全文获取类型
收费全文 | 3795篇 |
免费 | 108篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 199篇 |
综合类 | 7篇 |
化学工业 | 1111篇 |
金属工艺 | 107篇 |
机械仪表 | 72篇 |
建筑科学 | 85篇 |
矿业工程 | 2篇 |
能源动力 | 114篇 |
轻工业 | 341篇 |
水利工程 | 9篇 |
石油天然气 | 2篇 |
无线电 | 368篇 |
一般工业技术 | 684篇 |
冶金工业 | 429篇 |
原子能技术 | 114篇 |
自动化技术 | 266篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 69篇 |
2020年 | 39篇 |
2019年 | 39篇 |
2018年 | 59篇 |
2017年 | 56篇 |
2016年 | 82篇 |
2015年 | 43篇 |
2014年 | 105篇 |
2013年 | 187篇 |
2012年 | 150篇 |
2011年 | 211篇 |
2010年 | 135篇 |
2009年 | 176篇 |
2008年 | 196篇 |
2007年 | 162篇 |
2006年 | 141篇 |
2005年 | 151篇 |
2004年 | 128篇 |
2003年 | 119篇 |
2002年 | 125篇 |
2001年 | 96篇 |
2000年 | 71篇 |
1999年 | 90篇 |
1998年 | 161篇 |
1997年 | 137篇 |
1996年 | 103篇 |
1995年 | 74篇 |
1994年 | 62篇 |
1993年 | 64篇 |
1992年 | 54篇 |
1991年 | 34篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 28篇 |
1987年 | 36篇 |
1986年 | 48篇 |
1985年 | 50篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 19篇 |
1980年 | 30篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1976年 | 35篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有3910条查询结果,搜索用时 15 毫秒
31.
32.
A high-speed monolithic optical interface switch LSI is developed using a GaAs MSM photodetector and large-scale integrated electric circuits. This LSI operates universally as a 1.8 Gb/s optical-input/optical-output four-channel time-division switch, a 1.8 Gb/s optical-input/electrical-output 1:4 demultiplexer, a 2.0 Gb/s electrical-output 4:1 multiplexer, and a 2.8 Gb/s electrical-input/electrical-output 4×4 space-division switch. It uses a new multistage 2×2 switch block with small hardware and high-speed operation. It can be expanded to a 16×16 optical-input/optical-output time-division switch operating at up to 1.8 Gb/s for broadband-ISDN 相似文献
33.
Using an Al-Mg-Cu alloy developed for auto body panels, strip sheets are experimentally produced by various cold-rolling and annealing procedures. Tensile and metallographic properties of the sheets and their relations are examined to attain high formability. The elongation is closely related to the grain size, and increases with the final annealing temperature. The rolling texture influences the plastic anisotropy, the Lankford value of the sheets. The comparatively high Lankford values are obtained under the condition that both the intermediate and the final annealing temperatures are higher and the reduction ratio after the intermediate annealing is smaller. 相似文献
34.
35.
K. Sueki K. Kobayashi K. Kikuchi K. Tomura Y. Achiba H. Nakahara 《Fullerenes, Nanotubes and Carbon Nanostructures》1994,2(3):213-221
HPLC elution behaviors of La-fullerenes were investigated by use of the radiochemical methods. Elution curves of La-fullerenes could be observed in detail for the first time, and the persistent presence of La in the whole elution curve was demonstrated. Production of La-fullerenes containing a radioactive 140La could be achieved for the first time. 相似文献
36.
Eiichi Haginomori Kenji Yoshimura Shunichi Kobayashi Sadanori Kaneko Takeshi Yokota Masayuki Ishikawa 《Electrical Engineering in Japan》1994,114(4):50-61
To cope with the high rate of increase of power demand in the main industrialized districts in Japan, 550-kV transmission systems covering the districts have been reinforced, with most of the main power plants connected directly to these systems. Through 550-/300-kV substations, the majority of power to the districts is supplied by 300-kV systems. To limit the excess short-circuit capacity in the 300-kV systems, they tend to be reconstructed as so-called radial networks. In radial networks with high short-circuit capacity and relatively small number of transmission lines connected to the substation busbars, the rate of rise of TRV can be far higher than standard value. This paper analyzes the transient recovery voltages (TRV) in such extra-high-voltage radial networks in Japan, together with the relevant stresses to circuit-breakers during fault clearings. Future system conditions have also been introduced. As the typical rate of rise of the TRV values, more than twice that of today's standard ones are probable. 相似文献
37.
This study was undertaken to compare the calcium-independent phospholipase A2 (PLA2) activities in the cytosols of twelve rat tissues and to determine whether their activities were distinct. 1-O-Alk-1′-enyl-2-[14C]-oleoyl-sn-glycero-3-phosphocho-line (PlsC) and 1-O-Alk-1′-enyl-2-[14C]oleoyl-sn-glycero-3-phosphethanolamine (PlsE) were synthesized and used as substrates, instead of phosphatidyl compounds, to exclude
hydrolysis by cytosolic PLA1 activity that could be present in some of the cytosolic preparations. For each tissue, we examined substrate specificity,
pH optimum, and effect of adenosine triphosphate (ATP) and ATP analogues. PLA2 activity was detected in eleven out of the twelve issues examined. Based on substrate specificity and pH optimum, cytosolic
calcium-independent PLA2 were classified in three groups. The first group, which included PLA2 from small intestine, stomach and spleen, had the highest specific activity with PlsC as substrate (1253, 309 and 75 nmol/mg
protein/hour, respectively) and an optimal pH at 6.5. Activity with PlsE as substrate was much lower (20–37%) than with PlsC.
The second group of PLA2 activities included the cytosolic activities from thymus, lung, liver and pancreas that showed lower specific activities
for both substrates (14–23 nmol/mg protein/hour with PlsC) and had a broader optimal pH range of 6.1 to 7.5. The cytosols
from brain, kidney, heart and muscle comprised the third PLA2 group that was found to have a higher specific activity with PlsE (5–20 nmol/mg protein/hour) than PlsC and an optimal pH
range from 7.4 to 7.9. Since the highest specific activity was found in the cytosol from small intestine, this PLA2 was examined further. PLA2 activity was found to be equally distributed in the cytosol of the submucosal portion of duodenum, jejunum and ileum with
an optimal pH of 6.1 and a 5-fold higher activity with PlsC than PlsE as substrate. Moreover, this PLA2 activity was inhibited by treatment with detergents. These results indicate the presence in the submucosal portion of the
intestine of a calcium-independent cytosolic PLA2 with a high specific activity toward PlsC and properties distinct from those described for the PLA2 found in the intestinal brush-border. 相似文献
38.
Characterization of C-S-H from Highly Reactive β-Dicalcium Silicate Prepared from Hillebrandite 总被引:1,自引:1,他引:0
Yoshihiko Okada Hideki Ishida Kaori Sasaki J. Francis Young Takeshi Mitsuda 《Journal of the American Ceramic Society》1994,77(5):1313-1318
β-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca2 (SiO3 )(OH)2 ) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29 Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form β-C2 S. The temperature at which βC2 S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes higher. The high activity of β-C2 S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed. 相似文献
39.
Okada M. Kikuchi H. Takizawa K. Fujikake H. 《Quantum Electronics, IEEE Journal of》1991,27(8):2003-2015
Optical bistability in a Fabry-Perot semiconductor laser amplifier when two optical inputs detuned from the resonant wavelength of a semiconductor laser amplifier are injected is discussed. A split branch is found in the optical output versus input characteristics in addition to conventional optical bistability behavior. It is shown analytically and experimentally that set and reset can be achieved in the optical output of the semiconductor laser amplifier for each wavelength by applying two detuned optical pulses and using the split branch 相似文献
40.
T Kikuchi 《Canadian Metallurgical Quarterly》1992,11(5):579-581
The prediction of the short-range compact regions of human atrial natriuretic peptide (alpha-hANP), one of the biologically active peptides, has been made by means of the Average Distance Map(ADM). We found out that the location of the predicted short-range compact regions is consistent with the structural units determined by the NMR analysis (Kobayashi et al., 1988). Furthermore, the short-range compact regions correspond well to the biologically active areas of atriopeptin (103-125)-amide (which is homologous peptide to alpha-hANP), detected by the glycine substitution technique (Konishi et al., 1987). The results suggest that a predicted short-range compact region can be regarded as a possible active site in a biologically active peptide. 相似文献