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   71篇
  免费   3篇
  国内免费   21篇
  2024年   1篇
  2023年   6篇
  2022年   6篇
  2021年   10篇
  2020年   7篇
  2019年   13篇
  2018年   9篇
  2017年   4篇
  2016年   7篇
  2015年   2篇
  2014年   6篇
  2013年   5篇
  2012年   7篇
  2011年   3篇
  2010年   1篇
  2009年   2篇
  2008年   1篇
  2007年   3篇
  2005年   1篇
  1995年   1篇
排序方式: 共有95条查询结果,搜索用时 31 毫秒
1.
基于生态系统服务供需的雄安新区生态网络构建与优化   总被引:4,自引:0,他引:4  
城市生态网络构建是城市生态系统服务有效发挥作用的保障,构建完善的生态网络对于城市生态格局的优化具有重要的意义。结合雄安新区总体规划,通过雄安新区生态系统服务供给、需求两个层面识别生态源地。基于源地-缓冲区-廊道-节点框架,构建新区生态网络。其中,基于生态源地与城镇用地驱动因子,运用最小累积阻力方法得到累积阻力差,构建新区三生空间布局。根据成本距离分析和路径分析,结合雄安新区规划绿带分布,生成生态廊道,并在廊道与廊道交汇点、重要生态功能与脆弱的关键点以及道路轨道交汇点识别生态节点。得出:(1)新区生态源地主要位于白洋淀、公园绿地与其他绿地,分为水域生态源和林地生态源两类生态源地,面积总共728 km2。城镇源地主要位于新区东部容城县与雄县城区以及一些零星的农村居民点区域,面积为166 km2。(2)在新区三生空间布局下,加强生态廊道的构建,提升生态源地之间、生态源地与城镇源地之间的连通性,新区生态廊道主要依赖河流廊道和林地廊道两种类型。(3)在新区未来生态网络的建设中,需要重点关注河流廊道交汇点、河流廊道与城区的交汇处、交通道路与生态用地交汇处等的生态节点的建设及其生态功能的提升。  相似文献   
2.
3.
Diversity indices (dominance and evenness) and ecological spatial structure (lifestyles and relative abundances) are important features of Changhsingian brachiopod communities prior to the end-Permian mass extinction (EPME) and could predict temporal and spatial extinction patterns during the EPME. In South China, Changhsingian brachiopod communities show higher diversity than other contemporaneous brachiopod communities in the world and have been reported from a variety of sedimentary environments. In this paper, brachiopods from 18 sections in South China were selected to divide communities and compare their ecological structure. Based on the results of network analysis, cluster analysis and quantitative data from the selected sections, we show that Changhsingian brachiopod communities in South China can be categorized into three assemblages along a marine depth gradient: the Neochonetes–Fusichonetes–Paryphella Assemblage from the shallow-water clastic-rock facies, Spinomarginifera–Peltichia–Oldhamina Assemblage from the shallow-water carbonate platform facies and Fusichonetes–Crurithyris Assemblage from the deep-water siliciclastic intracontinental basin facies. Compared with communities from carbonate platform facies, the communities from siliciclastic facies were characterized by high dominance, low evenness and low lifestyle diversity, which might be important biotic factors leading to earlier extinctions. After the extinction began in all environments, the whole earliest Triassic brachiopod community was first dominated by Fusichonetes and then by Crurithyris. These patterns of domination and replacement could be explained by morphological and ecological advantages. The domination of these two genera, which were already adapted to the oxygen and food-limited deep-water habitat, indicates that the cooler deep-water environment might have been a relatively less stressed habitat after the beginning of the EPME. This suggests that global warming might be the main trigger among the previously proposed synergistic environmental stresses, while anoxia might not, at least for the beginning of EPME.  相似文献   
4.
5.
著: 《生物信息学》2019,26(9):132-141
近20 年来,对风景园林的文化阐释成为埃尔夫特应用科技大学文化景观研究组持续以来的关注焦点。期间,该研究组系统地分析了决定图林根州文化景观的各种文化因素和要素,深入了解文化和自然环境中的复杂相互作用,以此来表述和研究图林根州的区域景观系统。首先,阐述了当下德国风景园林学术语境中“文化景观”的含义,强调文化对于景观质量的价值。继而,论述了对景观进行优化、保护和设计中无法否定和回避的文化与经济因素。这样既要发展经济又要保护文化的矛盾性质,是文化景观概念所理解的人类生存的重要性质所在。文化景观研究能够在看似统一的地理区域中,形成和发展为具有可识别性的、差异化的动态结构。此外,文化景观研究还涉及其他因素,诸如生物多样性与文化多样性的丧失、生态系统服务功能滞后、经济价值的低估、国土空间连接性以及缺少实质性评价的人文特征。对历史性文化景观价值的认知给风景园林学带来了机遇,对历史景观不仅要保护,而且要创造并提供各种富有成效的展示,以参与文化景观的未来发展。维护和整合风景园林规划设计中文化景观遗产的研究实践,可以通过基础设施项目的环境影响评估到建成区的景观设计整体过程中得以贯彻。更好地理解文化景观,有助于在空间规划和发展中对其更加谨慎地进行处理,以提高文化景观研究的科学和策略意识。  相似文献   
6.
Human nasopharyngeal carcinoma is a common head and neck malignancy with high incidence in Southeast Asia and Southern China. It is necessary to develop safe, effective and inexpensive anticancer agents to improve the therapeutics of patients with nasopharyngeal carcinoma. A series of small molecular compounds based on 6‐(pyrimidin‐4‐yl)‐1H‐indazole were synthesized and evaluated for antiproliferative activities against human nasopharyngeal carcinoma cell lines SUNE1. Compounds 6b , 6c , 6e and 6l showed potent antiproliferative activities similar to positive control drug cisplatin in vitro with lower nephrotoxicity than it. N‐[4‐(1H‐Indazol‐6‐yl)pyrimidin‐2‐yl]benzene‐1,3‐diamine ( 6l ) was selected for further study. It was found that 6l induced mitochondria‐mediated apoptosis and G2/M phase arrest in SUNE1 cells. Furthermore, compound 6l at 10 mg/kg can suppress the growth of an implanted SUNE1 xenograft with a TGI% (tumor growth inhibition) value of 50 % and did not cause serious side effects in BALB/c nude mice. This study suggests that 6‐(pyrimidin‐4‐yl)‐1H‐indazole derivatives are a series of small molecule compounds with anti‐nasopharyngeal carcinoma activities.  相似文献   
7.
张惠婷  王宏卫  雷军  张飞  王正伟  谈波  高一薄 《生态学报》2021,41(11):4393-4405
基于共生理论,选取乌鲁木齐市、五家渠市、昌吉市为研究案例区,构建"三生"空间评价指标体系及"三生"功能评价指标体系,探讨乌五昌地区"三生"空间时空分异格局,借助共生度模型,识别兵团城市与地方城市"三生"功能共生发展模式,并对兵地城市跨界融合发展提供理论建议。结果表明:(1)研究区生产和生活空间面积呈上升趋势,生态空间面积呈下降趋势。(2)在生产功能方面,五家渠市与乌鲁木齐市、昌吉市共生模式分别为正向非对称共生、反向非对称共生,生活功能与生态功能方面,均为正向非对称共生,各功能城市间影响程度不同。(3)基于"三生"空间格局及"三生"功能共生模式,提出兵地融合发展建议,生产方面建立四区,三轴,一基地,生活方面加强交通路网建设,生态方面兵地协同建立生态保护区。  相似文献   
8.
拟除虫菊酯农药降解菌HP-S-01培养基的筛选及优化   总被引:2,自引:0,他引:2  
通过比较高氏合成1号培养基、查彼氏培养基、马铃薯葡萄糖培养基、燕麦片培养基和理查德培养基等5种培养基对拟除虫菊酯农药降解菌Streptomyces sp.HP-S-01生长的影响,确定了高氏合成1号培养基为菌株生长最适宜的培养基.以高氏合成1号培养基为基础培养基,采用中心组分旋转设计法(RRCD)和响应曲面法(RSM),优化了培养基关键组分中可溶性淀粉、硝酸钾和磷酸氢二钾的组成,以降解率为主要衡量指标,最佳配方包括可溶性淀粉25.9549 g/L、硝酸钾1.9975 g/L和磷酸氢二钾0.9505 g/L,最终优化出的培养基处理1 d后对50 mg/L高效氯氰菊酯的降解率达到99.61%,与期望降解率99.92%相一致,比优化前84.10%提高了15.51%.  相似文献   
9.
Bispecific antibodies (biAbs) that mediate cytotoxicity by recruiting and activating endogenous immune cells are an emerging class of next-generation antibody therapeutics. Of particular interest are biAbs of relatively small size (~50 kDa) that can redirect cytotoxic T cells through simultaneous binding of tumor cells. Here we describe a conceptually unique class of biAbs in which the tumor cell specificity of a humanized antibody fragment that recognizes CD3 on T cells is chemically programmed through a C-terminal selenocysteine (Sec) residue. We demonstrate that through chemically programmed specificity for integrin α(4)β(1) or folate receptor 1 (FOLR1), and common specificity for CD3, these hybrid molecules exert potent and specific in vitro and ex vivo cytotoxicity toward tumor cell lines and primary tumor cells in the presence of primary T cells. Importantly, the generic nature of chemical programming allows one to apply our approach to virtually any specificity, promising a broad utility of chemically programmed biAbs in cancer therapy.  相似文献   
10.
Fan J  Zhou H  Wang S  Wang H  Zhang Y  Guo Y  Li Q  Li Z  Zhao Z 《Glycoconjugate journal》2012,29(5-6):305-313
Rheumatoid arthritis (RA) is an inflammatory disorder that is characterized by persistent recurrence of joint inflammation leading to cartilage and bone destruction. The present anti-arthritis therapies failed to achieve satisfactory remission in all patients; therefore, it is still necessary to develop novel approaches to fulfill the demand in clinic. Here, we reported the therapeutic effects of lactosyl derivative Gu-4, a synthetic compound that was previously identified as a selective inhibitor against leukocyte integrin CD11b, in a bovine type II collagen induced arthritis (CIA) rat model. First, prophylactic administration of Gu-4 (1.2728?mg/kg) to rats by intraperitoneal injection every 2?days from the first day of collagen immunization significantly decreased the incidence of CIA, diminished the mean paw volume increase, and reduced the number of swollen paws. Second, administration of Gu-4 (1.2728?mg/kg) to rats at early-onset stage of CIA prevented the progression of the pathological process of RA, accelerated the remission of paw edema, and declined the arthritis score; after 5?weeks treatment, X-ray and histological examinations were carried out, the ankle joint of hind limb of Gu-4 treated CIA rats exhibited slighter bone erosion and much less inflammatory cell infiltration compared to those of saline treated animals; furthermore, Gu-4 remarkably attenuated the production of rheumatoid factor (RF) in the serum of CIA rats as determined by ELISA. Moreover, we performed in vitro lymphocyte proliferation assay and found that Gu-4 significantly inhibited the proliferation of splenic lymphocytes isolated from CIA rats in a dose-dependent manner. Our results suggest that Gu-4 can effectively ameliorate CIA and might be an alternative option for the treatment of RA.  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