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   1263篇
  免费   61篇
  1324篇
  2023年   8篇
  2022年   11篇
  2021年   29篇
  2020年   15篇
  2019年   20篇
  2018年   40篇
  2017年   18篇
  2016年   39篇
  2015年   46篇
  2014年   55篇
  2013年   79篇
  2012年   92篇
  2011年   95篇
  2010年   58篇
  2009年   46篇
  2008年   65篇
  2007年   65篇
  2006年   56篇
  2005年   47篇
  2004年   48篇
  2003年   48篇
  2002年   43篇
  2001年   38篇
  2000年   21篇
  1999年   22篇
  1998年   10篇
  1997年   5篇
  1996年   9篇
  1995年   6篇
  1994年   7篇
  1993年   13篇
  1992年   14篇
  1991年   7篇
  1990年   8篇
  1989年   7篇
  1988年   15篇
  1987年   10篇
  1986年   9篇
  1985年   15篇
  1984年   7篇
  1982年   8篇
  1981年   6篇
  1980年   9篇
  1979年   10篇
  1978年   4篇
  1976年   5篇
  1973年   4篇
  1972年   7篇
  1970年   6篇
  1969年   6篇
排序方式: 共有1324条查询结果,搜索用时 0 毫秒
71.
BackgroundHeart failure (HF) with preserved ejection fraction (HFpEF) is increasingly recognized as an important clinical entity. Preclinical studies have shown differences in the pathophysiology between HFpEF and HF with reduced ejection fraction (HFrEF). Therefore, we hypothesized that a systematic metabolomic analysis would reveal a novel metabolomic fingerprint of HFpEF that will help understand its pathophysiology and assist in establishing new biomarkers for its diagnosis.ConclusionsThe metabolomics approach employed in this study identified a unique metabolomic fingerprint of HFpEF that is distinct from that of HFrEF. This metabolomic fingerprint has been utilized to identify two novel panels of metabolites that can separate HFpEF patients from both non-HF controls and HFrEF patients.

Clinical Trial Registration

ClinicalTrials.gov NCT02052804  相似文献   
72.
Many diseases cause significant changes to the concentrations of small molecules (a.k.a. metabolites) that appear in a person’s biofluids, which means such diseases can often be readily detected from a person’s “metabolic profile"—i.e., the list of concentrations of those metabolites. This information can be extracted from a biofluids Nuclear Magnetic Resonance (NMR) spectrum. However, due to its complexity, NMR spectral profiling has remained manual, resulting in slow, expensive and error-prone procedures that have hindered clinical and industrial adoption of metabolomics via NMR. This paper presents a system, BAYESIL, which can quickly, accurately, and autonomously produce a person’s metabolic profile. Given a 1D 1H NMR spectrum of a complex biofluid (specifically serum or cerebrospinal fluid), BAYESIL can automatically determine the metabolic profile. This requires first performing several spectral processing steps, then matching the resulting spectrum against a reference compound library, which contains the “signatures” of each relevant metabolite. BAYESIL views spectral matching as an inference problem within a probabilistic graphical model that rapidly approximates the most probable metabolic profile. Our extensive studies on a diverse set of complex mixtures including real biological samples (serum and CSF), defined mixtures and realistic computer generated spectra; involving > 50 compounds, show that BAYESIL can autonomously find the concentration of NMR-detectable metabolites accurately (~ 90% correct identification and ~ 10% quantification error), in less than 5 minutes on a single CPU. These results demonstrate that BAYESIL is the first fully-automatic publicly-accessible system that provides quantitative NMR spectral profiling effectively—with an accuracy on these biofluids that meets or exceeds the performance of trained experts. We anticipate this tool will usher in high-throughput metabolomics and enable a wealth of new applications of NMR in clinical settings. BAYESIL is accessible at http://www.bayesil.ca.  相似文献   
73.
PurposeTo compare the rate of mean deviation (MD) change on 24-2 versus 10-2 VFs in treated glaucomatous eyes with 5 or more examinations.MethodsIn a retrospective study, 24-2 and 10-2 VFs of 131 glaucoma patients (167 eyes) who had undergone at least 5 VFs examinations during their follow-up were analyzed. All these patients had VF defects both on 24-2 and 10-2 VFs. Rates of MD change were calculated using best linear unbiased predictions (BLUP).ResultsMedian age, MD on 24-2 VF at baseline, number of VFs performed during follow-up and follow-up duration were 55 years, -16.9 dB, 9 and 9 years respectively. Median rate of MD change was significantly greater (p<0.001) on 10-2 VF (-0.26 dB/year; interquartile range [IQR]: -0.47, -0.11) compared to 24-2 VFs (-0.19 dB/year; IQR: -0.41, -0.03). Comparing the rates of MD change in eyes with different severities of VF loss (early [MD better than -6 dB], moderate [-6 dB to -12 dB], advanced [-12 to -20 dB] and severe [MD worse than -20 dB]) at baseline (based on the MD on 24-2 VF), median rate of MD change was comparable between 10-2 and 24-2 VFs in mild (-0.45 dB/year vs. -0.40 dB/year, P = 0.42) and moderate (-0.32 dB/year vs. -0.40 dB/year, P = 0.26) VF loss categories, while the same were significantly greater on 10-2 VFs in advanced (-0.28 dB/year vs. -0.21 dB/year, P = 0.04) and severe (-0.18 dB/year vs. -0.06 dB/year, P<0.001) VF loss categories.ConclusionsIn patients with VF defects both on 24-2 and 10-2 VFs, evaluating the rate of MD change on 10-2 VFs may help in better estimation of glaucoma progression, especially so in eyes with advanced glaucoma at baseline.  相似文献   
74.
Visceral leishmaniasis is a vector-borne disease caused by an obligate intracellular protozoan parasite Leishmania donovani. The molecular mechanism involved in internalization of Leishmania is poorly understood. The entry of Leishmania involves interaction with the plasma membrane of host cells. We have previously demonstrated the requirement of host membrane cholesterol in the binding and internalization of L. donovani into macrophages. In the present work, we explored the role of the host actin cytoskeleton in leishmanial infection. We observed a dose-dependent reduction in the attachment of Leishmania promastigotes to host macrophages upon destabilization of the actin cytoskeleton by cytochalasin D. This is accompanied by a concomitant reduction in the intracellular amastigote load. We utilized a recently developed high resolution microscopy-based method to quantitate cellular F-actin content upon treatment with cytochalasin D. A striking feature of our results is that binding of Leishmania promastigotes and intracellular amastigote load show close correlation with cellular F-actin level. Importantly, the binding of Escherichia coli remained invariant upon actin destabilization of host cells, thereby implying specific involvement of the actin cytoskeleton in Leishmania infection. To the best of our knowledge, these novel results constitute the first comprehensive demonstration on the specific role of the host actin cytoskeleton in Leishmania infection. Our results could be significant in developing future therapeutic strategies to tackle leishmaniasis.  相似文献   
75.
76.
77.
Inocula were collected from four different sources such as Jajmau tannery waste treatment plant (ITW), Jajmau municipal waste treatment (IMW), Unnao distillery (IDW) and a batch reactor, in which the sludge of a field scale biogas reactor was added to cow dung slurry to develop inoculum (IBS). A combination of these mixed inocula were used for biogas production at 35°C in laboratory scale reactor (10 L capacity) and the average yield of biogas (0.547 Lg?1 volatile solid (VS)) and methane (0.323 Lg?1VS) in 41 d was higher in case of mixed inoculum IMW 1 (IMW+IBS), with maximum methane content in biogas (68% during 27–30 d), as compared to other mixed inocula as well as control i.e. ITW 1 (ITW+IBS), IDW1 (IDW+IBS) and IBS. The corresponding yields of gas were biogas (0.505, 0.536 and 0.456 Lg?1VS), methane (0.288, 0.305, and 0.245 Lg?1VS) where as, the corresponding maximum methane content in biogas was 62% during 29–33d, 64% during 29–33 d and 62% during 27–29 d in ITW1, IDW1 and IBS.  相似文献   
78.
Downy mildew (Peronospora plantaginis) caused two different types of infection in the floral parts of isabgol (Plantago ovata). Systemic infection resulted in long spikes bearing weak and sterile florets, which later turned black due to saprophytic growth. Localised infection produced various symptoms ranging between normal flower opening and failure to bloom. Different parts of infected flowers such as sepal, petal, filament and anther were reduced in size compared to healthy flowers. However, gynoecium was elongated in localised infection. P. plantaginis induced gradual sterility of isabgol flowers. Androecium was affected more than the gynoecium was. Pollen number, pollen viability and germination reduced drastically due to localised infection. On the contrary, there were no significant differences between healthy and locally infected flowers in terms of stigma receptivity. In systemically infected spikes, bud development was arrested leading to sterility. When localised disease severity was high, secondary systemic infection caused similar symptoms. Microscopic observations showed presence of the pathogen in different parts of the flowers. Downy mildew adversely affected seed yield and quality; producing seeds, which were smaller and lighter than the healthy ones and later, became black. Seed yield was reduced by as much as 73.45 percent. Husk content per unit seed mass increased relatively as the total surface area of infected seeds increased.  相似文献   
79.

Background  

CABYR is a polymorphic calcium-binding protein of the sperm fibrous sheath (FS) which gene contains two coding regions (CR-A and CR-B) and is tyrosine as well as serine/threonine phosphorylated during in vitro sperm capacitation. Thus far, the detailed information on CABYR protein expression in mouse spermatogenesis is lacking. Moreover, because of the complexity of this polymorphic protein, there are no data on how CABYR isoforms associate and assemble into the FS.  相似文献   
80.

Background

Impact assessment (IA) of all major European Union (EU) policies is now mandatory. The form of IA used has been criticised for favouring corporate interests by overemphasising economic impacts and failing to adequately assess health impacts. Our study sought to assess how, why, and in what ways corporations, and particularly the tobacco industry, influenced the EU''s approach to IA.

Methods and Findings

In order to identify whether industry played a role in promoting this system of IA within the EU, we analysed internal documents from British American Tobacco (BAT) that were disclosed following a series of litigation cases in the United States. We combined this analysis with one of related literature and interviews with key informants. Our analysis demonstrates that from 1995 onwards BAT actively worked with other corporate actors to successfully promote a business-oriented form of IA that favoured large corporations. It appears that BAT favoured this form of IA because it could advance the company''s European interests by establishing ground rules for policymaking that would: (i) provide an economic framework for evaluating all policy decisions, implicitly prioritising costs to businesses; (ii) secure early corporate involvement in policy discussions; (iii) bestow the corporate sector with a long-term advantage over other actors by increasing policymakers'' dependence on information they supplied; and (iv) provide businesses with a persuasive means of challenging potential and existing legislation. The data reveal that an ensuing lobbying campaign, largely driven by BAT, helped secure binding changes to the EU Treaty via the Treaty of Amsterdam that required EU policymakers to minimise legislative burdens on businesses. Efforts subsequently focused on ensuring that these Treaty changes were translated into the application of a business orientated form of IA (cost–benefit analysis [CBA]) within EU policymaking procedures. Both the tobacco and chemical industries have since employed IA in apparent attempts to undermine key aspects of European policies designed to protect public health.

Conclusions

Our findings suggest that BAT and its corporate allies have fundamentally altered the way in which all EU policy is made by making a business-oriented form of IA mandatory. This increases the likelihood that the EU will produce policies that advance the interests of major corporations, including those that produce products damaging to health, rather than in the interests of its citizens. Given that the public health community, focusing on health IA, has largely welcomed the increasing policy interest in IA, this suggests that urgent consideration is required of the ways in which IA can be employed to undermine, as well as support, effective public health policies. Please see later in the article for the Editors'' Summary  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