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   1062篇
  免费   141篇
  国内免费   82篇
  2024年   7篇
  2023年   27篇
  2022年   36篇
  2021年   31篇
  2020年   49篇
  2019年   57篇
  2018年   63篇
  2017年   63篇
  2016年   60篇
  2015年   43篇
  2014年   70篇
  2013年   108篇
  2012年   55篇
  2011年   53篇
  2010年   34篇
  2009年   66篇
  2008年   49篇
  2007年   73篇
  2006年   44篇
  2005年   52篇
  2004年   41篇
  2003年   34篇
  2002年   23篇
  2001年   11篇
  2000年   15篇
  1999年   15篇
  1998年   10篇
  1997年   12篇
  1996年   14篇
  1995年   4篇
  1994年   7篇
  1993年   4篇
  1992年   4篇
  1991年   2篇
  1989年   5篇
  1988年   6篇
  1987年   4篇
  1986年   5篇
  1985年   6篇
  1984年   4篇
  1983年   3篇
  1982年   2篇
  1980年   2篇
  1979年   3篇
  1978年   3篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有1285条查询结果,搜索用时 15 毫秒
161.
The templating approach is a powerful method for preparing porous electrodes with interconnected well‐controlled pore sizes and morphologies. The optimization of the pore architecture design facilitates electrolyte penetration and provides a rapid diffusion path for lithium ions, which becomes even more crucial for thick porous electrodes. Here, NaCl microsize particles are used as a templating agent for the fabrication of 1 mm thick porous LiFePO4 and Li4Ti5O12 composite electrodes using spark plasma sintering technique. These sintered binder‐free electrodes are self‐supported and present a large porosity (40%) with relatively uniform pores. The electrochemical performances of half and full batteries reveal a remarkable specific areal capacity (20 mA h cm?2), which is 4 times higher than those of 100 µm thick electrodes present in conventional tape‐casted Li–ion batteries (5 mA h cm?2). The 3D morphological study is carried out using full field transmission X‐ray microscopy in microcomputed tomography mode to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results also demonstrate that the coupling between the salt templating method and the spark plasma sintering technique turns out to be a promising way to fabricate thick electrodes with high energy density.  相似文献   
162.
163.
164.
The loss of bone tissue represents a critical clinical condition that is frequently faced by surgeons. Substantial progress has been made in the area of bone research, providing insight into the biology of bone under physiological and pathological conditions, as well as tools for the stimulation of bone regeneration. The present review discusses recent advances in the field of gene‐enhanced bone tissue engineering. Gene transfer strategies have emerged as highly effective tissue engineering approaches for supporting the repair of the musculoskeletal system. By contrast to treatment with recombinant proteins, genetically engineered cells can release growth factors at the site of injury over extended periods of time. Of particular interest are the expedited technologies that can be applied during a single surgical procedure in a cost‐effective manner, allowing translation from bench to bedside. Several promising methods based on the intra‐operative genetic manipulation of autologous cells or tissue fragments have been developed in preclinical studies. Moreover, gene therapy for bone regeneration has entered the clinical stage with clinical trials for the repair of alveolar bone. Current trends in gene‐enhanced bone engineering are also discussed with respect to the movement of the field towards expedited, translational approaches. It is possible that gene‐enhanced bone tissue engineering will become a clinical reality within the next few years.  相似文献   
165.
Plants respond to changing environmental conditions, and their ability to adjust intra‐specifically to such shifts represents an ecological and evolutionary advantage. We studied seven plant traits for two common, rhizomatous granite outcrop species (the fern Cheilanthes austrotenuifolia, and the herb Stypandra glauca) with seasonal foliage during the cooler, wetter winter months at seven sites across an aridity gradient in southwestern Australia. We investigated trait patterns at regional and habitat scale, by investigating changes in trait values along the aridity gradient, and by comparing two different habitats types (sun‐exposed and sheltered). We expected plants occurring in more arid sites and highly irradiated, shallow‐soil (sun‐exposed) habitats, to exhibit traits indicative of more conservative resource acquisition, retention and use strategies. At the habitat scale, we found support for our prediction, with plants in more stressful, sun‐exposed habitats showing traits’ values associated with more conservative strategies (especially for water), such as smaller plants, denser leaves, higher foliar δ13C and C/N. However, at the regional scale many traits displayed the opposite pattern, suggesting less conservative resource acquisition in more arid sites. This evidence was particularly pronounced for specific leaf area (SLA), which exhibited a significant, positive relationship with increasing aridity. We suggest that the unexpected regional trends in foliar traits relate to shorter lived, faster growing leaves linked to highly efficient resource acquisition and use strategies during the shorter growing season in the more arid regions. These highly exploitative strategies may enable plants to avoid climate extremes, that is, hot and dry periods in the more arid sites. Our findings of contrasting foliar traits responses at different scales support the importance of multi‐scale approaches to quantify the role of intraspecific trait variability.  相似文献   
166.
目的:研究案例教学法结合多媒体教学法在超声专业教学中的应用效果。方法:选择2015年3月到2017年3月在我院超声科实习的112名医学院学生进行研究,按照随机数字表法将医学生分成观察组及对照组,各56例,对照组采用传统教学法实施教学,观察组则采用案例教学法以及多媒体教学法实施综合教学,在每学期末,统计并对比两组学生理论成绩和实践成绩,以及两组学生对教学方式的满意度。结果:观察组的理论成绩和实践成绩各项目分值均分别明显高于对照组,差异均有统计学意义(均P0.05)。观察组学生对教学方式的满意度为98.21%,明显高于对照组的87.50%,差异有统计学意义(P0.05)。结论:案例教学法与多媒体教学法的综合应用能够有效提升超声专业学生的理论成绩和实践成绩,还可改善其对教学方式的满意度,效果较好,临床超声教学可考虑将此种教学方式进行广泛推广,从而更有利于培养专业人才。  相似文献   
167.
目的:观察放射线引导下经椎间盘入路毁损内脏神经治疗上腹部癌痛的疗效及安全性。方法:选择上腹部癌痛患者26例,在放射线引导下经T11~12椎间盘入路穿刺,注射无水乙醇5.0 mL毁损内脏大、小神经,观察穿刺成功率,并记录术前、术后1天、1周、2周、1月、2月的疼痛强度(NRS评分)、生活质量评分(QOL),阿片类药物的用量以及手术不良反应的发生情况。结果:所有患者均穿刺到位,无严重并发症出现。和术前相比,术后各时点的NRS评分、每日吗啡消耗量下降,QOL评分增加(P0.05)。其中,6例患者发生暂时性腹泻,一周内恢复;5例患者出现不同程度的腹背部烧灼感,未经特殊处理24 h后症状消失。结论:在放射线引导下经椎间盘入路毁损内脏神经治疗上腹部癌痛的操作简单,疗效好,可显著提高患者的生活质量,且安全性高。  相似文献   
168.
目的:研究神经内镜辅助下经鼻蝶窦入路术对垂体瘤的临床观察及对肾上腺素(epinephrine,E)、去甲肾上腺素(Norepinephrine,NE)、肾素(Renin,R)、血管紧张素(Angiotensin,ATⅡ)的影响。方法:收集2015年3月-2017年3月我院收治的60例垂体瘤患者,随机分为实验组和对照组,每组30例,实验组采用神经内镜辅助下经鼻蝶窦入路术治疗,对照组采用经口鼻下鼻中隔垂体瘤切除术治疗。观察并比较两组治疗疗效,手术时间、术中出血量、住院时间,血清E、NE、R及ATⅡ水平,激素下降程度、肿瘤残留、肿瘤体积减少程度、复发率及不良反应。结果:实验组总有效率显著高于对照组(P0.05);手术时间、术中出血量、住院时间均显著小于对照组(P0.05);E、NE、R、ATⅡ水平显著低于对照组(P0.05);激素下降程度、肿瘤残留、肿瘤体积减少程度、复发率显著低于对照组(P0.05);不良反应总发生率显著低于对照组(P0.05)。结论:神经内镜辅助下经鼻蝶窦入路术对垂体瘤的疗效显著,可减少应激反应,提高肿瘤全切除率,可减少术后并发症,利于患者预后。  相似文献   
169.
The importance of the plant microbiome for host fitness has led to the concept of the “plant holobiont”. Seeds are reservoirs and vectors for beneficial microbes, which are very intimate partners of higher plants with the potential to connect plant generations. In this study, the endophytic seed microbiota of numerous barley samples, representing different cultivars, geographical sites and harvest years, was investigated. Cultivation-dependent and -independent analyses, microscopy, functional plate assays, greenhouse assays and functional prediction were used, with the aim of assessing the composition, stability and function of the barley seed endophytic bacterial microbiota. Associations were consistently detected in the seed endosphere with Paenibacillus, Pantoea and Pseudomonas spp., which were able to colonize the root with a notable rhizocompetence after seed germination. In greenhouse assays, enrichment with these bacteria promoted barley growth, improved mineral nutrition and induced resistance against the fungal pathogen Blumeria graminis. We demonstrated here that barley, an important crop plant, was consistently associated with beneficial bacteria inside the seeds. The results have relevant implications for plant microbiome ecology and for the holobiont concept, as well as opening up new possibilities for research and application of seed endophytes as bioinoculants in sustainable agriculture.  相似文献   
170.
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