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   85703篇
  免费   6195篇
  国内免费   2893篇
电工技术   4311篇
技术理论   9篇
综合类   4643篇
化学工业   15071篇
金属工艺   4443篇
机械仪表   5236篇
建筑科学   6974篇
矿业工程   1974篇
能源动力   2478篇
轻工业   4894篇
水利工程   1438篇
石油天然气   4477篇
武器工业   492篇
无线电   10414篇
一般工业技术   11224篇
冶金工业   4617篇
原子能技术   828篇
自动化技术   11268篇
  2024年   220篇
  2023年   1251篇
  2022年   1781篇
  2021年   2976篇
  2020年   2298篇
  2019年   1990篇
  2018年   2225篇
  2017年   2473篇
  2016年   2321篇
  2015年   2927篇
  2014年   4007篇
  2013年   5063篇
  2012年   5259篇
  2011年   5543篇
  2010年   4916篇
  2009年   4725篇
  2008年   4474篇
  2007年   4410篇
  2006年   4663篇
  2005年   4142篇
  2004年   2795篇
  2003年   2506篇
  2002年   2202篇
  2001年   2035篇
  2000年   2290篇
  1999年   2571篇
  1998年   2391篇
  1997年   1885篇
  1996年   1742篇
  1995年   1443篇
  1994年   1218篇
  1993年   879篇
  1992年   656篇
  1991年   542篇
  1990年   403篇
  1989年   365篇
  1988年   311篇
  1987年   167篇
  1986年   156篇
  1985年   104篇
  1984年   91篇
  1983年   59篇
  1982年   57篇
  1981年   50篇
  1980年   37篇
  1979年   32篇
  1978年   13篇
  1977年   33篇
  1976年   16篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用镁渣作混合材生产复合硅酸盐水泥试验研究   总被引:6,自引:0,他引:6  
我国现在不仅有传统混合材生产的复合水泥,也有新开辟混合材的复合水泥。传统的混合材为高炉水渣、火山灰、粉煤灰、石灰石、炉渣等;新开辟的混合材有磷渣、增钙液态渣、玄武岩、页岩、铬铁渣等,镁渣是金属镁厂提炼金属镁之后排放出的工业废渣,我国在镁渣复合水泥方面的研究与开发资料报导很少。制备优良性能的复合水泥,关键在于所使用的不同种类的混合材能够优势互补,本实验拟采用镁渣与矿渣进行复合生产镁渣复合硅酸盐水泥。  相似文献   
992.
Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hv bituminous and Wyodak Black Thunder subbituminous coals.

ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390°C. A corresponding decrease in the hydroxyl content of these residues was also noted.  相似文献   

993.
In the field of water quality management, it is vital to determine the main precursory anomalies from the precursor of intricate water bloom in the context of a given area. In this paper, a water bloom precursor analysis method, based on two direction singular rough set, was proposed. This approach was produced on the basis of the different sections and pre-water bloom of water bloom precursor anomalies and characteristic of elements transferred in singular rough set. For testing the validity of two direction singular rough set application in water bloom precursor analysis, Xiangxi River, which is one of the typical tributaries of Three Gorges Reservoir in China, was selected as study area. The result showed that compared with other indexes, pH and dissolved oxygen (DO) are the most valuable indicators of water bloom in the precursory anomalies. Furthermore, regarding with water bloom precursory anomalies in Xiangxi River, most of the nutrient loading and biological community are the key indicators. Hence, this method can determine the main precursory anomaly for water bloom in the study area, which provides powerful knowledge support to water quality specialists for them to comprehensively analyze precursory anomaly so as to find out its relationship with occurrence law of water bloom.  相似文献   
994.
The spatial characteristics and the high-duty water regions of the Water Usage Patterns (WUP) are very important for the allocation and management of water resources. Taken Hubei province, China as an example, we adopted the exploratory spatial data analysis (ESDA) method to investigate the spatial dependence and local patterns of the WUP from 2003 to 2012. Subsequently, the spatial variation mechanisms were analyzed through the gravity center model. The results indicated that the overall spatial dependence of the agricultural WUP was detected (more significant after 2008). Moreover, the global spatial autocorrelation analysis results on the domestic WUP showed statistical significance (Moran’s I?>?0.1, P?<?0.05). These indicated that the local patterns were presented. The high values clustering areas of the agricultural and domestic WUP were mainly distributed in the central province and in the western province respectively. However, the approximate random distribution was identified for the industrial WUP because the industrial development had been conducted widely in the whole province during these years. Furthermore, the governmental policies and natural environment contributed to the spatial evolution tendency of the WUP. An increasing trend of the spatial association of the agricultural WUP and a significant decreasing trend of that of the domestic WUP, which suggested that the natural circumstance superiority and the industrial structure adjustment related to water utilization has been utilized and implemented effectively. This study can provide a useful reference and guidance for scientific planning of water resource systems.  相似文献   
995.
In this study, a scenario-based interval-stochastic fraticle optimization with Laplace criterion (SISFL) method is developed for sustainable water resources allocation and water quality management (WAQM) under multiple uncertainties. SISFL can tackle uncertainties presented as interval parameters and probability distributions; meanwhile, it can also quantify artificial fuzziness such as risk-averse attitude in a decision-making issue. Besides, it can reflect random scenario occurrence under the supposition of no data available. The developed method is applied to a real case of water resources allocation and water quality management in the Kaidu-kongque River Basin, where encounter serve water deficit and water quality degradation simultaneously in Northwest China. Results of water allocation pattern, pollution mitigation scheme, and system benefit under various scenarios are analyzed. The tradeoff between economic activity and water-environment protection with interval necessity levels and Laplace criterions can support policymakers generating an effective and robust manner associated with risk control for WAQM under multiple uncertainties. These discoveries avail local policymakers gain insight into the capacity planning of water-environment to satisfy the basin’s integrity of socio-economic development and eco-environmental sustainability.  相似文献   
996.
ABS/PVC合金的研究   总被引:14,自引:1,他引:14  
研究了ABS/PVC合金的相结构和ABS含量对合金力学性能、加工性能的影响,借助TGA、IR等方法研究了ABS/PVC合金的热稳定性,结果表明,ABS/PVC合金具有良好的综合性能。  相似文献   
997.
喷混凝土拱肋是加固软弱围岩的一种有效支护形式,其间距主要根据经验确定,可能偏大或偏小。为了揭示拱肋间距对加筋拱肋加固效应的影响,采用基于有限差分法的FLAC3D软件对施工期某地下厂房交通洞软弱围岩在拱肋间距分别在1.0―5.0m之间变化情况下变形、应力和屈服区等分布规律进行了对比仿真模拟。仿真结果表明:拱肋间距越大,围岩变形、顶拱最大主压应力和塑性屈服区越大,拱肋承受荷载越大;且拱肋间距介于2.0―3.0m时,能充分发挥围岩自承作用和拱肋支护潜力,围岩变形稳定满足要求,支护成本最低。本文的研究成果为确定喷混凝土拱肋合理间距提供了重要参考。  相似文献   
998.
综述了国内外大分子相容剂在填充聚烯烃塑料中的应用,以及大分子相容剂改性填充聚烯烃塑料的物理与力学性能;指出大分子相容剂用于填充塑料,能改善高分子基体与填料间界面粘结,提高填充塑料复合材料的物理与力学性能,比传统有机偶联剂更具特点。  相似文献   
999.
天然珊瑚有三维贯通的多孔网络结构,它的主要成分碳酸钙(CaC03)在人体环境可降解。模拟珊瑚的组成与结构,研制新型的组织工程支架材料有着良好的应用前景。本文探索了多孔碳酸钙陶瓷的制备方法,并通过盐析法制备了一种多孔的碳酸钙陶瓷,有望获得高的孔隙率和孔连通性。  相似文献   
1000.
MAH接枝EPDM增韧PA66的研究   总被引:7,自引:0,他引:7  
研究了MAH(马来酸酐)接枝三元乙丙橡胶(EPDM—g-MAH)对尼龙66(PA66)的增韧作用。利用SEM(扫描电镜)观察了共混体系的微观形貌(形态结构),并运用小角激光散射(SALS)方法研究了EPDM的加入对PA66结晶性能的影响。结果表明,未接枝的EPDM与PA66的相容性很差,而EPDM—g—MAH与PA66相容性明显增加,EPDM-g—MAH粒子均匀分散在PA66中,共混体系力学性能有很大提高。随着EPDM—g—MAH用量的增加,PA66球晶尺寸变小,共混体系界面结合更加紧密。  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