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   2402篇
  免费   14篇
  国内免费   2篇
电工技术   2篇
化学工业   44篇
机械仪表   3篇
建筑科学   5篇
能源动力   2篇
轻工业   18篇
石油天然气   1篇
无线电   14篇
一般工业技术   23篇
冶金工业   2289篇
自动化技术   17篇
  2023年   1篇
  2022年   4篇
  2021年   3篇
  2019年   4篇
  2018年   2篇
  2017年   2篇
  2016年   3篇
  2015年   7篇
  2014年   9篇
  2013年   6篇
  2012年   4篇
  2011年   4篇
  2010年   4篇
  2009年   2篇
  2008年   6篇
  2007年   6篇
  2006年   8篇
  2005年   6篇
  2004年   3篇
  2003年   6篇
  2002年   3篇
  2001年   4篇
  2000年   1篇
  1999年   56篇
  1998年   702篇
  1997年   391篇
  1996年   271篇
  1995年   140篇
  1994年   134篇
  1993年   124篇
  1992年   18篇
  1991年   26篇
  1990年   24篇
  1989年   41篇
  1988年   36篇
  1987年   22篇
  1986年   25篇
  1985年   30篇
  1983年   6篇
  1982年   12篇
  1981年   19篇
  1980年   23篇
  1978年   6篇
  1977年   67篇
  1976年   140篇
  1975年   6篇
  1965年   1篇
排序方式: 共有2418条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
The Word Accentuation Test assesses the accentuation of 30 infrequent Spanish words written without the accentuation mark and is an easy-to-use tool for estimating premorbid intelligence of Spanish-speaking people. Its intraobserver (0.97) and interobserver (0.93) reliabilities and its correlation with the Wechsler Adult Intelligence Scale (.837) and Raven's Progressive Matrices (.655) are high, offering a good prediction of general intelligence. It is resistant to mental deterioration; 20 demented and 40 controls matched by sex, age, and education obtained similar scores. The discrepancies between current and predicted scores in Raven's scale can diagnose mild-moderate dementia with 0.79 accuracy (sensitivity, 0.78; specificity, 0.82).  相似文献   
5.
The effect of caseinate and soy protein in the diet on the mutagenicity induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was assessed in-vivo and ex-vivo in the DNA-repair host-mediated assay and liquid suspension assay, respectively. Of the two proteins only casein showed a strong antimutagenic activity over the whole digestive tract, except in the stomach. It is suggested that the molecular structure of a protein determines its protective effect against mutagens: casein lacks secondary and tertiary structure so that amino acids are more readily available for interaction with the mutagen than with the amino acids in soy protein which is a globular protein.  相似文献   
6.
A case is described in which a pericardial branch of a nongrafted left internal mammary artery communicated directly with the distal left anterior descending artery, following saphenous vein bypass grafting. This type of collateralization following coronary artery bypass surgery seems to be very rare, and perhaps could protect the myocardium from severe ischemia.  相似文献   
7.
A liquid chromatographic method for the determination of the enantiomers of mefloquine has been improved. The chromatography involved two columns: an achiral cyanopropyl stationary phase for the quantification of (+/-)-mefloquine and a chiral naphthyl-urea stationary phase for the determination of the enantiomeric ratio. Compared with the previous method, which needed two detectors, this one used one detector-integrator to which the two columns are connected alternately by an automated column-switching system. The method is suitable for the quantification (0.05 microgram/ml) of mefloquine and the determination of enantiomeric ratios from 500-microliters plasma samples with ultraviolet detection.  相似文献   
8.
Scattered radiation from within the treatment head can contribute significant dose to all parts of a radiotherapy treatment field. A multileaf collimator may be used to create an arbitrarily shaped field, and may also be used, under dynamic control, to modulate the beam intensity over the field. This method of intensity modulation is effectively a superposition of a large number of fields which have the same beam direction, but different shapes, and some of these shapes may have unusually small dimensions, particularly in the direction of the leaf movement. Two models for predicting the head scatter under these conditions have been investigated. These are a first-order Compton scatter approximation from the flattening filter, and an empirical fit to measured data using an exponential function. The first model only considers scatter from the flattening filter and has been applied to field sizes between 2 cm by 2 cm and 10 cm by 10 cm, where agreements are all within 1%. However it is not satisfactory at larger field sizes where small scatter contributions, from scattering sources other than the flattening filter, are integrated over large areas. The second model uses measured data between 4 cm by 4 cm and 30 cm by 30 cm to optimize the exponential function and is used to calculate the head scatter contribution for all field sizes. In this case good agreement is achieved over the full field size range, and hence this is a more generally applicable model. Results are presented for static irregularly shaped fields and intensity modulated beams created using a Philips multileaf collimator.  相似文献   
9.
We report herein the phenotypic and functional analysis of human bone marrow and thymus derived early T cells. Commitment to T cell lineage is acquired during CD7 antigen expression by CD34+ precursors in human bone marrow and before thymus colonization. Early thymocytes show similar phenotypic characteristics as bone marrow T cells. They rapidly acquire CD4 before the dual expression of CD4 and CD8. Their expansion and differentiation is regulated by two major factors: thymic stroma and cytokines produced by these stroma cells or by thymocytes themselves. Among cytokines, IL1 and sCD23 produced by thymic epithelial cells support in vitro early T cell development.  相似文献   
10.
Two hundred thirty-three newly enrolled medical and nursing students at the American University of Beirut, Lebanon, were tested for antibodies to measles and mumps. Antibodies to measles were detected in 95% of the sample, and antibodies to mumps in 84% of the sample. Susceptible individuals were appropriately immunized.  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