全文获取类型
收费全文 | 4130篇 |
免费 | 388篇 |
国内免费 | 251篇 |
出版年
2024年 | 3篇 |
2023年 | 37篇 |
2022年 | 106篇 |
2021年 | 208篇 |
2020年 | 123篇 |
2019年 | 161篇 |
2018年 | 178篇 |
2017年 | 130篇 |
2016年 | 173篇 |
2015年 | 284篇 |
2014年 | 290篇 |
2013年 | 346篇 |
2012年 | 363篇 |
2011年 | 348篇 |
2010年 | 208篇 |
2009年 | 179篇 |
2008年 | 241篇 |
2007年 | 196篇 |
2006年 | 157篇 |
2005年 | 161篇 |
2004年 | 115篇 |
2003年 | 121篇 |
2002年 | 89篇 |
2001年 | 84篇 |
2000年 | 70篇 |
1999年 | 69篇 |
1998年 | 43篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 39篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4769条查询结果,搜索用时 15 毫秒
951.
Achene germination of the spring ephemeroid species Carex physodes in the Gurbantunggut Desert
下载免费PDF全文
![点击此处可从《Nordic Journal of Botany》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Buhailiqiemu Abudureheman Lingwei Zhang Huiliang Liu Daoyuan Zhang Kaiyun Guan 《Nordic Journal of Botany》2016,34(2):228-234
Much of the seed germination research on Carex has focused on wetland species, and little is known about the species of arid habitats. Here, we investigated seed dormancy and germination of Carex physodes, which is an important component of the plant community of the Gurbantunggut Desert of the Junggar Basin in Xinjiang, China. Our studies included the effects of mechanical and chemical scarification, dry storage, treatment with GA3, wet‐cold stratification, and burial in the field. No freshly matured achenes germinated over a range of temperature regimes after treatment with GA3, 6 months of dry storage or removal of part of the endosperm. The mechanical scarification resulted in < 5% achene germination, however, higher percentage of achene germination occurred after removal of the pericarp (60%), H2SO4 scarification (30%) or scarification in 10% NaOH (85%). Six and nine months of wet‐cold stratification promoted < 40% achene germination. The optimal germination temperatures ranged from 25/10°C to 35/20°C. Maximum germination after 9 months of burial at a depth of 3 cm in the field was 36%. These results indicate that the seeds have non‐deep physiological dormancy (PD) and that the pericarp contains germination inhibitors and has strong mechanical resistance to germination. 相似文献
952.
Shasha Zhou Shuangxun Ma Mingjun Li Cuiying Li Xiaoqing Gong Qingmei Guan Yanxiao Tan Yun Shao Chao Li Fengwang Ma 《Acta Physiologiae Plantarum》2016,38(9):231
Argonaute proteins are key players in small RNA-guided gene-silencing, which plays an important role in plant stress tolerance. However, little is known about how Argonaute genes affect the water-use efficiency (WUE) of apple (Malus domestica) or its responses to different abiotic stresses. We identified and characterized MdAGOs in apple and analyzed their chromosome locations, exon/intron structures, phylogeny, and the distribution of conserved motifs. We also examined the expression profiling of responses to abiotic stress and conducted molecular cloning of MdAGO4.1. In all, 16 MdAGOs were identified and characterized, then grouped into three separate clusters. Our qRT-PCR data demonstrated that these genes are induced by drought, salt, cold, and ABA treatments, indicating that they are good candidates for further analysis of their activities and functions. We have previously shown that, during long-term moderate drought, the abundance of MdAGO4.1 protein is increased in ‘Qinguan’ apple (a cultivar with high WUE) leaves, but not in ‘Naganofuji No. 2’. These changes are in accordance with alterations in their WUE and expression of MdAGO4.1 under the same test conditions as those used in the current study. Therefore, MdAGO4.1 is a putative gene that positively regulates WUE. Our findings provide evidence that MdAGOs have a role in plant adaptations to abiotic stress and can be exploited to improve WUE. These results will serve as a framework for future functional studies of that gene family in apple. 相似文献
953.
954.
955.
Jinting?Guan Ence?Yang Jizhou?Yang Yong?Zeng Guoli?JiEmail author James?J.?CaiEmail author 《Human genetics》2016,135(7):797-811
Autism spectrum disorder (ASD) is characterized by substantial phenotypic and genetic heterogeneity, which greatly complicates the identification of genetic factors that contribute to the disease. Study designs have mainly focused on group differences between cases and controls. The problem is that, by their nature, group difference-based methods (e.g., differential expression analysis) blur or collapse the heterogeneity within groups. By ignoring genes with variable within-group expression, an important axis of genetic heterogeneity contributing to expression variability among affected individuals has been overlooked. To this end, we develop a new gene expression analysis method—aberrant gene expression analysis, based on the multivariate distance commonly used for outlier detection. Our method detects the discrepancies in gene expression dispersion between groups and identifies genes with significantly different expression variability. Using this new method, we re-visited RNA sequencing data generated from post-mortem brain tissues of 47 ASD and 57 control samples. We identified 54 functional gene sets whose expression dispersion in ASD samples is more pronounced than that in controls, as well as 76 co-expression modules present in controls but absent in ASD samples due to ASD-specific aberrant gene expression. We also exploited aberrantly expressed genes as biomarkers for ASD diagnosis. With a whole blood expression data set, we identified three aberrantly expressed gene sets whose expression levels serve as discriminating variables achieving >70 % classification accuracy. In summary, our method represents a novel discovery and diagnostic strategy for ASD. Our findings may help open an expression variability-centered research avenue for other genetically heterogeneous disorders. 相似文献
956.
957.
958.
β‐Carotene Induces Apoptosis in Human Esophageal Squamous Cell Carcinoma Cell Lines via the Cav‐1/AKT/NF‐κB Signaling Pathway
下载免费PDF全文
![点击此处可从《Journal of biochemical and molecular toxicology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xiangzhan Zhu Yanting Zhang Qinghua Li Lu Yang Nannan Zhang Shanshan Ma Kun Zhang Jishi Song Fangxia Guan 《Journal of biochemical and molecular toxicology》2016,30(3):148-157
β‐carotene, a type of terpenoid, has many metabolic and physiological functions. In particular, β‐carotene has an antitumor effect. However, the efficacy of β‐carotene against esophageal squamous cell carcinoma (ESCC) remains unclear. In our study, β‐carotene inhibited the growth of ESCC cells and downregulated expression of the Caveolin‐1 (Cav‐1) protein. Cav‐1 protein was expressed only in ESCC cells, not in Het‐1A cells. Moreover, β‐carotene triggered apoptosis, induced cell cycle G0?G1 phase arrest, and inhibited cell migration. To explore the mechanism involved in these processes, we further examined the effect of β‐carotene on the Cav‐1‐mediated AKT/NF‐κB pathway. The results showed that the level of AKT and NF‐κB phosphorylation was dramatically inhibited, which led to an increase in the Bax/Bcl‐2 ratio. Correspondingly, the activity of Caspase‐3 was also enhanced. These data suggest that β‐carotene has an antiproliferative role in ESCC cells and may be a promising chemotherapeutic agent for use against ESCC cells. 相似文献
959.
Ru Lin Yu‐Zhou Guan Rui‐Jun Li Xiao‐Ming Xu Jian‐Guang Luo Ling‐Yi Kong 《化学与生物多样性》2016,13(7):884-890
Four new 13,14‐seco‐withanolides, minisecolides A – D ( 1 – 4 ), together with three known analogues 5 – 7 , were isolated from the whole plants of Physalis minima. The structures of new compounds were determined on the basis of spectroscopic analysis, including 1H‐, 13C‐NMR, 2D‐NMR (HMBC, HSQC, ROESY), and HR‐ESI‐MS. Evaluation of all isolates for their inhibitory effects on nitric oxide (NO) production was conducted on lipopolysaccaride‐activated RAW264.7 macrophages. Compounds 2 , 3 , 5 , and 6 showed inhibitory activities, especially for compound 5 with IC50 value of 3.87 μm . 相似文献
960.
High‐Performance Flexible Solid‐State Ni/Fe Battery Consisting of Metal Oxides Coated Carbon Cloth/Carbon Nanofiber Electrodes
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cao Guan Wei Zhao Yating Hu Qingqing Ke Xin Li Hua Zhang John Wang 《Liver Transplantation》2016,6(20)
Aqueous Ni/Fe batteries have great potential as flexible energy storage devices, owing to their low cost, low toxicity, high safety, and high energy density. However, the poor cycling stability has limited the widely expected application of Ni/Fe batteries, while the use of heavy metal substrates cannot meet the basic requirement for flexible devices. In this work, a flexible type of solid‐state Ni/Fe batteries with high energy and power densities is rationally developed using needle‐like Fe3O4 and flake‐like NiO directly grown on carbon cloth/carbon nanofiber (CC–CF) matrix as the anode and cathode, respectively. The hierarchical CC–CF substrate with high electric conductivity and good flexibility serves as an ideal support for guest active materials of nanocrystalline Fe3O4 and NiO, which can effectively buffer the volume change giving rise to good cycling ability. By utilizing a gel electrolyte, a robust and mechanically flexible quasi‐solid‐state Ni/Fe full cell can be assembled. It demonstrates optimal electrochemical performance, such as high energy density (5.2 mWh cm?3 and 94.5 Wh Kg?1), high power density (0.64 W cm?3 and 11.8 KW Kg?1), together with excellent cycling ability. This work provides an example of solid‐state alkaline battery with high electrochemical performance and mechanical flexibility, holding great potential for future flexible electronic devices. 相似文献