首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   514篇
  免费   8篇
  国内免费   4篇
电工技术   26篇
化学工业   71篇
金属工艺   22篇
机械仪表   24篇
建筑科学   14篇
能源动力   15篇
轻工业   56篇
水利工程   2篇
石油天然气   1篇
无线电   41篇
一般工业技术   74篇
冶金工业   127篇
原子能技术   6篇
自动化技术   47篇
  2022年   8篇
  2021年   13篇
  2020年   4篇
  2019年   2篇
  2018年   6篇
  2017年   7篇
  2016年   11篇
  2015年   4篇
  2014年   6篇
  2013年   23篇
  2012年   16篇
  2011年   20篇
  2010年   16篇
  2009年   12篇
  2008年   17篇
  2007年   20篇
  2006年   17篇
  2005年   6篇
  2004年   14篇
  2003年   11篇
  2002年   15篇
  2001年   20篇
  2000年   13篇
  1999年   22篇
  1998年   51篇
  1997年   28篇
  1996年   25篇
  1995年   16篇
  1994年   15篇
  1993年   7篇
  1992年   5篇
  1991年   4篇
  1990年   8篇
  1989年   7篇
  1988年   3篇
  1987年   3篇
  1986年   3篇
  1985年   4篇
  1984年   10篇
  1983年   1篇
  1982年   3篇
  1981年   4篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   5篇
  1976年   7篇
  1975年   2篇
  1974年   1篇
  1973年   1篇
排序方式: 共有526条查询结果,搜索用时 15 毫秒
31.
Bone marrow-mesenchymal stem/stromal cells (MSCs) may offer promise for skeletal muscle repair/regeneration. Growing evidence suggests that the mechanisms underpinning the beneficial effects of such cells in muscle tissue reside in their ability to secrete bioactive molecules (secretome) with multiple actions. Hence, we examined the effects of MSC secretome as conditioned medium (MSC-CM) on ex vivo murine extensor digitorum longus muscle injured by forced eccentric contraction (EC). By combining morphological (light and confocal laser scanning microscopies) and electrophysiological analyses we demonstrated the capability of MSC-CM to attenuate EC-induced tissue structural damages and sarcolemnic functional properties’ modifications. MSC-CM was effective in protecting myofibers from apoptosis, as suggested by a reduced expression of pro-apoptotic markers, cytochrome c and activated caspase-3, along with an increase in the expression of pro-survival AKT factor. Notably, MSC-CM also reduced the EC-induced tissue redistribution and extension of telocytes/CD34+ stromal cells, distinctive cells proposed to play a “nursing” role for the muscle resident myogenic satellite cells (SCs), regarded as the main players of regeneration. Moreover, it affected SC functionality likely contributing to replenishment of the SC reservoir. This study provides the necessary groundwork for further investigation of the effects of MSC secretome in the setting of skeletal muscle injury and regenerative medicine.  相似文献   
32.
An improved method is described for the sol–gel preparation of PLZT thin layers in the perovskite structure. The method uses a PbO cover coat. Details are reported for the sol-gel processing route and heat-treatment conditions. Through use of this method it is possible to prepare singlephase perovskite material with improved properties. The deleterious effect of additional phases—which are not present when a PbO cover coat is used—is attributed to Pb loss from the surface during thermal processing. Examples are given for PLZT thin layers integrated on Si with and without a PbO cover coat. The dielectric and ferroelectric properties were always found to be superior for coated structures.  相似文献   
33.
The influence of crystal thickness of metal-coated <100>-cut GaAs (M-G-M) on Cherenkov-phase-matched terahertz (THz) pulse detection was studied. The M-G-M detectors were utilized in conjunction with a metallic tapered parallel-plate waveguide (TPPWG). Polarization-sensitive measurements were carried out to exemplify the efficacy of GaAs in detecting transverse magnetic (TM)- and transverse electric (TE)-polarized THz waves. The reduction of GaAs’ thickness increased the THz amplitude spectra of the detected TM-polarized THz electro-optic (EO) signal due to enhanced electric field associated with a more tightly-focused and well-concentrated THz radiation on the thinner M-G-M. The higher-fluence THz beam coupled to the thinner M-G-M improved the integrated intensity of the detected THz amplitude spectrum. This trend was not observed for TE-polarized THz waves, wherein the integrated intensities were almost comparable. Nevertheless, good agreement of spectral line shapes of the superposed TM- and TE-polarized THz-EO signals with that of elliptically polarized THz-EO signal demonstrates excellent polarization-resolved detection capabilities of M-G-M via Cherenkov-phase-matched EO sampling technique.  相似文献   
34.
Shown in this paper is a practical method of control using neural network and fuzzy control techniques, where a neural network estimates the target of fuzzy control. The neural network is used to estimate the transient state of a plant which has nonlinear processes such as refrigerating and filtering. The suitable control target pattern for fuzzy control is selected according to this estimation. This method is applied to control the tank level of a solvent dewaxing plant for: 1) changing the tank outflow rate smoothly, and 2) keeping the tank level stable. The results show that this system can control the tank level effectively in both steady state and transient state  相似文献   
35.
Optically active alcohol is an important building block as a versatile chiral synthon for the asymmetric synthesis of pharmaceuticals and agrochemicals. We purified and characterized glycerol dehydrogenase from Hansenula ofunaensis and prepared optically active 1,2-octanediol using a recombinant Escherichia coli harboring the glycerol dehydrogenase gene. The deduced amino acid sequence was investigated for identities with those of other alcohol dehydrogenases in the NCBI databank. The identification of the unknown product of a resting-cell reaction was performed by GC-MS. In the deduced amino acid sequence composed of 376 residues, the NAD(H) binding pattern and cysteine residues that correspond to the cysteine ligands at the zinc atom were conserved as they are in alcohol dehydrogenases from other origins. Glycerol dehydrogenase from Hansenula polymorpha DL-1 (Pichia angusta, DDBJ/EMBL/GenBank accession no. BAD32688) had the highest identity to our enzyme, showing 73% identity. Our glycerol dehydrogenase catalyzed the NAD(+)-dependent oxidation of long-chain secondary alcohols such as 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and 1,2-octanediol. Activities toward 2,4-pentanediol and 2,5-hexanediol were hardly detected. From these results, it was confirmed that our enzyme requires two hydroxyl groups on adjacent carbon atoms for oxidation. 2,3-Pentanedione, 2,3-hexanedione, and 3,4-hexanedione were significantly reduced. The transformants oxidized only (R)-1,2-octanediol in 50 mM racemate (R:S=52:48), and produced (S)-1,2-octanediol (24 mM, <99.9% e.e.) after 24 h of incubation. The reaction product was suggested to be 1-hydroxy-2-octanone by GC-MS, which showed secondary hydroxyl groups oxidized. Glycerol dehydrogenase from H. ofunaensis could be useful for the production of long-chain optically active secondary alcohols.  相似文献   
36.
功能纤维的现状和展望   总被引:3,自引:0,他引:3  
综述了日本已开发的功能纤维的品种 ,技术措施 ;日本、美国在新世纪研究开发新纤维的规划、设想 ,中长期开发课题、技术战略 ,指出了 2 1世纪功能纤维的开发应用前景。  相似文献   
37.
The piezoresistive mechanisms of composite thick films based on RuO2 particles and both calcium-borosilicate and bismuth-borosilicate glass matrices were investigated by chemical and electrical microanalyses. The resistor based on bismuth-borosilicate glass showed higher sensitivity than that based on calcium-borosilicate glass. It was confirmed that the diffusion of ruthenium into glass affects the binding state of RuO2 at the interface of the glass. Furthermore, an intermediate resistive layer is detected around the RuO2 particle. These results suggest that the piezoresistive effect is related to a change in the electrical conductivity of the interfacial reaction layer caused by the diffusion of ruthenium into glass.  相似文献   
38.
A photoconductive dipole antenna can be used as a transceiver, which alternately transmits pulsed electromagnetic radiation and receives the return signal. Preliminary results of using a photoconductive terahertz transceiver with femtosecond optics are reported  相似文献   
39.
The confinement of alpha particle is important in tokamaks. The trajectory or confinement of alpha particles is often calculated with guiding center approximation. The features of spherical tokamak can break the approximation. We investigate finite Larmor radius effect. The orbit calculated by equation of motion is different, especially in toroidal direction, from that by guiding center equations. This difference causes difference of ripple resonance energy and the difference of the peaks of the diffusion coefficients. Furthermore, because of the additional free parameter, Larmor phase, the peaks of diffusion coefficient calculated by equation of motion are broader than those by guiding center equations.  相似文献   
40.
We found 11 genes (FAO1-11) encoding putative oxidoreductases in the Aspergillus oryzae genome, which are similar to fungal fructosyl-amino acid oxidases. The cDNAs corresponding to the genes were cloned and expressed in Escherichia coli. rFao2 had fructosyl-amino acid oxidase activity, whereas rFao1 did not show any enzyme activity, even though the deduced amino acid sequence of Fao1 is identical to that of one of the fructosyl-amino acid oxidase isozymes from Aspergillus oryzae. rFao7 and rFao8 showed oxidase activity toward sarcosine, L-pipecolate, and L-proline. rFao10 was active toward only sarcosine, of the substrates tested. The functions of the other proteins were also predicted from a phylogenetic analysis.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号