全文获取类型
收费全文 | 2526篇 |
免费 | 117篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 29篇 |
综合类 | 26篇 |
化学工业 | 838篇 |
金属工艺 | 47篇 |
机械仪表 | 42篇 |
建筑科学 | 161篇 |
矿业工程 | 4篇 |
能源动力 | 40篇 |
轻工业 | 243篇 |
水利工程 | 16篇 |
石油天然气 | 4篇 |
无线电 | 154篇 |
一般工业技术 | 482篇 |
冶金工业 | 100篇 |
原子能技术 | 24篇 |
自动化技术 | 440篇 |
出版年
2023年 | 31篇 |
2022年 | 57篇 |
2021年 | 77篇 |
2020年 | 44篇 |
2019年 | 51篇 |
2018年 | 56篇 |
2017年 | 55篇 |
2016年 | 66篇 |
2015年 | 62篇 |
2014年 | 102篇 |
2013年 | 122篇 |
2012年 | 115篇 |
2011年 | 183篇 |
2010年 | 128篇 |
2009年 | 135篇 |
2008年 | 134篇 |
2007年 | 114篇 |
2006年 | 111篇 |
2005年 | 104篇 |
2004年 | 87篇 |
2003年 | 71篇 |
2002年 | 67篇 |
2001年 | 63篇 |
2000年 | 50篇 |
1999年 | 52篇 |
1998年 | 41篇 |
1997年 | 38篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 35篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 34篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 21篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 7篇 |
1931年 | 3篇 |
排序方式: 共有2650条查询结果,搜索用时 0 毫秒
91.
Peter Mechnich Martin Schmücker Hartmut Schneider 《Journal of the American Ceramic Society》1999,82(9):2517-2522
A promising technique for the fabrication of mullite ceramics and mullite-matrix composites with low dimensional changes ("near-net-shape processing") is reaction bonding using Si metal and α-Al2 O3 as starting materials, because sintering-induced shrinkage is compensated by Si-oxidation-induced volume expansion. A mullite reaction bonding (RBM) route which proceeds at much lower temperatures (lessthan equal to1350°C) than in conventional RBM systems (greaterthan equal to1500°C) is based on Ce doping which provides accelerated Si oxidation and mullite formation due to the formation of transient, low-viscosity Ce-Al-Si-O liquids. The present study shows that the required Ce-Al-Si-O liquids form in a reducing environment with Ce occurring as Ce3+ . In an oxidizing environment, Ce is present as Ce4+ , giving rise to precipitation of crystalline CeO2 . Ce3+ left and right arrow Ce4+ redox reactions in the temperature range under consideration appear to be controlled by the presence of nonoxidized Si in the samples. According to the present investigation the amount of CeO2 added to the starting powders must be tailored carefully: Exaggerated CeO2 content produces large amounts of low-viscosity Ce-Al-Si-O liquids which may have the disadvantage of excessive sealing of the open porosity. This slows the oxygen diffusion velocity into the specimen considerably, with the consequence that nonoxidized Si and a residual Ce-Al-Si-O glass coexist in the ceramics after processing. A solution to this problem is to simultaneously enhance mullite crystal growth through seeding which works against excessive liquid-phase-induced shrinkage of the samples. This in turn enables complete oxidation and recrystallization of all liquid phases. 相似文献
92.
Carl-Friedrich Krger Ralf Miethchen Hanna Mann Klaus Hoffmann Kurt Wiechert 《Advanced Synthesis \u0026amp; Catalysis》1978,320(6):881-903
Acid-catalyzed Reactions of Aromatic Hydrocarbons with Alkanes and Cycloalkanes. IX. Alkylations with 2,2,4-Trimethylpentane (Isooctane) The non-conventional alkylation of benzene, toluene, ethyl- and isopropylbenzene, fluoro- and chlorobenzene with 2,2,4-trimethylpentane in the presence of acid catalysts is described. The composition of the rather complex reaction mixtures is determined by gas-liquid chromatography and mass spectrometry, tert. butylarenes being the main products beside alkylsubstituted indanes and tetralines. Their formation is interpreted as a competition between fragmentation and isomerization of the alkylating agent. By use of trifluoromethanesulfonic acid or combinations of catalysts from HF or HSO3F with variant metallic fluorides at lower temperatures the selectivity of the reaction may be partially raised. 相似文献
93.
94.
Patrick J. Riss Dr. Fabian Debus Dr. René Hummerich Ulrich Schmidt Dr. Patrick Schloss Dr. Hartmut Lueddens Dr. Frank Roesch Dr. 《ChemMedChem》2009,4(9):1480-1487
N‐4‐Fluorobut‐2‐yn‐1‐yl‐2β‐carbomethoxy‐3β‐phenyltropane (PR04.MZ) has been developed as dopamine transporter (DAT) ligand for molecular imaging. It contains a terminally fluorinated, conformationally constrained nitrogen substituent that is well suited for the introduction of fluorine‐18. The present report describes the pharmacological characterisation of [18F]PR04.MZ. The ligand shows an IC50 value of 2 nM against human DAT, whereas the IC50 value against human serotonin transporter and human noradrenalin transporter are lower (110 nM and 22 nM , respectively). Furthermore, its ex vivo organ distribution, its binding profile in the rat brain and reversibility of binding were examined. A μPET study illuminates a fast kinetic profile and specific binding to rat DAT. 相似文献
95.
96.
97.
Joachim Mittendorf Prof. Dr. Stefan Weigand Dr. Cristina Alonso‐Alija Dr. Erwin Bischoff Dr. Achim Feurer Dr. Michael Gerisch Dr. Armin Kern Dr. Andreas Knorr Dr. Dieter Lang Dr. Klaus Muenter Dr. Martin Radtke Dr. Hartmut Schirok Dr. Karl‐Heinz Schlemmer Dr. Elke Stahl Dr. Alexander Straub Dr. Frank Wunder Dr. Johannes‐Peter Stasch Dr. 《ChemMedChem》2009,4(5):693-693
98.
Landscape structure is a main determinant of ecological landscape potentials. The basic differentiation of relief into depressions and elevations at deliberately chosen scales can be managed comfortably by the Fourier transformation. The automated extraction of these structures from an elevation map using Fourier transformation or singular value decomposition can help to overcome complicated and errorprone procedures based on the determination of numerical structure parameters such as slope and aspect. The combination of automated extraction methods and moving window technology can lead to further, more integrated insights related to complex landscape patterns. 相似文献
99.
Sania Saljoughian Alaa El-Din A. Bekhit Ralf Greiner Alireza Omidizadeh Nooshin Nikmaram 《Critical reviews in food science and nutrition》2018,58(10):1688-1705
Essential oils (EO) are complex secondary metabolites, which are produced by aromatic plants and identified by their powerful odors. Present studies on EO and their isolated ingredients have drawn the attention of researchers to screen these natural products and evaluate their effect on the cardiovascular system. Some EO, and their active ingredients, have been reported to improve the cardiovascular system significantly by affecting vaso-relaxation, and decreasing the heart rate and exert a hypotension activity. Several mechanisms have been proposed for the role of EO and their main active components in promoting the health of the cardiovascular system. The objective of this review is to highlight the current state of knowledge on the functional role of EO extracted from plants for reducing the risk of cardiovascular diseases and their mechanisms of action. Research on EO has the potential to identify new bioactive compounds and formulate new functional products for the treatment of cardiovascular diseases such as arterial hypertension, angina pectoris, heart failure, and myocardial infarction. 相似文献
100.