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   2944篇
  免费   156篇
  国内免费   40篇
电工技术   42篇
综合类   56篇
化学工业   814篇
金属工艺   73篇
机械仪表   98篇
建筑科学   123篇
矿业工程   10篇
能源动力   121篇
轻工业   252篇
水利工程   25篇
石油天然气   21篇
武器工业   1篇
无线电   229篇
一般工业技术   440篇
冶金工业   294篇
原子能技术   29篇
自动化技术   512篇
  2023年   24篇
  2022年   114篇
  2021年   133篇
  2020年   61篇
  2019年   71篇
  2018年   78篇
  2017年   86篇
  2016年   100篇
  2015年   81篇
  2014年   100篇
  2013年   182篇
  2012年   128篇
  2011年   206篇
  2010年   125篇
  2009年   139篇
  2008年   140篇
  2007年   122篇
  2006年   102篇
  2005年   78篇
  2004年   86篇
  2003年   105篇
  2002年   120篇
  2001年   105篇
  2000年   87篇
  1999年   58篇
  1998年   86篇
  1997年   56篇
  1996年   52篇
  1995年   34篇
  1994年   21篇
  1993年   29篇
  1992年   20篇
  1991年   15篇
  1990年   11篇
  1989年   14篇
  1988年   8篇
  1987年   6篇
  1986年   16篇
  1985年   22篇
  1984年   12篇
  1983年   13篇
  1982年   11篇
  1981年   12篇
  1980年   9篇
  1979年   6篇
  1978年   9篇
  1977年   5篇
  1976年   10篇
  1975年   4篇
  1965年   4篇
排序方式: 共有3140条查询结果,搜索用时 0 毫秒
91.
Cooldry针织物导湿性能研究   总被引:5,自引:1,他引:5  
从理论与实验两个方面分析了影响织物导湿性能的因素,认为后整理对织物导湿性能有着重要的影响。  相似文献   
92.
This paper describes the design, realization and use of an analogical, fully reconfigurable experimental setup to analyze the complex dynamics of networks of chaotic circuits. It reports details of the implementation and characterization of the setup, together with representative results, showing its flexibility and potential. The setup allows to choose arbitrarily the coupling strength and interconnection structure among the circuits, the type of link and to select the parameters of the node dynamics. It has a modular structure, and it can accommodate up to 32 nodes interconnected by at most 32 links. The collective dynamics of a relatively large set of different network structures and configurations has been investigated using the setup. Synchronization, pattern formation and other interesting collective phenomena were observed experimentally, their evidence being reported here as an illustration of the potential of the proposed setup. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
93.
Abstract

The main topic of this paper is the nondestructive inspection of adhesively bonded lap joints by using ultrasonic guided (plate) waves. A noncontact, couplant-free method that employs capacitive air-coupled transducers is demonstrated for the inspection of thin aluminum joints with dimensions typical of aircraft fuselage and wing panels. Two types of bond defects, disbonded regions and regions of poorly cured (low-cohesive-strength) adhesive, are successfully detected by measuring the amplitude decrease of selected plate waves leaking from one adherend to the other one through the bondline. It is shown that proper choice of the vibrating mode structure, in terms of cross-sectional displacement distributions, is needed in order to maximize the sensitivity of the inspection to the presence of the low-cohesive-strength bond.

Results from a dynamic photoelasticity study are also presented to visualize fundamental behavior of propagating plate waves and study their interaction with bond defects in glass lap joints. The photoelastic results confirm in a clear, pictorial manner certain assumptions on plate wave leakage through the bond, including the influence of vibrating mode structure on the detection of low-strength bonds.  相似文献   
94.
Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (1H, 13C, 135‐DEPT and 29Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 105–2 × 105, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between ? 78 and ? 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm?1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry  相似文献   
95.
This paper is a report about the use of Matita, an interactive theorem prover under development at the University of Bologna, for the solution of the POPLmark Challenge, part 1a. We provide three different formalizations, including two direct solutions using pure de Bruijn and locally nameless encodings of bound variables, and a formalization using named variables, obtained by means of a sound translation to the locally nameless encoding. According to this experience, we also discuss some of the proof principles used in our solutions, which have led to the development of a generalized inversion tactic for Matita.  相似文献   
96.
经过几十年的发展与实践,试验设计与数据处理在我国经济发展中的重要性有目共睹。目前,大多数高校化学相关专业的本科生和研究生均开设了这门工具课。本文从教材的选择、教学内容、教学方式和课程考查方式等几方面进行了探讨。探讨该课程的教学方法,有利于激发学生的学习热情和学习兴趣,从而提高教学质量。  相似文献   
97.
A study of the crystallization of the mesomorphic form of isotactic polypropylene (iPP) in samples of different stereoregularity prepared with metallocene catalysts is presented. Contrary to what claimed in the literature, we have found that the mesomorphic form can be obtained by quenching of the melt at 0 °C also in the case of low stereoregular samples, provided that the samples are kept at 0 °C for long time. The key is the formation of mesomorphic bundles with chains in ordered 3/1 helical conformation of size large enough to be stable and inhibit the crystallization of the α form at room temperature. For stereoirregular samples the concentration of long ordered helical stretches is low and this requires long residence time at 0 °C for the formation of mesomorphic aggregates of size larger than the critical size. This result provides evidence that the mesomorphic aggregates are not formed as a result of a cooperative process driven by entropy, as in the case of liquid crystals, but rather they form via a nucleation and growth mechanism, as in the normal crystallization processes, according to the idea that the mesophase of iPP is a highly defective crystalline form.  相似文献   
98.
We are reporting on a series of two patients with end‐stage renal disease on hemodialysis, presented for surgical parathyroidectomy secondary refractory hyperparathyroidism. Both patients had failed maximized medical managements, including higher‐than‐usual doses of the calcimimetic cinacalcet (270 and 180 mg/day, respectively). On physical exam, both patients had marked symmetrical craniofacial hypertrophy with coarse distortion of facial features, similar in appearance to past reports of Sagliker syndrome. On X‐ray and computed tomographic exam, they had peculiar areas of bone absorption on the skull, imitating the radiologic appearance of multiple myeloma. Bone biopsy of the maxilla, however, did not show the expected brown tumor, but rather described only fibrosis and reactive bone formations. This phenotype developed while being on cinacalcet, progressed despite escalation of therapy, and improved only after parathyroidectomy. Both patients developed massive “hungry bone syndrome” after parathyroidectomy necessitating prolonged IV calcium infusion. This pattern of severe facial distortion likely represented an adverse consequence of severe tertiary hyperparathyroidism, along with supraphysiologic dose of cinacalcet administration and 25‐hydroxy vitamin D deficiency in sensitive individuals. The genetic base of this observation remained unexplained.  相似文献   
99.
100.
Magnum photos     
Abstract

For over fifty years, since Magnum's birth in 1947, the history of this remarkable photographic cooperative has been awash in myth and legend. The gifted, colourful, principled, and often disorderly members of the agency created some of the twentieth century's most memorable still images. These photographs, appearing on the pages of magazines like LIFE, Picture Post and the Ladies' Home Journal, pricked and provoked the consciences of millions worldwide. In the process, Magnum photographers bridged that illdefined, vexatious gap between photojournalism and art. Readers interested in learning more about this phenomenon now have two new choices. One is to reach for a copy of Russell Miller's Magnum: Fifty Years at the Front Line of History. This unauthorized biography, by an outsider, examines the operation ‘of a large, unruly and highly talented family which, by some miracle has stayed together for 50 years ... (with an) aim simply to tell a cracking good story as impartially and truthfully and entertainingly as was within my capabilities, and to disregard the notoriously fragile sensibilities of the participants’. The book fulfils the criteria. Illustrated by lively quotes, twenty-six photos, and numerous anecdotes from members such as Ernst Haas, Robert Capa and Eve Arnold, the book conveys a sense of energy and excitement. The volume concludes with a look towards the future of the agency and the crucial structural importance of maintaining hannony in the union of its practitioners. Russell Miller is perceptive and his treatment of the subject comprehensive.  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