全文获取类型
收费全文 | 9422篇 |
免费 | 237篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 127篇 |
综合类 | 39篇 |
化学工业 | 2308篇 |
金属工艺 | 227篇 |
机械仪表 | 187篇 |
建筑科学 | 665篇 |
矿业工程 | 20篇 |
能源动力 | 302篇 |
轻工业 | 911篇 |
水利工程 | 97篇 |
石油天然气 | 43篇 |
武器工业 | 2篇 |
无线电 | 727篇 |
一般工业技术 | 1519篇 |
冶金工业 | 571篇 |
原子能技术 | 59篇 |
自动化技术 | 1869篇 |
出版年
2024年 | 80篇 |
2023年 | 110篇 |
2022年 | 214篇 |
2021年 | 366篇 |
2020年 | 238篇 |
2019年 | 253篇 |
2018年 | 273篇 |
2017年 | 239篇 |
2016年 | 341篇 |
2015年 | 239篇 |
2014年 | 346篇 |
2013年 | 634篇 |
2012年 | 487篇 |
2011年 | 623篇 |
2010年 | 432篇 |
2009年 | 501篇 |
2008年 | 469篇 |
2007年 | 422篇 |
2006年 | 349篇 |
2005年 | 301篇 |
2004年 | 275篇 |
2003年 | 264篇 |
2002年 | 192篇 |
2001年 | 140篇 |
2000年 | 143篇 |
1999年 | 120篇 |
1998年 | 139篇 |
1997年 | 135篇 |
1996年 | 100篇 |
1995年 | 79篇 |
1994年 | 82篇 |
1993年 | 88篇 |
1992年 | 59篇 |
1991年 | 61篇 |
1990年 | 63篇 |
1989年 | 69篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 50篇 |
1985年 | 54篇 |
1984年 | 62篇 |
1983年 | 44篇 |
1982年 | 38篇 |
1981年 | 37篇 |
1980年 | 39篇 |
1978年 | 36篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 40篇 |
1973年 | 36篇 |
排序方式: 共有9673条查询结果,搜索用时 62 毫秒
41.
Jan Olsson 《Planning Theory & Practice》2013,14(2):167-187
This article contributes to an understanding of policy change. Exploring a local land planning case, it investigates how an environmental advocacy coalition effectively challenged road and housing plans, with the result that an area was instead developed into a nature reserve. In the course of the article, the value and practical effectiveness of the Advocacy Coalition Framework (ACF) is examined and developed with the help of two central concepts—the “value network” and “inside activist”. The outcome of the case is explained by the powerful influence of a value network of ornithologists, with particular inside activists of that network playing important roles in presenting a challenge to development of the area. Instead of trying to build an abstract theory of the ACF, the article argues the need to develop the ACF as a framework, opening it up to insights from policy network and social constructionist research as well as from practical processes. 相似文献
42.
To further our understanding on policymaking and policy change we need to recognize the significance of individual key actors in policy and planning processes. This article theorizes on the characteristics and policy influence of inside activism in which individual public officials act strategically from inside public administration to change government policy and action in line with a civic engagement and value commitment. Based on initial empirical findings from Swedish local government, we argue that inside activism is empirically relevant but not satisfactorily covered by other key actor concepts. We theorize that inside activism is 1) dualistic: open, deliberative, consensus-seeking and tacit, tactical, power-driven; 2) influential through informal networking inside and outside of government; and 3) dynamic as it varies over time and between critical situations. Due to current trends in society and public administration (e.g. governance), we expect inside activism to be increasingly relevant and we encourage further theoretical, empirical as well as normative research and discussion on this phenomenon. 相似文献
43.
In Friedberg (Hessen) wurde im Juli 2008 erstmals in Deutschland eine Straßenbrücke unter Verwendung von glasfaserverstärktem Kunststoff (GFK) fertig gestellt. Das Bauwerk überspannt mit 27 m die Bundesstraße B 3a bei der Stadt Friedberg (Hessen) und wurde in Stahl‐GFK‐Verbundbauweise realisiert. Die hohe Dauerhaftigkeit des neuen Werkstoffs und die zügige Montage der Brücke waren die entscheidenden Gründe pro GFK. In den letzten Jahren wurden in den USA, Japan und auch in Europa einige Leichtbaubrücken mit faserverstärkten Kunststoffen realisiert. Dabei konnten wertvolle Erfahrungen zum Bau und Betrieb gesammelt und die Leistungsfähigkeit von Verbundwerkstoffen unter Beweis gestellt werden. Die Brücke in Friedberg geht über diese Vorbilder hinaus, indem hier erstmals die Verbundwirkung zwischen der GFK‐Fahrbahn und dem Haupttragwerk aus Stahl berücksichtigt wird. Außerdem wurde konsequent der Ansatz eines wartungsarmen und langlebigen Bauwerks verfolgt, indem auf Lager und Fahrbahnübergänge verzichtet wurde. Bridges with Glass Fibre Reinforced Polymers (GFRP) decks – The new Road Bridge in Friedberg (Hessen, Germany). In July 2008 the first road bridge in Germany using glass fibre reinforced polymers (GFRP) was finished in Friedberg (Hessen). The structure has a span of 27 m and acts as overfly of the federal road B 3 near Friedberg (Hessen). The high durability of the new construction material and the fast assembly of the bridge were decisive factors in favour of GFRP. Within the last years several light weight bridges using FRP were realised in USA, Japan and also in Europe. Through this valuable experiences could be gathered regarding construction, the use and performance of composites could be demonstrated. The bridge in Friedberg extends this experience with the approach of considering the composite action of the FRP deck and the steel girders. It also follows consequently the approach of durable bridge construction by omitting any bearings or expansion joints. 相似文献
44.
Urban Åkesson Jan Erik Lindqvist Björn Schouenborg Bent Grelk 《Bulletin of Engineering Geology and the Environment》2006,65(1):73-79
The use of thin (20–40 mm) marble as cladding for building facades has increased substantially during the last few decades. Many of the marble facades perform but some durability problems have occurred, especially with calcite marble, when the cladding starts to bow indicating a decrease in strength. This study considers the influence of the microstructure on the bowing of the calcite marble using adjacent grains analysis. Samples with a granoblastic texture all had six adjacent grains while those with a more complex microstructure had up to 13 adjacent grains. The samples with a granoblastic texture had the greatest degree of bowing, suggesting that the microstructure is a crucial parameter for the durability of marble and that adjacent grains analysis could be a fast and easy method to assess the suitability of marble for cladding purposes. 相似文献
45.
2)香波洗涤条件
按照泡沫均质搅拌测试的要求备好香波样品,将样品加热至40℃后放入颗粒图像测量仪的玻璃贮液器。启动测量仪成像系统后,将发束放入配方液,浸泡约30s,随后清洗30s,风干。 相似文献
46.
One of the CHRISGAS project objectives is to study the shift catalysts in biomass-generated synthesis gas. The water gas shift
reaction is ruled by equilibrium, and the state of the gas can for a given H2/CO ratio be shifted by addition/removal of water, CO2 and/or by a change in the temperature. Stability area in respect to gas composition, sulphur content, pressure and temperature
for FeCr shift catalyst has been investigated by thermodynamic equilibrium calculations. The calculations show that carbide
formation is favourable in the “Normal water” case without sulphur in the gas. If sulphur is present in the gas, the situation
improves due to sulphide formation. 相似文献
47.
Julian Chojnowski Slawomir Rubinsztajn Witold Fortuniak Jan Kurjata 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):173-187
Summary Reactions of hexamethylcyclotrisiloxane, D3, with 1,1,3,3-tetramethyldisiloxane, HMMH, 1,1,1,3,3-pentamethyldisiloxane, HMM, phenyldimethylsilane and phenylmethylsilane catalyzed by tris(pentafluorophenyl)borane were studied. These reactions lead
to ring opening of D3 by the SiH reactant producing open chain oligomers with hydrosilane functionality at one or both chain ends. The reactivity
of the hydrosilanes toward D3 decreases in the series: PhMeSiH2 > HMMH > PhMe2SiH > HMM. Competitive self-oligomerization of HMMH and HMM also occurs. Primary products of these processes are able to enter into reactions with the SiH and D3 reactants; some also undergo cyclization. Thus, consecutive and competitive processes lead to a series of various oligohomologues.
Gas chromatography in conjunction with chemical ionization mass spectroscopy permitted identification of structure and determination
of the basic directions of these oligomerization processes. Polysiloxanes of higher molecular weight may be also formed in
some of these systems. The reactions, which occur in the systems studied, are rationalized on the basis of the mechanism involving
the hydride transfer from silicon to trivalent boron. This includes the transient formation of tertiary trisilyloxonium borate
which decomposes by the hydride transfer to one of the silicon atoms of the trisilyloxonium center.
Footnote: This paper is dedicated to Professor Ian Manners in recognition of his significant contributions to the field of
organometallic polymers. 相似文献
48.
Anions are essential species in biological systems and, particularly, in enzyme-substrate recognition. Therefore, the design and preparation of anion receptors is a topical field of supramolecular chemistry. Most host-guest systems successfully developed are based on noncovalent (ionic and hydrogen-bonded) interactions between anions and ammonium-type functionalities or Lewis acid groups. However, since the past 5 years, an alternative route toward the synthesis of efficient anion hosts has emerged, namely, the use of "anion-pi" interactions involving nitrogen-containing electron-deficient aromatic rings, as the result of several favorable theoretical investigations. In this Account, the state of the (new) art in this growing area of anion-binding research is presented and several selected examples from our work and that of other groups will be discussed. 相似文献
49.
Nadal A Coll A Aviñó A Esteve T Eritja R Pla M 《Chembiochem : a European journal of chemical biology》2006,7(7):1039-1047
Parallel clamps can interact in a sequence-specific manner with homopyrimidine DNA and RNA oligonucleotides to form triplexes. For longer nucleic acids, we have previously demonstrated the inhibitory effect of DNA-target secondary structures on triplex formation. We further designed a modification of these molecules-that is, tail-clamps formed by addition of a tail sequence to the parallel clamp-and proved efficient binding of the molecules with structured single-stranded DNA targets. Here we explore the possible application of the tail-clamp strategy for triplex formation with RNA targets, which are typically found as strongly folded single-stranded molecules. Efficient and specific binding of a tail-clamp designed to form a parallel triplex with Listeria innocua iap mRNA sequences has been verified by UV melting curves and triplex affinity capture techniques. Furthermore, we show for the first time the formation of stable complexes of mRNA with tail-clamps not only under acidic but also under neutral and slightly basic pH conditions. These results signify a further step towards the possible applications of triplexes with mRNA molecules; research, analytical, and therapeutic uses can be envisaged. As an example, our tail-clamp-based triplex affinity capture assay allowed the specific capture and recovery of iap mRNA molecules from an L. innocua total RNA solution with 45 % yield. 相似文献
50.
Anne Sofie Biong Paula Berstad Jan I. Pedersen 《European Journal of Lipid Science and Technology》2006,108(10):827-834
The aim of this study was to correlate the fatty acids characteristic of dairy fat (14:0, 14:1, 15:0, 17:0 and 17:1) in adipose tissue, serum lipid fractions and the estimated intake of dairy fat, and to investigate whether they can be used as biomarkers for dairy fat/product intake. The highest correlations were observed between 14:0 in adipose tissue and the estimated intakes of 14:0 (r = 0.60) and dairy fat (r = 0.50), and between 15:0 in adipose tissue and the estimated intakes of 15:0 (r = 0.55) and dairy fat (r = 0.55). Among the fatty acids in serum lipid fractions, 15:0 in cholesteryl esters (CE) and triacylglycerols showed the highest correlation to both 15:0 in adipose tissue, intakes of 15:0, dairy fat and dairy products. The results from our study suggest that the contents of fatty acids characteristic of dairy fat (14:0, 14:1, 15:0, 17:0, 17:1) in adipose tissue might be used as markers not only for the intake of dairy fat, but also of dairy products (times/day). When adipose tissue specimens are not available, 15:0 in serum CE appears to be the best marker for dairy fat intake. It was also observed that fatty acids from dairy fat are incorporated differently into serum lipid fractions and adipose tissue. 相似文献