全文获取类型
收费全文 | 3909篇 |
免费 | 89篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 132篇 |
综合类 | 8篇 |
化学工业 | 803篇 |
金属工艺 | 178篇 |
机械仪表 | 76篇 |
建筑科学 | 50篇 |
矿业工程 | 6篇 |
能源动力 | 102篇 |
轻工业 | 184篇 |
水利工程 | 14篇 |
石油天然气 | 3篇 |
无线电 | 447篇 |
一般工业技术 | 740篇 |
冶金工业 | 864篇 |
原子能技术 | 86篇 |
自动化技术 | 315篇 |
出版年
2023年 | 29篇 |
2022年 | 47篇 |
2021年 | 95篇 |
2020年 | 39篇 |
2019年 | 57篇 |
2018年 | 53篇 |
2017年 | 65篇 |
2016年 | 65篇 |
2015年 | 51篇 |
2014年 | 91篇 |
2013年 | 194篇 |
2012年 | 146篇 |
2011年 | 198篇 |
2010年 | 163篇 |
2009年 | 185篇 |
2008年 | 172篇 |
2007年 | 131篇 |
2006年 | 113篇 |
2005年 | 97篇 |
2004年 | 91篇 |
2003年 | 94篇 |
2002年 | 95篇 |
2001年 | 70篇 |
2000年 | 60篇 |
1999年 | 67篇 |
1998年 | 331篇 |
1997年 | 183篇 |
1996年 | 170篇 |
1995年 | 97篇 |
1994年 | 91篇 |
1993年 | 94篇 |
1992年 | 45篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 39篇 |
1986年 | 25篇 |
1985年 | 34篇 |
1984年 | 28篇 |
1983年 | 30篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 35篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 33篇 |
1975年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有4008条查询结果,搜索用时 0 毫秒
41.
A poled ferroelectric LiNbO3 single crystal with high spontaneous polarization was employed as a catalyst support, and the static and dynamic effects of the polar substrate surfaces on the adsorptive and catalytic properties of thin film catalysts deposited were shown. For the static effect, it was demonstrated that the surface conductivity of copper and metal-free phthalocyanine films increased by the adsorption of NO gas, to a larger extent, when the substrate was the negative polar surface, compared to the positive one. The role of the polar substrates is explained In terms of a band bending model. For the dynamic effect, the Rayleigh surface acoustic wave generated on the LiNbO3 substrate was shown to enhance the catalytic activity for ethanol oxidation on Cu and Ag thin film catalysts deposited on the propagation path. It is proposed that the catalyst activation is mainly due to an electric Held produced. The use of poled LiNbO3 is suggested to be effective for the development of a device-type catalyst with activity controllable functions. 相似文献
42.
Curing catalyst for epoxy resins was newly found. The catalyst consists of aluminum complex and silanol. Lack of one component of the pair does not cure epoxy resins. The epoxy resins cured with the catalyst are characterized by excellent electrical properties, especially at high temperature, due to the absence of strong acid species in the cured epoxy resin matrix. Heat-resistant property of the resin was also excellent. These properties were compared with those of epoxy resin cured with commonly used BF3 complex. 相似文献
43.
Ichiro Kudo Shoshichi Nojima Hyeun Wook Chang Ryohei Yanoshita Hidetoshi Hayashi Eri Kondo Hiroaki Nomura Keizo Inoue 《Lipids》1987,22(11):862-867
1-O-Octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OMe) has been reported to possess definite antitumor activity in vivo. Twenty-two alkyl lysophospholipid analogs were chemically synthesized, and their antitumor activity against mouse experimental tumors (Sarcoma 180, MM46, P388) was examined. Among them, 1-O-octadecyl-2-O-acetoacetyl-rac-glycerol-3-phosphocholine was found to show antitumor activity similar to ET-18-OMe with less acute toxicity. Intravenous injection of the ET-18-OMe withsn-3 configuration retarded the subcutaneous growth of Sarcoma 180 cells effectively, while the growth inhibition by thesn-1 isomer was much less effective. This stereospecificity was similar to that observed in their activities as platelet-activating factor (PAF) agonists. The acetoacetyl compound, another PAF agonist, showed similar stereospecific antitumor action in vivo. These findings suggest that some alkyl lysophospholipids may activate host cells to a cytostatic stage against tumor cells in vivo through binding to a PAF receptor. Our preliminary results indicated that the responsible cells under these conditions might be primarily immature macrophages present in the bone marrow. No appreciable or even adverse stereospecificity was observed in the different sets of experiments where the activity of ET-18-OMe against MM46 tumor cells in vivo or the direct cytotoxicity against human promyelocytic leukemia HL-60 cells in vitro was examined. Under, some conditions, the antitumor activity of ET-18-OMe in vivo may be revealed through direct cytotoxicity and/or modulation of the host defense system by “nonspecific” mechanisms. Some alkylphospholipids without PAF activity may also show antitumor activity through similar, “nonspecific” mechanisms. 相似文献
44.
Photocatalytic activities for water decomposition were examined for photocatalysts using hexa- and octa-titanates and TiO2(B) with different tunnel space in the structure. Using RuO2 as promoter, M2Ti6O13 (M = Li, Na, K, Rb) showed the stoichiometric production of Hz and O2 except for Li, whereas H2Ti8O17 and TiO2(B) had very low activity producing only hydrogen as a product. The effects of promoters on Na2Ti6O13 showed that the activity increased in the order of RuO2 > RuO2 + IrO2 > IrO2 > RuO2 + Pt > MnO2. These effects along with other related ones are discussed: it emerges that the presence of the tunnels is important for the achievement of high photocatalytic activity. 相似文献
45.
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
46.
Hai -Hang Li Masafumi Inoue Hiroyuki Nishimura Junya Mizutani Eiji Tsuzuki 《Journal of chemical ecology》1993,19(8):1775-1787
Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10–4 M and seed germination above 10–3 M. Coumarin inhibited seedling growth and seed germination at 10–5 M or above. Chlorogenic acid inhibited seedling growth above 10–4 M, but did not inhibit seed germination at 10–5–5×10–3 M. Low concentrations (below 10–3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10–3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10–3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration. 相似文献
47.
Ichiro Kudo Toshiyuki Kato Hidetoshi Hayashi Ryohei Yanoshita Koichi Ikizawa Hiroko Uda Keizo Inoue 《Lipids》1991,26(12):1065-1070
We have previously reported that platelet-activating factor (PAF) induces proliferation and microbicidal activity of guinea
pig bone marrow cells. In the present study, we have found that the conditioned medium of PAF- or nonmetabolizable PAF agonist-treated
guinea pig bone marrow cells augmented DNA synthesis and induced microbicial activity of bone marrow cells. A PAF specific
antagonist, CV-6209, inhibited generation of the active conditioned medium by PAF. Addition of the PAF antagonist only partially
suppressed the augmentative effect of the active conditioned medium on DNA synthesis; this is consistent with the fact that,
because of the rapid breakdown, no appreciable amount of PAF remained in the conditioned medium of PAF-treated cells. Although
mouse bone marrow cells did not respond to PAF unlike guinea pig cells, their DNA synthesis was significantly enhanced by
the conditioned medium of PAF-treated guinea pig bone marrow cells. Thus, some newly generated factor(s) distinct from the
originally inoculated PAF seemed to modulate the bioactions of PAF on bone marrow cells. An appreciable amount of PAF was
produced by calcium ionophore-treated guinea pig bone marrow cells. These findings indicate that PAF synthesized in guinea
pig bone marrow cells induces generation in the cells of some factor(s) which affects proliferation or microbicidal activity.
Presented at The Third International Conference on Platelet-Activating Factor and Structurally Related Ether Lipids, Tokyo,
Japan, May 1989. 相似文献
48.
Masaru Takahashi Noriyuki Inoue Tatsuya Takeguchi Shinji Iwamoto Masashi Inoue Tsunenori Watanabe 《Journal of the American Ceramic Society》2006,89(7):2158-2166
The reaction of mixtures of aluminum isopropoxide and gallium acetylacetonate in 1,4-butanediol or 1,5-pentanediol at high temperatures (glycothermal reaction) directly gave the γ-Ga2 O3 –Al2 O3 solid solutions, which had high catalytic activities for selective reduction of NO using methane as the reducing agent. However, the reaction with a higher Al/(Ga+Al) charged ratio yielded the glycol derivative of boehmite as a by-product and the catalytic activity of the solid solution decreased. Therefore, synthesis of the solid solution using various glycols was examined and it was found that solid solutions with high Al contents without contamination of the glycol derivative of boehmite were obtained by using 1,6-hexanediol as a reaction medium. The solid solution exhibited a higher NO conversion than that synthesized in other glycols. 相似文献
49.
Two problems were solved theoretically on the heat transfer to circular tube flow with internal heat source. The one problem is to maintain the mixed-mean temperature of fluid at the inlet temperature. The other is a conjugated problem with a uniformly specified temperature at the outside surface of the wall, accounting for the wall conduction. From the numerical example for the former, it is shown that the mixed-mean temperature can be controlled within 15% error under the estimated condition. From the numerical results for the latter, it is concluded that the influence of wall conduction is more serious than the case without heat generation. 相似文献
50.
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