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   86篇
  免费   5篇
  91篇
  2018年   1篇
  2013年   1篇
  2011年   2篇
  2010年   8篇
  2009年   3篇
  2008年   5篇
  2007年   5篇
  2006年   2篇
  2005年   1篇
  2004年   2篇
  2003年   1篇
  2000年   1篇
  1999年   1篇
  1998年   4篇
  1997年   1篇
  1995年   1篇
  1993年   1篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1975年   1篇
  1972年   2篇
  1971年   2篇
  1970年   1篇
  1966年   1篇
  1958年   1篇
  1957年   3篇
  1956年   2篇
  1955年   2篇
  1954年   2篇
  1952年   3篇
  1951年   5篇
  1950年   2篇
  1949年   2篇
  1946年   1篇
  1941年   1篇
排序方式: 共有91条查询结果,搜索用时 0 毫秒
11.
12.
13.
14.
15.
The one feature that characterizes all shock, regardless of its cause, is a reduction in the effective circulating blood volume. The reduced blood volume leads to decreased venous return, decreased cardiac output, vasoconstriction, tachycardia, hypotension, tissue anoxia and death if the sequence of events is uninterrupted. Immediate therapy must be directed at restoration of the blood volume, preferably with whole blood. Infection must be controlled by use of antibiotics intramuscularly and intravenously. If shock persists, aqueous adrenal extract should be administered in large quantities. As a last resort, a vasopressor should be tried.  相似文献   
16.
Great Bitterns Botaurus stellaris have experienced a population decline in the UK, such that in 1997 the total number of breeding males was just 11. This study aimed to identify factors affecting productivity, and how management could be used to manipulate this. An intensive study of Great Bittern breeding success was conducted between 1997 and 2001. The date that males established their booming territories was closely correlated with when females started nesting. Wetter sites with greater fish densities had males that established their booming territories earlier in the season. However, only the date that males started booming determined when females started nesting. The mean clutch size of Great Bitterns was four and the only cause of nest failure was predation. Of eight nests suspected to be second attempts the mean interval between these first and second attempts was 12.25 ± 0.88 (sd) days (range 8–15). The fate of radiotagged chicks followed to fledging revealed that the overall probability of a chick surviving to fledge was 39.1%. Daily losses of Great Bittern chicks due to starvation/exposure accounted for 76.25% and predation 21.25%. The youngest chicks in poor condition were most likely to die, particularly in periods of high rainfall. A simulated renesting model allowed estimation of Great Bittern productivity as 1.24 chicks per female and 1.52 nesting attempts per female. Habitat management, or lack of water control that resulted in sites being drier in spring, delayed nesting, although statistically there was no difference in productivity compared with wetter sites.  相似文献   
17.
We present a case of a 45-year-old woman with a benign breast lump in which collagenous spherulosis was an incidental finding. Since collagenous spherulosis has a similar appearance to adenoid cystic carcinoma of breast on fine needle aspiration cytology, the two conditions can easily be confused. The problem of making this important distinction is discussed.  相似文献   
18.
ABSTRACT In west-central Texas, USA, abatement efforts for the gray fox (Urocyon cinereoargenteus) rabies epizootic illustrate the difficulties inherent in large-scale management of wildlife disease. The rabies epizootic has been managed through a cooperative oral rabies vaccination program (ORV) since 1996. Millions of edible baits containing a rabies vaccine have been distributed annually in a 16-km to 24-km zone around the perimeter of the epizootic, which encompasses a geographic area >4 × 105 km2. The ORV program successfully halted expansion of the epizootic into metropolitan areas but has not achieved the ultimate goal of eradication. Rabies activity in gray fox continues to occur periodically outside the ORV zone, preventing ORV zone contraction and dissipation of the epizootic. We employed a landscape-genetic approach to assess gray fox population structure and dispersal in the affected area, with the aim of assisting rabies management efforts. No unique genetic clusters or population boundaries were detected. Instead, foxes were weakly structured over the entire region in an isolation by distance pattern. Local subpopulations appeared to be genetically non-independent over distances >30 km, implying that long-distance movements or dispersal may have been common in the region. We concluded that gray foxes in west-central Texas have a high potential for long-distance rabies virus trafficking. Thus, a 16-km to 24-km ORV zone may be too narrow to contain the fox rabies epizootic. Continued expansion of the ORV zone, although costly, may be critical to the long-term goal of eliminating the Texas fox rabies virus variant from the United States.  相似文献   
19.
Hydrogen metabolism was studied in the anaerobic bacterium, Sporomusa sp. strain DMG 58, by measuring natural abundance levels of deuterium in H2, H2O, and individual fatty acids during acetogenic growth on H2/CO2. Four cultures were grown, each in medium with a distinct hydrogen‐isotopic composition (δD‐H2O). The δD value of H2 was quantified in the residual gas exiting the growth chambers and found to decrease concurrently with net H2 consumption, indicating rapid isotope exchange between H2 and H2O. An isotopic mass balance was used to constrain the efficiency with which H2 was activated by the cell and the reducing equivalents catabolized, which we term the H2 utilization efficiency. Results indicate that H2 utilization efficiency in these cultures is less than 20% during the growth phase, and less than 2% after the growth phase. The gross rate of cellular H2 activation was similar in the growth phase and afterward. Biomass harvested at the end of each experiment was used to analyse the D/H of individual membrane lipids. Values of δD were highly correlated between lipids and water (δD‐lipids = 0.59 × δD‐water – 381‰; R2 = 0.995), indicating the source of lipid hydrogen is in isotopic equilibrium with water. Results are consistent with two possibilities: (i) water is the sole source of hydrogen to lipids, and the fractionation during biosynthesis is significantly larger than previously observed (α = 0.59), or (ii) hydrogen from H2 is incorporated into lipids, but only after reaching isotopic equilibrium with H2O. Fatty acids were strongly depleted in deuterium relative to all other organisms studied thus far, and such large depletions may prove useful as biomarkers for studying H2 cycling in anoxic environments as well as in the geological record.  相似文献   
20.
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