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   134篇
  免费   13篇
  国内免费   5篇
  2023年   1篇
  2022年   2篇
  2021年   2篇
  2020年   4篇
  2019年   7篇
  2018年   10篇
  2016年   8篇
  2015年   7篇
  2014年   5篇
  2013年   15篇
  2012年   8篇
  2011年   7篇
  2010年   8篇
  2009年   7篇
  2008年   5篇
  2007年   6篇
  2006年   1篇
  2005年   7篇
  2004年   5篇
  2003年   3篇
  2002年   9篇
  2001年   3篇
  2000年   2篇
  1999年   5篇
  1997年   5篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1992年   3篇
  1991年   1篇
  1988年   1篇
  1985年   1篇
  1980年   1篇
排序方式: 共有152条查询结果,搜索用时 109 毫秒
71.
Bacterial isolates were obtained from two sites in New Zealand contaminated with polycyclic aromatic hydrocarbons. Isolates capable of degrading polycyclic aromatic hydrocarbons were characterized in two mycobacterial groups according to phenotypic properties. These groups were supported by random amplified polymorphic DNA analysis. Nucleotide sequences of 16S ribosomal RNA genes from isolates representing each group were determined and compared with other mycobacterial 16S ribosomal RNA sequences. The taxonomic relationships of these isolates are considered.  相似文献   
72.
Attachment relationships between animals are often studied by separating a pair of individuals and recording their subsequent behavior. Studies of non‐human primates have shown that separation results in changes that are indicative of both psychological and physiological stress. Similar results have been found in several non‐primate species with differing social structures. This study examined the behavior of two female giraffe at Zoo Atlanta after the removal of the resident male. Data were collected on the giraffe before and after separation, using an instantaneous scan sampling technique to record levels of activity, social behaviors, solitary behaviors, proximity, and habitat utilization. After the removal of the resident male, both giraffe exhibited increased levels of activity, stereotypical behavior, contact behavior (particularly neck‐rubbing), and decreased habitat utilization. These results are similar to those found in earlier primate separation studies, supporting the hypothesis that complex social structure is not necessary for the formation of social attachments. Because social separation is often accompanied by behavioral and physiological indications of stress, an understanding of the variables involved in a species' response to separation is vital to the promotion of the psychological and physical well‐being of captive animals. Zoo Biol 19:41–51, 2000. © 2000 Wiley‐Liss, Inc.  相似文献   
73.
A START POINT FOR EXTRACELLULAR NUCLEOTIDE SIGNALING
The recent discovery of a plant receptor for extracellu- lar nucleotides, reported by Choi et al. (2014), is a major breakthrough that had been anticipated for over a dec- ade. Plants release ATP into their extracellular matrix (ECM) during growth and when they are induced by vari- ous biotic and abiotic stimuli (Clark and Roux, 2011). That these extracellular nucleotides would activate receptors in plants was predicted by two sets of discoveries: that low- and sub-micromolar ATP could induce increases in [Ca2+]cyt, NO, and superoxide signaling intermediates that led to downstream growth, stomatal, and defense responses, and that these changes could be blocked by antagonists that blocked extracellular nucleotide receptors in animals (Demidchik et al., 2003; Song et al., 2006; Clark et al., 2011; Demidchik et al., 2009, 2011). Although mammalian biolo- gists had discovered two classes of receptors for extracel- lular nucleotides (P2X and P2Y) decades ago (Burnstock, 2007), there were no plant proteins obviously similar to these in any sequence data available. Clearly, if there were plant purinoceptors, they would be different from the mammalian receptors, and they could not be discovered by motif searches.  相似文献   
74.
介绍细胞共培养的两种方法   总被引:1,自引:0,他引:1  
本文设计了两种共培养装置:微孔底膜套皿和循环培养,观察了培养的小牛肺动脉内皮细胞(PAEC)和肺动脉平滑肌细胞(PASM)在上述装置中的生长情况,并用套皿法观察了两者共培养对~3H-TdR掺入的影响。结果发现,PAEC和PASM在上述装置中生长良好,两者共培养时,PAEC的~3H-TdR掺入明显降低(与对照组相比p<0.05),而PASM的~3H-TdR掺入明显升高(与对照组相比p<0.01)。上述结果表明:本文设计的两种装置可用于细胞共培养,以研究细胞间的相互调节关系。  相似文献   
75.
76.
77.
In summer 2007, with the help of a written questionnaire, the attitudes of more than 400 visitors to the zoological garden of Zurich, Switzerland, toward the idea of feeding live insects to lizards, live fish to otters, and live rabbits to tigers were investigated. The majority of Swiss zoo visitors agreed with the idea of feeding live prey (invertebrates and vertebrates) to zoo animals, both off‐ and on‐exhibit, except in the case of feeding live rabbits to tigers on‐exhibit. Women and frequent visitors of the zoo disagreed more often with the on‐exhibit feeding of live rabbits to tigers. Study participants with a higher level of education were more likely to agree with the idea of feeding live invertebrates and vertebrates to zoo animals off‐exhibit. In comparison to an earlier study undertaken in Scotland, zoo visitors in Switzerland were more often in favor of the live feeding of vertebrates. Feeding live prey can counter the loss of hunting skills of carnivores and improve the animals' well‐being. However, feeding enrichments have to strike a balance between optimal living conditions of animals and the quality of visitor experience. Our results show that such a balance can be found, especially when live feeding of mammals is carried out off‐exhibit. A good interpretation of food enrichment might help zoos to win more support for the issue, and for re‐introduction programs and conservation. Zoo Biol 29:344–350, 2010. © 2009 Wiley‐Liss, Inc.  相似文献   
78.
2D Ruddlesden–Popper perovskites (RPPs) have emerged as a promising solar cell material. A group of novel RPPs with cyclohexane methylamine (CMA) as a spacer cation is presented. Unlike previously reported RPPs, the deposited films of (CMA)2(MA)n?1PbnI3n+1 (MA is CH3NH3+, n = 1, 2, 3, …) exhibit multiple phases with reverse‐graded quantum well (QW) distribution; small n (n = 2) RPPs are located at the surface and large n (n ≥ 10) RPPs at the bottom. This has three advantages: (a) The outer, more moisture resistant, small n RPPs create a stable barrier that protects the vulnerable large n RPP lattice from being attacked by water molecules. (b) It forms a type‐II band alignment between different phases, which favors self‐driven charge transport. (c) The natural structure of graded QWs expands the range of photon collection. Attributed to these properties, the best efficiency of 15.05%, with high open‐circuit voltage (Voc) of 1.10 V for a first‐generation solar cell containing (CMA)2(MA)8Pb9I28, is achieved. A notable enhancement in short wavelength is observed in the Incident photon‐to‐current conversion efficiency spectra. This device shows significantly improved long‐term stability, retaining ≈95% of the initial efficiency after 4600 h exposure in ambient conditions with 40–70% relative humidity.  相似文献   
79.
This paper summarizes the findings for the African Region of the WPA Task Force on Steps, Obstacles and Mistakes to Avoid in the Implementation of Community Mental Health Care. We present an overview of mental health policies, plans and programmes in the African region; a summary of relevant research and studies; a critical appraisal of community mental health service components; a discussion of the key challenges, obstacles and lessons learned, and some recommendations for the development of community mental health services in the African region.  相似文献   
80.
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