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   586篇
  免费   69篇
  国内免费   23篇
  2023年   3篇
  2022年   29篇
  2021年   21篇
  2020年   10篇
  2019年   11篇
  2018年   25篇
  2017年   18篇
  2016年   29篇
  2015年   29篇
  2014年   35篇
  2013年   66篇
  2012年   53篇
  2011年   70篇
  2010年   61篇
  2009年   38篇
  2008年   34篇
  2007年   16篇
  2006年   16篇
  2005年   16篇
  2004年   13篇
  2003年   7篇
  2002年   15篇
  2001年   2篇
  2000年   4篇
  1999年   3篇
  1998年   3篇
  1997年   3篇
  1996年   6篇
  1994年   1篇
  1993年   6篇
  1992年   1篇
  1989年   2篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1980年   2篇
  1979年   1篇
  1976年   2篇
  1973年   2篇
  1972年   5篇
  1971年   6篇
  1968年   3篇
  1963年   1篇
  1954年   1篇
  1950年   1篇
  1937年   1篇
  1929年   2篇
  1928年   1篇
排序方式: 共有678条查询结果,搜索用时 15 毫秒
61.
Some hot springs located in the west of Turkey were investigated with respect to the presence of thermophilic microorganisms. Based on phenotyping characteristics and 16S rRNA gene sequence analysis, 16 of the isolates belonged to the genus Geobacillus and grew optimally at about 60 degrees C on nutrient agar. 16S rRNA gene sequence analysis showed that these isolates resembled Geobacillus species by > or = 97%, but SDS-PAGE profiles of these 16 isolates differ from some of the other species of the genus Geobacillus. However, it is also known that analysis of 16S rRNA gene sequences may be insufficient to distinguish between some species. It is proposed that recN sequence comparisons could accurately measure genome similarities for the Geobacillus genus. Based on recN sequence analysis, isolates 11, IT3, and 12 are strains of G stearothermophilus; isolate 14.3 is a strain of G thermodenitrificans; isolates 9.1, IT4.1, and 4.5 are uncertain and it is required to make further analysis. The presence of xylanase and arabinofuranosidase activities, and their optimum temperature and pH were also investigated. These results showed that 7 of the strains have both xylanase and arabinofuranosidase activities, 4 of them has only xylanase, and the remaning 5 strains have neither of these activities. The isolates 9.1, 7.1, and 3.3 have the highest temperature optima (80 degrees C), and 7.2, 9.1, AO4, 9.2, and AO17 have the highest pH optima (pH 8) of xylanase. Isolates 7.2, AO4, AC15, and 12 have optimum arabinofuranosidase activities at 75 degrees C, and only isolate AC 15 has the lowest pH of 5.5.  相似文献   
62.
【目的】通过筛选西伯利亚蝗Gomphocerus sibiricus卵滞育基因及代谢通路,初步明确西伯利亚蝗卵滞育分子机理。【方法】利用Illumina NovaSeq 6000测序平台对西伯利亚蝗早期发育(ES)、滞育(DS)和滞育后发育阶段(PS)的卵进行转录组测序;采用GO和KEGG富集分析并结合文献,预测滞育相关通路并聚类热图分析,筛选蝗卵滞育关联基因,并选取其中6个重要基因进行qRT-PCR验证。【结果】DSvs ES和PS vs DS两比较组分别富集到12 419和4 789个差异表达基因,且多上调表达;两比较组共表达差异基因为2 206个,主要与糖代谢、环境胁迫和生长发育相关。DS vs ES组富集最显著的GO条目为蛋白结合,PS vs DS组GO条目主要包含酶活性、细胞骨架构建及蛋白结合等过程。滞育关联基因主要集中在Wnt信号通路、胰岛素信号通路、细胞周期通路以及昆虫激素生物合成等通路。6个重要的滞育关联基因的表达量变化趋势与转录组数据结果基本一致。【结论】本研究初步明确了西伯利亚蝗卵滞育调控的重要代谢途径,并筛选出20个滞育关联基因,为后续深入研究该物种的适应机理奠定了基础。  相似文献   
63.
Molecular Biology Reports - Polycystic ovary syndrome (PCOS) is a metabolic disease that causes infertility due to anovulation in women in reproductive age. It is known that clomiphene citrate (CC)...  相似文献   
64.
Neurochemical Research - Parkinson’s disease (PD) is one of the most common forms of neurodegenerative diseases and research on potential therapeutic agents for PD continues. Rotenone is a...  相似文献   
65.
66.
Leaf age alters the balance between the use of end‐product of plastidic isoprenoid synthesis pathway, dimethylallyl diphosphate (DMADP), in prenyltransferase reactions leading to synthesis of pigments of photosynthetic machinery and in isoprene synthesis, but the implications of such changes on environmental responses of isoprene emission have not been studied. Because under light‐limited conditions, isoprene emission rate is controlled by DMADP pool size (SDMADP), shifts in the share of different processes are expected to particularly strongly alter the light dependency of isoprene emission. We examined light responses of isoprene emission in young fully expanded, mature and old non‐senescent leaves of hybrid aspen (Populus tremula x P. tremuloides) and estimated in vivo SDMADP and isoprene synthase activity from post‐illumination isoprene release. Isoprene emission capacity was 1.5‐fold larger in mature than in young and old leaves. The initial quantum yield of isoprene emission (αI) increased by 2.5‐fold with increasing leaf age primarily as the result of increasing SDMADP. The saturating light intensity (QI90) decreased by 2.3‐fold with increasing leaf age, and this mainly reflected limited light‐dependent increase of SDMADP possibly due to feedback inhibition by DMADP. These major age‐dependent changes in the shape of the light response need consideration in modelling canopy isoprene emission.  相似文献   
67.
Hypertension is a major health problem with increasing prevalence around the world. Tannic acid is water-soluble polyphenol that is present in tea, green tea, coffee, red wine, nuts, fruits and many plant foods. It has been reported to serve as an antioxidant or a pro-oxidant depending on the type of cells and its concentration. The purpose of our study was to evaluate the effect of tannic acid on systolic blood pressure, oxidative stress and some urinary parameters in the rat model of essential hypertension. Blood pressures of all rats were measured using the tail-cuff method. The nitric oxide synthase inhibitor N (omega)-nitro-L-arginine was administered orally at a dose of 0.5 g/l/day for 15 days to rats in order to create an animal model of hypertension. Tannic acid was intraperitoneally injected at a dose of 50 mg/kg for 15 days. Superoxide dismutase, catalase activity and the concentration of malondialdehyde (MDA) were determined in blood plasma and homogenates of heart, liver and kidney. In order to evaluate renal functions, urine pH, urine volume, urine creatine, uric acid, and urea nitrogen values were measured. Compared with the hypertension group, a decrease in MDA concentrations of heart tissue (p < 0.01), urea nitrogen values (p < 0.01) and urine volumes (p < 0.001) were established in hypertension + tannic acid group. There was also a decrease in blood pressure values (20th and 30th days) of this group, but there was no a statistical difference according to hypertension group. The findings of our research show the effect of tannic acid in lowering blood pressure in hypertensive rats.  相似文献   
68.
69.
70.
The aim of this study was to investigate whether excess of vitamin B6 leads to ultrastructural changes in cerebral cortex of forty-eight healthy albino rats which were included in the study. Saline solution was injected to to the control groups (CG-10, n = 12 for 10 days; CG-15, n = 12 for 15 days; CG-20, n=12 for 20 days). The three experimental groups (EG-10, n = 12; EG-15, n = 12; EG-20, n = 12) were treated with 5 mg/kg vitamin B6 daily for 10 days (EG-10), 15 days (EG-15) and 20 days (EG-20). Brain tissues were prepared by glutaraldehyde-osmium tetroxide double fixation for ultrastructural analysis. No significant changes were observed in the control groups. The ultrastructural analysis revealed that the numbers of damaged mitochondria, lipofuscin granules and vacuoles were significantly higher in all the experimental groups than in the control groups (p < 0.05). However, synaptic density was significantly decreased in the experimental groups as compared to the control groups (p < 0.05). The results suggest that the excess of vitamin B6 intake causes damage to the cerebral cortex due to cellular intoxication and decreased synaptic density. Thus, careful attention should be paid to the time and dose of vitamin B6 recommended for patients who are supplemented with this vitamin.  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