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   353篇
  免费   34篇
  国内免费   1篇
  388篇
  2023年   2篇
  2021年   4篇
  2020年   17篇
  2019年   40篇
  2018年   29篇
  2017年   4篇
  2016年   8篇
  2015年   7篇
  2014年   7篇
  2013年   22篇
  2012年   5篇
  2010年   10篇
  2009年   5篇
  2008年   12篇
  2007年   15篇
  2006年   17篇
  2005年   11篇
  2004年   2篇
  2003年   6篇
  2002年   9篇
  2001年   14篇
  2000年   5篇
  1999年   11篇
  1998年   16篇
  1997年   7篇
  1996年   19篇
  1995年   15篇
  1994年   4篇
  1993年   11篇
  1992年   9篇
  1991年   4篇
  1990年   3篇
  1989年   12篇
  1988年   2篇
  1987年   4篇
  1986年   1篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1981年   2篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1976年   1篇
  1974年   1篇
排序方式: 共有388条查询结果,搜索用时 15 毫秒
101.
We assayed the diurnal concentrations of growth hormone (GH) and prolactin (PRL) in 6 healthy male volunteers to evaluate the self-similar features in the time series of each hormone on the basis of fractal theory and to determine the fractal dimension as an index of the complexity of the diurnal variation. In addition, we assessed the effects of a 6-hour delay in the sleep period on the complexity of the diurnal variaton of these hormones. There was a statistically significant fractal feature in the serum levels of GH both under the nocturnal-sleep and delayed-sleep conditions in all subjects. The time series of the serum PRL concentrations also showed a statistically significant fractal feature under the nocturnal-sleep and delayed-sleep conditions in all subjects. The fractal dimensions of the patterns of the GH or PRL levels were 1.879 and 1.929 or 1.754 and 1.785 under the nocturnal-sleep and delayed-sleep conditions, respectively. Two-way ANOVA revealed no significant difference in the fractal dimension between the two sleep conditions but did reveal a significant difference between the fractal dimensions of the GH and PRL levels. These results showed (1) that delayed sleep had no significant effect on the complexity of the diurnal pattern of these hormones, and (2) that the diurnal pattern of the GH levels was more complex than that of the PRL levels.  相似文献   
102.
The aim of this study is to investigate the effects of type I collagen on bone defects and on genes specifically for osteogenesis in a rat model. Two millimeter drill hole bone defect was created in the femur of rats. In the experimental group, type I collagen was applied in bone defects whereas in control group defects were left empty. Inflammation, development of connective tissue, osteogenesis, and foreign body reaction parameters evaluated with histologically and genes evaluated by blood samples. In the experimental group, the histopathologically significant change was found in favor of bone healing only at the first week. A significant increase was found in genetic expressions of BMP-1, 2, 3, 4, 5, 6, 7, TGF-βRII, Smad-1, IL-6, BMPR-IA, BMPR-IB, Eng, BMPR-II, c-fos, Cdkn1a, Chrd, Gdf-5, Id-1, PDGF-β, IGF-1, Serpine-1, and TGF-βRI at the first hour. At the first, third, and sixth week, no significant increase was found in any of the gene expressions. Type I collagen is found to be effective in favor of bone healing through increased inflammatory cytokines and expression of BMP genes in the early stages of fracture healing.  相似文献   
103.
Spinal cord injury (SCI) is characterized by dramatic neurons loss and axonal regeneration suppression. The underlying mechanism associated with SCI-induced immune suppression is still unclear. Weighted gene coexpression network analysis (WGCNA) is now widely applied for the identification of the coexpressed modules, hub genes, and pathways associated with clinic traits of diseases. We performed this study to identify hub genes associated with SCI development. Gene Expression Omnibus (GEO) data sets GSE45006 and GSE20907 were downloaded and the significant correlativity and connectivity between them were detected using WGCNA. Three significant consensus modules, including 567 eigengenes, were identified from the master GSE45006 data following the preconditions of approximate scale-free topology for WGCNA. Further bioinformatics analysis showed these eigengenes were involved in inflammatory and immune responses in SCI. Three hub genes Rac2, Itgb2, and Tyrobp and one pathway “natural killer cell-mediated cytotoxicity” were identified following short time-series expression miner, protein-protein interaction network, and functional enrichment analysis. Gradually upregulated expression patterns of Rac2, Itgb2, and Tyrobp genes at 0, 3, 7, and 14 days after SCI were confirmed based on GSE45006 and GSE20907 data set. Finally, we found that Rac2, Itgb2, and Tyrobp genes might take crucial roles in SCI development through the “natural killer cell–mediated cytotoxicity” pathway.  相似文献   
104.
【背景】随着CO_2排放增加,全球变暖愈发严峻,嗜热蓝细菌作为能够在45°C及以上环境中生长并实现生物固碳的微生物,具有重要的研究意义。【目的】对从广东惠州地区采集的藻种进行分离鉴定,并筛选出2株嗜热蓝细菌,研究其生长特性,为嗜热蓝细菌的后续应用提供依据。【方法】通过16SrRNA基因、藻蓝蛋白链A基因(PhycoA)序列分析确定从惠州地区采集到的菌株的分类学位置。对PKUAC-GDTS1-24和PKUAC-GDTS1-29两株嗜热蓝细菌进行形态观察和主要细胞成分(灰分、糖类、脂质、蛋白质和色素)分析。【结果】共分离出12株嗜热蓝细菌,其中PKUAC-GDTS1-24和PKUAC-GDTS1-29菌株,形态上呈蓝绿色球形毛状体,是由细胞形成密集的簇,彼此附着形成的。两株嗜热蓝细菌的主要细胞成分是糖类,分别占细胞干重的36.42%和28.46%。PKUAC-GDTS1-24的灰分、脂质和蛋白质含量分别为24.41%、21.40%和26.64%。PKUAC-GDTS1-29的细胞中,灰分、脂质和蛋白质含量分别为24.72%、23.92%和12.93%。藻蓝蛋白(Phycocyanin,PC)在PKUAC-GDTS1-24和PKUAC-GDTS1-29中的含量分别为157.29 mg/g DW和374.86 mg/g DW,类胡萝卜素分别为65.13 mg/g DW和18.87 mg/g DW。【结论】基于系统发育树研究,本实验的2个分离株属于细鞘丝藻亚科(Leptolyngbyaceae),与研究较少的纤发鞘丝蓝细菌属(Leptolyngbya)菌株相近,可能是广东和四川温泉中存在的一种新型丝状轻度嗜热蓝细菌属或Leptolyngbya新种。嗜热菌株PKUAC-GDTS1-24和PKUAC-GDTS1-29的形态和细胞组成相似,通过比较,2个菌株的藻胆蛋白含量远远高于其他研究报道的Leptolyngbya蓝细菌,尤其是PKUAC-GDTS1-29可以作为藻蓝蛋白生产的潜在菌株。  相似文献   
105.
INTRODUCTION AND NEUROEPIDEMIO- LOGY OF HIV/AIDS AIDS was first recognized as a new and distinct clini- cal entity in 1981 [1] and the HIV-1 as their casual agent in 1983 [2]. Since then, the HIV/AIDS epidemic has reached epidemic proportions with a total accumulative number of more than 60 million people, according to the Joint United Nations Programme on HIV/AIDS (UNAIDS) and WHO. The extensive spread of HIV-1 epidemics in Asia was not appreciated in the 1980s,…  相似文献   
106.
Arteriosclerotic vascular disease manifests as heart disease, stroke, aortic aneurysms, and peripheral vascular disease, and is a growing problem world-wide. The preventive efforts made so far have demonstrated that lowering LDL-C is one action that individuals and populations can do with significant success in delaying the onset of clinical events. Epidemiological studies and small clinical trials suggest that more aggressive and sustained lowering to LDL-C below 100 mg/dl could result in 50 to 70% reductions in vascular death. The full benefit of reducing LDL-C is only now being tested in adequate clinical trials.  相似文献   
107.
The cotton bollworm, Helicoverpa armigera is a polyphagous pest in Asia, Africa, and the Mediterranean Europe. Salicylic acid (SA) and jasmonic acid (JA) are the cell signaling molecules produced in response to insect attack in plants. The effect of these signaling molecules was investigated on the oxidative phosphorylation and oxidative stress of H. armigera. SA significantly inhibited the state III and state IV respiration, respiratory control index (RCI), respiratory complexes I and II, induced mitochondrial swelling, and cytochrome c release in vitro. Under in vivo conditions, SA induced state IV respiration as well as oxidative stress in time- and dose-dependent manner, and also inhibited the larval growth. In contrast, JA did not affect the mitochondrial respiration and oxidative stress. SA affected the growth and development of H. armigera, in addition to its function as signaling molecules involved in both local defense reactions at feeding sites and the induction of systemic acquired resistance in plants.  相似文献   
108.
Epilepsy is one of the most common neurological disorders and is characterized by recurrent, unprovoked epileptic seizures. Seizures are generated by spontaneous, synchronous neuronal discharges which induce disturbances of perception or behaviour. About one third of all epilepsies are primarily caused by genetic factors. These so-called idiopathic epilepsies occur without observable structural alterations in the brain. Mutations in genes encoding neuronal ion channels play a central role in the etiology of such epilepsies. In this review, mutations in ion channel genes associated with idiopathic epilepsies and their functional consequences are described. The underlying pathomechanisms and consequences for treatment are discussed.  相似文献   
109.
110.
In preparing for testing a pharmaceutical grade preparation of chimeric (mouse/human) antibody CGP 47 439 in HIV-1 infected individuals, it was administered toMacaca fascicularis (cynomolgus) monkeys to study tolerability, immunogenicity and pharmacokinetics. Four groups of monkeys, three males and three females per group, received respectively four infusions of 0, 1.43, 4.3, and 14.3 mg of CGP 47 4391 kg body weight at one-week intervals. The chimeric antibody induced no fever, was tolerated well throughout the 50-day observation period, elicited no tissue damage and no anti-antibody response. The pharmacokinetic profile was similar at all dose levels with a mean T1/2 of 14.2 h (range 11.8–19.3 h) and a mean T1/2 of 172.6h (range 137.2–220.5h). Following four successive antibody infusions serum concentrations of CGP 47 439 increased without reaching a steady state, and its measured concentrations were comparable to the simulated values. Collectively the study has provided safety and pharmacokinetic data that would allow human studies with this antibody in AIDS patients.  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