全文获取类型
收费全文 | 276250篇 |
免费 | 28531篇 |
国内免费 | 27553篇 |
专业分类
电工技术 | 23274篇 |
技术理论 | 13篇 |
综合类 | 22139篇 |
化学工业 | 51039篇 |
金属工艺 | 13168篇 |
机械仪表 | 15608篇 |
建筑科学 | 12788篇 |
矿业工程 | 3503篇 |
能源动力 | 8839篇 |
轻工业 | 19055篇 |
水利工程 | 4394篇 |
石油天然气 | 8307篇 |
武器工业 | 2670篇 |
无线电 | 36051篇 |
一般工业技术 | 32890篇 |
冶金工业 | 6500篇 |
原子能技术 | 5436篇 |
自动化技术 | 66660篇 |
出版年
2024年 | 829篇 |
2023年 | 3264篇 |
2022年 | 5714篇 |
2021年 | 7634篇 |
2020年 | 7497篇 |
2019年 | 6803篇 |
2018年 | 6445篇 |
2017年 | 8371篇 |
2016年 | 9533篇 |
2015年 | 11322篇 |
2014年 | 13210篇 |
2013年 | 17152篇 |
2012年 | 18394篇 |
2011年 | 20874篇 |
2010年 | 15621篇 |
2009年 | 16787篇 |
2008年 | 18131篇 |
2007年 | 19957篇 |
2006年 | 18809篇 |
2005年 | 16032篇 |
2004年 | 13649篇 |
2003年 | 11423篇 |
2002年 | 9617篇 |
2001年 | 7324篇 |
2000年 | 6854篇 |
1999年 | 6035篇 |
1998年 | 5035篇 |
1997年 | 4423篇 |
1996年 | 4161篇 |
1995年 | 3955篇 |
1994年 | 3555篇 |
1993年 | 2331篇 |
1992年 | 2178篇 |
1991年 | 1555篇 |
1990年 | 1235篇 |
1989年 | 1010篇 |
1988年 | 908篇 |
1987年 | 533篇 |
1986年 | 387篇 |
1985年 | 587篇 |
1984年 | 613篇 |
1983年 | 571篇 |
1982年 | 520篇 |
1981年 | 502篇 |
1980年 | 308篇 |
1979年 | 138篇 |
1978年 | 130篇 |
1977年 | 96篇 |
1976年 | 54篇 |
1975年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Effect of cationic surfactant and inorganic anions on the electrochemical behavior of carbon steel in formation water 总被引:2,自引:0,他引:2
M.A. Deyab 《Corrosion Science》2007,49(5):2315-2328
Corrosion behavior of carbon steel in formation water associated crude oil from Egyptian western desert was studied at various concentrations of dodecyl dimethyl ammonium chloride (CS) as a cationic surfactant. Polarization curves indicate that CS has a good inhibition efficiency for carbon steel in formation water and behaves as cathodic inhibitor. The inhibition efficiency was found to increase with increase in CS concentration until reaches a maximum constant value corresponding to the critical micelle concentration of CS and decrease with increase in solution temperature. The adsorption of CS follows the kinetic thermodynamic model and Flory-Huggins isotherm. Thermodynamic parameters obtained indicate that that the presence of the CS increases the activation energy. Polarization and Impedance measurements indicate that the addition of KI has a significant synergistic effect with CS and results in increase the inhibition efficiency of CS in formation water. 相似文献
952.
BT项目实施模式分析 总被引:1,自引:0,他引:1
根据实践中出现的各种BT项目管理模式,归纳出了具有代表性的“施工二次招标型BT模式,直接施工型BT模式,施工同体型BT模式,带资承包型BT模式”四种BT项目管理模式,并根据现行法律法规对其适用性和实施中应注意的问题进行了论述。 相似文献
953.
S. Mändl 《Surface & coatings technology》2007,201(15):6833-6838
PIII is a powerful method to obtain hard and wear resistant surface on Ti alloys and NiTi by oxygen or nitrogen implantation. By adjusting the temperature, treatment time and heating regime, different phase compositions and layer thickness can be obtained. Depending on the specific system, a strong influence of the resulting microstructure on the wear and fatigue properties was observed. By considering these restrictions, successful animal tests can be designed and executed, as shown in this review article. 相似文献
954.
有机发光显示(OLED)作为下一代显示器倍受关注。本文简要介绍OLED显示器的几项新技术和制作方法,以及其研究现状和今后的发展趋势。 相似文献
955.
Haiying Wang 《Materials Research Bulletin》2005,40(6):911-919
Eu3+-doped Y2O3, YOF, La2O3, LaOF hollow spheres have been synthesized by a facile template route. Eu3+ were doped into the various host materials to make the hollow sphere red-luminescent. Difference in fluorescence spectra recorded on the hollow spheres were compared in detail and attributed to the different crystal symmetry of host materials. These phosphors might find applications in the fields such as light phosphor powders, advanced flat panel display, or biological labeling. 相似文献
956.
A. E. Barabanov 《Automation and Remote Control》2006,67(10):1547-1572
A new algorithm to solve the H ∞ control problem in the case of full information was presented. It combines the spectral and matrix methods. The polynomial Lur’e-Riccati operator was introduced. Parametrization of all solutions of the controlled plant equation by hidden variables was presented within the framework of the J.C. Willems behavioral approach. The kernel of the polynomial Lur’e-Riccati operator was decomposed into the direct sum of subspaces that are similar to the Jordan blocks. The saddle point of the linear-quadratic game which was found by V.A. Yakubovich in 1970 was shown to provide solution to the H ∞ control problem for a considerable class of controlled plants. 相似文献
957.
KS Min AR Khan MK Kwon YJ Jung Z Yun Y Kiso 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(8):909-915
The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO2 and CH4), the organic matter was converted into CO2 through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFAproduced g?1 VSfed day?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry 相似文献
958.
Yong Ma Yong‐zhen Peng Xiao‐lian Wang Shu‐ying Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(10):1118-1124
The laboratory scale anaerobic–anoxic–aerobic (A2O) process fed with synthetic brewage wastewater was designed to investigate the effects of changing feed C/P ratio on the performance of biological nutrient removal (BNR) processes. In the experiment, the influent chemical oxygen demand (COD) concentration was kept at approximately 300 mg L?1 while the total phosphorus concentration was varied to obtain the desired C/P ratio. Results showed that when the C/P ratio was lower than 32, phosphorus removal efficiency increased as C/P ratio increased linearly, while when the C/P ratio was higher than 32, the P removal efficiency was maintained at 90–98%, and effluent P concentration was lower than 0.5 mg L?1. However, regardless of the C/P ratio, excellent COD removal (90% or higher) and good total nitrogen removal (75–84%) were maintained throughout the experiments. It was also found that very good linear correlation was obtained between COD uptake per unit P released in the anaerobic zone and C/P ratio. In addition, the P content in the wasted activated sludge increased with the decrease in the C/P ratio. Based on the results, it was recommended that the wastewater C/P ratio and its effects be incorporated into BNR design and operational procedures, appropriate C/P ratios were used to achieve the effluent treatment goals. Copyright © 2005 Society of Chemical Industry 相似文献
959.
Mamata Mukhopadhyay Sameer V Dalvi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(4):445-454
A supercritical antisolvent (SAS) process is employed for production of solid nanoparticles from atomized droplets of dilute solution in a flowing supercritical carbon dioxide (SC CO2) stream by attaining extremely high, very rapid, and uniform supersaturation. This is facilitated by a two‐way mass transfer of CO2 and solvent, to and from the droplet respectively, rendering rapid reduction in equilibrium solubility of the solid solute in the ternary solution. The present work analyses the degree of supersaturation and nucleation kinetics in a single droplet of cholesterol solution in acetone during its flight in a flowing SC CO2 stream. Both temperature and composition are assumed to be uniform within the droplet, and their variations with time are calculated by balancing the heat and mass transfer fluxes to and from the droplet. The equilibrium solubility of cholesterol with CO2 dissolution has been predicted as being directly proportional to the Partial Molar Volume Fraction (PMVF) of acetone in the binary (CO2–acetone) system. The degree of supersaturation has been simulated up to the time required to attain almost zero cholesterol solubility in the droplet for evaluating the rate of nucleation and the size of the stable critical nuclei formed. The effects of process parameters have been analysed in the pressure range of 7.1–35.0 MPa, temperature range of 313–333 K, SC CO2 flow rate of 0.1136–1.136 mol s?1, the ratio of the volumetric flow rates of CO2‐to‐solution in the range of 100–1000, and the initial mole fraction of cholesterol in acetone solution in the range of 0.0025–0.010. The results confirm an extremely high and rapid increase in degree of supersaturation, very high nucleation rates and stable critical nucleus diameter of the order of a nanometre. Copyright © 2005 Society of Chemical Industry 相似文献
960.
在氯化铵-氨水(pH=11)支持电解质中用微银汞膜电极进行试验,锰、铁不干扰测定,用EDTA滴定氯化钙获得令人满意的结果。对三种样品进行分析,变异系数为0.08%—0.11%。该法快速准确,适用于氯化钙主要成份的测定。 相似文献