全文获取类型
收费全文 | 2873篇 |
免费 | 78篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 256篇 |
综合类 | 7篇 |
化学工业 | 612篇 |
金属工艺 | 81篇 |
机械仪表 | 64篇 |
建筑科学 | 48篇 |
能源动力 | 106篇 |
轻工业 | 195篇 |
水利工程 | 9篇 |
石油天然气 | 4篇 |
无线电 | 256篇 |
一般工业技术 | 502篇 |
冶金工业 | 462篇 |
原子能技术 | 124篇 |
自动化技术 | 228篇 |
出版年
2023年 | 12篇 |
2022年 | 39篇 |
2021年 | 58篇 |
2020年 | 19篇 |
2019年 | 29篇 |
2018年 | 26篇 |
2017年 | 37篇 |
2016年 | 38篇 |
2015年 | 40篇 |
2014年 | 52篇 |
2013年 | 134篇 |
2012年 | 86篇 |
2011年 | 145篇 |
2010年 | 128篇 |
2009年 | 121篇 |
2008年 | 152篇 |
2007年 | 123篇 |
2006年 | 103篇 |
2005年 | 99篇 |
2004年 | 79篇 |
2003年 | 89篇 |
2002年 | 84篇 |
2001年 | 51篇 |
2000年 | 71篇 |
1999年 | 73篇 |
1998年 | 203篇 |
1997年 | 117篇 |
1996年 | 89篇 |
1995年 | 72篇 |
1994年 | 67篇 |
1993年 | 58篇 |
1992年 | 39篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 28篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 25篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1980年 | 26篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 21篇 |
1975年 | 7篇 |
1974年 | 8篇 |
排序方式: 共有2954条查询结果,搜索用时 250 毫秒
51.
Masayuki Hirukawa 《时间序列分析杂志》2006,27(3):441-476
Abstract. This paper proposes a fully modified version of the spectral matrix estimator (and the long‐run variance estimator as a special case) proposed originally by Xiao and Linton [Journal of Time Series Analysis (2002) Vol. 23, pp. 215–250], and derives its asymptotic results. A striking feature of the modified spectral matrix estimator is to achieve the convergence rate of O(T ?8/9) in the mean squared error (MSE), which is usually achieved under the fourth‐order spectral window. However, this estimator does not sacrifice the positive definiteness of the resulting estimate for the rate improvement; it is Hermitian and positive definite in finite samples by construction. The faster convergence rate is established by a multiplicative bias correction of the crude spectral estimator under the second‐order spectral window. The approximations to some sensible definitions of the MSE of the estimator and the bandwidths that minimize the asymptotic MSEs are also derived. Monte Carlo results indicate that for a wide variety of processes the modified spectral matrix estimator reduces the bias without inflating the variance and thus improves the MSE, compared with the crude, bias‐uncorrected estimator. 相似文献
52.
Shingo Kanehira Soshu Kirihara Yoshinari Miyamoto Kazuaki Sakoda Mitsuo Wada Takeda 《Journal of the American Ceramic Society》2003,86(10):1691-1694
Photonic crystals with a diamond structure of epoxy lattices in which TiO2 -based ceramic particles are dispersed were fabricated by stereolithography. The periodicity of the lattice was designed to reflect electromagnetic waves in the gigahertz range. The volume fraction (β) of the dielectric lattice medium was modified from 14% to 33% by changing the rod diameter of the lattice. The photonic band gap was observed along Γ-L 〈111〉, Γ-X 〈100〉, and Γ-K 〈110〉 directions and the complete photonic band gap was formed at over β= 20%. The width of the forbidden gap increased gradually when the β increased over 14%, and reached 2.4 GHz at β= 33%. These results agreed with the band calculation using the plane wave expansion method. 相似文献
53.
Shin'ichiro Asai Ueki Saruta Masayuki Tobita Minoru Takano Yasuo Miyashita 《应用聚合物科学杂志》1995,56(7):769-777
A thermoset type anisotropic conductive adhesive film (ACAF), which electrically connects an ITO glass and a flex circuit both having conducting pattersn of less than 100 μm in pitch, has been developed. In this development, bisphenol A and bisphenol F epoxy resins were tested to formulate an ACAF with easy-to-handle tackiness, flexibility, and strenght. A curing agent that gives fast cure and long shelf-life properties to the epoxy resin was also selected. The tensile stress–strain responses of obtained adhesive films were successfully used for determining the formulation. Good aftercure physical properties (electrical and mechanical) were obtained. Durability against high temperature and high humidity were also tested to confirm long-term stability of the conduction of this ACAF. © 1995 John Wiley & Sons, Inc. 相似文献
54.
Kimihiro Yamashita Motohide Matsuda Yasushi Inda Takao Umegaki Masayuki Ito Toshinori Okura 《Journal of the American Ceramic Society》1997,80(7):1907-1909
Dielectric depression and dispersion were observed in BaTiO3 ceramic films fabricated by electrophoretic deposition followed by sintering. The dielectric constants were depressed down to 6800–4600 around the Curie point ( T C ). The dielectric dispersion occurred above T C . These dielectric properties are attributable to a surface layer formed during sintering. XRD analysis indicated that the surface layer was a hexagonal-like BaTiO3 phase. A mixed solvent of acetylacetone and alcohol employed in the present work may have been responsible for the formation of the surface layer. 相似文献
55.
Masaaki Suzuki Yoshihisa Hasegawa Masayuki Aizawa Yoshinori Nakata Takeshi Okutani Kohei Uosaki 《Journal of the American Ceramic Society》1995,78(1):83-89
The structure of silicon carbide–silicon nitride (SiC–Si3 N4 ) composite particles synthesized using a CO2 laser was studied by magic angle spinning nuclear magnetic resonance (MAS-NMR) and electron spin resonance (ESR). The structure around Si atoms changed by introducing N. C atoms around Si were substituted by N atoms, and N-rich configurations around Si atoms increased stepwise as the N content increased. The low N content composite particles consisted of mainly SiC phase containing dissolved N. N atoms were partly present in β-SiC microcrystal and partly in the grain boundary layer in the particle. N atoms were tetrahedrally surrounded by four Si atoms in β-SiC microcrystal and were trivalent state bonded to three Si atoms in the grain boundary layer. The high N content particles consisted of SiC, Si3 N4 , and amorphous phases, whose amount depended on N content. 相似文献
56.
Masayuki Nogami Yoshihiro Abe Ayako Kato 《Journal of the American Ceramic Society》1995,78(4):1066-1070
Silica glasses doped with small-sized CdSx -Se1-x crystals were prepared by the sol-gel method. Gels synthesized by the hydrolysis of Si(OC2 H5 )4 , in the presence of CdSeO4 with NH4 SCN dissolved in HNO3 or NH4 OH, were heated in H2 -N2 atmosphere. The pH value of solutions for CdSeO4 and NH4 SCN primarily determined the fraction of anions in CdSx Se1-x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat-treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red-shifted as the selenium content and the crystal size increased, and the emission spectra showed a sharp band near the absorption edge position and a broad tail extending into the long wavelength. The optical band gap energies increased reciprocally proportional to the square of the crystal size. 相似文献
57.
New bismaleimides containing ether bonds were prepared. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC). The effects of structure of the bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (Td), glass transition temperature (Tg), and flexural strength were studied. The introduction of ether bonds to bismaleimide resins decreased the brittleness of the resins without reductions in their heat-resistant properties. 相似文献
58.
Masayuki Shirai Chandrashekhar V. Rode Eiichi Mine Akiyoshi Sasaki Osamu Sato Norihito Hiyoshi 《Catalysis Today》2006,115(1-4):248-253
Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst. 相似文献
59.
Advanced Sn/C composite anodes for lithium ion batteries 总被引:2,自引:0,他引:2
Metallic tin was deposited in fine particulate form on the surface of carbonaceous mesophase spherules (CMS) and in the pores of porous carbon by the decomposition and reduction of tin(II) 2-ethylhexanoate at 450 °C. The Sn/C composite powders obtained were used as anode materials for lithium ion cells. Electrochemical cycling tests of coin cells show that the dispersion of tin into the carbonaceous materials enhances the reversible capacity of the electrodes. The capacity retention at the 50th cycle is 91 % for Sn/CMS composite containing 22% tin, against 428 mAh g–1 at the first cycle. With further increase in tin content, the capacity fade upon cycling is more rapid. 相似文献
60.
Dehydration of gels prepared by the sol-gel process from metal alkoxides in the systems B2 O3 -SiO2 and ZrO2 -SiO2 was determined by measuring the shrinkage of the gel on heating. Dehydration was enhanced with increased ZrO2 content, whereas it decreased with B2 O3 content. Diffusion of water was also measured in the nonporous glasses obtained by heating the gels. The diffusion rate was independent of the composition of the glass. 相似文献