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   133篇
  免费   1篇
  2021年   1篇
  2019年   2篇
  2017年   1篇
  2016年   1篇
  2014年   1篇
  2013年   2篇
  2012年   6篇
  2011年   4篇
  2010年   11篇
  2009年   5篇
  2008年   4篇
  2007年   4篇
  2006年   5篇
  2005年   5篇
  2004年   5篇
  2003年   14篇
  2002年   6篇
  2001年   2篇
  2000年   4篇
  1999年   3篇
  1998年   1篇
  1997年   6篇
  1996年   3篇
  1994年   5篇
  1992年   3篇
  1990年   1篇
  1989年   7篇
  1988年   6篇
  1987年   3篇
  1986年   3篇
  1985年   2篇
  1983年   1篇
  1980年   1篇
  1977年   1篇
  1974年   1篇
  1970年   1篇
  1967年   2篇
  1937年   1篇
排序方式: 共有134条查询结果,搜索用时 15 毫秒
111.
Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO2 effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta‐analysis to test the hypotheses that: (1) elevated atmospheric CO2 stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO2 induces a C allocation shift towards below‐ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO2. Soil N concentration strongly interacted with CO2 fumigation: the effect of elevated CO2 on fine root biomass and –production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO2 are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.  相似文献   
112.
113.
Among the hunting strategies employed by members of the order Carnivora (Mammalia), two, stalk and ambush and sustained pursuit, are particularly prevalent among larger species of the order. It has been difficult to identify morphological traits that support this distinction and ecological observations have shown that most carnivorans adopt a continuum of strategies, depending on available habitat and prey. In this paper, the shape of the distal humerus articulation is analysed, with the aim of exploring the use of the forelimb in prey procurement, and as a guide to such behaviour among fossil carnivorans. The results suggest that manual manipulation and locomotion are conflicting functions. Elbow‐joint morphology supports a division between grapplers (i.e. ambushers) and nongrapplers (i.e. pursuers). Joints of the former are characterized by being relatively wide and the latter, by being relatively narrow and box‐like with pronounced stabilizing features. At intermediate and large body sizes, carnivorans show a pattern suggesting mutually exclusive feeding strategies that involve either grappling with prey or sustained pursuit. The former allows for large body sizes, such as pantherine felids and ursids; the latter includes species of only moderate size, such as hyenids and canids. Elbow‐joint morphology is closely linked to phylogeny, but the morphology of the cheetah converges with that of nongrapplers, showing that strong selective forces may override the phylogenetic component. Two taxa of giant mustelids from the Miocene were analysed to test whether this sort of analysis is applicable to carnivorans of the past. The African Late Miocene species Ekorus ekakeran has a joint morphology comparable to that of modern‐day nongrapplers. Two joint morphologies were found in the North American Late Oligocene‐Early Miocene Megalictis ferox. The first morphology is comparable to that of modern pantherine cats and the second forms an intermediate between grapplers and nongrapplers that is not present in the modern carnivoran fauna. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 142 , 91–104.  相似文献   
114.
115.
The experience of the world leading hospitals confirms the high efficacy and appropriateness of radiation therapy of nontumorous diseases. The authors consider the general principles of the organization of radiotherapeutic service, discuss reasons that have led to a decrease in the use of this method for therapy of nontumorous diseases in this country. They also emphasize the fact that radiation therapy must have its place among therapeutic modalities used for nontumorous diseases.  相似文献   
116.
117.
Despite the wide and daunting array of cross‐cultural obstacles that the formulation of a global policy on advance directives will clearly pose, the need is equally evident. Specifically, the expansion of medical services driven by medical tourism, just to name one important example, makes this issue urgently relevant. While ensuring consistency across national borders, a global policy will have the additional and perhaps even more important effect of increasing the use of advance directives in clinical settings and enhancing their effectiveness within each country, regardless of where that country's state of the law currently stands. One cross‐cultural issue that may represent a major obstacle in formulating, let alone applying, a global policy is whether patient autonomy as the underlying principle for the use of advance directives is a universal norm or a construct of western traditions that must be reconciled with alternative value systems that may place lesser significance on individual choice. A global policy, at a minimum, must emphasize respect for patient autonomy, provision of medical information, limits to the obligations for physicians, and portability. And though the development of a global policy will be no easy task, active engagement in close collaboration with the World Health Organization can make it possible.  相似文献   
118.
The Middle–Upper Oxfordian foraminifera were studied from the borehole section drilled in the east of the Moscow Region (Russia). The foraminiferal zones were distinguished in Oxfordian clays: Opthalmidium strumosum–Lenticulina brestica and Lenticulina russiensis–Epistomina uhligi. It was established that the distribution of foraminiferal assemblages varies throughout the Moscow Region.  相似文献   
119.
The duration of exercise tolerance of the circulatory system in different ethnic populations of Yakutia early in and at the end of the last decade of the 20th century (1988–1989 and 1998–1999) was studied. Compared to the native population (Yakuts), those born in Yakutia (Europoids) demonstrated a higher tolerance at both stages of the study. It was found that the work capacity and exercise tolerance significantly decreased in both ethnic groups during the last decade of the 20th century.  相似文献   
120.
The liver, kidney, skin biopsies are able to incorporate actively 3H-uridine, and the maximum rate of RNA synthesis over the hepatocyte nuclei in the peripheral zone of the biopsies corresponds to relevant rates in vivo. Only the skin biopsies were distinguished by total cell labelling. Liver, renal, skin capillary endotheliocytes can serve intertissue marker of the diffusion depth of 3H-uridine.  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