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   2934篇
  免费   376篇
  国内免费   3篇
  3313篇
  2022年   25篇
  2021年   65篇
  2020年   32篇
  2019年   38篇
  2018年   48篇
  2017年   29篇
  2016年   75篇
  2015年   120篇
  2014年   137篇
  2013年   132篇
  2012年   177篇
  2011年   156篇
  2010年   98篇
  2009年   92篇
  2008年   108篇
  2007年   122篇
  2006年   99篇
  2005年   106篇
  2004年   99篇
  2003年   93篇
  2002年   77篇
  2001年   80篇
  2000年   64篇
  1999年   71篇
  1998年   30篇
  1997年   26篇
  1996年   29篇
  1995年   26篇
  1994年   28篇
  1992年   54篇
  1991年   49篇
  1990年   52篇
  1989年   48篇
  1988年   42篇
  1987年   38篇
  1986年   37篇
  1985年   45篇
  1984年   34篇
  1983年   35篇
  1982年   25篇
  1980年   24篇
  1979年   38篇
  1978年   27篇
  1977年   29篇
  1976年   31篇
  1974年   33篇
  1973年   33篇
  1972年   29篇
  1971年   35篇
  1966年   32篇
排序方式: 共有3313条查询结果,搜索用时 0 毫秒
101.

Objective

Adequate symptom control is a problem for many people with asthma. We asked whether weekly email reports on monitored use of inhaled, short-acting bronchodilators might improve scores on composite asthma-control measures.

Methods

Through an investigational electronic medication sensor attached to each participant''s inhaler, we monitored 4 months'' use of inhaled, short-acting bronchodilators. Participants completed surveys, including the Asthma Control TestTM (ACT), to assess asthma control at entry and monthly thereafter. After the first month, participants received weekly email reports for 3 months. The reports summarized inhaled bronchodilator use during the preceding week and provided suggestions derived from National Asthma Education and Prevention Program (NAEPP) guidelines. Paired t-tests and random-effects mixed models were implemented to assess changes in primary asthma endpoints.

Results

Thirty individuals participated in the 4-month study; 29 provided complete asthma control information. Mean age was 36.8 years (range: 19–74 years); 52% of respondents were female. Mean ACT scores were 17.6 (Standard Deviation [SD]  = 3.35) at entry and 18.4 (SD = 3.60) at completion of the first month. No significant difference appeared between ACT values at entry and completion of the first month (p = 0.66); however, after participants began receiving email reports and online information about their inhaler use, mean ACT scores increased 1.40 points (95% CI: 0.61, 2.18) for each subsequent study month. Significant decreases occurred in 2-week histories of daytime symptoms (β = −1.35, 95% CI: −2.65, −0.04) and nighttime symptoms (β = −0.84, 95% CI: −1.25, −0.44); no significant change in activity limitation (β = −0.21, 95% CI: −0.69, 0.26) was observed. Participants reported increased awareness and understanding of asthma patterns, level of control, bronchodilator use (timing, location) and triggers, and improved preventive practices.

Conclusions

Weekly email reports and access to online charts summarizing remote monitoring of inhaled bronchodilator frequency and location were associated with improved asthma control and a decline in day-to-day asthma symptoms.  相似文献   
102.
103.
104.
In colorectal cancer (CRC), chromosomal instability (CIN) is typically studied using comparative-genomic hybridization (CGH) arrays. We studied paired (tumor and surrounding healthy) fresh frozen tissue from 86 CRC patients using Illumina's Infinium-based SNP array. This method allowed us to study CIN in CRC, with simultaneous analysis of copy number (CN) and B-allele frequency (BAF)--a representation of allelic composition. These data helped us to detect mono-allelic and bi-allelic amplifications/deletion, copy neutral loss of heterozygosity, and levels of mosaicism for mixed cell populations, some of which can not be assessed with other methods that do not measure BAF. We identified associations between CN abnormalities and different CRC phenotypes (histological diagnosis, location, tumor grade, stage, MSI and presence of lymph node metastasis). We showed commonalities between regions of CN change observed in CRC and the regions reported in previous studies of other solid cancers (e.g. amplifications of 20q, 13q, 8q, 5p and deletions of 18q, 17p and 8p). From Therapeutic Target Database, we identified relevant drugs, targeted to the genes located in these regions with CN changes, approved or in trials for other cancers and common diseases. These drugs may be considered for future therapeutic trials in CRC, based on personalized cytogenetic diagnosis. We also found many regions, harboring genes, which are not currently targeted by any relevant drugs that may be considered for future drug discovery studies. Our study shows the application of high density SNP arrays for cytogenetic study in CRC and its potential utility for personalized treatment.  相似文献   
105.
106.
107.
Although great advances have been made in the treatment of pediatric acute lymphoblastic leukemia, up to one of five patients will relapse, and their prognosis thereafter is dismal. We have previously identified recurrent deletions in TBL1XR1, which encodes for an F-box like protein responsible for regulating the nuclear hormone repressor complex stability. Here we model TBL1XR1 deletions in B-precursor ALL cell lines and show that TBL1XR1 knockdown results in reduced glucocorticoid receptor recruitment to glucocorticoid responsive genes and ultimately decreased glucocorticoid signaling caused by increased levels of nuclear hormone repressor 1 and HDAC3. Reduction in glucocorticoid signaling in TBL1XR1-depleted lines resulted in resistance to glucocorticoid agonists, but not to other chemotherapeutic agents. Importantly, we show that treatment with the HDAC inhibitor SAHA restores sensitivity to prednisolone in TBL1XR1-depleted cells. Altogether, our data indicate that loss of TBL1XR1 is a novel driver of glucocorticoid resistance in ALL and that epigenetic therapy may have future application in restoring drug sensitivity at relapse.  相似文献   
108.
嵌合体大鼠是研究人类疾病的重要动物模犁.用囊胚注射法研究了大鼠内细胞团(ICM)和胎儿神经干细胞(FNS)构建嵌合体的潜力.结果发现来自黑色(DA)大鼠第5天(D5)和第6天(D6)囊胚的ICM细胞注入D5 Sprague-Dawley(SD)大鼠囊胚后得到3只嵌合体大鼠:D5 SD大鼠ICM细胞注射入D5 DA囊胚后得到4只嵌合体大鼠:而体外培养的DA或SD人鼠ICM细胞注射后均未能获得嵌合体大鼠.本研究用大鼠胎儿神经干细胞(rFNS)和LacZ转染的rFNS构建嵌介体,未能获得嵌合体人鼠:但在LacZ转染的SD rFNS注射到DA大鼠囊胚后发育来的41只胎儿中,有2只胎儿其组织切片中发现少量LacZ阳性细胞.结果表明DA和SD大鼠ICM具有参与嵌合体发育的潜力,但ICM细胞经体外培养后构建嵌合体的潜力显著F降(P<0.05);大鼠胎儿神经干细胞构建嵌合体的潜力较低,可能仅具有参与早期胚胎发育的潜力.  相似文献   
109.
110.
Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems.  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