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   7篇
化学   94篇
力学   1篇
数学   1篇
物理学   9篇
无线电   13篇
  2023年   1篇
  2020年   4篇
  2019年   1篇
  2016年   3篇
  2015年   3篇
  2014年   5篇
  2013年   3篇
  2012年   1篇
  2011年   4篇
  2010年   3篇
  2009年   3篇
  2008年   3篇
  2007年   4篇
  2006年   9篇
  2005年   2篇
  2004年   8篇
  2003年   5篇
  2002年   6篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   2篇
  1997年   2篇
  1994年   1篇
  1992年   1篇
  1991年   4篇
  1990年   5篇
  1989年   2篇
  1988年   4篇
  1987年   6篇
  1986年   3篇
  1985年   4篇
  1984年   3篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
排序方式: 共有118条查询结果,搜索用时 46 毫秒
71.
72.
A new type of flow-through cell for an enzyme-modified field effect transistor (FET) is described. The cell makes it possible to use a FET without polymeric encapsulation and wire bonding. Electrical evaluation of a FET used with the flow cell demonstrates that the flow cell has no practical problems causing sensor malfunctions. The noise and drift levels of tbe FET sensor with the flow cell are shown to be similar to those of an epoxy-encapsulated FET sensor. The application of the flow cell with a urease-modified FET is described. Useful responses are obtained for 0.25–50 mg l?1 urea with relative standard deviations of <3%.  相似文献   
73.
Four hypotensive peptides called elapherine-A, -B, -C and -D were isolated from the body of Elaphe climacophora after removal of the internal organs. Elapherine-A, which had the lowest molecular weight, exhibited a prolonged fall for 5 min in the blood pressure of spontaneously hypertensive rats, whereas elapherin-B, -C and -D displayed a transient fall in the blood pressure. The molecular weights of elapherine-A---D estimated from sodium dodecyl sulfate (SDS) gel disk electrophoresis were 6600, 6900, 7000 and 7200, respectively. The isoelectric points of these peptides were 10.4, 10.6, 10.7 and 10.5, respectively. They possessed a single polypeptide chain of 34-35 (elapherine-A), 56-58 (elapherine-B), 56-57 (elapherine-C) and 52-53 (elapherine-D) amino acid residues.  相似文献   
74.
To achieve diversity with a single antenna, fractional sampling has been proposed. The imaging component of a desired signal must be transmitted by increasing the baseband filter bandwidth. This paper proposes and evaluates a system in which the imaging component is transmitted on the adjacent channel to the desired signal. The adjacent channel interference is cancelled by the precoding generated based on the basis of the channel state information of all the terminals. In this paper, the performance with perfect feedback and limited feedback is evaluated. Numerical results obtained through computer simulation show that the proposed scheme with a 6 bit random codebook for QPSK modulation improves the performance compared with that with the conventional scheme in the low $E_b/N_0$ region.  相似文献   
75.
76.
77.
The yeast cell walls of the budding yeast Saccharomyces cerevisiae are well studied and the results show the existence of a framework composed of beta-1,3-glucan. It is reported that the cell wall of the fission yeast Schizosaccharomyces pombe has different components and our analysis by 13C-nuclear magnetic resonance (NMR) spectroscopy also showed there is alpha-1,3-glucan in its cell wall. To refine our understanding of the architecture of the yeast cell wall, we re-examined the cell wall glucans of S. pombe by NMR spectroscopy and prepared antibody against alpha-1,3-glucan, which is a characteristic component of this yeast. By the competitive enzyme-linked immunosorbent assay (ELISA) system, specificity of the antibody was restricted to alpha-1,3-glucan, which did not take a highly ordered structure. We analysed the localization of the cell wall glucans by immunoelectron microscopy. Transmission electron microscope (TEM) images showed that most of the alpha-1,3-glucan was along the cell membrane and appeared to enclose the cytoplasm, supporting previous reports that this glucan is synthesized on the cell membrane.  相似文献   
78.
79.
80.
3,3'-Dihydroxy-alpha,beta-diethyldiphenylethane (I), an isomer of hexestrol (II), was found to have a strong hypotensive effect on rats and antifungal activity against some pathogenic fungi. The hypotensive effect of I (-100.0 +/- 21.0 mmHg, 10 mg/kg, i.v.) was stronger than that of II (-40.0 +/- 2.60 mmHg, i.v.). Unlike II and other oxystilbene-related compounds already tested, I showed prolonged hypotensive action at the dose of 10 mg/kg, and the blood pressure was not restored to the original level within 20 min. I also showed antifungal activity against all fungi tested (minimal inhibitory concentration: 10-120 micrograms/ml). It should be emphasized that by shifting the phenolic hydroxyl group to m-position, the biological activities were greatly increased.  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