全文获取类型
收费全文 | 1809篇 |
免费 | 77篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 17篇 |
综合类 | 6篇 |
化学工业 | 414篇 |
金属工艺 | 41篇 |
机械仪表 | 30篇 |
建筑科学 | 112篇 |
矿业工程 | 3篇 |
能源动力 | 31篇 |
轻工业 | 156篇 |
水利工程 | 2篇 |
无线电 | 193篇 |
一般工业技术 | 353篇 |
冶金工业 | 277篇 |
原子能技术 | 29篇 |
自动化技术 | 224篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 40篇 |
2020年 | 29篇 |
2019年 | 25篇 |
2018年 | 30篇 |
2017年 | 37篇 |
2016年 | 39篇 |
2015年 | 39篇 |
2014年 | 55篇 |
2013年 | 94篇 |
2012年 | 66篇 |
2011年 | 88篇 |
2010年 | 61篇 |
2009年 | 74篇 |
2008年 | 73篇 |
2007年 | 68篇 |
2006年 | 67篇 |
2005年 | 67篇 |
2004年 | 52篇 |
2003年 | 39篇 |
2002年 | 48篇 |
2001年 | 35篇 |
2000年 | 32篇 |
1999年 | 40篇 |
1998年 | 89篇 |
1997年 | 61篇 |
1996年 | 49篇 |
1995年 | 31篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1974年 | 14篇 |
1973年 | 7篇 |
排序方式: 共有1888条查询结果,搜索用时 15 毫秒
11.
12.
The presented integrated optical distance measurement sensor works on the time-of-flight principle. The distance information is obtained from the correlation of received light and the transmitted signal. The PIN-bridge circuit concept ensures suppression of background light by equally charging and discharging the capacitor within one period, while integrating the wanted signal. The advantages of the included PIN-photodiode are high bandwidth f/sub 3 dB/>1.35 GHz together with high responsivity R=0.36 A/W at 660 nm. A single distance measurement is performed in 2 ms. With averaging, an accuracy of better than 1% is achieved for distances up to 3.7 m. Effective pixel size is 250/spl times/200 /spl mu/m/sup 2/ having a fill-factor of /spl sim/16%. The sensor was manufactured in a 0.6-/spl mu/m BiCMOS process. 相似文献
13.
14.
Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure 总被引:1,自引:0,他引:1
Martin Friess Joachim Bill Jerzy Golczewski re Zimmermann Fritz Aldinger Ralf Riedel Rishi Raj 《Journal of the American Ceramic Society》2002,85(10):2587-2589
The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si3 N4 ·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si3 N4 are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si3 N4 crystals is calculated to be 30 kJ/mol. 相似文献
15.
M Abele-Horn C Wolff P Dressel A Zimmermann W Vahlensieck F Pfaff G Ruckdeschel 《Canadian Metallurgical Quarterly》1996,15(7):595-598
The efficiency of the polymerase chain reaction (PCR) was compared with that of culture for detection of Ureaplasma urealyticum and Mycoplasma hominis in 726 clinical specimens comprising 189 gynecological samples, 362 urological samples, and 175 samples from newborn infants. The sensitivity of PCR versus culture was 95% for both organisms, while the sensitivity of culture versus PCR was 91% for Ureaplasma urealyticum and 84% for Mycoplasma hominis. Furthermore, PCR tests were faster than culture tests, allowing the time to diagnosis to be reduced from two to five days to 24 h. 相似文献
16.
17.
18.
Mary J. Garson Mary P. Zimmermann Christopher N. Battershill Janet L. Holden Peter T. Murphy 《Lipids》1994,29(7):509-516
The tropical marine spongeAmphimedon terpenensis (family Niphatidae, order Haplosclerida) has previously been shown to possess unusual lipids, including unusual fatty acids.
The biosynthetic origin of these fatty acids is of interest as the sponge supports a significant population of eubacterial
and cyanobacterial symbionts. The total fatty acid composition of the sponge was analyzed by gas chromatography/mass spectrometry
of the methyl esters. Among the most abundant of the fatty acids in intact tissue were 16∶0, 18∶0 and 3,7,11,15-tetramethylhexadecanoic
(phytanic) acid. In addition, three brominated fatty acids, (5E,9Z)-6-bromo-5,9-tetracosadienoic acid (24∶2Br), (5E,9Z)-6-bromo-5,9-pentacosadienoic acid (25∶2Br) and (5E,9Z)-6-bromo-5,9-hexacosadienoic acid (26∶2Br) were also present. The three brominated fatty acids, together with phytanic acid,
were isolated from both ectosomoal (superficial) and choanosomal (internal) regions of the sponge. Analysis of extracts prepared
from sponge/symbiont cells, partitioned by density gradient centrifugation on Ficoll, indicated that phytanic acid and the
three brominated fatty acids were associated with sponge cells only. Further, a fatty acid methyl ester sample from intact
tissue ofA. terpenensis was partitioned according to phospholipid class, and the brominated fatty acids were shown to be associated with the phosphatidylserine
and phosphatidylethanolamine fractions that are commonly present in marine sponge lipids. The phosphatidylcholine and phosphatidylglycerol
fractions were rich in the relatively shorter chain fatty acids (16∶0 and 18∶0). The association of brominated long-chain
fatty acids (LCFA) with sponge cells has been confirmed. The findings allow comment on the use of fatty acid profiles in chemotaxonomy
and permit further interpretation of LCFA biosynthetic pathways in sponges. The assignment of the sponge studied, which is
currently placed asA. terpenensis, is being supported to some extent, but the species is unusual in having C25 fatty acids as the major constituent in this group. Other factors, such as season or microenvironmental conditions, may influence
observed fatty acid composition which tends to reduce the usefulness of fatty acid profiles as markers in sponge chemotaxonomy. 相似文献
19.
de Murcia M. Richard E. Vanbremeersch J. Zimmermann J. 《Electron Devices, IEEE Transactions on》1994,41(11):2082-2086
Hot electron noise measurements are performed in Si doped Alx Ga1-xAs n+nn+ devices, for three different Al concentrations: x=0.15, 0.2, 0.25. Noise temperatures are obtained using a pulsed measurement technique as functions of electric field and frequency. Longitudinal diffusion coefficients D(E) are deduced at 4 GHz. Results are analyzed through the scattering mechanisms which greatly affect the electron velocity properties of AlxGa1-xAs materials. Comparisons with n+ nn+ GaAs devices are made 相似文献
20.
Ohne Zusammenfassung 相似文献