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   1116篇
  免费   72篇
  国内免费   2篇
电工技术   8篇
化学工业   327篇
金属工艺   9篇
机械仪表   19篇
建筑科学   41篇
矿业工程   8篇
能源动力   49篇
轻工业   166篇
水利工程   13篇
石油天然气   4篇
无线电   54篇
一般工业技术   185篇
冶金工业   73篇
原子能技术   5篇
自动化技术   229篇
  2023年   9篇
  2022年   30篇
  2021年   54篇
  2020年   26篇
  2019年   53篇
  2018年   38篇
  2017年   45篇
  2016年   50篇
  2015年   38篇
  2014年   44篇
  2013年   84篇
  2012年   56篇
  2011年   77篇
  2010年   71篇
  2009年   65篇
  2008年   50篇
  2007年   58篇
  2006年   36篇
  2005年   37篇
  2004年   32篇
  2003年   22篇
  2002年   24篇
  2001年   13篇
  2000年   13篇
  1999年   14篇
  1998年   27篇
  1997年   22篇
  1996年   14篇
  1995年   11篇
  1994年   9篇
  1993年   11篇
  1992年   3篇
  1991年   2篇
  1990年   2篇
  1989年   5篇
  1988年   3篇
  1987年   2篇
  1986年   3篇
  1985年   5篇
  1984年   4篇
  1983年   4篇
  1982年   8篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
  1976年   1篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
排序方式: 共有1190条查询结果,搜索用时 15 毫秒
1.
This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning® technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible membranes could be used in power actuators, sensors and portable, and wireless devices to mention some.  相似文献   
2.
3.
In the present work blends of polystyrene (PS) with sepiolites have been produced using a melt extrusion process. The dispersion degree of the sepiolites in the PS has been analyzed by dynamic shear rheology and X-ray micro-computed tomography. Sepiolites treated with quaternary ammonium salts (O-QASEP) are better dispersed in the PS matrix than natural sepiolites (N-SEP) or sepiolites organo-modified with silane groups (O-SGSEP). A percolated network is obtained when using 6.0 wt% of O-QASEP, 8.0 wt% of N-SEP and 10.0 wt% of O-SGSEP. It has been shown that multiple extrusion processes have a negative effect on the polymer architecture. They produce a reduction in the length of the polymeric chains, and they do not lead to a better dispersion of the particles in the polymer matrix. Foams have been produced using a gas dissolution foaming process, where a strong effect of the dispersion degree on the cellular structure of the different foams was found. The effects on the cellular structure obtained by using different types of sepiolites, different contents of sepiolites and different extrusion conditions have been analyzed. The foams produced with the formulations containing O-QASEP present the lowest cell size and the most homogeneous cellular structures.  相似文献   
4.
It is very common to find meta-analyses in which some of the studies compare 2 groups on continuous dependent variables and others compare groups on dichotomized variables. Integrating all of them in a meta-analysis requires an effect-size index in the same metric that can be applied to both types of outcomes. In this article, the performance in terms of bias and sampling variance of 7 different effect-size indices for estimating the population standardized mean difference from a 2 × 2 table is examined by Monte Carlo simulation, assuming normal and nonnormal distributions. The results show good performance for 2 indices, one based on the probit transformation and the other based on the logistic distribution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
5.
6.
In this work we extend the radix-4 CORDIC algorithm to the vectoring mode (the radix-4 CORDIC algorithm was proposed recently by the authors for the rotation mode). The extension to the vectoring mode is not straightforward, since the digit selection function is more complex in the vectoring case than in the rotation case; as in the rotation mode, the scale factor is not constant. Although the radix-4 CORDIC algorithm in vectoring mode has a similar recurrence as the radix-4 division algorithm, there are specific issues concerning the vectoring algorithm that demand dedicated study. We present the digit selection for nonredundant and redundant arithmetic (following two different approaches: arithmetic comparisons and table look-up), the computation and compensation of the scale factor, and the implementation of the algorithm (with both types of digit selection) in a word-serial architecture. When compared with conventional radix-2 (redundant and non-redundant) architectures, the radix-4 algorithms present a significant speed up for angle calculation. For the computation of the magnitude the speed up is very slight, due to the nonconstant scale factor in the radix-4 algorithm.  相似文献   
7.
8.
The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect - thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading.  相似文献   
9.
One of the prime reasons inhibiting the widespread use of discrete-event simulation in construction planning is the absence of appropriate visual communication tools. Visualizing modeled operations in 3D is arguably the best form of communicating the logic and the inner working of simulation models and can be of immense help in establishing the credibility of analyses. New software development technologies emerge at incredible rates that allow engineers and scientists to create novel, domain-specific applications. The authors capitalized on a computer graphics technology based on the concept of the scene graph to design and implement a general-purpose 3D visualization system that is simulation and CAD-software independent. This system, the Dynamic Construction Visualizer, enables realistic visualization of modeled construction operations and the resulting products and can be used in conjunction with a wide variety of simulation tools. This paper describes the scene graph architecture and the frame updating algorithms used in designing the Dynamic Construction Visualizer.  相似文献   
10.
Oil and triglyceride contents and fatty acid composition were determined for seeds in nine taxa belonging to the genusCoincya (Brassicaceae) on the Iberian Peninsula (Spain and Portugal). The oil content ranges from 11.1 to 24.6%, triglycerides from 68.7 to 88.5%. The major fatty acids were erucic (24.6–30.5%), linolenic (17.7–27.7%), linoleic (13.9–24.6%) and oleic acid (12.3–21.8%).  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