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   102894篇
  免费   1434篇
  国内免费   1226篇
电工技术   1927篇
综合类   138篇
化学工业   10508篇
金属工艺   5458篇
机械仪表   3191篇
建筑科学   2032篇
矿业工程   159篇
能源动力   2960篇
轻工业   6065篇
水利工程   704篇
石油天然气   668篇
武器工业   15篇
无线电   15948篇
一般工业技术   21774篇
冶金工业   25283篇
原子能技术   1382篇
自动化技术   7342篇
  2022年   455篇
  2021年   698篇
  2020年   522篇
  2019年   677篇
  2018年   1130篇
  2017年   1093篇
  2016年   1173篇
  2015年   925篇
  2014年   1489篇
  2013年   4671篇
  2012年   2571篇
  2011年   3840篇
  2010年   3101篇
  2009年   3721篇
  2008年   3896篇
  2007年   4080篇
  2006年   3694篇
  2005年   3332篇
  2004年   3179篇
  2003年   3028篇
  2002年   2672篇
  2001年   2971篇
  2000年   2720篇
  1999年   3077篇
  1998年   9450篇
  1997年   6160篇
  1996年   4764篇
  1995年   3165篇
  1994年   2792篇
  1993年   2724篇
  1992年   1629篇
  1991年   1596篇
  1990年   1520篇
  1989年   1324篇
  1988年   1171篇
  1987年   861篇
  1986年   888篇
  1985年   918篇
  1984年   805篇
  1983年   699篇
  1982年   699篇
  1981年   681篇
  1980年   567篇
  1979年   478篇
  1978年   414篇
  1977年   534篇
  1976年   959篇
  1975年   300篇
  1974年   277篇
  1973年   256篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
The Frizzled genes encode receptors for WNTs, secreted glycoproteins implicated in development as well as in carcinogenesis. In this paper, we report molecular cloning of Hfz6, the human homologue of Mfz6. Nucleotide sequence analysis showed that the Hfz6 gene encodes the 706 amino-acid protein with seven transmembrane domains, a cystein-rich domain in the N-terminal extracellular region, two N-linked glycosylation sites, and two cystein residues in the second and third extracellular loops. Hfz6 mRNA 4.4-kb in size was detected in various normal adult and fetal tissues, and a larger amount of Hfz6 mRNA was detected in both fetal lung and fetal kidney. The Hfz6 gene has been mapped to human chromosome 8q22.3-q23.1. In conclusion, we have cloned Hfz6, which encodes a seven-transmembrane receptor with the cystein-rich domain in the N-terminal extracellular region, but without the Ser/Thr-X-Val motif in the C-terminus.  相似文献   
93.
Vaccination with peptides that induce a specific immune response is a potential prophylactic or therapeutic strategy against viral infections and tumors. Because of the extensive polymorphism of the HLA loci, synthetic peptide vaccines must consist of a cocktail of peptides that bind specifically to different HLA molecules. Such cocktails should be optimized for the target population as each population has its specific HLA gene frequencies. To achieve maximum population coverage with a minimum number of peptides, information is needed on the ranking of the most frequent HLA phenotypes. We introduce the minimal phenotype panel, which is the smallest combination of HLA antigens selected so that the proportion of individuals in a population that express at least one of the antigens in the panel exceeds a desired minimum value. We developed a method for assembling minimal phenotype panels based on known HLA class I gene frequencies. We give an example based on a set of 2446 well-defined HLA-typed, random, healthy, unrelated, Dutch Caucasoid individuals. In addition, we discuss the possibility of assembling minimal phenotype panels based on two-locus haplotypes, which enables the assembly of phenotype panels from the antigens of both loci.  相似文献   
94.
95.
96.
97.
98.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication  相似文献   
99.
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead.  相似文献   
100.
PURPOSE: To report the disappearance of traumatic macular hole in three eyes of three patients. METHODS: Clinical data of the patients were reviewed. RESULTS: The three patients were relatively young, ranging in age from 12 to 18 years old. In one eye of each patient, a small traumatic macular hole was observed at the first visit. Visual acuities ranged from 20/100 to 20/40. The macular holes resolved spontaneously 3 to 4 months after the trauma, and final visual acuity improved to 20/20 in all patients. CONCLUSION: Small traumatic macular holes in young patients can resolve spontaneously, and this can be associated with good visual recovery.  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