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   1229篇
  免费   28篇
  国内免费   3篇
电工技术   141篇
综合类   2篇
化学工业   314篇
金属工艺   32篇
机械仪表   55篇
建筑科学   27篇
能源动力   88篇
轻工业   99篇
水利工程   1篇
石油天然气   2篇
无线电   72篇
一般工业技术   199篇
冶金工业   93篇
原子能技术   43篇
自动化技术   92篇
  2023年   4篇
  2022年   5篇
  2021年   17篇
  2020年   8篇
  2019年   10篇
  2018年   11篇
  2017年   24篇
  2016年   23篇
  2015年   16篇
  2014年   41篇
  2013年   93篇
  2012年   44篇
  2011年   66篇
  2010年   51篇
  2009年   54篇
  2008年   61篇
  2007年   57篇
  2006年   40篇
  2005年   39篇
  2004年   42篇
  2003年   54篇
  2002年   32篇
  2001年   24篇
  2000年   24篇
  1999年   37篇
  1998年   39篇
  1997年   38篇
  1996年   21篇
  1995年   22篇
  1994年   19篇
  1993年   13篇
  1992年   12篇
  1991年   13篇
  1990年   16篇
  1989年   10篇
  1988年   10篇
  1987年   19篇
  1986年   14篇
  1985年   18篇
  1984年   16篇
  1983年   13篇
  1982年   13篇
  1981年   8篇
  1980年   16篇
  1979年   9篇
  1978年   11篇
  1977年   5篇
  1976年   8篇
  1973年   3篇
  1969年   3篇
排序方式: 共有1260条查询结果,搜索用时 15 毫秒
1.
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.  相似文献   
2.
3.
4.
This paper presents a novel on‐line parameter identification method for sensorless control of Synchronous Reluctance Motors (SynRMs). Although conventional sensorless control methods based on mathematical models usually need some complex measurements of motor parameters in advance, the proposed identification method does not require them and can be realized on‐line. The proposed method identifies motor parameters under sensorless control, so rotor position and velocity cannot be used to identify these parameters. However, the proposed method does not need rotor position and velocity, and identified parameters are not affected by these estimation errors. The sensorless control using identified motor parameters is realized, and the effectiveness of the proposed method is verified by experimental results. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 62–69, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20258  相似文献   
5.
This paper describes a load dispatch method which minimizes power cost—[fuel cost]/[electric output]—for a power system with thermal plants and energy storage facilities. The proposed method employs fractional programming to convert a minimization problem with fractional objective function to a series of quadratic minimization problems, and semidefinite programming to solve converted problems. The method provides the optimum time‐dependent power output/input and storage level of energy storage facilities as well as time‐dependent power output of thermal plants. The method has been applied to a power system with five thermal plants, two energy storage facilities of various performances, and five load demands. The optimum load scheme of four time mesh points is obtained for the thermal plants and energy storage facilities. The fractional programming successfully converges the optimal scheme through a few iterations. The semidefinite programming deals with a variable matrix of 164 dimensions, and 185 inequality constraints. © 2001 Scripta Technica, Electr Eng Jpn, 138(2): 49–58, 2002  相似文献   
6.
Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)-tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, -(CF2)3CF3 and -CF3, respectively. In the case of E/TFE/NFH copolymer (ET-C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3 mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET-CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET-C4F9 and ET-CF3 copolymers is reasonably interpreted as follows: the short side groups (-CF3) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [-(CF2)3CF3] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data.  相似文献   
7.
A finite difference simulation method for the time dependent viscous incompressible flow around a transversely and longitudinally oscillating circular cylinder at Reynolds numbers of Re=4×103 and 4×104 is presented. The Navier-Stokes equations in finite difference form are solved on a moving grid system, based on a time dependent coordinate transformation. Solution of the vortex street development behind the cylinder is obtained when the cylinder remains stationary and also when it is oscillating. Time eholution of the flow configuration is studied by means of stream lines, pressure contours and vorticity contours. The computer results predict the lock-in phenomenon which occurs when the oscillation frequency is close to the vortex shedding frequency in the transverse mode or around double the vortex shedding frequency in the longitudinal mode. The time dependent lift and drag coefficients are obtained by the integration of the pressure and shear forces around the body. The drag, lift and the displacement relations are also discussed.  相似文献   
8.
9.
The rapidly quenched films in the Bi2O3-TiO2 system (0 to 60% TiO2) were prepared using a twin-roller type apparatus. The films precipitated Bi2O3 solid solutions of different types in the composition ranges, with TiO2 contents of 0 to 5, 7.5 to 10 and 12.5 to 40%, respectively. The first solid solution had a tetragonal structure of -form. The second, though also crystallized in the tetragonal structure, adopted a disordered modification of the -form. The third solid solution was -form (defect fluorite structure). The formation of amorphous phase commenced in the composition with 30% TiO2, and the films became completely amorphous beyond 50% TiO2. The quenched films showed a certain instability to decompose or transform into the different phase assemblage by annealing at higher temperatures (about 400 to 500° C, except 260° C for the pure Bi2O3 film). The quenched films were also characterized by a high photoconductivity. The photoconduction mechanism was suggested to be associated with a structural imperfection of Bi2O3 accompanied by a certain amount of pentavalent bismuth ion.  相似文献   
10.
Poly(2-hydroxyethyl methacrylate)/polystyrene (PHEMA/PS) composite microspheres were produced by emulsifier-free seeded emulsion polymerization for styrene in the presence of PHEMA seed particles. Effects of the surface characteristics of the PHEMA/PS composite microspheres on the adsorption immobilization of trypsin and on its enzymatic activity were discussed. Above 5 mol% of HEMA content, trypsin molecules adsorbed had high activity, 65–100% of the activity of free trypsin. The excellence of the composite microspheres as a carrier for trypsin seems to be closely related with the surface heterogeneity consisting of both hydrophilic and hydrophobic parts.  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