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   1847篇
  免费   107篇
  国内免费   4篇
电工技术   35篇
综合类   3篇
化学工业   435篇
金属工艺   60篇
机械仪表   65篇
建筑科学   71篇
矿业工程   4篇
能源动力   129篇
轻工业   192篇
水利工程   18篇
石油天然气   8篇
无线电   157篇
一般工业技术   328篇
冶金工业   114篇
原子能技术   16篇
自动化技术   323篇
  2024年   7篇
  2023年   20篇
  2022年   48篇
  2021年   64篇
  2020年   49篇
  2019年   60篇
  2018年   82篇
  2017年   58篇
  2016年   86篇
  2015年   51篇
  2014年   92篇
  2013年   161篇
  2012年   100篇
  2011年   138篇
  2010年   98篇
  2009年   171篇
  2008年   115篇
  2007年   80篇
  2006年   83篇
  2005年   46篇
  2004年   48篇
  2003年   42篇
  2002年   40篇
  2001年   22篇
  2000年   21篇
  1999年   14篇
  1998年   32篇
  1997年   16篇
  1996年   10篇
  1995年   10篇
  1994年   9篇
  1993年   6篇
  1992年   10篇
  1991年   7篇
  1990年   5篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   3篇
  1984年   4篇
  1983年   7篇
  1982年   5篇
  1980年   4篇
  1979年   8篇
  1978年   5篇
  1976年   1篇
  1975年   1篇
  1974年   5篇
  1973年   4篇
  1971年   1篇
排序方式: 共有1958条查询结果,搜索用时 31 毫秒
191.
In this study, a decomposition method for approximating the solution of the Pochhammer-Chreeequation is implemented. By using this scheme, explicit exact solution is calculated in the form of a convergent power series with easily computable components. To illustrate the application of this method numerical results are derived by using the calculated components of the decomposition series. The obtained results are found to be in good agreement with the exact solutions known for some special cases.  相似文献   
192.
Space and force diagrams are presented for a family of simply-supported minimum-weight beam structures. The analytical methods, used to determine volume and displacements for a structure with different strength in tension and compression, are reviewed using the simplest circular arc beam example. The full design of a non-trivial symmetrical beam is described. The use of power series solutions and a matrix operator numerical method, developed for plane-strain slip-line field theory, are described to determine the beam layouts. The results of testing beam models, manufactured using both laser free-form sintering of nylon powder and CNC milling of aluminum alloy plate, are compared to the theoretical predictions of stiffness and maximum load capability. The theoretical predictions are shown to provide excellent agreement with both the isotropic aluminum test structure, and with the strongly bi-modulus nylon test structures.  相似文献   
193.
BACKGROUND: Although hydatidiform mole is not commonly encountered following ovulation induction, patients who have already had molar pregnancies are at increased risk of developing further molar diseases with worsening histologic characteristics. That fact underlies the ethical dilemma of repeat ovulation induction. CASE: A 38-year-old woman, gravida 3, para 0, had three consecutive episodes of hydatidiform subsequent to clomiphene citrate and gonadotropin ovulation induction. She seems to be the first in the literature to develop three consecutive molar pregnancies without a normal intrauterine pregnancy. CONCLUSION: Although ovulation induction commenced again in this patient after she gave informed consent, the risks underlying the ethical dilemma persist.  相似文献   
194.
In this paper, we evaluate and quantify the energy losses associated with compressed‐air systems, and their costs to manufacturers. We also show how to reduce the cost of compressed air in existing facilities by making some modifications with attractive payback periods. Among the measures, we investigate to reduce the compressed air are: (1) repairing air leaks, (2) installing high‐efficiency motors, (3) reducing the average air inlet temperature by using outside air (4) reducing compressor air pressure. We also illustrate the potential saving associated with each measure by using realistic examples. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
195.
Printing from an NTSC source and conversion of NTSC source material to high-definition television (HDTV) format are some of the applications that motivate superresolution (SR) image and video reconstruction from low-resolution (LR) and possibly blurred sources. Existing methods for SR image reconstruction are limited by the assumptions that the input LR images are sampled progressively, and that the aperture time of the camera is zero, thus ignoring the motion blur occurring during the aperture time. Because of the observed adverse effects of these assumptions for many common video sources, this paper proposes (i) a complete model of video acquisition with an arbitrary input sampling lattice and a nonzero aperture time, and (ii) an algorithm based on this model using the theory of projections onto convex sets to reconstruct SR still images or video from an LR time sequence of images. Experimental results with real video are provided, which clearly demonstrate that a significant increase in the image resolution can be achieved by taking the motion blurring into account especially when there exists large interframe motion.  相似文献   
196.
Dynamic consolidation techniques were employed to investigate the retention of tetragonal zirconia and degree of consolidation in alumina/zirconia powder compacts. Heating the specimens prior to explosive shock compaction increased the tetragonal-phase retention significantly. Low shock pressures yielded no macrocracking, although final densities were low (60% to 70% of the theoretical density). Heat treatment following dynamic consolidation enhanced the retention of the tetragonal zirconia polymorph regardless of the shock pressure employed. Compact densities were increased to over 90% of theoretical at relatively low sintering temperatures (1300°C). Hardness, toughness, and Young's modulus of the compacts were comparable to those achieved in composites that were synthesized using more conventional techniques. Dynamic compaction offers an alternative method for the fabrication of zirconia-toughened alumina ceramics.  相似文献   
197.
Since Salvia species (Lamiaceae) have been recorded to be used against memory loss in European folk medicine, we herein examined in vitro anticholinesterase and antioxidant activities of 56 extracts prepared with petroleum ether, chloroform, ethyl acetate and methanol obtained from 14 Salvia species (Salvia albimaculata Hedge and Hub, Salvia aucheri Bentham var. canescens Boiss and Heldr, Salvia candidissima Vahl. ssp. occidentalis, Salvia ceratophylla L., Salvia cryptantha Montbret and Bentham, Salvia cyanescens Boiss and Bal., Salvia frigida Boiss, Salvia forskahlei L., Salvia halophilaHedge, Salvia migrostegia Boiss and Bal., Salvia multicaulis Vahl., Salvia sclarea L., Salvia syriaca L., Salvia verticillata L. ssp. amasiaca) growing in Turkey. The antioxidant activities were assessed by both chemical and enzymatic methods against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging and xanthine/xanthine oxidase (XO) system generated superoxide anion radical inhibition. Anticholinesterase effect of the extracts was tested against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at concentrations of 0.2 and 1 mg/ml using a microplate-reader assay based on the Ellman method. Most of the extracts did not show any activity against AChE at 0.2 mg/ml, while the chloroform extracts had noticeable inhibition against BChE between 47.7% and 74.7%. The most active extracts at 1 mg/ml for AChE inhibition were observed to be petroleum ether extract of Salvia albimaculata (89.4%) and chloroform extract of Salvia cyanescens (80.2%), whereas ethyl acetate extracts of Salvia frigida and Salvia migrostegia, chloroform extracts of Salvia candidissima ssp. occidentalis and Salvia ceratophylla, as well as petroleum ether extract of Salvia cyanescens were found to inhibit potently BChE (92.2%, 89.6%, 91.1%, 91.3%, and 91.8%, respectively). Particularly, the ethyl acetate and methanol extracts were observed to be highly active against both DPPH and XO. Our data indicates that nonpolar extracts of Salvia species for anticholinesterase activity and the polar extracts for antioxidant activity are worth further phytochemical evaluation for identifying their active components.  相似文献   
198.
In this study, the change in the load-bearing system cost of a reinforced concrete office building has been investigated in relation to the earthquake regions and soil types. Three different office projects each with five stories were investigated. The structural design calculations have been made according to four different soil types and four different earthquake regions. According to each combination, concrete, steel and formwork adopted approximations were calculated to reach the rough cost of each office building. The changes in the cost of projects according to the soil type and earthquake region were examined with multiple regression analysis and analysis of variance. In general, the change in cost has been observed around 22% between first and fourth soil type and 14% between first and fourth earthquake region.  相似文献   
199.
We explore the breakdown of universal mobility behavior in sub-100-nm Si MOSFETs, using a novel three-dimensional (3-D) statistical simulation approach. In this approach, carrier trajectories in the bulk are treated via 3-D Brownian dynamics, while the carrier-interface roughness scattering is treated using a novel empirical model. Owing to the high efficiency of the transport kernel, effective mobility in 3-D MOSFETs with realistic Si-SiO/sub 2/ interfaces reconstructed from a Gaussian or exponential correlation function can be simulated in a statistical manner. We first demonstrate a practical calibration procedure for the interface mobility and affirm the universal behavior in the long channel limit. Next, effective mobility in ensembles of MOSFETs with a gate length down to 10 nm is investigated. It is found that the random-discrete nature of the Si-SiO/sub 2/ interface leads to a distribution of carrier mobility below the interface, which can deviate considerably from universal mobility curves when L/sub gate/<6/spl Lambda/, where /spl Lambda/ is the correlation length for the SiO/sub 2/ interface.  相似文献   
200.
The effects of frozen storage and initial baking time of par‐baked cake on baking loss, volume, moisture, colour and textural properties of cake obtained after thawing and rebaking were investigated. Cakes, par‐baked at 175 °C for 15, 20 and 25 min, were stored at ?18 °C for 3, 6 and 9 months. After storage, par‐baked cakes were thawed and rebaked at 175 °C for 10, 15 and 20 min. Baking loss, moisture content, L and +b colour values, firmness, gumminess and chewiness of the resulting full‐baked cakes were significantly affected by both par‐baking and frozen storage time, while specific volume, cohesiveness, springiness and resilience values were significantly affected by frozen storage time. The increase in the time of frozen storage of the par‐baked cake leads to a decrease in the quality of the rebaked cake, namely an increase of baking loss and cake crumb firmness, and a loss in the moisture content and specific volume. Moisture of cake crumb, L and +b colour values, firmness, gumminess and chewiness significantly increased as the par‐baking time increased. However, regarding baking loss, specific volume, moisture content and textural properties, 3‐month intermediate storage at ?18 °C and 20‐min initial baking time gave the best result among the cakes produced by using the two‐step baking procedure.  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