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   712篇
  免费   42篇
电工技术   13篇
综合类   3篇
化学工业   126篇
金属工艺   8篇
机械仪表   8篇
建筑科学   14篇
矿业工程   2篇
能源动力   12篇
轻工业   106篇
水利工程   3篇
石油天然气   3篇
无线电   39篇
一般工业技术   91篇
冶金工业   213篇
原子能技术   8篇
自动化技术   105篇
  2023年   8篇
  2022年   5篇
  2021年   14篇
  2020年   18篇
  2019年   10篇
  2018年   31篇
  2017年   25篇
  2016年   31篇
  2015年   31篇
  2014年   28篇
  2013年   45篇
  2012年   32篇
  2011年   31篇
  2010年   24篇
  2009年   25篇
  2008年   25篇
  2007年   26篇
  2006年   14篇
  2005年   12篇
  2004年   13篇
  2003年   7篇
  2002年   13篇
  2001年   12篇
  1999年   10篇
  1998年   80篇
  1997年   46篇
  1996年   27篇
  1995年   19篇
  1994年   14篇
  1993年   17篇
  1992年   6篇
  1991年   5篇
  1990年   7篇
  1988年   4篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   3篇
  1981年   3篇
  1979年   1篇
  1977年   8篇
  1976年   6篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1966年   1篇
排序方式: 共有754条查询结果,搜索用时 470 毫秒
61.
Although asthma and chronic obstructive pulmonary disease COPD represent the two most common chronic respiratory diseases worldwide, the mechanisms underlying their pathobiology need to be further elucidated. Presently, differentiation of asthma and COPD are largely based on clinical and lung function parameters. However, the complexity of these multifactorial diseases may lead to misclassification and to inappropriate management strategies. Recently, tremendous progress in MS has extended the sensitivity, accuracy, and speed of analysis, enabling the identification of thousands of proteins per experiment. Beyond identification, MS has also greatly implemented quantitation issues allowing to assess qualitative–quantitative differences in protein profiles of different samples, in particular diseased versus normal. Herein, we provide a summary of recent proteomics-based investigations in the field of asthma/COPD, highlighting major issues related to sampling and processing procedures for proteomic analyses of specific airway and parenchymal specimens (induced sputum, exhaled breath condensate, epithelial lining fluid, bronchoalveolar and nasal lavage fluid), as well as blood-derived specimen (plasma and serum). Within such a context, together with current difficulties and limitations mainly due to lack of general standardization in preanalytical sampling procedure, our discussion will focus on the challenges and possible benefits of proteomic studies in phenotypic stratification of asthma and COPD.  相似文献   
62.
The surface urban heat island (SUHI) effect is defined as the increased surface temperatures in urban areas in contrast to cooler surrounding rural areas. In this article, the evaluation of the SUHI effect in the city of Madrid (Spain) from thermal infrared (TIR) remote-sensing data is presented. The data were obtained from the framework of the Dual-use European Security IR Experiment (DESIREX) campaign that was carried out during June and July 2008 in Madrid. The campaign combined the collection of airborne hyperspectral and in situ measurements. Thirty spectral and spatial high-resolution images were acquired with the Airborne Hyperspectral Scanner (AHS) sensor in a 11, 21, and 4 h UTC scheme. The imagery was used to retrieve the SUHI effect by applying the temperature and emissivity separation (TES) algorithm. The results show a nocturnal SUHI effect with a highest value of 5 K. This maximum value agrees within 1 K with the highest value of the urban heat island (UHI) observed using air temperature data (AT). During the daytime, this situation is reversed and the city becomes a negative heat island.  相似文献   
63.
Canopy temperature retrieval was one of the purposes during the Solar Induced FLuorescence EXperiment (SIFLEX‐2002) of the European Space Agency, carried out in a Finnish boreal forest. In this work, we describe the strategy used to determine this temperature from ground thermal infrared (TIR) data under skies with variable cloud cover. TIR radiance was measured by a CIMEL Electronique CE 312 radiometer. An analysis of the radiative transfer equation showed which terms were necessary to obtain accurate surface temperatures during the campaign. Atmospheric correction was considered negligible due to the small atmospheric path, but hemispheric downwelling sky radiance determination was needed for the emissivity correction. Since most days during the campaign the sky showed partial cloudiness, a methodology to estimate this last term was proposed, using continuous information of cloudiness amount and cloud height given by a weather station. These thermal data were used to analyse some correlations between canopy and air temperatures and plant‐activity‐related variables in the context of the SIFLEX‐2002 campaign.  相似文献   
64.
Thin zinc oxide films were deposited potentiostatically from zinc nitrate aqueous solutions on ITO substrates. The influence of experimental parameters (temperature, electrolyte concentration, deposition potential) on structure and morphology of films was investigated. Deposited films were generally polycrystalline in structure, even if growth according to preferential planes occurs in certain conditions. The effect of thermal treatments in air at 150 and 350 °C was also studied. In some cases, Cl species were incorporated into deposit by adding zinc chloride to the electrolyte. A photoelectrochemical investigation, performed in neutral solution before and after thermal treatment, gives more information on film structure and reveals improvement of n-type semiconducting properties after annealing, suggesting diminution of defects and traps originated from the disordered regions of the oxide. In fact, after thermal treatment, the optical gap of the films decreases towards the value reported for the crystalline oxide. No apparent benefits in the semiconducting properties of the films were observed after incorporation of Cl species into the films.  相似文献   
65.
We propose and study nonlinear mathematical models describing the intracellular time dynamics of viral RNA accumulation for positive-sense single-stranded RNA viruses. Our models consider different replication modes ranging between two extremes represented by the geometric replication (GR) and the linear stamping machine replication (SMR). We first analyse a model that quantitatively reproduced experimental data for the accumulation dynamics of both polarities of turnip mosaic potyvirus RNAs. We identify a non-degenerate transcritical bifurcation governing the extinction of both strands depending on three key parameters: the mode of replication (α), the replication rate (r) and the degradation rate (δ) of viral strands. Our results indicate that the bifurcation associated with α generically takes place when the replication mode is closer to the SMR, thus suggesting that GR may provide viral strands with an increased robustness against degradation. This transcritical bifurcation, which is responsible for the switching from an active to an absorbing regime, suggests a smooth (i.e. second-order), absorbing-state phase transition. Finally, we also analyse a simplified model that only incorporates asymmetry in replication tied to differential replication modes.  相似文献   
66.
67.
The aim of the present paper is to investigate the feasibility of bio-ethanol production by batch fermentation of ricotta cheese whey (“Scotta”), a dairy industry waste characterized by lactose concentration ranging from 4.5% to 5.0% (w/w) and, with respect to traditional (raw) whey, by much lower protein content. Scotta, therefore, could represent an effective non-vegetable source for renewable energy production. The microrganism used to carry out the fermentation processes was the yeast Kluyveromyces marxianus. Preliminary experiments, performed in aerobic conditions on different volumes of scotta, have shown the actual growth of the yeast. The subsequent fermentation experiments were carried out, in anaerobic conditions, on three different substrates: scotta, raw cheese whey and deproteinized whey. The experimental data have demonstrated the process feasibility: scotta is an excellent substrate for fermentation and exhibits better performance with respect to both raw cheese whey and deproteinized whey. Complete lactose consumption, indeed, was observed in the shortest time (13 h) and with the highest ethanol yield (97% of the theoretical value).  相似文献   
68.
Current technological possibilities for implementing multi-service networks include both single technology ATM or IP networks and multi-technology networks such as SONET-based or flat networks. However, regardless of the technology employed, the synthesis problem – to optimally route traffic and divide the network's transmission resources between its virtual links – remains of prime importance.In this paper, we review, compare, and classify the extensive recent literature concerning multi-service network synthesis methods. In order to do this, we propose a typology based on switching and control strategies and a general notation that reflects the layered nature of the network. Technology independent mathematical models describe the various, essentially different, approaches presently found in the literature.  相似文献   
69.
The present work re-examines the assumptions that are required for a steady-state charge distribution analysis to be valid. First, the common approximation that there are only 11 charge states available to the distribution is relaxed to allow for 201 charge states to be available to the particle distribution. This is found to have large repercussions on the behavior of the distribution for radii greater than 0.5 μm. The steady-state assumption itself is then re-examined by calculating the time required to reach steady state for many different ion-pair production rates and initial particle charge states as a function of radius. In the steady-state model, the ion populations are often assumed to decouple completely from the aerosol; this is shown to be false throughout the troposphere. Finally, the number of positive and negative charge states needed to accurately model a particle population of a given size is determined.

© 2013 American Association for Aerosol Research  相似文献   
70.
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