全文获取类型
收费全文 | 2920篇 |
免费 | 212篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 26篇 |
综合类 | 4篇 |
化学工业 | 1028篇 |
金属工艺 | 69篇 |
机械仪表 | 77篇 |
建筑科学 | 89篇 |
矿业工程 | 1篇 |
能源动力 | 175篇 |
轻工业 | 379篇 |
水利工程 | 33篇 |
石油天然气 | 29篇 |
无线电 | 361篇 |
一般工业技术 | 399篇 |
冶金工业 | 116篇 |
原子能技术 | 25篇 |
自动化技术 | 343篇 |
出版年
2024年 | 9篇 |
2023年 | 35篇 |
2022年 | 78篇 |
2021年 | 138篇 |
2020年 | 115篇 |
2019年 | 134篇 |
2018年 | 149篇 |
2017年 | 144篇 |
2016年 | 153篇 |
2015年 | 125篇 |
2014年 | 154篇 |
2013年 | 295篇 |
2012年 | 176篇 |
2011年 | 162篇 |
2010年 | 129篇 |
2009年 | 153篇 |
2008年 | 117篇 |
2007年 | 81篇 |
2006年 | 89篇 |
2005年 | 42篇 |
2004年 | 69篇 |
2003年 | 43篇 |
2002年 | 43篇 |
2001年 | 45篇 |
2000年 | 42篇 |
1999年 | 36篇 |
1998年 | 46篇 |
1997年 | 43篇 |
1996年 | 33篇 |
1995年 | 27篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1976年 | 13篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 8篇 |
排序方式: 共有3154条查询结果,搜索用时 515 毫秒
31.
Lignin‐based chemicals, starch, and urea were used as modifiers for phenol–formaldehyde resol resins. The effects of the addition stage of the modifiers used in the synthesis of the resins and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The modifications with corn starch and lignin promoted condensation; this was verified by increased molar masses and high ratios of methylene bridges to the sum of free ortho and para aromatic groups with respect to the corresponding reference resin without a modification reagent. The later the modifier was added to the resin condensation mixture, the more methylene bridges were formed with respect to the amounts of free ortho and para aromatic groups. In addition, when urea or wheat starch was added in the later condensation stage, the final condensation also reached high stages. The modifications with lignosulfonate and starch, as well as the early addition of urea, enhanced p–p′ bridge structures. The lowest condensation stage and, therefore, the highest reactivity were found when wheat starch was added with the starting reagents. The curing heat of the wheat‐starch‐modified resins decreased according to the deferred addition point of starch. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 582–588, 2003 相似文献
32.
Effect of Zn and Pb as alloying elements on the electrochemical behavior of brass in NaCl solutions 总被引:4,自引:0,他引:4
The electrochemical behavior of brasses with various Zn content (5.5–38 mass%) and brass (Cu–38Zn) with different Pb contents (1–3.4 mass%) in 0.6 M NaCl was investigated. The effects of temperature, immersion time, and concentration of chloride ions on the behavior of the different alloys were studied. The pitting corrosion behavior of Cu–Zn alloys and leaded–brass alloys in 0.6 M NaCl solution was also investigated. Open-circuit potential measurements (OCP), polarization techniques and electrochemical impedance spectroscopy (EIS) were used. The results show that the increase in the Zn content increases the corrosion rate of the brass alloys in chloride solutions, while the increase of Pb content in Cu–38Zn–Pb decreases the corrosion rate of the alloy. Long immersion time of the alloys in the aqueous electrolyte improves their stability due to the formation of passive film on the alloy surface. The breakdown potential is shifted to more negative direction with increasing the Zn content, whereas it shifts towards positive values with increasing Pb content. Equivalent circuit model for the electrode/electrolyte interface under different conditions was proposed to illustrate the electrochemical processes taking place at the interface. The electrochemical behavior of the different alloys was discussed in view of the fitting results. 相似文献
33.
Nor Aziah Buang Zaiton Abd. Majid Yusran Sulaiman Suhaila M. Sanip Ahmad Fauzi Ismail 《Journal of Porous Materials》2006,13(3-4):331-334
Production of novel porous material is a major target in current material science research due to its wide applications. As carbon nanotube (CNTs) is a one dimensional hollow structure it is also one of the promising materials in applications ranging from electronics to hydrogen storage medium. Catalytic chemical vapor deposition (CCVD) is a method whereby CNTs can be produced in large amount. Thus, in this work, we have synthesized CNTs via pyrolysis of acetylene using various supported transition-metal catalysts in a fixed-bed reactor. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to investigate the CNTs structure. The structures of nanotubes formed by acetylene pyrolysis were dependent on the catalysts used. It was found that alumina supported Ni/Fe catalyst inhibited the formation of CNTs growth while alumina supported Ni/Co catalyst gave high density of CNTs. However, nanotubes grown over alumina supported Ni/Fe catalyst were less dense due to the deactivation of the catalyst at the early stage of the pyrolysis process. 相似文献
34.
Mohamed I. Ismail 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1979,29(6):361-366
The kinetics of the reaction of chalcopyrite, iron sulphide, copper sulphide, and nickel sulphide with sulphur trioxide gas were studied using a fluidised bed technique. O2, N2, or air was used as a carrier gas for the sulphur trioxide in fluidisation. Binary mixtures of finely ground (0.37–75 μm) samples were reacted with the sulphur trioxide in a Pyrex column at 373–673 K. The reaction products were leached with water and the soluble metals in the solution were determined by atomic absorption spectrometry. The total soluble reaction products were determined gravimetrically. The results obtained showed that a higher yield of soluble salts was obtained when O2 or air was used as a carrier gas for sulphur trioxide than when an inert gas was used. Higher yields of soluble salts were obtained when the samples were most finely ground. Increase of copper sulphide content in binary mixtures with iron or nickel sulphide led to an increase in the yield of soluble salts. For iron sulphide/nickel sulphide mixtures, the yield of soluble salts increased with the nickel sulphide content. There were maximum values for the soluble metal ratios Ni/Fe and Cu/Ni in the corresponding sulphide binary mixtures and this maximum was at about 50% weight. The soluble Cu/Fe ratio increased with copper sulphide content in mixtures with iron sulphide. 相似文献
35.
Helson M. da Costa Valéria D. Ramos Leila L. Y. Visconte Cristina R. G. Furtado 《Polymer Bulletin》2007,58(3):597-610
Summary White rice husk ash (WRHA) and black rice husk ash (BRHA) were incorporated into natural rubber (NR) using a laboratory-sized
two-roll mill. A conventional vulcanization system was used for curing and physical tests of the NR vulcanized involved determining
of tensile and tear resistances. For comparison purposes, precipitated silica (Zeosil-175) and carbon black (N774) were used
too. Using the analysis of variance of single-factor experiments, it can be concluded that: BRHA is non-reinforcing filler
and its use is limited to 20 phr; WRHA is semi-reinforcing filler and the variation of filler loading (0 up to 50 phr) causes
the maximum variation upon tensile strength of NR compounds; and, that although carbon black and silica are reinforcing fillers,
a real reinforcement is reached up to 20 phr for tensile strength. 相似文献
36.
Philip L. Walker Shiro Matsumoto Tamotsu Hanzawa Takatoshi Muira Ismail M.K. Ismail 《Fuel》1983,62(2):140-149
Calcium is the most important in-situ catalyst for gasification of US coal chars in O2, CO2 and H2O. It is a poor catalyst for gasification of chars by H2. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O2, CO2 and H2O. Carbon monoxide inhibits catalysis of the CH2O reaction by calcium, potassium and sodium; H2 inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH2O reaction. Iron is not an important catalyst for the gasification of chars in O2, CO2 and H2O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H2 + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H2O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron. 相似文献
37.
Sari Heikkinen Leila Alvila Tuula T. Pakkanen Terhi Saari Pekka Pakarinen 《应用聚合物科学杂志》2006,100(2):937-945
Drying, water fractions, and water distribution were investigated for pine, birch, and reed pulps and pine–birch, pine–reed, and pine–birch–reed pulp mixtures. Gravimetrically determined drying times showed that the drying rates of the pulps decreased at two to four inflection points. Characterizations of the dried pulps by differential scanning calorimetry (DSC) showed a faster removal of free water than freezing and nonfreezing bound waters; all decreased simultaneously, however. DSC also revealed the critical water contents at which the free water and freezing bound water disappeared. The gravimetrically determined inflection points of the drying curves corresponded with the critical points determined by DSC. NMR line widths and images produced by 1H‐NMR imaging revealed the nature and regions of the pulp drying. The constant growth rate of the NMR line widths with decreasing water content appeared to change at two inflection points, which fell approximately in the same water content regions as the inflection points of the drying curves. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 937–945, 2006 相似文献
38.
Ismail Koyuncu 《Desalination》2002,143(3):243-253
In this study, DS5 DK type nanofiltration membranes were tested to recycle the reactive dye bath effluents. Reactive black 5 (RB5), reactive orange 16 (RO16), reactive blue 19 (RB19) and NaCl were used in the experiments to prepare the synthetic dye and salt mixtures. Effects of feed concentration, pressure and cross flow velocity on the permeate flux and color removal were investigated. Permeate flux increased with increasing pressure for all NaCl solutions. Dye concentration had a significant effect on flux values. Under the fixed NaCl concentrations the flux decreased with increasing dye concentrations. Dye rejections greater than 99% were achieved. Permeate was almost colorless. A gel layer formed by the rejected dye on membrane surface operates as a resistance to the permeation of dyes due to complete rejection of high molecule weight dyes, especially for the low salt concentrations. The presence of salt concentration has an interesting effect on color removal. Color removal decreased with increasing salt concentration. Cross flow velocities had also a significant effect on flux values. The dye formed agglomerates at high NaCl concentrations. High cross flow velocities decreased this effect. 相似文献
39.
Graphite electrodes were prepared by mixing calcined coke and coal tar pitch. They were pressed under 250 kg cm–2 and heat treated up to 2800° C. Rectangles measuring 70 mm x 40 mm x 8 mm were anodically polarized under galvanostatic and potentiostatic conditions. Electrolyses were conducted at 10–50 mA cm–2 for periods ranging from 10–120 hours in Na2SO4 solutions acidified with sulphuric acid to various pH values. The wear of graphite anodes increased with decreasing bath temperature, increasing acid concentration, decreasing pH of the electrolyte and increasing current density. A model is suggested which assumes that corrosion takes place via the formation of a lamellar crystal compound with the formula (C
8
0
O)(OH)3HSO
4
–
·2H2SO4.The compound is unstable at higher temperatures when corrosion is effected by oxidation of graphite by atomic oxygen. The formation of the carbon ions was found to be a necessary precondition for the formation of the complex. 相似文献
40.
The performance of an experimental pilot-scale electrochemical reactor using a rotating cylindrical electrode equipped with wiper blades is described. Data obtained from monopolar depositing and bipolar stripping—depositing of copper from dilute aqueous electrolytes are presented and certain economic aspects of metal recovery are discussed. 相似文献