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   1275篇
  免费   64篇
  国内免费   2篇
  1341篇
  2024年   2篇
  2023年   20篇
  2022年   20篇
  2021年   42篇
  2020年   30篇
  2019年   42篇
  2018年   25篇
  2017年   25篇
  2016年   39篇
  2015年   62篇
  2014年   76篇
  2013年   120篇
  2012年   122篇
  2011年   109篇
  2010年   69篇
  2009年   55篇
  2008年   77篇
  2007年   69篇
  2006年   60篇
  2005年   55篇
  2004年   30篇
  2003年   29篇
  2002年   23篇
  2001年   14篇
  2000年   8篇
  1999年   15篇
  1998年   10篇
  1997年   6篇
  1996年   7篇
  1995年   4篇
  1994年   4篇
  1993年   6篇
  1992年   2篇
  1991年   6篇
  1990年   4篇
  1988年   6篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   5篇
  1982年   4篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1976年   2篇
  1975年   2篇
  1972年   2篇
  1966年   1篇
  1960年   1篇
排序方式: 共有1341条查询结果,搜索用时 0 毫秒
51.
BackgroundThe lower airways harbor a community of bacterial species which is altered in asthma.ObjectivesWe examined whether the lower airway microbiota were related to measures of asthma severity.MethodsWe prospectively recruited 26 severe asthma, 18 non-severe asthma and 12 healthy subjects. DNA was extracted from induced sputum and PCR amplification of the V3-V5 region of bacterial 16S rRNA gene was performed.ResultsWe obtained 138,218 high quality sequences which were rarefied at 133 sequences/sample. Twenty OTUs had sequences ≥1% of total. There were marked differences in the distribution of Phyla between groups (P = 2.8x10-118). Bacteroidetes and Fusobacteria were reduced in non-severe and severe asthmatic groups. Proteobacteria were more common in non-severe asthmatics compared to controls (OR = 2.26; 95% CI = 1.94–2.64) and Firmicutes were increased in severe asthmatics compared to controls (OR = 2.15; 95%CI = 1.89–2.45). Streptococcal OTUs amongst the Firmicutes were associated with recent onset asthma, rhinosinusitis and sputum eosinophilia.ConclusionsSputum microbiota in severe asthma differs from healthy controls and non-severe asthmatics, and is characterized by the presence of Streptococcus spp with eosinophilia. Whether these organisms are causative for the pathophysiology of asthma remains to be determined.  相似文献   
52.
Osteoarthritis (OA) is a chronic disease affecting the cartilage of over 15% of Canadians. Synovial fluid mesenchymal progenitor cells (sfMPCs) are present in joints and are thought to contribute to healing. OA sfMPCs have a greater proliferative ability but decreased chondrogenic potential. However, little is known about the factors influencing/regulating the differences between normal and OA sfMPCs. Recently, our lab has shown that sfMPC chondrogenic differentiation in vitro is favorably biased toward a similar osmotic environment as they experience in vivo. The current study now examines the expression and functionality of a variety of ion channels in sfMPCs derived from normal individuals and early OA patients. Results indicated that there is differential ion channel regulation at the functional level and expression level in early OA sfMPCs. All ion channels were upregulated in early OA compared to normal sfMPCs with the exception of KCNMA1 at the mRNA level. At the protein level, TRPV4 was over expressed in early OA sfMPCs, while KCNJ12 and KCNMA1 were unchanged between normal and early OA sfMPCs. At the functional level, the inward rectifying potassium channel was under expressed in early OA sfMPCs, however the membrane potential was unchanged between normal and early OA sfMPCs. In the synovial environment itself, a number of differences in ion concentration between normal and early OA synovial fluid were observed. These findings suggest that normal and OA progenitor cells demonstrate functional differences in how they interact with the synovial ion environment.  相似文献   
53.

Background

The World Health Organization recommends direct observation of treatment (DOT) to support patients with tuberculosis (TB) and to ensure treatment completion. As per national programme guidelines in India, a DOT provider can be anyone who is acceptable and accessible to the patient and accountable to the health system, except a family member. This poses challenges among children with TB who may be more comfortable receiving medicines from their parents or family members than from unfamiliar DOT providers. We conducted a non-inferiority trial to assess the effect of family DOT on treatment success rates among children with newly diagnosed TB registered for treatment during June–September 2012.

Methods

We randomly assigned all districts (n = 30) in Gujarat to the intervention (n = 15) or usual-practice group (n = 15). Adult family members in the intervention districts were given the choice to become their child’s DOT provider. DOT was provided by a non-family member in the usual-practice districts. Using routinely collected clinic-based TB treatment cards, we compared treatment success rates (cured and treatment completed) between the two groups and the non-inferiority limit was kept at 5%.

Results

Of 624 children with newly diagnosed TB, 359 (58%) were from intervention districts and 265 (42%) were from usual-practice districts. The two groups were similar with respect to baseline characteristics including age, sex, type of TB, and initial body weight. The treatment success rates were 344 (95.8%) and 247 (93.2%) (p = 0.11) among the intervention and usual-practice groups respectively.

Conclusion

DOT provided by a family member is not inferior to DOT provided by a non-family member among new TB cases in children and can attain international targets for treatment success.

Trial Registration

Clinical Trials Registry–India, National Institute of Medical Statistics (Indian Council of Medical Research) CTRI/2015/09/006229  相似文献   
54.
55.
Hyperglycaemia in diabetes is either caused by reduced availability of insulin (type 1 diabetes, T1D) or insulin resistance to the cells (type 2 diabetes, T2D). In recent years, the prevalence of T2D has increased to an alarming proportion, encompassing 95% of the total diabetic burden, probably due to economy-driven changes in lifestyle. Recent epidemiological studies show comorbid depression, anxiety and related mental illness. To explore the molecular mechanisms underlying this comorbid conditions, we used Sprague–Dawley rats on high-fructose diet for 8 weeks to induce prediabetic condition. Rats with this metabolic syndrome also showed hyper-anxiety when they were subjected to anxiety-related behavioural assays. Rats were administered with resveratrol, an activator of sirtuins, and metformin, a standard antidiabetic drug, simultaneously with fructose. We observed that resveratrol was more effective in protecting from both the metabolic (prediabetic) and affective (anxiety) disorders than metformin. Molecular studies showed that recovery was associated with the upregulation of few nuclear sirtuins that act epigenetically – Sirt 1 and 7, which were significantly attenuated in the striatum of prediabetic rats. In conclusion, our study showed that hyper-anxiety associated with prediabetic condition is ameliorated by resveratrol through modulation of sirtuins, which is more or less similar to metformin.  相似文献   
56.
Metabolomics - Microalgae produce metabolites that could be useful for applications in food, biofuel or fine chemical production. The identification and development of suitable strains require...  相似文献   
57.
Bioprocess and Biosystems Engineering - In the present study, the effect of irradiance on growth performance of Scenedesmus obliquus was investigated, and various non-linear growth models were...  相似文献   
58.
Members of the Chenopodiaceae are the most dominant elements in the central Asian desert. The different genera and species within this family are common in desert vegetation types. Should it prove possible to link pollen types in this family to specific desert vegetation, it would be feasible to trace vegetation successions in the geological past. Nevertheless, the morphological similarity of pollen grains in the Chenopodiaceae rarely permits identification at the generic level. Although some pollen classifications of Chenopodiaceae have been proposed, none of them tried to link pollen types to specific desert vegetation types in order to explore their ecological significance. Based on the pollen morphological characters of 13 genera and 24 species within the Chenopodiaceae of eastern central Asia, we provide a new pollen classification of this family with six pollen types and link them to those plant communities dominated by Chenopodiaceae, for example, temperate dwarf semi‐arboreal desert (Haloxylon type), temperate succulent halophytic dwarf semi‐shrubby desert (Suaeda, Kalidium, and Atriplex types), temperate annual graminoid desert (Kalidium type), temperate semi‐shrubby and dwarf semi‐shrubby desert (Kalidium, Iljini, and Haloxylon types), and alpine cushion dwarf semi‐shrubby desert (Krascheninnikovia type). These findings represent a new approach for detecting specific desert vegetation types and deciphering ecosystem evolution in eastern central Asia.  相似文献   
59.
Three new pyrene‐based derivatives P1 , P2 and P3 with a substituted pyrazole were designed, synthesized and characterized using standard spectroscopic techniques. Ultraviolet–visible (UV–vis) spectroscopic studies for P1–P3 uncovered a finite bathochromic shift of the molecules in solvents of varying polarity. Photoluminescence (PL) studies revealed the significant fluorescence emission of all molecules in higher polar solvents such as MeOH and dimethylformamide (DMF). Fluorescence quantum yield studies demonstrated the importance of P3 possessing cyanofunctionality for imparting higher emission with a quantum yield of 0.36%. Ratiometric studies performed in a tetrahydrofuran (THF)/H2O mixture indicated fluorescence enhancement with increasing overall percentage of water, confirming the aggregation‐induced emission effect. Cyclic voltammetry study of molecules P1–P3 revealed an irreversible oxidation peak and the band gaps were calculated to be 2.26 eV for P1 and 2.31 eV for P2 and P3 respectively. Density functional theory (DFT) studies performed on molecules P1–P3 validate the structure correlation of the molecules. Theoretically estimated highest occupied molecular orbital ( HOMO), lowest unoccupied molecular orbital (LUMO) and bandgap correlated well with the experimental values. Furthermore, time‐dependent (TD)DFT showed that the major contribution for the electronic transitions occurring in the system was governed by HOMO‐1 and LUMO+1 orbitals.  相似文献   
60.
Alzheimer’s disease (AD) is a genetically complex, progressive and irreversible neurodegenerative disorder of the brain which involves multiple associated etiological targets. The complex pathogenesis of AD gave rise to multi-target-directed ligands (MTDLs) principle to combat this dreaded disease. Within this approach, the design and synthesis of hybrids prevailed greatly because of their capability to simultaneously target the intertwined pathogenesis components of the disease. The hybrids include pharmacophoric hybridization of two or more established chemical scaffolds endowed with the desired pharmacological properties into a single moiety. In AD, the primary foundation of medication therapy and drug design strategies includes the inhibition of cholinesterase (ChE) enzymes. Hence the development of ChE inhibition based hybrids is the central choice of AD medicinal chemistry research. To illustrate the progress of ChE inhibition based hybrids and novel targets, we reviewed the medicinal chemistry and pharmacological properties of the multi-target molecules published since 1998-December 2018. We hope that this article will allow the readers to easily follow the evolution of this prominent medicinal chemistry approach to develop a more efficient inhibitor.  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