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   529篇
  免费   24篇
  国内免费   5篇
电工技术   3篇
化学工业   160篇
金属工艺   11篇
机械仪表   24篇
建筑科学   12篇
矿业工程   1篇
能源动力   24篇
轻工业   48篇
水利工程   2篇
石油天然气   4篇
无线电   74篇
一般工业技术   85篇
冶金工业   39篇
原子能技术   7篇
自动化技术   64篇
  2024年   2篇
  2023年   9篇
  2022年   13篇
  2021年   27篇
  2020年   17篇
  2019年   25篇
  2018年   20篇
  2017年   18篇
  2016年   24篇
  2015年   14篇
  2014年   22篇
  2013年   42篇
  2012年   25篇
  2011年   38篇
  2010年   29篇
  2009年   44篇
  2008年   24篇
  2007年   22篇
  2006年   23篇
  2005年   21篇
  2004年   10篇
  2003年   8篇
  2002年   9篇
  2001年   9篇
  2000年   8篇
  1999年   4篇
  1998年   12篇
  1997年   5篇
  1996年   3篇
  1995年   7篇
  1994年   5篇
  1993年   4篇
  1990年   3篇
  1989年   3篇
  1987年   3篇
  1981年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1970年   1篇
排序方式: 共有558条查询结果,搜索用时 15 毫秒
21.
This paper deals with a human-assisted knowledge extraction method to extract “if…then…” rules from a small set of machining data. The presented method utilizes both probabilistic reasoning and fuzzy logical reasoning to benefit from the machining data and from the judgment and preference of a machinist. Using the extracted rules, one can determine the values of operational parameters (feed, cutting velocity, etc.) to ensure the desired machining performance (keep surface roughness within the stipulated range (e.g., moderate)). Applying the presented method in a real-life machining knowledge extraction situation and comparing it with the inductive learning based knowledge extraction method (i.e., ID3), the usefulness of the method is demonstrated. As the concept of manufacturing automation is shifting toward “how to support humans by computers”, the presented method provides some valuable hints to the developers of futuristic computer integrated manufacturing systems.  相似文献   
22.
Olopatadine (AL-4943A; KW-4679) [(Z)-11-[3-(dimethylamino)propylidene]-6, 11-dihydrodibenz[b,e]oxepine-2-acetic acid hydrochloride] is an antiallergic/antihistaminic drug under development for topical ocular use. The effects of the compound on release of proinflammatory mediators (histamine, tryptase and prostaglandin D2) from monodispersed human conjunctival mast cells were assessed. Histamine receptor subtype binding affinities and functional potencies were determined with ligand binding and phosphoinositide turnover assays, respectively. Olopatadine inhibited the release of histamine, tryptase and prostaglandin D2, in a concentration-dependent manner (IC50 = 559 microM). Evaluation of the interaction of olopatadine with histamine receptors revealed a relatively high affinity for the H1 receptor (Ki = 31.6 nM, pKi = 7.5 +/- 0.1, n = 7) but lower affinities for H2 receptors (Ki = 100 microM, pKi = 4.0 +/- 0.19, n = 7) and H3 receptors (Ki = 79.4 microM, pKi = 4.1 +/- 0.16, n = 7). The H1 selectivity of olopatadine was superior to that of other ocularly used antihistamines studied, such as ketotifen, levocabastine, antazoline and pheniramine. The profiling of olopatadine in 42 nonhistamine receptor binding assays revealed that olopatadine interacts with only two nonhistamine receptor/uptake sites to any significant degree (pIC50 < or = 5-6). Olopatadine inhibited histamine-induced phosphoinositide turnover in human conjunctival epithelial cells (IC50 = 10 nM, pIC50 = 8.0, n = 4) and in other human ocular cells (IC50 = 15.8-31.6 nM, pIC50 = 7.5-7.8) and exhibited apparent noncompetitive antagonist properties in these cells, with an estimated dissociation constant (Kb) of 19.9 nM (pKb = 7.7, n = 6). This combination of mast cell mediator release inhibition and selective H1 receptor antagonism suggests that olopatadine may be particularly useful in the treatment of ocular allergic diseases. Indeed, olopatadine has recently shown clinical efficacy in an allergic conjunctivitis model in human subjects.  相似文献   
23.
Measurement of soft x-ray emission from a low-energy plasma focus operated with nitrogen within the pressure range of 0.1–1.0 mbar is presented. The x-rays are detected by using an assembly of Quantrad Si PIN-diodes with differential filtering and with a multipinhole camera. In the 1.0–1.3 keV and 1.0–1.5 keV windows, the x-ray yield in 4 geometry is 1.03 J and 14.0 J, respectively, at a filling pressure of 0.25 mbar and the corresponding efficiencies are 0.04% and 1.22%. The total x-ray emission in 4 geometry is estimated at 21.8 J, which corresponds to the system efficiency of about 1.9%. The soft x-ray emission is found dominantly as a result of electron beam activity on the anode tip, which is confirmed by the images recorded by a pinhole camera.  相似文献   
24.
This paper presents an efficient dynamic spectrum allocation (DSA) scheme in a flexible spectrum licensing environment where multiple networks coexist and interfere with each other. In particular, an extension of virtual boundary concept in DSA is proposed, which is spectrally efficient than the previous virtual boundary concept applied to donor systems only. Here, the same technique is applied to both donor and rental systems so as to further reduce the occurrences where the insertion of guard bands is obligatory and as a result provides better spectral efficiency. The proposed extension improves the spectrum utilization without any compromise on interference and fairness issues.  相似文献   
25.
To estimate the thermohydraulic efficiency of different types of swirlers of heat exchange in pipes, we have generalized the experimental data, which has made it possible to determine the optimal range of Reynolds numbers and the optimal geometric sizes of swirlers. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 23–30, January–February, 2009.  相似文献   
26.
The elastic properties of single-crystalline erbia (Er2O3) at room temperature have been investigated using resonant ultrasound spectroscopy. The three independent stiffness constants of anisotropic Er2O3 cubic type-C crystals have been measured. The values of the stiffness constants were c 11= 256.4 GPa, c 12= 146.8 GPa, and c 44= 75.2 GPa. From the stiffness constants, the estimated values for dense polycrystalline erbia for Young's modulus, the shear modulus, the bulk modulus, and Poisson's ratio at room temperature were 179 GPa, 67 GPa, 183.3 GPa, and 0.337, respectively. The value of Young's modulus is a minimum along [001] and a maximum along [111]. The value of the shear modulus is independent of the direction in the (001) and (111) planes, whereas it decreases in (11¯0) from 75 GPa along [001] to 55 GPa along [110].  相似文献   
27.
This paper presents a low voltage low noise open loop automatic amplitude control method for voltage-controlled oscillators (VCO’s). In this method a feedback mechanism keeps the VCO at its optimum amplitude over temperature and process variations and then the loop is broken to avoid noise injection form the control circuitry to the VCO. The loop does not add extra noise to the VCO. Based on the proposed method, a low voltage low noise LC-VCO was designed for a low phase noise application in TSMC 0.18 micron RFCMOS technology. Simulations show considerable improvement in the phase noise with the application of the proposed method.  相似文献   
28.
The object of this study was to review the developments taking place during 1990–2005 regarding the use of quaternary ammonium salts as dye fixing agents for improving the fastness properties of anionic dyes on cellulose fibres. As far as fastness properties are concerned, this review is restricted only to fastness to light, washing and water treatments.  相似文献   
29.
An investigation has been carried out to study the dissolution of the Cu pad of the ball-grid-array (BGA) substrate into the molten Sn–9%In–3.5%Ag–0.5%Cu, Sn–3.5%Ag–0.5%Cu and Sn–0.7%Cu (wt.%) solder alloys. A fixed volume of BGA solder ball (760 μm dia) was used on a 13 μm thick Cu pad with a diameter of 650 μm. The dissolution measurement was carried out by measuring the change of Cu pad thickness as a function of time and temperature. Scanning electron microscopy was used to examine the microstructure of the solder joint and to measure the consumed thickness of Cu. The dissolution of Cu in Sn–3.5%Ag–0.5%Cu solder is higher than the other two lead-free solders. The presence of indium in the solder plays a major role in inhibiting the consumption of Cu in the soldering reaction. The intermetallic compounds (IMCs) formed at the Sn–9%In–3.5%Ag–0.5%Cu/Cu interface are determined as a scallop-shaped Cu6(Sn, In)5. Bulk of the Sn–9%In–3.5%Ag–0.5%Cu solder also contains Cu6(Sn, In)5 and Ag–In–Sn precipitates embedded in the Sn-rich matrix. It is also found that more Cu-containing Sn–0.7%Cu solder shows lower Cu consumption than Sn–3.5%Ag–0.5%Cu solder at the same heat treatment condition.  相似文献   
30.
This article presents a new level‐cut, inhomogeneous, filtered Poisson random field model for representing two‐phase microstructures of statistically inhomogeneous, functionally graded materials with fully penetrable embedded particles. The model involves an inhomogeneous, filtered Poisson random field comprising a sum of deterministic kernel functions that are scaled by random variables and a cut of the filtered Poisson field above a specified level. The resulting level‐cut field depends on the Poisson intensity, level, kernel functions, random scaling variables, and random rotation matrices. A reconstruction algorithm including model calibration and Monte Carlo simulation is presented for generating samples of two‐phase microstructures of statistically inhomogeneous media. Numerical examples demonstrate that the model developed is capable of producing a wide variety of two‐ and three‐dimensional microstructures of functionally graded composites containing particles of various sizes, shapes, densities, gradations, and orientations. An example involving finite element analyses of random microstructures, leading to statistics of effective properties of functionally graded composites, illustrates the usefulness of the proposed model. Copyright © 2008 John Wiley & Sons, Ltd.  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