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   315篇
  免费   15篇
  国内免费   1篇
电工技术   20篇
化学工业   54篇
金属工艺   2篇
机械仪表   4篇
建筑科学   4篇
矿业工程   1篇
能源动力   15篇
轻工业   24篇
水利工程   2篇
无线电   31篇
一般工业技术   68篇
冶金工业   25篇
原子能技术   2篇
自动化技术   79篇
  2024年   1篇
  2023年   5篇
  2022年   8篇
  2021年   18篇
  2020年   18篇
  2019年   14篇
  2018年   9篇
  2017年   5篇
  2016年   9篇
  2015年   13篇
  2014年   17篇
  2013年   30篇
  2012年   13篇
  2011年   19篇
  2010年   11篇
  2009年   13篇
  2008年   20篇
  2007年   14篇
  2006年   4篇
  2005年   5篇
  2004年   6篇
  2003年   3篇
  2002年   3篇
  2001年   3篇
  2000年   3篇
  1999年   2篇
  1998年   5篇
  1997年   10篇
  1996年   1篇
  1995年   3篇
  1994年   3篇
  1993年   2篇
  1992年   3篇
  1991年   4篇
  1990年   1篇
  1989年   2篇
  1987年   2篇
  1986年   1篇
  1985年   5篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1977年   7篇
  1976年   2篇
  1971年   2篇
  1969年   1篇
排序方式: 共有331条查询结果,搜索用时 317 毫秒
41.
An unsupervised segmentation approach to classification of multispectral image is suggested here in Markov random field (MRF) frame work. This work generalizes the work of Sarkar et al. (2000) on gray value images for multispectral images and is extended for landuse classification. The essence of this approach is based on capturing intrinsic characters of tonal and textural regions of any multispectral image. The approach takes an initially oversegmented image and the original. multispectral image as the input and defines a MRF over region adjacency graph (RAG) of the initially segmented regions. Energy function minimization associated with the MRF is carried out by applying a multivariate statistical test. A cluster validation scheme is outlined after obtaining optimal segmentation. Quantitative evaluation of classification accuracy of test data for three illustrations are shown and compared with conventional maximum likelihood procedure. Comparison of the proposed methodology with a recent work of texture segmentation in the literature has also been provided. The findings of the proposed method are found to be encouraging  相似文献   
42.
Carbonic anhydrase VI (CA VI) is a secreted enzyme produced predominantly by serous acinar cells of submandibular and parotid glands. We have investigated the developmental pattern of CA VI production by these glands in the sheep, from fetal life to adulthood, using immunohistochemistry. Also, a specific radioimmunoassay for CA VI was used to measure changes in enzyme expression in the parotid gland postnatally. CA VI is detectable by immunohistochemistry in parotid excretory ducts from 106 days gestation (term is 145 days), in striated ducts from 138 days and in acinar cells from 1 day postnatal. The duct cell content of CA VI declined as the acinar cell population increased, a feature also of CA VI immunoreactivity in the submandibular gland. Production of CA VI by submandibular duct cells was detectable initially at 125 days gestation, and acinar production was not seen before 29 days post-natal. Apart from the differing ontogeny of CA VI production in ducts and acini of parotid and submandibular glands, there was a parallel pattern of CA VI expression during the development of these major salivary glands. With the development of the acinar tissues in the postnatal lamb, there was a dramatic increase (about 600-fold) in the level of expression of CA VI in the parotid gland between days 7 and 59 as measured by radioimmunoassay.  相似文献   
43.
Microbial fuel cells (MFCs) represent a novel platform for treating wastewater and at the same time generating electricity. Using Pseudomonas putida (BCRC 1059), a wild-type bacterium, we demonstrated that the refinery wastewater could be treated and also generate electric current in an air-cathode chamber over four-batch cycles for 63 cumulative days. Our study indicated that the oil refinery wastewater containing 2213 mg/L (ppm) chemical oxygen demand (COD) could be used as a substrate for electricity generation in the reactor of the MFC. A maximum voltage of 355 mV was obtained with the highest power density of 0.005 mW/cm2 in the third cycle with a maximum current density of 0.015 mA/cm2 in regard to the external resistor of 1000 Ω. A maximum coulombic efficiency of 6 × 10−2% was obtained in the fourth cycle. The removal efficiency of the COD reached 30% as a function of time. Electron transfer mechanism was studied using cyclic voltammetry, which indicated the presence of a soluble electron shuttle in the reactor. Our study demonstrated that oil refinery wastewater could be used as a substrate for electricity generation.  相似文献   
44.
Distinct differences between how model proteins interact in‐cell and in vitro suggest that the cytosol might have a profound effect in modulating protein–protein and/or protein–ligand interactions that are not observed in vitro. Analyses of in‐cell NMR spectra of target proteins interacting with physiological partners are further complicated by low signal‐to‐noise ratios, and the long overexpression times used in protein–protein interaction studies may lead to changes in the in‐cell spectra over the course of the experiment. To unambiguously resolve the principal binding mode between two interacting species against the dynamic cellular background, we analyzed in‐cell spectral data of a target protein over the time course of overexpression of its interacting partner by using single‐value decomposition (SVD). SVD differentiates between concentration‐dependent and concentration‐independent events and identifies the principal binding mode between the two species. The analysis implicates a set of amino acids involved in the specific interaction that differs from previous NMR analyses but is in good agreement with crystallographic data.  相似文献   
45.
An increasing prevalence of hypertension in the world implies the necessity of further study of antihypertensive peptides as an alternative means for hypertension management. The purpose of this study was to evaluate systematically the potential of major food proteins as precursors of ACE inhibitory peptides using QSAR-aided in silico approach, and thus to establish the rationale for choosing the appropriate substrate proteins in preparing ACE inhibitory peptides. In silico digestion of proteins from 15 common food commodities by thermolysin generated 5709 peptides ranging from 2 to 6 amino acid residues. Peptides were divided into three categories based on the potency of their predicted activities. Our results showed that meat proteins from pork, beef and chicken contain the largest number of potent peptides (IC50 < 10 ??M), followed by proteins from milk, egg, soybean and canola, whereas proteins from fish (with the exception of salmon) and cereals (oat and barley) contain the least number of potent peptides. This study demonstrated that proteins from livestock meat, milk, egg, soybean and canola are good sources of ACE inhibitory peptides.  相似文献   
46.
A multistage field emitter based on graphene-linked ZnO nanowire array is realized by means of spin-coating a graphene dispersion (reduced graphene oxide) over a nanostructured platform followed by plasma modification. Spin-coating leads to interlinking of graphene sheets between the neighboring nanowires whereas plasma etching in the subsequent step generates numerous ultra-sharp graphene edges at the nanowire tips. The inherent tendency of graphene to lay flat over a plane substrate can easily be bypassed through the currently presented nanostructure platform based technique. The turn-on and threshold field significantly downshifted compared to the individual components in the cascade emitter. Through the facile electron transfer from nanowires to graphene due to band bending at the ZnO-graphene interface together with multistage geometrical field enhancement at both the nanowire and graphene edges remain behind this enriched field emission from the composite cold cathode. This strategy will open up a new direction to integrate the functionalities of both the graphene array and several other inorganic nanostructure array for practical electronic devices.  相似文献   
47.
Mott has suggested that the ideal creep-resistant material will be one with a fine grain size in which the grain boundaries are filled with some substance, say a refractory oxide, to inhibit the motion of grain boundaries. Such a system, alumina-dispersed copper, was prepared by high rate physical vapour deposition. The process parameters and their effect on structure and texture have been studied. The room temperature mechanical properties have also been reported. This paper deals with a high temperature mechanical property, i.e. tensile creep. Tests were made on a constant-stress vacuum creep rig with a Ferrometic feedthrough to ensure a zero leakage rotary seal. A vacuum of 1.33 X 10?3 Pa was maintained. The test temperatures were 500°C (0.57Tm) and 700°C (0.72Tm). The stresses applied were 2.07, 3.45, 4.14 and 6.89 X 107 Nm?2. Tests were made on as-deposited films and on cold-rolled condensates.Minimum creep rate curves showed the effect of the alumina content in raising the creep resistance of copper. Cold rolling also reduced the minimum creep rate markedly. Varying the temperature and stress affected the shape of these curves. Stress-rupture plots were used to summarize the data.Grain refinement together with a fine stable dispersion seem to give improved creep strength. The critical barrier of the Orowan stress was noted. The stress exponent for a low alumina deposit (0.21 vol.%) was about 8, and the apparent activation energy for creep was about 202 kJ mol?1 (0.13 vol.%). There was an inverse relationship between the rupture life and the minimum creep rate, their product being constant (about 0.2).  相似文献   
48.
An RBS study has been carried out to study the relative extent of Pb diffusion in the substrate from PZT films. It is found that extensive diffusion of Pb occurs into the quartz substrate making the film severely deficient in Pb. No such diffusion occurs in the case of PZT films on sapphire and the concentration of Pb is near stoichiometric, except for a small loss due to volatilization. Excessive Pb deficiency, rather than any epitaxial effect, has earlier been proposed by us to be the crucial factor responsible for the existence of the pyrochlore phase in PZT thin films on substrates such as Si, glass, quartz etc. The present results confirm this. The effects of other process variables such as thickness and chemical composition (Zr/Ti ratio) of the film can also be understood in terms of the same phenomenon.  相似文献   
49.
50.
Approximate locations of axes of symmetry of a 2-dimensional region are detected on the basis of its border. The border, described in terms of certain directional codes, is treated as a regular polygon in a hierarchical manner where a lower level means a greater number of sides. At each level of the hierarchy, the best axis of symmetry is found which for a lower level gives a more accurate position of the unknown axis of symmetry than for a higher level. Along with an axis of symmetry, a certain error is found on the basis of which the degree of symmetry of a 2-dimensional region is defined. Programs are written in FORTRAN IV and are implemented on an EC-1033 computer.  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