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   1523篇
  免费   82篇
  国内免费   2篇
  1607篇
  2024年   4篇
  2023年   18篇
  2022年   42篇
  2021年   73篇
  2020年   37篇
  2019年   40篇
  2018年   75篇
  2017年   47篇
  2016年   58篇
  2015年   76篇
  2014年   100篇
  2013年   91篇
  2012年   102篇
  2011年   75篇
  2010年   52篇
  2009年   54篇
  2008年   77篇
  2007年   78篇
  2006年   55篇
  2005年   50篇
  2004年   58篇
  2003年   43篇
  2002年   29篇
  2001年   23篇
  2000年   32篇
  1999年   17篇
  1998年   7篇
  1997年   6篇
  1996年   10篇
  1995年   7篇
  1994年   6篇
  1993年   8篇
  1992年   16篇
  1991年   15篇
  1990年   16篇
  1989年   18篇
  1988年   7篇
  1987年   4篇
  1986年   10篇
  1985年   7篇
  1984年   13篇
  1983年   6篇
  1981年   9篇
  1980年   7篇
  1977年   4篇
  1975年   5篇
  1974年   2篇
  1973年   3篇
  1972年   2篇
  1965年   2篇
排序方式: 共有1607条查询结果,搜索用时 0 毫秒
41.
Allergic inflammation develops in tissues that have large epithelial surface areas that are exposed to the environment, such as the lung, skin and gut. In the steady state, antigen-experienced memory T cells patrol these peripheral tissues to facilitate swift immune responses against invading pathogens. In at least two allergy-prone organs, the skin and the gut, memory T cells are programmed during the initial antigen priming to express trafficking receptors that enable them to preferentially home to these organs. In this review we propose that tissue-specific memory and inflammation-specific T cell trafficking facilitates the development of allergic disease in these organs. We thus review recent advances in our understanding of tissue-specific T cell trafficking and how regulation of T cell trafficking by the chemokine system contributes to allergic inflammation in mouse models and in human allergic diseases of the skin, lung and gut. Inflammation- and tissue-specific T lymphocyte trafficking pathways are currently being targeted as new treatments for non-allergic inflammatory diseases and may yield effective new therapeutics for allergic diseases.  相似文献   
42.
Anther culture responsiveness of three H. spontaneum derived spring barley lines, RS170-47(A), RS20-1(B) and 1B-152B(C) was investigated using only one type of culture medium and treatment. The line 1B-152B was identified as highly responsive producing 22.4 total and 12.4 green regenerants per 100 anthers plated. 74% of these green regenerants were spontaneous double haploids. A genetic analysis involving F1 and F2 plants derived from crosses A × B and B × C revealed that the factor(s) determining high anther culture responsiveness in line 1B-152B was heritable and behaved as dominant in the F1. There was an indication that genotypic responsiveness in anther culture for green plant regeneration was different from total or albino plant regeneration.  相似文献   
43.
Summary Hereditary cystatin C amyloid angiopathy has recently been shown to be caused by a point mutation in the cystatin C gene. To determine the chromosomal localization of the gene, 20 human-rodent somatic cell hybrids and a fulllength cystatin C cDNA probe were used. Southern blot analysis of BamHI digested cell hybrid DNA revealed that the probe recognizes a 10.6 kb human specific fragment and that this fragment cosegregates with human chromosome 20. Therefore, the human cystatin C gene (CST3) was assigned to chromosome 20.  相似文献   
44.
Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic interactions. We previously reported that, in leaf palisade cells of Arabidopsis thaliana, mitochondria exhibit blue‐light‐dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue‐light receptor phototropins. In this study, precise motility analyses by fluorescent microscopy revealed that the individual mitochondria in palisade cells, labeled with green fluorescent protein, exhibit typical stop‐and‐go movement. When exposed to blue light, the velocity of moving mitochondria increased in 30 min, whereas after 4 h, the frequency of stoppage of mitochondrial movement markedly increased. Using different mutant plants, we concluded that the presence of both phototropin1 and phototropin2 is necessary for the early acceleration of mitochondrial movement. On the contrary, the late enhancement of stoppage of mitochondrial movement occurs only in the presence of phototropin2 and only when intact photosynthesis takes place. A plasma‐membrane ghost assay suggested that the stopped mitochondria are firmly adhered to chloroplasts. These results indicate that the physical interaction between mitochondria and chloroplasts is cooperatively mediated by phototropin2‐ and photosynthesis‐dependent signals. The present study might add novel regulatory mechanism for light‐dependent plant organelle interactions.  相似文献   
45.
Habib  K. A.  Islam  Md. J.  Nahar  N.  Neogi  A. K.  Fraser  T. H. 《Journal of Ichthyology》2021,61(4):505-513
Journal of Ichthyology - Three species of cardinalfishes viz. Ostorhinchus cookii (Macleay, 1881), Lepidamia kalosoma (Bleeker, 1852) and Apogonichthyoides sialis (Jordan et Thompson, 1914)...  相似文献   
46.
Amino Acids - The antidiabetic effect of l-leucine has been attributed to its modulatory effect on glucose uptake and lipid metabolism in muscles. However, there is a dearth on its effect on...  相似文献   
47.

Background

Guillain-Barré syndrome (GBS) is the most common cause of acute flaccid paralysis (AFP) in the post-poliomyelitis eradication era. This is the first study done to identify the epidemiology, clinical features, and outcome of GBS in Iraqi children over 15 years.

Methods

The surveillance database about AFP cases?<?15 years reported during January 1997-December 2011 was used.

Results

GBS represented 52.5% of AFP cases, with an incidence of 1.33 case/100,000 population?<?15 years/year. There was a higher incidence in the Southern provinces, age group 1–4 years, males, and outside the capital city of province, with no significant seasonal variations (p?=?.22). Survival probability after the 1 year of onset for those with respiratory muscle involvement was .76 (95% CI: .60-.86), versus .97 (95% Cl: .96-.98) for those who did not develop it (p?<?.001); and .97 (95% CI: .96-.98) for those living inside the capital city, versus .94 (.93-.95) for those living outside (p?=?.001). Cumulative incidence of residual paralysis for patients living inside the capital city was .21 (95% CI: .18-.24), versus .27 (95% CI: .25-.29) for those living outside (p?<?.001).

Conclusions

The incidence, age and gender distribution, and seasonality of GBS among Iraqi children is similar to those reported from other previous studies. It is the most important cause of AFP, especially in those between the age of 1 to 4 years living in rural areas.
  相似文献   
48.
49.
In vegetation science and forest management, tree density is often used as a variable. To determine the value of this variable, reliable field methods are necessary. When vegetation is sparse or not easily accessible, the use of sample plots is not feasible in the field. Therefore, plotless methods, like the Point Centred Quarter Method, are often used as an alternative. In this study we investigate the accuracy of different plotless sampling methods. To this end, tree densities of a mangrove forest were determined and compared with estimates provided by several plotless methods. None of these methods proved accurate across all field sites with mean underestimations up to 97% and mean overestimations up to 53% in the field. Applying the methods to different vegetation patterns shows that when random spatial distributions were used the true density was included within the 95% confidence limits of all the plotless methods tested. It was also found that, besides aggregation and regularity, density trends often found in mangroves contribute to the unreliability. This outcome raises questions about the use of plotless sampling in forest monitoring and management, as well as for estimates of density-based carbon sequestration. We give recommendations to minimize errors in vegetation surveys and recommendations for further in-depth research.  相似文献   
50.
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