全文获取类型
收费全文 | 261039篇 |
免费 | 4290篇 |
国内免费 | 1827篇 |
专业分类
电工技术 | 5425篇 |
技术理论 | 5篇 |
综合类 | 1197篇 |
化学工业 | 42054篇 |
金属工艺 | 11034篇 |
机械仪表 | 7769篇 |
建筑科学 | 6610篇 |
矿业工程 | 1677篇 |
能源动力 | 5597篇 |
轻工业 | 25861篇 |
水利工程 | 2901篇 |
石油天然气 | 6003篇 |
武器工业 | 247篇 |
无线电 | 27799篇 |
一般工业技术 | 49197篇 |
冶金工业 | 47228篇 |
原子能技术 | 5616篇 |
自动化技术 | 20936篇 |
出版年
2021年 | 2478篇 |
2019年 | 2125篇 |
2018年 | 3391篇 |
2017年 | 3364篇 |
2016年 | 3688篇 |
2015年 | 2806篇 |
2014年 | 4595篇 |
2013年 | 11359篇 |
2012年 | 7710篇 |
2011年 | 10210篇 |
2010年 | 8143篇 |
2009年 | 8688篇 |
2008年 | 9503篇 |
2007年 | 9603篇 |
2006年 | 8462篇 |
2005年 | 7417篇 |
2004年 | 6666篇 |
2003年 | 6213篇 |
2002年 | 6216篇 |
2001年 | 6318篇 |
2000年 | 5913篇 |
1999年 | 5876篇 |
1998年 | 12854篇 |
1997年 | 9534篇 |
1996年 | 7275篇 |
1995年 | 5526篇 |
1994年 | 5081篇 |
1993年 | 4947篇 |
1992年 | 3943篇 |
1991年 | 3751篇 |
1990年 | 3823篇 |
1989年 | 3770篇 |
1988年 | 3530篇 |
1987年 | 3019篇 |
1986年 | 3050篇 |
1985年 | 3408篇 |
1984年 | 3321篇 |
1983年 | 3074篇 |
1982年 | 2698篇 |
1981年 | 2902篇 |
1980年 | 2643篇 |
1979年 | 2839篇 |
1978年 | 2736篇 |
1977年 | 2841篇 |
1976年 | 3693篇 |
1975年 | 2457篇 |
1974年 | 2290篇 |
1973年 | 2320篇 |
1972年 | 1981篇 |
1971年 | 1785篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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
112.
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
113.
114.
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
115.
116.
One requirement in designing and operating and operating system is to minimize the moisture change in stored grain. Moisture transfer during the aeration process is generally believed to be caused by the partial pressure difference between water in grain and water in air (P3-P4). A mathematical model was developed for rough rice, which predicts the partial pressure difference under various grain and ambient conditions. Observations of moisture change over 10 aeration tests confirmed the good correlation between sorption phenomena and partial pressure differences. Studies indicated that air relative humidity, air temperature, grain temperature and grain moisture are significant factors influencing the partial pressure differences and, thus, affecting 相似文献
117.
L. Palermo Jr.
M. Rachid
W. S. Venturini 《Engineering Analysis with Boundary Elements》1992,9(4):359-363In this article the direct boundary element formulations of stretching and bending plate problems are combined together to solve thin walled structures and other similar frames. The final system is obtained by assuming each individual plane structural element as a subregion. After the necessary transforms of these equations they can be combined together taking into account the displacement compatibility and equilibrium conditions. 相似文献
118.
In this paper, we present efficient VLSI architectures for full-search block-matching motion estimation (BMME) algorithm. Given a search range, we partition it into sub-search arrays called tiles. By fully exploiting data dependency within a tile, efficient VLSI architectures can be obtained. Using the proposed VLSI architectures, all the block-matchings in a tile can be processed in parallel. All the tiles within a search range can be processed serially or concurrently depending on various requirements. With the consideration of processing speed, hardware cost, and I/O bandwidth, the optimal tile size for a specific video application is analyzed. By partitioning a search range into tiles with appropriate size, flexible VLSI designs with different throughput can be obtained. In this way, cost effective VLSI designs for a wide range of video applications, from H.261 to HDTV, can be achieved. 相似文献
119.
R. L. Dotson 《Journal of Applied Electrochemistry》1993,23(9):897-904
Perchloric acid, HCLO4, and ammonium perchlorate, NH4ClO4, of high purity have been produced by electrolysis of chloric acid and subsequent reaction with high purity ammonium hydroxide
to produce ammonium perchlorate. The process involves no alkali metals, chlorides or transition metals such as chromates,
and thus produces propellant and explosive grade ammonium perchlorate of high purity and with no associated instability or
pollution problems. The products can be recovered by solution crystallization-drying or direct spray-drying, respectively. 相似文献
120.