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   20714篇
  免费   1052篇
  国内免费   2973篇
  2024年   33篇
  2023年   260篇
  2022年   320篇
  2021年   516篇
  2020年   497篇
  2019年   655篇
  2018年   525篇
  2017年   548篇
  2016年   609篇
  2015年   770篇
  2014年   1014篇
  2013年   1270篇
  2012年   909篇
  2011年   1000篇
  2010年   852篇
  2009年   1162篇
  2008年   1275篇
  2007年   1356篇
  2006年   1254篇
  2005年   1265篇
  2004年   1105篇
  2003年   1072篇
  2002年   865篇
  2001年   723篇
  2000年   611篇
  1999年   546篇
  1998年   592篇
  1997年   438篇
  1996年   440篇
  1995年   419篇
  1994年   358篇
  1993年   272篇
  1992年   256篇
  1991年   200篇
  1990年   163篇
  1989年   116篇
  1988年   139篇
  1987年   94篇
  1986年   57篇
  1985年   55篇
  1984年   43篇
  1983年   24篇
  1982年   24篇
  1981年   12篇
  1980年   8篇
  1979年   4篇
  1978年   6篇
  1977年   1篇
  1976年   3篇
  1950年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Recent studies suggest that the use of vegetable oils at expense of fish oil in aquaculture feeds might have potential negative effects on fish redox homeostasis and adiposity. Resveratrol (RESV) is a lipid-soluble phytoalexin present in fruits and vegetables with proven in vivo antioxidant function in animals. The present study aims to assess the potential use of RESV in Atlantic salmon feeds. To this end, post-smolt salmons with an initial BW of 148±3 g were fed four experimental diets for 15 weeks. A diet low in fish oil served as a control and was supplemented with 0, 0.5, 1.5 and 2.5 g/kg of RESV, respectively. The effect of the experimental diets on animal performance, tissue fatty acid composition, and the expression of genes encoding proteins involved in antioxidant signalling, lipid peroxidation, and metabolism were studied. Resveratrol significantly reduced feed intake and final BW of the salmon. Feeding RESV did not affect the sum of saturated and monounsaturated fatty acids or total lipids in the fillet. While the content of total polyunsaturated fatty acids was not affected, the percentages of some fatty acids in the liver and fillet were changed by RESV. Furthermore, in liver, the relative expression of glutathione peroxidase 4b, nuclear factor-like 2, and arachidonate 5-lipoxygenase remained unchanged across treatment groups. In conclusion, the negative impact of dietary RESV on FI and hence reduction of the BW discourages its inclusion in low fish oil diets for Atlantic salmon.  相似文献   
995.
996.

Purpose

To explore how the use of a laser needle-knife affects vertebroarterial morphology and protein expression of PI-3K, AKT and VEGF in the carotid artery of a rabbit model of cervical spondylotic arteriopathy (CSA), and to determine its primary treatment mechanism.

Methods

The CSA rabbit model consisted of 30 rabbits with CSA that were randomly divided into a model group (n?=?10), an acupuncture group (n?=?10) and a laser needle-knife group (n?=?10) plus a further 10 wild type rabbits placed into a normal group. Rabbits in the acupuncture group were treated by needling the Fengchi (GB 20) and Jiaji (EX-B2) acupoints, while those in the laser needle-knife group were treated with a laser needle-knife on the Jiaji (EX-B2) near the spinous process of the fifth cervical vertebra, the rabbit in both groups immobilized during treatment. Rabbits in the other two groups received no treatment, but were immobilized for a similar duration. The morphology of the right vertebral artery and the distribution of pore size before and after treatment were compared using BET and SEM, and the protein expression of PI-3K, AKT and VEGF in the carotid artery of the four groups measured using Western blot analysis.

Results

The pore diameter and specific surface area of the right vertebral artery increased after treatment, as did the number of micropores. Compared with the normal group, the protein expression of PI-3K, AKT and VEGF in the carotid artery of the model group was significantly lower (P?<?0.05), while that of the laser needle-knife group was significantly higher (P?<?0.05 and P?<?0.01). In addition, rabbits from the acupuncture and laser needle-knife groups demonstrated significantly higher levels of protein expression of PI-3K and VEGF in the carotid artery compared with the model group (P?<?0.05 and P?<?0.01).

Conclusions

By promoting micrangium hyperplasia within the vertebral artery of rabbits with CSA, treatment with a laser needle-knife modified the protein expression of PI-3K, AKT and VEGF, suggesting that laser needle-knife therapy possibly treats CSA though these signaling pathways.  相似文献   
997.

Objective

To determine the effect of laser needle-knife on PI-3K, AKT and VEGF mRNA expression of vertebral arteries in a rabbit model of cervical spondylotic arteriopathy (CSA) and the mechanism of action involved.

Methods

Forty healthy general-grade rabbits were divided into a normal control group, model group, acupuncture group, and laser needle-knife group (n?=?10 rabbits per group), and the CSA rabbit model was established in all but groups but the normal control group. CSA model rabbits in the acupuncture group were treated by acupuncture at the Fengchi (GB 20) and Cervical Jiaji (EX-B 2) points, whereas rabbits in the laser needle-knife group were treated with laser needle-knife targeting the Jiaji points near the C5 spinous process. Rabbits in the normal control and model groups were fixed using similar methods. Behavioral characteristics of all rabbits were evaluated before and after treatment. Peak systolic velocity (PSV) of the right carotid and vertebral arteries in each group were examined using beside B ultrasound, and PI-3K, AKT, VEGF mRNA expression in vertebral arteries were determined by real-time PCR.

Results

The behavioral signs of rabbits were improved after treatment in both the acupuncture and laser needle-knife groups. In comparison with control group, PSV of right carotid arteries in acupuncture group and laser needle-knife group were enhanced significantly (P?<?0.05 and P?<?0.01), PSV of right vertebral arteries in acupuncture group and laser needle-knife group were enhanced significantly too (P?<?0.01 and P?<?0.05). PI-3K mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group (P?<?0.01, P?<?0.05). AKT mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group (P?<?0.01). VEGF mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group too (P?<?0.01, P?<?0.05). No significant differences were found in PI-3K, AKT and VEGF mRNA expression levels among acupuncture and laser needle-knife groups (P?>?0.05).

Conclusion

Laser needle-knife could effectively intervene the mRNA expression of PI-3K, AKT and VEGF, this may be one of the mechanisms of the effect of laser needle-knife in treating CSA in rabbits.  相似文献   
998.
999.
1000.
Background: Circulating microRNAs (miRNA) are present in body fluids in stable, cell-free form. Likewise, these miRNAs can be identified in various stages of coronary artery disease (CAD) such as inflammation, endothelial dysfunction, proliferation and atherosclerosis among others. miRNA expression levels can be identified.

Aims and objectives: To determine the expression of circulating miRNAs (miR-126, miR-92, miR-33, miR-145 and miR-155) in CAD patients of Indian origin.

Material and methods: miRNA profiling analysis in blood plasma was performed by quantitative real-time-PCR (qRT-PCR) in 60 angiographically verified subjects including 30 CAD patients and 30 age- and gender-matched controls. Association between the expression of all five circulating miRNAs and clinical characteristics of patients with CAD were analysed using Medcalc statistics. The severity of CAD was assessed using SYNTAX score (SS).

Results: Expression of plasma miR-33 increased by 2.9 folds in CAD patients than in control group (p value ≥0.002) also it was found that miR-33 expression levels in mild cases (SS: ≤22) were significantly higher than CAD controls. There was a modest negative correlation between miR-33 and total cholesterol/high density lipoprotein ratio, triglycerides and very low density lipoprotein.

Conclusion: The study reports a significant association between increased levels of plasma miR-33 and CAD. Thus, plasma miR-33 appears to be a promising non-invasive biomarker, but requires further validation in a large cohort.  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