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   973篇
  免费   82篇
电工技术   7篇
综合类   1篇
化学工业   478篇
金属工艺   3篇
机械仪表   26篇
建筑科学   48篇
能源动力   15篇
轻工业   185篇
水利工程   4篇
石油天然气   1篇
无线电   21篇
一般工业技术   103篇
冶金工业   103篇
原子能技术   3篇
自动化技术   57篇
  2024年   3篇
  2023年   12篇
  2022年   111篇
  2021年   96篇
  2020年   42篇
  2019年   31篇
  2018年   31篇
  2017年   36篇
  2016年   34篇
  2015年   31篇
  2014年   45篇
  2013年   67篇
  2012年   57篇
  2011年   71篇
  2010年   42篇
  2009年   28篇
  2008年   38篇
  2007年   37篇
  2006年   32篇
  2005年   24篇
  2004年   20篇
  2003年   19篇
  2002年   18篇
  2001年   10篇
  2000年   9篇
  1999年   3篇
  1998年   8篇
  1997年   6篇
  1996年   12篇
  1995年   7篇
  1994年   4篇
  1993年   8篇
  1992年   9篇
  1991年   2篇
  1990年   6篇
  1989年   5篇
  1988年   2篇
  1987年   5篇
  1986年   5篇
  1985年   8篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1976年   3篇
  1975年   1篇
  1970年   1篇
  1969年   1篇
排序方式: 共有1055条查询结果,搜索用时 15 毫秒
991.
The setting up of efficient early warning systems is a challenge to research for preventing environmental alteration and human disease. In this paper, we report the development and the field application of a new biomonitoring methodology for assessing soil genotoxicity. In the first part, the use of amplified fragment length polymorphism and flow cytometry techniques to detect DNA damage induced by soils artificially contaminated with heavy metals as potentially genotoxic compounds is explained. Results show that the combination of the two techniques leads to efficient detection of the sublethal genotoxic effect induced in the plant bioindicator by contaminated soil. By contrast, the classic mortality, root, and shoot growth vegetative endpoints prove inappropriate for assessing soil genotoxicity because, although they cause genotoxic damage, some heavy metals do not affect sentinel plant development negatively. The statistical elaboration of the data obtained led to the development of a statistical predictive model which differentiates four different levels of soil genotoxic pollution and can be used everywhere. The second part deals with the application of the biomonitoring protocol in the genotoxic assessment of two areas surrounding a steelworks in northern Italy and the effectiveness of this methodology. In this particular case, in these areas, the predictive model reveals a pollution level strictly correlated to the heavy metal concentrations revealed by traditional chemical analysis.  相似文献   
992.
Amorati R  Rizzi R 《Applied optics》2002,41(9):1604-1614
A fast-forward radiative transfer (RTF) model is presented that includes cloud-radiation interaction for any number of cloud layers. Layer cloud fraction and transmittance are treated separately and combined with that of gaseous transmittances. RTF is tested against a reference procedure that uses line-by-line gaseous transmittances and solves the radiative transfer equation by use of the adding-doubling method to handle multiple-scattering conditions properly. The comparison is carried out for channels 8, 12, and 14 of the High Resolution Infrared Radiation Sounder (HIRS/2) and for the geostationary satellite METEOSAT thermal infrared and water vapor channels. Fairly large differences in simulated radiances by the two schemes are found in clear conditions for upper- and mid-tropospheric channels; the cause of the differences is discussed. For cloudy situations an improved layer source function is shown to be required when rapid changes in atmospheric transmission are experienced within the model layers. The roles of scattering processes are discussed; results with and without scattering, both obtained by use of a reference code, are compared. Overall, the presented results show that the fast model is capable of reproducing the cloudy results of the much more complex and time-consuming reference scheme.  相似文献   
993.
994.
We present an implementation of strategies to deposit single-molecule magnets (SMMs) using microcontact printing microCP). We describe different approaches of microCP to print stripes of a sulfur-functionalized dodecamanganese (III, IV) cluster on gold surfaces. Comparison by atomic force microscopy profile analysis of the patterned structures confirms the formation of a chemically stable single layer of SMMs. Images based on chemical contrast, obtained by time-of-flight secondary ion mass spectrometry, confirm the patterned structure.  相似文献   
995.
This article deals with the solution structure determination of paramagnetic metalloproteins by NMR spectroscopy. These proteins were believed not to be suitable for NMR investigations for structure determination until a decade ago, but eventually novel experiments and software protocols were developed, with the aim of making the approach suitable for the goal and as user-friendly and safe as possible. In the article, we also give hints for the optimization of experiments with respect to each particular metal ion, with the aim of also providing a handy tool for nonspecialists. Finally, a section is dedicated to the significant progress made on 13C direct detection, which reduces the negative effects of paramagnetism and may constitute a new chapter in the whole field of NMR spectroscopy.  相似文献   
996.
The aim of this paper is to quantify the coupling during phase-locking patterns by using the recurrence plot quantification approach. We found that the percent determinism of the recurrences and the entropy of recurrences--corrected for border effect induced by finite data lenght--succeeded in distinguishing three coupling conditions both in simulation signals and in real data from cardiorespiratory synchronization experiments.  相似文献   
997.
998.
Ion chromatography and colorimetry were used to determine nitrate ion concentration in 76 different pork meat products (salami, mortadella, wurstel, raw and cooked ham and other whole-muscle cooked products) and the results were compared. The comparison revealed that the two techniques yield quantitatively similar results, except in cases where the matrix was so complex that it might have influenced the analytical data. These results are consistent with those obtained by other authors who used UV spectrophotometric detection.
Vergleich zwischen ionenchromatographischer und spektrophotometrischer Methode zur Bestimmung von Nitrat in Fleischwaren
Zusammenfassung Es wurden zwei Analysetechniken, Ionenchromatographie mit konduktimetrischem Detektor und Kolorimetrie, für die Mengenbestimmung des Nitrat-Ions in Fleischerzeugnissen verglichen. Die Ergebnisse der Untersuchungen an 76 verschiedenen Schweinefleischprodukten (Salami, Mortadella, Würstchen, Roh- und Kochschinken und andere gekochte Erzeugnisse mit ganzem Muskel) beweisen, daß die beiden Methoden im allgemeinen sich entsprechende Werte liefern, außer in den Fällen, in denen der komplizierte Charakter der Matrix den Analysewert beeinflussen kann. Die Ergebnisse sind mit denen von Autoren vergleichbar, die mit UV-Detektor gearbeitet haben.
  相似文献   
999.
1000.
In Experiment 1, blindfolded observers judged (a) the distance of pathways felt by hand and (b) the straight-line distance between pathway endpoints inferred from such exploration. In Experiment 2, blindfolded observers made corresponding estimates after traversing similar pathways on foot. Pathways were explored under three different speeds. Under both manipulatory and ambulatory exploration, there was substantial length distortion of inferred distance; the straight-line distance was increasingly overestimated with increases in the length of the explored pathway. With manipulatory exploration, slower movements increased length distortion, but duration effects proved secondary to effects of spatial extent. For ambulatory exploration, no duration effects were obtained. Observers used time-independent heuristics, that is, a footstep metric for estimating the pathway actually travelled and a spatial imaging strategy for estimating the inferred line between pathway endpoints. The studies establish length distortion as a general phenomenon in movement space and identify its major causes as spatial rather than temporal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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