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   260947篇
  免费   3437篇
  国内免费   822篇
电工技术   5146篇
综合类   330篇
化学工业   37403篇
金属工艺   10262篇
机械仪表   8493篇
建筑科学   6140篇
矿业工程   1077篇
能源动力   6406篇
轻工业   22931篇
水利工程   2568篇
石油天然气   3915篇
武器工业   68篇
无线电   34830篇
一般工业技术   50185篇
冶金工业   46960篇
原子能技术   5424篇
自动化技术   23068篇
  2021年   2046篇
  2019年   2040篇
  2018年   3481篇
  2017年   3548篇
  2016年   3739篇
  2015年   2324篇
  2014年   4055篇
  2013年   11327篇
  2012年   6579篇
  2011年   8897篇
  2010年   7011篇
  2009年   7873篇
  2008年   8710篇
  2007年   8643篇
  2006年   7832篇
  2005年   7163篇
  2004年   6912篇
  2003年   6759篇
  2002年   6397篇
  2001年   6493篇
  2000年   6185篇
  1999年   6281篇
  1998年   14368篇
  1997年   10325篇
  1996年   8164篇
  1995年   6451篇
  1994年   5743篇
  1993年   5613篇
  1992年   4566篇
  1991年   4229篇
  1990年   4071篇
  1989年   3789篇
  1988年   3630篇
  1987年   3182篇
  1986年   3071篇
  1985年   3621篇
  1984年   3390篇
  1983年   3036篇
  1982年   2857篇
  1981年   2960篇
  1980年   2777篇
  1979年   2653篇
  1978年   2508篇
  1977年   2964篇
  1976年   3586篇
  1975年   2332篇
  1974年   2322篇
  1973年   2326篇
  1972年   1854篇
  1971年   1750篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A...  相似文献   
72.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for...  相似文献   
73.
74.
Hypoxia formation and breakdown were tracked during 2015 in Muskegon Lake estuary at multiple locations, and five years (2011–2015) of time-series buoy observatory data were evaluated for the effect of episodic wind-events on lake mixing. Bi-weekly water temperature and dissolved oxygen (DO) profiles at four locations revealed that hypoxia occurred at all sites and persisted for 2–3 months during summer 2015. On one date in late-summer, up to 24% of the lake’s volume was estimated to be mildly hypoxic (DO < 4 mg L?1) as defined by lake sturgeon requirements. Patterns of wind speed and water column stability in late spring indicated that high winds and low stability delayed the onset of hypoxia while in late summer low winds and high stability delayed degradation of hypoxia. Wind speeds appear to play a great role in the interannual variability of stratification and subsequent hypoxia. Water temperature and DO profiles taken before and after one mid-summer mixing event (wind speed >7.7 m s?1 for 10 h), indicated that while the wind was unable to completely mix the entire water column, it deepened the epilimnion by ~1.5 m and sheared a thin layer from the upper hypolimnion. By entraining internally loaded nutrients, such episodic wind-events may initiate and sustain algal blooms in nutrient limited surface waters. Quantifying the variable role of wind and mixing events will be key to integrating limnological processes into climate models of the future.  相似文献   
75.
Hyperbaric storage (HS) was evaluated as a new food preservation methodology at room temperature (RT) for beef and pork meat, both minced and in pieces, and compared to refrigeration (RF) storage. The meat samples were stored at 50, 75 and 100 MPa and variable RT up to 60 days. HS at 75 and 100 MPa could not only inhibit microbial growth but also inactivate microorganisms. Regarding physicochemical analyses, an overall equal to better pH maintenance in HS samples was achieved, and similar colour differences between HS and RF were observed. Generally, similarities in moisture content and drip loss between HS (mostly 75 and 100 MPa) and RF were detected (tendency for lower values in the former and higher values in the latter for the higher pressure level). Protein solubility revealed a decrease of sarcoplasmic protein values during storage with a pressure level dependency in some samples.  相似文献   
76.
The dynamic characteristics of a saw gin as a subsystem with lumped and distributed parameters are considered in the paper. On the basis of investigation of the machine assembly, graphs are drawn that allow establishing the maximum values of the angle of relative rotation and the angle of rotation of the saw cylinder shaft under torsion.  相似文献   
77.
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size.  相似文献   
78.
Technical Physics Letters - The influence of excitation photons energy on the relaxation times of photoexcited carriers is studied. The involved relaxation mechanisms are evaluated and the...  相似文献   
79.
Technical Physics Letters - We present the results of a comparative investigation of the friction and wear characteristics of MoSx and MoSex coatings in an oxidizing medium (argon–air...  相似文献   
80.
Technical Physics Letters - The C–V characteristics of Au/Al2O3/In0.52Al0.48As and Au/SiO2/In0.52Al0.48As metal–insulator–semiconductor structures have been studied. It has been...  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