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   1603篇
  免费   154篇
  国内免费   14篇
电工技术   44篇
综合类   8篇
化学工业   425篇
金属工艺   72篇
机械仪表   62篇
建筑科学   83篇
矿业工程   4篇
能源动力   124篇
轻工业   127篇
水利工程   26篇
石油天然气   17篇
无线电   167篇
一般工业技术   241篇
冶金工业   73篇
原子能技术   16篇
自动化技术   282篇
  2024年   7篇
  2023年   36篇
  2022年   55篇
  2021年   98篇
  2020年   80篇
  2019年   103篇
  2018年   144篇
  2017年   130篇
  2016年   149篇
  2015年   85篇
  2014年   110篇
  2013年   179篇
  2012年   120篇
  2011年   88篇
  2010年   78篇
  2009年   56篇
  2008年   42篇
  2007年   32篇
  2006年   18篇
  2005年   9篇
  2004年   10篇
  2003年   13篇
  2002年   13篇
  2001年   11篇
  2000年   8篇
  1999年   4篇
  1998年   13篇
  1997年   3篇
  1996年   5篇
  1995年   12篇
  1994年   5篇
  1993年   4篇
  1992年   6篇
  1991年   5篇
  1990年   4篇
  1989年   6篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1985年   3篇
  1984年   1篇
  1983年   3篇
  1982年   5篇
  1979年   3篇
  1975年   1篇
  1973年   2篇
  1970年   2篇
  1969年   1篇
排序方式: 共有1771条查询结果,搜索用时 62 毫秒
991.
992.
Achillea millefolium L. comprises several relevant species for the food, cosmetic, perfumery, and pharmaceutical industries. Gas chromatography/mass spectrometry analysis revealed borneol to be a major component of A. millefolium, with its contribution to the essential oil being 36.35%. Borneol exhibited significant lipid peroxidation inhibition and antimicrobial activity against all tested bacterial strains. In addition, borneol had the highest antioxidant activity in all conducted assays. The borneol had significantly greater radical scavenging activity than other component essential oil and the reference antioxidant Trolox. In addition, a correlation between antioxidant activity and the total phenolic content was found. The borneol significantly inhibited nitric oxide production in lipopolysaccharide-activated macrophages (an in vitro model of inflammation). These results clearly show the antimicrobial, antioxidant, and anti-inflammatory effects of the plant essential oils.  相似文献   
993.
Food Science and Biotechnology - The safety of feeding transgenic potato (Solanum tuberosum), resistant to the potato tuber moth, to Wistar rats was examined from an immunological perspective. The...  相似文献   
994.
995.
In the present study the effect of room temperature rolling on microstructure and mechanical properties of a new Cr–Mn austenitic stainless steel (containing 12 %Cr, 23 %Mn and 0.13 %C) and AISI 316 steel was investigated. The specimens of these steels were cold rolled at various thickness reductions of 0, 12, 25, 37 and 50 %. Microstructural investigations were carried out using optical microscopy, magnetic field test and X-ray diffraction technique. Hardness and tensile test methods were also done to evaluate the mechanical properties. Results showed that some of austenite phase transformed to martensite during cold rolling in the 316 steel, while there was no strain induced transformation in the Cr–Mn steel. It was also found that the newly developed steel had higher strength and higher specific strength than those of the 316 steel, while its ductility was the same as that of the 316.  相似文献   
996.
The artificial neural network (ANN) and hybrid of artificial neural network and genetic algorithm (GANN) were applied to predict the optimized conditions of column leaching of copper oxide ore with relations of input and output data. The leaching experiments were performed in three columns with the heights of 2, 4 and 6 m and in particle size of <25.4 and <50.8 mm. The effects of different operating parameters such as column height, particle size, acid flow rate and leaching time were studied to optimize the conditions to achieve the maximum recovery of copper using column leaching in pilot scale. It was found that the recovery increased with increasing the acid flow rate and leaching time and decreasing particle size and column height. The efficiency of GANN and ANN algorithms was compared with each other. The results showed that GANN is more efficient than ANN in predicting copper recovery. The proposed model can be used to predict the Cu recovery with a reasonable error.  相似文献   
997.
In this study, the electrochemical behavior of commercial pure titanium with both coarse-grained (annealed sample with the average grain size of about 45 µm) and nano-grained microstructure was compared by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis. Nano-grained Ti, which typically has a grain size of about 90 nm, is successfully made by six-cycle accumulative roll-bonding process at room temperature. Potentiodynamic polarization plots and impedance measurements revealed that as a result of grain refinement, the passive behavior of the nano-grained sample was improved compared to that of annealed pure Ti in H2SO4 solutions. Mott-Schottky analysis indicated that the passive films behaved as n-type semiconductors in H2SO4 solutions and grain refinement did not change the semiconductor type of passive films. Also, Mott-Schottky analysis showed that the donor densities decreased as the grain size of the samples reduced. Finally, all electrochemical tests showed that the electrochemical behavior of the nano-grained sample was improved compared to that of annealed pure Ti, mainly due to the formation of thicker and less defective oxide film.  相似文献   
998.
The effects of heat-shock pretreatment conditions on the efficiency of dark hydrogen fermentation from glucose were investigated. Anaerobic sludge was pretreated at different temperatures of 70°C, 80°C, and 90°C for different time durations including 7.5, 15, 22.5, 30, 37.5, and 45 min. All pretreatments suppressed the methanogens and no detectable methane was produced after pretreatments. Pretreatments at 90°C led to the higher hydrogen contents than 70°C and 80°C. The pretreatment at 90°C for 37.5 min led to the highest biogas yield, hydrogen yield, and hydrogen production rate of 4.31?mol/mol-glucose, 3.15?mol/mol-glucose, and 70.2?mL/h.g-VS, respectively.  相似文献   
999.
Hydrate formation may be a common occurrence during oil and gas drilling and production operation when temperature of these solid crystalline compounds that formed in the presence of free water decreases at elevated pressure. Also, they have often been found responsible for operating difficulties at wellheads, pipelines and other processing equipment. Nowadays, because of the importance of predicting hydrate formation condition, different accurate methods have been used. Besides the experiential correlations that are common for predicting, the developments in the field of modelling led to the use of different methods in a thermodynamic way. In fact, because of the risk of experimental uncertainties and to remove the need for intricate analytic equations and empirical correlations, the computational intelligence model, which result in the lowest error and based on experimental data, is strongly proposed, in attempts to solve complex industrial problems. In this article, in order to predict gas hydrate formation condition, two smart techniques are established based on feed-forward neural network (artificial neural network (ANN)) which is optimised by imperialist competitive algorithm (ICA). The ICA-ANN model is conducted utilising the empirical data released in the literature and finally the performance of ICA-ANN model is compared with the conventional ANN model. Furthermore, they have been compared with an accurate thermodynamic model at different operating conditions. The outcomes, contrary to expectations, establish that the ICA-ANN model has poor performance when compared with the ANN.  相似文献   
1000.
We have developed a CCD-camera-based nonmydriatic instrument that detects fluorescence from retinal lipofuscin chromophores ("autofluorescence") as a means to indirectly quantify and spatially image the distribution of macular pigment (MP). The lipofuscin fluorescence intensity is reduced at all retinal locations containing MP, since MP has a competing absorption in the blue-green wavelength region. Projecting a large diameter, 488 nm excitation spot onto the retina, centered on the fovea, but extending into the macular periphery, and comparing lipofuscin fluorescence intensities outside and inside the foveal area, it is possible to spatially map out the distribution of MP. Spectrally selective detection of the lipofuscin fluorescence reveals an important wavelength dependence of the obtainable image contrast and deduced MP optical density levels, showing that it is important to block out interfering fluorescence contributions in the detection setup originating from ocular media such as the lens. Measuring 70 healthy human volunteer subjects with no ocular pathologies, we find widely varying spatial extent of MP, distinctly differing distribution patterns of MP, and strongly differing absolute MP levels among individuals. Our population study suggests that MP imaging based on lipofuscin fluorescence is useful as a relatively simple, objective, and quantitative noninvasive optical technique suitable to rapidly screen MP levels and distributions in healthy humans with undilated pupils.  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