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   662篇
  免费   26篇
电工技术   10篇
综合类   1篇
化学工业   125篇
金属工艺   18篇
机械仪表   18篇
建筑科学   32篇
矿业工程   6篇
能源动力   19篇
轻工业   47篇
水利工程   2篇
无线电   77篇
一般工业技术   106篇
冶金工业   85篇
原子能技术   12篇
自动化技术   130篇
  2023年   9篇
  2022年   8篇
  2021年   26篇
  2020年   14篇
  2019年   27篇
  2018年   20篇
  2017年   14篇
  2016年   21篇
  2015年   23篇
  2014年   22篇
  2013年   31篇
  2012年   28篇
  2011年   53篇
  2010年   40篇
  2009年   33篇
  2008年   34篇
  2007年   17篇
  2006年   20篇
  2005年   23篇
  2004年   14篇
  2003年   17篇
  2002年   10篇
  2001年   6篇
  2000年   9篇
  1999年   10篇
  1998年   24篇
  1997年   15篇
  1996年   13篇
  1995年   8篇
  1994年   8篇
  1993年   7篇
  1992年   3篇
  1991年   9篇
  1990年   6篇
  1988年   3篇
  1986年   2篇
  1985年   8篇
  1984年   3篇
  1982年   3篇
  1980年   5篇
  1977年   3篇
  1976年   6篇
  1975年   2篇
  1973年   3篇
  1971年   2篇
  1970年   2篇
  1968年   2篇
  1967年   2篇
  1965年   2篇
  1963年   4篇
排序方式: 共有688条查询结果,搜索用时 15 毫秒
101.
Intercultural student exchange can positively impact education, research, and society. Research-by-design has been put forward in design education as an approach to explicitly address the integration of education and research. The problem is that design schools develop their own interpretation of this approach, which brings difficulty in virtually comparing and learning from the generated design proposals. This case is evident in intercultural parallel design studios that deal with diverging socio-cultural and institutional traditions. In addressing this problem and maximizing the benefits of intercultural exchange, this study proposes to adopt a meta perspective and use the design as co-evolution model as a framework for analyzing and comparing design data generated by different research-by-design approaches. The study applies this meta perspective on an intercultural architectural design studio jointly organized by Ton Duc Thang University (Vietnam) and Hasselt University (Belgium).  相似文献   
102.
In a sequence of temperature-dependent solid-state reactions in the system CaO–Al2O3–MgO the formation of the ternary phase Ca3Al4MgO10 or C3A2M has been studied. Whereas the compound could not be prepared at 1200°C, a yield of 85 wt.-% of Ca3Al4MgO10 was obtained at 1320°C (incongruent melting point: 1330°C). Powder diffraction data compare well with results of previous investigations from the 1960s. Single crystals of Ca3Al4MgO10 could be retrieved from the sinter-pellets. Basic crystallographic data are as follows: orthorhombic symmetry, space group Pbcm, a = 5.14073(8), b = 16.7576(2), c = 10.70977(16) Å, V = 922.61(2) Å3, Z = 4. Using synchrotron diffraction data it was possible to solve the crystal structure. Least-squares refinements resulted in a residual of R(|F|) = 0.021 for 1000 independent observed reflections with I > 2σ(I) and 97 parameters. The structure contains [TO4]-tetrahedra (T=Al,Mg) forming a three-dimensional (3-D) framework whose topological characteristics have been determined. Al-Mg distributions on the different T-sites have been studied. The calcium cations are located in voids of the network. More than 50 years after its first observation our investigation clarifies the crystal structure of a compound belonging to a system that is of relevance for several fields of materials science.  相似文献   
103.
With the recent ban of pentabromodiphenyl ether (technical PentaBDE) and octabromodiphenyl ether (technical OctaBDE) mixtures in the European Union (EU) and in parts of the United States, decabromodiphenyl ether (technical DecaBDE) remains as the only polybrominated diphenyl ether (PBDE) based flame retardant available, today. The EU risk assessment report for DecaBDE identified a high level of uncertainty associated with the suitability of the current risk assessment approach for secondary poisoning by debromination of DecaBDE to toxic lower brominated diphenylethers. Addressing this still open question, we investigated concentrations and temporal trends of DecaBDE, NonaBDE, and OctaBDE congeners in the sediments of Greifensee, a small lake located in an urban area close to Zürich, Switzerland. PBDE appeared first in sediment layers corresponding to the mid 1970s. While total Tri-HeptaBDE (BDE-28, -47, -99, -100, -153, -154 and -183) concentrations leveled off in the mid 1990s to about 1.6 ng/g dw (dry weight), DecaBDE levels increased steadily to 7.4 ng/g dw in 2001 with a doubling time of 9 years. Hexabromocyclododecanes (HBCD) appeared in Greifensee sediments in the mid 1980s. They are an important class of flame retardants that are being used in increasing amounts, today. As was observed for DecaBDE, HBCD concentrations were continuously increasing to reach 2.5 ng/g dw in 2001. Next to DecaBDE, all 3 NonaBDE congeners (BDE-208, BDE-207, and BDE-206) and at least 7 out of the 12 possible OctaBDE congeners (BDE-202, BDE-201, BDE-197/204, BDE-198/203, BDE-196/200, BDE-205, and BDE-194) were detected in the sediments of Greifensee. Highest concentrations were found in the surface sediments with 7.2, 0.26, 0.14, and 1.6 ng/g dw for Deca-, Nona-, Octa-, and the sum of Tri-HeptaBDE, respectively. While DecaBDE and NonaBDE were found to increase rapidly, the increase of OctaBDE was slower. Congener patterns of Octa- and NonaBDE present in sediments of Greifensee did not change with time. Consequently, there was no evidence for sediment mediated long-term transformation of PBDE within the observed time span of almost 30 years. Despite the high persistence of DecaBDE, environmental debromination occurs, as shown by the detection of a shift in congener patterns of Octa- and NonaBDE in sediments, compared to the respective congener patterns in technical PBDE products. The OctaBDE congener BDE-202 was detected in sediments, representing a transformation product that is not reported in any of the technical PBDE products. Comparison of OctaBDE congener patterns in sediments with OctaBDE congener patterns from known sources reveals that (i) they were distinctively different from the congener patterns in technical PBDE products and (ii) that they were similar to the OctaBDE patterns in house dust and photodegradation products of DecaBDE, suggesting contributions from these sources.  相似文献   
104.
Im Folgenden wird über die Chronologie der Ereignisse im Rahmen des EHEC O104:H4 Ausbruchsgeschehen aus Sicht der Lebensmittelüberwachung in Schleswig-Holstein bis zur Gründung der nationalen Task Force EHEC berichtet. Am Beispiel des Kreises Schleswig-Flensburg wird die Zusammenarbeit und der Informationsaustausch zwischen Gesundheitsbeh?rde und Lebensmittelüberwachung dargestellt. Die erste Information über einen Anstieg an Erkrankungen mit blutigem Durchfall und HUS-Symptomatik in den Kreisen anliegend an und aus Hamburg erhielt das Ministerium für Landwirtschaft, Umwelt und l?ndliche R?ume des Landes Schleswig-Holstein am 19. Mai 2011. Der Fachdienst Veterin?rmedizin und Verbraucherschutz des Kreises Schleswig-Flensburg wurde ebenfalls am 19. Mai 2011 über eine solche H?ufung im Kreis Schleswig-Flensburg in Kenntnis gesetzt. Daraufhin wurden auf Landes- und Kreisebene Ma?nahmen eingeleitet, um zusammen mit den Gesundheitsbeh?rden diesen lebensmittelassoziierten Ausbruch aufzukl?ren. Am 01. Juni 2011 fand erstmalig in Schleswig-Holstein eine Telefonkonferenz zwischen den betroffenen Ministerien und allen Lebensmittelüberwachungs- und Gesundheitsbeh?rden der Kreise und kreisfreien St?dte statt, um das weitere Vorgehen gemeinsam zu koordinieren. Am 03. Juni 2011 wurde in Berlin am Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL) die nationale Task Force EHEC gegründet. Zwei Wochen nachdem die Gesundheitsbeh?rden von geh?uften und l?nderübergreifenden Erkrankungsf?llen Kenntnis hatten, geht damit die Koordinierung der Aufkl?rung von den Gesundheitsbeh?rden auf das BVL über. Am 07. Juni 2011 wurde durch das MLUR ein Mitarbeiter des Kreises Schleswig-Flensburg als Vertreter für Schleswig-Holstein in die Task-Force EHEC nach Berlin entsandt. Als Ergebnis ist aus diesem Erkrankungsgeschehen auch die Lehre zu ziehen, dass vermehrt pflanzliche Lebensmittel zu den „gef?hrlichen Lebensmitteln“ geh?ren. Diese müssen in Zukunft viel st?rker in den Fokus genommen werden.  相似文献   
105.
Reducing micropollutant pollution of water bodies is an important objective of water management and an integral part of environmental policy. Ceramic nanofiltration membranes were developed as multichannel membranes of increased membrane area and rotating disk filters. The membranes developed show retention of over 80 % for PEG 400. The membranes are currently being tested for the separation of micropollutants from wastewater contaminated with pharmaceuticals. With the help of a downstream oxidative process, the trace substances remaining in the permeate are degraded.  相似文献   
106.
This paper describes the development and fabrication of pastes suitable for screen printing process using Ti3SiC2 as the ceramic filler and ethyl cellulose as the binder. With the aim of obtaining high quality screen printed films, the influence of different amounts of Ti3SiC2 filler (20–40?vol%) and binder (0–5?vol%) on the rheological properties of the pastes was investigated. Samples with higher viscosity, such as pastes containing 30?vol% and 40?vol% Ti3SiC2 filler, regardless of the amount of ethyl cellulose, showed a higher printing quality compared to the samples with other compositions. The different paste compositions were screen printed onto paper-derived Al2O3 substrates containing 28.6 ± 4.8% open porosity and sintered for 1?h under an argon atmosphere at 1600?°C. X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) analysis showed that the sintered films contained TiC as a primary phase and Ti3SiC2 as a secondary phase. The partial decomposition of Ti3SiC2 after sintering can be attributed to residual carbon from the organic additives, which decreases the thermal stability of this material.  相似文献   
107.
Protein-splicing domains are frequently used engineering tools that find application in the in vivo and in vitro ligation of protein domains. Directed evolution is among the most promising technologies used to advance this technology. However, the available screening systems for protein-splicing activity are associated with bottlenecks such as the selection of pseudo-positive clones arising from off-pathway reaction products or fragment complementation. Herein, we report a stringent screening method for protein-splicing activity in cis and trans, that exclusively selects productively splicing domains. By fusing splicing domains to an intrinsically disordered region of the antidote from the Escherichia coli CcdA/CcdB type II toxin/antitoxin system, we linked protein splicing to cell survival. The screen allows selecting novel cis- and trans-splicing inteins catalyzing productive highly efficient protein splicing, for example, from directed-evolution approaches or the natural intein sequence space.  相似文献   
108.
109.
正UNStudio由Ben van Berkel和Caroline Bos创立,是一个国际性的建筑设计网络。拥有三个全方位服务的国际事务所,分别位于阿姆斯特丹、香港和上海。专于建筑、室内建筑、产品设计、城市发展和基础设施项目。地址:浙江省杭州市钱江新城富春路业主方:凯德集团建筑面积:392526m~2项目年份:2017醒目的裙楼之上坐落着两座流线型的高楼,从中可以饱览钱塘江和西湖的迷人风光。  相似文献   
110.
A chemical method was developed for low‐temperature synthesis of DAG from MAG followed by an easy purification procedure in order to obtain high‐purity DAG. Solvent‐assisted and solvent‐free reaction conditions were used, combined with different catalysts (sodium methoxide, p‐toluenesulfonic acid, methanesulfonic acid, and sulfuric acid). All reactions were performed at 35 and 70 °C. By increasing both acidity and polarity of the catalyst the equilibrium shifts towards the formation of DAG. When using sulfuric acid in solvent‐assisted condition at 70 °C, 88 % conversion was obtained after 20 min of reaction (77 % w/w DAG in the reaction mixture after evaporation of the solvent). After purifying by means of column chromatography, 96 % pure DAG were obtained. The overall yield of DAG was 81 %.  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