全文获取类型
收费全文 | 1716篇 |
免费 | 64篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 95篇 |
综合类 | 1篇 |
化学工业 | 520篇 |
金属工艺 | 58篇 |
机械仪表 | 35篇 |
建筑科学 | 30篇 |
能源动力 | 94篇 |
轻工业 | 103篇 |
水利工程 | 3篇 |
无线电 | 125篇 |
一般工业技术 | 372篇 |
冶金工业 | 120篇 |
原子能技术 | 75篇 |
自动化技术 | 153篇 |
出版年
2023年 | 7篇 |
2022年 | 30篇 |
2021年 | 58篇 |
2020年 | 18篇 |
2019年 | 27篇 |
2018年 | 42篇 |
2017年 | 21篇 |
2016年 | 40篇 |
2015年 | 36篇 |
2014年 | 56篇 |
2013年 | 120篇 |
2012年 | 60篇 |
2011年 | 105篇 |
2010年 | 80篇 |
2009年 | 100篇 |
2008年 | 71篇 |
2007年 | 78篇 |
2006年 | 68篇 |
2005年 | 56篇 |
2004年 | 48篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 29篇 |
2000年 | 34篇 |
1999年 | 39篇 |
1998年 | 62篇 |
1997年 | 48篇 |
1996年 | 41篇 |
1995年 | 28篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 24篇 |
1988年 | 14篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有1784条查询结果,搜索用时 15 毫秒
971.
972.
Tomaru T Miyoki S Ohashi M Kuroda K Uchiyama T Suzuki T Yamamoto A Shintomi T Ueda A Tatsumi D Sato S Arai K Ando M Watanabe K Nakamura K Watanabe M Ito K Kataoka I Yamamoto H Bochner B Hefetz Y 《Applied optics》2002,41(28):5913-5920
We evaluated the performance of polished mirror surfaces for the TAMA interferometric gravitational wave detector by comparing the experimental results with a wave-front tracing simulation. The TAMA mirror surfaces were polished to a roughness of a few nanometer rms. We confirmed that these polished mirrors do not limit the present TAMA sensitivity and that the target shot-noise sensitivity will be achieved with these mirrors, even if a power-recycling technique is introduced in the next stage of the TAMA. 相似文献
973.
Moriyama M Sato Y Naito H Hanayama M Ueguchi T Harada T Yoshimoto F Tamura S 《IEEE transactions on medical imaging》2002,21(7):773-785
This paper reports on the clinical application of a system for recovering the time-varying three-dimensional (3-D) left-ventricular (LV) shape from multiview X-ray cineangiocardiograms. Considering that X-ray cineangiocardiography is still commonly employed in clinical cardiology and computational costs for 3-D recovery and visualization are rapidly decreasing, it is meaningful to develop a clinically applicable system for 3-D LV shape recovery from X-ray cineangiocardiograms. The system is based on a previously reported closed-surface method of shape recovery from two-dimensional occluding contours with multiple views. To apply the method to "real" LV cineangiocardiograms, user-interactive systems were implemented for preprocessing, including detection of LV contours, calibration of the imaging geometry, and setting of the LV model coordinate system. The results for three real LV angiographic image sequences are presented, two with fixed multiple views (using supplementary angiography) and one with rotating views. 3-D reconstructions utilizing different numbers of views were compared and evaluated in terms of contours manually traced by an experienced radiologist. The performance of the preprocesses was also evaluated, and the effects of variations in user-specified parameters on the final 3-D reconstruction results were shown to be sufficiently small. These experimental results demonstrate the potential usefulness of combining multiple views for 3-D recovery from "real" LV cineangiocardiograms. 相似文献
974.
Suzuki K Hirayama E Sugiyama T Yasuda K Okabe H Citterio D 《Analytical chemistry》2002,74(22):5766-5773
Digital color analysis (DCA), utilizing colors themselves or digital information of colors, can not only be applied to various quantitative analysis using chromaticity coordinates but can also be used to develop suitable sensors for visual colorimetry based on the characteristics of human visual perception by virtual simulations based on digital color information. To achieve a clear visual color variation for lithium ion determination, we designed and prepared a color-changeable film sensor (film optode) by the use of two kinds of lipophilic dyes, KD-C4 and KD-M11, whose colors and pKa values are different. This film sensor is a plasticized PVC membrane containing the mixture of two kinds of dyes with the lithium ionophore TTD14C4 and the lipophilic anionic additive tetrakis-[3,5-bis(trisfluoromethyl)phenyl]borate sodium salt dihydrate. The simulation of the color variation using the mixed dyes was evaluated by plotting the values on a uniform chromaticity scale diagram in a*b* coordinates, after converting the tristimulus values of each dye into its L*a*b* values. When the lithium ion concentration was actually determined by the PVC film optode containing the mixed dyes whose molecular ratio of KD-C4/KD-Ml 1 was 3:1, the hues of red --> orange --> yellow --> green --> blue could be realized in the range of 10(-6)-1 M. This observed color variation was similar to the result of the virtual simulation based on DCA. 相似文献
975.
Factors affecting seasonal variation of membrane filtration resistance caused by Chlorella algae 总被引:1,自引:0,他引:1
A seasonal fluctuation pattern was observed in membrane filtration resistance by Chlorella algae cultured in open ponds in the tropical environment. In order to investigate the causes of this phenomenon, Chlorella was cultivated under controlled conditions and the cake resistance was measured by batch filtration in dead-end mode. The filtration resistance was found to be a function of environmental conditions. Algae could grow favourably and offered low specific cake resistance (R,s) on the order of 10(11) m/g for the culture temperature from 28 degrees C to 35 degrees C. The algal growth was inhibited and the specific cake resistance increased to the order of 10(12) m/g below or above this optimum temperature range. Strong solar radiation, coupled with high temperatures, also inhibited the growth of algae and resulted in higher specific cake resistance. The specific cake resistance of algae cultured at different temperatures increased with the amount of the extracellular organic matter (EOM) extracted by 0.1 N NaOH. Hence EOM, rather than bacteria present in the mono-algal culture, was considered to be the primary factor affecting the cake resistance. The specific cake resistance increased drastically after actively growing cells were stored in nutrient-free water under dark conditions. However, the resistance was slightly decreased when the algal cells were stored in NSIII nutrient media in a dark room, indicating the effect of nutrient availability on the change of the specific cake resistance under the light-limiting conditions. EOM extracted from the cells kept in the nutrient-free water contained less sugar than the fresh culture, whereas the EOM extracted from the cells stored in the NSIII media contained more sugar. The molecular distribution of the EOM shifted from below 1,000 kDa before storage to more than 2,000 kDa after storage in both the nutrient-free and NSIII media. 相似文献
976.
Yukio Itakura Masaki Hashiyada Toshio Nagashima Shigeo Tsujii 《International Journal of Information Security》2002,1(3):149-160
The individual differences in the repeat count of several bases, short tandem repeat (STR), among all of the deoxyribonucleic
acid (DNA) base sequences, can be used as unique DNA information for a personal identification (ID). We propose a method to
generate a personal identifier (hereafter referred to as a “DNA personal ID”) by specifying multiple STR locations (called
“loci”) and then sequencing the repeat count information. We also conducted a validation experiment to verify the proposed
principle based on actual DNA data.
We verified that the matching probability of DNA personal IDs becomes exponentially smaller, to about 10-n, as n stages of loci are used and that no correlation exists among the loci.
Next, we considered the various issues that will be encountered when applying DNA personal IDs to information security systems,
such as biometric personal authentication systems.
Published online: 9 April 2002 相似文献
977.
The reaction of methyl iodide with cellulose β-mercaptoethylaminocarboxylate (RDTC) made from cotton was investigated. The product was found to contain dimethyl sulfonium groups in addition to S-methyl groups, with accompanying hydrolytic cleavage of some of urethane linkages. The iodide counterions could be easily exchanged with hydroxide and chloride ions. The dyeabilty of RDTC and its sulfonium derivatives toward Direct Sky Blue A was studied. The equilibrium uptake of the dye by RDTC decreased with increasing sulfur content, while the uptake by the sulfonium derivatives was higher than that of control cotton and increased with increasing sulfonium content. The counterions did not affect the dyeability. The dye adsorbed onto the sulfonium derivatives was very fast against solvent extraction, and could be extracted only with Cadoxen containing 0.5% sodium hydroxide. The equilibrium uptake of the dye was much more than the amount calculated on basis of the 1 : 1 ionic bonding between the sulfonic acid group in the dye molecule and the sulfonium group in the modified cotton. The spatial effect in the dye–sulfonium bonding is discussed. 相似文献
978.
Keizou Tsukamoto Chitake Yamagishi Kunihito Koumoto Hiroaki Yanagida 《Journal of Materials Science》1984,19(8):2493-2500
The electrical properties of poly-phase ceramics in the system Li2O-ZnO were studied. The specimens obtained were confirmed to be composed of Li2ZnO2, ZnO and some Li4ZnO3, by X-ray diffraction. Li2ZnO2 was assumed to possess a hexagonal structure with cell parametersa=0.812 nm andc=0.673 nm. Electrical conductivity increased with increasing temperature up to 420° C, and decreased abruptly above 420° C. The temperature dependence of the ionic transference number showed that ionic conduction was dominating above 300° C, while mixed conduction occurred below 300° C. The dependence of electrical resistivity on relative humidity was also measured at room temperature. Electrical resistivity exponentially decreased five orders of magnitude with increasing relative humidity from 5 to 95%. The decrease in electrical resistivity with increasing relative humidity might be caused by LiOH formed on the surface of the specimens. 相似文献
979.
Kawachi T Kado M Tanaka M Hasegawa N Nagashima K Sukegawa K Lu P Takahashi K Namba S Koike M Nagashima A Kato Y 《Applied optics》2003,42(12):2198-2205
A two-beam chirped-pulse-amplification Nd:glass laser system dedicated to x-ray laser research is described. Each beam provides an output energy of 20 J with a typical pulse duration of 1.3 ps. A prepulse of variable duration is generated by use of a novel, to our knowledge, optical system. A reflection optical system, comprised of an off-axis parabolic mirror and a spherical mirror, produces a line focus with 6-mm length and 165-microm width without chromatic aberration. By use of this pumping laser system, the nickel-like silver x-ray laser at a wavelength of 13.9 nm has been demonstrated. 相似文献
980.
The effects of dietary stearidonic acid (18∶4n−3) on inflammatory mediator release in whole blood and splenocytes was investigated
in Balb/c mice, and the effects were compared with those of two other n−3 PUFA: α-linolenic acid (18∶3n−3) and EPA (20∶5n−3).
TAG mixtures containing 10% of 18∶4n−3, 18∶3n−3, or 20∶5n−3 as the respective sole n−3 PUFA were enzymatically synthesized.
Diets containing synthesized TAG mixtures were fed to Balb/c mice for 3 wk. The release of prostaglandin E2 (PGE2) and tumor necrosis factor (TNF) were measured in whole blood and splenocytes stimulated with lipopolysaccharide. In whole
blood, the production of INF was suppressed by all dietary n−3 PUFA (18∶3n−3, 18∶4n−3, and 20∶5n−3) as compared with the control
diet, which contained TAG prepared from safflower oil. PGE2 production was not significantly changed. Differences among the n−3 PUFA (18∶3n−3), 18∶4n−3, and 20∶5n−3) were not observed.
In splenocytes, PGE2 production was suppressed by dietary n−3 PUFA, but TNF production was not. GC analysis of plasma and splenocyte FA profiles
showed an increase in the levels of 20∶4n−3, 20∶5n−3, and 22∶6n−3 in mice fed the diet containing 18∶4n−3. 相似文献