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   247124篇
  免费   3393篇
  国内免费   777篇
电工技术   4037篇
综合类   812篇
化学工业   36270篇
金属工艺   10857篇
机械仪表   7901篇
建筑科学   4852篇
矿业工程   2561篇
能源动力   5045篇
轻工业   14838篇
水利工程   3479篇
石油天然气   7831篇
武器工业   31篇
无线电   23293篇
一般工业技术   48525篇
冶金工业   54360篇
原子能技术   6818篇
自动化技术   19784篇
  2021年   2194篇
  2019年   2073篇
  2018年   4162篇
  2017年   4437篇
  2016年   5056篇
  2015年   3030篇
  2014年   4237篇
  2013年   9208篇
  2012年   7785篇
  2011年   9628篇
  2010年   6548篇
  2009年   7259篇
  2008年   7234篇
  2007年   7153篇
  2006年   6148篇
  2005年   8402篇
  2004年   7171篇
  2003年   6582篇
  2002年   5200篇
  2001年   5209篇
  2000年   4472篇
  1999年   4797篇
  1998年   15846篇
  1997年   10670篇
  1996年   7812篇
  1995年   5493篇
  1994年   4599篇
  1993年   4861篇
  1992年   3203篇
  1991年   3277篇
  1990年   3162篇
  1989年   3099篇
  1988年   3136篇
  1987年   2709篇
  1986年   2742篇
  1985年   2999篇
  1984年   2744篇
  1983年   2626篇
  1982年   2420篇
  1981年   2436篇
  1980年   2533篇
  1979年   2413篇
  1978年   2470篇
  1977年   3070篇
  1976年   4144篇
  1975年   2277篇
  1974年   2103篇
  1973年   2209篇
  1972年   1973篇
  1971年   1800篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
31.
Journal of Machinery Manufacture and Reliability - A device based on smart alloys has been designed for use in machine building items, in particular, in nuclear engineering, for preventing...  相似文献   
32.
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   
33.
Theoretical Foundations of Chemical Engineering - New research results, as well as those published earlier by the authors, on the synthesis of azo compounds based on nitroanilines obtained by the...  相似文献   
34.
Russian Journal of Non-Ferrous Metals - Rolling bearing rings comprise a large reserve for expanding powder metallurgy production. This reserve is being incompletely implemented. The hot forging of...  相似文献   
35.
36.
37.
38.
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape.  相似文献   
39.
40.
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019  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