全文获取类型
收费全文 | 1631篇 |
免费 | 41篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 165篇 |
综合类 | 4篇 |
化学工业 | 430篇 |
金属工艺 | 64篇 |
机械仪表 | 48篇 |
建筑科学 | 36篇 |
矿业工程 | 5篇 |
能源动力 | 30篇 |
轻工业 | 91篇 |
水利工程 | 4篇 |
石油天然气 | 7篇 |
无线电 | 118篇 |
一般工业技术 | 326篇 |
冶金工业 | 160篇 |
原子能技术 | 48篇 |
自动化技术 | 145篇 |
出版年
2022年 | 12篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 26篇 |
2014年 | 40篇 |
2013年 | 97篇 |
2012年 | 52篇 |
2011年 | 66篇 |
2010年 | 72篇 |
2009年 | 61篇 |
2008年 | 110篇 |
2007年 | 60篇 |
2006年 | 62篇 |
2005年 | 53篇 |
2004年 | 44篇 |
2003年 | 39篇 |
2002年 | 42篇 |
2001年 | 42篇 |
2000年 | 31篇 |
1999年 | 34篇 |
1998年 | 69篇 |
1997年 | 53篇 |
1996年 | 47篇 |
1995年 | 31篇 |
1994年 | 32篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 21篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1969年 | 2篇 |
排序方式: 共有1681条查询结果,搜索用时 15 毫秒
21.
Panjian Li Ilkka Kangasniemi Klaas de Groot Tadashi Kokubo 《Journal of the American Ceramic Society》1994,77(5):1307-1312
Gel-derived titania coating on commercial pure (c.p.) titanium induces hydroxyapatite formation onto its surface from a simulated body fluid (SBF, a metastable calcium phosphate solution). The induced apatite is similar to bone apatite in that it is poorly crystallized, calcium-deficient, and carbonate-containing. Furthermore, the carbonate (CO2–3 ) groups go into the apatite lattice and lie at the positions of PO3–4 and OH– to replace these ionic groups, resembling the (CO2–3 ) groups of bone apatite. Therefore, the apatite induced by the gel-derived titania is said to be bonelike. A chemical stimulation, stemming from abundant hydroxyl groups and negative charges at the surface of the titania gel, is believed to be responsible for the bonelike apatite induction. The potential of bone-bonding is predicted for the gel-derived titania, for it is an efficient bonelike apatite inducer in the SBF. 相似文献
22.
Summary The permeation and separation characteristics of methanol/n-pentanol systems and n-propanol/n-heptane systems through nylon 12 membranes were studied by changing the feed composition of the binary organic mixtures. These characteristics were discussed from the viewpoints of physical and chemical nature of the permeating molecules and the membrane. 相似文献
23.
The kinetic parameters of the first stage of polystyrene degradation have been investigated to elucidate the reaction mechanisms using the flow reactor system. The decrease in molecular weight of polystyrene was recorded at minute intervals over the temperature range 310°–390°C. Generally, the first and second stages were observed by thermogravimetric analysis (t.g.a.), however in the early stage of the degradation volatile yields of at least 5% occurred. Therefore, using t.g.a. analysis it is difficult to detect this earlier stage. It became evident that the first stage in the earlier part of the reaction could be detected by g.p.c. analysis. We have observed the hidden kinetic parameters of the nature of the first stage of the polystyrene degradation. The results indicate that the main chains were degraded randomly with the small quantitative volatile groups in the first stage and the rates of decrease in molecular weight in the first stage against reaction temperatures were evaluated as log ks = 12.0 ? 41300/RT. 相似文献
24.
In order to improve the weatherability of acryonitrile—styrene—butadiene rubber graft polymer (ABS resin), an attempt was made to develop a resin (AAS resin) in which acrylic rubber of good weatherability was used instead of butadiene rubber. First, by copolymerizing dicyclopentenyl-methacrylate (DCP-MA,3%) with butyl acrylate, crosslinked acrylic rubber was obtained. This also introduced grafting sites into the rubber. Next, methods of graft copolymerizing styrene and acrylonitrile with this rubber were examined. An emulsion–suspension polymerization method was developed in which the initial stage of the polymerization, emulsion polymerization, changed into suspension polymerization during the process. By this method of polymerization, rubber particles were combined and enlarged, bringing about a graft-type resin with high impact resistance. This polymerization method is industrially useful because particle-shaped resins are obtained without the need of a salting-out process. The AAS resin, obtained in this way, has much improved weatherability over ABS resin and shows strength equal to that of ABS resin. © 1992 John Wiley & Sons, Inc. 相似文献
25.
26.
Imoto Taiji; Ueda Tadashi; Tamura Tomohiro; Isakari Yoshimasa; Abe Yoshito; Inoue Makoto; Miki Takeyoshi; Kawano Keiichi; Yamada Hidenori 《Protein engineering, design & selection : PEDS》1994,7(6):743-748
Mutations around His15 which lie far away from the active site,stimulated glycol chitin activity of lysozyme at physiologicaltemperature. Del-Argl4Hisl5 lysozyme, a mutant lysozyme whoseArgl4 and Hisl5 were deleted together, and has the highest activityamong these mutant lysozymes, had a similar binding abilityto a trimer of N-acetyl-glucosamine, a substrate analogue, relativeto native lysozyme. This suggests that the increased activitywas due to an increased kcat in the catalysis reaction. TheH-D exchange rate of the N-1 proton in the Trp63 which is locatedin the active site cleft, was enhanced in the Del-Argl4Hisl5lysozyme, while 2-D proton NMR analysis revealed no conformationalchange around Trp63. We conclude that some sort of fluctuationat the active site might be required for the manifestation ofactivity. This theory is supported by the finding that the Del-Argl4Hisl5lysozyme showed a shift in temperature dependency of activityto lower temperatures compared with that of native lysozyme. 相似文献
27.
Uphill transport of ammonium ions through a membrane with sulfonic acid groups were investigated with pH-controllers which keep the solution at a constant pH. A membrane with sulfonic acid groups was prepared by casting an aqueous solution containing poly(styrenesulfonic acid) and poly(vinyl alcohol) on a glass plate. When a membrane with one side alkaline and the other acidic was fixed as a diaphragm in a cell, ammonium ions were transported from the alkaline side to the acidic side through the membrane against the concentration gradient of the adjacent solutions. Uphill transport of ammonium ions with pH-controllers was more efficient than without, thus keeping the pH difference between both sides of the membrane constant, which is a driving force for the uphill transport. Furthermore, the effect of pH of the acidic side on the uphill transport was investigated and the mechanism of the pH-controlled uphill transport is discussed. 相似文献
28.
The wettability of cement particles is related to the fluidity of cement paste. This paper describes the mechanism of the higher fluidity imparted by the spherical cement particles in light of their wettability. In addition, the effects of gypsum on the wettability were also studied. This study has shown the following: (1) The weight of water and water-reducing agent solution penetrating the spherical cement powder bed is 24-150% higher than that for the ordinary Portland cement powder bed. This results in the improvement of the wettability of the particle surfaces of spherical cement. The high wettability of spherical cement contributes to its high fluidity. (2) The presence of many fine gypsum particles on the spherical cement particle surface reduces the wettability. (3) To prepare spherical cement, the optimum amount of gypsum added is determined by the acceleration of the formation of spherical particles and the wettability of particle surfaces. 相似文献
29.
Summary The permeabilities of various cellulose ester membranes and cellulose membranes were investigated using pure water and aqueous solution of glycerol as feed. In all membranes, the permeation rate for aqueous solution of glycerol was greater than for pure water. The permeation rates of cellulose ester membranes increased with an increase in number of carbon atoms of the substituent group in cellulose ester. 相似文献
30.
Yujiro Watanabe Yusuke Moriyoshi Yasushi Suetsugu Toshiyuki Ikoma Takeshi Kasama Tadashi Hashimoto Hirohisa Yamada Junzo Tanaka 《Journal of the American Ceramic Society》2004,87(7):1395-1397
Type-A zeolite evenly covered with hydroxyapatite thin layers was prepared using hydrothermal treatment at 120°C for 8 h under autogenous pressure. The hydroxyapatite needlelike nanocrystals, 100–200 nm in diameter and 30 nm in thickness, were grown under the reaction between discharged Ca2+ ions from type-A zeolite and PO4 3− ions in (NH4 )3 PO4 solution. The preferential orientations of the c -axis of hydroxyapatite crystals perpendicular to a zeolite surface were observed using transmission electron microscopy. The crystal structure of type-A zeolite was not destroyed under the reaction, but the surface morphology was changed only with complete covering of scaly hydroxyapatite particles. 相似文献