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   363篇
  免费   11篇
  国内免费   1篇
电工技术   24篇
化学工业   138篇
金属工艺   6篇
机械仪表   5篇
建筑科学   4篇
矿业工程   1篇
能源动力   12篇
轻工业   23篇
石油天然气   1篇
无线电   16篇
一般工业技术   91篇
冶金工业   20篇
原子能技术   17篇
自动化技术   17篇
  2023年   2篇
  2022年   3篇
  2021年   5篇
  2019年   4篇
  2018年   1篇
  2017年   8篇
  2016年   10篇
  2015年   5篇
  2014年   9篇
  2013年   33篇
  2012年   21篇
  2011年   22篇
  2010年   15篇
  2009年   15篇
  2008年   11篇
  2007年   15篇
  2006年   9篇
  2005年   9篇
  2004年   11篇
  2003年   15篇
  2002年   8篇
  2001年   4篇
  2000年   13篇
  1999年   10篇
  1998年   10篇
  1997年   6篇
  1996年   8篇
  1995年   7篇
  1994年   12篇
  1993年   9篇
  1992年   4篇
  1991年   2篇
  1990年   5篇
  1989年   6篇
  1988年   3篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   7篇
  1980年   7篇
  1979年   4篇
  1978年   3篇
  1977年   1篇
  1976年   4篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
  1966年   1篇
排序方式: 共有375条查询结果,搜索用时 15 毫秒
31.
New biomarkers are needed to further stratify the risk of malignancy in intraductal papillary mucinous neoplasm (IPMN). Although microRNAs (miRNAs) are expected to be stable biomarkers, they can vary owing to a lack of definite internal controls. To identify universal biomarkers for invasive IPMN, we performed miRNA sequencing using tumor-normal paired samples. A total of 19 resected tissues and 13 pancreatic juice samples from 32 IPMN patients were analyzed for miRNA expression by next-generation sequencing with a two-step normalization of miRNA sequence data. The miRNAs involved in IPMN associated with invasive carcinoma were identified from this tissue analysis and further verified with the pancreatic juice samples. From the tumor-normal paired tissue analysis of the expression levels of 2792 miRNAs, 20 upregulated and 17 downregulated miRNAs were identified. In IPMN associated with invasive carcinoma (INV), miR-10a-5p and miR-221-3p were upregulated and miR-148a-3p was downregulated when compared with noninvasive IPMN. When these findings were further validated with pancreatic juice samples, miR-10a-5p was found to be elevated in INV (p = 0.002). Therefore, three differentially expressed miRNAs were identified in tissues with INV, and the expression of miR-10a-5p was also elevated in pancreatic juice samples with INV. MiR-10a-5p is a promising additional biomarker for invasive IPMN.  相似文献   
32.
Sub-micron sized Zn2SiO4:Mn2+ phosphors particles were continuously synthesized in supercritical water with a flow reactor. Colloidal silica or sodium silicate was used as the Si source. Zn and Mn sources were chosen from their nitrates, sulfates, and acetates. The syntheses were carried out at temperatures from 400 to 500 °C, at pressures from 30 to 35 MPa, at NaOH concentrations from 0.014 to 0.025 M, and for residence times from 0.025 to 0.18 s. Sodium silicate formed α- and β-Zn2SiO4:Mn2+ phases regardless of the Zn and Mn sources, while colloidal silica formed phases dependent on the type of Zn and Mn sources used in addition to the use of alkali. As the reaction temperature increased, the crystallinity of α-Zn2SiO4:Mn2+ phase increased and the Mn substitution into the Zn sites of the α-Zn2SiO4 phase decreased. Of the conditions studied, the most highly crystalline α-Zn2SiO4:Mn2+ was produced at a temperature of 400 °C, a pressure of 30 MPa, a NaOH concentration of 0.14 M, and a residence time of 0.13 s with Zn and Mn sulfates and colloidal silica as starting materials. The α-Zn2SiO4:Mn2+ fine particles synthesized were round in shape, had an average diameter of 268 nm, and exhibited a green-emission with a peak wavelength of 524 nm.  相似文献   
33.
野外试验场黄土的理化分析   总被引:7,自引:6,他引:7  
本实验为低,中水平放射性废物浅地层处置安全评价提供现场土壤的物理化学参数。采样深度在0.5-9.1m范围内,每个样品进行10项测定;矿物组成,粒度分布、密度、总孔隙度、有效孔隙度、给水度、持水度、渗透系数、阳离子交换容量、含水量。  相似文献   
34.
Niobium- or vanadium-doped anatase sols were prepared by hydrothermal treatment of 0.1 mol/dm3 peroxotitanium complex aqueous solutions dissolving 0–10 mol% niobium or vanadium at 100°C for 8 h. Niobium-doping caused the increase of lattice constants of anatase and the shape change of anatase crystal from spindle-like to cubic-like structure, but no change of the optical absorbance. Vanadium-doping caused the decrease of lattice constant of c -axis, the miniaturization of anatase crystal and the increase of optical absorbance at the wavelength from 350–700 nm.  相似文献   
35.
This paper proposes a new belt drive control method for reducing a belt velocity-fluctuation that is caused by a belt thickness-variation in the circumferential direction. A belt driving system performs feedback control with a rotary encoder-output mounted on a driven roller. This proposed method correct the reference value of the feedback control for the purpose of the belt velocity regulation. The correction includes two steps. The first step acquires the encoder-output of the driven roller and calculates the rotational angular velocity-fluctuation with one cycle of the belt rotation. The second step converts from the velocity-fluctuation to the correction value of the feedback reference. The correction value cancels a detection error of the driven roller caused by the belt thickness-variation. After these steps, the belt driving system controls the belt velocity as compensating the belt velocity-fluctuation. Experimental result showed the significant fluctuation reduction on a typical tandem-engine printer.  相似文献   
36.
In this letter, we have developed a novel technique for improving the temperature stability of an athermal silica-based arrayed-waveguide grating with a resin-filled groove. We compensated for the residual second-order temperature dependence of the passband wavelength using the pressure-induced refractive index change in a resin inserted into the optical paths. Pressure control under the temperature variation was achieved by using a structure composed of an optical fiber piston and bimetal actuators. We demonstrated that the passband wavelength variation was successfully reduced from 0.080 to 0.025 nm in a -40degC - 85degC temperature range, without any insertion loss increase or spectral change.  相似文献   
37.
38.
Sintered spheres(made of glass beads) were simply produced with a definite diameter, with a precision of ±0·5 mm in diameter, for a wide range of sintered angles (0-27°). The experimental values of the porosity of the sintered spheres were consistent with the calculated results for the coordination number N ≠ 8. The residual equilibrium saturation, as one of the basic physical properties of sintered glass beads was investigated experimentally and theoretically, resulting in the presence of a distribution in the angle of pendular ring.  相似文献   
39.
The problem of handling the fragile carbon foils (mounting on the frame, placing in the stripper changer) that easily break when self-supporting has been solved by coating carbon foils with poly-monochloro-para-xylylene. It was found that the polymer-coating method could also be used to produce carbon foils thicker than 100 μg/cm2 by alternated deposition of carbon and poly-monochloro-para-xylylene layers. Carbon foil of 500 μg/cm2 thick and 10 cm in diameter was produced by this method and mounted to a foil holder. Results of lifetime measurement for singly coated foils are also presented.  相似文献   
40.
A reactive solid-phase epitaxy (R-SPE) method combines deposition of a thick amorphous or polycrystalline layer with a desired chemical composition and post-deposition solid-phase epitaxial growth. The solid-phase epitaxial growth is invoked by thermal annealing with an assistance of a sacrificial layer working as an epitaxial template. Thereby it enables us to grow high-quality epitaxial films of complex oxides whose epitaxial films are not grown by conventional high-temperature growth techniques. It was reported that 2-nm-thick ZnO layers worked as template for growing InGaO3(ZnO)m (m = integer) epitaxial films. The present study extended the R-SPE technique to growth of various complex oxides with chemical compositions of RAO3(MO)m and to use of various epitaxial template layers. We found that mono oxide epitaxial layers such as In2O3 and Ga2O3 work as template layers as well. Alternatively, a ZnO epitaxial layer is also applicable to ZnO-free compounds. The films obtained were grown heteroepitaxially on YSZ(111) and single-crystalline when the fabrication conditions are optimized.  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