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   10167篇
  免费   896篇
  国内免费   939篇
  12002篇
  2024年   29篇
  2023年   157篇
  2022年   337篇
  2021年   582篇
  2020年   410篇
  2019年   440篇
  2018年   427篇
  2017年   318篇
  2016年   447篇
  2015年   629篇
  2014年   806篇
  2013年   776篇
  2012年   971篇
  2011年   809篇
  2010年   565篇
  2009年   458篇
  2008年   496篇
  2007年   519篇
  2006年   445篇
  2005年   360篇
  2004年   316篇
  2003年   246篇
  2002年   210篇
  2001年   179篇
  2000年   158篇
  1999年   156篇
  1998年   72篇
  1997年   71篇
  1996年   72篇
  1995年   53篇
  1994年   63篇
  1993年   51篇
  1992年   75篇
  1991年   59篇
  1990年   39篇
  1989年   51篇
  1988年   29篇
  1987年   34篇
  1986年   26篇
  1985年   25篇
  1984年   8篇
  1983年   11篇
  1982年   3篇
  1981年   1篇
  1980年   5篇
  1979年   6篇
  1978年   1篇
  1970年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
In 2007, the Chinese State Food and Drug Administration (SFDA) implemented a management system for lot release of all plasma-derived products. Since then, there have been only a few systematic studies of the blood supply, which is a concern when considering the small amount of plasma collected per capita (approximately 3 L/1000 people). As a result, there may be a threat to the safety of the available blood supply. In this study, we examined the characteristics of the supply of Chinese plasma-derived products. We investigated the reports of lot-released biological products derived from all 8 national or regional regulatory authorities in China from 2007 to 2011. The market supply characteristics of Chinese plasma-derived products were analyzed by reviewing the changes in supply varieties, the batches of lot-released plasma-derived products and the actual supply. As a result, the national regulatory authorities can more accurately develop a specific understanding of the production and quality management information provided by Chinese plasma product manufacturers. The implementation of the lot release system further ensures the clinical validity of the plasma-derived products in China and improves the safety of using plasma-derived products. This work provides an assessment of the future Chinese market supply of plasma-derived products and can function as a theoretical basis for the establishment of hemovigilance.  相似文献   
102.
The possible protective effects of resveratrol (RVT) against cardiotoxicity were investigated in Wistar albino rats treated with saline, saline+doxorubicin (DOX; 20 mg/kg) or RVT (10 mg/kg)+DOX. Blood pressure and heart rate were recorded on the 1st week and on the 7th week, while cardiomyopathy was assessed using transthoracic echocardiography before the rats were decapitated. DOX-induced cardiotoxicity resulted in decreased blood pressure and heart rate, but lactate dehydrogenase, creatine phosphokinase, total cholesterol, triglyceride, aspartate aminotransferase and 8-OHdG levels were increased in plasma. Moreover, DOX caused a significant decrease in plasma total antioxidant capacity along with a reduction in cardiac superoxide dismutase, catalase and Na+,K+-ATPase activities and glutathione contents, while malondialdehyde, myelopreoxidase activity and the generation of reactive oxygen species were increased in the cardiac tissue. On the other hand, RVT markedly ameliorated the severity of cardiac dysfunction, while all oxidant responses were prevented; implicating that RVT may be of therapeutic use in preventing oxidative stress due to DOX toxicity.  相似文献   
103.
104.
Wheat-Dasypyrum villosum translocated chromosomes T6V#2S?6AL and T6V#4S?6DL are known to confer excellent resistance to wheat powdery mildew (PM). However, it is difficult to distinguish the two sources of PM resistance genes through multi-pathotype testing because to date no virulence for them has been found. To reveal the relationship between the PM resistance genes from the two translocations, the sequence of the Stpk-V gene, a key member of powdery mildew resistance locus Pm21, was used as a reference to isolate homologous genes from a D. villosum accession No.1026 and its derivatives 6V#4(6D) disomic substitution (DS) line RW15 and T6V#4S?6DL translocation line Pm97033. Two genes Stpk-V2 and Stpk-V3 were cloned from No.1026. Sequence alignment showed that Stpk-V2 and Stpk-V3 shared 98.2 % and 96.2 % of their DNA and 99.3 % and 100 % of their amino acids in identity with Stpk-V. Compared with Stpk-V, a 22-bp direct sequence repeat and a miniature inverted-repeat transposable element (MITE) were found in the intron 4 of Stpk-V2 and Stpk-V3, respectively. However, Stpk-V2 was not present in DS line RW15 and translocation line Pm97033 based on the PCR result, indicating that Stpk-V2 did not contribute to the PM resistance of RW15 and Pm97033. In the promoter region, a 78-bp insertion was found not only in Stpk-V2 and Stpk-V3, but also in its orthologous gene Stpk-A of wheat. In addition, there was a 17 bp/8 bp deletion/insertion in the putative promoter of Stpk-V3 in comparison with that of Stpk-V/Stpk-V2. Real-time quantitative RT-PCR analysis indicated that the expression levels of Stpk-V and Stpk-V3 genes in the translocation lines were induced by the pathogen, but Stpk-V had a higher expression level than Stpk-V3 at 12 h after inoculation with Bgt. The diversity of Stpk-V gene will help to explore new resistance genes to PM in D. villosum for wheat breeding.  相似文献   
105.
Hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF) has a poor prognosis with high in-hospital mortality. Hepatic and circulating inflammatory cytokines, such as fibrinogen like protein 2 (fgl2), FasL/Fas, and TNFα/TNFR1, play a significant role in the pathophysiology of ACLF. This study aimed to investigate the therapeutic effect of recombinant adenoviral vectors carrying constructed DNA code for non-native microRNA (miRNA) targeting mouse fgl2 (mfgl2) or both mFas and mTNFR1 on murine hepatitis virus (MHV)-3-induced fulminant hepatitis in BALB/cJ mice. Artificial miRNA eukaryotic expression plasmids against mfgl2, mFas, and mTNFR1 were constructed, and their inhibitory effects on the target genes were confirmed in vitro. pcDNA6.2-mFas-mTNFR1- miRNA,which expresses miRNA against both mFas and mTNFR1 simultaneously,was constructed. To construct a miRNA adenovirus expression vector against mfgl2, pcDNA6.2-mfgl2-miRNA was cloned using Gateway technology. Ad-mFas-mTNFR1- miRNA was also constructed by the same procedure. Adenovirus vectors were delivered by tail-vein injection into MHV-3-infected BALB/cJ mice to evaluate the therapeutic effect. 8 of 18 (44.4%) mice recovered from fulminant viral hepatitis in the combined interference group treated with Ad-mfgl2-miRNA and Ad-mFas-mTNFR1-miRNA. But only 4 of 18 (22.2%) mice receiving Ad-mfgl2-miRNA and 3 of 18 (16.7%) mice receiving Ad-mFas-mTNFR1- miRNA survived. These adenovirus vectors significantly ameliorated inflammatory infiltration, fibrin deposition, hepatocyte necrosis and apoptosis, and prolonged survival time. Our data illustrated that combined interference using adenovirus-mediated artificial miRNAs targeting mfgl2, mFas, and mTNFR1 might have significant therapeutic potential for the treatment of fulminant hepatitis.  相似文献   
106.
107.

Objective

To evaluate the effect of an improved salt-restriction spoon on the attitude of salt-restriction, the using rate of salt-restriction-spoon, the actual salt intake, and 24-hour urinary sodium excretion (24HUNa).

Design

A community intervention study.

Setting

Two villages in Beijing.

Participants

403 local adult residents being responsible for home cooking.

Intervention

Participants were randomly assigned to the intervention group or the control group. Those in the intervention group were provided with an improved salt-restriction-spoon and health education, and were informed of their actual salt intake and 24HUNa. Not any intervention was given to those in the control group.

Main Outcome Measures

The scores on the variables of Health Belief Model, the using rate of salt-restriction-spoon, the actual salt intake, and 24HUNa.

Analysis

Covariance analyses, Chi-square tests, Student’s t tests, and repeated measures analyses of variance.

Results

After 6 months of intervention, the intervention group felt significantly less objective barriers, and got access to significantly more cues to action as compared to the control group. The using rate and the correctly using rate of salt-restriction-spoon were significantly higher in the intervention group. The daily salt intake decreased by 1.42 g in the intervention group and by 0.28 g in the control group, and repeated measures analysis of variance showed significant change over time (F = 7.044, P<0.001) and significant difference between groups by time (F = 2.589, P = 0.041). The 24HUNa decreased by 34.84 mmol in the intervention group and by 33.65 mmol in the control group, and repeated measures analysis of variance showed significant change over time (F = 14.648, P<0.001) without significant difference between groups by time (F = 0.222, P = 0.870).

Conclusions

The intervention effect was acceptable, therefore, the improved salt-restriction-spoon and corresponding health education could be considered as an alternative for salt reduction strategy in China and other countries where salt intake comes mainly from home cooking.  相似文献   
108.
The PTEN tumor suppressor gene is frequently inactivated in human prostate cancer. Using Osr1 (odd skipped related 1)-Cre mice, we generated a novel conditional Pten knockout mouse strain, PtenLoxP:Osr1-Cre. Conditional biallelic and monoallelic Pten knockout mice were viable. Deletion of Pten expression was detected in the prostate of PtenLoxP/LoxP:Osr1-Cre mice as early as 2 weeks of age. Intriguingly, PtenLoxP/LoxP:Osr1-Cre mice develop high-grade prostatic intraepithelial neoplasms (PINs) with high penetrance as early as one-month of age, and locally invasive prostatic tumors after 12-months of age. PtenLoxP/+:Osr1-Cre mice show only mild oncogenic changes after 8-weeks of age. Castration of PtenLoxP/LoxP:Osr1-Cre mice shows no significant regression of prostate tumors, although a shift of androgen receptor (AR) staining from the nuclei to cytoplasm is observed in Pten null tumor cells of castrated mice. Enhanced Akt activity is observed in Pten null tumor cells of castrated PtenLoxP/LoxP:Osr1-Cre. This study provides a novel mouse model that can be used to investigate a primary role of Pten in initiating oncogenic transformation in the prostate and to examine other genetic and epigenetic changes that are required for tumor progression in the mouse prostate.  相似文献   
109.
110.
Six new triterpenoids, meliasenins S–X ( 1 – 6 , resp.), were isolated from the stem bark of Melia toosendan. Their structures were elucidated by mass spectrometry, NMR experiments, and comparison with the known compounds. Particularly, the absolute configuration at C(24) in new compounds was determined through their CD spectra of the [Pr(FOD)3] complex (fod=1,1,1,2,2,3,3,7,7,7‐decafluoroheptane‐4,6‐dione) in CCl4, as well as by using Mosher's method.  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