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   554篇
  免费   34篇
电工技术   1篇
化学工业   197篇
金属工艺   11篇
机械仪表   12篇
建筑科学   31篇
能源动力   13篇
轻工业   99篇
水利工程   7篇
石油天然气   2篇
无线电   29篇
一般工业技术   91篇
冶金工业   32篇
原子能技术   2篇
自动化技术   61篇
  2024年   3篇
  2023年   5篇
  2022年   38篇
  2021年   57篇
  2020年   21篇
  2019年   23篇
  2018年   23篇
  2017年   27篇
  2016年   25篇
  2015年   10篇
  2014年   28篇
  2013年   46篇
  2012年   38篇
  2011年   43篇
  2010年   29篇
  2009年   26篇
  2008年   21篇
  2007年   22篇
  2006年   12篇
  2005年   7篇
  2004年   19篇
  2003年   7篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   3篇
  1998年   9篇
  1997年   5篇
  1996年   4篇
  1995年   1篇
  1994年   3篇
  1993年   4篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
  1976年   1篇
排序方式: 共有588条查询结果,搜索用时 624 毫秒
181.
An intermediate step in the construction of a polyhedron from a partial-view sketch is the derivation of a realizable wireframe sketch, i.e., a complete sketch which is guaranteed to be the projection of a polyhedron. This paper presents a robust realizability-test based on the classical “cross-section criterion” that was developed in a geometric “ruler-and-compass” framework.  相似文献   
182.
183.
The aim of the present research was to examine the relationship between Greek young people aged 12–18 and the Internet through their patterns of Internet use in the home. A particular objective of the study was the investigation of the possible effects of social stratification, gender and age on their domestic Internet use. A sample of 418 high school students selected from 17 schools in four Greek cities completed a structured self-reported questionnaire primarily concerned with Internet use (frequency, purpose and behaviour patterns) at home and the types of the parental supervision. The research was carried out during the period 2004–2005. The main findings of the study were the following: (a) Internet access remains at a very low level and is insufficiently used for school purposes, (b) younger students (aged 12–15 years) use it more frequently than older ones for information seeking concerning school work, (c) the Internet is an indicator of social and economic stratification since most young people with access to it come from family environments with a higher educational and socioeconomic background and live in urban and semi urban areas, (d) boys make up the majority of systematic users, mainly for entertainment purposes, (e) the Internet is a place and space safeguarding the “privacy” of young people with the majority of them preferring to surf alone, (f) parental supervision and monitoring seems to be absent largely from the relationship between youth and the Internet, and (g) in general, the frequency and type of Internet use are not significantly affected by students’ places of residence or the educational level and profession of their parents.  相似文献   
184.
Modeling software product lines shall imply modeling from different perspectives with different modeling artifacts such as use case diagrams, component diagrams, class diagrams, activity diagrams, sequence diagrams and others. In this paper, we elaborate on use cases for modeling product lines and we explore them from the perspective of variability by working with the unified modeling language (UML) ?extend? relationship. We also explore them from the perspective of detail by (functionally) refining use cases with ?extend? relationships between them. This paper’s intent is to provide for comprehension about use case modeling with functional refinement when variability is present.  相似文献   
185.
We herein investigated the detection frequency and clinical relevance of circulating tumor cells (CTCs) in chemotherapy-naïve stage IIIB/IV non-small cell lung cancer (NSCLC), by using the CellSearch and real-time CEACAM5mRNA assays. Blood samples from 43 patients were obtained at different time points during first-line chemotherapy. CellSearch revealed the detection of ≥1 CTCs in 41.9%, 40.9%, and 16.7% of patients at baseline, post-1st, and post-2nd treatment cycle, respectively, and of ≥5 CTCs in 11.6%, 9.1%, and 5.6%, respectively. CEACAM5mRNA+ CTCs were detected in 29.3% and 16% of patients pre- and post-treatment, respectively. The positivity concordance between the two assays was 2.2%. CTC-detection by CellSearch (≥5 CTCs: p = 0.004), CEACAM5mRNA (p = 0.010), or by any assay (p = 0.000) was associated with disease progression. Reduced survival was demonstrated for patients harboring ≥5 CTCs (progression-free survival; PFS: p = 0.000; overall survival; OS: p = 0.009), CEACAM5mRNA+ CTCs (PFS: p = 0.043; OS: p = 0.039), and CTCs by any assay (PFS: p = 0.005; OS: p = 0.006, respectively). CTC-detection by any assay independently predicted for increased risk of relapse (hazard ratio; HR: 3.496; p = 0.001) and death (HR: 2.866; p = 0.008). CellSearch-positivity either pre-, post-1st, or post-2nd cycle, was predictive for shorter PFS (p = 0.036) compared to negativity in all time points. Persistent CEACAM5mRNA-positivity pre- and post-treatment was associated with reduced PFS (p = 0.036) and OS (p = 0.026). In conclusion, CTC detection and monitoring using the CellSearch and CEACAM5mRNA assays provides valuable and complementary clinical information for chemo-naïve advanced or metastatic NSCLC.  相似文献   
186.
UV filters are potentially harmful to marine organisms. Given their worldwide dissemination and the scarcity of studies on marine fish, we evaluated the toxicity of an organic (oxybenzone) and an inorganic (titanium dioxide nanoparticles) UV filter, individually and in a binary mixture, in the turbot (Scophthalmus maximus). Fish were intraperitoneally injected and a multi-level assessment was carried out 3 and 7 days later. Oxybenzone and titanium dioxide nanoparticles induced mild effects on turbot, both isolated and in mixture. Neither oxidative stress (intestine, liver and kidney) nor neurotoxicity (brain) was found. However, liver metabolic function was altered after 7 days, suggesting the impairment of the aerobic metabolism. An increased motility rate in oxybenzone treatment was the only behavioural alteration (day 7). The intestine and liver were preferentially targeted, while kidney and brain were unaffected. Both infra- and supra-additive interactions were perceived, with a toxicodynamic nature, resulting either in favourable or unfavourable toxicological outcomes, which were markedly dependent on the organ, parameter and post-injection time. The combined exposure to the UV filters did not show a consistent increment in toxicity in comparison with the isolated exposures, which is an ecologically relevant finding providing key information towards the formulation of environmentally safe sunscreen products.  相似文献   
187.
188.
Pheochromocytoma (Pheo) is a tumor derived from chromaffin cells. It can be studied using 18F-dihydroxyphenylalanine (DOPA)—positron emission tomography (PET) due to its overexpression of L-type amino acid transporters (LAT1 and LAT2). The oncogenic pathways involved are still poorly understood. This study examined the relationship between 18F-DOPA-PET uptake and LAT1 expression, and we explored the role of miR-375 and putative target genes. A consecutive series of 58 Pheo patients were retrospectively analyzed, performing 18F-DOPA-PET in 32/58 patients. Real-time quantitative PCR was used to assess the expression of LAT1, LAT2, phenylethanolamine N-methyltransferase (PNMT), miR-375, and the major components of the Hippo and Wingless/Integrated pathways. Principal germline mutations associated with hereditary Pheo were also studied. Pheo tissues had significantly higher LAT1, LAT2, and PNMT mRNA levels than normal adrenal tissues. MiR-375 was strongly overexpressed. Yes-associated protein 1 and tankyrase 1 were upregulated, while beta-catenin, axin2, monocarboxylate transporter 8, and Frizzled 8 were downregulated. A positive relationship was found between 18F-DOPA-PET SUV mean and LAT1 gene expression and for 24 h-urinary norepinephrine and LAT1. This is the first experimental evidence of 18F-DOPA uptake correlating with LAT1 overexpression. We also demonstrated miR-375 overexpression and downregulated (Wnt) signaling and identified the Hippo pathway as a new potentially oncogenic feature of Pheo.  相似文献   
189.
190.
The plasma powder transferred arc welding process which uses feed stock in a powder form has similarities with plasma wire transferred arc welding. This paper describes a comparative study of the two processes using a cobalt-based alloy commercially known as stellite 6. This Co-based alloy is recognized for its superior cavitation erosion resistance. The aim of this paper is to investigate the potential of plasma transferred arc coatings for the protection and refurbishment of hydraulic turbine blades. Coatings were evaluated for the influence of plasma gas flow rate on coating dilution, geometry, hardness and microstructure. Coatings processed with the atomized stellite 6 powder feedstock showed a superior surface quality, lower dilution, better wettability and wider tracks. This study provided new information about the refurbishing of worn hydraulic turbine blades, leading to a longer service working life.  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