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   29963篇
  免费   2767篇
  国内免费   1477篇
电工技术   2014篇
技术理论   2篇
综合类   2073篇
化学工业   4845篇
金属工艺   1486篇
机械仪表   1994篇
建筑科学   2996篇
矿业工程   807篇
能源动力   827篇
轻工业   2413篇
水利工程   532篇
石油天然气   1328篇
武器工业   232篇
无线电   3660篇
一般工业技术   3501篇
冶金工业   1151篇
原子能技术   399篇
自动化技术   3947篇
  2024年   112篇
  2023年   536篇
  2022年   984篇
  2021年   1420篇
  2020年   1009篇
  2019年   834篇
  2018年   897篇
  2017年   998篇
  2016年   930篇
  2015年   1160篇
  2014年   1541篇
  2013年   1786篇
  2012年   2014篇
  2011年   2137篇
  2010年   1996篇
  2009年   1878篇
  2008年   1737篇
  2007年   1637篇
  2006年   1572篇
  2005年   1341篇
  2004年   892篇
  2003年   831篇
  2002年   820篇
  2001年   740篇
  2000年   668篇
  1999年   695篇
  1998年   492篇
  1997年   470篇
  1996年   462篇
  1995年   366篇
  1994年   307篇
  1993年   204篇
  1992年   157篇
  1991年   109篇
  1990年   82篇
  1989年   78篇
  1988年   62篇
  1987年   40篇
  1986年   23篇
  1985年   20篇
  1984年   12篇
  1983年   9篇
  1982年   11篇
  1981年   8篇
  1980年   10篇
  1979年   10篇
  1977年   4篇
  1962年   42篇
  1961年   39篇
  1960年   16篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
In recent years, the conservation of industrial heritage in China has gained increasing attention within the broader context of urban conservation practices. For both policy-makers and scholars, accommodating this industrial heritage will emerge as a pertinent issue for consideration as a growing number of industrial architectural legacies dating from the Republican and Maoist eras come under (re)development pressures. This paper thus traces the development of industrial heritage conservation practices in China and discusses several dilemmas intrinsic to this type of conservation, including issues of authenticity, representativeness, and distinction. Based on comparative case studies from China and other international precedents, this paper also seeks to illustrate the different approaches that could be pursued while still attaining a balance between competing interests and claims.  相似文献   
992.
正1概述丰满水电站始建于1937年的伪满时期,1943年第一台机组发电,1953年大坝建成,1959年一期机组(552.5 MW)全部投产,并在20世纪90年代陆续扩建了二期、三期厂房。丰满水电站总装机容量为1 002.5 MW,丰满水电站在东北电力系统中担负着发电、调峰、调频、事故备用等任务,是东北电力系统中的主力调峰电源和事故备用电源。由于工程建设于特殊性的历史时期,大坝设计与施工存在严  相似文献   
993.
A synthesized chromium‐based metal organic framework (Cr‐MOF) was used for the adsorption of halogenated anesthetics, i.e., sevoflurane (SF). Adsorption isotherm and breakthrough experiments involving SF (reference sorbate) and water vapor were measured at 298 K and atmospheric pressure on both Cr‐MOF and a commercially used reference adsorbent. The Cr‐MOF MIL‐101 showed a significantly higher SF adsorption capacity and much higher selectivity relative to water vapor compared to the reference adsorbent. Binary‐mixture breakthrough tests demonstrated a “roll‐up effect” for SF on the reference adsorbent while no such effect was observed on MIL‐101.  相似文献   
994.
995.
福宝山盆地位于川东-鄂西地区,是中国东部重要的含盐层系盆地,共包含4个含盐层系,分别为嘉陵江组二段、四段、五段和巴东组一段。由于受到地表水的溶蚀和淋滤,岩溶塌陷普遍发育,构成呈层分布的盐溶角砾岩带。该区盐溶角砾岩可分为3种类型,碳酸盐质盐溶角砾岩、泥质盐溶角砾岩和杂砾盐溶角砾岩。盐溶角砾岩的成因指示了其成盐环境,为寻找地下盐类矿床指明方向。  相似文献   
996.
近些年随着人们生活水平的提高,中国人在美容方面的需求不断加大,使得医学美容行业的发展极具活力,与之相应的美容医疗设备及技术的未来市场容量将非常可观。  相似文献   
997.
In this study, after purification, the content of betacyanins in dragon fruit peels was 9.22 mg g−1 dry sample. The stability of betacyanins under the effect of different concentration of metal cation (K+, Na+, Cu2+, Fe2+, Fe3+, Mg2+, Al3+) solutions and sugars (glucose, sucrose, fructose, maltose and lactose) solutions was observed. The results showed that 10% lactose and 0.08 mol L−1 potassium chloride solution increased the stability of betacyanins and could be used as stabiliser agents. The degradation reaction under different temperatures (20, 30, 40, 50, 60, 70, 80 °C), pH (2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0) and light conditions (light and dark) of mixed solution (betacyanins and stabiliser), including aqueous pigments solution (APS), lactose pigments solution (LPS) and potassium chloride pigments solution (PCPS), accorded with the first-order reaction kinetics. The t1/2 values (the hours needed for 50.0% degradation of betacyanins) of LPS even up to 330.0 h at 20 °C and dark condition.  相似文献   
998.
Perforated blockages with inclined impingement holes are one of the cooling methods that can be used in the trailing edge of gas turbine. This method has a high heat transfer enhancement as well as high frictional resistance. Numerical investigation has been conducted to make a deep insight into the flow fields and pressure distribution of this cooling structure. Split of high heat transfer region has been detected in the impingement region, which may enlarge the thermal stress of metal bulk. The pressure gradient and counter rotating vortex is found to be the mainspring of this phenomenon. Large total pressure dissipation is founded within the impingement chambers.  相似文献   
999.
Effects of droplet characteristics of mist/air cooling on heat transfer for three pin-fin structures are investigated. The round-tip pin-fin structure is newly proposed with partial detachment from one endwall with a round-shaped tip structure. A flat-tip pin-fin with partial detachment and a traditional pin-fin with full attachment serve as references. Reynolds-averaged Navier-Stokes equations and the shear-stress-transport turbulence model are applied. Influences of initial mist temperature, initial mist diameter and initial mist velocity are analyzed in the Reynolds number range 15,000 to 50,000. The round-tip pin-finned channel has highest heat transfer coefficient and lowest pressure loss among the structures. Heat transfer enhancement increases first gradually and then decreases sharply with increasing initial mist diameter but an optimal diameter exists for the highest Nusselt numbers. Nusselt number decreases monotonically with increasing initial mist temperature. Droplet movement and heat transfer are nearly independent of initial mist velocity.  相似文献   
1000.
In this paper, a discontinuous least-squares (DLS) finite-element method is introduced. The novelty of this work is twofold, to develop a DLS formulation that works for general polytopal meshes and to provide rigorous error analysis for it. This new method provides accurate approximations for both the primal and the flux variables. We obtain optimal-order error estimates for both the primal and the flux variables. Numerical examples are tested for polynomials up to degree 4 on non-triangular meshes, i.e. on rectangular and hexagonal meshes.  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