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   717篇
  免费   86篇
  国内免费   1篇
  2024年   3篇
  2023年   6篇
  2022年   12篇
  2021年   14篇
  2020年   8篇
  2019年   17篇
  2018年   22篇
  2017年   18篇
  2016年   27篇
  2015年   32篇
  2014年   38篇
  2013年   72篇
  2012年   61篇
  2011年   56篇
  2010年   33篇
  2009年   31篇
  2008年   40篇
  2007年   36篇
  2006年   39篇
  2005年   35篇
  2004年   30篇
  2003年   25篇
  2002年   29篇
  2001年   10篇
  2000年   16篇
  1999年   14篇
  1998年   11篇
  1997年   5篇
  1996年   7篇
  1995年   5篇
  1994年   1篇
  1993年   5篇
  1992年   5篇
  1991年   4篇
  1990年   3篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   2篇
  1984年   5篇
  1982年   1篇
  1980年   2篇
  1979年   2篇
  1976年   1篇
  1974年   2篇
  1973年   1篇
  1972年   6篇
  1971年   3篇
  1969年   1篇
排序方式: 共有804条查询结果,搜索用时 15 毫秒
731.
Anorexia, nausea/emesis and peripheral sensorial neuropathy are frequent adverse effects associated with chemotherapy. Cannabinoids have been proposed to alleviate these effects, but their preventive properties in long-term experimental models have not been tested. This study was conducted to determine whether or not a cannabinoid agonist (WIN-55,212-2) can prevent anorexia, pica (an indirect marker of nausea in non-vomiting species, consisting of the ingestion of non-nutritive substances such as kaolin) and mechanical allodynia (a marker of peripheral neuropathy) induced by the antineoplastic drug cisplatin chronically administered. Isolated rats with free access to food and kaolin received either saline, cannabinoid vehicle, WIN-55,212-2 (1-2 mg kg(-1)), cisplatin (1-2 mg kg(-1)), or both drugs once per week for five consecutive weeks. Modifications in temperature, body weight gain, food and kaolin intake, and the threshold for mechanical allodynia were recorded. Additionally, the acute psychoactive effects of the cannabinoid (hypomotility, hypothermia, analgesia and catalepsia) were assayed by means of the cannabinoid tetrad. WIN 55,212-2 prevented the development of mechanical allodynia but not anorexia, pica and reduction in weight gain induced by chronic cisplatin. The effect of WIN 55,212-2 was evident even at a dose lacking activity in the cannabinoid tetrad. The preventive effect on cisplatin-induced mechanical allodynia exerted by the cannabinoid could be due to a neuroprotective role, as has been suggested for other conditions. The present results support the interest in the evaluation of cannabinoids for treatment of patients suffering or likely to suffer neuropathic pain.  相似文献   
732.
A fully automated anthrax smoke detector (ASD) has been developed and tested. The ASD is intended to serve as a cost effective front-end monitor for anthrax surveillance systems. The principle of operation is based on measuring airborne endospore concentrations, where a sharp concentration increase signals an anthrax attack. The ASD features an air sampler, a thermal lysis unit, a syringe pump, a time-gated spectrometer, and endospore detection chemistry comprised of dipicolinic acid (DPA)-triggered terbium ion (Tb(3+)) luminescence. Anthrax attacks were simulated using aerosolized Bacillus atrophaeus spores in fumed silica, and corresponding Tb-DPA intensities were monitored as a function of time and correlated to the number of airborne endospores collected. A concentration dependence of 10(2)-10(6) spores/mg of fumed silica yielded a dynamic range of 4 orders of magnitude and a limit of detection of 16 spores/L when 250 L of air were sampled. Simulated attacks were detected in less than 15 min.  相似文献   
733.

The invasive brown seaweed Undaria pinnatifida was first recorded in 1992 in Golfo Nuevo, northern Patagonia, Argentina (hereafter Undaria). Like other brown seaweeds, Undaria synthesizes fucoidans, a unique class of sulfated polysaccharides, which display an array of biological activities and have important commercial value. In this work we have measured the content, sulfate, and monosaccharide composition of fucoidans in Undaria sporophylls from Golfo Nuevo. These results were analyzed in relation to harvest month and development stage of algal thalli. Samples were collected between November 2015 and March 2016 and classified according to morphological traits into previously defined development stages. Acid extraction (0.01 M HCl, pH 2) was carried out at room temperature and at 70 °C. Average fucoidan content was 18.1% dry wt. and slightly increased with month progression and in senescent individuals. Average sulfate content in fucoidan extracts was 20.3% dry wt. decreasing with month and development. Predominant sugars were fucose and galactose averaging a total of 91 mol% of neutral sugars. This study confirms that sporophyll fucoidans from Patagonian Undaria are sulfated galactofucans. Fucoidan content significantly increases from 14.5 to 19.2% dry wt. with sporophyte development. Slight increments with month progression are not statistically significant. Molar proportion of neutral sugars is constant between maturity stages and varies slightly with month progression. Sulfate content of fucoidan decreased significantly with development and month progression. Pooled with previous reports about abundance and seasonality of Undaria in Patagonia, our results suggest that sporophylls could be harvested for fucoidan production at least during 5 months between November and March.

  相似文献   
734.
We prepared, by solution‐phase methods, and fully characterized three analogs of the membrane‐active peptaibiotic alamethicin F50/5, bearing a single trifluoroacetyl (Tfa) label at the N‐terminus, at position 9 (central region) or at position 19 (C‐terminus), and with the three Gln at positions 7, 18, and 19 replaced by Glu(OMe) residues. To add the Tfa label at position 9 or 19, a γ‐trifluoroacetylated α,γ‐diaminobutyric acid (Dab) residue was incorporated as a replacement for the original Val9 or Glu(OMe)19 amino acid. We performed a detailed conformational analysis of the three analogs (using FT‐IR absorption, CD, 2D‐NMR, and X‐ray diffraction), which clearly showed that Tfa labeling does not introduce any dramatic backbone modification in the predominantly α‐helical structure of the parent peptaibiotic. The results of an initial solid‐state 19F‐NMR study on one of the analogs favor the conclusion that the Tfa group is a very promising reporter for the analysis of peptaibiotic? membrane interactions. Finally, we found that the antimicrobial activities of the three newly synthesized analogs depend on the position of the Tfa label in the peptide sequence.  相似文献   
735.

Objectives

To describe the use of health and social services, and to analyze the influence of functional capacity for Instrumental Activities of Daily Living (IADL) and other factors in their use.

Method

Cross-sectional study in a non-institutionalized population older than 64 years old in a basic rural health area of Zaragoza. Dependent variables: use of different health and social services. Main independent variable: functional capacity for IADL according to the Lawton-Brody. Confounding variables: sociodemographic, physical exercise, comorbidity, self-perceived health, walking aids, social resources and economic resources (OARS-MAFQ). The relationship between the use of services and functional capacity for IADL was assessed using crude OR (ORC) and adjusted (adjusted OR) with CI95% by means of multivariate logistic regression models.

Results

The use of social and health services increased with age and worse functional capacity for IADL. The increased use of health services was related with bad stage of health, limited social and economic resources, physical inactivity and female. The increased use of home help services was related with limited social resources, low education level and male. Regular physical activity and using walking aids were associated with greater participation in recreational activities.

Conclusions

The probability of using social and health services increased in older people with impaired functional capacity for IADL. The specific use of them changed according to differences in health, demographic and contextual features.  相似文献   
736.

Background and Aims

The TERMINAL FLOWER 1 (TFL1) gene is pivotal in the control of inflorescence architecture in arabidopsis. Thus, tfl1 mutants flower early and have a very short inflorescence phase, while TFL1-overexpressing plants have extended vegetative and inflorescence phases, producing many coflorescences. TFL1 is expressed in the shoot meristems, never in the flowers. In the inflorescence apex, TFL1 keeps the floral genes LEAFY (LFY) and APETALA1 (AP1) restricted to the flower, while LFY and AP1 restrict TFL1 to the inflorescence meristem. In spite of the central role of TFL1 in inflorescence architecture, regulation of its expression is poorly understood. This study aims to expand the understanding of inflorescence development by identifying and studying novel TFL1 regulators.

Methods

Mutagenesis of an Arabidopsis thaliana line carrying a TFL1::GUS (β-glucuronidase) reporter construct was used to isolate a mutant with altered TFL1 expression. The mutated gene was identified by positional cloning. Expression of TFL1 and TFL1::GUS was analysed by real-time PCR and histochemical GUS detection. Double-mutant analysis was used to assess the contribution of TFL1 to the inflorescence mutant phenotype.

Key Results

A mutant with both an increased number of coflorescences and high and ectopic TFL1 expression was isolated. Cloning of the mutated gene showed that both phenotypes were caused by a mutation in the ARGONAUTE1 (AGO1) gene, which encodes a key component of the RNA silencing machinery. Analysis of another ago1 allele indicated that the proliferation of coflorescences and ectopic TFL1 expression phenotypes are not allele specific. The increased number of coflorescences is suppressed in ago1 tfl1 double mutants.

Conclusions

The results identify AGO1 as a repressor of TFL1 expression. Moreover, they reveal a novel role for AGO1 in inflorescence development, controlling the production of coflorescences. AGO1 seems to play this role through regulating TFL1 expression.  相似文献   
737.

Purpose

Vaspin (visceral-adipose-tissue-derived-serine-protease-inhibitor) is a recently identified adipokine with putative insulin-sensitizing properties. Plasma vaspin responses to surgery-induced weight loss are sparse and contradictory.

Design and Participants

We evaluated changes in vaspin levels and relationship to post-operative outcomes in men (n = 22) and women (n = 55) undergoing biliopancreatic-diversion/duodenal-switch bariatric surgery. Body composition and plasma parameters were measured at baseline, acutely (1 and 5 days) and medium-term (6 and 12 months) post-surgery.

Results

Fasting preoperative vaspin concentrations were comparable in men vs women. The distribution was biphasic (both men and women) with a nadir of 2.5 ng/ml. Subjects were divided into high (≥2.5 ng/mL, HI-group) and low (<2.5 ng/mL, LO-group) vaspin level. Both groups had comparable sex distribution, age and BMI, but the HI-vaspin group had lower insulin, HOMA, and triglyceride and higher HDL-cholesterol, acylation stimulating protein (ASP) and IL-6 levels (all p<0.05). Post-operatively, both groups decreased BMI comparably over 12 months; the HI-vaspin group maintained high vaspin levels, while the LO-vaspin group gradually increased their levels with weight loss over 12 months. The HI-vaspin group maintained a better glucose, insulin, HOMA, fructosamine, HDL-cholesterol, and triglyceride profile throughout. The HI-vaspin group also had higher gamma-glutamyltransferase and ASP profiles. Finally, baseline vaspin level inversely correlated significantly with baseline and 12-month insulin, HOMA, triglyceride and positively correlated with HDL and ASP. Twelve-month vaspin also correlated similarly, including an inverse correlation with BMI.

Conclusion

Globally, this study supports the concept of vaspin as a beneficial adipokine in obesity, which may potentially lead to possible therapeutic targets.  相似文献   
738.
Nicotine stimulation of α7 nicotinic acetylcholine receptor (α7 nAChR) powerfully inhibits pro-inflammatory cytokine production in lipopolysaccharide (LPS)-stimulated macrophages and in experimental models of endotoxemia. A signaling pathway downstream from the α7 nAChRs, which involves the collaboration of JAK2/STAT3 and NF-κB to interfere with signaling by Toll-like receptors (TLRs), has been implicated in this anti-inflammatory effect of nicotine. Here, we identifiy an alternative mechanism involving interleukin-1 receptor-associated kinase M (IRAK-M), a negative regulator of innate TLR-mediated immune responses. Our data show that nicotine up-regulates IRAK-M expression at the mRNA and protein level in human macrophages, and that this effect is secondary to α7 nAChR activation. By using selective inhibitors of different signaling molecules downstream from the receptor, we provide evidence that activation of STAT3, via either JAK2 and/or PI3K, through a single (JAK2/PI3K/STAT3) or two convergent cascades (JAK2/STAT3 and PI3K/STAT3), is necessary for nicotine-induced IRAK-M expression. Moreover, down-regulation of this expression by small interfering RNAs specific to the IRAK-M gene significantly reverses the anti-inflammatory effect of nicotine on LPS-induced TNF-α production. Interestingly, macrophages pre-exposed to nicotine exhibit higher IRAK-M levels and reduced TNF-α response to an additional LPS challenge, a behavior reminiscent of the ‘endotoxin tolerant’ phenotype identified in monocytes either pre-exposed to LPS or from immunocompromised septic patients. Since nicotine is a major component of tobacco smoke and increased IRAK-M expression has been considered one of the molecular determinants for the induction of the tolerant phenotype, our findings showing IRAK-M overexpression could partially explain the known influence of smoking on the onset and progression of inflammatory and infectious diseases.  相似文献   
739.
Mycetoma is a chronic granulomatous disease. It is classified into eumycetoma caused by fungi and actinomycetoma due to filamentous actinomycetes. Mycetoma can be found in geographic areas in close proximity to the Tropic of Cancer. Mexico is one of the countries in which this disease is highly endemic. In this retrospective study we report epidemiologic, clinical and microbiologic data of mycetoma observed in the General Hospital of Mexico in a 33 year-period (1980 to 2013). A total of 482 cases were included which were clinical and microbiology confirmed. Four hundred and forty four cases (92.11%) were actinomycetomas and 38 cases (7.88%) were eumycetomas. Most patients were agricultural workers; there was a male predominance with a sex ratio of 3∶1. The mean age was 34.5 years old (most ranged from 21 to 40 years). The main affected localization was lower and upper limbs (70.74% and 14.52% respectively). Most of the patients came from humid tropical areas (Morelos, Guerrero and Hidalgo were the regions commonly reported). The main clinical presentation was as tumor-like soft tissue swelling with draining sinuses (97.1%). Grains were observed in all the cases. The principal causative agents for actinomycetoma were: Nocardia brasiliensis (78.21%) and Actinomadura madurae (8.7%); meanwhile, for eumycetomas: Madurella mycetomatis and Scedosporium boydii (synonym: Pseudallescheria boydii) were identified. This is a single-center, with long-follow up, cross-sectional study that allows determining the prevalence and characteristics of mycetoma in different regions of Mexico.  相似文献   
740.

Background

Endocannabinoids and temperament traits have been linked to both physical activity and body mass index (BMI) however no study has explored how these factors interact in females. The aims of this cross-sectional study were to 1) examine differences among distinct BMI groups on daytime physical activity and time spent in moderate-vigorous physical activity (MVPA), temperament traits and plasma endocannabinoid concentrations; and 2) explore the association and interaction between MVPA, temperament, endocannabinoids and BMI.

Methods

Physical activity was measured with the wrist-worn accelerometer Actiwatch AW7, in a sample of 189 female participants (43 morbid obese, 30 obese, and 116 healthy-weight controls). The Temperament and Character Inventory-Revised questionnaire was used to assess personality traits. BMI was calculated by bioelectrical impedance analysis via the TANITA digital scale. Blood analyses were conducted to measure levels of endocannabinoids and endocannabinoid-related compounds. Path-analysis was performed to examine the association between predictive variables and MVPA.

Results

Obese groups showed lower MVPA and dysfunctional temperament traits compared to healthy-weight controls. Plasma concentrations of 2-arachidonoylglyceryl (2-AG) were greater in obese groups. Path-analysis identified a direct effect between greater MVPA and low BMI (b = −0.13, p = .039) and high MVPA levels were associated with elevated anandamide (AEA) levels (b = 0.16, p = .049) and N-oleylethanolamide (OEA) levels (b = 0.22, p = .004), as well as high Novelty seeking (b = 0.18, p<.001) and low Harm avoidance (b = −0.16, p<.001).

Conclusions

Obese individuals showed a distinct temperament profile and circulating endocannabinoids compared to controls. Temperament and endocannabinoids may act as moderators of the low MVPA in obesity.  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