全文获取类型
收费全文 | 3437篇 |
免费 | 294篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 122篇 |
综合类 | 78篇 |
化学工业 | 647篇 |
金属工艺 | 91篇 |
机械仪表 | 144篇 |
建筑科学 | 198篇 |
矿业工程 | 42篇 |
能源动力 | 125篇 |
轻工业 | 260篇 |
水利工程 | 32篇 |
石油天然气 | 22篇 |
武器工业 | 15篇 |
无线电 | 474篇 |
一般工业技术 | 653篇 |
冶金工业 | 354篇 |
原子能技术 | 27篇 |
自动化技术 | 513篇 |
出版年
2024年 | 9篇 |
2023年 | 64篇 |
2022年 | 126篇 |
2021年 | 208篇 |
2020年 | 140篇 |
2019年 | 123篇 |
2018年 | 134篇 |
2017年 | 128篇 |
2016年 | 131篇 |
2015年 | 138篇 |
2014年 | 179篇 |
2013年 | 242篇 |
2012年 | 193篇 |
2011年 | 244篇 |
2010年 | 160篇 |
2009年 | 144篇 |
2008年 | 128篇 |
2007年 | 154篇 |
2006年 | 120篇 |
2005年 | 102篇 |
2004年 | 84篇 |
2003年 | 91篇 |
2002年 | 74篇 |
2001年 | 66篇 |
2000年 | 54篇 |
1999年 | 55篇 |
1998年 | 110篇 |
1997年 | 55篇 |
1996年 | 53篇 |
1995年 | 50篇 |
1994年 | 22篇 |
1993年 | 36篇 |
1992年 | 17篇 |
1991年 | 27篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有3797条查询结果,搜索用时 506 毫秒
41.
Silicon - In recent times, the study on machining characteristics of combined (hybrid) fiber polymer composites has drawn a remarkable research attention because of its emerging industrial... 相似文献
42.
43.
44.
Zvi Mendel Lev Zegelman Alfred Hassner Fabienne Assael Miriam Harel Shlomo Tam Ezra Dunkelblum 《Journal of chemical ecology》1995,21(3):331-341
The active component of the sex pheromone ofMatsucoccus josephi is (2E,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one; the chemical is also a powerful kairomone of adult males and females of the bugElatophilus hebraicus the principal predator ofM. josephi. The presence of theZ isomer (2E,6Z,8E)-5,7-dimethyl-2,6,8-decatrien-4-one does not interfere with the attractancy of the activeE component forM. josephi males or the bug. Our results show a clear dose-response between trap catch ofM. josephi males andE. hebraicus. Conversely, increasing amounts of theZ isomer in the mixture did not affect the attraction of the scale insect males or the bug. The catch ofM. josephi males did not differ significantly among traps of different color, and was significantly higher with traps attached to the tree trunk than those suspended between trees. Comparison of the catch ofM. josephi among the three forests and between pine species suggests that the level of infestation ofPinus halepepsis andPinus brutia ssp.brutia is similar, despite the fact that the latter pine is resistant to the scale insect. Both sexes ofE. hebraicus were trapped in much lower numbers at the more infested sites. This may be related to interference with the activity ofE. hebraicus due to deterioration and drying of parts of the tree crowns and heavy colonization by generalist predators in injured trees. 相似文献
45.
Shen TJ; Ho NT; Zou M; Sun DP; Cottam PF; Simplaceanu V; Tam MF; Bell DA Jr; Ho C 《Protein engineering, design & selection : PEDS》1997,10(9):1085-1097
A hemoglobin expression system in Escherichia coli is described. In order
to produce authentic human hemoglobin, we need to co-express both
methionine aminopeptidase and globin genes under the control of a strong
promoter. We have constructed three plasmids, pHE2, pHE4 and pHE7, for the
expression of human normal adult hemoglobin and a plasmid, pHE9, for the
expression of human fetal hemoglobin, in high yields. The globin genes can
be derived from either synthetic genes or human globin cDNAs. The extra
amino-terminal methionine residues of the expressed globins can be removed
by the co-expressed methionine aminopeptidase. The heme is inserted
correctly into the expressed alpha- globin from our expression plasmids. A
fraction (approximately 25%) of the heme is not inserted correctly into the
expressed beta- or gamma- globin. However, the incorrectly inserted hemes
can be converted into the correct conformation by carrying out a simple
oxidation-reduction process on the purified hemoglobin molecule. We have
investigated the functional properties of the expressed hemoglobins by
measuring their oxygen-binding properties and their structural features by
obtaining their 1H-NMR spectra. Our results show that authentic human
normal adult and fetal hemoglobins can be produced from our expression
plasmids in E. coli and in high yields. Our expression system allows us to
design and to produce any recombinant hemoglobins needed for our research
on the structure-function relationship in hemoglobin.
相似文献
46.
Downham MC Hall DR Chamberlain DJ Cork A Farman DI Tamò M Dahounto D Datinon B Adetonah S 《Journal of chemical ecology》2003,29(4):989-1011
The legume podborer, Maruca vitrata (syn. M. testulalis) (F.) (Lepidoptera: Pyralidae) is a pantropical pest of legume crops. Sex pheromone was collected by gland extraction or trapping of volatiles from virgin female moths originating in India, West Africa, or Taiwan. Analysis by GC-EAG and GC-MS confirmed previously published findings that (E,E)-10,12- hexadecadienal is the most abundant EAG-active component with 2–5% of (E,E)-10,12-hexadecadienol also present. At least one other EAG response was detected at retention times typical of monounsaturated hexadecenals or tetradecenyl acetates, but neither could be detected by GC-MS. Laboratory wind-tunnel bioassays and a field bioassay of blends of (E,E)-10,12-hexadecadienal with (E,E)-10,12-hexadecadienol and a range of monounsaturated hexadecenal and tetradecenyl acetate isomers indicated greatest attraction of males was to those including (E,E)-10,12-hexadecadienol and (E)-10-hexadecenal as minor components. In subsequent trapping experiments in cowpea fields in Benin, traps baited with a three-component blend of (E,E)-10,12-hexadecadienal and these two minor components in a 100:5:5 ratio caught significantly more males than traps baited with the major component alone, either two-component blend, or virgin female moths. Further blend optimization experiments did not produce a more attractive blend. No significant differences in catches were found between traps baited with polyethylene vials or rubber septa, or between lures containing 0.01 and 0.1 mg of synthetic pheromone. Significant numbers of female M. vitrata moths, up to 50% of total catches, were trapped with synthetic blends but not with virgin females. At present there is no clear explanation for this almost unprecedented finding, but the phenomenon may improve the predictive power of traps for population monitoring. 相似文献
47.
48.
We propose a dynamic model for the copolymerization of α‐methyl styrene (α‐MS) and methyl methacrylate (MMA) in a batch reactor. The parameters are based on data from the literature and our own laboratories over the full conversion range. A two‐parameter model with constant reactivity ratios shows the most reasonable results. The dynamic model depicts the reaction kinetics and reactor behavior more clearly. Termination occurs mainly by the cross reaction of unlike radicals, and its rate increases with the molar ratio of α‐MS to MMA. The model enables us to predict the instantaneous and cumulative properties of the copolymer and also provides us with a basic tool for the optimization and control of industrial reactors. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 261–270, 2004 相似文献
49.
Hydration and strength behavior of supersulfated cement produced by activating a granulated Indian blastfurnace slag by plaster of Paris has been investigated. It is shown that plaster of Paris is a better activator than the conventional hard burnt gypsum (anhydrite) at least for a class of blastfurnace slags which are ordinarily considered less than ideal for this purpose. The setting characteristics of the plaster of Paris activated slag were controlled by small additions of a set retarder which does not adversely affect the strength properties of the cement. X-ray analysis and DTA have been used to identify the hydration products, interpret the strength data, and to compare the plaster of Paris activated cement with anhydrite activated slag cement. 相似文献
50.
The provision of a downcomer to classical turbulent bed Contactor (TBC) increases the gas treating capacity of the equipment. When the downcomer is provided, it is expected that all the liquid passes through the downcomer only without any liquid flow through the distributor. In the present study, the operational regime for the flow of liquid only through the downcomer is experimentally evaluated for various geometric parameters and particle characteristics. It is observed that the preferred operational regime without dumping and weeping increases with an increase in Archimedes number and downcomer diameter, and decreases with an increase in static bed height and downcomer weir height. Correlations are proposed to satisfactorily predict experimentally observed operational regime. 相似文献