全文获取类型
收费全文 | 1780篇 |
免费 | 45篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 118篇 |
综合类 | 5篇 |
化学工业 | 466篇 |
金属工艺 | 30篇 |
机械仪表 | 23篇 |
建筑科学 | 37篇 |
矿业工程 | 2篇 |
能源动力 | 52篇 |
轻工业 | 186篇 |
水利工程 | 5篇 |
石油天然气 | 7篇 |
无线电 | 168篇 |
一般工业技术 | 266篇 |
冶金工业 | 258篇 |
原子能技术 | 47篇 |
自动化技术 | 159篇 |
出版年
2022年 | 17篇 |
2021年 | 25篇 |
2019年 | 14篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 28篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 79篇 |
2012年 | 71篇 |
2011年 | 69篇 |
2010年 | 76篇 |
2009年 | 63篇 |
2008年 | 68篇 |
2007年 | 66篇 |
2006年 | 67篇 |
2005年 | 59篇 |
2004年 | 57篇 |
2003年 | 49篇 |
2002年 | 41篇 |
2001年 | 43篇 |
2000年 | 33篇 |
1999年 | 34篇 |
1998年 | 113篇 |
1997年 | 70篇 |
1996年 | 40篇 |
1995年 | 38篇 |
1994年 | 42篇 |
1993年 | 39篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1977年 | 15篇 |
1976年 | 16篇 |
1972年 | 16篇 |
1971年 | 13篇 |
1961年 | 12篇 |
1959年 | 11篇 |
1958年 | 12篇 |
1957年 | 13篇 |
排序方式: 共有1829条查询结果,搜索用时 15 毫秒
21.
Whole body gamma-ray irradiation of rats with caesium-137 (137Cs) at embryonic day 20 induced marked reduction of the weight of the testis. Body weight and other tissues, however, seemed to remain normal. By light microscopy, complete loss of germ cells was observed in the testis. Other components, such as Sertoli cells and interstitial cells, seemed to be normal. The testes from day 8 postpartum rats contained very few spermatogonia compared with newborn rats, indicating loss of germ cells between days 0 and 8. In the adult, 137Cs-irradiated testes showed two conspicuous features other than the loss of germ cells: empty vacuolar spaces between Sertoli cells and multilayered seminiferous tubule basal laminae (lamina densa). The junctional structures (ectoplasmic specializations) between Sertoli cells, however, seemed normal. The thickness of each layer of multilayered basal laminae was the same as that of normal rats and electron-lucent layers similar to lamina lucida were interposed between them. Of the empty vacuolar spaces between Sertoli cells, basal laminae bridge the gap. The basal laminae contained laminin, type IV collagen and heparan sulphate proteoglycan evenly distributed among layers, suggesting a normal composition. Rough estimation of the amount of basal laminae deposited in 137Cs-irradiated rats indicates that it is within a range similar to that in normal testis. These features imply that Sertoli cells are, in part, determined perinatally to produce basal laminae for germ-line cells. 相似文献
22.
Takaya Kawamura 《电信纪事》2007,62(7-8):734-752
This article explores some imperatives of Knowledge Management for organizational knowledge creation in the era of globalization. As the transformation of Knowledge Management practices of Japanese firms in 1990s shows, Nonaka and TakeuchVs original model of organizational knowledge creation needs to be expanded by incorporating the concept of “community of practice” as the “engine” of knowledge creation. As an attempt for such expansion, it proposes a model of knowledge-creating organization as a self-organizing network of interactive, overlapping, and self-managing communities of practice. This article also explores some organizational conditions and managerial implications to prevent “malfunction” of communities of practice in the threats of globalization and to facilitate their dynamic evolution. Knowledge-creating organizations and their managers need to give due recognition to and support for “differences” that exist not only among diverse communities of practices but also within each communities. At a micro level approach, they need to “empower” community members by encouraging “ story-telling” or “narrative” of members’ lives in the communities and by assuring “transparency” of activities and resources to the members. As a macro level approach, they need to develop a “communitarian” organizational structure that fits to organizational knowledge creation in “multiculturalization” of societies. 相似文献
23.
Self-healing virtual path architecture in ATM networks 总被引:1,自引:0,他引:1
ATM network techniques have been actively researched and developed with the goal of realizing B-ISDN. ATM networks can transport signals of various services efficiently and economically, and offer the benefit of enhanced flexibility if the virtual path (VP) concept is adopted. Therefore, the ATM network will provide the infrastructure for B-ISDN. One of the most important themes in B-ISDN is the increased level of network reliability required to to match the high volume of data transmission that will be incurred by the information society and the “mission critical” nature of such data. The authors summarize self-healing network (SHN) schemes they have developed, and discuss problems that must be solved to realize SHN 相似文献
24.
Kazuki Yanome Takayuki Kiba Midori Kawamura Yoshio Abe Kyung Ho Kim Junichi Takayama Akihiro Murayama 《Journal of Electronic Materials》2017,46(7):3873-3879
We report the ellipsometric and photoluminescence (PL) properties of Indium zinc oxide (IZO) films, which were grown by radio frequency sputtering under Ar and O2 atmospheres. IZO films grown under an O2 atmosphere (IZO (O2)) showed enhanced PL properties when compared to the films grown under an Ar atmosphere (IZO (Ar)), particularly with respect to the band-edge emission. The enhancement of band-edge emission can be attributed to the reduction in the non-emissive defect states related to oxygen vacancies, which were repaired by sputtering under O2 atmosphere, whereas the PL enhancement in green region is probably due to the formation of the different types of defects under the excess oxygen environment. This was also supported by the results of time-resolved PL measurements, where the band-edge emission of IZO (Ar) showed rapid decay with a 50 ps lifetime, which indicates the dominance of the relaxation pathway to underlying defect states. In contrast, the PL decay profiles of IZO (O2) for band-edge and emissive defect states showed moderate decay with time-constants of 2.3 ns and 5.7 ns, respectively. The exciton relaxation dynamics were sensitive to the presence and its kinds of defect states, which were controlled by the growth conditions. 相似文献
25.
解释了为什么以利润为目的的公司参与标准化活动和特别关注标准与专利的关系,并从经济学角度,使用反公共的悲剧和跨越式发展的概念分析了这个问题.反公共的悲剧解释了为什么公司交叉授权他们的专利许可以及为什么标准化组织的专利政策包含交叉授权.跨越式发展解释了为什么拥有为实施标准的必要专利的公司将他们的专利许可授予没有相关专利的公司.通过向外授予专利许可,公司在短期内可以获得经济利益,在长期可以获得影响市场发展的战略机会,并为民营公司提供一些建议. 相似文献
26.
In the speed sensorless control of the induction motor, the machine parameters (especially rotor resistance R2) have a strong influence on the speed estimation. It is known that the simultaneous estimation of the rotor speed and R2 is impossible in the slip frequency type vector control, because the rotor flux is constant. But the rotor flux is not always constant in the speed transient state. In this paper, the R2 estimation in the transient state without signal injection to the stator current is proposed. This algorithm uses the least mean square algorithm and the adaptive algorithm, and it is possible to estimate R2 exactly. This algorithm is verified by the digital simulations and experiments 相似文献
27.
Characteristic signals were detected from As-doped (< 1 at.%) regions of silicon by dark-field transmission electron microscopy and convergent-beam electron diffraction. A slight intensity increase was observed in 220 dark-field images, which may be explained by an increase of scattering amplitude due to the As doping. The doped region showed a much higher intensity in 004 dark-field images. The characteristic high intensity was observed for specimens with As concentrations of about 0.09-0.8 at.%. Convergent-beam electron diffraction patterns obtained from the As-doped region showed a characteristic rocking curve for 004 reflection. These characteristics should originate from incoherent elastically scattered electrons due to a static lattice distortion around the doped As atoms. The observed characteristics in dark-field images and rocking curves of the 004 reflection should be a good probe not only for investigating the concentration of doped atoms in Si lattice, but also for the amount of impurity and/or point defects in other crystalline materials. 相似文献
28.
Peeramed Chodkaveekityada Hajime Fukuchi 《International Journal of Satellite Communications and Networking》2017,35(4):281-293
The effects of rain attenuation on communication systems will become more pronounced in future satellite communication systems, especially with the planned use of the 21‐GHz band or higher‐frequency bands. Diversity techniques provide a solution to mitigate rain attenuation effects. This study proposes a time diversity technique, one such technique that is likely to demonstrate high effectiveness. To model the system, rainfall rate statistics are necessary, and reliability is improved as the amount of statistical data increases. This paper derives the cumulative distribution of the rainfall rate across Japan over 4 years using rain radar data from the automated meteorological data acquisition system and ground‐based rain radar network and evaluates the rainfall rate at 23 observation points across Japan. We carry out a performance evaluation for all locations within Japan to confirm the efficiency of the time diversity method. Finally, we propose prediction model of the time diversity gain for Japan and other significant parameter which is time correlation of rainfall rate that was found from the time diversity results for further investigation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
29.
Wakita K. Kawamura Y. Yoshikuni Y. Asahi H. Uehara S. 《Quantum Electronics, IEEE Journal of》1986,22(9):1831-1836
The first measurements to be made of large anistropic electroabsorption and modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported. Photocurrent response of waveguide p-i-n diodes is studied for incident light polarization parallel and perpendicular to the MQW layers. Photocurrent increase with reverse bias throughout the entire photoresponse spectrum is observed for both polarizations. The MQW p-in optical modulator shows a capacitance-limited pulse response of 250 ps and the modulation depth is 14 percent. 相似文献
30.
Warapong Krengvirat Srimala Sreekantan M. N. Ahmad-Fauzi Charoen Chinwanitcharoen Go Kawamura Atsunori Matsuda 《Journal of Materials Science》2012,47(9):4019-4027
The volatilization of bismuth (Bi) species and bismuth oxide (Bi2O3) leads to the presence of the oxygen vacancies (V
O00) and consequently restrains the properties of bismuth titanate (BIT; Bi4Ti3O12). This report presents the incorporation of different atomic ratios of praseodymium ion (Pr3+: x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) into the BIT (Bi4−x
Pr
x
Ti3O12) ceramics through an intermediate fuel agent-assisted self-combustion synthesis (IFSC). X-ray diffraction and Raman spectroscopy
results revealed that some of bismuth ion (Bi3+) in the pseudo-perovskite layer containing Ti–O octahedra was substituted by Pr3+ ion. The substitution by ion with a smaller ionic radius caused the structure distortion and consequently resulted in the
phase transformation from an orthorhombic symmetry to a tetragonal symmetry. Besides, it suppressed the volatilization of
Bi and Bi2O3 and increased the stability of metal–oxygen octahedra in the BIT. These play a crucial role to control the crystal growth,
as well as limit the V
O00. Dense ceramic with a relative density up to 96.2% was obtained by incorporating Pr3+ with atomic ratio of 1.0. It exhibited high dielectric constant as 908.19 and low dissipation factor as 0.0011. The results
address the possibility to control the structure, morphology and dielectric properties of BIT ceramic by incorporating Pr3+ ion through IFSC. 相似文献