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   1718篇
  免费   17篇
  国内免费   5篇
电工技术   7篇
综合类   1篇
化学工业   114篇
金属工艺   18篇
机械仪表   12篇
建筑科学   30篇
矿业工程   1篇
能源动力   18篇
轻工业   57篇
水利工程   13篇
石油天然气   4篇
无线电   68篇
一般工业技术   112篇
冶金工业   1221篇
原子能技术   7篇
自动化技术   57篇
  2023年   5篇
  2021年   9篇
  2020年   4篇
  2019年   5篇
  2018年   7篇
  2017年   10篇
  2016年   6篇
  2015年   7篇
  2014年   13篇
  2013年   28篇
  2012年   19篇
  2011年   21篇
  2010年   19篇
  2009年   23篇
  2008年   12篇
  2007年   15篇
  2006年   24篇
  2005年   30篇
  2004年   18篇
  2003年   29篇
  2002年   21篇
  2001年   17篇
  2000年   13篇
  1999年   52篇
  1998年   371篇
  1997年   204篇
  1996年   136篇
  1995年   95篇
  1994年   67篇
  1993年   75篇
  1992年   17篇
  1991年   27篇
  1990年   21篇
  1989年   26篇
  1988年   15篇
  1987年   17篇
  1986年   12篇
  1985年   22篇
  1984年   11篇
  1983年   14篇
  1982年   6篇
  1981年   19篇
  1980年   9篇
  1979年   9篇
  1978年   9篇
  1977年   43篇
  1976年   80篇
  1975年   4篇
  1974年   5篇
  1968年   3篇
排序方式: 共有1740条查询结果,搜索用时 0 毫秒
11.
This paper proposes a method for the sensorless online vibration monitoring of induction machines based on the relationship between the current harmonics in the machine and their related vibration harmonics. Initially, the vibration monitoring system records two baseline measurements of current and vibration with the machine operating under normal conditions. The baseline data is then evaluated to determine the critical frequencies to monitor online. Once these frequencies are determined, the baseline vibration measurement is simply used to scale the current harmonic signal to an estimated vibration level. Based on theoretical analysis, simulation results and the experimental results shown here, a linear relationship between the current harmonics and vibration level can be assumed. The results of two experiments on a three-phase 230 V 10 hp induction motor operating under no load are discussed and show the feasibility of this method for sensorless online vibration monitoring  相似文献   
12.
This paper presents a new stereo feature matching method that extracts the disparity measure for the recovery of depth information in 2-D stereo images. In this method, a stereo pair of images are transformed row for row into strings carrying spatially varying Walsh coefficients as attributes. The significance of the information carried by the Walsh coefficients is expressed mathematically and through experimental evaluations. The choice of the Walsh coefficients in contrast to other orthogonal transform coefficients is a direct result of their computational simplicity and their interpretative meaning in terms of the information contained in the spatial domain. The string-to-string matching technique used to bring the two strings into correspondence integrates, into a unified process, both the feature detection and the feature matching processes. The uniqueness and the ordering constraints are explicitly integrated into this string-to-string matching technique. Both the issues of Gaussian filtering and the importance of enforcing the epipolar line constraint are addressed in view of the application of the proposed method. Experimental results are given and assessed in terms of both the accuracy in stereo matching and the ensuing computational requirements  相似文献   
13.
Measured ionospheric distortion of HF ground-backscatter spectra   总被引:3,自引:0,他引:3  
Skywave-radar measurements of backscatter from land are used to estimate some statistical properties of the ionospheric distortion encountered by sea-state radars. We confirm that samples of the path spectrumP(omega)are normally distributed and uncorrelated in frequency, and we estimate the first two moments ofP(omega)and their spatial and temporal correlation, for quiet F-layer daytime propagation. An empirical relation connects the equivalent width ofP(omega)and expected errors in estimating ocean wave height.  相似文献   
14.
15.
Circulating immune complexes in the sera of patients with thyroid disorders or bronchogenic carcinoma were investigated using an assay system based on the inhibition of the ADCC activity of rat spleen cells. Increased inhibition, as compared with that of the sera of age and sex matched controls, was found in patients with thashimoto thyroiditis, primary hypothyroidism and bronchogenic carcinoma. The degree of inhibition in the first two groups was markedly increased compared with control sera of the same IgG content. However, the results in the lung cancer group were slightly but not significantly greater than in controls with the same level of IgG. Increased IgG levels were found in patients with thashimoto thyroiditis and thyrotoxicosis, and also in patients with bronchogenic carcinoma who had mediastinal gland involvement. The lower level of sensitivity of the assay system was approximately 600 ng added aggregated IgG, corresponding to a concentration of 6mu g/ml in the sample assayed. It is possible that circulating immune complexes may exist in lung cancer, but at a level below that of the present assay system.  相似文献   
16.
17.
On the basis of own observations of courses the author adopts a definite attitude to the early symptomatology of the rheumatoid arthritis. During the first weeks of the rheumatoid arthritis the following symptoms are found: articular syndromes, more frequently in form of obstinate polyarthralgias, mono-oligoarthritis, accompanied by morning rigidity and accelerated BSR as well as impairment of the general condition. In the majority of the patients only the tentative diagnosis rheumatoid arthritis may be made. After a one to three months' course of the disease the diagnosis becomes more probable. It is above all based on constancy and symmetry, characteristic localisation of the articular process, morning rigidity, radiologically paraarticular loosening of the structure and morphological symptoms of an acute and subacute synovialitis. 6 to 12 months after the beginning of the disease a clinical picture forms which allows to make the diagnosis of a certain or classical rheumatoid arthritis in accordance with the criteria of the ARA. The occurrence of a high activity of multiple affection of the joints (permanent symmetrical polyarthritis including the small joints of the hands and feet), distinctive morning rigidity, high fever and much accelerated BSR, beginning with the first weeks of the disease, speaks for the possibility of the development of an arthrovisceral form of the course of rheumatoid arthritis.  相似文献   
18.
Proteins and cytochrome b556 were solubilized from Micrococcus lysodeikticus membranes using Triton X-100 treatment. Passing of this preparation through DEAE cellulose column in the presence of Triton X-100 made possible to isolate cytochrome b556 from other membrane cytochromes and to purify it up to the content of 2.3 nmol per mg of protein. The prostetic group of cytochrome b556 is determined to be protoheme for the spectrum of alkaline pyridinehemochrome.  相似文献   
19.
To investigate the control of aldosterone secretion, non-stress levels of serum aldosterone, corticosterone, and prolactin, and renin activity were determined at 4-h intervals during 24-h light-dark cycles in adult male rats on regular and low-sodium diets. Circadian rhythms of plasma aldosterone, prolactin, and corticosterone concentrations and of serum renin activity were demonstrated during a regular sodium diet. When the rats were on a low-sodium diet, a circadian rhythm of serum corticosterone and aldosterone concentration was observed, but there was no circadian variation in serum renin activity or in serum prolactin concentration. Serum aldosterone concentration correlated with serum corticosterone concentration (r = 0.48) and serum renin activity (r = 0.36) during a low-sodium diet. Serum prolactin concentration did not correlate with serum aldosterone concentration or serum osmolality. These data are compatible with a role for renin and ACTH, but not for prolactin, in the modulation of aldosterone secretion in the rat.  相似文献   
20.
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