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   268篇
  免费   2篇
  国内免费   1篇
电工技术   6篇
化学工业   43篇
金属工艺   2篇
机械仪表   1篇
建筑科学   6篇
能源动力   4篇
轻工业   17篇
无线电   31篇
一般工业技术   54篇
冶金工业   78篇
原子能技术   4篇
自动化技术   25篇
  2023年   1篇
  2022年   4篇
  2021年   5篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   6篇
  2016年   1篇
  2014年   2篇
  2013年   2篇
  2012年   6篇
  2011年   4篇
  2010年   5篇
  2009年   6篇
  2008年   8篇
  2007年   10篇
  2006年   4篇
  2005年   8篇
  2004年   9篇
  2003年   8篇
  2002年   7篇
  2001年   5篇
  2000年   6篇
  1999年   5篇
  1998年   36篇
  1997年   25篇
  1996年   7篇
  1995年   13篇
  1994年   16篇
  1993年   10篇
  1992年   1篇
  1991年   5篇
  1990年   3篇
  1989年   7篇
  1988年   4篇
  1987年   5篇
  1986年   2篇
  1985年   5篇
  1984年   5篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1972年   1篇
  1969年   1篇
排序方式: 共有271条查询结果,搜索用时 10 毫秒
1.
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach.  相似文献   
2.
Abstract— We have developed a process to fabricate optical components, such as a lens, prism, or diffuser, directly on to a glass substrate. Processes include precision mastering by diamond cutting and multi‐layer photopolymer (2P) molding to realize flat surfaces and the integration of multiple components with an alignment within a few micrometers.  相似文献   
3.
Microspherical solar cells and modules have been fabricated. The spherical nature of these semi-transparent devices allows the microspherical cells to harvest both directly incident and diffuse components of sunlight thereby improving the solar energy conversion efficiency. Indoor and outdoor characterizations of these three dimensional semi-transparent cells and modules are carried out using a Lambertian reflector in order to assess the maximum efficiency of the devices. In the absence of the reflector the cell efficiency is 13.5% under standard illumination (100 mW cm−2, A.M. 1.5, 25 °C). However, this is significantly enhanced in the presence of the reflector. Microspherical modules with the reflector are directly compared to similar semi-transparent modules comprised of traditional planar devices, in outdoor tests at low light intensity (2.5–25 mW cm−2) to further demonstrate the benefits of the design particularly at low angle of incident radiation.  相似文献   
4.
High-purity Si3N4 (with 2.5 wt% glassy SiO2) doped with 0 to 450 at.ppm of Ca was prepared as a model system to investigate the effects of grain-boundary segregants on fracture phenomenology at 1400°C. Subcritical crack-growth (SCG) resistance as well as creep resistance was degraded significantly by the presence of a small amount of Ca. The internal friction of the doped materials exhibited the superposition of a grain-boundary relaxation peak and a high-temperature background, and the apparent viscosity of the grain-boundary film was determined from the peak. Based on these experimental data, the fracture mechanism at 1400°C was divided into three regions: "brittle," SCG, and creep failure as a function of both external strain rate and Ca concentration, C Ca. From the investigation of the C Ca dependence of the critical strain rate for the transition from "brittle" to SCG fractures, the SCG phenomenon is suggested to be triggered by small-scale, grain-boundary sliding. The C Ca dependence of "steady-state" creep rate was far from the theoretical dependence of diffusional creep via a solution-precipitation mechanism. The discrepancy was interpreted to be due to the presence of an impurity-insensitive creep component. This component may correspond to the lowest limit of the tensile creep rate in Si3N4 polycrystalline materials containing intergranular glassy-SiO2 film.  相似文献   
5.
The temperature dependence of Young's modulus and internal friction (Q−1)in alumina, silicon nitride, and partially stabilized zirconia (Y-PSZ) ceramics was studied. Little change in Q−1 was found for alumina, whereas Q−1 for silicon nitride ceramics increased above 700°C. The Q−1 of Y-PSZ increased markedly with increasing temperature up to a peak at ∼200°C.  相似文献   
6.
We have studied the cooperative manipulation of floating object by several space robots. For these cooperative motions, we have reported that a tracking control method using the transpose of the generalized Jacobian matrix (GJM) can be utilized for robots with joint torque controllers. For cooperative motions by some robots with joint velocity controllers, we proposed a tracking control method using the transpose of the GJM. Simulation results show the effectiveness of the proposed control method.  相似文献   
7.
This paper deals with a motion control system for a space robot with a manipulator. Many motion controllers require the positions of the robot body and the manipulator hand with respect to an inertial coordinate system. In order to measure them, a visual sensor using a camera is frequently used. However, there are two difficulties in measuring them by means of a camera. The first one is that a camera is mounted on the robot body, and hence it is difficult to directly measure the position of the robot body by means of it. The second one is that the sampling period of a vision system with a general-purpose camera is much longer than that of a general servo system. In this paper, we develop an adaptive state observer that overcomes the two difficulties. In order to investigate its performance, we design a motion control system that is constructed by combining the observer with a PD control input, and then conduct numerical simulations for the control system. Simulation results demonstrate the effectiveness of the proposed observer.  相似文献   
8.
During iron-carbon eutectic solidification, the coefficients for partition of a third element between the eutectic liquid and its solid were evaluated thermodynamically. The coefficientk M A/L for the equilibrium partition of the third element (M) between austenite and liquid iron largely depended on the interaction between carbon and the third element and a simplified method for the evaluation ofk M A/L was introduced. The coefficients,K S andK M, for the partition of the element between the eutectic liquid and its solid in the stable and metastable eutectic solidification, respectively, were also calculated fromk M A/L and the coefficientk M C/A for the equilibrium partition of the element between cementite and austenite. It was indicated by the thermodynamics of the free energy for the co-existing phases that the effect of a third element on graphitization occurring during eutectic solidification was related quantitatively to the value of K which was represented byK S-K M. The effect of a third element on the difference between the stable and metastable eutectic temperatures and on the carbon activity of liquid iron was closely related to K or the equilibrium partition coefficient,k M C/A .  相似文献   
9.
We present a simple design rule for diode-laser pumped quasi-three-level lasers by using the M2 factor. The validity of this model was demonstrated by diode-pumped Yb:YAG laser experiments. The maximum output power of 1.33 W and optical slope efficiency of 63% were obtained in a 400-μm Yb:YAG chip miniature laser. Using a 200-μm Yb:YAG chip, a 70% optical slope efficiency was reached. In a coupled-cavity configuration, with a quartz birefringent tuning filter, 8.2 THz (29 nm) of tuning was obtained at room temperature. By changing to a calcite birefringent filter, single-axial-mode oscillation with an output power of 500 mW was observed  相似文献   
10.
The GH-16 type β-1,3-glucanase (BgluC16MK) gene of Lysobacter sp. MK9-1 was cloned to study its antifungal activities. BgluC16MK displays amino acid sequence similarity with GluC from L. enzymogenes strain N4-7. BgluC16MK includes a signal sequence, a catalytic domain and carbohydrate-binding module family 6-type β-glucan binding domain (B-GBD). The expression of the BgluC16MK gene in Escherichia coli without the signal sequence resulted in antifungal activity at a dose of 0.6-0.8 nmol/disk. However, BgluC16MK displayed antifungal activity at a dose of 0.025 nmol/disk in combination with Chi19MK. Substrate-specific assay revealed that purified BgluC16MK hydrolyzed insoluble curdlan more readily than the soluble substrate. Furthermore, to explore the binding selectivity of B-GBD of BgluC16MK, we constructed a fusion protein (B-GBD-GFP) using the B-GBD and green fluorescent protein. The activity of the fusion protein against various substrates indicates that B-GBD was selective for glucans with β-1,3-linkages. An additional study demonstrated the binding ability of B-GBD-GFP to the cell-wall of living fungi, such as T. reesei and Aspergillus oryzae. These findings suggest that BgluC16MK can be utilized to generate antifungal enzyme preparations and that the fusion protein B-GBD-GFP can be used to identify the fungal cell surface structure using β-glucans.  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