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   3203篇
  免费   207篇
  3410篇
  2023年   14篇
  2022年   30篇
  2021年   51篇
  2020年   39篇
  2019年   59篇
  2018年   79篇
  2017年   55篇
  2016年   83篇
  2015年   131篇
  2014年   142篇
  2013年   227篇
  2012年   242篇
  2011年   251篇
  2010年   153篇
  2009年   122篇
  2008年   217篇
  2007年   218篇
  2006年   179篇
  2005年   150篇
  2004年   150篇
  2003年   159篇
  2002年   158篇
  2001年   27篇
  2000年   16篇
  1999年   25篇
  1998年   26篇
  1997年   32篇
  1996年   20篇
  1995年   29篇
  1994年   22篇
  1993年   22篇
  1992年   25篇
  1991年   24篇
  1990年   28篇
  1989年   12篇
  1988年   11篇
  1987年   13篇
  1986年   10篇
  1985年   13篇
  1984年   15篇
  1983年   8篇
  1982年   11篇
  1981年   18篇
  1980年   12篇
  1979年   8篇
  1978年   8篇
  1977年   8篇
  1976年   10篇
  1975年   7篇
  1971年   4篇
排序方式: 共有3410条查询结果,搜索用时 10 毫秒
301.

Background

Inflammatory bowel disease is a group of pathologies characterised by chronic inflammation of the intestine and an unclear aetiology. Its main manifestations are Crohn’s disease and ulcerative colitis. Currently, biopsies are the most used diagnostic tests for these diseases and metabolomics could represent a less invasive approach to identify biomarkers of disease presence and progression.

Objectives

The lipid and the polar metabolite profile of plasma samples of patients affected by inflammatory bowel disease have been compared with healthy individuals with the aim to find their metabolomic differences. Also, a selected sub-set of samples was analysed following solid phase extraction to further characterise differences between pathological samples.

Methods

A total of 200 plasma samples were analysed using drift tube ion mobility coupled with time of flight mass spectrometry and liquid chromatography for the lipid metabolite profile analysis, while liquid chromatography coupled with triple quadrupole mass spectrometry was used for the polar metabolite profile analysis.

Results

Variations in the lipid profile between inflammatory bowel disease and healthy individuals were highlighted. Phosphatidylcholines, lyso-phosphatidylcholines and fatty acids were significantly changed among pathological samples suggesting changes in phospholipase A2 and arachidonic acid metabolic pathways. Variations in the levels of cholesteryl esters and glycerophospholipids were also found. Furthermore, a decrease in amino acids levels suggests mucosal damage in inflammatory bowel disease.

Conclusions

Given good statistical results and predictive power of the model produced in our study, metabolomics can be considered as a valid tool to investigate inflammatory bowel disease.
  相似文献   
302.
303.
Several microRNAs (miRNAs) that are either specifically enriched or highly expressed in neurons and glia have been described, but the identification of miRNAs modulating neural stem cell (NSC) biology remains elusive. In this study, we exploited high throughput miRNA expression profiling to identify candidate miRNAs enriched in NSC/early progenitors derived from the murine subventricular zone (SVZ). Then, we used lentiviral miRNA sensor vectors (LV.miRT) to monitor the activity of shortlisted miRNAs with cellular and temporal resolution during NSC differentiation, taking advantage of in vitro and in vivo models that recapitulate physiological neurogenesis and gliogenesis and using known neuronal- and glial-specific miRNAs as reference. The LV.miRT platform allowed us monitoring endogenous miRNA activity in low represented cell populations within a bulk culture or within the complexity of CNS tissue, with high sensitivity and specificity. In this way we validated and extended previous results on the neuronal-specific miR-124 and the astroglial-specific miR-23a. Importantly, we describe for the first time a cell type- and differentiation stage-specific modulation of miR-93 and miR-125b in SVZ-derived NSC cultures and in the SVZ neurogenic niche in vivo, suggesting key roles of these miRNAs in regulating NSC function.  相似文献   
304.
Thalli of epiphytic lichen Hypogymnia physodes (L.) Nyl. and terricolous Cladonia furcata (Huds.) Schrad., collected from an area with background arsenic concentrations, were exposed to 0, 0.1, 1 and 10 μg mL−1 arsenate (As(V)) solutions for 24 h. After exposure they were kept in the metabolically active state for 0, 24 and 48 h in a growth chamber. In the freeze dried samples glutathione (GSH), glutathione disulphide (GSSG), cysteine (Cys) and cystine were analysed and induction of phytochelatin (PC) synthesis measured by reversed-phase high-performance liquid chromatography in combination with fluorescence detection or UV spectrometry. Total arsenic content in thalli was measured by instrumental neutron activation analysis (INAA). In H. physodes, which contained higher amounts of arsenic compared to C. furcata, total glutathione content significantly decreased in samples exposed to 10 μg mL−1 As(V), whereas in C. furcata a significant increase was observed. In both species PC synthesis was induced in thalli exposed to 10 μg mL−1.  相似文献   
305.
306.
Summary Fifty workers from two grain elevator terminals were examined to evaluate the prevalence of respiratory symptoms and their relationship with grain dust exposure.Fifty per cent of subjects complained of respiratory symptoms (rhinitis, asthma, chronic cough and dyspnea on exertion). In 34% of the workers the ventilatory function revealed some abnormalities (slight or moderate obstruction).Twenty-two (44%) showed a positive cutaneous reaction to one or more of the allergens tested, mostly towardsDermatophagoides and storage mites. The self-measurement of PEF over 14 days in 27 workers, showed significant differences between symptomatic and asymptomatic subjects. In particular, the results obtained from the cutaneous reactions could suggest a bronchial hypereactivity, worsened by the working exposure to dusts. The monitoring of PEF appears to be a simple and useful method for investigating the relationship between respiratory symptoms and the working environment.  相似文献   
307.
Human adipose tissue is partitioned into two large depots (subcutaneous and visceral), and many small depots associated with internal organs, e.g. heart, blood vessels, major lymph nodes, pancreas, prostate gland and ovaries. Since the adipose 'Big Bang' led to the discovery of leptin (Zhang, Proenca, Maffei, Barone, Leopold and Friedman, Nature 1994;372:425-32), adipose tissue has been seen not merely as a lipid store, but as a secretory - endocrine and paracrine - organ, particularly in the pathogenesis of a number of diseases. Accordingly, two major sub-fields of adipobiology have emerged, viz. adipoendocrinology and adipoparacrinology, the latter herein being illustrated by PAAT (periadventitial adipose tissue) in vascular walls. A long-standing paradigm holds that the vascular wall consists of three coats, tunica intima, tunica media and tunica adventitia. It is now imperative that 'to further elucidate vascular function, we should no longer, as hitherto, separate adventitia and PAAT from the vascular wall, but keep them attached and in place, and subject to thorough examination' (Chaldakov, Fiore, Ghenev, Stankulov and Aloe, Int Med J 2000;7:43-9; Chaldakov, Stankulov and Aloe, Atherosclerosis 2001;154:237-8; Chaldakov GN, Stankulov IS, Fiore M, Ghenev PI and Aloe L, Atherosclerosis 2001;159:57-66). From the available data, we propose that it is time to rethink about vascular wall composition, and suggest that the PAAT may be considered the fourth and outermost vascular coat, hence, tunica adiposa (regarding the proximal segment of coronary artery, it is the innermost part of the EAT (epicardial adipose tissue) situated around the coronary adventitia). Its significance in the pathogenesis and therapy of CMDs (cardiometabolic diseases), particularly atherosclerosis and hypertension, requires further basic, translational and clinical studies.  相似文献   
308.
Leucine-rich repeat kinase 2 (LRRK2) has been suggested as a potential therapeutic target for Parkinson’s disease. Herein we report the discovery of 5-substituent-N-arylbenzamide derivatives as novel LRRK2 inhibitors. Extensive SAR study led to the discovery of compounds 8e, which demonstrated potent LRRK2 inhibition activity, high selectivity across the kinome, good brain exposure, and high oral bioavailability.  相似文献   
309.
The aim in this study was to compare two estrus synchronization protocols in buffaloes. Animals were divided into two groups: Group A (n=111) received 100 microg GnRH on Day 0, 375 microg PGF(2alpha) on Day 7 and 100 microg GnRH on Day 9 (Ovsynch); Group B (n=117) received an intravaginal drug release device (PRID) containing 1.55 g progesterone and a capsule with 10mg estradiol benzoate for 10 days and were treated with a luteolytic dose of PGF(2alpha) and 1000 IU PMSG at the time of PRID withdrawal. Animals were inseminated twice 18 and 42 h after the second injection of GnRH (Group A) and 60 and 84 h after PGF(2alpha) and PMSG injections (Group B). Progesterone (P(4)) concentrations in milk samples collected 12 and 2 days before treatments were used to determine cyclic and non-cyclic buffaloes, and milk P(4) concentrations 10 days after Artificial insemination (AI) were used as an index of a functional corpus luteum. Cows were palpated per rectum at 40 and 90 days after AI to determine pregnancies. All previously non-cyclic animals in Group B had elevated P(4) (>120 pg/ml milk whey) on Day 10 after AI. Accordingly, a greater (P<0.01) relative percentage of animals with elevated P(4) 10 days after AI were observed in Group B (93.2%) than in Group A (81.1%). However, there was no difference in overall pregnancy rates between the two estrus synchronization protocols (Group A, 36.0%; Group B 28.2%). When only animals with elevated P(4) on Day 10 after AI were considered, pregnancy rate was higher (P<0.05) for animals in Group A (44.4%) than Group B (30.3%). The findings indicated that treatment with PRID can induce ovulation in non-cyclic buffalo cows. However, synchronization of estrus with Ovsynch resulted in a higher pregnancy rate compared with synchronization with PRID, particularly in cyclic buffalo.  相似文献   
310.
Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a natural phytoalexin found in grapes and wine. It has antioxidant and antiproliferative activities, and has been shown to induce NAD(P)H:quinone oxidoreductase, also known as DT-diaphorase, in cultured mouse hepatoma cells. DT-diaphorase is a detoxifying enzyme for quinone-containing substances, due to its ability to prevent their one-electron reduction and the consequent generation of reactive oxygen species (ROS). The aim of the present study was to investigate whether oral administration of trans-resveratrol to guinea pigs (60 mg/l in tap water for 16 days, ad libitum) increases cardiac DT-diaphorase and, consequently, reduces the response of isolated atria to 2-methyl-1,4-naphthoquinone (menadione), the positive inotropic effect of which is related to the amount of ROS generated by its cardiac metabolism. In the cardiac tissue of resveratrol-treated animals, DT-diaphorase activity was significantly higher than that measured in control animals, the V(max) of the enzyme reaction being 75.47 +/- 3.87 and 50.73 +/- 0.63 nmoles/mg protein/min, respectively (p < 0.05). Resveratrol administration also significantly increased the activity of cardiac catalase (32.20 +/- 2.39 vs. 25.14 +/- 3.85 units/mg protein in treated and control animals, respectively; p < 0.001). As a consequence, menadione metabolism by the cardiac homogenate obtained from resveratrol-treated animals generated a smaller amount of ROS and, in electrically driven left atria, menadione produced a significantly lower increase in the force of contraction than in atria isolated from control animals. These results indicate that oral administration of resveratrol exerts cardioprotection against ROS-mediated menadione toxicity.  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