全文获取类型
收费全文 | 1142篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 54篇 |
化学工业 | 326篇 |
金属工艺 | 38篇 |
机械仪表 | 27篇 |
建筑科学 | 21篇 |
能源动力 | 44篇 |
轻工业 | 68篇 |
水利工程 | 3篇 |
无线电 | 111篇 |
一般工业技术 | 197篇 |
冶金工业 | 131篇 |
原子能技术 | 36篇 |
自动化技术 | 115篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 33篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 26篇 |
2015年 | 16篇 |
2014年 | 27篇 |
2013年 | 68篇 |
2012年 | 51篇 |
2011年 | 78篇 |
2010年 | 43篇 |
2009年 | 69篇 |
2008年 | 64篇 |
2007年 | 58篇 |
2006年 | 46篇 |
2005年 | 39篇 |
2004年 | 39篇 |
2003年 | 45篇 |
2002年 | 35篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 20篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有1171条查询结果,搜索用时 15 毫秒
71.
Monodispersed ellipsoidal hematite particles were synthesized and coated with silicone using a silane-coupling agent, phenyltriethoxysilane.
The thickness of the silicone shell was controlled by the concentration of phenyltriethoxysilane and the presence of n-hexadecyltrimethylammonium chloride, which was thought to modify the surface properties of the hematite particles to be organophilic.
The hematite/silicone core-shell particles were strongly hydrophobic and had a good dispersibility and stability in toluene.
Hollow ellipsoidal silicone particles were obtained by the dissolution of hematite with hydrochloric acid from the core-shell
particles. 相似文献
72.
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
73.
Osamu Kitao Ersan Demiralp Tahir Cagin Siddharth Dasgupta Masuhiro Mikami Kazutoshi Tanabe William A. Goddard III 《Computational Materials Science》1999,14(1-4):135-137
Aluminophosphate zeolite is an artificial material which shows strange hydrophilicity. We have been investigating the reason by quantum mechanics, and found that the hydrophilicity of this zeolite depended on the local geometric deformation, and speculated that the site-specific hydrophilicity might be explained by differences in the stiffness of the local deformation determined by the location with the pore structure. In order to test these ideas, we construct a reliable force field based on the new MS-Q approach developed by Demiralp, Cagin, and Goddard. Our force field well reproduces the experimental structure of VPI-5. 相似文献
74.
Tomoya Nagira Shugo Morita Hiroyoshi Yokota Hideyuki Yasuda Christopher M. Gourlay Masato Yoshiya Akira Sugiyama Kentaro Uesugi Akihisa Takeuchi Yoshio Suzuki 《Metallurgical and Materials Transactions A》2014,45(12):5613-5623
Synchrotron X-ray radiography at 125 frames per second was used to study deformation mechanisms in semi-solid Fe-C alloys at high solid fraction and shear strain rates of 10?1/s. An image correlation approach was also used to quantify the shear strain fields and study shear-induced dilation and the origin of shear cracking. It was shown that, at high solid fraction (90 to 93 pct solid), rearrangement including rotation and translation of solid particles became restricted and shear strain localized into narrow liquid-filled channels/fissures. Shear cracking was shown to originate from inadequate liquid flow into the expanding spaces between solid particles caused by shear-induced dilation. At lower solid fraction (~85 pct solid), solid particles rearranged with a significantly higher component of rotation leading to more shear-induced dilation and a wider shear band. 相似文献
75.
Sintering Kinetics at Isothermal Shrinkage: Effect of Specific Surface Area on the Initial Sintering Stage of Fine Zirconia Powder 总被引:1,自引:0,他引:1
Koji Matsui Akira Matsumoto Masato Uehara Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2007,90(1):44-49
The isothermal shrinkage behaviors of fine zirconia powders (containing 2.8–2.9 mol% Y2 O3 ) with specific surface areas of about 6 and 16 m2 /g were investigated to clarify the effect of specific surface area on the initial sintering stage. The shrinkage of powder compact was measured under constant temperatures in the range of 1000°–1100°C. The increase in specific surface area enhanced the densification rate with increasing temperature. The values of activation energy ( Q ) and frequency-factor term (β0 ) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. The Q of diffusion changes little but the β0 increases with the increase in specific surface area. It is therefore concluded that the increase in the specific surface area of fine zirconia powder enhances the shrinkage rate because of an increase in the β0 at the initial stage of sintering. 相似文献
76.
Almost all the single reinforced concrete (RC) piers from P35 to P350 received consistently severe damage, considering the large residual inclination of piers included in earthquake-induced severe damage. However, some of the piers in the section from P35 to P350 remained lightly damaged, and this phenomenon is observed especially in many piers under fixed bearings in continuous girder bridges. In this study, using experimentally based models for metal bearings and installing them to an existing FEM code, a nonlinear dynamic response analysis of a continuous girder bridge system is conducted. It is shown that the results depend on the ground motion, but the fuse effect of the breaking of the bearings could have been a reason for the phenomenon. 相似文献
77.
S Mikami S Kawashima K Kanazawa K Hirata H Hotta Y Hayashi H Itoh M Yokoyama 《Canadian Metallurgical Quarterly》1997,81(4):504-511
Recent reports demonstrated the expression of inducible-type NO synthase in the heart of viral myocarditis. Since NO has multiple biological actions, a substantial amount of NO produced in the diseased heart may act either as a cytotoxic or as a cytoprotective molecule in the process of myocarditis. In the present study, we examined the effect of inhibition of NO synthesis on the mortality and the extent of myocardial injury in a murine model of coxsackievirus B3-induced myocarditis. We fed the infected mice drinking water containing a relatively low concentration (0.37 mmol/L) of N omega-nitro-L-arginine methyl ester (L-NAME) for 14 days after virus inoculation. This dose of L-NAME did not change virus titers in the heart. However, L-NAME-fed mice showed a significant reduction in mortality compared with those fed normal drinking water (nontreated mice). On the contrary, mice given a higher concentration of L-NAME (3.7 mmol/L) exhibited increased mortality. In addition, mice fed a low concentration of L-NAME showed reductions in the severity of heart failure and in the area of myocardial necrosis. Although systemic blood pressure was reduced in nontreated mice, in mice fed a low concentration of L-NAME, it was maintained at a level similar to that in uninfected control mice, L-NAME-treated mice also exhibited a reduction in the degree of inflammatory cell infiltration associated with decreased production of tissue prostaglandin E2 levels in the heart compared with nontreated mice. Therefore, NO is likely to be involved in the pathogenic mechanisms of myocardial injury and resultant cardiac dysfunction in a murine model of coxsackievirus B3-induced viral myocarditis. 相似文献
78.
A STEM analysis is made of the Mn distribution around grain boundary allotriomorphs of proeutectoid ferrite in an Fe-1.6 at.
Pct C-2.8 at. Pct Mn alloy. Whereas the Mn enriched region is readily observed to extend along the austenite grain boundary,
no substantial build-up or depletion of Mn near the ferrite : austenite interface is detected, consistent with the electron
probe microanalysis previously reported. In the temperature range where the partition-local equilibrium (P-LE) mode has been
proposed to prevail, measured parabolic growth rate constantsfall 1 to 2 orders of magnitude above that predicted from this model, but also below that calculated from the paraequilibrium (PE) model by roughly the same
amount. A modification of the theory of grain boundary diffusion-aided growth of precipitates,i.e., the collector/rejector plate mechanism, on the other hand, accounts fairly well for the observed growth kinetics of ferrite
allotriomorphs. However, only a slightly better accounting than the P-LE model is provided by this mechanism for the temperature
dependence of Mn partition. Data on Ni partition, obtained in an Fe-0.5 at. Pct C-3.1 at. Pct Ni alloy, are also analyzed
with the rejector plate model. 相似文献
79.
Takashi Fujii Masato Nakajima Tsuguo Fukuda Kouichi Nitta Takeshi Komatsubara 《Journal of Electronic Materials》1987,16(4):219-222
Dislocation-free and low dislocation densityn-type conductive GaAs crystals, 50 mm in diameter, were grown by the In and Si co-doping LEC technique. Two-dimensional LED
arrays were fabricated on substrates obtained from these crystals by the MOCVD technique and the influence of the In doping
on the LED characteristics was examined. The light output power of LEDs fabricated on co-doped substrate with an In concentration
of 1 ×1020atoms/cm3 are low and are non-uniformly distributed, as compared with the boat-grown substrate, even though the co-doped substrate
is dislocation-free. However, the LED properties of a substrate with an In concentration of 2 × 1018atoms/cm3 are the same as those of a boat-grown substrate. The light output power of the LEDs becomes higher as the In concentration
in the substrate decreased. 相似文献
80.
High-purity undoped InP epitaxial layers (ND ? NA = 5 × 1014 cm?3, ?77?105 cm2/Vs) are grown by low-pressure metalorganic chemical vapour deposition. The carrier concentrations decrease and the electron mobilities increase as the growth temperature decreases from 700°C to 575°C and the mole fraction ratios ([PH3]/[In(C2H5)3]) increase from 29 to 290. 相似文献