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   267330篇
  免费   3957篇
  国内免费   539篇
电工技术   4659篇
综合类   486篇
化学工业   44201篇
金属工艺   9961篇
机械仪表   7934篇
建筑科学   6403篇
矿业工程   1480篇
能源动力   6027篇
轻工业   28295篇
水利工程   2705篇
石油天然气   5234篇
武器工业   38篇
无线电   27064篇
一般工业技术   48459篇
冶金工业   51031篇
原子能技术   6153篇
自动化技术   21696篇
  2021年   2853篇
  2020年   1981篇
  2019年   2592篇
  2018年   4152篇
  2017年   4161篇
  2016年   4367篇
  2015年   2776篇
  2014年   4711篇
  2013年   11563篇
  2012年   7297篇
  2011年   9788篇
  2010年   7614篇
  2009年   8356篇
  2008年   8568篇
  2007年   8594篇
  2006年   7597篇
  2005年   6809篇
  2004年   6664篇
  2003年   6345篇
  2002年   6412篇
  2001年   6190篇
  2000年   5857篇
  1999年   5756篇
  1998年   14331篇
  1997年   10053篇
  1996年   7656篇
  1995年   5864篇
  1994年   5146篇
  1993年   5098篇
  1992年   3866篇
  1991年   3645篇
  1990年   3800篇
  1989年   3653篇
  1988年   3503篇
  1987年   3035篇
  1986年   3089篇
  1985年   3542篇
  1984年   3351篇
  1983年   2984篇
  1982年   2863篇
  1981年   2942篇
  1980年   2822篇
  1979年   2704篇
  1978年   2769篇
  1977年   3076篇
  1976年   4017篇
  1975年   2449篇
  1974年   2287篇
  1973年   2429篇
  1972年   2005篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
2.
Alcohol-free beer with isotonic properties is getting more popular and its production can be carried out by different production strategies; however, interrupted fermentation is still a challenge. Therefore, the objective of this study was to develop a low-alcohol isotonic beer (<0.5% v/v) by interrupted fermentation. Moreover, the major objective is to compare the developed product to commercial beverages (sports drinks, ‘Pilsen' regular beer, alcohol-free beers and low-alcohol isotonic beer). The beverages were evaluated based on pH, alcohol content (% v/v), total titratable acidity (mEq L−1), osmolality (mOsmol kg−1), bitterness International Bitterness Units, colour European Brewery Convention, total phenolic compounds (mg L−1 gallic acid), reducing and total sugars (%) and Na and K contents (mg L−1). The developed low-alcohol isotonic beer presented characteristics similar to sports drinks, with the advantage of being richer in phenolic compounds and suitable osmolality. Despite salts were added in its formulation, the grades attributed to all beers employed in the sensory evaluation, as well as the purchase intention did not present significant differences.  相似文献   
3.
4.
5.
6.
A layer-by-layer analysis of the structures, the phase compositions, and the defect substructures of differentially hardened rails has been carried by optical and transmission electron microscopy. It is found that the material volume of the rail head fillet is cooled faster than the volume located along the central axis.  相似文献   
7.
8.
9.
Here we report some recent biophysical issues on the preparation of solute-filled lipid vesicles and their relevance to the construction of “synthetic cells.” First, we introduce the “semi-synthetic minimal cells” as the liposome-based cell-like systems, which contain a minimal number of biomolecules required to display simple and complex biological functions. Next, we focus on recent aspects related to the construction of synthetic cells. Emphasis is given to the interplay between the methods of synthetic cell preparation and the physics of solute encapsulation. We briefly introduce the notion of structural and compositional “diversity” in synthetic cell populations.  相似文献   
10.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  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