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   241篇
  免费   1篇
  2013年   4篇
  2012年   4篇
  2011年   4篇
  2010年   6篇
  2009年   7篇
  2008年   9篇
  2007年   8篇
  2006年   14篇
  2005年   4篇
  2004年   3篇
  2003年   4篇
  2001年   5篇
  2000年   3篇
  1998年   2篇
  1997年   5篇
  1996年   14篇
  1995年   3篇
  1994年   3篇
  1993年   4篇
  1992年   7篇
  1991年   8篇
  1990年   5篇
  1989年   7篇
  1988年   3篇
  1987年   3篇
  1986年   7篇
  1985年   4篇
  1984年   6篇
  1983年   8篇
  1982年   3篇
  1981年   7篇
  1980年   6篇
  1979年   4篇
  1978年   3篇
  1977年   4篇
  1976年   4篇
  1975年   8篇
  1974年   5篇
  1973年   5篇
  1972年   6篇
  1971年   6篇
  1970年   1篇
  1969年   1篇
  1968年   5篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
  1962年   2篇
  1959年   1篇
  1958年   1篇
排序方式: 共有242条查询结果,搜索用时 41 毫秒
91.
92.
This paper provides guidance on the steps, obstacles and mistakes to avoid in the implementation of community mental health care. The document is intended to be of practical use and interest to psychiatrists worldwide regarding the development of community mental health care for adults with mental illness. The main recommendations are presented in relation to: the need for coordinated policies, plans and programmes, the requirement to scale up services for whole populations, the importance of promoting community awareness about mental illness to increase levels of help-seeking, the need to establish effective financial and budgetary provisions to directly support services provided in the community. The paper concludes by setting out a series of lessons learned from the accumulated practice of community mental health care to date worldwide, with a particular focus on the social and governmental measures that are required at the national level, the key steps to take in the organization of the local mental health system, lessons learned by professionals and practitioners, and how to most effectively harness the experience of users, families, and other advocates.  相似文献   
93.
94.
The hypothesis that mitogen‐activated protein kinase (MAPK) signalling is important in plant defences against metal stress has become accepted in recent years. To test the role of oxidative signal‐inducible kinase (OXI1) in metal‐induced oxidative signalling, the responses of oxi1 knockout lines to environmentally realistic cadmium (Cd) and copper (Cu) concentrations were compared with those of wild‐type plants. A relationship between OXI1 and the activation of lipoxygenases and other initiators of oxylipin production was observed under these stress conditions, suggesting that lipoxygenase‐1 may be a downstream component of OXI1 signalling. Metal‐specific differences in OXI1 action were observed. For example, OXI1 was required for the up‐regulation of antioxidative defences such as catalase in leaves and Fe‐superoxide dismutase in roots, following exposure to Cu, processes that may involve the MEKK1‐MKK2‐WRKY25 cascade. Moreover, the induction of Cu/Zn superoxide dismutases in Cu‐exposed leaves was regulated by OXI1 in a manner that involves fluctuations in the expression of miRNA398. These observations contrast markedly with the responses to Cd exposure, which also involves OXI1‐independent pathways but rather involves changes in components mediating intracellular communication.  相似文献   
95.
ABSTRACT

Underwater sound recording of animals uses specialized techniques to obtain faithful copies of sounds produced by animals during their normal activities underwater. Techniques have to be unobtrusive as well as nondisturbing to avoid changing the animal behaviors. The first scientific recording of underwater sounds from a marine mammal at sea was by William E. Schevill and Barbara Lawrence in 1948. Although the equipment has changed considerably since then, the techniques, approaches to animals and environmental impediments have remained essentially the same. However, the frequency and dynamic ranges of underwater sounds can easily exceed terrestrial sounds, so the selection of suitable equipment is critical. The elements of a useful system for bioacoustic recording of marine animals include the hydrophone, impedance transformer/preamplifier, cable, signal amplifier, recorder and sound monitor. The important criteria for each of these is discussed, along with directional listening systems, and the need for calibrations to verify the performance of the entire underwater recording system. For each situation, the ideal system is the one with the best compromise of interactive components to record that particular sound spectrum.  相似文献   
96.
We investigated the effects of body mass on the selectivity of female mating preferences in two different sensory channels (acoustic and chemical) using the field cricket, Gryllus integer. We found that body mass affected female selectivity for acoustic cues: larger females were more selective than smaller females for long‐distance calls of males. In contrast, body mass did not affect selectivity for chemical cues of males, which are assessed at close range. Nevertheless, we observed selectivity for these cues. Finally, selectivity for acoustic cues was not correlated with selectivity for chemical cues. These results suggest that energetic concerns may influence mating decisions made at a distance and that the effects of body mass on mating decisions are not necessarily shared across different sensory modalities. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 160–168.  相似文献   
97.
The body plan of turtles is unique among tetrapods in the presenceof the shell. The structure of the carapace involves a uniquerelationship between the axial and the appendicular skeletons.A common developmental mechanism, an epithelial-mesenchymalinteraction, has been identified in the early stages of carapacedevelopment by means of basic histological and immunofluorescencetechniques. By analogy to other structures initiated by epithelial-mesenchymalinteractions, it is hypothesized that carapace development isdependent on this interaction in the body wall. Surgical perturbationswere designed to test the causal connection between the epithelial-mesenchymalinteraction in the body wall and the unusual placement of theribs in turtles. By comparison to data available on body wallformation in avian embryos, these experiments also shed lighton the segregation of somitic and lateral plate cell populationsand the embryonic origin of the scapula in turtles. This study specifically addresses the ontogeny of a unique tetrapodbody plan. The ontogenetic information can be used to make inferencesabout the phytogeny of this body plan and how it could haveevolved from the more typical primitive tetrapod. On a moregeneral level this studyexplores the potential role of commondevelopmental mechanisms in the generation of evolutionary novelties,and the developmental incongruities between homologous skeletalelements in different groups of tetrapods.  相似文献   
98.
How strong is the current carbon sequestration of an Atlantic blanket bog?   总被引:1,自引:0,他引:1  
Although northern peatlands cover only 3% of the land surface, their thick peat deposits contain an estimated one‐third of the world's soil organic carbon (SOC). Under a changing climate the potential of peatlands to continue sequestering carbon is unknown. This paper presents an analysis of 6 years of total carbon balance of an almost intact Atlantic blanket bog in Glencar, County Kerry, Ireland. The three components of the measured carbon balance were: the land‐atmosphere fluxes of carbon dioxide (CO2) and methane (CH4) and the flux of dissolved organic carbon (DOC) exported in a stream draining the peatland. The 6 years C balance was computed from 6 years (2003–2008) of measurements of meteorological and eddy‐covariance CO2 fluxes, periodic chamber measurements of CH4 fluxes over 3.5 years, and 2 years of continuous DOC flux measurements. Over the 6 years, the mean annual carbon was ?29.7±30.6 (±1 SD) g C m?2 yr?1 with its components as follows: carbon in CO2 was a sink of ?47.8±30.0 g C m?2 yr?1; carbon in CH4 was a source of 4.1±0.5 g C m?2 yr?1 and the carbon exported as stream DOC was a source of 14.0±1.6 g C m?2 yr?1. For 2 out of the 6 years, the site was a source of carbon with the sum of CH4 and DOC flux exceeding the carbon sequestered as CO2. The average C balance for the 6 years corresponds to an average annual growth rate of the peatland surface of 1.3 mm yr?1.  相似文献   
99.
100.
Survival of 5 strains of the plant pathogen, Erwinia carotovora var. atroseptica and 3 strains of the plant pathogen E. carotovora var. carotovora , grown in a liquid tryptone medium and held as 'captive'aerosols on gossamer microthreads, was determined under different atmospheric conditions in a controlled environment room and in the open air. Although these bacteria lost viability more quickly than a robust reference strain of Escherichia coli , sufficient numbers survived for 15 min or more to indicate that airborne spread of viable propagules could take place, especially under cool humid atmospheric conditions. Cells of one strain of each organism extracted from rotted potato tuber tissue were shown to behave rather like those cultured in the tryptone medium.  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