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   364198篇
  免费   6603篇
  国内免费   1907篇
电工技术   7283篇
技术理论   5篇
综合类   1267篇
化学工业   57920篇
金属工艺   17857篇
机械仪表   13709篇
建筑科学   8905篇
矿业工程   2415篇
能源动力   7056篇
轻工业   32358篇
水利工程   4216篇
石油天然气   7345篇
武器工业   248篇
无线电   35838篇
一般工业技术   72912篇
冶金工业   59615篇
原子能技术   6739篇
自动化技术   37020篇
  2022年   2130篇
  2021年   3512篇
  2020年   2410篇
  2019年   2989篇
  2018年   12728篇
  2017年   13132篇
  2016年   9550篇
  2015年   4370篇
  2014年   5986篇
  2013年   14030篇
  2012年   12193篇
  2011年   19932篇
  2010年   17151篇
  2009年   16439篇
  2008年   16940篇
  2007年   18858篇
  2006年   9416篇
  2005年   11592篇
  2004年   9239篇
  2003年   8406篇
  2002年   7443篇
  2001年   6821篇
  2000年   6484篇
  1999年   6339篇
  1998年   15010篇
  1997年   10984篇
  1996年   8250篇
  1995年   6140篇
  1994年   5549篇
  1993年   5495篇
  1992年   4164篇
  1991年   3974篇
  1990年   3978篇
  1989年   3923篇
  1988年   3685篇
  1987年   3151篇
  1986年   3173篇
  1985年   3544篇
  1984年   3436篇
  1983年   3165篇
  1982年   2833篇
  1981年   3050篇
  1980年   2801篇
  1979年   2918篇
  1978年   2823篇
  1977年   3096篇
  1976年   4229篇
  1975年   2511篇
  1974年   2339篇
  1973年   2389篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
Professional software engineering continues to face problems that involve large-scale (complex) software systems development. Such efforts typically require team collaboration over months, possibly years. Once implemented, the system must be maintained for sometimes decades. This development and maintenance life cycle requires not only technical knowledge and skills in software development, but also the knowledge and skills associated with software process. We believe the traditional computer science curriculum fails to consider this spectrum of needs. We also believe, however, that software engineering must use certain elements of the core knowledge and skills taught by computer scientists as its foundation. We describe lessons learned from the 10-year collaboration between Monmouth University and the Software Engineering Center of the US Army's CECOM (Communications Electronics Command). The center recruits electrical engineering and computer science graduates from academic institutions in the geographic regions surrounding its various installations to be part of its intern program; Monmouth University, in turn, incorporates the demands of the intern program in its Master of Science in software engineering curriculum  相似文献   
892.
893.
The authors report the case of a woman admitted to hospital for minor trauma of the left hip and who presented major ST segment elevation on the second day suggesting an acute anterior wall myocardial infarction at the same time as a cerebrovascular accident. Complementary investigations and follow-up excluded the diagnosis of myocardial infarction with normalisation of the ECG on the 5th day. ECG changes during cerebrovascular accidents may be very variable ranging from extrasystoles to ST elevation mimicking myocardial infarction. They carry a poor prognosis with an increased risk of sudden death necessitating continuous ECG monitoring until the ECG reverts to normal. The cardiac involvement is not ischaemic but due to disease of the insular cortex of the brain which induces myocytolysis (centered around the intra-cardiac nerve endings) due to the sudden liberation of catecholamines. These lesions may be treated by propranolol or phentolamine.  相似文献   
894.
895.
The Effect on the subgingival microflora of a single topical administration of a 95% collagen and 5% metronidazole device in combination with debridement was investigated in 30 adult periodontitis patients in comparison with mechanical treatment alone. For each patient, plaque samples from test and control sites in cuspids and bicuspids were collected for culture and enumeration of total anaerobically cultivable bacteria (TA), black-pigmented anaerobes (BPA), and Actinobacillus actinomycetemcomitans (Aa). Spirochetes and fusiforms were quantified by direct microscopic examination after Giemsa staining. A decrease was observed for all parameters, and a significant difference in comparison with the control group was found for fusiforms. After treatment, a lower number of Aa positive sites were observed in the test group (13/25). These results show that a single application of topical metronidazole seems to be effective as adjunctive antimicrobial treatment in adult periodontitis.  相似文献   
896.
OBJECTIVE: To investigate if unexpected behaviour of neonatal and paediatric patients connected to syringe pumps could be explained by transient elevation of these devices. DESIGN: Five different commercially available syringe-pumps were set at an infusion rate of 1 ml/h and then subjected to a vertical displacement manoeuvre (height 1 m). The actual delivered infusion volumes in association with the displacement manoeuvre were measured by a high precision weight scale connected to a computer. SETTING: A medical technology laboratory in a university hospital. MEASUREMENTS AND RESULTS: Elevation of the devices resulted in a rapid bolus injection of 0.19-2.28 ml. Returning the devices to their original positions resulted in an aspiration into the system of 0.06-0.34 ml. The times both for bolus injection and for aspiration into the system were less than 1 min in all cases. The updown manoeuvre was followed by a period with zero infusion ranging from 8 to 105 min. CONCLUSIONS: Design flaws in the construction of syringe pumps can expose patients to substantial danger following vertical displacement if potent drugs are being infused. If potent drugs are infused, care should be taken not to change the vertical position of the syringe pump even for short periods of time. Before buying new equipment, the authors recommend that the delivery characteristics of these devices should not only be tested during ordinary bench testing but should also include the reaction to a vertical displacement manoeuvre.  相似文献   
897.
Algorithm for cosine transform of Toeplitz matrices   总被引:1,自引:0,他引:1  
An algorithm for calculating the 2D cosine transform of a Toeplitz matrix is presented. The algorithm is based on the application of 1D cosine transforms. More specifically, four 1D cosine transforms of size N are needed to obtain the transform of a Toeplitz matrix of size N×N. This is an improvement over previously published algorithms. The algorithm is also simple and regular  相似文献   
898.
A generator of chaos in wavelength is reported. It is formed by a wavelength-tunable laser diode with a time delayed feedback loop in which a wavelength nonlinear-linear device is introduced. The dynamical regime of wavelength emission thus obtained is ruled by a differential difference equation. Experimental results are compared with numerical simulations and with previous theoretical and experimental results  相似文献   
899.
A method based on use of Hardin's homogeneous model is proposed for calculation of the deformation modulus of noncohesive soils. Completely satisfactory correspondence between computed and experimental values of the deformation modulus of sands is demonstrated. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 2–5, July–August, 1994.  相似文献   
900.
The use of conventional ultrasound systems to image the upper airway has been limited because ultrasound energy is attenuated by the air column. In an attempt to study upper airway geometry, we developed a computer controlled bi-directional ultrasound system which combines two conventional ultrasound devices with computer image processing to yield images of upper airway structures. Human studies and cadaver studies were performed to evaluate the system. Images acquired by the bi-directional ultrasound system were comparable to images from 3D volume rendered CT scans. This system may provide valuable data in the study of upper airway physiology and pathology.  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