首页 | 官方网站   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   9085篇
  免费   991篇
  国内免费   379篇
工业技术   10455篇
  2024年   80篇
  2023年   234篇
  2022年   425篇
  2021年   564篇
  2020年   408篇
  2019年   327篇
  2018年   384篇
  2017年   415篇
  2016年   352篇
  2015年   442篇
  2014年   489篇
  2013年   574篇
  2012年   586篇
  2011年   618篇
  2010年   516篇
  2009年   498篇
  2008年   415篇
  2007年   387篇
  2006年   401篇
  2005年   354篇
  2004年   226篇
  2003年   242篇
  2002年   219篇
  2001年   188篇
  2000年   201篇
  1999年   177篇
  1998年   127篇
  1997年   99篇
  1996年   106篇
  1995年   88篇
  1994年   68篇
  1993年   45篇
  1992年   43篇
  1991年   43篇
  1990年   27篇
  1989年   23篇
  1988年   16篇
  1987年   15篇
  1986年   6篇
  1985年   3篇
  1984年   5篇
  1983年   3篇
  1982年   1篇
  1981年   4篇
  1980年   7篇
  1975年   1篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
在研究不同钢渣掺量胶凝体系稳定性的基础上,以40%的钢渣粉掺加15%矿渣粉、5%硅灰粉,采用自配复合激发剂成功地制备出早期抗折强度、抗压强度达到4.5MPa、18.8MPa且满足42.5强度等级的复合胶凝材料,通过其孔隙率及微观结构测试分析表明:钢渣复合胶凝材料水化产物致密,孔隙率低,后期抗压强度、抗折强度发展较好。  相似文献   
952.
Copper wire is used to remove vanadium from crude TiCl4 in titania and titanium sponge production which produces a copper–vanadium precipitate. The recovery of copper and vanadium from this precipitate was studied. Experiments found that the precipitate can be naturally oxidized by stacking for one month in air, converting > 90% metallic copper contained in the original precipitate into CuCl2·2H2O, Cu2Cl(OH)3 and Cu2(OH)3Cl. The copper oxy-chlorides were easily converted to Cu(OH)2 by stirring in dilute NaOH at pH 11 and 80 °C under a liquid-to-solid ratio of 4:1. When the pH was lowered to about pH 2.5 by sulfuric acid, iron, titanium and vanadium oxides remained in the first acid leach residue and copper was selectively leached into solution. By evaporating and cooling the leach solution, a product of CuSO4·5H2O with 99.7% purity was obtained.To recover the vanadium, the filter cake was roasted with Na2CO3 at 700 °C for 3 h under the stoichiometric proportion of 2.5 for V. The calcine was then leached with water at 70 °C and NH4VO3 was precipitated by the addition of NH4Cl. Calcination of NH4VO3 at 550 °C for 2 h produced V2O5 with a purity of 98.6%. After vanadium recovery, the residue was leached once again with sulfuric acid and the total recoveries of copper and vanadium were 98.6% and 95.7% respectively.  相似文献   
953.
复合材料三维整体编织结构技术与特性   总被引:5,自引:1,他引:5       下载免费PDF全文
复合材料三维整体编织技术是国外八十年代发展起来的高新纺织技术。采用这种技术,创造了一类新的复合材料结构型式,显著改善了多方面的力学特性。已有的应用表明.这种高新技术与结构型式,可广泛应用于航空航天、交通运输、石油化工、武器装备、体育用品等诸多领域。本文综述了复合材料三维整体编织工艺的特点,三维编织结构物,以及某些优异的特性。   相似文献   
954.
杨志波  赵莹莹  谭奇峰 《城市勘测》2020,(1):112-114,119
正在施工的矿坑除存在占地面积大、地形复杂多变等特点外,施测难度也十分巨大、存在安全隐患。本文利用无人机航空摄影和三维激光扫描相结合的技术手段,基于点云和实景三维模型对冰雪世界非拱角区矿坑覆绿岩壁现状进行表面测量,此法较传统方式更安全、更高效,测量成果精度更加可靠,为矿坑表面积及其他体征指标的测绘提供了一种有效的途径。  相似文献   
955.
Cyclic nucleotide-gated channels (CNGCs) constitute a family of non-selective cation channels that are primarily permeable to Ca2+ and activated by the direct binding of cyclic nucleotides (i.e., cAMP and cGMP) to mediate cellular signaling, both in animals and plants. Until now, our understanding of CNGCs in cotton (Gossypium spp.) remains poorly addressed. In the present study, we have identified 40, 41, 20, 20, and 20 CNGC genes in G. hirsutum, G. barbadense, G. herbaceum, G. arboreum, and G. raimondii, respectively, and demonstrated characteristics of the phylogenetic relationships, gene structures, chromosomal localization, gene duplication, and synteny. Further investigation of CNGC genes in G. hirsutum, named GhCNGC1-40, indicated that they are not only extensively expressed in various tissues and at different developmental stages, but also display diverse expression patterns in response to hormones (abscisic acid, salicylic acid, methyl jasmonate, ethylene), abiotic (salt stress) and biotic (Verticillium dahlia infection) stimuli, which conform with a variety of cis-acting regulatory elements residing in the promoter regions; moreover, a set of GhCNGCs are responsive to cAMP signaling during cotton fiber development. Protein–protein interactions supported the functional aspects of GhCNGCs in plant growth, development, and stress responses. Accordingly, the silencing of the homoeologous gene pair GhCNGC1&18 and GhCNGC12&31 impaired plant growth and development; however, GhCNGC1&18-silenced plants enhanced Verticillium wilt resistance and salt tolerance, whereas GhCNGC12&31-silenced plants had opposite effects. Together, these results unveiled the dynamic expression, differential regulation, and functional diversity of the CNGC family genes in cotton. The present work has laid the foundation for further studies and the utilization of CNGCs in cotton genetic improvement.  相似文献   
956.
对于太阳能电池系统、汽车挡风玻璃、相机镜头等光学器件,高透明性是其功能的最重要指标之一.由于这些设备经常暴露在室外,大量的灰尘污垢会严重影响其性能.透明超疏水表面由于具有优异的光学和抗污性能,在光学器材领域有着很高的应用前景.首先总结了表面润湿性理论,主要包括Young润湿方程、Wenzel润湿模型和Cassie润湿模型,通过润湿性理论指出制备超疏水表面的条件——低表面能物质和粗糙结构二者缺一不可.其次,讨论了粗糙度和透明度之间的竞争关系,通过瑞利散射和米氏散射理论,得出制备透明超疏水表面还需要同时满足材料表面粗糙度小于100 nm.然后,归纳总结了近十年来透明超疏水表面常见的制备方法,如溶胶凝胶法、化学气相沉积法、模板法、相分离等方法,并对这些制备思路和方法进行了分析,概括了这些方法当前存在的一些问题.最后,简单介绍了透明超疏水表面在太阳能电池、光学元器件、光催化材料等领域的应用,并对透明超疏水表面的未来研究方向和应用前景进行了展望.  相似文献   
957.
随着聚丙烯酰胺驱油技术在我国油田的大面积推广,含聚污水量也在逐年增加,处理难度逐渐增大。应用微生物降解技术处理含聚污水是一种可行手段,其核心技术是微生物降解聚丙烯酰胺。分析了微生物降解聚丙烯酰胺的机理及评价方法,介绍了微生物利用聚丙烯酰胺作为氮源和碳源的国内外研究进展,对今后含聚污水的微生物处理研究提出了建议。  相似文献   
958.
Crystalline hierarchical hydroxyapatite [Ca10(PO4)6(OH)2, HAp)] fibers were successfully synthesized via a biomimetic route by using cotton cloth as a natural bio-template. The effects of pH value, aging time, ultrasonic cleaning time, and calcination temperature on the purity and morphology of the resulting hydroxyapatite (HAp) were monitored by scanning election microscope (SEM), X-ray diffraction (XRD), and infrared spectrophotometer (IR) to obtain an optimized reaction condition, namely, pH 9, ultrasonic cleaning for 1 min, aging for 24 h, and calcination at 600 °C for 4 h. We found that the natural cellulose could not only control the morphology of HAp but also lower its phase transformation temperature. The impact of this method lies in its low cost and successful production of large-scale patterning of three-dimensional hierarchical HAp fibers.  相似文献   
959.
ZnO thin films were synthesized via hydrothermal method on silicon substrate at various solution concentrations. The thin films were characterized by X-ray diffraction, field-emission scanning electron microscope and UV–Vis spectrophotometer. The results show that the thin films are polycrystalline with wurtzite hexagonal structure. The T c values of (101) surface of the thin film increase from 0.929 to 1.840 at first, and then decrease to 0.779 with increasing solution concentration. The preferential orientation along the (101) crystal surface can be controlled by changing the solution concentration. Solution concentration has a significant effect on surface morphology of the thin films. The optical band gap of the thin films decreases, when the solution concentration of zinc nitrate hexahydrate increases from 0.01 to 0.06 mol/L and then increases when the solution concentration of zinc nitrate hexahydrate further increases to 0.08 mol/L. Photocatalytic activity of the thin films on degradation of methyl orange under UV light irradiation was studied in detail. The ZnO thin film with many cracks prepared from 0.01 mol/L shows the higher photocatalytic activity but the tower-like ZnO thin film prepared from 0.08 mol/L reveals the lower photocatalytic activity. Therefore, the photocatalytic activity of the thin films are mainly relate to surface morphology and crystallographic orientation.  相似文献   
960.
对采用近液相线铸造法制备的ZL201合金半固态坯料进行了热模拟压缩试验。根据试验获得的ZL201合金不同温度与应变速率下的应力-应变曲线,采用多元回归线性方法建立了能够表征ZL201合金半固态变形行为的本构方程。同时,根据半固态浆料的表观粘度与热模拟压缩试验中的应变速率等参数间的关系式,对表观粘度和剪切速率之间的关系进行了研究。利用仿真软件Anycasting对ZL201合金半固态触变压铸成形过程进行了数值模拟,研究了内浇道厚度对ZL201合金半固态触变压铸过程的影响,并预测了铸件缺陷。结果表明,当内浇道厚度为3mm时,半固态金属浆料充型过程最为理想。  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-23

京公网安备 11010802026262号