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   1043篇
  免费   22篇
  国内免费   10篇
化学   586篇
晶体学   47篇
力学   16篇
数学   53篇
物理学   373篇
  2019年   11篇
  2018年   12篇
  2017年   7篇
  2016年   13篇
  2015年   17篇
  2014年   13篇
  2013年   59篇
  2012年   37篇
  2011年   45篇
  2010年   32篇
  2009年   38篇
  2008年   45篇
  2007年   74篇
  2006年   47篇
  2005年   33篇
  2004年   61篇
  2003年   41篇
  2002年   31篇
  2001年   45篇
  2000年   23篇
  1999年   31篇
  1998年   13篇
  1997年   14篇
  1996年   15篇
  1995年   16篇
  1994年   18篇
  1993年   33篇
  1992年   26篇
  1991年   15篇
  1990年   11篇
  1989年   16篇
  1988年   12篇
  1987年   8篇
  1986年   12篇
  1985年   11篇
  1984年   11篇
  1983年   7篇
  1982年   7篇
  1981年   9篇
  1980年   7篇
  1979年   11篇
  1978年   10篇
  1977年   5篇
  1976年   9篇
  1975年   11篇
  1974年   12篇
  1973年   8篇
  1972年   6篇
  1971年   4篇
  1970年   4篇
排序方式: 共有1075条查询结果,搜索用时 15 毫秒
21.
To disclose the basic mechanisms of nuclear polarization creation realized by the tilted foil technique, hyperfine quantum beats of the nuclear polarization of the short-lived beta-emitter8Li(I =2+,T 1/2=840 ms) were measured as a function of the distance between two tilted foils. From the observed beats of the8Li nuclear polarization, it was found that the Fermi-contact interaction of the8Li nucleus with the ground 1s-electron in LiIII plays a main role in the final stage of polarization transfer from polarized orbital electrons to the8Li nucleus.  相似文献   
22.
Quadrupole effects in -NMR spectra of41Sc(I =7/2,T 1/2=0.596 s) implanted in a TiO2 single crystal were detected by use of a modified -NMR technique. Using the field gradient in the crystal determined by the pulsed-Fourier-transformed NMR of45Sc in TiO2, the quadrupole moment of41Sc has been determined as |Q(41Sc; 7/2)|=166±8 mb.  相似文献   
23.
In order to study the basic mechanism of polarization enhancement realized by the multitilted foil technique, nuclear polarization of short-lived beta-emitter8B(T1/2=769 ms,I =2+) was induced. Utilizing up to ten tilted foils, the polarization enhancement was measured as a function of the foil numbers. The observed enhancement for8B was combined with the previous results for12B(I =1+,T 1/2=20 ms) which has the same atomic configurations but different nuclear spin. Analyzing these results in the framework of the classical vector model, the essential features of the enhancement depending on the nuclear spin was disclosed.  相似文献   
24.
25.
It is known that for simple arrangements in thed-dimensional Euclidean spaceR d The average number ofj-dimensional subfaces of ak-dimensional face is less than . In this paper, we show that this is also true for all arrangements inR d and for all oriented matroids, and we give combinatorial proofs.  相似文献   
26.
Four possible diastereomers of pentenocin B were synthesized in a stereocontrolled manner, and the first total synthesis of a natural enantiomer of (+)-pentenocin B unequivocally established the absolute stereochemistry to be 4S,5R,6R.  相似文献   
27.
28.
The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.  相似文献   
29.
Two new phenolic compounds, glicoricone (3) and licofuranone (4), were isolated from a species of licorice brought from the northwestern region of China, and their structures were assigned. Among the twelve licorice constituents examined for the inhibition of monoamine oxidase (MAO), six compounds, 3, 4, genistein (6), licopyranocoumarin (7), licocoumarone (14) and glycyrrhisoflavone (15), inhibited the enzyme with the IC50 (concentration required for 50% inhibition of the enzyme activity) values of 6.0 x 10(-5)-1.4 x 10(-4) M. Glycyrrhizin (1) also inhibited MAO with the IC50 value of 1.6 x 10(-4) M.  相似文献   
30.
Abstract— The absorption and fluorescence spectra, and the fluorescence lifetime of acridine orange (AO) were measured in a wide range of the sodium dodecyl sulfate (SDS) concentration below and above the critical micelle concentration (cmc). The fluorescence consisted of two components with different lifetimes; short (<3 ns) and long (>3 ns). The short and long lifetime components are attributed to the AO monomer and dimer associated with detergent, respectively. The lifetime of the dimer increased with increasing the SDS concentration just below the cmc. It decreased suddenly to a constant value just above the cmc. The lifetime of the monomer showed only a slight increase in the concentration range of SDS employed.  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