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   294篇
  免费   6篇
  国内免费   1篇
电工技术   4篇
化学工业   9篇
金属工艺   2篇
机械仪表   4篇
建筑科学   10篇
能源动力   10篇
轻工业   44篇
水利工程   2篇
石油天然气   2篇
无线电   17篇
一般工业技术   39篇
冶金工业   113篇
原子能技术   1篇
自动化技术   44篇
  2021年   2篇
  2019年   4篇
  2018年   2篇
  2017年   1篇
  2016年   2篇
  2015年   3篇
  2014年   6篇
  2013年   6篇
  2012年   11篇
  2011年   11篇
  2010年   6篇
  2009年   8篇
  2008年   8篇
  2007年   12篇
  2006年   13篇
  2005年   10篇
  2004年   11篇
  2003年   11篇
  2002年   13篇
  2001年   9篇
  2000年   11篇
  1999年   6篇
  1998年   25篇
  1997年   19篇
  1996年   8篇
  1995年   10篇
  1994年   10篇
  1993年   6篇
  1992年   4篇
  1991年   1篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1986年   2篇
  1985年   3篇
  1984年   5篇
  1983年   4篇
  1982年   3篇
  1981年   4篇
  1980年   1篇
  1978年   4篇
  1977年   6篇
  1976年   2篇
  1975年   2篇
  1972年   2篇
  1967年   1篇
  1966年   1篇
排序方式: 共有301条查询结果,搜索用时 15 毫秒
31.
1. Despite demonstrable benefits in terms of symptomatic relief and improvement in prognosis, even the best treatments of heart failure currently available fall short of being ideal. We review the basis for newer approaches to the treatment of heart failure and discuss some of the agents which capitalize on current understanding of the underlying patho-physiology. 2. Several drugs, old and new, are presently being investigated by major clinical trials. We also consider some of the difficulties related to the design and conduct of such trials and suggest how drugs might be better assessed in the future.  相似文献   
32.
Red cell anisocytosis as assessed using the Coulter Channelyzer C-1000 showed an increase with progressive anaemia in 25 patients with macrocytosis due to B12 and/or folate deficiency. In deficiency of a single factor, the degree of anisocytosis increased with progressive anaemia. In five cases with B12 and folate deficiency combined, anisocytosis was markedly increased out of proportion to the degree of anaemia present. Iron stores were also reduced in four of these cases. It is suggested that objective measurement of anisocytosis is of early diagnostic value in the assessment of multiple haematinic factor deficiency, for example, in macrocytic anaemia associated with malabsorption states and unexpected multiple deficiency states.  相似文献   
33.
The optical fractional Fourier transform (OFRT) in combination with speckle photography has previously been used to measure the magnitude of surface tilting and translation. Previous OFRT techniques used to determine motion have not been able to discern the direction of the tilt and translation. A simple new approach involving use of correlation is presented to overcome this limitation. Controlled variation of the minimum resolution and dynamical range of measurement is demonstrated. It is then experimentally confirmed that if a rigid body's motion is captured by two OFRT systems of different orders, the direction and magnitude of both the tilting and the in-plane translation motion of the body can be independently determined without a priori knowledge. The experimental results confirm the validity of previous theoretical predictions.  相似文献   
34.
Fast numerical algorithm for the linear canonical transform   总被引:1,自引:0,他引:1  
The linear canonical transform (LCT) describes the effect of any quadratic phase system (QPS) on an input optical wave field. Special cases of the LCT include the fractional Fourier transform (FRT), the Fourier transform (FT), and the Fresnel transform (FST) describing free-space propagation. Currently there are numerous efficient algorithms used (for purposes of numerical simulation in the area of optical signal processing) to calculate the discrete FT, FRT, and FST. All of these algorithms are based on the use of the fast Fourier transform (FFT). In this paper we develop theory for the discrete linear canonical transform (DLCT), which is to the LCT what the discrete Fourier transform (DFT) is to the FT. We then derive the fast linear canonical transform (FLCT), an N log N algorithm for its numerical implementation by an approach similar to that used in deriving the FFT from the DFT. Our algorithm is significantly different from the FFT, is based purely on the properties of the LCT, and can be used for FFT, FRT, and FST calculations and, in the most general case, for the rapid calculation of the effect of any QPS.  相似文献   
35.
Argues that past psychologies of women are dated and are based on societal constructs of former eras, reflecting limited conceptualizations of the roles of women in society that are no longer valid. Psychotherapists are facing women clients presenting life choices and goals inadequately addressed by many personality theories of the past. Behavioral scientists and psychotherapists must adopt fresh attitudes, recognizing and appreciating the transitional and incomplete data on women in society. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
36.
37.
Botulinum neurotoxin (BoNT) is known to produce cationic channels in artificial bilayers. This study examined ion channels formed by BoNT in native membranes from cultured PC12 cells under conditions approximating those thought to occur during toxin internalization. Membrane patches were excised from PC12 cells using patch electrodes and exposed to symmetrical solutions containing either 200 mM CsCl, RbCl or KCl. The patch pipettes also contained 1-5 microg/ml BoNT buffered to pH 5.3 while the bath solutions were buffered to pH 7.0. In the presence of toxin, bursts of ion channel openings were observed. These toxin-induced channels were most active with a negative voltage applied to the same side as the toxin (cis). The increased activity at negative voltages was due to an increase in mean open time of e-fold per 120 mV and a decrease in mean closed time between bursts of e-fold per 110 mV. The shorter mean closed time within a burst was independent of membrane voltage. While BoNT-induced ion channels started as a single conductance level of 27 pS (KCl), 34 pS (RbCl) or 46 pS (CsCl) they typically increased in roughly equal steps to five or more times the original channel conductance. These higher conductance BoNT 'channels' opened and closed synchronously and could be distinguished from superposition of multiple independent channels. Despite differences in putative transmembrane sequences between BoNT/A and BoNT/E, both serotypes evidenced the same channel conductance and mean open time.  相似文献   
38.
Cusp catastrophe model of employee turnover.   总被引:8,自引:0,他引:8  
A cusp catastrophe model is developed to explain job turnover of nursing employees. The temporal dynamics of the catastrophe model suggest that leavers experience lower organization commitment than do stayers prior to termination. Leavers' perceptions of job tension and commitment appear to cross the threshold levels prior to the termination dates.  相似文献   
39.
We discuss a projection system for real world three-dimensional objects using spatial light modulators (SLM). An algorithm to encode the digital holograms of real world objects on to an SLM is presented. We present results from experiments to project holograms of real world holograms using a nematic liquid crystal SLM. We discuss the case when the pixel sizes of the charge-coupled device (CCD) and SLM used for recording the hologram and projection are different.  相似文献   
40.
Sources of pharmaceutical pollution in the New York City Watershed   总被引:2,自引:0,他引:2  
An investigation was carried out in the New York City Watershed for the presence of selected pharmaceuticals. In four seasonal sampling events between August 2003 and May 2004, surface water was collected from eight reservoir keypoints and effluent was collected from four wastewater treatment plants. We evaluated the following twelve compounds: amoxicillin, atenolol, caffeine, carbamazepine, cephalexin, estrone, 17alpha-ethinylestradiol, 17beta-estradiol, ibuprofen, sulfamethoxazole, trimethoprim, and valproic acid. In the treated effluents, carbamazepine was detected most frequently (100%; concentration range: 22-551 ng/L), followed by atenolol (94%; ND - 14,200 ng/L), trimethoprim (83%; ND - 37,000 ng/L), ibuprofen (61%; ND - 14,600 ng/L), and caffeine (49%; ND - 37,200 ng/L), while estrone was detected once (56 ng/L). In the reservoir keypoint samples, only ibuprofen (2.5%; ND - 932 ng/L) and caffeine (2.9%; ND - 177 ng/L) were detected. The other analytes were not detected in any sample. It is expected that investigation of other wastewater treatment plants in the New York City Watershed would show that their effluents are also a potential source of pharmaceuticals, but that these pharmaceuticals are unlikely to be detected in the Watershed's surface waters.  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