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   3534篇
  免费   94篇
  国内免费   2篇
电工技术   55篇
综合类   3篇
化学工业   680篇
金属工艺   76篇
机械仪表   53篇
建筑科学   131篇
矿业工程   21篇
能源动力   78篇
轻工业   297篇
水利工程   23篇
石油天然气   2篇
无线电   386篇
一般工业技术   546篇
冶金工业   939篇
原子能技术   59篇
自动化技术   281篇
  2023年   23篇
  2022年   32篇
  2021年   44篇
  2020年   28篇
  2019年   43篇
  2018年   46篇
  2017年   43篇
  2016年   58篇
  2015年   64篇
  2014年   58篇
  2013年   126篇
  2012年   93篇
  2011年   142篇
  2010年   85篇
  2009年   110篇
  2008年   133篇
  2007年   90篇
  2006年   92篇
  2005年   71篇
  2004年   73篇
  2003年   78篇
  2002年   83篇
  2001年   75篇
  2000年   73篇
  1999年   80篇
  1998年   270篇
  1997年   189篇
  1996年   124篇
  1995年   102篇
  1994年   91篇
  1993年   91篇
  1992年   58篇
  1991年   76篇
  1990年   53篇
  1989年   54篇
  1988年   50篇
  1987年   43篇
  1986年   35篇
  1985年   55篇
  1984年   44篇
  1983年   34篇
  1982年   25篇
  1981年   27篇
  1980年   35篇
  1979年   24篇
  1978年   21篇
  1977年   36篇
  1976年   63篇
  1975年   24篇
  1972年   23篇
排序方式: 共有3630条查询结果,搜索用时 14 毫秒
61.
Quasi-flat zones are morphological operators which segment the image into homogeneous regions according to certain criteria. They are used as an image simplification tool or an image segmentation pre-processing, but they induced a very important oversegmentation. Several filtering methods have been proposed to deal with this issue but they suffer from different drawbacks, e.g., loss of quality or edge deformation. In this article, we propose a new method based on existing approaches which achieves better or similar results than existing approaches, does not suffer from their drawbacks and requires less computation time. It consists of two successive steps. First, small quasi-flat zones are removed according to a minimal area threshold. They are then filled through the growth of remaining zones.  相似文献   
62.
Measurement techniques for conducted HPEM signals   总被引:2,自引:0,他引:2  
High-power electromagnetic (HPEM) signals are a serious threat for modern electronic systems. Intentionally generated electromagnetic interferences might cause upsets or permanent defects in electronics, particularly in the electronics' interface. There are numerous military and especially civil targets, which might be interesting for criminals or terrorists to interfere. Therefore, there is a need to characterize the overall problem by means of simulations and measurements. This paper discusses measurement procedures for conducted HPEM signals. The measurement of transmission line coupled HPEM signals with a steepness in the order of 10-10E14 V/s is a very challenging task. This paper discusses the state of the art in electromagnetic pulse measurements with a focus on conducted ultra wide band and RPEM signals respectively.  相似文献   
63.
A method is presented for the identification of system states near system failure before its occurrence, from observations of component states. State vectors of components are classified into finite system states, based on two measures of the distance from system failure; the logical distance and the probabilistic distance. The method first obtains the Boolean function representing the structural relation between component states and system states classified by the logical distance and then computes the probabilistic distance of the current state vector from system failure.  相似文献   
64.
An efficient scalable 1.06-μm continuous-wave (CW) Nd:YAG slab laser longitudinally pumped by diode lasers is discussed. The 809-nm diode radiation is focused into every laser channel emerging from the reflection points of the 1.06-μm beam on the coated slab surfaces. A maximum CW TEM00 output power of 675 mW has been obtained at a diode pump power of 2 W resulting in a slope efficiency of 40%  相似文献   
65.
Attaching a tire pressure monitoring system (TPMS) on the inner liner of a tire allows sensing of important additional technical parameters, such as vehicle load or tire wearout. The maximum weight of the sensor is limited to 5 grams including package, power supply, and antenna. Robustness is required against extreme levels of acceleration. The node size is limited to about 1 cm3 to avoid high force-gradients due to device-deformation and finally, a long power supply lifetime must be achieved. In this paper a low-power FSK transceiver is presented. Exploiting BAW resonators the use of a bulky and shock-sensitive crystal and a PLL can be avoided. This makes the system more robust and radically reduces the start-up time to 2 ?s from few ms as in state-of-the-art crystal oscillator based systems. The current consumption of the transceiver is 6 mA in transmit mode with a transmit output power of 1 dBm and 8 mA in receive mode with a sensitivity of -90 dBm at a data rate of 50 kBit/s and a bit error rate of 10-2. The transceiver ASIC and a microcontroller ASIC, a MEMS sensor, and a BAW die are arranged in a 3-D chip stack for best compactness, lowest volume, and highest robustness. The sensor node allows sensing of pressure, acceleration, supply voltage and temperature.  相似文献   
66.
Microcavity arrays represent millions of different reaction compartments to screen, for example, molecular interactions, exogenous factors for cells or enzymatic activity. A novel method is presented to selectively synthesize different compounds in arrays of microcavities with up to 1 000 000 cavities per cm2. In this approach, polymer microparticles with embedded pre‐activated monomers are selectively transferred into microcavities with laser radiation. After particle patterning, heating of the particle matrix simultaneously leads to diffusion and coupling of the monomers inside each microcavity separately. This method exhibits flexibility, not only in the choice of compounds, but also in the choice of particle matrix material, which determines the chemical reaction environment. The laser‐assisted selective functionalization of microcavities can be easily combined with the intensively growing number of laser applications for patterning of molecules and cells, which is useful for the development of novel biological assays.  相似文献   
67.
68.
Metabolite identification is of central importance to metabolomics as it provides the route to new knowledge. Automated identification of the thousands of peaks detected by high resolution mass spectrometry is currently not possible, largely due to the finite mass accuracy of the spectrometer and the complexity that one peak can be assigned to one or more empirical formula(e) and each formula maps to one or more metabolites. Biological samples are not, however, composed of random metabolite mixtures, but instead comprise of thousands of compounds related through specific chemical transformations. Here we evaluate if prior biological knowledge of these transformations can improve metabolite identification accuracy.Our identification algorithm - which uses metabolite interconnectivity from the KEGG database to putatively identify metabolites by name - is based on mapping an experimentally-derived empirical formula difference for a pair of peaks to a known empirical formula difference between substrate-product pairs derived from KEGG, termed transformation mapping (TM). To maximize identification accuracy, we also developed a novel semi-automated method to calculate a mass error surface associated with experimental peak-pair differences. The TM algorithm with mass error surface has been extensively validated using simulated and experimental datasets by calculating false positive and false negative rates of metabolite identification. Compared to the traditional identification method of database searching accurate masses on a single-peak-by-peak basis, the TM algorithm reduces the false positive rate of identification by > 4-fold, while maintaining a minimal false negative rate. The mass error surface, putative identification of metabolite names, and calculation of false positive and false negative rates collectively advance and improve upon related previous research on this topic [1, 2]. We conclude that inclusion of prior biological knowledge in the form of metabolic pathways provides one route to more accurate metabolite identification.  相似文献   
69.
Some Lactobacillus delbrueckii ssp. bulgaricus strains are able to synthesize exopolysaccharides (EPS) and are therefore highly important for the dairy industry as starter cultures. The aim of this study was to investigate the nutritional requirements for growth and EPS production of Lactobacillus delbrueckii ssp. bulgaricus DSM 20081. A medium was developed from a semi-defined medium (SDM) in which glucose was replaced by lactose and different combinations of supplements (nucleobases, vitamins, salts, sodium formate and orotic acid) were added. Constant pH batch fermentation with the modified medium resulted in an EPS yield of approximately 210 mg glucose equivalents per liter medium. This was a 10-fold increase over flask cultivation of this strain in SDM. Although not affecting cell growth, the mixture of salts enhanced the EPS synthesis. Whereas EPS production was approximately 12 mg/g dry biomass without salt supplementation, a significantly higher yield (approximately 20 mg/g dry biomass) was observed after adding the salt mixture. In continuous fermentation, a maximal EPS concentration was obtained at a dilution rate of 0.31/h (80 mg EPS/L), which corresponded to a specific EPS production of 49 mg/g dry biomass.  相似文献   
70.
The chemical factors influencing iron solubility (soluble iron/total iron) were investigated in source emission (e.g., biomass burning, coal fly ash, mineral dust, and mobile exhaust) and ambient (Atlanta, GA) fine particles (PM2.5). Chemical properties (speciation and mixing state) of iron-containing particles were characterized using X-ray absorption near edge structure (XANES) spectroscopy and micro-X-ray fluorescence measurements. Bulk iron solubility (soluble iron/total iron) of the samples was quantified by leaching experiments. Major differences were observed in iron solubility in source emission samples, ranging from low solubility (<1%, mineral dust and coal fly ash) up to 75% (mobile exhaust and biomass burning emissions). Differences in iron solubility did not correspond to silicon content or Fe(II) content. However, source emission and ambient samples with high iron solubility corresponded to the sulfur content observed in single particles. A similar correspondence between bulk iron solubility and bulk sulfate content in a series of Atlanta PM2.5 fine particle samples (N = 358) further supported this trend. In addition, results of linear combination fitting experiments show the presence of iron sulfates in several high iron solubility source emission and ambient PM2.5 samples. These results suggest that the sulfate content (related to the presence of iron sulfates and/or acid-processing mechanisms by H(2)SO(4)) of iron-containing particles is an important proxy for iron solubility.  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