全文获取类型
收费全文 | 1758篇 |
免费 | 132篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
综合类 | 1篇 |
化学工业 | 488篇 |
金属工艺 | 61篇 |
机械仪表 | 74篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 63篇 |
轻工业 | 362篇 |
水利工程 | 24篇 |
石油天然气 | 10篇 |
无线电 | 79篇 |
一般工业技术 | 316篇 |
冶金工业 | 131篇 |
原子能技术 | 40篇 |
自动化技术 | 176篇 |
出版年
2024年 | 7篇 |
2023年 | 25篇 |
2022年 | 78篇 |
2021年 | 90篇 |
2020年 | 59篇 |
2019年 | 88篇 |
2018年 | 78篇 |
2017年 | 69篇 |
2016年 | 75篇 |
2015年 | 61篇 |
2014年 | 92篇 |
2013年 | 113篇 |
2012年 | 119篇 |
2011年 | 133篇 |
2010年 | 115篇 |
2009年 | 105篇 |
2008年 | 81篇 |
2007年 | 77篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 34篇 |
2003年 | 31篇 |
2002年 | 31篇 |
2001年 | 24篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 38篇 |
1997年 | 32篇 |
1996年 | 28篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1892条查询结果,搜索用时 15 毫秒
101.
Gisele Atsuko Medeiros Hirata André Bernardo Everson Alves Miranda 《Powder Technology》2010,197(1-2):54-57
Recent studies on the use of volatile electrolytes such as CO2 in protein precipitation showed that these agents are a promising alternative to the conventional acids. This use of volatile electrolytes prevents protein denaturation due to local pH extremes, and saline effluent generation is greatly reduced, as the volatile electrolyte may be separated and recovered from solution just by pressure release. In this work, insulin was successfully crystallized in the presence of zinc using CO2 as acidifying agent. The crystals obtained were rhombohedral, a common shape for porcine insulin crystals that contain zinc in their structure, and their average size varied with the mixing applied. 相似文献
102.
Maria do Socorro M. Rufino Jara Pérez‐Jiménez María Tabernero Ricardo E. Alves Edy S. De Brito Fulgencio Saura‐Calixto 《International Journal of Food Science & Technology》2010,45(11):2227-2233
Several tropical fruits have been described as natural sources of dietary fibre (DF) and phenolic compounds, associated with different health effects. The aim of this work was to ascertain the DF, phenolic compounds content (including non‐extractable polyphenols, mostly associated with DF) and antioxidant capacity in acerola fruits and cashew apples from selected clones. ‘BRS 236’ acerola fruits presented a high antioxidant capacity because of the combination of both extractable polyphenols and l ‐ascorbic acid (providing together a Folin value of 170 kg?1 g d.m.). ‘CCP 76’ cashew apples contained 28 g kg?1 d.m. of extractable polyphenols and 13 g kg?1 d.m. of ascorbic acid as well as a high amount of non‐extractable condensed tannins (52 g kg?1 d.m.). DF content was of 260 g kg?1 d.m. in acerola fruit and of 209 g kg?1 d.m. in cashew apple. Acerola fruits and cashew apple should therefore be considered as new natural sources of DF and phenolic compounds. 相似文献
103.
N. O. Ardiaca S. P. Bressa J. A. Alves O. M. Martínez G. F. Barreto 《Catalysis Today》2001,64(3-4):205-215
A study of the liquid-phase hydrogenation of 1,3-butadiene on commercial Pd/Al2O3 catalysts of the “egg-shell” type has been performed. Experimental conditions (40°C, 4 atm and high conversion of the di-olefin) were selected in accordance to industrial operating conditions employed for selective hydrogenation of 1,3-butadiene. Three experimental schemes were tested: a slurry reactor, a rotating-basket reactor, and a recirculation system with an external fixed-bed reactor. Significant drawbacks shown by the two former devices were mainly derived from the very high activity and the egg-shell structure of the catalysts. Instead, the recirculation system was found to be an excellent alternative.
Although Pd is present only within a very thin external layer (around 50–250 μm), strong diffusion effects impairing selectivity were observed. Plausible kinetic expressions corresponding to nine series–parallel overall reactions are derived from a mechanistic model. To deal with this network of fast reactions, a rather complex set of computational and predictive tools were employed. A worked out example from several replicates demonstrates the capability of both, experimental and data analysis procedures, for inferring kinetic parameters of the proposed model. 相似文献
104.
The damage microstructure and optical properties of sapphire implanted with boron, nitrogen and iron were examined by RBS-C, TEM, and optical absorption. Implantations were conducted at RT and 1000 °C at 150 keV and fluences of 3 × 1016-1 × 1017 ions/cm2. Optical absorption measurements indicate that the boron-implanted samples contained the highest number of F-type centers and the nitrogen-implanted samples the fewest. The microstructure of the boron-implanted samples shows only ‘black-spot’ defect clusters, as did the iron-implanted samples at the lower fluences. At higher fluences, the iron implanted samples revealed the presence of nanometer-sized precipitates of single crystal bcc iron that contributed to additional optical scattering. Bubbles formed in samples implanted with low fluences of nitrogen. A second damage region is apparent in the RBS-C patterns for higher fluences of nitrogen. 相似文献
105.
Claudia Valéria Távora Cabral Antônia Sônia Alves C. Diniz Olga Moraes Toledo 《Solar Energy》2010,84(9):1628-1636
Photovoltaic systems utilize solar energy to generate electrical energy to meet load demands. Optimal sizing of these systems includes the characterization of solar radiation. Solar radiation at the Earth’s surface has random characteristics and has been the focus of various academic studies. The objective of this study was to stochastically analyze parameters involved in the sizing of photovoltaic generators and develop a methodology for sizing of stand-alone photovoltaic systems. Energy storage for isolated systems and solar radiation were analyzed stochastically due to their random behavior. For the development of the methodology proposed stochastic analysis were studied including the Markov chain and beta probability density function. The obtained results were compared with those for sizing of stand-alone using from the Sandia method (deterministic), in which the stochastic model presented more reliable values. Both models present advantages and disadvantages, however, the stochastic one is more complex and provides more reliable and realistic results. 相似文献
106.
S.M.C. MirandaM. Peres T. MonteiroE. Alves H.D. SunT. Geruschke R. ViandenK. Lorenz 《Optical Materials》2011,33(7):1139-1142
Zinc oxide epilayers grown by metal organic vapour phase epitaxy on (0 0 0 1) sapphire substrates were doped with Praseodymium and Europium by ion implantation. The as-implanted samples were either annealed in air for 20 min in a tube furnace or rapid thermal annealing (RTA) was performed, for 2 min, in a nitrogen atmosphere. The samples were characterized by Rutherford Backscattering Spectrometry/Channelling and photoluminescence. The presented results indicate that in the as-implanted samples the majority of the rare earth (RE) ions are incorporated into substitutional Zn-sites. Furnace annealing at 1000 °C recovers the crystal quality of the samples but leads to an out-diffusion of the RE. RTA suppresses diffusion but lattice damage is not fully recovered at 1000 °C. More importantly, during RTA the RE ions are driven from the substitutional site and are now found mainly on random interstitial sites and no optical activation could be achieved. 相似文献
107.
André S. Polo M.C. SantosRodrigo F.B. de Souza Wendel A. Alves 《Journal of power sources》2011,196(2):872-876
Novel photoelectrocatalysts composed of PtRuTiO2/C are prepared by the polymeric precursor method and are characterized by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and cyclic voltammetry. The onset potential for methanol oxidation is similar (0.3 V vs. RHE) for all of the photoelectrocatalyst layers investigated, although the peak current density is dependent on the layer composition. Irradiation of UV light on the photoelectrocatalyst surfaces enhances the chronoamperometric responses up to 18%, which clearly demonstrates a synergistic effect between the photo- and electrocatalysts. The comparison between all the layers prepared indicates that there is an appropriate ratio of metallic nanoparticles and TiO2 to obtain the best performance of these photoelectroactive layers. These results demonstrate that methanol oxidation is achieved by electro- and photocatalysis using a simple and affordable method. This procedure can be conveniently exploited to enhance the response of direct methanol fuel cell electrodes. 相似文献
108.
Magalhaes KD Costa LS Fidelis GP Oliveira RM Nobre LT Dantas-Santos N Camara RB Albuquerque IR Cordeiro SL Sabry DA Costa MS Alves LG Rocha HA 《International journal of molecular sciences》2011,12(5):3352-3365
In the present study, six families of sulfated polysaccharides were obtained from seaweed Dictyopteris delicatula by proteolytic digestion, followed by acetone fractionation and molecular sieving on Sephadex G-100. Chemical analyses demonstrated that all polysaccharides contain heterofucans composed mainly of fucose, xylose, glucose, galactose, uronic acid, and sulfate. The fucans F0.5v and F0.7v at 1.0 mg/mL showed high ferric chelating activity (~45%), whereas fucans F1.3v (0.5 mg/mL) showed considerable reducing power, about 53.2% of the activity of vitamin C. The fucan F1.5v presented the most prominent anticoagulant activity. The best antiproliferative activity was found with fucans F1.3v and F0.7v. However, F1.3v activity was much higher than F0.7v inhibiting almost 100% of HeLa cell proliferation. These fucans have been selected for further studies on structural characterization as well as in vivo experiments, which are already in progress. 相似文献
109.
110.
Juliana Alvarenga Alves Luiz Carlos de Oliveira Lima Disney Ribeiro Dias Cleiton Antônio Nunes Rosane Freitas Schwan 《International Journal of Food Science & Technology》2010,45(11):2358-2365
The aim of this study was to evaluate the contribution of yeast to the volatile profile of beverages obtained by the fermentation of lychee must through inoculated (Saccharomyces cerevisiae strains UFLA CA116 , UFLA CA1183 and UFLA CA1174 ) and spontaneous fermentation. Higher alcohols and esters were the primary volatiles detected by SPME/GC–MS. A Principal Component Analysis indicated similarities between UFLA CA116 and UFLA CA1183 and between UFLA CA1174 and spontaneous fermentation. Changing the yeast strain used in the fermentation process has the potential to modulate the volatile profile of fermented beverages. The beverage produced by the inoculation of yeast CA1183 showed the most complex aroma profile compared to the other beverages. 相似文献