首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   207篇
  免费   3篇
  国内免费   1篇
化学   167篇
晶体学   1篇
力学   3篇
数学   20篇
物理学   20篇
  2019年   2篇
  2018年   2篇
  2015年   5篇
  2014年   2篇
  2013年   8篇
  2012年   3篇
  2011年   2篇
  2010年   7篇
  2009年   2篇
  2008年   2篇
  2007年   4篇
  2006年   6篇
  2005年   10篇
  2004年   5篇
  2003年   4篇
  2002年   2篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1997年   8篇
  1996年   5篇
  1995年   14篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   3篇
  1990年   6篇
  1989年   9篇
  1988年   3篇
  1987年   6篇
  1986年   3篇
  1985年   2篇
  1984年   9篇
  1982年   5篇
  1981年   1篇
  1980年   3篇
  1979年   4篇
  1978年   4篇
  1977年   3篇
  1975年   8篇
  1974年   2篇
  1973年   3篇
  1972年   4篇
  1971年   2篇
  1970年   6篇
  1969年   1篇
  1968年   1篇
  1937年   1篇
  1933年   1篇
  1892年   1篇
排序方式: 共有211条查询结果,搜索用时 15 毫秒
81.
Dynamic or quasi-elastic light scattering (LS) from polymers in solution arises from concentration fluctuations. With the aid of modern photomultipliers these can be followed as a function of time. A proper evaluation allows to study the center of mass motion and the dynamics of individual chains. The relevance of simultaneous recording of static and dynamic LS is emphazised. Various aspects are discussed in three main sections. In the first part basic relationships are reviewed. The particle scattering factor P(8), structure factor S(q,c) and osmotic compressibility RT(∂c/∂T) occuring in static LS are defined. The time correlation functions (TCF) in dynamic LS are described. The TCF of the scattered electric field contains the time dependent structure factor S(q,t) and the static structure factor S(q). The initial part of the TCF (short delay times) can be approximated by a cumulant expansion; the first cumulant is related to the translational diffusion coefficient D. The concentration dependence of D contains a thermodynamic and a hydrodynamic contribution where the thermodynamic part is identical with the osmotic compressibility in static LS. The second part deals with the behaviour of various polymeric architectures in dilute solutions. Two new structure sensitive parameters, C and = Rg/Rh, are introduced. Chain stiffness and branching are extensively discussed. In the third part properties of different macromolecular architectures in semi-dilute solution are considered. The inverse osmotic compressibility = osmotic modulus and the concentration dependence of the translational diffusion coefficient are discussed in the light of re-normalization group and scaling theories.  相似文献   
82.
83.
84.
85.
In addition to the antibiotics, mycotoxins represent a second large group of biologically active substances of microbial origin. Over 300 mycotoxins are so far known and can be subdivided into 25 structural types. They are formed by approximately 350 molds of which there are 10 000 different strains. As mycotoxin-producing molds tend to spread aggressively on foodstuffs, they can cause epidemic mycotoxicoses.—The mycotoxins have been isolated, their structures determined, and their biological activities investigated; their biosynthesis has now also largely been elucidated. Accordingly, mycotoxins are derived from only three groups of key biogenetic building blocks: polyketides, isopentenyl pyrophosphate, and amino acids. Mycotoxins are mainly non-polar, chemically stable, are formed in high concentrations, and do not contain—unlike antibiotics—any sugars. Mycotoxins display an enormous variety of toxic-pharmacological activities, e.g. liver degradation, hemorrhages, carcinomas. The identification of mycotoxicoses is impeded by their long incubation periods and the fact that the mycotoxins tend to accumulate in the mammalian organism, which means that even very low concentrations in food are a potential danger. The particularly dangerous aflatoxin B1 1 may not exceed a limit in food of 5 ppb (5 μg/kg), which is difficult to control.  相似文献   
86.
87.
    
Ohne Zusammenfassung  相似文献   
88.

Information

Competitions for gold medals and prizes named after outstanding scientists held by the Russian Academy of Sciences in the field of chemical sciences in 1996  相似文献   
89.
The synthesis of macrocycles with intraannular polar ester groups and extraannular oligo-alkyl groups is described. The compounds exhibit stable liquid crystalline phases showing fan-shaped textures under the polarizing microscope, typical for a columnar order of the molecules. X-ray powder diffraction data of the LC phase indicate that the unit cell contains two symmetry-related units, a feature pointing most probably to a restricted rotation of the macrocycles within a stack. The X-ray data were further supported by solid-state NMR experiments, showing that the rigid core of the compounds does not rotate with kHz or higher frequencies within the column in the LC phase. Apart from the organization of the molecules in the LC phase, the 2D organization of the macrocycles at the solvent-highly oriented pyrolytic graphite (HOPG) interface was investigated and showed that these compounds are capable of nanofunctionalizing the HOPG surface in the multinanometer regime.  相似文献   
90.
On the Problem of the Existence of a Cubic Pyrochlore Pb2Sb2O7 The reaction of PbO, PbO2, PbCO3 or Pb(CH3CO2)2 · 3 H2O with Sb2O3 (ratio 2:1 Mol.) gives up to 700°C a cubic pyrochlore together with PbSb2O6. The pyrochlore contains Pb(IV) and has the approximate composition Pb[PbSb]O6,75 with a = 1066–1069 pm. After heating up to 900°C rhombohedral Pb2Sb2O7 is formed. There is no evidence for the existence of a cubic Pb2Sb2O7 with Pyrochlore structure.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号