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   98篇
  免费   4篇
  国内免费   1篇
电工技术   1篇
化学工业   27篇
金属工艺   7篇
机械仪表   4篇
建筑科学   3篇
能源动力   6篇
轻工业   6篇
水利工程   1篇
无线电   7篇
一般工业技术   15篇
冶金工业   17篇
原子能技术   3篇
自动化技术   6篇
  2023年   2篇
  2022年   2篇
  2021年   5篇
  2020年   3篇
  2019年   1篇
  2018年   2篇
  2017年   3篇
  2016年   4篇
  2015年   1篇
  2014年   2篇
  2013年   2篇
  2012年   4篇
  2011年   3篇
  2010年   5篇
  2009年   12篇
  2008年   6篇
  2007年   6篇
  2006年   2篇
  2005年   5篇
  2004年   2篇
  2003年   3篇
  2002年   3篇
  2001年   1篇
  1998年   3篇
  1997年   5篇
  1996年   3篇
  1995年   1篇
  1994年   4篇
  1993年   1篇
  1992年   2篇
  1991年   1篇
  1989年   1篇
  1984年   2篇
  1983年   1篇
排序方式: 共有103条查询结果,搜索用时 15 毫秒
51.
High quality piezoelectric single crystals, such as Pb(Zn1/3 Nb2/3)O3-PbTiO3 (PZNT) and Pb(Mg 1/3Nb2/3)O3-PbTiO3 (PMNT), have been investigated, and, because their piezoelectric properties are greatly superior to those of Pb(Zr1-xTix)O3 (PZT) ceramics, they have been used for certain transducer applications since the late 1990s. The present situation for these relaxor-PT (lead titanate) single crystals is summarized. In this review, some possible high Tc > 200°C single crystals are also introduced. Single crystals of Pb(In1/2Nb1/2)O3-PbTiO3 (PINT) binary system and Pb(Mg1/3Nb2/3)O3 -Pb(Sc1/2Nb1/2)O3-PbTiO3 (PSMNT) tertiary system have been synthesized, and their electrical properties are reported. In addition, a novel guiding principle for discovering excellent piezoelectric materials, namely the presence of low molecular mass B-site ions that can enter the lead-perovskite Pb(B'B")O3 structure, is introduced  相似文献   
52.
The most common primary site of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is the gastrointestinal tract, particularly the stomach. The relationship of MALT lymphomas, however, with the more commonly occurring large B-cell gastric lymphoma has not been directly discussed except in the report of Chan et al. (1990), which lacked clinical information regarding the behavior of these tumors. To elucidate the relationship between high-grade large-cell lymphoma and MALT lymphoma, we studied in detail the histopathological and clinicopathologic features with the survival date of 77 Japanese cases of primary gastric lymphoma (PGL) of B-cell type. Based on degree of morphologically recognizable low- or high-grade components of the tumor, PGL was divided into four types: 18 cases of pure MALT lymphoma (type I); 13 cases of MALT lymphoma with small area of high-grade lymphoma (type II); 22 cases of high-grade lymphoma with small areas of MALT lymphoma (type III); and 24 cases pure high-grade lymphoma (type IV). Corresponding to the differences in the histologic pictures of each type, there were differences in the gross appearance, pathologic stage (including depth of invasion) and prognosis. These data suggests that both MALT and high-grade lymphomas of the stomach belong to the same cell lineage and constitute a pathological spectrum and that the histological grouping of PGL is clinico-pathologically useful.  相似文献   
53.
The menstrual and premenstrual experiences of black Zimbabwean women were examined. Twenty-five professional women and twenty-five domestic workers were interviewed using semistructured, open-ended interviews designed to explore their experiences. An analysis of consensual data indicated a number of predominant themes, including secrecy associated with menstruation, the negativity surrounding menarche, the breakdown of the traditional family network that passes on information about menstruation, and the acceptance of menstrual cycle experiences by the women. The main differences between the two groups concerned explanations of the functions and purpose of menstruation and the reporting of physical and affective symptoms. These differences are suggestive of the impact of educational level on experiences of menstruation.  相似文献   
54.
Accumulating evidence shows that the repertoire of major histocompatibility complex class I-restricted epitopes extends beyond conventional translation reading frames. Previously, we reported that scanthrough translation, where the initiating AUG of a primary open reading frame is bypassed, is most likely to account for the presentation of cryptic epitopes from alternative reading frames within the influenza A PR/8/34 nucleoprotein gene. Here, we confirm and extend these findings using an epitope cassette construct that features two well-defined CD8(+) T cell (TCD8+) epitopes in alternative reading frames, each preceded by a single start codon. Expression of one epitope depends on scanning of the ribosome over the first AUG with translation initiation occurring at the second AUG. We find that scanthrough translation has great potency in our system, with its impact being modulated, as predicted, by the base composition surrounding the first initiation codon, the number of start codons preceding the point of alternate reading frame initiation, and the efficiency with which the epitope itself is generated. Additionally, we investigated the efficiency of eukaryotic translation termination codons, to assess codon readthrough as a mechanism for cryptic epitope expression from 3' untranslated regions. In contrast with initiation codons, eukaryotic stop codons appear to be highly efficient at preventing expression of epitopes encoded in 3' untranslated regions, suggesting that 3' untranslated regions are not a common source of cryptic epitope substrate. We conclude that scanthrough is a powerful mechanism for the expression of epitopes encoded in upstream alternative open reading frames that may contribute significantly to TCD8+ responses and to tolerance induction.  相似文献   
55.
Acid-base disorders are frequently recognized in a wide variety of clinical settings such as severe systemic hospitalized patients. The principal object is to assessment of acid-base equilibrium and to obtain an appropriate guide to therapy. The approach is centered to a systemic analysis of blood gas evaluation. To establish this complex matter is followed. Is an acid-base disorder present? Is the disorder a simple or a mixed abnormality? What is the primary cause? These evaluations should be obtained by accurate history taking, physical examination, and routine laboratory tests. In addition, the supporting analysises such as anion gap (AG) calculation, urine AG assessment, urine chloride concentration and so on are also useful for correct diagnosis. In view of the complexty and difficult expression of acid-base disorders, it is desirable that clinicians must have full knowledges of systemic approach to the blood gas analysis and its evaluation.  相似文献   
56.
Location-Based Services (LBS), an emerging new business based on smartphone and mobile networks, are becoming more and more popular. Most of these LBSs, however, only offer non-seamless indoor/outdoor applications and simple applications without giving stakeholders the chance to play an active role. Our specific aim is to solve these issues. This paper presents concepts to solve these issues by expanding the Open Location Services Interface Standard (OpcnLS) to allow seamless indoor/outdoor positioning and to extend the content of the services to include information recommended by stakeholders.  相似文献   
57.
Strength is one of the most important properties of cover glass. In this study, fracture analysis is used to classify the breakage mode of cover glass into four typical modes. Moreover, the mechanism and evaluation method of each mode are investigated. Consequently, a chemical strengthening design with high compressive stress (CS) and low center tension (CT) is obtained. In addition, processing design is determined to be an important factor. Fining of edge processing and surface polishing after chemical strengthening are shown to enhance the edge and surface strength, respectively.  相似文献   
58.
Molluscicidal activity of the herebicides 2,4-D and Graminol, as well as both extracts and dry powder of the plant Azolla pinnata were evaluated against B. alexandrina snails. It was observed that 2,4-D proved to be the most toxic compound among he tested ones, showing LC90 of 52 ppm after 24 h of exposure. Ethanol extract of Azolla showed the highest molluscicidal activity against the tested snails compared with the other extracts and dry powder (LC90 = 3300 ppm). Ethanol extract at 6600 ppm after 3 h of exposure killed 100% and 19.4% of S. mansoni miracidia and cercariae, respectively. The molluscicidal activity of 2,4-D was not influenced by the presence of Azolla (900 plants/liter) for 7 days, while Graminol effect was significantly reduced. However, the infectivity of S. mansoni miracidia to B. alexandrina snails was not affected by Azolla existence.  相似文献   
59.
60.
The preparation of ion-track membranes of thermally stable poly(p-phenylene terephthalamide) (PPTA) was performed by ion beam irradiation followed by chemical etching with a sodium hypochlorite solution. Cylindrical pores were observed in the membrane irradiated with 197Au and 238U ions at an energy of 11.1 MeV/n. In contrast, funnel shape pores appeared in the membrane irradiated with 84Kr, 102Ru and 129Xe ion at energies of 6.2, 3.6 and 3.5 MeV/n, respectively. The 197Au and 238U ion irradiation was found to exhibit more than four times larger sensitivity to the track etching under the same etching conditions. Consequently, the pore shape can be controlled by the masses and energies of the irradiated ions, in close relation to the etching sensitivity of the track.  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