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   1577篇
  免费   124篇
  国内免费   5篇
电工技术   35篇
化学工业   376篇
金属工艺   18篇
机械仪表   20篇
建筑科学   50篇
矿业工程   1篇
能源动力   62篇
轻工业   278篇
水利工程   3篇
石油天然气   8篇
无线电   96篇
一般工业技术   222篇
冶金工业   286篇
原子能技术   5篇
自动化技术   246篇
  2023年   10篇
  2022年   25篇
  2021年   51篇
  2020年   42篇
  2019年   38篇
  2018年   49篇
  2017年   49篇
  2016年   39篇
  2015年   53篇
  2014年   51篇
  2013年   93篇
  2012年   70篇
  2011年   97篇
  2010年   79篇
  2009年   78篇
  2008年   87篇
  2007年   74篇
  2006年   62篇
  2005年   38篇
  2004年   41篇
  2003年   35篇
  2002年   38篇
  2001年   40篇
  2000年   28篇
  1999年   29篇
  1998年   103篇
  1997年   67篇
  1996年   52篇
  1995年   28篇
  1994年   25篇
  1993年   27篇
  1992年   3篇
  1991年   12篇
  1990年   4篇
  1989年   4篇
  1988年   4篇
  1987年   6篇
  1986年   5篇
  1985年   9篇
  1984年   10篇
  1983年   4篇
  1982年   6篇
  1981年   5篇
  1980年   4篇
  1978年   3篇
  1977年   3篇
  1976年   13篇
  1975年   3篇
  1973年   2篇
  1972年   2篇
排序方式: 共有1706条查询结果,搜索用时 15 毫秒
1.
2.
Senescent cells accumulate in the adipose tissue (AT) of individuals with obesity and secrete multiple factors that constitute the senescence-associated secretory phenotype (SASP). This paper aimed at the identification of B cells with a SASP phenotype in the AT, as compared to the peripheral blood, of individuals with obesity. Our results show increased expression of SASP markers in AT versus blood B cells, a phenotype associated with a hyper-metabolic profile necessary to support the increased immune activation of AT-derived B cells as compared to blood-derived B cells. This hyper-metabolic profile is needed for the secretion of the pro-inflammatory mediators (cytokines, chemokines, micro-RNAs) that fuel local and systemic inflammation.  相似文献   
3.
4.
INTRODUCTION: Heterozygous beta-thalassemia manifests hematologically with microcytosis, reduced red blood cell hemoglobin concentration and high hemoglobin A2 levels. Almost all molecular alterations are due to point mutations. We attempt to determinate the frequency of that mutations in the Oriental Andalusia Area, and its relationship with the hematological phenotype. PATIENTS AND METHODS: We have studied 45 heterozygous patients. DNA samples were amplified by PCR, using the printers CD7 and HI1. A 16 Kb fragment corresponding to beta globin gene was obtained and analyzed by Dot Blot assay and hybridized with allelic specific oligonucleotide (ASO) probes to detect the 6 more frequent mutations found in the South of Spain. RESULTS: Codon 39 nonsense mutation (31.1%) was the most frequent finding followed by IVS-1 NT 110 (26.7%). The relationship between hematological parameters and molecular mutations concluded that IVS-I NT 6 mutation developed a minimal anemia. DISCUSSION: From the practical point of view, this study indicates that we were able to detect more than 90% of heterozygous beta-tal. with 5 out of 6 ASO probes used in this work. Thus, our data also provides a further implication in prenatal diagnosis.  相似文献   
5.
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of 4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately 8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure.  相似文献   
6.
7.
Development of new burner technology is common practice nowadays. Standardized test codes are available to conduct tests to determine operating characteristics and thermal performance of different parts of steam generating units. This paper describes the results of testing performed to evaluate thermal efficiency of a 74.5?kW fire-tube steam generator fired with a new premixed flame burner in comparison to a typical standard-retrofit diffusion flame burner system. Two premixed flame burners sized at 7.6 and 10.1?cm were tested. Testing was performed in accordance with the ASME PTC 4.1 Power Test Code. The evaluation was conducted in the range of small- to mid-sized, natural gas-fired applications, from 1.06?to?2.64×106?kJ/h. The environmental nitrogen oxide (NOx) emissions performance was also compared for both burner technologies. The results of this evaluation indicate that firing the test boiler with the 7.6?cm new burner slightly improves unit thermal efficiency by 4.0–3.3% for a unit load ranging from approximately 1.06?to?1.79×106?kJ/h, respectively. Operation with the 10.1?cm new burner improves the thermal efficiency by approximately 1.6% at 2.32×106?kJ/h. The uncertainty in the measurements used in the efficiency calculations should account for approximately ±1.5% uncertainty in the reported gross efficiency. Reductions in NOx emissions of the order of 10% resulted from operation with the new premixed flame burners.  相似文献   
8.
9.
Lithiasis may develop in the prostate loge following prostate surgery. Calculus formation in the prostate can be ascribed basically to foreign bodies, residual adenomatous spheroids and clots or fragments of sphacelous mucosa in the presence of a stenotic area after surgery and/or infection. The diagnosis is based on the physical examination and particularly on the radiological findings. Treatment is by open surgery or endoscopic or extracorporeal lithotripsy.  相似文献   
10.
The authors provide a convergence analysis for the Kohonen learning algorithm (KLA) with respect to vector quantizer (VQ) optimality criteria and introduce a stochastic relaxation technique which produces the global minimum but is computationally expensive. By incorporating the principles of the stochastic approach into the KLA, a deterministic VQ design algorithm, the soft competition scheme (SCS), is introduced. Experimental results are presented where the SCS consistently provided better codebooks than the generalized Lloyd algorithm (GLA), even when the same computation time was used for both algorithms. The SCS may therefore prove to be a valuable alternative to the GLA for VQ design  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