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   1430篇
  免费   145篇
  国内免费   47篇
电工技术   65篇
综合类   74篇
化学工业   265篇
金属工艺   48篇
机械仪表   86篇
建筑科学   57篇
矿业工程   35篇
能源动力   33篇
轻工业   142篇
水利工程   23篇
石油天然气   62篇
武器工业   4篇
无线电   204篇
一般工业技术   181篇
冶金工业   175篇
自动化技术   168篇
  2024年   11篇
  2023年   26篇
  2022年   37篇
  2021年   51篇
  2020年   34篇
  2019年   38篇
  2018年   51篇
  2017年   52篇
  2016年   51篇
  2015年   43篇
  2014年   62篇
  2013年   88篇
  2012年   72篇
  2011年   104篇
  2010年   70篇
  2009年   67篇
  2008年   85篇
  2007年   70篇
  2006年   58篇
  2005年   66篇
  2004年   28篇
  2003年   44篇
  2002年   47篇
  2001年   32篇
  2000年   28篇
  1999年   35篇
  1998年   75篇
  1997年   47篇
  1996年   31篇
  1995年   18篇
  1994年   24篇
  1993年   16篇
  1992年   11篇
  1991年   1篇
  1990年   11篇
  1989年   6篇
  1988年   3篇
  1987年   1篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1982年   2篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1977年   4篇
  1976年   3篇
  1975年   2篇
  1970年   1篇
排序方式: 共有1622条查询结果,搜索用时 31 毫秒
101.
This article describes a high efficient and economical method to synthesize a liquid crystalline epoxy resin (LCER) containing biphenol and aromatic ester group, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-(oxiran-2-ylmethoxy) benzoate) (4). First, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-hydroxybenzoate) (3) was prepared by direct esterification of 3,3′,5,5′-tetramethylbiphenyl-4,4′-diol (2) with p-hydroxybenzoic acid (1) in the presence of a certain amount of p-toluene sulfonic acid (p-TSA) as catalyst. And then (4) was synthesized by the reaction of (3) with epichlorohydrin. The chemical structure, melting range, and liquid crystalline phase transition behavior of (4) were characterized by FT-IR, 1H-NMR, 13C-NMR, mass spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM).  相似文献   
102.
The flower-like tin disulphide (SnS2) microspheres have been synthesised by a facile solution-based route using polyethylene glycol 200 as the solvent and template. The products are characterised by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Experimental results show that the flower-like SnS2 microspheres with diameters around 2-5--m are made of many interleaving petal-like nanostructures. These nanopetals are 1-3--m in side length and less than 60-nm in thickness. The influences of solvent and sulphur source on the morphology of SnS2 nanostructures have also been investigated. The possible growth mechanism is discussed. Furthermore, the room-temperature Raman spectrum of the flower-like SnS2 microspheres is also studied.  相似文献   
103.
Hair shedding and hair thinning have been reported to be affected by dandruff and seborrhoeic dermatitis. The present study was conducted in 150 men presenting with telogen effluvium related to androgenic alopecia associated with dandruff. They were randomly allocated to three groups receiving each one of the three shampoos in the market containing either 1% ketoconazole (KTZ), 1% piroctone olamine (PTO) or 1% zinc pyrithione (ZPT). Shampoos had to be used 2-3 times a week for 6 months. Hair shedding during shampoo was evaluated semiquantitatively. Hair density on the vertex was evaluated on photographs using a Dermaphot. Trichograms were used for determining the anagen hair percentage and the mean proximal hair shaft diameter using computerized image analysis. The sebum excretion rate (SER, mug cm(-2) h(-1)) was also measured using a Sebumeter. The three treatments cleared pruritus and dandruff rapidly. At end point, hair density was unchanged, although hair shedding was decreased (KTZ: -17.3%, PTO: -16.5%, ZPT: -10.1%) and the anagen hair percentage was increased (KTZ: 4.9%, PTO: 7.9%, ZPT: 6.8%). The effect on the mean hair shaft diameter was contrasted between the three groups of volunteers (KTZ: 5.4%, PTO: 7.7%, ZPT: -2.2%). In conclusion, telogen effluvium was controlled by KTZ, PTO and ZPT shampoos at 1% concentration. In addition, KTZ and PTO increased the mean hair shaft thickness while discretely decreasing the sebum output at the skin surface.  相似文献   
104.
In this paper we propose a new variational model for image denoising and segmentation of both gray and color images. This method is inspired by the complex Ginzburg–Landau model and the weighted bounded variation model. Compared with active contour methods, our new algorithm can detect non-closed edges as well as quadruple junctions, and the initialization is completely automatic. The existence of the minimizer for our energy functional is proved. Numerical results show the effectiveness of our proposed model in image denoising and segmentation. Fang Li received the MSc degree in Mathematics from the South West China Normal University in 2004 and from then on she works in the South West University. Meanwhile, she studies mathematics at the East China Normal University as a doctoral student. Her research interests include anisotropic diffusion filtering, the variational methods and PDEs in image processing. Chaomin Shen received the MSc degree in Mathematics from the National University of Singapore (NUS) in 1998. He worked in the Centre for Remote Imaging, Sensing and Processing (CRISP), NUS as an associate scientist during 1998 to 2004. Currently he is a lecturer in Joint Laboratory for Imaging Science & Technology and Department of Computer Science, East China Normal University. His research interests include remote sensing applications and variational methods in image processing. Ling Pi received her MSc degree from the Department of Mathematics, East China Normal University in 2003. She is currently a lecturer in the Department of Applied Mathematics, Shanghai Jiaotong University. Her work involves the application of geometric and analytic methods to problems in image processing.  相似文献   
105.
以柴油机 13工况排放试验结果为依据 ,研究了污染物中的碳氢化合物 (HC)与微粒 (PM )之间的关系 ,并考虑了影响因素 提出了通过每工况的HC来预测其微粒的新方法 ,计算结果和试验数据有较好的吻合 此预测模型对高压共轨柴油机ECU的设计是一个有力的工具  相似文献   
106.
辽化医院检验科通用管理软件能够准确及时地利用Visual Basic 6.0采集检验科检测仪器的串口数据,存储到Microsoft Access数据库,能够对数据进行处理、查询、显示、打印,整个界面简洁、美观、功能完整.  相似文献   
107.
In the present work, the mechanical properties and the microstructural evolution of a duplex stainless steel in the as-cast and wrought conditions during deformation under hot-working conditions have been studied. Hot torsion tests, at strain rates of = 1 s−1, have been carried out using prepolished samples on which surface parallel scratches have been practiced. The observation of the surface of the samples shows a large displacement of the scratches produced by two different mechanisms, sliding on the δ/γ interface, and shearing of the ferrite. The displacements in the as-cast condition have been found to concentrate in a reduced set of ferrite/austenite interfaces leading to the formation of cracks along them. In the wrought material, the distribution of the sliding is more homogeneous over all the ferrite/austenite interfaces, and no damage has been produced. These behavioral differences between both materials have been related in the present work, to the characteristics of the corresponding microstructures, to the spatial phase distribution, and to the nature of the ferrite/austenite interface, among others.  相似文献   
108.
Skin colour assessment in safety testing of cosmetics. An overview   总被引:1,自引:0,他引:1  
Synopsis
Few subjects are as problematical to dermatologists, cosmetologists and related experimenters involved in safety testing as the clinical assessment of skin colour. At the core of the problem is the word erythema, which does not communicate a sense for the nuance of red. In addition, light shades of red are not visible in dark-skinned people. Human assays aiming at evaluating the irritancy and allergic potential of cosmetics take advantage to use instrumental assessments of skin colour. However, there are pitfalls related to the complex biological aspects of the cutaneous reactivity, to the design of the in vivo assay, and to technical aspects bound to the principle of the measuring methods. Sound information can only be reached when these concerns are solved.
Résumé
Peu de sujets sont aussi problématiques pour les dermatologues, cosmétologues et autres expérimentateurs impliqués dans les tests de sûreté que l'évaluation clinique des couleurs cutanées. Au centre du problème est le mot érythème qui ne communique pas la notion des nuances de rouge. De plus, un érythème discret peut ne pas être visible chez des individus à la peau foncée. Les tests humains visant àévaluer les potentialités d'irritation et d'allergie aux cosmétiques bénéficient des évaluations instrumentales de la couleur cutanée. Cependant, il existe des pièges liés aux aspects biologiques complexes de la réactivité cutanée, au choix du test in vivo et à des aspects techniques en relation avec le principe du système de mesure. Une information adéquate ne peut être obtenue qu'après avoir résolu ces problèmes.  相似文献   
109.
We present a study of phase separation from supersaturated 3 He- 4 He liquid mixtures at low temperatures addressing both the degree of critical supersaturation xcr and the thermal-to-quantum crossover temperature T* for the nucleation process. Two different nucleation seeds are investigated, namely 3 He droplets and 4 He vortex lines with cores filled with 3 He. We have found that the experimental T* is reproduced when we consider that nucleation proceeds from 3 He droplets, whereas xcr is reproduced when we consider 4 He vortex lines filled with 3 He. However, neither nucleation configuration is able to simultaneously reproduce the current experimental information on xcr and T*.  相似文献   
110.
There exists two distinct types of patches aiming at increasing the pain threshold either systematically or locally. The first type of analgesic patch is a real transdermal delivery system releasing fentanyl. Such potent opioid drug exerts a systemic effect. The other type of patch associates lidocain and prilocain to induce a local anesthesia of the skin without inducing a systemic effect.  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