全文获取类型
收费全文 | 20184篇 |
免费 | 1521篇 |
国内免费 | 1382篇 |
专业分类
23087篇 |
出版年
2024年 | 53篇 |
2023年 | 292篇 |
2022年 | 643篇 |
2021年 | 1084篇 |
2020年 | 716篇 |
2019年 | 916篇 |
2018年 | 824篇 |
2017年 | 636篇 |
2016年 | 904篇 |
2015年 | 1309篇 |
2014年 | 1526篇 |
2013年 | 1553篇 |
2012年 | 1830篇 |
2011年 | 1578篇 |
2010年 | 996篇 |
2009年 | 856篇 |
2008年 | 991篇 |
2007年 | 804篇 |
2006年 | 762篇 |
2005年 | 610篇 |
2004年 | 558篇 |
2003年 | 497篇 |
2002年 | 443篇 |
2001年 | 392篇 |
2000年 | 357篇 |
1999年 | 329篇 |
1998年 | 211篇 |
1997年 | 192篇 |
1996年 | 179篇 |
1995年 | 160篇 |
1994年 | 121篇 |
1993年 | 113篇 |
1992年 | 136篇 |
1991年 | 115篇 |
1990年 | 104篇 |
1989年 | 64篇 |
1988年 | 50篇 |
1987年 | 52篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Jun Sun Wei Wu Xiaofeng Tang Feifei Zhang Cheng Ju Renfeng Liu Yiping Liang Bo Yu Bin Lv Yuhong Guo Duo Zeng Xuchang Tao Min Wang Zhiping Zhang Changhua Zhang Xiao-Bin Lv 《Bioscience reports》2021,41(4)
Background: WT161, as a selective HDAC6 inhibitor, has been shown to play anti-tumor effects on several kinds of cancers. The aim of the present study is to explore the roles of WT161 in osteosarcoma and its underlying mechanisms.Methods: The anti-proliferative effect of WT161 on osteosarcoma cells was examined using MTT assay and colony formation assay. Cell apoptosis was analyzed using flow cytometer. The synergistic effect was evaluated by isobologram analysis using CompuSyn software. The osteosarcoma xenograft models were established to evaluate the anti-proliferative effect of WT161 in vivo.Results: WT161 suppressed the cell growth and induced apoptosis of osteosarcoma cells in a dose- and time-dependent manner. Mechanistically, we found that WT161 treatment obviously increased the protein level of PTEN and decreased the phosphorylation level of protein kinase-B (AKT). More importantly, WT161 showed synergistic inhibition with 5-FU on osteosarcoma cells in vitro and in vivo.Conclusions: These results indicate that WT161 inhibits the growth of osteosarcoma through PTEN and has a synergistic efficiency with 5-FU. 相似文献
992.
993.
Lei Su Mengzhou Liu Chengming You Qun Guo Zhongmin Hu Zhongling Yang Guoyong Li 《Ecology and evolution》2021,11(21):15020
Previous studies have demonstrated changes in plant growth and reproduction in response to nutrient availability, but responses of plant growth and reproduction to multiple levels of nutrient enrichment remain unclear. In this study, a factorial field experiment was performed with manipulation of nitrogen (N) and phosphorus (P) availability to examine seed production of the dominant species, Stipa krylovii, in response to N and P addition in a temperate steppe. There were three levels of N and P addition in this experiment, including no N addition (0 g N m−2 year−1), low N addition (10 g N m−2 year−1), and high N addition (40 g N m−2 year−1) for N addition treatment, and no P addition (0 g P m−2 year−1), low P addition (5 g P m−2 year−1), and high P addition (10 g P m−2 year−1) for P addition treatment. Low N addition enhanced seed production by 814%, 1371%, and 1321% under ambient, low, and high P addition levels, respectively. High N addition increased seed production by 2136%, 3560%, and 3550% under ambient, low, and high P addition levels, respectively. However, P addition did not affect seed production in the absence of N addition, but enhanced it under N addition. N addition enhanced seed production mainly by increasing the tiller number and inflorescence abundance per plant, whereas P addition stimulated it by decreasing the plant density yet stimulating height of plants and their seed number per inflorescence. Our results indicate seed production is not limited by P availability but rather by N availability in the temperate steppe, whereas seed production will be increased by P addition when N availability is improved. These findings enable a better understanding of plant reproduction dynamics in the temperate steppe under intensified nutrient enrichment and can inform their improved management in the future. 相似文献
994.
Lijun Gao Hongfang Wang Zhenguo Liu Shuchang Liu Guangdong Zhao Baohua Xu Xingqi Guo 《Cell stress & chaperones》2017,22(6):867-877
Serine proteinases play important roles in innate immunity and insect development. We isolated a serine proteinase gene, designated AccSp10, from the Chinese honeybees (Apis cerana cerana). RT-qPCR and a Western blot analysis at different pupal development stages indicated that AccSp10 might be involved in melanin formation in pupae and promote pupal development. In adult workers, the expression of AccSp10 was upregulated by treatments mimicking harmful environments such as the presence of Bacillus bombysepticus, different temperatures (4, 24 and 42 °C), HgCl2, H2O2 and paraquat; the exception was treatment with VC (vitamin C), which did not upregulate AccSp10 expression. Western blot confirmed the results. A disc diffusion assay indicated that recombinant AccSp10 accelerated E. coli cell death during stimulation with harmful substances (HgCl2, paraquat and cumene hydroperoxide). These findings suggest that AccSp10 may be involved in the pupal development of Chinese honeybees and protection against microorganisms and abiotic harms. 相似文献
995.
Peng Xu Jin Gao Zhibin Cao Peng W. Chee Qi Guo Zhenzhen Xu Andrew H. Paterson Xianggui Zhang Xinlian Shen 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2017,130(6):1309-1319
Key message
A fiber length QTL, qFL-chr1, was fine mapped to a 0.9 cM interval of cotton chromosome 1. Two positional candidate genes showed positive correlation between gene expression level and fiber length.Abstract
Prior analysis of a backcross-self mapping population derived from a cross between Gossypium hirsutum L. and G. barbadense L. revealed a QTL on chromosome 1 associated with increased fiber length (qFL-chr1), which was confirmed in three independent populations of near-isogenic introgression lines (NIILs). Here, a single NIIL, R01-40-08, was used to develop a large population segregating for the target region. Twenty-two PCR-based polymorphic markers used to genotype 1672 BC4F2 plants identified 432 recombinants containing breakpoints in the target region. Substitution mapping using 141 informative recombinants narrowed the position of qFL-chr1 to a 1.0-cM interval between SSR markers MUSS084 and CIR018. To exclude possible effects of non-target introgressions on fiber length, different heterozygous BC4F3 plants introgressed between SSR markers NAU3384 and CGR5144 were selected to develop sub-NILs. The qFL-chr1 was further mapped at 0.9-cM interval between MUSS422 and CIR018 by comparisons of sub-NIL phenotype, and increased fiber length by ~1 mm. The 2.38-Mb region between MUSS422 and CIR018 in G. barbadense contained 19 annotated genes. Expression levels of two of these genes, GOBAR07705 (encoding 1-aminocyclopropane-1-carboxylate synthase) and GOBAR25992 (encoding amino acid permease), were positively correlated with fiber length in a small F2 population, supporting these genes as candidates for qFL-chr1.996.
Hypoxic preconditioning‐induced autophagy enhances survival of engrafted endothelial progenitor cells in ischaemic limb 下载免费PDF全文
Pei Zhou Yu‐zhen Tan Hai‐jie Wang Guo‐dong Wang 《Journal of cellular and molecular medicine》2017,21(10):2452-2464
Recent clinical studies have suggested that endothelial progenitor cells (EPCs) transplantation provides a modest benefit for treatment of the ischaemic diseases such as limb ischaemia. However, cell‐based therapies have been limited by poor survival of the engrafted cells. This investigation was designed to establish optimal hypoxia preconditioning and evaluate effects of hypoxic preconditioning‐induced autophagy on survival of the engrafted EPCs. Autophagy of CD34+VEGFR‐2+ EPCs isolated from rat bone marrow increased after treatment with 1% O2. The number of the apoptotic cells in the hypoxic cells increased significantly after autophagy was inhibited with 3‐methyladenine. According to balance of autophagy and apoptosis, treatment with 1% O2 for 2 hrs was determined as optimal preconditioning for EPC transplantation. To examine survival of the hypoxic cells, the cells were implanted into the ischaemic pouch of the abdominal wall in rats. The number of the survived cells was greater in the hypoxic group. After the cells loaded with fibrin were transplanted with intramuscular injection, blood perfusion, arteriogenesis and angiogenesis in the ischaemic hindlimb were analysed with laser Doppler‐based perfusion measurement, angiogram and the density of the microvessels in histological sections, respectively. Repair of the ischaemic tissue was improved significantly in the hypoxic preconditioning group. Loading the cells with fibrin has cytoprotective effect on survival of the engrafted cells. These results suggest that activation of autophagy with hypoxic preconditioning is an optimizing strategy for EPC therapy of limb ischaemia. 相似文献
997.
Structural analysis of the N- and C-termini in a peptide with consensus sequence. 总被引:1,自引:2,他引:1 下载免费PDF全文
Y. Gong H. X. Zhou M. Guo N. R. Kallenbach 《Protein science : a publication of the Protein Society》1995,4(8):1446-1456
We present a structural analysis of a peptide, the sequence of which includes amino acids that show preferences for specific positions near the N- and C-termini in protein helices. This peptide has the sequence ac-YMSEDELKAAEAAFKRHGVP-amide, which includes a strong version of an N-terminal Harper-Rose capping box structure as well as a Gly located close to the C-terminus designed to elucidate its role in C-terminal capping. The sequence of five residues at the middle is inserted to separate effects at the two ends via a helix-stabilizing linker. Application of a simulated annealing procedure using interproton distance constraints derived from 1H NOESY experiments in water reveals the presence of a C-terminal structure in this model. The C-terminus forms a folded back structure in a significant fraction of structures generated by the annealing, in most of which Gly assumes an alpha L conformation. This structure occurs within a highly flexible region of the molecule and hence is occupied only a fraction of the time. 相似文献
998.
人脑神经元特异性烯醇化酶的纯化方法 总被引:1,自引:0,他引:1
采用改良的Grace层析方法,经一次DEAE-Sephadex A50柱层析即从人脑中纯化了神经元特异性烯醇化酶,比活力为92.1U/mg,纯化倍数为59.4.该酶纯化后,经SDS-聚丙烯酰胺凝胶电泳鉴定为单一蛋白质谱带.此外,还测定了其部分理化性质,其亚单位分子量为45000,等电点pI为4.7,氨基酸组成分析表明其为一种酸性蛋白质;对2-磷酸甘油酸的Km值为5.6×10-4mol/L. 相似文献
999.
外域杂草的产生、传播及生物与生态学特性的分析 总被引:28,自引:4,他引:28
本文分析了浙江省境内较近期传入的外域杂草区系成分,介绍了我国一些常见外域杂草的产生及传播特点,并通过对北美车前(Plantagovirginica)繁殖机制,种群生态、分布及危害特点等方面的研究.阐述了外域杂草所具的生物与生态学特性. 相似文献
1000.
研制了依赖于鲁米诺化学发光反应和固定化尿酸酶柱的测定血清尿酸的生物传感器。其测定血清样品响应时间47s。测定每份样品需时1.5min,样品体积17μl。工作曲线的线性范围1~20mg/dl。批内不精密度3.22%~4.36%,批间6.18%~7.8%。测定值回收率为93%~109%。与医院常规酶试剂盘方法比较相关系数r=0.9909。固定化尿酸酶柱室温使用,4℃冰箱保存,连续使用5个半月测定样品2000次以上,仍保持原酶柱活力的94%。 相似文献