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   267篇
  免费   23篇
  290篇
  2022年   4篇
  2021年   3篇
  2020年   3篇
  2019年   4篇
  2018年   7篇
  2017年   5篇
  2016年   6篇
  2015年   10篇
  2014年   9篇
  2013年   9篇
  2012年   18篇
  2011年   14篇
  2010年   13篇
  2009年   20篇
  2008年   13篇
  2007年   14篇
  2006年   14篇
  2005年   14篇
  2004年   7篇
  2003年   10篇
  2002年   7篇
  2001年   9篇
  2000年   4篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1994年   2篇
  1989年   6篇
  1988年   2篇
  1986年   2篇
  1979年   2篇
  1976年   4篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1970年   2篇
  1968年   3篇
  1967年   2篇
  1964年   2篇
  1960年   2篇
  1955年   3篇
  1954年   1篇
  1953年   1篇
  1952年   1篇
  1951年   3篇
  1945年   1篇
  1944年   1篇
  1943年   1篇
  1917年   1篇
  1904年   1篇
排序方式: 共有290条查询结果,搜索用时 7 毫秒
61.
62.
One hundred consecutive superficial mass lesions in various body sites were sampled by both conventional fine needle aspiration (FNA) and by a fine needle without the application of syringe suction. The latter technique is based on the principle of capillarity and may be termed "fine needle capillary" (FNC) sampling. The two sampling techniques were compared using five objective parameters: (1) the amount of diagnostic cellular material present, (2) the retention of appropriate architecture and cellular arrangement, (3) the degree of cellular degeneration, (4) the cellular trauma and (5) the volume of obscuring background blood and clots. There was no statistically significant difference between the efficacies of the two sampling techniques for any of the parameters studied. FNA sampling was diagnostic in a greater number of cases than was FNC sampling, but this difference was not statistically significant at a level of P = .05. When FNC sampling was diagnostic, it more frequently produced superior-quality material; conventional FNA, although diagnostic in a greater number of cases, mostly produced adequate, rather than superior-quality, material. This trend was not, however, statistically significant at a level of P = .05. These findings differ from those of previous studies (which have shown overall superiority of FNC sampling over conventional FNA sampling) and suggest that the technique of fine needle sampling employed for cytodiagnosis can be left to the personal preference of the operator.  相似文献   
63.
64.
The concentrations of arginine vasopressin (AVP), somatostatin (SS), and the primary brain metabolites of norepinephrine (MHPG), serotonin (5-HIAA), and dopamine (HVA) were measured in samples of lumbar CSF obtained from ten amnesics with Korsakoff's psychosis, four patients with a history of Korsakoff's psychosis who had recovered from the amnesic symptoms of this disease, and control subjects. Significant deficits were observed in the amnesic group for AVP and MHPG, but not for the other substances measured. Subjects who had recovered from the amnesic symptoms of Korsakoff's psychosis had increased concentrations of AVP and MHPG, but not of SS or the other monoamine metabolites.  相似文献   
65.
66.
Vagal nerve stimulation in cardiac therapy involves delivering electrical current to the vagal sympathetic complex in patients experiencing heart failure. The therapy has shown promise but the mechanisms by which any benefit accrues is not understood. In this paper we model the response to increased levels of stimulation of individual components of the vagal sympathetic complex as a differential activation of each component in the control of heart rate. The model provides insight beyond what is available in the animal experiment in as much as allowing the simultaneous assessment of neuronal activity throughout the cardiac neural axis. The results indicate that there is sensitivity of the neural network to low level subthreshold stimulation. This leads us to propose that the chronic effects of vagal nerve stimulation therapy lie within the indirect pathways that target intrinsic cardiac local circuit neurons because they have the capacity for plasticity.  相似文献   
67.
68.

Aim

Climate change is expected to have major impacts on terrestrial biodiversity at all ecosystem levels, including reductions in species‐level distribution and abundance. We aim to test the extent to which land use management, such as setting‐aside forest from production, could reduce climate‐induced biodiversity impacts for specialist species over large geographical gradients.

Location

Sweden.

Methods

We applied ensembles of species distribution models based on citizen science data for six species of red‐listed old‐forest indicator fungi confined to spruce dead wood. We tested the effect on species habitat suitabilities of alternative climate change scenarios and varying amounts of forest set‐aside from production over the coming century.

Results

With 3.6% of forest area set‐aside from production and assuming no climate change, overall habitat suitabilities for all six species were projected to increase in response to maturing spruce in set‐aside forest. However, overall habitat suitabilities for all six species were projected to decline under climate change scenario RCP4.5 (intermediate–low emissions), with even greater declines projected under RCP 8.5 (high emissions). Increasing the amount of forest set‐aside to 16% resulted in significant increases in overall habitat suitability, with one species showing an increase. A further increase to 32% forest set‐aside resulted in considerably more positive trends, with three of six species increasing.

Main conclusions

There is interspecific variation in the importance of future macroclimate and resource availability on species occurrence. However, large‐scale conservation measures, such as increasing resource availability through setting aside forest from production, could reduce future negative effects from climate change, and early investment in conservation is likely to reduce the future negative impacts of climate change on specialist species.  相似文献   
69.
70.
In a retrospective study of the incidence of mesothelioma in Scotland for 1950-67 80 cases were traced from pathological reports and biopsy material of malignant tumours invading the pleura and peritoneum. These cases were matched with two sets of controls. Detailed histories of residence, occupation, and degree of exposure to asbestos confirmed that the incidence of mesothelioma in Scotland is similar to that in other parts of Britain.  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