全文获取类型
收费全文 | 6841篇 |
免费 | 118篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 376篇 |
综合类 | 3篇 |
化学工业 | 1222篇 |
金属工艺 | 206篇 |
机械仪表 | 162篇 |
建筑科学 | 112篇 |
能源动力 | 174篇 |
轻工业 | 473篇 |
水利工程 | 33篇 |
石油天然气 | 6篇 |
无线电 | 636篇 |
一般工业技术 | 1207篇 |
冶金工业 | 1795篇 |
原子能技术 | 136篇 |
自动化技术 | 435篇 |
出版年
2023年 | 23篇 |
2022年 | 49篇 |
2021年 | 110篇 |
2020年 | 50篇 |
2019年 | 54篇 |
2018年 | 71篇 |
2017年 | 67篇 |
2016年 | 76篇 |
2015年 | 76篇 |
2014年 | 96篇 |
2013年 | 235篇 |
2012年 | 205篇 |
2011年 | 286篇 |
2010年 | 197篇 |
2009年 | 216篇 |
2008年 | 230篇 |
2007年 | 233篇 |
2006年 | 222篇 |
2005年 | 196篇 |
2004年 | 186篇 |
2003年 | 189篇 |
2002年 | 186篇 |
2001年 | 161篇 |
2000年 | 141篇 |
1999年 | 167篇 |
1998年 | 671篇 |
1997年 | 431篇 |
1996年 | 306篇 |
1995年 | 219篇 |
1994年 | 220篇 |
1993年 | 176篇 |
1992年 | 99篇 |
1991年 | 105篇 |
1990年 | 94篇 |
1989年 | 84篇 |
1988年 | 75篇 |
1987年 | 64篇 |
1986年 | 75篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 60篇 |
1982年 | 49篇 |
1981年 | 56篇 |
1980年 | 57篇 |
1979年 | 33篇 |
1978年 | 28篇 |
1977年 | 54篇 |
1976年 | 56篇 |
1975年 | 31篇 |
1973年 | 27篇 |
排序方式: 共有6976条查询结果,搜索用时 672 毫秒
991.
In situ high-temperature visible microspectroscopy has been developed in order to study color change kinetics of volcanic materials. Olivine thin sections put on a synthetic alumina plate are heated on a heating stage at 600-800 degrees C under a visible microspectroscope. Changes in visible absorption spectra are monitored every 60 s for 5 hours. The obtained high-temperature visible spectra showed a gradual increase with time in absorbance in the shorter wavelength region (400-600 nm). The 430 nm absorbance (ligand field transition of Fe3+ increased more with time at higher temperatures. Assuming diffusional transport in plane sheets, apparent diffusion coefficients were determined at temperatures of 600-800 degrees C. The activation energy for this diffusion in olivine is 208 +/- 17 kJ/mol. This activation energy value is similar to those for the metal vacancy diffusion in olivine. This newly developed in situ high-temperature visible microspectroscopy can provide kinetic measurements of visible spectral change of materials at high temperatures such as volcanic materials. 相似文献
992.
Taniguchi M Kato K Shimauchi A Ping X Nakayama H Fujita K Tanaka T Tarui Y Hirasawa E 《Journal of Bioscience and Bioengineering》2005,99(3):245-251
Cross-linked poly-gamma-glutamic acid (C-L gamma-PGA) markedly purified polluted water collected from rivers and ponds by flocculation and precipitation. This effect of C-L gamma-PGA occasionally required pretreatment with polyaluminum chloride (PAC). Components of polluted water in rivers or ponds are generally thought to be clay minerals, microorganisms and chemical compounds. In this study, the flocculating activities of C-L gamma-PGA against suspensions of bentonite, diatomaceous earth, Escherichia coli and Mycrocystis aeruginosa, and against solutions of crystal violet and bisphenol A were investigated. The mode of action of C-L gamma-PGA is thought to be based on electrostatic interaction between flocculants, C-L gamma-PGA and PAC, and the surface of polluted water components, which may lead to neutralization of the zeta-potential of those components. 相似文献
993.
Tarui Y Iida H Ono E Miki W Hirasawa E Fujita K Tanaka T Taniguchi M 《Journal of Bioscience and Bioengineering》2005,100(4):443-448
Transient expression of genes coding for the poly-gamma-glutamate (gammaPGA) synthetase system (pgs) was investigated in tobacco plants. Three genes of the pgs, pgsA, pgsB and pgsC, were separately placed under the control of the CaMV 35S promoter and introduced into tobacco leaves via Agrobacterium infection. Synthesized gammaPGA in plant tissues was detected immunologically with mouse anti-gammaPGA antiserum which specifically reacts with gammaPGA on a nitrocellulose membrane. Confirmation of gammaPGA biosynthesis in the transient expression analysis in tobacco tissue indicates that subunits of pgs complex were expressed and reassembled in a functional form. 相似文献
994.
995.
996.
Uesugi N. Murakami Y. Tanaka C. Ishida Y. Mitsunaga Y. Negishi Y. Uchida N. 《Electronics letters》1983,19(19):762-764
Loss increase characteristics of optical fibre in cable filled with water are reported. Drastic loss increase around 1.24 ?m is observed for both graded-index and single-mode fibres. The origin of the loss increase is found to be due to hydrogen gas diffused into the silica glass interstitially. 相似文献
997.
Small-angle neutron scattering measurements were made on poly(ethylene oxide) (PEO) crystallized from the melt. Samples with the deuterated species (DPEO) as a matrix present distinct Bragg peaks from which the lamella spacings can be determined. As a result of strong void-scattering, quantitative analysis of the low-angle regime of these scattering curves is not possible. Samples with the protonous species as a matrix, for which void-scattering is expected to be negligibly small, present unusual scattering curves indicating that they consist of two components, i.e. the intramolecular and intermolecular interference terms. A quantitative analysis of these curves indicates: (1) the solute DPEO molecules are embedded in the crystalline structure of the matrix, assuming rod-like conformations but (2) forming essentially homogeneous aggregates of a few to tens of the DPEO molecules, depending on the crystallization temperature and the DPEO concentration; (3) the DPEO molecules or aggregates are distributed in space in a non-random manner that corresponds to the presence of inhomogeneous ‘domains’ having root-mean-square radii of about 250 Å, and each containing about 100 DPEO molecules. 相似文献
998.
999.
Two new structures of lateral-injection transverse junction stripe (TJS) lasers, in which the stripe geometry is formed by the double heterojunctions, have been developed. These lasers, the homojunction type and the single-heterojunction type, have a self-reverse-biased p-n junction for concentrating current into the narrow active region. The temperature dependence of the threshold current has been very much improved in one of the new structures, the homojunction type, and is fair compared with those of good conventional broad-contact lasers. The threshold current does not increase rapidly up to 350 K in the homojunction lasers. These lasers exhibit improved characteristics of low threshold, the single longitudinal mode oscillation as well as the single fundamental transverse-mode oscillation, and "kink-free" behavior in the current depedence of the light-output power. 相似文献
1000.
K Makiya H Tanaka EA Ba?ez BL Blas N Kumada AT Santos 《Canadian Metallurgical Quarterly》1982,52(1):33-37
For the comparative study of densities of Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum in the Philippines, the survey data should be transformed to stabilize the variance in determining the significant difference of densities among populations and to evaluate control measures by the difference, since the snail is distributed unevenly in the field. Comparison was made for the efficiency of stabilizing variance among 7 transformation formulas so far reported, and 2 new additional formulas in the present study. As a result, a simple transformation by y=log (x+0.01) was found to be most reliable. This nonparametric transformation can be applied to any snail population irrespective of the type of distribution and the degree of clumping. By this formula, there is no need to discard snail-free samples which are important to evaluate control measures. Using this transformation, snail survey data were analyzed in the areas where control measures were undertaken during the past several years. And significant reduction of snail densities was proven using the t-test. 相似文献