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   111篇
  免费   2篇
电工技术   13篇
化学工业   18篇
机械仪表   1篇
建筑科学   5篇
能源动力   1篇
轻工业   3篇
水利工程   1篇
无线电   7篇
一般工业技术   25篇
冶金工业   25篇
原子能技术   1篇
自动化技术   13篇
  2023年   1篇
  2022年   3篇
  2021年   3篇
  2020年   1篇
  2019年   3篇
  2018年   2篇
  2017年   2篇
  2016年   2篇
  2015年   3篇
  2014年   3篇
  2013年   4篇
  2012年   3篇
  2011年   4篇
  2010年   3篇
  2009年   1篇
  2008年   6篇
  2007年   1篇
  2006年   2篇
  2005年   1篇
  2004年   5篇
  2003年   3篇
  2002年   2篇
  2001年   2篇
  2000年   2篇
  1999年   3篇
  1998年   13篇
  1997年   5篇
  1996年   5篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1986年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   3篇
排序方式: 共有113条查询结果,搜索用时 15 毫秒
101.
We have investigated in detail the self-assembly of a chiral porphyrin trimer in different solvents and correlated this behavior to the aggregation of the molecule at a solid-liquid interface. In n-hexane and cyclohexane, CD spectroscopy and dynamic and static light scattering studies showed that the porphyrin trimer self-assembles already at micromolar concentrations into long, chiral supramolecular polymers, which precipitate as fibers when the solution is drop-cast onto a mica surface. In contrast, in chloroform, the compound is molecularly dissolved up to concentrations of 0.2 mM and when micromolar solutions are drop-cast onto mica, no precipitation of large assemblies occurs. Instead, at the moment that the chloroform film becomes subject to spinodal dewetting and the porphyrin trimers within this film start to self-assemble, extended patterns of equidistant lines of single molecule thick columnar stacks are formed.  相似文献   
102.
Graphene's unparalleled strength, stiffness, and low mass per unit area make it an ideal material for nanomechanical resonators, but its relatively low quality factor is an important drawback that has been difficult to overcome. Here, we use a simple procedure to fabricate circular mechanical resonators of various diameters from graphene grown by chemical vapor deposition. In addition to highly reproducible resonance frequencies and mode shapes, we observe a striking improvement of the membrane quality factor with increasing size. At room temperature, we observe quality factors as high as 2400 ± 300 for a resonator 22.5 μm in diameter, about an order of magnitude greater than previously observed quality factors for monolayer graphene. Measurements of quality factor as a function of modal frequency reveal little dependence of Q on frequency. These measurements shed light on the mechanisms behind dissipation in monolayer graphene resonators and demonstrate that the quality factor of graphene resonators relative to their thickness is among the highest of any mechanical resonator demonstrated to date.  相似文献   
103.
The relationship between the bioenergetic status of human glioma xenografts in nude mice and morphometric parameters of the perfused vascular architecture was studied using (31)P magnetic resonance spectroscopy (MRS), fluorescence microscopy and two-dimensional digital image analysis. Two tumour lines with a different vascular architecture were used for this study. Intervascular distances and non-perfused area fractions varied greatly between tumours of the same line and tumours of different lines. The inorganic phosphate-nucleoside triphosphate (P(i)/NTP) ratio increased rapidly as mean intervascular distances increased from 100 microm to 300 microm. Two morphometric parameters - the percentage of intervascular distances larger than 200 microm (ivd200) and the non-perfused area fraction at a distance larger than 100 microm from a nearest perfused vessel (area100), - were deduced from these experiments and related to the P(i)/NTP ratio of the whole tumour. It is assumed that an aerobic to anaerobic transition influences the bioenergetic status, i.e. the P(i)/NTP ratio increased linearly with the percentage of ivd200 and the area100.  相似文献   
104.
Barium titanate single crystals are grwon in two ways, i.e. by the Remeika and the Czochralski method. Doping ions (FeCoCu) are introduced into Remeika crystals and determined by a spectro photometric method. Impurity ions (FKPtSb) are determined in both kinds of crystals; pulled crystals are purer than Remeika crystals. The stoichiometry Ti/Ba + Sr is excellent in pulled crystals but the Ti, Ba, Sr, K concentrations in Cu-doped crystals show ion size effects in the compensation mechanism.  相似文献   
105.
106.
107.
Mixed LaAlO3-SrTiO3 single crystals have been grown by using flame fusion, starting from homogeneously synthesized solid-solution powders. X-ray powder diffraction of the latter show the solid-solution system to be continuous over the whole composition range. Phase boundaries were determined by means of optical and calorimetric measurements. In the composition range of 100% to 20% LaAlO3, a cubic Pm3m to trigonal R3?c phase boundary was observed.  相似文献   
108.
A 12 mm tissue-equivalent proportional counter (TEPC) was designed, constructed and successfully tested. This detector achieves features common to others TEPCs, but it does not use field shaping electrodes and it is able to work at higher bias voltages which makes it capable of measuring the whole range of energy deposition events for gamma rays. The following approach was used to design the detector: first of all the use of a cylindrical shape detector featured as simple as possible but keeping its performance as well, the next point is to avoid the use of field shaping tubes and the last one is to make the preamplifier small and as close as possible to the detector. Its construction is based on a cylindrical proportional counter with A-150 tissue-equivalent material as cathode, TE-methane gas as a proportional gas and a 20 microns diameter wire as anode.  相似文献   
109.
110.
The European Commission recently sponsored an international research and development project, in which three 'active' personal neutron dosemeters were developed. Comparative irradiation experiments showed good results with respect to sensitivity and energy dependence of the response.  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