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   2851篇
  免费   177篇
  国内免费   38篇
电工技术   104篇
技术理论   2篇
综合类   187篇
化学工业   208篇
金属工艺   72篇
机械仪表   256篇
建筑科学   918篇
矿业工程   128篇
能源动力   146篇
轻工业   191篇
水利工程   71篇
石油天然气   109篇
武器工业   14篇
无线电   166篇
一般工业技术   100篇
冶金工业   50篇
原子能技术   27篇
自动化技术   317篇
  2024年   2篇
  2023年   23篇
  2022年   26篇
  2021年   64篇
  2020年   65篇
  2019年   35篇
  2018年   40篇
  2017年   51篇
  2016年   93篇
  2015年   112篇
  2014年   158篇
  2013年   175篇
  2012年   186篇
  2011年   193篇
  2010年   163篇
  2009年   178篇
  2008年   126篇
  2007年   179篇
  2006年   152篇
  2005年   133篇
  2004年   123篇
  2003年   117篇
  2002年   86篇
  2001年   81篇
  2000年   73篇
  1999年   66篇
  1998年   68篇
  1997年   75篇
  1996年   39篇
  1995年   42篇
  1994年   30篇
  1993年   23篇
  1992年   17篇
  1991年   11篇
  1990年   10篇
  1989年   11篇
  1988年   9篇
  1987年   3篇
  1986年   8篇
  1985年   2篇
  1984年   8篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
  1968年   2篇
  1956年   1篇
排序方式: 共有3066条查询结果,搜索用时 15 毫秒
1.
To investigate whether China's coal consumption has actually peaked, this study tests the national and regional coal Kuznets curve (CKC) hypothesis by using a panel dataset of 30 provinces covering 2000 to 2016. To fully capture the trends of coal consumption at the national, regional, and provincial levels, this study proposes a novel regional division method based on coal dependence and economic level. Considering the potential cross-sectional dependence and slope homogeneity, the newly developed methods allowing for heterogeneous slope coefficients are employed. The whole panel and subpanel results validate the CKC hypothesis for China, and province-specific results are mixed. The subpanel results reveal that only in the coal-dependent developing region has the peak of coal consumption not been reached, and for other regions, coal consumption displays a downward trend along with gross domestic product (GDP) increases. Furthermore, the province-specific results suggest that coal consumption will continue to increase slightly in certain provinces. This study implies that to reduce coal consumption, the coal-dependent developing region and provinces with a future turning point should act with great urgency to achieve a balance of economic growth and environmental responsibility. In addition, policymakers formulating coal consumption reduction policy in China must consider the remarkable differences across regions and provinces.  相似文献   
2.
《云南化工》2018,(12):114-115
鄂尔多斯盆地白豹-南梁地区延长组长4+5油层段是重要的储集层之一,包括长4+51和长4+52。由于白豹-南梁地区长4+51油气富集规律尚未明确,亦有必要对白豹-南梁地区4+51储层开展评价。通过岩心铸体薄片、物性分析、压汞分析等资料对研究区长4+51储层特征进行了研究。结果表明,研究区岩石类型以长石砂岩和岩屑长石砂岩为主,分选性以中-好为主,磨圆度以次棱角状为主;孔隙类型主要为粒间孔、长石溶孔,孔隙空间分选性较差,喉道分布不集中;研究区整体以Ⅱ类储层分布为主。  相似文献   
3.
The balance between low carbon development and rapid economic growth is a ‘Gordian knot’ for most countries. This study aims to explore the practicable route of lowering carbon intensity with the expansion of the Information and Communication Technologies (ICT) industry in China. Using the provincial panel data from 2000 to 2017, the paper employs five indicators to empirically investigate the determinant mechanism of carbon intensity based on the refined Stochastic Impact by Regression on Population, Affluence, and Technology (STIRPAT) and spatial econometric models. The findings demonstrate that the ICT industry is the main force in adjusting carbon intensity. Despite constraint by the rebound effect, the net effect of the ICT industry shows a significant positive impact on lowering carbon intensity under the consideration of spatial dependence. Furthermore, compared with developed regions, the contribution of ICT on regional inequality of carbon intensity shows a higher share in developing regions. By applying the Oaxaca-Ransom counterfactual decomposition, the results reveal that there are substantial regional gaps between multi-comparable groups. The composite effect of informatization, industrialization, and urbanization accounts for the major share of the regional gap. Thus, policymakers should pay more attention to enhancing the ICT infrastructure in developing regions, boosting the ICT-related technology investment in specific sectors, coordinating regional cooperation, and balancing the migration of skilled workers.  相似文献   
4.
Robust Parametric Sensitivity Analysis (PSA) is a prerequisite for efficient shape optimisation via parametric modelling. A major challenge PSA has to handle is related to the fact that a parameter can be sensitive in certain local areas of the design space but become insensitive in others. Therefore, setting an applicable space for this analysis becomes a difficult task. In this paper, we introduce the concept of intra-sensitivity to identify parameters whose perturbation has a major impact on the sensitivity index of the remaining parameters. For this purpose, we firstly appeal to Active Subspace Method (ASM) and develop an ASM-based regional sensitivity analysis, which investigates parametric sensitivity in local regions of the design space and aids conducing to parameters’ intra-sensitivity. This regional analysis is applied in conjunction with a Dynamic Propagation Sampling approach, for tackling the computational complexity arising when high-dimensional problems are concerned. Once sensitive and intra-sensitive parameters are identified, then free-form features, correlated to these parameters, are evaluated using a feature saliency map built with the aid of Hausdorff distance. The so resulting methodology has been validated in the area of computer-aided ship design using two parametric modellers: the first one is a Procedural Deformation (PD) modeller which is based on T-splines and involves 24 parameters while the second one is based on Free-Form Deformation (FFD) and involves 104 parameters. The corresponding design spaces have been generated using a parent hull close to the KCS container ship and are analysed against hull’s volume of displacement and total resistance. Finally, the convergence performance of the various components of this approach is compared with state-of-the-art techniques.  相似文献   
5.
Water culture is one of the key issues in Water Ecological Civilization. China’s traditional water cultural landscape embodies rich water cultures, and have a significance in related research and protection practice. This paper proposes the concept of “water cultural landscape,” that is, the landscape formed through humans’ environmental alteration during water activities—including how people use, transform, and manage it. The traditional water cultural landscapes in Huizhou Region have developed over hundreds of years, reflecting the locals’ wisdom in sustainable water use. The water cultural landscape in Huizhou Region should be interpreted as a systematic notion, in which all landscape elements such as ponds, weirs, and shuikous are interdependent, composing the landscape components e.g. valleys, hills, and basins, and establishing water security patterns for cities, towns, villages, and for production. The traditional water cultural landscape in Huizhou Region requires local generations’ long-term maintenance and management, and in turn it is also vital to Huizhou people's life and Huizhou culture. Today, it acts as an ecological infrastructure for sponge countryside and sponge city construction, and an important resource for heritage protection and tourism development.  相似文献   
6.
While technological transformations have redrawn the boundaries of regional innovation systems, the effect of such transformations on the development of cross-border regional innovation systems (CBRISs) – defined here as the innovation system spanning neighboring territories belonging to different nation-states – has not been well understood. The Hong Kong-Shenzhen region presents a unique opportunity to study the potential of CBRISs, as Hong Kong and Shenzhen are adjacent to each other though there is a border between them and the two cities have their own political and legal systems under the “one country, two systems” arrangement. In this research, we examine the development of the Hong Kong-Shenzhen region by focusing on cognitive proximity, innovation actors, collaboration, and global connectivity through an analysis of patent and publication data for the 2001–2015 period. Our findings point to a good potential given the growing convergence in scientific research among the two cities, steadily increasing collaboration output, and a complementarity among innovation actors. However, compared with other cross-border regions, the technological linkages between Hong Kong and Shenzhen remain limited.  相似文献   
7.
诸多的化工单元操作过程中,普遍存在着"边界层"现象。"边界层"的存在对化工单元的操作过程会产生明显的影响。本文描述和类比了多种"边界层"的特征,并在物理化学的知识层面上对其产生机理进行了阐述,最后指出通过削弱边界层可以提高动量传递、质量传递和热量传递的速率和效率。  相似文献   
8.
采用异丙基黄原酸钠SIP、N-乙基-N-苯基二硫代氨基甲酸PX的复合促进剂体系(用量分别为1.5phhr和0.5phhr)可使天然橡胶/顺丁橡胶并用胶(并用比为70∶30)在90℃~95℃内快速硫化,硫化特性符合缓冲胶工艺的要求,但其性能与HG/T 4124-2009《预硫化缓冲胶》存在一定的差距。  相似文献   
9.
以氟橡胶与丁字铁粘接为例,研究了氟橡胶与金属铁粘接的课题,发现粘接效果与橡胶配方的硬度、焦烧特性以及硫化体系都有着密切的关系。研究表明,氟橡胶的邵尔A硬度为65时,其与基材的粘接强度优于其他硬度时;在硫化体系方面,双酚AF/BPP硫化体系优于3#硫化剂体系和过氧化物硫化体系;随着t10、t90时间差的延长,粘接性能提高。  相似文献   
10.
那陵郭勒河沙丘地区位于东昆仑祁漫塔格早古生代裂陷槽,经历了早古生代及晚古生代—早中生代的复合造山作用,发育多期次岩浆活动和成矿作用,具有较好的铁多金属找矿前景。文章通过研究沙丘铁多金属矿的成矿地质背景、矿床特征、地磁异常和地球化学异常等,探讨了其找矿标志。研究表明:沙丘地区铁多金属矿床成因类型属接触交代型(矽卡岩型),矽卡岩与磁铁矿体在空间分布紧密共生,是重要的找矿标志;引起该区磁异常的主要地质体为闪锌磁铁矿矿石、闪锌磁铁矿化矽卡岩、矽卡岩、闪长岩、硅质岩、玄武岩、钾长花岗斑岩;利用物探磁异常找寻磁铁矿作用显著,在低缓磁异常区、正负异常接触部位是找寻铁多金属矿最重要也是最直接的找矿标志。  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