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   1384篇
  免费   2篇
  国内免费   3篇
电工技术   4篇
化学工业   42篇
金属工艺   2篇
机械仪表   2篇
建筑科学   8篇
能源动力   2篇
轻工业   8篇
石油天然气   1篇
无线电   52篇
一般工业技术   16篇
冶金工业   1230篇
原子能技术   4篇
自动化技术   18篇
  2024年   5篇
  2021年   2篇
  2013年   14篇
  2012年   1篇
  2011年   2篇
  2010年   2篇
  2009年   2篇
  2008年   4篇
  2007年   3篇
  2006年   4篇
  2005年   6篇
  2004年   3篇
  2003年   7篇
  2002年   4篇
  2001年   5篇
  1999年   48篇
  1998年   390篇
  1997年   216篇
  1996年   153篇
  1995年   83篇
  1994年   72篇
  1993年   77篇
  1992年   6篇
  1991年   18篇
  1990年   11篇
  1989年   20篇
  1988年   14篇
  1987年   6篇
  1986年   9篇
  1985年   9篇
  1984年   7篇
  1983年   6篇
  1982年   16篇
  1981年   12篇
  1980年   8篇
  1979年   4篇
  1978年   6篇
  1977年   31篇
  1976年   74篇
  1975年   12篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1959年   1篇
  1955年   1篇
  1947年   1篇
  1945年   1篇
  1944年   2篇
  1941年   1篇
  1940年   2篇
排序方式: 共有1389条查询结果,搜索用时 31 毫秒
61.
Various analytical, iterative and rebinning algorithms have been proposed for 3D reconstruction in positron emission tomography. This paper examines execution times of five analytical and rebinning algorithms. Meaningful comparisons are obtained by using similar software modules in all implementations. Reconstruction times are shown to differ by vast amounts: the Favor algorithm of Defrise et al is more than twice as fast as the widely used reprojection algorithm of Kinahan and Rogers; the Fourier rebinning algorithm (Fore) recently developed by Defrise is more than 15 times faster than the reprojection algorithm.  相似文献   
62.
63.
64.
Homomeric and heteromeric alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunits GluR1o and GluR3o were expressed in Spodoptera frugiperda (Sf9) insect cells. Membranes containing the recombinant receptors showed a doublet of bands of the expected size (99-109 kDa) after western immunoblotting which was shifted to a single band upon deglycosylation. In (R,S)-[3H]AMPA binding experiments, high expression was seen (Bmax = 0.8-3.8 pmol/mg protein) along with high affinity binding to a single site (Kd, nM+/-S.D.): GluR1o, 32.5+/-2.7; GluR3o, 23.7+/-2.4; GluR1o + GluR3o, 18.1+/-2.9. The pharmacological profiles of these receptors resembled that of native rat brain AMPA receptors: AMPA analogues > L-glutamate > quinoxaline-2,3-diones > kainate. In the Xenopus oocyte expression system we had previously shown that the agonist (R,S)-2-amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionate (ACPA) exhibited an 11-fold selectivity for GluR3o vs. GluR1o. In this study, it was found that ACPA has 3-fold higher affinity at homomeric GluR3o and heteromeric receptors than at homomeric GluR1o, suggesting that its efficacy and/or desensitisation properties are different at GluR1o vs. GluR3o.  相似文献   
65.
Fecal neutral steroids and bile acids were measured in patients with familial polyposis, family controls who are immediate relatives of patients, and controls other than relatives. All subjects were consuming a mixed Western diet at the time of collection of stool specimens. Although the total fecal neutral sterol concentrations were not different between the groups, the patients with familial polyposis excreted a high amount of cholesterol and low levels of coprostanol and coprostanone compared with other groups. Patients with familial polyposis excreted levels of total bile acids in their feces comparable to those excreted by controls; lithocholic acid excretion was decreased in patients with familial polyposis. These findings suggest that analysis of stools for cholesterol and its metabolites be useful in screening the siblings of polyposis families for latent disease.  相似文献   
66.
Four cases of intrauterine fetal demise in term infants are presented. From these cases and other published reports, a sequence of fetal heart rate changes preceding intrapartum death is presented. Late or variable decelerations, if unrelieved or uncorrected, lead to baseline heart rate changes of tachycardia and loss of variability reflecting loss of fetal reserve and fetal distress. This is followed by an unstable heart rate, a sinusoidal pattern, or a rapidly changing fetal heart rate. The final event is a profound bradycardia just prior to fetal demise.  相似文献   
67.
68.
69.
Fortification of salt with iron has been suggested as a practical method of iron supplementation. In an effort to identify a suitable method for fortifying salt with iron two approaches were investigated. In one the possibility of fortifying salt with ferrous sulfate and a stabilizing agent was tried. Of the several stabilizing agents studied orthophosphoric acid was found to be the most promising one. Salt fortified with ferrous sulfate and orthophosphoric acid was found to keep well on storage without color development. Bioavailability of iron from this fortified salt, although satisfactory at the beginning, deteriorated on storage. An alternative approach in which salt was fortified with ferric orthophosphate, a stable iron compound and an absorption promoter like sodium acid sulfate was found to be more satisfactory. Salt fortified with ferric orthophosphate (3,500 ppm) and sodium acid sulfate (5,000 ppm) kept well without any color development for several months. The bioavailability of iron from this formula was comparable to that from ferrous sulfate and bioavailability did not decrease even after storage for 4-5 months. This fortified salt was also acceptable. This formula offers a practical solution to fortification of salt with iron.  相似文献   
70.
Gray scale B-scans in renal sinus lipomatosis show a variety of features which must be differentiated from clinically significant pathological processes. Normal kidneys show dense homogeneous central echoes. In renal sinus lipomatosis, however, the central echoes are divided and become more sparse (Type I), interspersed with small relatively echo-free areas (Type II), or outline a single relatively echo-free area resembling a mass (Type III). In contrast to similar features in hydronephrosis or multiple cysts, the relatively echo-free areas in lipomatosis are ill-defined and do present several weak internal echoes.  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