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   5025篇
  免费   723篇
  国内免费   809篇
  2024年   30篇
  2023年   261篇
  2022年   346篇
  2021年   567篇
  2020年   456篇
  2019年   508篇
  2018年   396篇
  2017年   327篇
  2016年   322篇
  2015年   385篇
  2014年   499篇
  2013年   358篇
  2012年   244篇
  2011年   208篇
  2010年   104篇
  2009年   117篇
  2008年   99篇
  2007年   98篇
  2006年   100篇
  2005年   105篇
  2004年   86篇
  2003年   96篇
  2002年   82篇
  2001年   77篇
  2000年   76篇
  1999年   66篇
  1998年   49篇
  1997年   56篇
  1996年   50篇
  1995年   52篇
  1994年   49篇
  1993年   22篇
  1992年   43篇
  1991年   27篇
  1990年   20篇
  1989年   21篇
  1988年   21篇
  1987年   15篇
  1986年   10篇
  1985年   20篇
  1984年   30篇
  1983年   17篇
  1982年   22篇
  1981年   6篇
  1980年   7篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1975年   1篇
排序方式: 共有6557条查询结果,搜索用时 218 毫秒
101.
102.
In the present study we describe the occurrence of fungi in 100 tap water and 16 groundwater samples from Slovenia. We used culture-dependent and culture-independent techniques. 28 fungal species belonging to 16 genera were isolated with selected culturing conditions, targeting human opportunistic yeasts and yeast-like fungi. Of special concern was the detection of Aureobasidium melanogenum, Exophiala dermatitidis, Rhinocladiella similis, Candida parapsilosis and Rhodotorula mucilaginosa. The DGGE analysis of ITS1 rDNA revealed from 6 to 16 bands hypothetically corresponding to different taxa, while pyrosequencing showed the presence of Aspergillus and Exophiala. According to the statistic machine learning methodology, the profile of fungi in water is determined by the concentration of calcium and magnesium ions and the presence of nitrate. Exophiala spp., C. parapsilosis and R. mucilaginosa are known as dominant contaminants of household appliances. It appears that they are transferred with water to dishwashers and washing machines, where they subsequently proliferate.  相似文献   
103.
《Free radical research》2013,47(4):523-530
Abstract

In the tide of science nouveau after the completion of genome projects of various species, there appeared a movement to understand an organism as a system rather than the sum of cells directed for certain functions. With the advent and spread of microarray techniques, systematic and comprehensive genome-wide approaches have become reasonably possible and more required on the investigation of DNA damage and the subsequent repair. The immunoprecipitation-based technique combined with high-density microarrays or next-generation sequencing is one of the promising methods to provide access to such novel research strategies. Oxygen is necessary for most of the life on earth for electron transport. However, reactive oxygen species are inevitably generated, giving rise to steady-state levels of DNA damage in the genome, that may cause mutations leading to cancer, ageing and degenerative diseases. Previously, we showed that there are many factors involved in the genomic distribution of oxidatively generated DNA damage including chromosome territory, and proposed this sort of research area as oxygenomics. Recently, RNA is also recognized as a target of this kind of modification.  相似文献   
104.
The molecular order of brain and liver membranes isolated from deep sea and continental shelf fish species have been estimated and compared using the fluorescence polarization technique in order to determine whether life in a high pressure habitat is associated with an adjustment of membrane order. Fish were trawled at depths between 200 m and 4000 m, liver and brain membranes were fractionated, and fluorescence polarization was measured at 4°C and ambient pressure. Polarization of the brain myelin fraction provided a statistically significant regression with depth of capture (P<0.001) with a slope of ?0.004 km?1. This change in polarization with depth was sufficient to offset approximately half of the pressure-induced increase in polarization and thus represents the first structural evidence of homeoviscous adaptation to pressure. Polarization of the brain synaptic and liver mitochondrial fraction was not significantly related to depth. This may be due, at least in part, to a high individual variability of polarization compared to laboratory-acclimated freshwater fish.  相似文献   
105.
Connectivity of marine populations is shaped by complex interactions between biological and physical processes across the seascape. The influence of environmental features on the genetic structure of populations has key implications for the dynamics and persistence of populations, and an understanding of spatial scales and patterns of connectivity is crucial for management and conservation. This study employed a seascape genomics approach combining larval dispersal modeling and population genomic analysis using single nucleotide polymorphisms (SNPs) obtained from RADseq to examine environmental factors influencing patterns of genetic structure and connectivity for a highly dispersive mud crab Scylla olivacea (Herbst, 1796) in the Sulu Sea. Dispersal simulations reveal widespread but asymmetric larval dispersal influenced by persistent southward and westward surface circulation features in the Sulu Sea. Despite potential for widespread dispersal across the Sulu Sea, significant genetic differentiation was detected among eight populations based on 1,655 SNPs (FST = 0.0057, p < .001) and a subset of 1,643 putatively neutral SNP markers (FST = 0.0042, p < .001). Oceanography influences genetic structure, with redundancy analysis (RDA) indicating significant contribution of asymmetric ocean currents to neutral genetic variation (Radj2 = 0.133, p = .035). Genetic structure may also reflect demographic factors, with divergent populations characterized by low effective population sizes (N e < 50). Pronounced latitudinal genetic structure was recovered for loci putatively under selection (FST = 0.2390, p < .001), significantly correlated with sea surface temperature variabilities during peak spawning months for S. olivacea (Radj2 = 0.692–0.763; p < .050), suggesting putative signatures of selection and local adaptation to thermal clines. While oceanography and dispersal ability likely shape patterns of gene flow and genetic structure of S. olivacea across the Sulu Sea, the impacts of genetic drift and natural selection influenced by sea surface temperature also appear as likely drivers of population genetic structure. This study contributes to the growing body of literature documenting population genetic structure and local adaptation for highly dispersive marine species, and provides information useful for spatial management of the fishery resource.  相似文献   
106.
杨斌  孟庆瑶  张凯  段义忠 《植物研究》2020,40(5):686-695
对第三纪孑遗濒危植物矮扁桃(Amygdalus nana)叶绿体全基因组进行结构特征分析,并探究其与近缘物种之间的系统进化关系。利用Illumina HiSeq Xten测序技术获取叶绿体全基因组序列,对其进行组装、注释和特征分析。结果表明:①矮扁桃叶绿体全基因组总长度为158 596 bp,其中LSC长度为86 771 bp,SSC长度为19 037 bp,2个IRs均为26 394 bp,为环状四分体结构。共注释130个基因,包括85个PCGs、37个tRNA和8个rRNA。②对6种植物进行IR边界区扩张和收缩分析,发现在4个边界区的基因类型和基因分布情况存在一定差异,并且亲缘关系越紧密差异程度越小。③在矮扁桃叶绿体全基因组中共预测了71个SSRs位点。④系统发育分析结果显示,在扁桃亚属中,矮扁桃在亲缘关系上与蒙古扁桃更近,而与长柄扁桃和榆叶梅的亲缘关系稍远。本研究对矮扁桃叶绿体全基因组进行了深度剖析,并且涉及大量被子植物的叶绿体全基因组资料,为桃属植物之间的进化关系和植物鉴定提供参考依据。  相似文献   
107.
There is a growing interest in developing experimental methods for tracking the developmental cell lineages of a complex organism.The recently developed CRISPR/Cas9-based barcoding method is,although highly promising,difficult to scale up because it relies on exogenous barcoding sequences that are engineered into the genome.In this study,we characterized 78 high-quality endogenous sites in the zebrafish genome that can be used as CRISPR/Cas9-based barcoding sites.The 78 sites are all highly expressed in most of the cell types according to single-cell RNA sequencing(scRNA-seq)data.Hence,the barcoding information of the 78 endogenous sites is recovered by the available scRNA-seq platforms,enabling simultaneous characterization of cell type and cell lineage information.  相似文献   
108.
麦红吸浆虫Sitodiplosis mosellana(Gehin)是一种世界性的小麦害虫。为获得其转录组信息,本研究采用新一代高通量测序技术Illumina HiSeq TM 2000对麦红吸浆虫成虫转录组进行测序。共获得转录组样本数据量为27.88 G,经分析共获得59257个Unigenes,总长度49861164 bp,最短20 bp,最长29282 bp,平均长度841 bp。将Unigenes序列与NR、NT、Swiss-Prot、KEGG、GO和KOG数据库进行比对(e≤10-10),共获得95029个结果。通过GO功能分类,共有19584个Unigenes在GO数据库中细胞组分、分子功能和生物学过程等3大类50个功能组中找到对应。与KOG数据库进行比对,共有11279个麦红吸浆虫Unigenes被注释,按功能大致可分为26类。通过KEGG pathways分析,共有9110个麦红吸浆虫Unigenes被注释,分别归属于细胞进程、环境信息进程、遗传信息进程、新陈代谢和有机体系统5大类代谢途径,主要包括细胞生长与死亡、细胞运动、信号转导、能量代谢等32类代谢途径。CDS预测发现30088条序列可被编码,占全部基因的50.78%。SSR位点查找发现,在59257个Unigenes中共找到36323个SSR位点,发生率为61.30%。本研究获得的巨大的麦红吸浆虫转录组信息,为麦红吸浆虫的功能基因挖掘提供了重要的信息资源。  相似文献   
109.
Anti-cancer activity of tolfenamic acid (TA) in preclinical models for pancreatic cancer (PaCa) is well established. Since the dosage for anti-cancer actions of TA is rather high, we recently demonstrated that IC50 values of Copper-TA are 30–80% less than TA in 12 cancer cell lines. This study elucidates the underlying mechanisms of Copper-TA in PaCa cells. Control and Copper-TA (IC50) treated PaCa cells were processed by next-generation sequencing (NGS) to determine differentially expressed genes using HTG EdgeSeq Oncology Biomarker panel. Ingenuity Pathway Analysis (IPA®) was used to identify functional significance of altered genes. The conformational studies for assessing the expression of key regulators and genes were conducted by Western blot and qPCR. IPA® identified several networks, regulators, as well as molecular and cellular functions associated with cancer. The top 5 molecular and cellular functions affected by Cu-TA treatment were cell death and survival, cellular development, cell growth and proliferation, cell cycle and cellular movement. The expression of top upstream regulators was confirmed by Western blot analysis while qPCR results of selected genes demonstrated that Copper-TA is efficacious at lower doses than TA. Results suggest that Copper-TA alters genes/key regulators associated with cancer and potentially serve as an effective anti-cancer agent.  相似文献   
110.
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