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   324篇
  免费   68篇
  国内免费   40篇
电工技术   45篇
综合类   57篇
化学工业   23篇
金属工艺   2篇
机械仪表   21篇
建筑科学   28篇
矿业工程   6篇
能源动力   18篇
轻工业   12篇
水利工程   23篇
石油天然气   4篇
武器工业   1篇
无线电   26篇
一般工业技术   27篇
冶金工业   3篇
自动化技术   136篇
  2023年   4篇
  2022年   10篇
  2021年   22篇
  2020年   11篇
  2019年   15篇
  2018年   12篇
  2017年   10篇
  2016年   13篇
  2015年   18篇
  2014年   16篇
  2013年   25篇
  2012年   24篇
  2011年   35篇
  2010年   29篇
  2009年   33篇
  2008年   36篇
  2007年   41篇
  2006年   22篇
  2005年   20篇
  2004年   14篇
  2003年   5篇
  2002年   4篇
  2001年   7篇
  2000年   1篇
  1997年   2篇
  1996年   1篇
  1994年   1篇
  1989年   1篇
排序方式: 共有432条查询结果,搜索用时 15 毫秒
1.
Under the circumstance of perceptual consumption, it is still challenging to grasp consumer's emotions and demands due to the large search space, diversified preferences, and easy fatigue of consumers. To reduce user fatigue and enlarge search space, a novel method was presented to design and optimize the pattern of yarn-dyed plaid fabric using the isolation niche genetic algorithm and rough set theory. Each pattern was encoded as a chromosome based on the real number code. The population was initialized and evolved using INGA to maintain the diversity. The rough set theory was adopted as the fitness function of isolation niche genetic algorithm to extract the consumer's demands. After multiple evolutions, a large set of practical patterns of the yarn-dyed plaid fabric are obtained. Experiments were carried out by 24 testers of different ages and genders. The results prove that the proposed method based on the isolation niche genetic algorithm and rough set theory is feasible and effective, supplying references to the designer.  相似文献   
2.
Tumor progression to a metastatic and ultimately lethal stage relies on a tumor-supporting microenvironment that is generated by reciprocal communication between tumor and stromal host cells. The tumor–stroma crosstalk is instructed by the genetic alterations of the tumor cells—the most frequent being mutations in the gene Tumor protein p53 (TP53) that are clinically correlated with metastasis, drug resistance and poor patient survival. The crucial mediators of tumor–stroma communication are tumor-derived extracellular vesicles (EVs), in particular exosomes, which operate both locally within the primary tumor and in distant organs, at pre-metastatic niches as the future sites of metastasis. Here, we review how wild-type and mutant p53 proteins control the secretion, size, and especially the RNA and protein cargo of tumor-derived EVs. We highlight how EVs extend the cell-autonomous tumor suppressive activity of wild-type p53 into the tumor microenvironment (TME), and how mutant p53 proteins switch EVs into oncogenic messengers that reprogram tumor–host communication within the entire organism so as to promote metastatic tumor cell dissemination.  相似文献   
3.
祁新华  毛蒋兴  程煜 《规划师》2007,23(2):89-91
土地利用担负着城市空间架构和空间优化的重要功能.从生态位的角度看,城市空间优化具有内在和外在两方面驱动力,分别是土地生态位扩充和土地生态位差.在内外两种驱动力的共同作用下,土地变化方向总是朝着效益最大化和生态适宜度最高的方向发展.根据土地生态位整体效益最大化原理,增城市城市空间优化应当采取以下策略:承接西南、充实中部、优化东部、平衡西部、联合南部、调控北部.  相似文献   
4.
岩体随机不连续面产状数据划分方法研究   总被引:2,自引:0,他引:2  
动态聚类算法从本质上讲是单目标组合优化算法,一般需要事先给定目标分类数和初始聚类中心,且初始聚类中心的选择对数据划分结果影响较大。为了解决该问题,提出将产状数据的划分问题转化为多目标优化问题,并采用小生境Pareto遗传算法进行求解。针对聚类问题的特殊性,采用基于链表的编码方案,并建议相应的遗传操作算子;通过引入小生境技术和Pareto支配集理论,仅通过一次求解可由Pareto支配集给出对应于不同目标组数的最优分组结果,而且不用事先给定目标组数以及初始聚类中心。最后,将算法应用于三峡船闸高边坡岩体实测不连续面产状数据的划分,得到较为符合实际的优势结构面分组。  相似文献   
5.
Species distribution models have recently become important tools in ecological research. Prediction of suitable habitats for threatened and endangered species is essential for the conservation and management of their native habitats. A landscape scale approach is relevant for biodiversity conservation since landscape planning and management are generally conducted at wide spatial scales, focusing on areas with complex landscape configuration as a consequence of human activities. The aims of this study were to test a maximum entropy approach (Maxent) to the development of a niche-based model for species of conservation interest and to relate this model to landscape structure metrics. The results obtained here showed a good predictive power of Maxent for the three target species and highlighted the importance of landscape structure analysis for the detection of patterns of habitat suitability. Moreover, this work stressed that combining classical environmental information with landscape structure in analysing habitat suitability for species of conservation interest may be used to guide conservation efforts and landscape management practices.  相似文献   
6.
Over the past few decades, studies on competition and organizational performance in the international construction market have been prolific. Construction companies are founded, then grow, compete, evolve, and die in the international landscape, a common process from an ecological perspective. However, few studies have considered the international construction market from this perspective. Using niche theory, which was initially populated in the field of natural bio-ecology and then introduced to business management and economics, a NW/O-L (niche width/overlap and location) framework is established in this study. With this framework, the niche evolution of the top 225 international contractors is explored along two dimensions—product and geography. The effects of a proper niche on an international construction company’s performance are also investigated using the cluster analysis method. It was discovered that, despite fluctuations over time, the contractor’s niche is highly related to its performance in the international construction market. The most appropriate niche for international construction contractors is a wide niche width, with a small niche overlap and with its location near to the market centre with comparatively more market resources. However, only a few contractors can survive in this niche, as the majority of contractors are in a narrow niche width, with a comparatively large niche overlap and far from the market centre. Contractors which do not fit either of these two niches have proved to be poor performers in this study.  相似文献   
7.
粒子群算法因其形式比较简洁,参数设置灵活,操作简便易行,并且能够快速收敛,从而引起广泛关注。但是传统的粒子群算法也有缺陷:收敛速度慢以及容易陷入局部最优等。针对这些问题,本文借鉴小生境的方法,在进化初始阶段,对种群进行划分,将初始种群分为子种群,对不同的子种群进行不同的变异策略;在进化过程中,针对不同的子种群,设置不同的惯性权重因子ω,用来增强全局搜索能力与局部搜索能力。实验结果表明,本文提出的算法较传统的粒子群算法具有较快的收敛性以及找寻的全局最优解更接近真实解集,收敛精度比较高。  相似文献   
8.
干靓  郭光普 《风景园林》2017,24(11):86-92
选择上海市浦东新区世纪大道沿线地区作为样地,基于鸟类群落微生境调查,研究鸟类的生态位需求和实际的微生境选择,重点分析鸟类对高密度城区特殊微生境—建筑物/构筑物的选择偏好。结果表明:1)鸟类群落的巢居空间和食性空间生态位需求以及实际微生境主要位于乔木层和地被层;2)立体硬质界面具备成为城市野生鸟类生境的潜力,可作为现有城市生物生境系统的有益补充;3)针对部分城市野生鸟类利用建筑物孔洞筑巢的习性,建议可在建筑立面、雕塑和街道家具的设计中有意识地预留孔洞,为鸟类提供巢居空间。  相似文献   
9.
Economically and culturally important salmonid species often compete with Atlantic salmon (Salmo salar) released from stocking programs or that escaped during aquaculture production. Such competitive interactions may lower the individual fitness of these species by reducing survival and body growth. Here, we exposed juvenile brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha), and coho salmon (O. kisutch) to juvenile Atlantic salmon in artificial streams for 10 months. Survival and fitness-related traits of the four species were not negatively impacted by the presence of Atlantic salmon. The results suggest that brown trout and rainbow trout have better competitive abilities than Atlantic salmon, and that Chinook salmon and coho salmon have limited competitive interactions with Atlantic salmon. Although we discuss certain environmental conditions that can favor Atlantic salmon as a competitor at the juvenile life stage, Atlantic salmon may have little impact on the productivity of these four species.  相似文献   
10.
肖勇军  崔晓云 《矿冶工程》2012,32(2):122-126
以生态位理论为基础,从科技园区创业环境的构成要素出发,综合考虑科技园区创业环境的现状和未来发展趋势,选取基础设施环境、创业文化环境、园区管理环境、融资环境、人力资源环境、技术环境、服务环境和政策环境八个维度,构建了科技园区创业环境的评价指标体系,并应用层次分析法与模糊综合评价法建立了模糊层次评价模型。最后,通过实证研究说明了该模型在评价科技园区创业环境中的可行性,以期为科技园区创业环境的完善与优化提供决策依据。  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