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   7851篇
  免费   190篇
  国内免费   14篇
电工技术   121篇
综合类   6篇
化学工业   1225篇
金属工艺   124篇
机械仪表   102篇
建筑科学   381篇
矿业工程   60篇
能源动力   204篇
轻工业   699篇
水利工程   81篇
石油天然气   41篇
武器工业   1篇
无线电   691篇
一般工业技术   1082篇
冶金工业   2309篇
原子能技术   90篇
自动化技术   838篇
  2022年   44篇
  2021年   96篇
  2020年   56篇
  2019年   95篇
  2018年   103篇
  2017年   92篇
  2016年   121篇
  2015年   61篇
  2014年   132篇
  2013年   438篇
  2012年   225篇
  2011年   335篇
  2010年   281篇
  2009年   237篇
  2008年   348篇
  2007年   306篇
  2006年   292篇
  2005年   284篇
  2004年   233篇
  2003年   206篇
  2002年   170篇
  2001年   166篇
  2000年   149篇
  1999年   186篇
  1998年   414篇
  1997年   271篇
  1996年   213篇
  1995年   147篇
  1994年   167篇
  1993年   167篇
  1992年   110篇
  1991年   78篇
  1990年   125篇
  1989年   119篇
  1988年   111篇
  1987年   103篇
  1986年   94篇
  1985年   112篇
  1984年   113篇
  1983年   80篇
  1982年   97篇
  1981年   96篇
  1980年   86篇
  1979年   69篇
  1978年   69篇
  1977年   76篇
  1976年   93篇
  1975年   64篇
  1974年   42篇
  1973年   43篇
排序方式: 共有8055条查询结果,搜索用时 31 毫秒
101.
Discusses the impact of asthma on children's educational experiences. Respiratory arrest or hypoxia may lead to neuropsychological changes in a few cases, and some medications may produce mild, temporary changes, affecting learning and classroom performance. For most asthmatic children, their illness does not result in permanent brain function changes that compromise their educational adaptation and performance. Increased school absence, stress of chronic illness, isolation from peers, diminished physical activities, reduced adult expectations and self esteem, and depression can compromise children's academic adaptation and progress. Co-occurrence of factors like severe illness, poverty, and family dysfunction may increase the risk for educational and psychosocial impairment. Systematic and comprehensive education of asthmatic patients, their parents, and school personnel is crucial to improving the control of asthma and activity level. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
103.
A Maximum Likelihood Stereo Algorithm   总被引:8,自引:0,他引:8  
A stereo algorithm is presented that optimizes a maximum likelihood cost function. The maximum likelihood cost function assumes that corresponding features in the left and right images are normally distributed about a common true value and consists of a weighted squared error term if two features are matched or a (fixed) cost if a feature is determined to be occluded. The stereo algorithm finds the set of correspondences that maximize the cost function subject to ordering and uniqueness constraints. The stereo algorithm is independent of the matching primitives. However, for the experiments described in this paper, matching is performed on the $cf4$individual pixel intensities.$cf3$ Contrary to popular belief, the pixel-based stereo appears to be robust for a variety of images. It also has the advantages of (i) providing adensedisparity map, (ii) requiringnofeature extraction, and (iii)avoidingthe adaptive windowing problem of area-based correlation methods. Because feature extraction and windowing are unnecessary, a very fast implementation is possible. Experimental results reveal that good stereo correspondences can be found using only ordering and uniqueness constraints, i.e., withoutlocalsmoothness constraints. However, it is shown that the original maximum likelihood stereo algorithm exhibits multiple global minima. The dynamic programming algorithm is guaranteed to find one, but not necessarily the same one for each epipolar scanline, causing erroneous correspondences which are visible as small local differences between neighboring scanlines. Traditionally, regularization, which modifies the original cost function, has been applied to the problem of multiple global minima. We developed several variants of the algorithm that avoid classical regularization while imposing several global cohesiveness constraints. We believe this is a novel approach that has the advantage of guaranteeing that solutions minimize the original cost function and preserve discontinuities. The constraints are based on minimizing the total number of horizontal and/or vertical discontinuities along and/or between adjacent epipolar lines, and local smoothing is avoided. Experiments reveal that minimizing the sum of the horizontal and vertical discontinuities provides the most accurate results. A high percentage of correct matches and very little smearing of depth discontinuities are obtained. An alternative to imposing cohesiveness constraints to reduce the correspondence ambiguities is to use more than two cameras. We therefore extend the two camera maximum likelihood toNcameras. TheN-camera stereo algorithm determines the “best” set of correspondences between a given pair of cameras, referred to as the principal cameras. Knowledge of the relative positions of the cameras allows the 3D point hypothesized by an assumed correspondence of two features in the principal pair to be projected onto the image plane of the remainingN− 2 cameras. TheseN− 2 points are then used to verify proposed matches. Not only does the algorithm explicitly model occlusion between features of the principal pair, but the possibility of occlusions in theN− 2 additional views is also modeled. Previous work did not model this occlusion process, the benefits and importance of which are experimentally verified. Like other multiframe stereo algorithms, the computational and memory costs of this approach increase linearly with each additional view. Experimental results are shown for two outdoor scenes. It is clearly demonstrated that the number of correspondence errors is significantly reduced as the number of views/cameras is increased.  相似文献   
104.
105.
Flavivirus genus includes many deadly viruses such as the Japanese encephalitis virus (JEV) and Zika virus (ZIKV). The 5′ terminal regions (TR) of flaviviruses interact with human proteins and such interactions are critical for viral replication. One of the human proteins identified to interact with the 5′ TR of JEV is the DEAD-box helicase, DDX3X. In this study, we in vitro transcribed the 5′ TR of JEV and demonstrated its direct interaction with recombinant DDX3X (Kd of 1.66 ± 0.21 µM) using microscale thermophoresis (MST). Due to the proposed structural similarities of 5′ and 3′ TRs of flaviviruses, we investigated if the ZIKV 5′ TR could also interact with human DDX3X. Our MST studies suggested that DDX3X recognizes ZIKV 5′ TR with a Kd of 7.05 ± 0.75 µM. Next, we performed helicase assays that suggested that the binding of DDX3X leads to the unwinding of JEV and ZIKV 5′ TRs. Overall, our data indicate, for the first time, that DDX3X can directly bind and unwind in vitro transcribed flaviviral TRs. In summary, our work indicates that DDX3X could be further explored as a therapeutic target to inhibit Flaviviral replication  相似文献   
106.
107.
Water ingress inside honeycomb sandwich panels during service has been linked to in-flight failure in some aircraft. There is an ongoing effort to develop nondestructive testing methods to detect the presence of water within the panels. Magnetic resonance (MR) represents an attractive approach in that it is sensitive to moisture. Using a unilateral MR sensor, testing can be applied directly to the surface of the panel. The viability of MR is demonstrated through laboratory imaging of both water within sandwich panels, as well as the adhesive itself. The detection of water using a one-sided handheld MR sensor is presented. It is shown that simple detection, as well as spatial localization of water within sandwich panels is possible.  相似文献   
108.
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.  相似文献   
109.
Li Y  Greiner RS  Salem N  Watkins BA 《Lipids》2003,38(6):683-686
The effect of dietary n−3 FA deficiency on bone tissue FA composition was evaluated in growing rats. Two mixtures combining hydrogenated coconut oil with safflower oil served as the n−3-deficient dietary treatments and provided two levels of linoleic acid (LA). The n−3 treatments were formulated with added α-linolenic acid (LNA) from flaxseed oil (diet LNA) or LNA plus DHA, and both were balanced for LA. This study showed that bone is sensitive to changes in dietary n−3 FA and that DHA is more effective than LNA in maintaining DHA levels in these tissues.  相似文献   
110.
The fatty acid composition of body lipids was determined by GLC for 14 species of saltwater fish, three species of freshwater fish and four species of shellfish. In addition, liver lipids of two species and egg lipids of one species were analyzed for comparison with the fish body lipids. The various species ranged from lean to fatty and contained from 0.7~15.5% oil in the tissues. Certain major fatty acids were found to vary widely among the species, as follows: 1.6~8.0% myristic, 9.5~33.4% palmitic, 2.0~11.2% palmitoleic, 5.2~29.1% oleic, 0.7~10.5% eicosenoic, 5.0~21.5% eicosapentaenoic, 0.2~11.6% docosenoic and 5.9~26.2% docosahexaenoic acids. Analyses of two separate mullet-oil samples illustrated the wide differences that are possible for a single species caught during different seasons. Significant differences in the amt of particular fatty acids were found in comparing freshwater-fish analyses with analyses for marine fish. Oysters and scallops showed large amt of pentaenoic and hexaenoic acids in their oils. Presented in part at the AOCS Meeting, New York, 1960.  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