanase activity were obtained
when α-cellulose-based media were used for growth, but formation of mannanase could not be enhanced by employing galactomannan
as the only carbon source. Although both xylanase and cellulase formation was almost completely repressed whenS. rolfsii was grown on more readily metabolizable carbohydrates, including glucose or mannose, considerable amounts of mannanase activity
were secreted under these growth conditions. Enhanced mannanase production only commenced when glucose was depleted in the
medium. The maximal mannanase activity of 240 IU/mL obtained in a laboratory fermentation is remarkable. Mannanase activity
formed under these derepressed conditions could be mainly attributed to one major, acidic mannanase isoenzyme with a pI value
of 2.75. 相似文献
994.
995.
996.
997.
Three polymers containing Bu2SnX (X=OAc or Cl) groups linked to the polymer through a C–Sn bond have been prepared by hydrostannation (via Bu2Sn HCl) of the following CH=CH2h-containing polymers: (1) a polybutadiene containing approx. 70% of 1,2 CH=CH2 units; (2) poly(allyl methacrylate); (3) poly(tetraethylene glycol monoallyl ether methacrylate). The first and third were tested for activity against a number of marine organisms and found to be inactive. Presumably this observed biological inactivity arises from the fact that R3Sn(H2O) ions are not released into the aqueous medium. 相似文献
998.
Information Congresses, Conferences, Symposia, Meetings, and Seminars in the Field of Chemical Sciences Held with the Participation of the Russian Academy of Sciences
First Russian Conference on Cluster Chemistry 相似文献999.
Dietmar Wendt Thomas Fricke Jürgen Schnakenberg 《Zeitschrift für Physik B Condensed Matter》1995,96(4):541-546
We present a stochastic simulation of the reaction-diffusion systemA+Binert based upon the algorithm of the minimal process method. In order to overcome the well known problems of this algorithm when selecting a reaction or diffusion event according to its rate contribution we introduce the concept of logarithmic classes which accelerates the algorithm by an order of magnitude. We simulate the systemA+Binert for integer dimensionsd=1,2,3,4 and confirm the predictions of the scaling theory by Kang and Redner. We extend our simulations to fractal structures, namely the Sierpinski carpet, triangle, the Menger sponge and HLA-clusters. Again we find agreement with the scaling theory if the fractal dimensions are defined as the spectral dimension. 相似文献
1000.
Constituents of Osmanthus-Absolute, 3rd communication: Derivatives of Theaspiranes Four isomeric new 7-oxo-dihydrotheaspiranes were identified in Osmanthus absolute. Their configuration was proved by synthetic correlations with racemic as well as optically active theaspiranes A and B. These two compounds also occurring in the same natural substrate were first correlated with the (?)-theaspirone A of known absolute configuration and the (+)-theaspirone B, respectively, thus giving the background for all further stereochemical relationship work. In depth studies in the 1H- and 13C-NMR.-spectroscopy field including all possible and now synthetically available hydroxy derivatives of the new oxo compounds enabled us to unambiguously assign structures 1 to 4 to the natural products. Some further constituents bearing the same spirocyclic skeleton were also detected in Osmanthus absolute. 相似文献