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   837篇
  免费   0篇
  国内免费   1篇
电工技术   1篇
综合类   6篇
化学工业   78篇
金属工艺   3篇
机械仪表   29篇
建筑科学   65篇
能源动力   1篇
轻工业   122篇
水利工程   8篇
石油天然气   4篇
无线电   15篇
一般工业技术   464篇
冶金工业   3篇
自动化技术   39篇
  2021年   1篇
  2013年   1篇
  2012年   117篇
  2011年   167篇
  2010年   36篇
  2009年   19篇
  2008年   105篇
  2007年   81篇
  2006年   72篇
  2005年   57篇
  2004年   36篇
  2003年   22篇
  2002年   23篇
  2001年   21篇
  2000年   11篇
  1999年   10篇
  1998年   10篇
  1997年   6篇
  1996年   5篇
  1995年   1篇
  1994年   3篇
  1992年   2篇
  1991年   3篇
  1990年   4篇
  1989年   7篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   4篇
  1982年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1973年   1篇
  1967年   1篇
  1966年   1篇
排序方式: 共有838条查询结果,搜索用时 15 毫秒
21.
Caffeic acid (CA), a natural phenolic compound, is abundant in medicinal plants. CA possesses multiple biological effects such as anti-bacterial and anti-cancer growth. CA was also reported to induce fore stomach and kidney tumors in a mouse model. Here we used two human lung cancer cell lines, A549 and H1299, to clarify the role of CA in cancer cell proliferation. The growth assay showed that CA moderately promoted the proliferation of the lung cancer cells. Furthermore, pre-treatment of CA rescues the proliferation inhibition induced by a sub-IC(50) dose of paclitaxel (PTX), an anticancer drug. Western blot showed that CA up-regulated the pro-survival proteins survivin and Bcl-2, the down-stream targets of NF-κB. This is consistent with the observation that CA induced nuclear translocation of NF-κB p65. Our study suggested that the pro-survival effect of CA on PTX-treated lung cancer cells is mediated through a NF-κB signaling pathway. This may provide mechanistic insights into the chemoresistance of cancer calls.  相似文献   
22.
Chitin is an abundant biopolymer composed of units of N-acetyl-D-glucosamine linked by β-1,4 glycosidic bonds. Chitin is the main component of the shells of mollusks, the cell wall of fungi and yeast and of the exoskeleton of crustaceans and insects. The degradation of chitin is catalyzed by chitinases that occur in a wide range of organisms. Among them, the chitinases from microorganisms are extremely important for the degradation and recycling of the carbon and nitrogen trapped in the large amount of insoluble chitin in nature. Streptomyces sp. TH-11 was isolated from the sediment of the Tou-Chien River, Taiwan. The chitinolytic enzyme activities were detected using a rapid in-gel detection method from the cell-free preparation of the culture medium of TH-11. The chitinolytic enzyme activity during prolonged liquid culturing was also analyzed by direct measurement of the chitin consumption. Decomposition of the exoskeleton of shrimps was demonstrated using electron microscopy and atomic force microscopy.  相似文献   
23.
A method to map the specific site on dengue virus envelope protein (E) that interacts with cells and a neutralizing antibody is developed using serially truncated dengue virus type 2 (DENV-2) E displayed on M13 phages as recombinant E-g3p fusion proteins. Recombinant phages displaying the truncated E consisting of amino acids 297-423 (EB2) and amino acids 379-423 (EB4) were neutralized by DENV-2 patient sera and the DENV-2 E-specific 3H5-1 monoclonal antibodies suggesting that the phages retained the DENV-2 E antigenic properties. The EB4 followed by EB2 recombinant phages bound the most to human monocytes (THP-1), African green monkey kidney (Vero) cells, mosquito (C6/36) cells, ScFv specific against E and C6/36 cell proteins. Two potential cell attachment sites were mapped to loop I (amino acids 297 to 312) and loop II (amino acids 379-385) of the DENV-2 E using the phage-displayed truncated DENV-2 E fragments and by the analysis of the E structure. Loop II was present only in EB4 recombinant phages. There was no competition for binding to C6/36 cell proteins between EB2 and EB4 phages. Loop I and loop II are similar to the sub-complex specific and type-specific neutralizing monoclonal antibody binding sites, respectively. Hence, it is proposed that binding and entry of DENV involves the interaction of loop I to cell surface glycosaminoglycan-motif and a subsequent highly specific interaction involving loop II with other cell proteins. The phage displayed truncated DENV-2 E is a powerful and useful method for the direct determination of DENV-2 E cell binding sites.  相似文献   
24.
NIOSH Method 7903 employs a silica gel tube for sulfuric acid mist measurement in workplaces. However, SO2 gas present in the sample volume can be transformed into sulfate in the sampling process causing an artifact that is reported as sulfuric acid. A sampling train incorporating a honeycomb denuder system was applied for field sampling at seven phosphate fertilizer plants to evaluate its use for reducing the artifact sulfate concentration while preserving the actual sulfuric acid mist concentration. The denuder system was designed to remove SO2 gas before the air entered the silica gel tube and to monitor SO2 concentration at the same time. A deactivation model was also applied to correct for the presence of the artifact. The denuder system had 95.7 +/- 6.8% collection efficiency for SO2 gas, and the impact of sulfate aerosol on SO2 collection was negligible. SO2 concentrations at the seven plants ranged from 34 ppb to 5.6 ppm. The honeycomb denuder system and the deactivation model were shown to reduce the artifact sulfate concentration by 70% and 39%, respectively. However, they were still higher than the sulfate aerosol concentration measured by a cascade impactor. One possible reason is the residual sulfate in the glass fiber filter and the silica gel.  相似文献   
25.
Methylene blue (MB) is a cationic dyestuff, which is particularly resistant to biodegradation. The molecular sieved gamma-MnO2 was used as an adsorbent/oxidant to remove the MB at room temperature and in visible light. The removal efficiency was mainly evaluated by X-ray diffractometer (XRD), UV-Vis spectrometer (UV-Vis), total organic carbon (TOC). The results revealed that the mechanisms of MB removal by gamma-MnO2 are significantly influenced by the pH. In acidic conditions, hypsochromic effects (i.e. blue shifts of UV-Vis spectra) resulting from N-demethylation of the dimethylamino group in MB may occur concomitantly with oxidative degradation by gamma-MnO2. However, the TOC in solution after gamma-MnO2 treatment in acidic conditions did not show a dramatic decrease. At near neutral pH conditions, there was almost no UV-Vis absorption for the MB solution, however, only 50% TOC removal was observed. It indicated that MB was not only adsorbed onto gamma-MnO2 but also partially oxidatively degraded to other organic compounds which were colourless for UV-Vis.  相似文献   
26.
Carcass properties and meat quality characteristics of 32 Belgian Blue White double-muscled bulls (DM) were compared with those of 59 bulls of the same breed with normal conformation (N). DM showed superior carcass quality as revealed in increased dressing percentage, meat production yield, conformation grade, muscle/fat and muscle/bone ratios (all P < 0·001). Longissimus dorsi (LD) shear force values, drip and cooking losses at 8 days post mortem (pm) were significantly higher (P < 0·001) for DM, whereas sarcomere lengths were not different. Calpain 1 and calpastatin levels at 1 h and 24 h pm were tremendously decreased in DM as were also cathepsin B and L levels at 1 and 8 days pm (P < 0·001). As evident from semi-quantitative SDS-PAGE, these differences were accompanied by higher titin and lower 30 kDa levels (P < 0·001) in DM. Troponin-t levels were not different, but very low. Intramuscular collagen content was significantly lower in DM (P < 0·001). This suggests that lower background toughness in DM was compensated for by reduced post-mortem proteolytic tenderization. Discrepancy with literature reports regarding tenderness of DM might be related to the extreme muscularity of the Belgian Blue White breed, compared to other DM breeds. The results also suggest that reduced protein turnover might be involved in the muscle hypertrophy phenomenon within this breed, because of likely reduced levels of calpains and cathepsins in living DM animals.  相似文献   
27.
A BNCT (Boron Neutron Capture Therapy) treatment planning system (BTPS) was developed for BNCT study and treatment planning. Three kinds of CT images, VHP, PINNACLE and DICOM images, were employed to make voxel phantoms for BNCT patient treatment using the BTPS. The thermal neutron, fast neutron, gamma and boron doses are calculated and background, tissue, and tumour doses for idealised standard reactor neutron field (ISRNF) neutron beam were calculated by using BTPS and MCNP code. It was noted that the total computing times needed for BNCT analysis could be greatly reduced since the BTPS system provides a dose analysis tool and a lengthy MCNP input in a short time. It is, thus, expected that the BTPS can significantly contribute the BNCT study for the treatment of patients.  相似文献   
28.
Strains representing four types of common heat-resistant spores of Bacillus spp., B. cereus CCRC 14655, B. coagulans CCRC10606, B. licheniformis CCRC14693, and B. subtilis CCRC14199, were heated with microwaves at different power levels and under different conditions in salt solutions, starch solutions, and containers. The results of this study showed that B. licheniformis spores had the highest microwave tolerance at a power level of 100% for different incubation times. B. coagulans spores showed the lowest microwave tolerance in salt solutions with water activity values of 0.6, 0.7, 0.8, and 0.9, and B. licheniformis spores were the most resistant in the tested salt solutions at different incubation times. An analysis of the effect of the viscosity of the medium revealed that the bacteria had the lowest microwave resistance in a medium containing <0.8% starch in solution. The microwave resistance levels of the test microorganisms were the lower in glass containers than in polypropylene containers and aluminum foil-enclosed pouches. Of the four species of bacilli, B. licheniformis had the highest microwave tolerance (P < 0.05) under all conditions.  相似文献   
29.
This study proposes a steady-state visual evoked potential (SSVEP)-based brain-computer interface (BCI) independent of amplitude-frequency and phase calibrations. Six stepping delay flickering sequences (SDFSs) at 32-Hz flickering frequency were used to implement a six-command BCI system. EEG signals recorded from Oz position were first filtered within 29-35 Hz, segmented based on trigger events of SDFSs to obtain SDFS epochs, and then stored separately in epoch registers. An epoch-average process suppressed the inter-SDFS interference. For each detection point, the latest six SDFS epochs in each epoch register were averaged and the normalized power of averaged responses was calculated. The visual target that induced the maximum normalized power was identified as the visual target. Eight subjects were recruited in this study. All subjects were requested to produce the "563241" command sequence four times. The averaged accuracy, command transfer interval, and information transfer rate (mean ± std.) values for all eight subjects were 97.38 ± 5.97%, 3.56 ± 0.68 s, and 42.46 ± 11.17 bits/min, respectively. The proposed system requires no calibration in either the amplitude-frequency characteristic or the reference phase of SSVEP which may provide an efficient and reliable channel for the neuromuscular disabled to communicate with external environments.  相似文献   
30.
Conventional watershed segmentation methods invariably produce over-segmented images due to the presence of noise or local irregularities in the source images. In this paper, a robust medical image segmentation technique is proposed, which combines watershed segmentation and the competitive Hopfield clustering network (CHCN) algorithm to minimize undesirable over-segmentation. In the proposed method, a region merging method is presented, which is based on employing the region adjacency graph (RAG) to improve the quality of watershed segmentation. The relation of inter-region similarities is then investigated using image mapping in the watershed and CHCN images to determine more appropriate region merging. The performance of the proposed technique is presented through quantitative and qualitative validation experiments on benchmark images. Significant and promising segmentation results were achieved on brain phantom simulated data.  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