首页 | 官方网站   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   1338篇
  免费   104篇
  国内免费   8篇
工业技术   1450篇
  2024年   2篇
  2023年   17篇
  2022年   11篇
  2021年   87篇
  2020年   54篇
  2019年   38篇
  2018年   40篇
  2017年   49篇
  2016年   55篇
  2015年   38篇
  2014年   53篇
  2013年   83篇
  2012年   78篇
  2011年   97篇
  2010年   64篇
  2009年   70篇
  2008年   68篇
  2007年   38篇
  2006年   58篇
  2005年   37篇
  2004年   24篇
  2003年   33篇
  2002年   33篇
  2001年   20篇
  2000年   12篇
  1999年   27篇
  1998年   45篇
  1997年   29篇
  1996年   28篇
  1995年   27篇
  1994年   16篇
  1993年   12篇
  1992年   9篇
  1991年   6篇
  1990年   6篇
  1989年   8篇
  1988年   8篇
  1987年   10篇
  1986年   16篇
  1985年   4篇
  1984年   5篇
  1983年   3篇
  1981年   4篇
  1980年   3篇
  1979年   3篇
  1978年   5篇
  1977年   6篇
  1976年   3篇
  1975年   2篇
  1972年   2篇
排序方式: 共有1450条查询结果,搜索用时 335 毫秒
1.
The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies.  相似文献   
2.
DNA methylation is one of the most studied epigenetic mechanisms that play a pivotal role in regulating gene expression. The epigenetic component is strongly involved in aging-bone diseases, such as osteoporosis and osteoarthritis. Both are complex multi-factorial late-onset disorders that represent a globally widespread health problem, highlighting a crucial point of investigations in many scientific studies. In recent years, new findings on the role of DNA methylation in the pathogenesis of aging-bone diseases have emerged. The aim of this systematic review is to update knowledge in the field of DNA methylation associated with osteoporosis and osteoarthritis, focusing on the specific tissues involved in both pathological conditions.  相似文献   
3.
Polyamines are ubiquitous, low-molecular-weight aliphatic compounds, present in living organisms and essential for cell growth and differentiation. Copper amine oxidases (CuAOs) oxidize polyamines to aminoaldehydes releasing ammonium and hydrogen peroxide, which participates in the complex network of reactive oxygen species acting as signaling molecules involved in responses to biotic and abiotic stresses. CuAOs have been identified and characterized in different plant species, but the most extensive study on a CuAO gene family has been carried out in Arabidopsis thaliana. Growing attention has been devoted in the last years to the investigation of the CuAO expression pattern during development and in response to an array of stress and stress-related hormones, events in which recent studies have highlighted CuAOs to play a key role by modulation of a multilevel phenotypic plasticity expression. In this review, the attention will be focused on the involvement of different AtCuAOs in the IAA/JA/ABA signal transduction pathways which mediate stress-induced phenotypic plasticity events.  相似文献   
4.
Inherited cardiomyopathies are frequent causes of sudden cardiac death (SCD), especially in young patients. Despite at the autopsy they usually have distinctive microscopic and/or macroscopic diagnostic features, their phenotypes may be mild or ambiguous, possibly leading to misdiagnoses or missed diagnoses. In this review, the main differential diagnoses of hypertrophic cardiomyopathy (e.g., athlete’s heart, idiopathic left ventricular hypertrophy), arrhythmogenic cardiomyopathy (e.g., adipositas cordis, myocarditis) and dilated cardiomyopathy (e.g., acquired forms of dilated cardiomyopathy, left ventricular noncompaction) are discussed. Moreover, the diagnostic issues in SCD victims affected by phenotype-negative hypertrophic cardiomyopathy and the relationship between myocardial bridging and hypertrophic cardiomyopathy are analyzed. Finally, the applications/limits of virtopsy and post-mortem genetic testing in this field are discussed, with particular attention to the issues related to the assessment of the significance of the genetic variants.  相似文献   
5.
6.
To date, the only effective means to respond to the spreading of the COVID-19 pandemic are non-pharmaceutical interventions (NPIs), which entail policies to reduce social activity and mobility restrictions. Quantifying their effect is difficult, but it is key to reducing their social and economic consequences. Here, we introduce a meta-population model based on temporal networks, calibrated on the COVID-19 outbreak data in Italy and applied to evaluate the outcomes of these two types of NPIs. Our approach combines the advantages of granular spatial modelling of meta-population models with the ability to realistically describe social contacts via activity-driven networks. We focus on disentangling the impact of these two different types of NPIs: those aiming at reducing individuals’ social activity, for instance through lockdowns, and those that enforce mobility restrictions. We provide a valuable framework to assess the effectiveness of different NPIs, varying with respect to their timing and severity. Results suggest that the effects of mobility restrictions largely depend on the possibility of implementing timely NPIs in the early phases of the outbreak, whereas activity reduction policies should be prioritized afterwards.  相似文献   
7.
OBJECTIVE: The reflex response to orotracheal intubation provokes an increase of arterial pressure accompanied by an increase of chorioides volume and a consequent ocular hypertone. There are several methods to reduce the reflex response due to intubation. One of the most effective is topical anaesthesia of larynx and trachea. Experiments were directed to evaluate the efficacy of topical anaesthesia to reduce the intraocular hypertone due to orotracheal intubation. DESIGN: A prospective randomized mask study was conduct on patients undergoing ophthalmologic (anterior segment) surgery at the Eye Clinic of Florence University. METHODS: Intraocular pressure was measured by a Goldman tonometer at four times: T0 = basal, T1 = 2' minutes after induction of general anaesthesia, T2 = 2' minutes after laryngoscopy, T3 = 2' minutes after orotracheal intubation. At the same moments, systolic blood pressure, heart rate, rate pressure pro duct were measured. Patients were randomly divided in two groups: Group L (n = 10) in which was evaluated the efficacy of laryngotracheal topical spray of lidocaine 4% (2 ml) and Group F (n = 10) in which saline was used instead of anesthetic. The filling of the LTA kit (Abbott) was made by a person not involved in the experiments. DATA ANALYSIS: Student's t test for unpaired data. RESULTS: Topical anaesthesia reduces the increase of intraocular pressure, hypertension and rate pressure product due to intubation. The intraocular pressure reduces to 13% less than basal value in Group L and increase to 50% more than basal value in Group F. CONCLUSION: The topical anaesthesia of larynx and trachea is effective to reduce the intraocular hypertension due to the reflex response evoked by orotracheal intubation.  相似文献   
8.
The participation of sarcoplasmic reticulum Ca2+ release channels in the activation of Ca(2+)-sensitive K+ currents (IK(Ca)) by cyclic dibutyryl GMP was investigated in smooth muscle cells from the circular layer of guinea-pig gastric fundus. All experiments were performed in the presence of 3 microM nicardipine into the bath and low Ca2+ buffering capacity of the pipette-filling solution (pCa 7.4). Ruthenium red (10 microM) as well as its combination with 10 microM heparin abolished the cyclic GMP-induced activation of IK(Ca), while 10 microM heparin remained ineffective. Ryanodine (10 microM) and the subsequently added 1 microM thapsigargin induced a relatively small increase in IK(Ca) amplitudes. The addition of 10 microM ryanodine to 1 microM thapsigargin-containing bath solution caused a vast increase in IK(Ca). It is hypothesyzed that protein kinase G-induced vectorial Ca2+ flux from the cell bulk and sarcoplasmic reticulum Ca2+ stores toward the plasma membrane is realized by a spontaneous Ca(2+)-induced Ca2+ release from a superficially situated Ca2+ store.  相似文献   
9.
In this work, a possible way for partial CO2 emissions reduction from gas turbine exhausts by co-firing with biomass is investigated. The basic principle is the recirculation of a fraction of the exhausts (still rich in oxygen) to a gasifier, in order to produce syngas to mix with natural gas fuel. As biomass is a CO2 neutral fuel, the fraction of replaced natural gas is a measure of CO2 removal potential of the powerplant.  相似文献   
10.
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-23

京公网安备 11010802026262号