全文获取类型
收费全文 | 3431篇 |
免费 | 145篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 39篇 |
综合类 | 14篇 |
化学工业 | 1111篇 |
金属工艺 | 61篇 |
机械仪表 | 41篇 |
建筑科学 | 188篇 |
矿业工程 | 4篇 |
能源动力 | 56篇 |
轻工业 | 330篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 182篇 |
一般工业技术 | 696篇 |
冶金工业 | 381篇 |
原子能技术 | 26篇 |
自动化技术 | 444篇 |
出版年
2023年 | 39篇 |
2022年 | 57篇 |
2021年 | 75篇 |
2020年 | 44篇 |
2019年 | 61篇 |
2018年 | 51篇 |
2017年 | 51篇 |
2016年 | 87篇 |
2015年 | 88篇 |
2014年 | 101篇 |
2013年 | 168篇 |
2012年 | 177篇 |
2011年 | 208篇 |
2010年 | 158篇 |
2009年 | 165篇 |
2008年 | 173篇 |
2007年 | 162篇 |
2006年 | 139篇 |
2005年 | 131篇 |
2004年 | 104篇 |
2003年 | 76篇 |
2002年 | 73篇 |
2001年 | 63篇 |
2000年 | 65篇 |
1999年 | 78篇 |
1998年 | 106篇 |
1997年 | 81篇 |
1996年 | 48篇 |
1995年 | 64篇 |
1994年 | 54篇 |
1993年 | 39篇 |
1992年 | 44篇 |
1991年 | 49篇 |
1990年 | 27篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 36篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 34篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1981年 | 24篇 |
1980年 | 20篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 29篇 |
1975年 | 19篇 |
1974年 | 17篇 |
排序方式: 共有3579条查询结果,搜索用时 15 毫秒
41.
Jens Eichler Jürgen Rödel Ulrich Eisele Mark Hoffman 《Journal of the American Ceramic Society》2007,90(9):2830-2836
This paper considers fracture strength, fracture origins, and hydrothermal degradation of 3Y-TZP with grain sizes in the range of 110–480 nm. Biaxial fracture strength testing was used to show that the fracture strength increases with grain size and is governed by the concurrent change in fracture toughness. Hydrothermal degradation was studied by means of fractography, Raman microscopy and its effect on fracture strength. Up to 200 nm grain size, hydrothermal degradation of strength is limited. Larger grain sizes exhibit either premature failure or an increase in strength. A surface transformation zone was found to be responsible for both phenomena. 相似文献
42.
Summary: The influence of number‐average molecular weight ranging from 1.4 · 104 to 1.2 · 106 g/mol on the thermal behaviour of polytetrafluoroethylene (PTFE) has been studied. Samples have been prepared by radiation‐induced degradation of commercial PTFE. The molecular weight has been calculated using end‐group concentration determined by infrared (IR) spectroscopy and 19F solid‐state nuclear magnetic resonance (NMR) spectroscopy. Melting and crystallisation heats were investigated by differential scanning calorimetry (DSC). The results have been discussed with respect to quantitative relationships between number‐average molecular weight and heat of crystallisation of PTFE described in the literature. The molecular weight calculated from Suwa's equation, which is often used in the literature, has been found to be too low.
43.
Purification of solvents containing air – Alternative methods. Different processes are used for the purification of solvents containing air: condensation, absorption, adsorption, combustion, membrane permeation, and biofilters or bioscrubbers. The processes will be explained by examples. The specifications required by “TA Luft” often cannot be reached only by condensation and membrane permeation. The success of absorption depends on the scrubbing liquid. Glycol ethers are useful scrubbing liquids – especially for chlorinated hydrocarbons. The choice of the process depends on the volume flow rate, the solvent concentration, and the kind of solvent. Recycling of the solvents reduces the costs of the process. 相似文献
44.
Nitrate radicals are being recognized as key intermediates in a growing list of important chemical processes in the atmosphere. Here, the role of nitrate radicals (NO3) in tropospheric chemistry is discussed, with special emphasis on results from field measurements, most of which have been made by differential optical absorption spectroscopy (DOAS), with matrix-isolation electron spin resonance being an alternative technique. Nitrate radicals were observed in the atmosphere at peak mixing ratios of 350 ppt. Long-term observation of NO3 shows that 24-h averages in rural air masses are closer to a few ppt. Nevertheless, the NO3 radical plays an important role in the non-photochemical conversion of NOx to HNO3. Also, NO3 is a strong oxidizing agent and initiates the night-time removal of atmospheric trace species such as olefins, aromatic hydrocarbons, and organic sulfur compounds. Finally, night-time peroxy radical production and release of reactive halogen species from sea salt aerosol might be initiated by NO3 reactions. 相似文献
45.
46.
47.
Summary: This paper describes a step on the ambitious aim to “design” application properties of ldPE by first simulating the detailed molecular structure of a high‐pressure tubular reactor product. The reactor of a certain configuration produces under well‐defined operating conditions. The next step is to correlate the structure with the application properties. Finally, the sequence will be reversed in order to deduce the operating conditions, which lead to the desired product quality. Two‐dimensional distributions, in molecular weight and branching frequency, as well a two compartment models with a core and a shell stream were simulated and compared with experimental results. Therefore, CFD simulations were carried out to discretize the reaction medium. Samples were taken from both pilot and commercial plants. The TREF‐SEC analytical method was successfully applied in order to measure the microscopic structure of the material. The tremendous numerical problems were solved with the help of the software PREDICI .
48.
Roland Schmidt Ulrich Hammon Stefan Gottfried M. Bruce Welch Helmut G. Alt 《应用聚合物科学杂志》2003,88(2):476-482
The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by 1H‐ and 13C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003 相似文献
49.
Maria Casapu Jan-Dierk Grunwaldt Marek Maciejewski Meike Wittrock Ulrich Gbel Alfons Baiker 《Applied catalysis. B, Environmental》2006,63(3-4):232-242
The formation and stability of BaAl2O4 and BaCeO3 in Pt-Ba/Al2O3 and Pt-Ba/CeO2 based NOx storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO3. The formation of BaAl2O4 started above 850 °C, whereas the formation of BaCeO3 was already observed at 800 °C and was faster than that of BaAl2O4. The stability of BaAl2O4 and BaCeO3 in various liquid and gaseous atmospheres was different. BaAl2O4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO3)2 and γ-alumina in the presence of HNO3, whereas BaCeO3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO3 was transformed to Ba(NO3)2/CeO2 in the presence of NO2/H2O at 300–500 °C. Also, the presence of CO2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NOx-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts. 相似文献
50.
The reactions of trans-2,5-dimethoxy-4′-aminostilbene with poly(maleic anhydride-co-methylvinyl ether) and trans-2,5-dimethoxy-4′-isocyanatostilbene with poly(oxy-1,4-phenyleneisopropylidene:1,4-phenyleneoxy-2-hydroxytrimethylene) yield polymeric systems which undergo rapid crosslinking upon short exposure to ultraviolet light. The extent of photocrosslinking as a function of exposure time was determined by the decrease of the trans-stilbene ultraviolet absorption at 350 nm. 相似文献