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   2106篇
  免费   132篇
  国内免费   1篇
  2023年   17篇
  2022年   44篇
  2021年   78篇
  2020年   40篇
  2019年   53篇
  2018年   54篇
  2017年   51篇
  2016年   71篇
  2015年   127篇
  2014年   118篇
  2013年   132篇
  2012年   190篇
  2011年   157篇
  2010年   113篇
  2009年   80篇
  2008年   118篇
  2007年   128篇
  2006年   89篇
  2005年   84篇
  2004年   71篇
  2003年   72篇
  2002年   68篇
  2001年   12篇
  2000年   19篇
  1999年   15篇
  1998年   13篇
  1997年   14篇
  1996年   7篇
  1995年   9篇
  1994年   6篇
  1993年   5篇
  1992年   8篇
  1990年   6篇
  1989年   8篇
  1987年   7篇
  1986年   9篇
  1985年   5篇
  1984年   9篇
  1983年   12篇
  1982年   12篇
  1981年   13篇
  1979年   8篇
  1978年   4篇
  1976年   6篇
  1975年   4篇
  1974年   6篇
  1973年   8篇
  1967年   4篇
  1965年   3篇
  1964年   3篇
排序方式: 共有2239条查询结果,搜索用时 31 毫秒
971.

Background

Some studies have reported associations between five uncoupling protein (UCP) 1–3 polymorphisms and type 2 diabetes mellitus (T2DM). However, other studies have failed to confirm the associations. This paper describes a case-control study and a meta-analysis conducted to attempt to determine whether the following polymorphisms are associated with T2DM: -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3).

Methods

The case-control study enrolled 981 T2DM patients and 534 nondiabetic subjects, all of European ancestry. A literature search was run to identify all studies that investigated associations between UCP1–3 polymorphisms and T2DM. Pooled odds ratios (OR) were calculated for allele contrast, additive, recessive, dominant and co-dominant inheritance models. Sensitivity analyses were performed after stratification by ethnicity.

Results

In the case-control study the frequencies of the UCP polymorphisms did not differ significantly between T2DM and nondiabetic groups (P>0.05). Twenty-three studies were eligible for the meta-analysis. Meta-analysis results showed that the Ala55Val polymorphism was associated with T2DM under a dominant model (OR = 1.27, 95% CI 1.03–1.57); while the -55C/T polymorphism was associated with this disease in almost all genetic models: allele contrast (OR = 1.17, 95% CI 1.02–1.34), additive (OR = 1.32, 95% CI 1.01–1.72) and dominant (OR = 1.18, 95% CI 1.02–1.37). However, after stratification by ethnicity, the UCP2 55Val and UCP3 -55C/T alleles remained associated with T2DM only in Asians (OR = 1.25, 95% CI 1.02–1.51 and OR = 1.22, 95% CI 1.04–1.44, respectively; allele contrast model). No significant association of the -3826A/G, -866G/A and Ins/Del polymorphisms with T2DM was observed.

Conclusions

In our case-control study of people with European ancestry we were not able to demonstrate any association between the UCP polymorphisms and T2DM; however, our meta-analysis detected a significant association between the UCP2 Ala55Val and UCP3 -55C/T polymorphisms and increased susceptibility for T2DM in Asians.  相似文献   
972.
Persistent DNA damage triggers cellular senescence, which may play an important role in the pathogenesis of cigarette smoke (CS)-induced lung diseases. Both p21CDKN1A (p21) and poly(ADP-ribose) polymerase-1 (PARP-1) are involved in DNA damage and repair. However, the role of p21-PARP-1 axis in regulating CS-induced lung DNA damage and cellular senescence remains unknown. We hypothesized that CS causes DNA damage and cellular senescence through a p21-PARP-1 axis. To test this hypothesis, we determined the levels of γH2AX (a marker for DNA double-strand breaks) as well as non-homologous end joining proteins (Ku70 and Ku80) in lungs of mice exposed to CS. We found that the level of γH2AX was increased, whereas the level of Ku70 was reduced in lungs of CS-exposed mice. Furthermore, p21 deletion reduced the level of γH2AX, but augmented the levels of Ku70, Ku80, and PAR in lungs by CS. Administration of PARP-1 inhibitor 3-aminobenzamide increased CS-induced DNA damage, but lowered the levels of Ku70 and Ku80, in lungs of p21 knockout mice. Moreover, 3-aminobenzamide increased senescence-associated β-galactosidase activity, but decreased the expression of proliferating cell nuclear antigen in mouse lungs in response to CS. Interestingly, 3-aminobenzamide treatment had no effect on neutrophil influx into bronchoalveolar lavage fluid by CS. These results demonstrate that the p21-PARP-1 pathway is involved in CS-induced DNA damage and cellular senescence.  相似文献   
973.

Context

Uncovering heterogeneities in the progression of early PTSD symptoms can improve our understanding of the disorder''s pathogenesis and prophylaxis.

Objectives

To describe discrete symptom trajectories and examine their relevance for preventive interventions.

Design

Latent Growth Mixture Modeling (LGMM) of data from a randomized controlled study of early treatment. LGMM identifies latent longitudinal trajectories by exploring discrete mixture distributions underlying observable data.

Setting

Hadassah Hospital unselectively receives trauma survivors from Jerusalem and vicinity.

Participants

Adult survivors of potentially traumatic events consecutively admitted to the hospital''s emergency department (ED) were assessed ten days and one-, five-, nine- and fifteen months after ED admission. Participants with data at ten days and at least two additional assessments (n = 957) were included; 125 received cognitive behavioral therapy (CBT) between one and nine months.

Approach

We used LGMM to identify latent parameters of symptom progression and tested the effect of CBT on these parameters. CBT consisted of 12 weekly sessions of either cognitive therapy (n = 41) or prolonged exposure (PE, n = 49), starting 29.8±5.7 days after ED admission, or delayed PE (n = 35) starting at 151.8±42.4 days. CBT effectively reduced PTSD symptoms in the entire sample.

Main Outcome Measure

Latent trajectories of PTSD symptoms; effects of CBT on these trajectories.

Results

Three trajectories were identified: Rapid Remitting (rapid decrease in symptoms from 1- to 5-months; 56% of the sample), Slow Remitting (progressive decrease in symptoms over 15 months; 27%) and Non-Remitting (persistently elevated symptoms; 17%). CBT accelerated the recovery of the Slow Remitting class but did not affect the other classes.

Conclusions

The early course of PTSD symptoms is characterized by distinct and diverging response patterns that are centrally relevant to understanding the disorder and preventing its occurrence. Studies of the pathogenesis of PTSD may benefit from using clustered symptom trajectories as their dependent variables.  相似文献   
974.
The Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis, causal agent of bacterial wilt and canker of tomato, is an economically devastating pathogen that inflicts considerable damage throughout all major tomato-producing regions. Annual outbreaks continue to occur in New York, where C. michiganensis subsp. michiganensis spreads via infected transplants, trellising stakes, tools, and/or soil. Globally, new outbreaks can be accompanied by the introduction of contaminated seed stock; however, the route of seed infection, especially the role of fruit lesions, remains undefined. In order to investigate the modes of seed infection, New York C. michiganensis subsp. michiganensis field strains were stably transformed with a gene encoding enhanced green fluorescent protein (eGFP). A constitutively eGFP-expressing virulent C. michiganensis subsp. michiganensis isolate, GCMM-22, was used to demonstrate that C. michiganensis subsp. michiganensis could not only access seeds systemically through the xylem but also externally through tomato fruit lesions, which harbored high intra- and intercellular populations. Active movement and expansion of bacteria into the fruit mesocarp and nearby xylem vessels followed, once the fruits began to ripen. These results highlight the ability of C. michiganensis subsp. michiganensis to invade tomato fruits and seeds through multiple entry routes.  相似文献   
975.
The canopy of an invasive tree species in the Pantanal floodplains, Vochysia divergens Pohl (Vochysiaceae; height 12 m) was sprayed once with 5% synthetic pyrethrum during the dry, non-flooded season near Poconé, Mato Grosso. About 4200 arthropods collected (43.7 ind./m 2) represented 14 orders. The Hymenoptera dominated (21.4 ind./ 2 ; mostly ants), followed by Coleoptera, Araneae and Diptera (85% of the total catch). Of the 26 Coleoptera families (6.2 ind./ 2) the Curculionidae, Scolytidae, Elateridae and Dryopidae were most abundant (70% of the total catch), and on trophic level the herbivores dominated (42%). This is the first quantitative canopy study of a tree species in the northern Pantanal floodplains. The type of data needed on arthropods from tree canopies in future studies to aid in the management and conservation of Pantanal floodplains is discussed.  相似文献   
976.
977.
doi: 10.1111/j.1741‐2358.2012.00665.x A preliminary report of the cost‐effectiveness of tooth replacement strategies for partially dentate elders Objective: To compare the cost‐effectiveness of conventional treatment using partial dentures with functionally orientated treatment to replace missing teeth for partially dentate elders using a randomised controlled clinical trial. Background: In many countries, including the Republic of Ireland, the only publically funded treatment option offered to partially dentate older patients is a removable partial denture. However, evidence suggests that these removable prostheses are unpopular with patients and can potentially increase the risk of further dental disease and subsequent tooth loss. Materials and Methods: Fourty‐four partially dentate patients aged 65 years and older were recruited. Patients were randomly assigned to the two treatment arms of the study. The conventional treatment group received removable partial dentures to replace all missing natural teeth. The functionally orientated group was restored to a Shortened Dental Arch (SDA) of 10 occluding contacts using resin‐bonded bridgework (RBB). The costs associated with each treatment were recorded. Effectiveness was measured in terms of the impact on oral health‐related quality of life (OHRQoL) using OHIP‐14. Results: Both groups reported improvements in OHRQoL 1 month after completion of treatment. The conventional treatment group required 8.3 clinic visits as compared to 4.4 visits for the functionally orientated group. The mean total treatment time was 183 min 19 s for the conventional group vs. 124 min 8 s for the functionally orientated group. The average cost of treatment for the conventional group was 487.74 Euros compared to 356.20 Euros for the functional group. Conclusions: Functionally orientated treatment was more cost‐effective than conventional treatment in terms of treatment effect and opportunity costs to the patients’ time.  相似文献   
978.
979.
The biogenic production of hydrogen sulfide gas by sulfate-reducing bacteria (SRB) causes serious economic problems for natural gas and oil industry. One of the key enzymes important in this biologic process is adenosine phosphosulfate reductase (APSr). Using virtual screening technique we have discovered 15 compounds that are novel potential APSr inhibitors. Three of them have been selected for molecular docking and microbiological studies which have shown good inhibition of SRB in the produced water from the oil industry.  相似文献   
980.
STIM1 acts as an endoplasmic reticulum Ca2 + sensor that communicates the filling state of the intracellular stores to the store-operated channels. In addition, STIM1 is expressed in the plasma membrane, with the Ca2 + binding EF-hand motif facing the extracellular medium; however, its role sensing extracellular Ca2 + concentrations in store-operated Ca2 + entry (SOCE), as well as the underlying mechanism remains unclear. Here we report that divalent cation entry stimulated by thapsigargin (TG) is attenuated by extracellular Ca2 + in a concentration-dependent manner. Expression of the Ca2 +-binding defective STIM1(D76A) mutant did not alter the surface expression of STIM1 but abolishes the regulation of divalent cation entry by extracellular Ca2 +. Orai1 and TRPC1 have been shown to play a major role in SOCE. Expression of the STIM1(D76A) mutant did not alter Orai1 phosphoserine content. TRPC1 silencing significantly attenuated TG-induced Mn2 + entry. Expression of the STIM1(K684,685E) mutant impaired the association of plasma membrane STIM1 with TRPC1, as well as the regulation of TG-induced divalent cation entry by extracellular Ca2 +, which suggests that TRPC1 might be involved in the regulation of divalent cation entry by extracellular Ca2 + mediated by plasma membrane-resident STIM1. Expression of the STIM1(D76A) or STIM1(K684,685E) mutants reduced store-operated divalent cation entry and resulted in loss of dependence on the extracellular Ca2 + concentration, providing evidence for a functional role of plasma membrane-resident STIM1 in the regulation of store-operated divalent cation entry, which at least involves the EF-hand motif and the C-terminal polybasic lysine-rich domain.  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