全文获取类型
收费全文 | 786篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 62篇 |
综合类 | 5篇 |
化学工业 | 244篇 |
金属工艺 | 9篇 |
机械仪表 | 10篇 |
建筑科学 | 23篇 |
能源动力 | 36篇 |
轻工业 | 88篇 |
水利工程 | 3篇 |
石油天然气 | 6篇 |
无线电 | 52篇 |
一般工业技术 | 160篇 |
冶金工业 | 21篇 |
原子能技术 | 15篇 |
自动化技术 | 90篇 |
出版年
2023年 | 4篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 16篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 40篇 |
2012年 | 44篇 |
2011年 | 37篇 |
2010年 | 49篇 |
2009年 | 43篇 |
2008年 | 43篇 |
2007年 | 37篇 |
2006年 | 30篇 |
2005年 | 32篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 24篇 |
2001年 | 23篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有824条查询结果,搜索用时 257 毫秒
51.
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
52.
Shujun Zhang Thomas R Shrout Hajime Nagata Yuji Hiruma Tadashi Takenaka 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(5):910-917
Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na0.5Bi0.5)TiO3-y(K0.5Bi0.5)TiO3-zBaTiO3 [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing. Dielectric maximum temperatures of 280 degrees C and 262 degrees C were found for tetragonal 0.79(Na0.5Bi0.5)TiO3-0.14(K0.5Bi0.5)TiO3-0.07BaTiO3 (BNBK79) and MPB composition 0.88(Na0.5Bi0.5)TiO3-0.08(K0.5Bi0.5)TiO3-0.04BaTiO3 (BNBK88), with depolarization temperatures of 224 degrees C and 162 degrees C, respectively. Piezoelectric coefficients d33 were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d31 was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy. Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively. The remanent polarization of BNBK88 (approximately 40 microC/cm2) was larger than that of BNBK79 (approximately 29 microC/cm2). The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed. 相似文献
53.
Yuji Hiruma Hajime Nagata Tadashi Takenaka 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(12):2493-2499
The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a. 相似文献
54.
Reinforcement learning (RL) attracts much attention as a technique for realizing computational intelligence such as adaptive
and autonomous decentralized systems. In general, however, it is not easy to put RL to practical use. This difficulty includes
the problem of designing a suitable action space for an agent, i.e., satisfying two requirements in trade-off: (i) to keep
the characteristics (or structure) of an original search space as much as possible in order to seek strategies that lie close
to the optimal, and (ii) to reduce the search space as much as possible in order to expedite the learning process. In order
to design a suitable action space adaptively, in this article, we propose a RL model with switching controllers based on Q-learning
and an actor-critic to mimic the process of an infant’s motor development in which gross motor skills develop before fine
motor skills. Then a method for switching controllers is constructed by introducing and referring to the “entropy.” Further,
through computational experiments by using a path-planning problem with continuous action space, the validity and potential
of the proposed method have been confirmed. 相似文献
55.
Chantamanee Poonjarernsilp Noriaki Sano Tawatchai Charinpanitkul Hiroki Mori Takeyuki Kikuchi Hajime Tamon 《Carbon》2011,(14):4920-4927
Single-walled carbon nanohorns (SWCNHs) hybridized with palladium (Pd) nanoparticles were synthesized by a single-step gas-injected arc-in-water method (GI-AIW) with a Pd wire inserted inside the anode hole. In the arc zone, carbon and Pd were vaporized simultaneously, leading to the formation of hybrid material of SWCNHs and Pd nanoparticles due to effective quenching. Based on TEM and CO chemisorption analyses, Pd nanoparticles were found to be embedded inside SWCNH aggregates. The size of Pd nanoparticles, determined by X-ray diffraction, was in the range of 3–6 nm when Pd wires with diameters of 0.1 and 0.3 mm were used. Using a Pd wire with a diameter larger than 0.5 mm results in larger Pd nanoparticles which tend to be exposed to the outer surface of the hybrid material. According to thermogravimetric analyses, the weight fraction of Pd nanoparticles is increased by increasing the Pd wire diameter although the yield of Pd nanoparticles decreased. SWCNHs hybridized with dispersed Pd nanoparticles, synthesized with 0.1 mm Pd wire, exhibited strong anti-oxidation resistance with a highly graphitic structure. 相似文献
56.
Iseri Hajime 《水处理信息报导》2008,(5)
通过投加(1)不只一种马来酸聚合物或它们的水溶性盐:(2)不只一种马来酸、马来酸酐的共聚物和它们的水溶性盐,以及非离子单烯不饱和单体,处理水,从而控制水中朗格里指数≥1.5并且(Si02)×(CaH)≥2000,其中(SiO2)为溶于水的SiO2浓度,而(CaH)为溶于水的钙硬度。以CaCO2(mg/L)计,防止腐蚀。该试剂为环境友好性药剂。 相似文献
57.
58.
59.
60.
Hirofumi Kakemoto Tohru Higuchi Hajime Shibata Satoshi Wada Takaaki Tsurumi 《Journal of Materials Science: Materials in Electronics》2008,19(4):311-314
The modification of thermoelectric figure of merit was estimated from enhanced mobility of [100] oriented beta-FeSi2 film. beta-FeSi2 on Si(001) substrate was prepared by molecular beam epitaxy method using an Fe source. The crystallographic orientation of
beta-FeSi2 film on Si(001) substrate was characterized by using X-ray diffraction. Using scanning electron microscopy, surface morphology
and film thickness of samples were observed and estimated, respectively. The mobility of beta-FeS2 film on Si(001) substrate were also characterized by Hall measurement at room temperature. A part of the enhancement of figure
of merit was evaluated as the functions of mobility and crystallographic orientation of samples. 相似文献