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   92499篇
  免费   6737篇
  国内免费   6400篇
  105636篇
  2024年   201篇
  2023年   1254篇
  2022年   2940篇
  2021年   4868篇
  2020年   3193篇
  2019年   4016篇
  2018年   3956篇
  2017年   2866篇
  2016年   4051篇
  2015年   5841篇
  2014年   6886篇
  2013年   7248篇
  2012年   8495篇
  2011年   7736篇
  2010年   4484篇
  2009年   4187篇
  2008年   4776篇
  2007年   4146篇
  2006年   3533篇
  2005年   2822篇
  2004年   2312篇
  2003年   2105篇
  2002年   1698篇
  2001年   1471篇
  2000年   1342篇
  1999年   1409篇
  1998年   822篇
  1997年   892篇
  1996年   814篇
  1995年   775篇
  1994年   673篇
  1993年   570篇
  1992年   682篇
  1991年   535篇
  1990年   455篇
  1989年   331篇
  1988年   278篇
  1987年   219篇
  1986年   185篇
  1985年   210篇
  1984年   124篇
  1983年   118篇
  1982年   54篇
  1981年   23篇
  1980年   20篇
  1979年   19篇
  1976年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
This study aims to evaluate the effects of Remifemin (isopropanolic extract of Cimicifuga Racemosa) on postmenopausal osteoporosis. 120 female Sprague-Dawley rats were randomly assigned to four groups: sham surgery with vehicle, ovariectomy with vehicle, ovariectomy with estradiol valerate, or ovariectomy with Remifemin. Daily oral administrations of the vehicle, estradiol valerate, or Remifemin began 2 weeks after surgery and lasted to 4, 8, or 12 weeks. Ten rats in each group were sacrificed at each timestep with assessment of bone mineral density, trabecular bone structure, and biomechanical parameters of the femur and lumbar vertebra. Bone turnover markers were evaluated 12 weeks after surgery. Both drugs prevented bone density loss in the distal end of the femur and preserved the trabecular bone structure in both the lumbar vertebra and distal end of the femur following ovariectomy. Both drugs protected bone stiffness at the tested regions and reduced bone reabsorption in ovariectomized rats. The preventive effects of Remifemin against bone-loss can rival those of estradiol valerate if treatment duration is adequately extended. In conclusion, Remifemin may demonstrate equivalent effects to estradiol valerate in terms of preventing postmenopausal osteoporosis.  相似文献   
982.
Recombinant adeno-associated viral (AAV) vectors have been shown to be one of the most promising vectors for therapeutic gene delivery because they can induce efficient and long-term transduction in non-dividing cells with negligible side-effects. However, as AAV vectors mostly remain episomal, vector genomes and transgene expression are lost in dividing cells. Therefore, to stably transduce cells, we developed a novel AAV/transposase hybrid-vector. To facilitate SB-mediated transposition from the rAAV genome, we established a system in which one AAV vector contains the transposon with the gene of interest and the second vector delivers the hyperactive Sleeping Beauty (SB) transposase SB100X. Human cells were infected with the AAV-transposon vector and the transposase was provided in trans either by transient and stable plasmid transfection or by AAV vector transduction. We found that groups which received the hyperactive transposase SB100X showed significantly increased colony forming numbers indicating enhanced integration efficiencies. Furthermore, we found that transgene copy numbers in transduced cells were dose-dependent and that predominantly SB transposase-mediated transposition contributed to stabilization of the transgene. Based on a plasmid rescue strategy and a linear-amplification mediated PCR (LAM-PCR) protocol we analysed the SB100X-mediated integration profile after transposition from the AAV vector. A total of 1840 integration events were identified which revealed a close to random integration profile. In summary, we show for the first time that AAV vectors can serve as template for SB transposase mediated somatic integration. We developed the first prototype of this hybrid-vector system which with further improvements may be explored for treatment of diseases which originate from rapidly dividing cells.  相似文献   
983.

Background

In the past twenty years, codeine-containing cough syrups (CCS) was recognized as a new type of addictive drugs. However, the exact neurobiologic mechanisms underlying CCS-dependence are still ill-defined. The aims of this study are to identify CCS-related modulations of neural activity during the resting-state in CCS-dependent individuals and to investigate whether these changes of neural activity can be related to duration of CCS use, the first age of CCS use and impulse control deficits in CCS-dependent individuals. We also want to observe the impact of gray matter deficits on these functional results.

Methodology/Principal Findings

Thirty CCS-dependent individuals and 30 control subjects participated. Resting-state functional MRI was performed by using gradient-echo echo-planar imaging sequence. Regional homogeneity (ReHo) was calculated by using REST software. Voxel-based analysis of the ReHo maps between controls and CCS-dependent groups was performed using two-sample t tests (p<0.05, corrected for multiple comparisons). The Barratt Impulsiveness Scale 11 (BIS.11) was surveyed to assess participants'' impulsivity trait soon after MR examination. Abnormal clusters revealed by group comparison were extracted and correlated with impulsivity, duration of CCS use, and age of first CCS use. ReHo was diminished in the bilateral medial orbitofrontal cortex (mOFC) and left dorsal striatum in CCS-dependent individuals. There were negative correlations between mean ReHo in the bilateral medial OFC, left dorsal striatum and duration of CCS use, BIS.11 total scores, and the subscale of attentional impulsivity in CCS-dependent individuals. There was a significantly positive correlation between mean ReHo in the left dorsal striatum and age of first CCS use in CCS-dependent individuals. Importantly, these results still remain significant after statistically controlling for the regional gray matter deficits.

Conclusion

Resting-state abnormalities in CCS-dependent individuals revealed in the present study may further improve our understanding about the neural substrates of impulse control dysfunction in CCS-dependent individuals.  相似文献   
984.
985.

Aim

Functional constipation (FC) is one of the common diseases among children. The aim of this study was to investigate the health-related quality of life (HRQOL) in preschool children diagnosed with FC and the impact of the condition on affected families.

Methods

In this cross-sectional, case-control study, 152 children aged 3–6 years with FC, 176 healthy children aged 3–6 years without FC, and their primary caregivers were selected. Chinese versions of the PedsQLTM 4.0 Generic Core Scale and the Family Impact Module (FIM) were used to assess childhood HRQOL and the impact of FC on family members, respectively. HRQOL scores were compared between children with FC and healthy children. In addition, a multiple step-wise regression with demographic variables of children and their caregivers, family economic status, duration and symptoms of FC, as independent variables, was used to determine factors that influenced HRQOL in children and had impacted caregivers.

Results

Scores of physical, emotional, social and school functions, and summary scales were significantly lower in children with FC than in healthy children (p < 0.05). Physical, emotional, social, cognitive, and communication scores for caregivers, as well as daily activities and relationships for families of children with FC, were significantly lower than those of caregivers and families with healthy children (p < 0.05). Children’s ages, duration of FC, symptoms of FC, the child-caregiver relationship, family economic status, and caregiver education level emerged as the main factors influencing HRQOL in children, caregivers, and family members.

Conclusions

FC had a significant impact on HRQOL of affected children and their caregivers, as well as their family functions. Social characteristics of children and caregivers, duration and symptoms of FC and family economic status significantly affected HRQOL of children and caregivers, as well as family functions of children with FC.  相似文献   
986.
987.
988.

Background

Paraquat poisoning is well known for causing multiple organ function failure (MODS) and high mortality. Acute lung injury and advanced pulmonary fibrosis are the most serious complications. Bosentan is a dual endothelin receptor antagonist. It plays an important role in treating PF. There is no related literature on the use of bosentan therapy for paraquat poisoning.

Objective

To study the use of bosentan to treat acute lung injury and pulmonary fibrosis as induced by paraquat.

Method

A total of 120 adult Wister male rats were randomly assigned to three groups: the paraquat poisoning group (rats were intragastrically administered with paraquat at 50 mg/kg body weight once at the beginning); the bosentan therapy group (rats were administered bosentan at 100 mg/kg body weight by intragastric administration half an hour after paraquat was administered, then the same dose was administered once a day); and a control group (rats were administered intragastric physiological saline). On the 3rd, 7th, 14th, and 21st days following paraquat exposure, rats were sacrificed, and samples of lung tissue and venous blood were collected. The levels of transforming growth factor-β1 (TGF-β1), endothelin-1 (ET-1), and hydroxyproline (HYP) in the plasma and lung homogenate were determined. Optical and electronic microscopes were used to examine pathological changes.

Result

The TGF-β1, ET-1, and HYP of the paraquat poisoning group were significantly higher than in the control group, and they were significantly lower in the 21st day therapy group than in the paraquat poisoning group on the same day. Under the optical and electronic microscopes, lung tissue damage was observed to be more severe but was then reduced after bosentan was administered.

Conclusion

Bosentan can reduce inflammation factor release. It has a therapeutic effect on acute lung injury as induced by paraquat.  相似文献   
989.
990.
Studies have revealed that catechol-O-methyltransferase (COMT) and dopaminegic receptor2 (DRD2) modulate human attention bias for palatable food or tobacco. However, the existing evidence about the modulations of COMT and DRD2 on attentional bias for facial expressions was still limited. In the study, 650 college students were genotyped with regard to COMT Val158Met and DRD2 TaqI A polymorphisms, and the attentional bias for facial expressions was assessed using the spatial cueing task. The results indicated that COMT Val158Met underpinned the individual difference in attentional bias for negative emotional expressions (P = 0.03) and the Met carriers showed more engagement bias for negative expressions than the Val/Val homozygote. On the contrary, DRD2 TaqIA underpinned the individual difference in attentional bias for positive expressions (P = 0.003) and individuals with TT genotype showed much more engagement bias for positive expressions than the individuals with CC genotype. Moreover, the two genes exerted significant interactions on the engagements for negative and positive expressions (P = 0.046, P = 0.005). These findings suggest that the individual differences in the attentional bias for emotional expressions are partially underpinned by the genetic polymorphisms in COMT and DRD2.  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