全文获取类型
收费全文 | 34293篇 |
免费 | 2385篇 |
国内免费 | 1206篇 |
专业分类
电工技术 | 1504篇 |
综合类 | 1924篇 |
化学工业 | 5921篇 |
金属工艺 | 1563篇 |
机械仪表 | 1894篇 |
建筑科学 | 2998篇 |
矿业工程 | 610篇 |
能源动力 | 1050篇 |
轻工业 | 2056篇 |
水利工程 | 480篇 |
石油天然气 | 1812篇 |
武器工业 | 210篇 |
无线电 | 4063篇 |
一般工业技术 | 4378篇 |
冶金工业 | 2794篇 |
原子能技术 | 435篇 |
自动化技术 | 4192篇 |
出版年
2024年 | 102篇 |
2023年 | 444篇 |
2022年 | 728篇 |
2021年 | 1098篇 |
2020年 | 841篇 |
2019年 | 721篇 |
2018年 | 792篇 |
2017年 | 932篇 |
2016年 | 853篇 |
2015年 | 1110篇 |
2014年 | 1442篇 |
2013年 | 1861篇 |
2012年 | 1963篇 |
2011年 | 2129篇 |
2010年 | 1784篇 |
2009年 | 1791篇 |
2008年 | 1744篇 |
2007年 | 1728篇 |
2006年 | 1775篇 |
2005年 | 1600篇 |
2004年 | 1100篇 |
2003年 | 992篇 |
2002年 | 979篇 |
2001年 | 830篇 |
2000年 | 910篇 |
1999年 | 1008篇 |
1998年 | 1227篇 |
1997年 | 951篇 |
1996年 | 900篇 |
1995年 | 703篇 |
1994年 | 556篇 |
1993年 | 518篇 |
1992年 | 318篇 |
1991年 | 244篇 |
1990年 | 244篇 |
1989年 | 178篇 |
1988年 | 157篇 |
1987年 | 113篇 |
1986年 | 91篇 |
1985年 | 68篇 |
1984年 | 47篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 30篇 |
1980年 | 29篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 38篇 |
1976年 | 74篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
详细介绍了进口的VPSA制氧装置的流程特点、工艺参数及主要设备的配置。实际运转证明 ,该制氧装置具有运行可靠、启动时间短、部分负荷性能优越、负荷转换速度快等优点 ,能满足金隆铜业有限公司的实际生产要求。 相似文献
122.
123.
This article presents a detailed investigation on the influence of the phosphorus element upon the laser sintering of a multicomponent
Cu-based metal powder system consisting of Cu, Cu-10Sn, and Cu-8.4P. Powder systems containing 0, 10, 15, and 20 wt pct CuP
were sintered in atmosphere at room temperature using the following optimal processing parameters: laser power of 350 W, scan
speed of 0.04 m/s, scan line spacing of 0.15 mm, and layer thickness of 0.25 mm. It was found that the relative density of
the sintered sample with 15 wt pct CuP increased by 24,4 pct as compared with the sample without phosphorus addition. A further
increase in the CuP content (≥20 wt pct), however, resulted in a poor densification with a serious delamination. The exact
metallurgical roles of the phosphorus element in the laser sintering process were addressed as follows. First, the phosphorus
could prevent the sintering system from oxidation by forming CuPO3, thereby improving the wetting characteristics and the sintering kinetics. Second, the phosphorus could decrease the surface
tension of molten materials, leading to a successive transition from highly discontinuous sintered tracks to fairly coherent
ones with increasing the phosphorus content. Third, the phosphorus could lower the melt viscosity, thereby improving the microstructural
homogeneity of the laser-sintered samples. 相似文献
124.
125.
Effect of Cerium on Expression and Activity of MMP-9 from Human Carcinoma of Bladder Cell Line 总被引:1,自引:0,他引:1
Rareearthshaveledtowidespreadinterestsinlifescience ,whilethescientistsdoresearchesdeeplyinmedicalandbiochemicalfields .Rareearthsplaypotentialrolesininhibitingcancer ,andalargenum berofscientistsdedicatethemselvestoit[1] .Thema trixmetalloproteinases (MMPs)areafamilyofatleast1 7humanzinc dependentendopeptidasesthatareca pableofdegradingalmostallextracellularmatrix(ECM)components .Theyareessentialinmanyphys iologicalprocessesandseveralpathologicalconditions ,suchastumorprogression .MMPsare… 相似文献
126.
单壁碳纳米管的制备及生长特性研究 总被引:1,自引:0,他引:1
采用Fe/MgO作为催化剂 ,催化裂解CH4制备了较纯的单壁碳纳米管 ,用TEM和Raman对碳纳米管进行了表征 ,对不同生长温度下制备的碳纳米管Raman径向呼吸振动峰 (RBM)进行了分析 ,研究了生长温度对单壁碳纳米管生长特性和结构特性的影响 相似文献
127.
城市化进程中的小城镇交通初探 总被引:4,自引:0,他引:4
通过对小城镇城市结构、路网结构、交通结构和交通管理特征进行详细分析,得出小城镇交通问题症结所在,并初步提出小城镇交通规划和交通治理的对策。 相似文献
128.
129.
It is well established that the indentation hardness of metallic alloys shows a reasonable correlation with their yield strength or ultimate strength. Experiments illustrate that such a unique correlation is nonexistent for discontinuously reinforced metal matrix composites, even when the indentation size is much greater than the reinforcement size. For aluminum alloys reinforced with silicon carbide particles, the same composite yield strength and tensile strength with different reinforcement fractions do not lead to similar hardness, or vice versa. Finite element analyses are carried out to rationalize the experimental findings. The modeling utilizes a two-dimensional plane-strain formulation. Discrete particles are included in the material model, and the overall stress-strain response and the indentation response are numerically simulated. The results confirm the lack of unique correspondence between the composite hardness and strength. The alteration of local heterogeneity in the composite is found to affect the indentation response. Effects of the geometrical arrangement of particles and thermal residual stresses on the indentation response are also investigated numerically. 相似文献
130.
Lin-Ping Shen Wei-Ping Huang Shui-Sheng Jian 《Lightwave Technology, Journal of》2003,21(7):1644-1651
A general procedure for design of photonic crystal fibers (PCFs) with desirable dispersion properties is presented. The design model is based on the combination of a rigorous vector mode solver and a scaling transformation for the dispersion properties of the PCFs. In comparison with the conventional design method, the new design procedure is more efficient and can be readily automated for the purpose of design optimization. Several applications of the design procedure, e.g., the design optimization for dispersion shifted fibers, dispersion flattened fibers, and dispersion compensation fibers, are demonstrated and discussed. 相似文献