全文获取类型
收费全文 | 429篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 50篇 |
化学工业 | 99篇 |
金属工艺 | 10篇 |
机械仪表 | 13篇 |
建筑科学 | 2篇 |
能源动力 | 11篇 |
轻工业 | 22篇 |
水利工程 | 1篇 |
无线电 | 30篇 |
一般工业技术 | 69篇 |
冶金工业 | 119篇 |
原子能技术 | 3篇 |
自动化技术 | 14篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 20篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 47篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有443条查询结果,搜索用时 234 毫秒
101.
102.
T Nagao S Leuzinger D Acampora A Simeone R Finkelstein H Reichert K Furukubo-Tokunaga 《Canadian Metallurgical Quarterly》1998,95(7):3737-3742
The molecular mechanisms of head development are a central question in vertebrate and invertebrate developmental biology. The anteriorly expressed homeobox gene otd in Drosophila and its homolog Otx in mouse are required for the early development of the most anterior part of the body, suggesting that a fundamental genetic program of cephalic development might be conserved between vertebrates and invertebrates. We have examined this hypothesis by introducing the human Otx genes into flies. By inducing expression of the human Otx homologs with a heat shock promoter, we found that both Otx1 and Otx2 functionally complement the cephalic defects of a fly otd mutant through specific activation and inactivation of downstream genes. Combined with previous morphological studies, these results are consistent with the view that a common molecular ground plan of cephalization was invented before the diversification of the protostome and the deuterostome in the course of metazoan evolution. 相似文献
103.
Individual glomeruli in the mammalian main olfactory bulb represent a single or at most a few types of odorant receptors. Thus the physical arrangement of glomeruli at the surface of the olfactory bulb can be viewed as a sensory map representing approximately 1,000 types of odorant receptors. This review summarizes the recent advance of the knowledge regarding the spatial organization of the sensory map in the main olfactory bulb. Recent studies show that individual olfactory bulbs contain dual sensory maps, one in the lateral hemisphere and the other in the medial hemisphere of the bulb. The tracings of selective subsets of olfactory axons to their target glomeruli in the olfactory bulb show that glomeruli are parceled into large zones or bands. The spatial arrangement of these zones and bands are stereotypical and conserved across individual mice. Optical imaging studies show that glomeruli in the most rostrodosal zone, zone I, are further parceled into smaller functional domains, and suggest that odorant receptors having a common or similar molecular feature receptive site are grouped together and represented by glomeruli within the functional domain. The possible relation between the functional domain organization and the subjectively perceived odor quality (olfactory submodality) is reviewed. 相似文献
104.
Surface‐Plasmon‐Enhanced Photodriven CO2 Reduction Catalyzed by Metal–Organic‐Framework‐Derived Iron Nanoparticles Encapsulated by Ultrathin Carbon Layers
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
105.
Atsushi Itadani Yasushige Kuroda Mahiko Nagao 《Microporous and mesoporous materials》2004,70(1-3):119-126
The adsorption of N2 on a copper ion-exchanged ZSM-5 sample (CuZSM-5) prepared by ion exchange using an aqueous solution of copper propionate, Cu(C2H5COO)2, was examined at room temperature by measuring the FT-IR spectra, adsorption isotherms and heat of adsorption. This sample was found to be extremely efficient in terms of N2 adsorption with regard to both the amount and the energy (i.e., heat) of adsorption, compared with samples prepared by a conventional ion-exchange method using an aqueous solution involving Cu2+ and simple counter ions, Cl− or NO3−. To clarify the specificity of the newly-prepared sample, the ion-exchange of ZSM-5 with Cu2+ was carried out by employing aqueous solutions involving Cu2+ and various types of counter ions [propionate (C2H5COO−), acetate (CH3COO−), formate (HCOO−), chloride (Cl−) and nitrate (NO3−) ions]. When the ion exchange was performed by using a Cu(C2H5COO)2 or Cu(CH3COO)2 solution, the Cu2+ species with propionate or acetate ligand (in the monomer state) were ion-exchanged in ZSM-5, as confirmed by the DR, EPR and FT-IR spectra for CuZSM-5. In contrast, Cu2+ species were present in the form of aquo-complexes in samples prepared with other solutions. This distinct difference can be ascribed to the difference in the pKa values of the counter ions; carboxylate ions, with a high pKa value, are inclined to form a complex with Cu2+. Using this newly applied Cu(C2H5COO)2 solution, the present ion-exchange method has the potential to develop new effective materials that possess the specific adsorption and catalytic properties of CuZSM-5. 相似文献
106.
Synthesis of 6-phosphatidyl-L-ascorbic acid by phospholipase D 总被引:1,自引:0,他引:1
Phospholipase D (EC 3.1.4.4) ofStreptomyces species was found to catalyze transphosphatidylation to L-ascorbic acid from phosphatidylcholine (PC) in a biphasic reaction
system. The product was identified as 1,2-diacyl-sn-glycero-3-phospho-6′-L-ascorbic acid (PA-AsA) by mass spectrometry and nuclear magnetic resonance spectroscopy. The optimal
pH of transphosphatidylation was 4.5 and the rate of PA-AsA formation increased as concentrations of L-ascorbic acid increased.
The conversion of PC to PA-AsA was greater than 80%. PA-AsA was found to be more resistant to hydrolysis by phospholipase
D than was PC. 相似文献
107.
Yoshinori?Hirota Toshihiro?Nagao Yomi?Watanabe Masaharu?Suenaga Seiichi?Nakai Aktohiro?Kitano Akio?Sugihara Yuji?ShimadaEmail author 《Journal of the American Oil Chemists' Society》2003,80(4):341-346
Soybean oil deodorizer distillate (SODD) contains steryl esters in addition to tocopherols and sterols. Tocopherols and sterols
have been industrially purified from SODD but no purification process for steryl esters has been developed. SODD was efficiently
separated to low b.p. substances (including tocopherols and sterols) and high b.p. substances (including 11.2 wt% DAG, 32.1
wt% TAG, and 45.4 wt% steryl esters) by molecular distillation. The high b.p. fraction is referred to as soybean oil deodorizer
distillate steryl ester concentrate (SODDSEC). We attempted to purify steryl esters after a lipase-catalyzed hydrolysis of
acylglycerols in SODDSEC. Screening of industrially available lipases indicated that Candida rugosa lipase was most effective. Based on the study of several factors affecting hydrolysis, the reaction conditions were determined
as follows: ratio of SODDSEC/water, 1∶1 (w/w); lipase amount, 15 U/g reaction mixture; temperature, 30°C. When SODDSEC was
agitated for 24 h under these conditions, acylglycerols were almost completely hydrolyzed and the content of steryl esters
did not change. However, study with a mixture of steryl oleate/trilinolein (1∶1, w/w) indicated that about 20% of constituent
FA in steryl esters were exchanged with constituent FA in acylglycerols. Steryl esters in the oil layer obtained by the SODDSEC
treatment with lipase were successfully purified by molecular distillation (purity, 97.3%; recovery, 87.7%). 相似文献
108.
Yuji Shimada Akio Sugihara Hirofumi Nakano Tomomi Yokota Toshihiro Nagao Sadao Komemushi Yoshio Tominaga 《Journal of the American Oil Chemists' Society》1996,73(11):1415-1420
An attempt was made to produce structured lipids containing essential fatty acid by acidolysis with 1,3-positional specificRhizopus delemar lipase. The lipase was immobilized on a ceramic carrier by coprecipitation with acetone and then was activated by shaking
for 2 d at 30°C in a mixture of 5 g safflower or linseed oil, 10 g caprylic acid, 0.3 g water and 0.6 g of the immobilized
enzyme. The activated enzyme was transferred into the same amount of oil/caprylic acid mixture without water, and the mixture
was shaken under the same conditions as for the activation. By this reaction, 45–50 mol% of the fatty acids in oils were exchanged
for caprylic acid, and the immobilized enzyme could be reused 45 and 55 times for safflower and linseed oils, respectively,
without any significant loss of activity. The triglycerides were extracted withn-hexane after the acidolysis and then were allowed to react again with caprylic acid under the same conditions as mentioned
above. When acidolysis was repeated three times with safflower oil as a starting material, the only products obtained were
1,3-capryloyl-2-linoleoylglycerol and 1,3-capryloyl-2-oleoyl-glycerol, with a ratio of 86∶14 (w/w). Equally, the products
from linseed oil were 1,3-capryloyl-2-α-linolenoyl-glycerol, 1,3-caprylol-2-linoleoyl-glycerol, and 1,3-capryloyl-2-oleoly-glycerol
(60∶22∶18, w/w/w). All fatty acids at the 1,3-positions in the original oils were exchanged for caprylic acid by the repeated
acidolyses, and the positional specificity ofRhizopus lipase was also confirmed to be strict. 相似文献
109.
Yomi?Watanabe Yoshie?Yamauchi-Sato Toshihiro?Nagao Takaya?Yamamoto Kentaro?Tsutsumi Akio?Sugihara Yuji?ShimadaEmail author 《Journal of the American Oil Chemists' Society》2003,80(9):909-914
We attempted to produce MAG of CLA through lipase-catalyzed esterification of a FFA mixture containing CLA (referred to as
FFA-CLA) with glycerol. Screening of lipases showed that MAG-CLA was produced efficiently at 5°C with Penicillium camembertii, Rhizopus oryzae, and Candida rugosa lipases. Among them, C. rugosa lipase was selected because the lipase is widely used as a catalyst for oils and fats processing. The reaction was conducted
with agitation of a 300-g mixture of FFA-CLA/glycerol (1∶5, mol/mol), a 200-U/g mixture of C. rugosa lipase, and 2% water. When the reaction was conducted at 30°C, the esterification scarcely proceeded, owing to inhibition
of the reaction by glycerol. But the reaction at 5°C eliminated the inhibition and produced MAG efficiently: The degree of
esterification reached 93.8% after 58 h, and MAG content in the reaction mixture was 88.4 wt%. To reduce the reaction time,
the reactor was connected with a vacuum pump after 24 h, and the reaction was continued with dehydration at 5 mm Hg. The degree
of esterification reached 94.7% after 24 h of dehydration (48 h in total), and MAG content increased to 93.0 wt%. Candida rugosa lipase acted a little more strongly on cis-9, trans-11 CLA than on trans-10,cis-12 CLA, but the contents of the two isomers in MAG obtained from a 48-h reaction were the same as the contents in FFA-CLA. 相似文献
110.
Y. Abe T. Ozai Y. Kuno Y. Nagao T. Misono 《Journal of Inorganic and Organometallic Polymers》1992,2(1):143-149
The synthesis and properties of polymethylsilazanes were investigated. Controlled ammonolysis of methyl(triisocyanato)silane (MTIS) at the molar ratios NH3/MTIS=4 and 6 gave polymethylsilazanes3 and4, which were soluble in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO) but insoluble when isolated as powders. The concentrated polymer solution showed spinnability and film formation. Thermogravimetric analysis of3 and4 showed weight losses of 67 and 16%, respectively. Species4 may be a precursor for silicon/carbon/nitrogen ceramics. 相似文献