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   479篇
  免费   6篇
  国内免费   1篇
电工技术   12篇
化学工业   93篇
金属工艺   20篇
机械仪表   7篇
建筑科学   8篇
能源动力   12篇
轻工业   20篇
水利工程   1篇
无线电   55篇
一般工业技术   104篇
冶金工业   120篇
原子能技术   27篇
自动化技术   7篇
  2022年   7篇
  2021年   3篇
  2018年   3篇
  2017年   5篇
  2016年   5篇
  2015年   4篇
  2014年   10篇
  2013年   14篇
  2012年   9篇
  2011年   16篇
  2010年   16篇
  2009年   12篇
  2008年   11篇
  2007年   10篇
  2006年   8篇
  2005年   10篇
  2004年   15篇
  2003年   11篇
  2002年   15篇
  2001年   4篇
  2000年   16篇
  1999年   14篇
  1998年   59篇
  1997年   15篇
  1996年   13篇
  1995年   13篇
  1994年   11篇
  1993年   15篇
  1992年   11篇
  1991年   2篇
  1990年   5篇
  1989年   7篇
  1988年   8篇
  1987年   11篇
  1986年   7篇
  1985年   9篇
  1984年   5篇
  1983年   11篇
  1982年   10篇
  1981年   2篇
  1980年   7篇
  1979年   5篇
  1978年   6篇
  1977年   4篇
  1976年   10篇
  1975年   2篇
  1974年   7篇
  1973年   3篇
  1970年   3篇
  1939年   2篇
排序方式: 共有486条查询结果,搜索用时 15 毫秒
41.
Interactions between low-energy ions and solid rare gases have been investigated by observing desorbed ions. When low-energy ions were injected into solid Ne, we found that the kinetic energy of desorbed cluster ions significantly increased with irradiation time for a film thickness of several hundred monolayers. This result can be explained by charge-up (i.e., electronic holes) in the solid Ne. The kinetic energy of the desorbed ions is considered to be proportional to the number of holes created in the solid by the ion impacts. The solid’s temperature effects on the desorbed-ion kinetic energy can be understood as a dependence on the diffusion rate of the holes. The temperature was controlled between 4.7 and 7.0 K. The activation energy of hole-hopping transport is estimated at 0.7 meV based on the slope of Arrhenius plots.  相似文献   
42.
π-Conjugated polymers based on 1-aminopyrrole and 4-amino-1,2,4-triazole were prepared. Pd-catalyzed organometallic polycondensation gave poly(arylene-ethynylene) (PAE)-type π-conjugated polymers consisting of BOC-protected 4-amino-1,2,4-triazole (Taz(BOC)) units (BOC = t-butoxycarbonyl). The number average molecular weights (Mn) were determined to be 5200–19,200 using GPC. An alternating copolymer of Taz(BOC) and bithiophene (Th–Th) units, P(Taz(BOC)-Th-Th)n-Pd, with an Mn of 10,800 was also prepared by Pd-catalyzed organometallic polycondensation. (Taz(BOC)-Th-Th)n-Pd showed a UV–Vis absorption peak at λmax = 425 nm, which is reasonable for a π-conjugated five-membered ring polymer with a coplanar structure. The deprotection of the BOC group of the polymers proceeded at 200 °C; this BOC-deprotection was investigated using a model compound. The optical and electrochemical properties of the π-conjugated polymers are reported.  相似文献   
43.
We recently isolated and characterized the lipopolysaccharide (LPS)-binding protein, BmLBP, from the larval hemolymph of the silkworm Bombyx mori. BmLBP is a pattern recognition molecule that recognizes the lipid A portion of LPS and participates in a cellular defense reaction. This paper describes the cDNA cloning of BmLBP. The deduced amino acid sequence of BmLBP revealed that BmLBP is a novel member of the C-type lectin superfamily with a unique structural feature that consists of two different carbohydrate-recognition domains in tandem, a short and a long form.  相似文献   
44.
High-pressure boiloff experiments in a wide range of bundle powers by using the Two-Phase Flow Test Facility (TPTF) were conducted. Two kinds of boiloff patterns were observed in these experiments. One is the boiloff pattern in a low bundle power, in which the dryout points of rods locate at a certain elevation in the bundle because the mixture level controls the dryout points. The other is the boiloff pattern in a high bundle power, in which the clear mixture level can not be observed and the dryout points of rods locate in a wide range of vertical directions. The vertical scatter of the dryout points is considered to be due to the break of the thin water film on the heater rods under the annular flow pattern.A simple model to predict the slug to annular flow transition in the rod bundle is proposed. In the model, the slug to annular flow transition takes place when the interferences of the water films on the neighboring rods cease. The model appeares to give good predictions of the previous flow transition experiment conducted in a rod bundle. The slug-annular transition below the dryout points was predicted with the present model in the high power boiloff experiments of TPTF. No slug-annular transition below the dryout points is predicted with the present model in the low power boiloff experiments.  相似文献   
45.
Fifty-five samples of pus were collected from 51 acute, non-perforated, two spontaneously ruptured and two recurrent peritonsillar abscesses (35 males and 18 females; median age 18 years) and analysed regarding (i) aerobic and anaerobic bacteria (standard culturing), (ii) morphology of bacteria and inflammatory cells (direct microscopy of acridine orange-stained material), and (iii) the percentage of bacteria coated with immunoglobulins IgG, secretory IgA (SIgA) and IgM and complement cleavage product C3b (immunofluorescence assay). Seventy-one per cent of the abscesses harboured a mixed bacterial flora of various aerobes and anaerobes. In none of the cases with a single bacterial species (27 per cent) could immunoglobulin- or complement-coated bacteria be found. In abscesses with a mixed flora, 18 per cent harboured IgG-coated, 15 per cent SIgA-coated, five per cent IgM-coated and five per cent C3b-coated bacteria, respectively. All pus samples contained inflammatory cells in abundance but they were mostly deformed and only occasionally could intracellular bacteria be recognized. Insufficient immunoglobulin-coating of bacteria might be an important aetiopathogenic factor in the development of a peritonsillar abscess. Bactericide in the abscesses is accomplished chiefly by protective mechanisms not dependent on antigen recognition by antibodies.  相似文献   
46.
1. The effects of secreted forms of beta-amyloid-precursor proteins (APP(S)s) on the intracellular Ca2+ concentration ([Ca2+]i) were investigated in rat cultured hippocampal neurones. APP695S, a secretory form of APP695, attenuated the increase in [Ca2+]i evoked by glutamate. In addition, APP695S itself evoked an increase in [Ca2+]i in 1 or 2 day-cultured hippocampal cells, but not in 7 to 13 day-cultured cells. 2. Eighty-one percent of neurones which were immunocytochemically positive for microtubule-associated protein 2 responded to APP695S with an increase in [Ca2+]i. 3. APP695S induced a transient rise in [Ca2+]i even in the absence of extracellular Ca2+ and produced an elevation in inositol-1,4,5-trisphosphate (IP3) in a concentration-dependent manner from 100 to 500 ng ml(-1). In the presence of extracellular Ca2+, APP695S caused a transient rise in [Ca2+]i followed by a sustained phase at high [Ca2+]i, suggesting Ca2+ entry from the extracellular space. 4. The [Ca2+]i elevation was mimicked by amino terminal peptides of APPs, but not by carboxy terminal peptides. 5. These results taken together suggest that APP695S induces an increase in [Ca2+]i in hippocampal neurones through an IP3-dependent mechanism that changes according to the stage of development.  相似文献   
47.
A flat-plate concentrator (FPC) module has been proposed and developed for cost reduction of PV modules. The FPC has V-grooved rear reflectors on spaces between adjacent cells. To find appropriate design parameters, yearly optical performance is simulated by using meteorological data and introducing a performance index. As a result of the simulation, it is shown that the FPC module can reduce occupation area of solar cells to 75% compared with that of a conventional module, although its module area increases to 1.16 times. Several prototypes are fabricated and measured under a solar simulator. The measured results are somewhat lower than the simulated ones, but generally show the validity of the simulation.  相似文献   
48.
A broad smooth supercontinuum has been generated at long wavelengths in a highly-nonlinear bismuth silicate fibre pumping near the zero-dispersion wavelength of the cladding glass.  相似文献   
49.
In order to evaluate the effects of the degree of unsaturation of triacylglycerols on cholesterol oxidation, mixtures of purified sardine oil triacylglycerols (iodine value, IV=182.6) and cholesterol; of partially hydrogenated sardine oil triacylglycerols (IV=174.5) and cholesterol; and of fully hydrogenated sardine oil triacylglycerols (IV=92.0) and cholesterol were incubated at 25°C in the dark. The oxidative stability of the samples decreased with increasing degree of unsaturation of the triacylglycerols in the sample mixtures; the induction period for peroxide values (PV) of the sardine oil triacylglycerols and cholesterol was shorter than that of the partially hydrogenated sardine oil triacylglycerols and cholesterol. Certain polyunsaturated fatty acids (PUFAs) in the constituent fatty acids of sardine oil triacylglycerols started to decrease after a shorter induction period compared with that of the partially hydrogenated triacylglycerols. The prominent cholesterol oxides accumulated in the samples were 7β-hydroxycholesterol, 7-ketocholesterol, β-epoxide and cholestane triol. The tendency for accumulation of cholesterol oxides in the time course coincided with the changes in PV as well as the decrease in PUFAs. Cholesterol was oxidized in conjunction with autoxidation of coexisting fish oil triacylglycerols. Although lowering the degree of unsaturation of fish oil triacylglycerols was effective in prolonging the induction period of cholesterol oxidation, the rate of cholesterol oxidation in the cholesterol oxides' formation phase after the induction period was not affected by the difference in the proportion of highly unsaturated fatty acids in the natural and partially hydrogenated triacylglycerols of fish oils.  相似文献   
50.
A light-trapping type concentrator module with a new asymmetric V-groove structure at the rear surface is proposed to improve the performance of static concentrator module. Fundamental optical properties of various asymmetric V-grooves are calculated using a ray-tracing method. Based on these results, yearly integrated irradiance ratios of the concentrator module to a conventional flat-plate module are calculated using meteorological data. By the use of Ag as a reflection material, yearly integrated irradiance ratio of concentrator module with an asymmetric V-groove is 1.34, and the occupation area of Si cells in a module can be reduced to 74% compared with a conventional flat-plate module.  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