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   391193篇
  免费   44126篇
  国内免费   38422篇
电工技术   32618篇
技术理论   41篇
综合类   35393篇
化学工业   59190篇
金属工艺   15267篇
机械仪表   25148篇
建筑科学   30596篇
矿业工程   11241篇
能源动力   13593篇
轻工业   26284篇
水利工程   12395篇
石油天然气   14716篇
武器工业   5782篇
无线电   48137篇
一般工业技术   35493篇
冶金工业   12350篇
原子能技术   4769篇
自动化技术   90728篇
  2024年   1950篇
  2023年   6101篇
  2022年   11485篇
  2021年   13521篇
  2020年   13545篇
  2019年   11392篇
  2018年   10729篇
  2017年   14354篇
  2016年   16023篇
  2015年   17575篇
  2014年   23125篇
  2013年   24761篇
  2012年   28935篇
  2011年   31790篇
  2010年   23833篇
  2009年   24109篇
  2008年   24794篇
  2007年   28248篇
  2006年   25923篇
  2005年   22487篇
  2004年   18797篇
  2003年   15763篇
  2002年   12364篇
  2001年   9855篇
  2000年   8193篇
  1999年   6518篇
  1998年   5222篇
  1997年   4185篇
  1996年   3565篇
  1995年   3006篇
  1994年   2511篇
  1993年   1814篇
  1992年   1476篇
  1991年   1164篇
  1990年   964篇
  1989年   749篇
  1988年   524篇
  1987年   330篇
  1986年   299篇
  1985年   339篇
  1984年   318篇
  1983年   190篇
  1982年   266篇
  1981年   138篇
  1980年   152篇
  1979年   73篇
  1978年   34篇
  1977年   32篇
  1974年   18篇
  1959年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
为了保持油井稳产,提高油藏采收率,姬塬油区拟采用面积法注水,急需对油藏分布规律进行详实、系统的研究,以保证井网建设的合理、高效。在前人研究成果基础上,对油区现有测井资料进行收集、整理、再解释,从油藏特征研究出发,对储集层进行测井分析,并使用克里金技术进行了地质建模。使用容积法计算油藏储量,为油区的注水开发提供了油藏资料。  相似文献   
992.
A pseudohyperbolic problem of optimal control of intratumoral drug distribution is formulated. It takes into account the heterogeneity of tumor tissues and effects of convection diffusion in a fissured porous medium. A mathematical model constructed and the corresponding optimal control problem are shown to be correct. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 147–154, November–December 2007.  相似文献   
993.
介绍了株洲硬质合金集团有限公司推进科技创新的具体做法,取得的主要成绩,以及今后的努力方向。  相似文献   
994.
在冶金热力学和动力学及反应工程学原理的基础上,建立了模拟复吹转炉冶炼过程的数学模型.在用梅钢150t复吹转炉工业试验的结果对模型加以验证之后,利用模型对具有中高磷铁水特点的梅钢转炉吹炼工艺进行了分析讨论.  相似文献   
995.
介绍了宝鸡民营钛工业在新材料、新技术、新设备、新应用方面的进展,提供了市场需求与发展前景方面的相关信息,并对中小型钛加工企业的发展提出建议。  相似文献   
996.
A series of low noble-metal coment monolithic catalysts for exhaust purification of small gasoline engines was investigated, and it was found that the Pt/Rh-OSM/Al2O3 (where OSM was oxygen storage material) catalyst with Ce0.5Zr0.5-MnOx(3%MnOx) OSM held low light-off temperature for CO, HC, and NO; quite wide three-way window, and outstanding thermal stability. The catalyst could efficiently comrol exhaust emission of small gasoline engines.  相似文献   
997.
简介了关系模型、键、完整性规则、E-R模型、函数依赖、模式分解和关系模式的范式等数据库技术基础和规范化设计理论,从键和完整性规则的实现、数据冗余的特殊情况和字典设计等方面论述了在实际设计工作中如何灵活运用关系数据库设计理论。  相似文献   
998.
This paper evaluated the capacity of SPOT VEGETATION time-series to monitor herbaceous fuel moisture content (FMC) in order to improve fire risk assessment in the savanna ecosystem of Kruger National Park in South Africa. In situ herbaceous FMC data were used to assess the Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Vegetation Dryness Index (VDI), Improved VDI (IVDI), and Accumulated Relative NDVI Decrement (ARND) during the dry season. The effect of increasing amounts of dead vegetation on the monitoring capacity of derived indices was studied by sampling mixed live and dead FMC. The IVDI was proposed as an improvement of the VDI to monitor herbaceous FMC during the dry season. The IVDI is derived by replacing NDVI with the integrated Relative Vegetation Index (iRVI), as an approximation of yearly herbaceous biomass, when analyzing the 2-dimensional space with NDWI. It was shown that the iRVI offered more information than the NDVI in combination with NDWI to monitor FMC. The VDI and IVDI exhibited a significant relation to FMC with R2 of 0.25 and 0.73, respectively. The NDWI, however, correlated best with FMC (R2 = 0.75), while the correlation of ARND and FMC was weaker (R2 = 0.60) than that found for NDVI, NDWI, and IVDI. The use of in situ herbaceous FMC consequently indicated that NDWI is appropriate as spatio-temporal information source of herbaceous FMC variation which can be used to optimize fire risk and behavior assessment for fire management in savanna ecosystems.  相似文献   
999.
Three dimensional models play an important role in many applications; the problem is how to select the appropriate models from a 3D database rapidly and accurately. In recent years, a variety of shape representations, statistical methods, and geometric algorithms have been proposed for matching 3D shapes or models. In this paper, we propose a 3D shape representation scheme based on a combination of principal plane analysis and dynamic programming. The proposed 3D shape representation scheme consists of three steps. First, a 3D model is transformed into a 2D image by projecting the vertices of the model onto its principal plane. Second, the convex hall of the 2D shape of the model is further segmented into multiple disjoint triangles using dynamic programming. Finally, for each triangle, a projection score histogram and moments are extracted as the feature vectors for similarity searching. Experimental results showed the robustness of the proposed scheme, which resists translation, rotation, scaling, noise, and destructive attacks. The proposed 3D model retrieval method performs fairly well in retrieving models having similar characteristics from a database of 3D models.  相似文献   
1000.
Reza  Alireza   《Pattern recognition》2007,40(12):3677-3690
A theoretical framework is presented to study the consistency of robust estimators used in vision problems involving extraction of fine details. A strong correlation between asymptotic performance of a robust estimator and the asymptotic bias of its scale estimate is mathematically demonstrated where the structures are assumed to be linear corrupted by Gaussian noise. A new measure for the inconsistency of scale estimators is defined and formulated by deriving the functional forms of four recent high-breakdown robust estimators. For each estimator, the inconsistency measures are numerically evaluated for a range of mutual distances between structures and inlier ratios, and the minimum mutual distance between the structures, for which each estimator returns a non-bridging fit, is calculated.  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