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   3681篇
  免费   138篇
  国内免费   27篇
电工技术   44篇
综合类   13篇
化学工业   435篇
金属工艺   52篇
机械仪表   61篇
建筑科学   80篇
矿业工程   4篇
能源动力   107篇
轻工业   253篇
水利工程   33篇
石油天然气   59篇
武器工业   2篇
无线电   188篇
一般工业技术   310篇
冶金工业   1914篇
原子能技术   5篇
自动化技术   286篇
  2023年   28篇
  2022年   66篇
  2021年   120篇
  2020年   116篇
  2019年   117篇
  2018年   137篇
  2017年   104篇
  2016年   128篇
  2015年   73篇
  2014年   101篇
  2013年   174篇
  2012年   132篇
  2011年   104篇
  2010年   86篇
  2009年   72篇
  2008年   44篇
  2007年   47篇
  2006年   37篇
  2005年   33篇
  2004年   22篇
  2003年   12篇
  2002年   14篇
  2001年   10篇
  2000年   14篇
  1999年   66篇
  1998年   650篇
  1997年   363篇
  1996年   198篇
  1995年   145篇
  1994年   107篇
  1993年   117篇
  1992年   18篇
  1991年   37篇
  1990年   32篇
  1989年   42篇
  1988年   35篇
  1987年   31篇
  1986年   26篇
  1985年   27篇
  1984年   2篇
  1983年   5篇
  1982年   12篇
  1981年   7篇
  1980年   18篇
  1978年   6篇
  1977年   23篇
  1976年   76篇
  1975年   2篇
  1973年   5篇
  1972年   2篇
排序方式: 共有3846条查询结果,搜索用时 15 毫秒
1.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
2.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  相似文献   
3.
Wireless Personal Communications - Current mobile communications technology relies heavily on efficient design of antennas, where the operational characteristics of the wireless communication...  相似文献   
4.
5.
Clean Technologies and Environmental Policy - The continuous growth of transport sector and the increase in carbon emissions from transportation attract the attention of policy makers in...  相似文献   
6.
OBJECTIVE: To study the effects of an aldose reductase inhibitor (ARI-509, Wyeth-Ayerst, Princeton, NJ) and aminoguanidine (AMG), agents that have been reported to prevent or delay diabetic retinopathy, on retinal vascular abnormalities and the immunocytochemical expression in the retina of vascular endothelial growth factor (VEGF) in rats maintained for up to 2 years on a 50% galactose diet. METHODS: Albino rats were placed on a control diet, a diet containing 50% galactose, or the 50% galactose diet containing either ARI-509 or AMG. Treatment with ARI-509 or AMG was initiated at the beginning of the experiment or after 12 months of galactose feeding. After 22 to 24 months, the rats were killed and the retinal vasculature from half of one eye was isolated by trypsin-elastase digestion for semiquantitative evaluation of retinal vascular lesions. The other half of the retina was prepared for immunocytochemistry and stained for the presence of VEGF, factor VIII, vimentin, and glial fibrillary acidic protein. Red blood cells, sciatic nerves, and a portion of the retina from the second eye were assayed for glucose, galactose, fructose, sorbitol, galactitol, and myo-inositol. Red blood cells were also assayed for galactosylated hemoglobin. RESULTS: Galactose-fed animals developed a vascular retinopathy characterized by severe cellular loss in the retinal capillaries and intensification of periodic acid-Schiff staining of the vascular basement membranes. Some animals also displayed dilation and hypercellularity of vessels in the posterior retina. These changes were substantially reduced in animals receiving ARI-509 from the beginning of the galactose diet, but were unaffected in all of the other treatment groups. None of the rats receiving ARI-509 or AMG treatment, whether initiated from the onset or after 12 months of galactosemia, demonstrated VEGF immunoreactivity. With the exception of the animals receiving ARI-509 from the beginning of the experiment, all of the galactose-fed animals developed dense cataracts within 6 weeks of the beginning of the galactose diet. Galactitol levels in animals receiving ARI-509 were 86% to 93% lower in red blood cells, retina, and sciatic nerve than those in the other galactose-fed groups. CONCLUSIONS: Although ARI-509 and AMG have different abilities to delay or prevent the diabetic-like retinopathy in galactosemic rats, even when substantial retinal microvascular acellularity occurs, both drugs prevent the immunocytochemical expression of VEGF. These results suggest that factors other than hypoxia may be responsible for VEGF expression in the retina, and that aldose reductase inhibitors and AMG have potential roles in preventing such expression and, thus, perhaps preventing retinal neovascularization.  相似文献   
7.
Lead content of rice collected from various areas in the world   总被引:1,自引:0,他引:1  
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world.  相似文献   
8.
9.
Pre-transplant nephrectomy was done in a 25-year-old man for calculous pyelonephritis using a retroperitoneal laparoscopic approach with a newly devised ligature applicator-dissector- kidney retractor.  相似文献   
10.
PURPOSE: To select ideal radiologic projections for mapping and ablation of tachycardias of right ventricular outflow tract (RVOT). METHODS: Ten hearts from human corpses were studied utilizing radiopaque material to identify the pulmonary valve and three distinct sites on this valve: septal anterior (A), septal posterior (P) and free-wall (L). Next, the hearts were filmed in the frontal plane and in oblique projections with 15 degrees increments to the right and to the left. The projections in which the sites were lateralized on the valve, eased radiologic interpretation and were considered ideal for mapping and ablation. Depending on the proximity of the sites to the lateral extremes of the pulmonary valve, the projections were considered ideal ( ), intermediary (++) and inadequate (+). RESULTS: Projections [table: see text] CONCLUSION: The A site of RVOT was best indicated in the 60 and 45 degrees left anterior oblique projections; the 0 degree postero anterior projection was best for mapping the P site; the L region was best explored in the 60 degrees right anterior oblique projection.  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