全文获取类型
收费全文 | 663篇 |
免费 | 55篇 |
国内免费 | 88篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 20篇 |
2020年 | 18篇 |
2019年 | 35篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 39篇 |
2014年 | 35篇 |
2013年 | 63篇 |
2012年 | 83篇 |
2011年 | 65篇 |
2010年 | 36篇 |
2009年 | 29篇 |
2008年 | 43篇 |
2007年 | 44篇 |
2006年 | 30篇 |
2005年 | 28篇 |
2004年 | 35篇 |
2003年 | 32篇 |
2002年 | 23篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有806条查询结果,搜索用时 442 毫秒
101.
药用植物蛇足石杉研究新进展 总被引:4,自引:0,他引:4
蛇足石杉[Huperzia serrata(Thunb.)Trey.]是石杉科石杉属多年生小型草本植物,土生、附生或生于苔藓层中,喜阴凉潮湿环境。蛇足石杉含石杉碱甲,为目前治疗老年痴呆等疾病的特效药。对蛇足石杉的分类学、生物学特性(形态学、生态学、生理学与共生真菌研究)、繁殖与栽培、药用成分及含量测定等方面的研究新进展进行综述。并对其应用与保护前景进行展望。 相似文献
102.
Measurements of tree canopy architecture were made at six savanna sites on deep, sandy soils, along a gradient of increasing aridity. There was substantial variation in the leaf area estimated within each site, using the same sample frame, but different measurement techniques. The trends in canopy properties in relation to the aridity gradient were consistent, regardless of the technique used for estimating the properties. The effective plant area index for the tree canopy (the sum of the stem area index and the leaf area index (LAI)) declined from around 2 to around 0.8 m2 m?2 over a gradient of mean annual rainfall from 1000 to 350 mm. Stems contributed 2–5% of the tree canopy plant area index. Since the tree canopy cover decreased from 50% to 20% over this aridity range, the leaf area index within the area covered by tree canopies remained fairly constant at 3–4 m2 m?2. Tree leaves tended from a horizontal orientation to a more random orientation as the aridity increased. On the same gradient, the leaf minor axis dimension decreased from around 30 mm to around 3 mm, and the mean specific leaf area decreased from 14 to 5 m2 kgha?1. There was good agreement between LAI observed in the field using a line ceptometer and the LAI inferred by the MODIS sensor on the Terra satellite platform, 2 months later in the same season. 相似文献
103.
104.
Asthma is a complex heritable inflammatory disorder of the airways in which the development of clinical disease depends on
environmental exposure. It has been well established that T helper type 2 (TH2) lymphocytes and their cytokines have an important role in allergic asthma. Interleukin (IL)-9, a member of the TH2 cytokine family, has recently been implicated as an essential factor in determining mucosal immunity and susceptibility
to atopic asthma. In this review we examine the critical experiments and observations that support this hypothesis. We also
discuss these results in comparison with the experiments supporting the involvement of other TH2 cytokines such as IL-4, IL-5 and IL-13. 相似文献
105.
Dongqing Jiang Xiannian Zhang Yuhong Pang Jianyun Zhang Jianbin Wang Yanyi Huang 《蛋白质与细胞》2019,10(3):229-233
Dear Editor,Since its invention,next generation sequencing(NGS)has greatly facilitated biomedical research and clinical diagnosis(Sikkema-Raddatz et al.,2013).Continuous dropping of the cost further accelerated the adaptation of sequencing as a standard analytical tool,from identification of drug candidates(Walker et al.,2015)to deciphering the complex biological systems(McConnell et al.,2013). 相似文献
106.
107.
108.
Exploration of interaction of canthaxanthin with human serum albumin by spectroscopic and molecular simulation methods 下载免费PDF全文
The interaction between the food colorant canthaxanthin (CA) and human serum albumin (HSA) in aqueous solution was explored by using fluorescence spectroscopy, three‐dimensional fluorescence spectra, synchronous fluorescence spectra, UV–vis absorbance spectroscopy, circular dichroism (CD) spectra and molecular docking methods. The thermodynamic parameters calculated from fluorescence spectra data showed that CA could result in the HSA fluorescence quenching. From the KSV change with the temperature dependence, it was concluded that HSA fluorescence quenching triggered by CA is the static quenching and the number of binding sites is one. Furthermore, the secondary structure of HSA was changed with the addition of CA based on the results of synchronous fluorescence, three‐dimensional fluorescence and CD spectra. Hydrogen bonds and van der Waals forces played key roles in the binding process of CA with HSA, which can be obtained from negative standard enthalpy (ΔH) and negative standard entropy (ΔS). Furthermore, the conclusions were certified by molecular docking studies and the binding mode was further analyzed with Discovery Studio. These conclusions can highlight the potential of the interaction mechanism of food additives and HSA. 相似文献
109.
Sodium 4‐mercaptophenolate capped CdSe/ZnS quantum dots as a fluorescent probe for pH detection in acidic aqueous media 下载免费PDF全文
Development of the fluorescent pH detection method is promising due to the sensitivity, easy operation, and low‐cost, etc. However, traditional organic fluorophores have still some disadvantages such as the tedious preparation and purification as well as low photostability and water solubility, which limits the rapid detection application. Semiconductor quantum dots (QDs) have recently risen to prominence as an alternative for organic fluorophores in fluorescence analysis by virtue of their convenient synthesis and superior optical properties. In this study, we report on sodium 4‐mercaptophenolate functionalized CdSe/ZnS QDs (denoted as ?OPhS‐QDs), which can serve as a selective “on–off” fluorescence probe for aqueous media pH. ?OPhS‐QDs exhibit strong fluorescence in near neutral medium. As a Lewis organic base, ?OPhS‐ moieties on QDs surface easily binds to proton under acidic conditions to yield 4‐mercaptophenol capped QDs (i.e. HOPhS‐QDs), which acts as an efficient hole trapper. As a result, the QDs photoluminescence (PL) is switched off. Under optimal conditions, the present probe exhibits a good linear relationship between fluorescence response and pH values in the pH range 3.0–5.2. Furthermore, the present probe exhibits a high selectivity for proton over other common cations and has been successfully used for pH detection in real water samples. 相似文献
110.
In recent decades, various types of bioactive substances have been identified from amphibian skin and its secretions. Bradykinin-related peptides (BRPs) are among these compounds that make up the host defence system of amphibians. In the present study, we identified six novel BRPs, amolopkinin-GN1, amolopkinin-RK1, amolopkinin-TR1, amolopkinin-LF1, ranakinin-MS1, and ranakinin-MS2, from five East Asian amphibians, Amolops granulosus, Amolops ricketti, Amolops torrentis, Amolops lifanensis, and Hylarana maosonensis. This is the first report on BRPs in the skin of these species. Physiological assays reveal that these peptides have a contractive effect on the smooth muscle of rat ileum. 相似文献