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   73588篇
  免费   4724篇
  国内免费   44篇
  78356篇
  2023年   268篇
  2022年   790篇
  2021年   1265篇
  2020年   819篇
  2019年   983篇
  2018年   1330篇
  2017年   1194篇
  2016年   1925篇
  2015年   3015篇
  2014年   3418篇
  2013年   4032篇
  2012年   5117篇
  2011年   4967篇
  2010年   3295篇
  2009年   2917篇
  2008年   3938篇
  2007年   3854篇
  2006年   3432篇
  2005年   3233篇
  2004年   3130篇
  2003年   2777篇
  2002年   2471篇
  2001年   2009篇
  2000年   1933篇
  1999年   1661篇
  1998年   737篇
  1997年   695篇
  1996年   595篇
  1995年   527篇
  1994年   466篇
  1993年   455篇
  1992年   925篇
  1991年   791篇
  1990年   799篇
  1989年   754篇
  1988年   607篇
  1987年   599篇
  1986年   513篇
  1985年   490篇
  1984年   489篇
  1983年   402篇
  1982年   351篇
  1981年   329篇
  1980年   300篇
  1979年   400篇
  1978年   319篇
  1977年   333篇
  1976年   259篇
  1975年   279篇
  1974年   304篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
ABSTRACT

Background: The disruption of circadian rhythm has been found to associate with obesity in vivo and in vitro. Sleep duration, eating habits, total feeding time, and nightshift work can also affect circadian rhythms. This study investigated the association between misalignment of circadian rhythm and obesity in Korean men, using a cross-sectional database.

Methods: This study used data from the Korean National Health and Nutrition Examination Survey (KNHANES), whose study population was 3,658 men aged 18 to 60 years. General and abdominal obesity was defined as a body mass index (BMI) ≥ 25 kg/m2 and waist circumference ≥ 90 cm, respectively. Circadian rhythm factors were determined with a self-report questionnaire and included breakfast frequency, sleep duration, and work time. Frequency of breakfast was divided into regular breakfast (five to seven times a week) and irregular breakfast (less than five times a week). Sleep duration was divided into less than 7 hours, 7–9 hours, and over 9 hours. Working time was defined as day/evening, night shift, and other type. The adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for general and abdominal obesity were calculated using multivariable logistic regression according to the number of factors that disturb the circadian rhythm.

Results: Participants with 1 (aOR 1.34, 95% Cl 1.10–1.61) and ≥2 (aOR 1.62, 95% Cl 1.29–2.05) factors disturbing circadian rhythms were associated with elevated risk for general obesity. Similarly, those with 1 (aOR 1.33, 95% Cl 1.09–1.63) and ≥2 (aOR 1.70, 95% Cl 1.32–2.20) factors had elevated risk for abdominal obesity.

Conclusions: Factors disturbing the circadian rhythm were associated with general and abdominal obesity. Additional studies are needed, and associations with metabolic diseases should be investigated.  相似文献   
3.
4.
5.
6.
Efficacy and safety of insulin glulisine in patients with type 1 diabetes.   总被引:4,自引:0,他引:4  
Insulin glulisine (glulisine), a human insulin analogue with a rapid-acting time-action profile, has been developed to fulfil the mealtime (bolus) insulin requirement in patients with diabetes. The aim of this multinational, multi-centre, controlled, open-label, randomized, parallel-group study was to compare the efficacy and safety of insulin glulisine (glulisine) to that of insulin lispro (lispro) in adults diagnosed with Type 1 diabetes. Of the 683 patients randomized, 672 received treatment (339 patients received glulisine, 333 patients received lispro). Over the 26-week study, a similar reduction in mean HbA1c occurred in both groups (adjusted mean change from baseline -0.14% in both groups). The basal insulin dose was relatively unchanged from baseline in the glulisine group but increased in the lispro group (glulisine: 0.12 IU vs. lispro: 1.82 IU; p = 0.0001). As a consequence, total daily insulin dose decreased in the glulisine group but increased in the lispro group (glulisine: -0.86 IU vs. lispro: 1.01 IU; p = 0.0123). There was no relevant difference between the two groups in the reporting of symptomatic hypoglycaemia (overall, nocturnal and severe). This study demonstrates that glulisine provides equivalent glycaemic control to lispro. The clinical relevance of any difference in total daily insulin dose remains to be established.  相似文献   
7.
Aralia elata is an edible mountain vegetable. Angiogenesis, the formation of new blood vessels, is a process involving migration, proliferation and cell differentiation, as well as the formation of new capillary structures. Matrix metalloproteinases (MMPs) plays an important role in angiogenesis. The development of a functional vascular system requires a variety of growth factors, their receptors, and intracellular signals. This study examines the effects of water extracts from: (i)A. elata root bark (Aralia extracts); (ii) a combination of Aralia extracts and fibroblast growth factors (FGF-2) on cultured porcine coronary artery endothelial cells (PCAECs). Aralia extracts induced the migration of PCAECs, which was inhibited by MMPs inhibitors. Combining Aralia extracts and FGF-2 enhanced the migration and the secretion of MMP-2 and MMP-9 from PCAECs. We postulated that the Aralia extracts, which induced migrating activity in PCAECs, may be accomplished by increased secretion levels of MMP-2 and MMP-9.  相似文献   
8.
The bioelectrochemical reduction of nitrate in the presence of various mediators including methyl viologen and azure A was studied using a 3-electrode voltammetric system. The catalytic potential for the reduction of the mediators was observed in the reactor, which for methyl viologen and azure A were −0.74 V and −0.32 V, respectively, with respect to the potential of Ag/AgCl reference electrode. This potential was then applied to a working electrode to reduce each mediator for enzymatic nitrate reduction. Nitrite, the product of the reaction, was measured to observe the enzymatic nitrate reduction in the reaction media. Methyl viologen was observed as the most efficient mediator among those tested, while azure A showed the highest electron efficiency at the intrinsic reduction potential when the mediated enzyme reactions were carried out with the freely solubilized mediator. The electron transfer of azure A with respect to time was due to the adhesion of azure A to the hydrophilic surface during the reduction. In addition, the use of the adsorbed mediator on conductive activated carbon was proposed to inhibit the change in the electron transfer rate during the reaction by maintaining a constant mediator concentration and active surface area of the electrode. Azure A showed better than nitrite formation than methyl viologen when used with activated carbon.  相似文献   
9.
10.
An Exploratory Framework for the Empirical Measurement of Resilience   总被引:12,自引:1,他引:11  
Deliberate progress towards the goal of long-term sustainability depends on understanding the dynamics of linked social and ecological systems. The concept of social-ecological resilience holds promise for interdisciplinary syntheses. Resilience is a multifaceted concept that as yet has not been directly operationalized, particularly in systems for which our ignorance is such that detailed, parameter-rich simulation models are difficult to develop. We present an exploratory framework as a step towards the operationalization of resilience for empirical studies. We equate resilience with the ability of a system to maintain its identity, where system identity is defined as a property of key components and relationships (networks) and their continuity through space and time. Innovation and memory are also fundamental to understanding identity and resilience. By parsing our systems into the elements that we subjectively consider essential to identity, we obtain a small set of specific focal variables that reflect changes in identity. By assessing the potential for changes in identity under specified drivers and perturbations, in combination with a scenario-based approach to considering alternative futures, we obtain a surrogate measure of the current resilience of our study system as the likelihood of a change in system identity under clearly specified conditions, assumptions, drivers and perturbations. Although the details of individual case studies differ, the concept of identity provides a level of generality that can be used to compare measure of resilience across cases. Our approach will also yield insights into the mechanisms of change and the potential consequences of different policy and management decisions, providing a level of decision support for each case study area.  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