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   543篇
  免费   13篇
电工技术   2篇
化学工业   160篇
金属工艺   18篇
机械仪表   3篇
建筑科学   42篇
矿业工程   1篇
能源动力   15篇
轻工业   82篇
水利工程   1篇
石油天然气   11篇
无线电   12篇
一般工业技术   55篇
冶金工业   70篇
自动化技术   84篇
  2024年   2篇
  2023年   4篇
  2022年   17篇
  2021年   12篇
  2020年   10篇
  2019年   7篇
  2018年   12篇
  2017年   7篇
  2016年   4篇
  2015年   12篇
  2014年   15篇
  2013年   24篇
  2012年   18篇
  2011年   26篇
  2010年   23篇
  2009年   33篇
  2008年   32篇
  2007年   32篇
  2006年   21篇
  2005年   18篇
  2004年   23篇
  2003年   17篇
  2002年   13篇
  2001年   11篇
  2000年   14篇
  1999年   10篇
  1998年   11篇
  1997年   8篇
  1996年   13篇
  1995年   7篇
  1994年   12篇
  1993年   5篇
  1992年   6篇
  1991年   11篇
  1990年   7篇
  1989年   8篇
  1988年   7篇
  1987年   7篇
  1985年   3篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1979年   6篇
  1978年   3篇
  1975年   2篇
  1972年   2篇
  1967年   2篇
  1954年   1篇
  1944年   2篇
  1943年   1篇
排序方式: 共有556条查询结果,搜索用时 0 毫秒
41.
The ability to select the larger of two quantities ranging from 1 to 5 (relative numerousness judgment [RNJ[) and the ability to select the larger of two pairs of quantities with each pair ranging from 1 to 8 (summation) were evaluated in young, middle-aged, and older adult orangutans (7 Pongo pygmaeus abelii and 2 Pongo pygmaeus pygmaeus). Summation accuracy and RNJ were similar to those of previous reports in apes; however, the pattern of age-related differences with regard to these tasks was different from that previously reported in gorillas. Older orangutans were less accurate than the young and middle-aged for RNJ, and summation accuracy was equivalent among age groups. Evidence was found to suggest that the young and middle-aged based their selection of the largest quantity pair on both quantities within each pair during the summation task. These results show a relationship between subject age and the quantitative abilities of adult orangutans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
42.
Real number theorem proving has many uses, particularly for verification of safety critical systems and systems for which design errors may be costly. We discuss a chain of developments building on real number theorem proving in PVS. This leads from the verification of aspects of an air traffic control system, through work on the integration of computer algebra and automated theorem proving to a new tool, NRV, first presented here that builds on the capabilities of Maple and PVS to provide a verified and automatic analysis of Nichols plots. This automates a standard technique used by control engineers and greatly improves assurance compared with the traditional method of visual inspection of the Nichols plots.  相似文献   
43.
Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.  相似文献   
44.
Hepatic lipidosis is a common pathological finding in the American mink (Neovison vison) and can be caused by nutritional imbalance due to obesity or rapid body weight loss. The objectives of the present study were to investigate the timeline and characterize the development of hepatic lipidosis in mink in response to 0–7 days of food deprivation and liver recovery after 28 days of re-feeding. We report here the effects on hematological and endocrine variables, body fat mobilization, the development of hepatic lipidosis and the alterations in the liver lipid classes and tissue fatty acid (FA) sums. Food deprivation resulted in the rapid mobilization of body fat, most notably visceral, causing elevated hepatosomatic index and increased liver triacylglycerol content. The increased absolute amounts of liver total phospholipids and phosphatidylcholine suggested endoplasmic reticulum stress. The hepatic lipid infiltration and the altered liver lipid profiles were associated with a significantly reduced proportion of n-3 polyunsaturated FA (PUFA) in the livers and the decrease was more evident in the females. Likewise, re-feeding of the female mink resulted in a more pronounced recovery of the liver n-3 PUFA. The rapid decrease in the n-3/n-6 PUFA ratio in response to food deprivation could trigger an inflammatory response in the liver. This could be a key contributor to the pathophysiology of fatty liver disease in mink influencing disease progression.  相似文献   
45.
Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the oxidative cleavage of l -Tryptophan (l -Trp) to yield N-formyl-kynurenine in the first and rate limiting step of the kynurenine pathway. Bioactive metabolites, involved in the regulation of important immunological responses and neurological processes, are then produced by downstream enzymes along the pathway. Inhibitors of IDO1 are being designed and developed as therapeutic agents for immuno-oncology. In this work, we investigated the molecular recognition path of l -Trp to IDO1, integrating biophysical methods with supervised molecular dynamics (suMD) and mutagenesis experiments. Results allowed disclosing for the first time high and low dissociation constants of l -Trp to IDO1, and the presence of a metastable interaction site located at the upper part of a channel whose borders are defined by the EF-loop and the C-terminal part of the JK-loop. Collectively, our results provide new clues for the design of next-generation IDO1 ligands.  相似文献   
46.
The adsorption and reaction of toluene on vanadyl pyrophosphate catalysts was studied by in situ infrared spectroscopy. Strongly adsorbed benzaldehyde and physically adsorbed cyclic anhydride species were observed at temperatures above 523 K. Water formed during reaction generates acid hydroxyl groups which cause a stronger adsorption of benzaldehyde and consecutive oxidation reactions. By co-adsorption of pyridine the acid sites are blocked and the deeper oxidation is suppressed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
47.
48.
A new setup is presented which enables simultaneous wide- and small-angle X-ray scattering (WAXS/SAXS) and Raman spectroscopic experiments during the synthesis of Mo-based mixed oxide catalyst precursors at the μ-spot beamline at the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung (BESSY). Furthermore, we report about the separate monitoring of the same reactions under comparable conditions by simultaneous combined ATR/UV–vis/Raman spectroscopic measurements. For testing the performance of both experimental setups two syntheses were described comprising the precipitation of metal molybdates by mixing solutions of metal nitrates and ammonium heptamolybdate. Additionally, the effect of H3PO4 admixture on precipitation was investigated. The combined evaluation of spectroscopic and WAXS/SAXS data allows the discrimination between different molybdate species appearing in solution and precipitate. Furthermore, these molybdate species could be assigned to separate phases of different crystallinity.  相似文献   
49.
We prove that any simplification order over arbitrary terms is an extension of an order by weight, by considering a related monadic term algebra called the spine. We show that any total ground-stable simplification order on the spine lifts to an order on the full term algebra. Conversely, under certain restrictions, a simplification ordering on the term algebra defines a weight function on the spine, which in turn can be lifted to a weight order on the original ground terms which contains the original order. We investigate the Knuth–Bendix and polynomial orders in this light. We provide a general framework for ordering terms by counting embedded patterns, which gives rise to many new orderings. We examine the recursive path order in this context.  相似文献   
50.
In the dieless drawing technology the drawing dies are replaced by a heating device, generally by an induction coil. Bars of different cross-sections, round or even rectangular, with varying dimensions along the length can be produced. By using a cooling box in connection with the heating device this deformation process may also be employed for a thermomechanical treatment of steels. The special cooling strategy with low cooling rates at high temperatures (during ferrite formation) and higher cooling rates at lower temperatures favours the formation of multiphase microstructures (ferrite - bainite/martensite) with a low yield strength but a strong work hardening effect. The experiments were carried out on rods with a diameter of 16 mm of a plain low carbon steel (0.1%C, 0.7%Mn). The specimens were locally heated up to the maximum temperature ?max that initiates the dieless drawing process, and subsequently cooled with different coolants. The change in yield strength and tensile strength and the corresponding change in the ratio of both could be achieved by variation of ?max and the cooling conditions. The multiphase microstructure with desired mechanical properties was produced at a strain of about more than 0.45 within the region of ?max ≈ 900–1000°C and a finale cooling rate of about 20 K/s.  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