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   13512篇
  免费   1041篇
  国内免费   856篇
  15409篇
  2024年   29篇
  2023年   138篇
  2022年   332篇
  2021年   601篇
  2020年   371篇
  2019年   485篇
  2018年   429篇
  2017年   334篇
  2016年   493篇
  2015年   824篇
  2014年   882篇
  2013年   1052篇
  2012年   1224篇
  2011年   1053篇
  2010年   642篇
  2009年   575篇
  2008年   792篇
  2007年   609篇
  2006年   616篇
  2005年   492篇
  2004年   419篇
  2003年   352篇
  2002年   291篇
  2001年   271篇
  2000年   222篇
  1999年   218篇
  1998年   155篇
  1997年   126篇
  1996年   136篇
  1995年   129篇
  1994年   115篇
  1993年   94篇
  1992年   134篇
  1991年   117篇
  1990年   81篇
  1989年   102篇
  1988年   60篇
  1987年   48篇
  1986年   58篇
  1985年   64篇
  1984年   18篇
  1983年   24篇
  1982年   28篇
  1981年   12篇
  1980年   25篇
  1979年   20篇
  1978年   16篇
  1977年   19篇
  1974年   9篇
  1972年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Oral squamous cell carcinoma (OSCC) is an oral and maxillofacial malignancy that exhibits high incidence worldwide. In diverse human cancers, the long non‐coding RNA (lncRNA) highly up‐regulated in liver cancer (HULC) is aberrantly expressed, but how HULC affects OSCC development and progression has remained mostly unknown. We report that HULC was abnormally up‐regulated in oral cancer tissues and OSCC cell lines, and that suppression of HULC expression in OSCC cells not only inhibited the proliferation, drug tolerance, migration and invasion of the cancer cells, but also increased their apoptosis rate. Notably, in a mouse xenograft model, HULC depletion reduced tumorigenicity and inhibited the epithelial‐to‐mesenchymal transition process. Collectively, our findings reveal a crucial role of the lncRNA HULC in regulating oral cancer carcinogenesis and tumour progression, and thus suggest that HULC could serve as a novel therapeutic target for OSCC.  相似文献   
63.
One of the several factors that contribute to the low efficiency of mammalian somatic cloning is poor fusion between the small somatic donor cell and the large recipient oocyte. This study was designed to test phytohemagglutinin (PHA) agglutination activity on fusion rate, and subsequent developmental potential of cloned bovine embryos. The toxicity of PHA was established by examining its effects on the development of parthenogenetic bovine oocytes treated with different doses (Experiment 1), and for different durations (Experiment 2). The effective dose and duration of PHA treatment (150 microg/mL, 20 min incubation) was selected and used to compare membrane fusion efficiency and embryo development following somatic cell nuclear transfer (Experiment 3). Cloning with somatic donor fibroblasts versus cumulus cells was also compared, both with and without PHA treatment (150 microg/mL, 20 min). Fusion rate of nuclear donor fibroblasts, after phytohemagglutinin treatment, was increased from 33 to 61% (P < 0.05), and from 59 to 88% (P < 0.05) with cumulus cell nuclear donors. The nuclear transfer (NT) efficiency per oocyte used was improved following PHA treatment, for both fibroblast (13% versus 22%) as well as cumulus cells (17% versus 34%; P < 0.05). The cloned embryos, both with and without PHA treatment, were subjected to vitrification and embryo transfer testing, and resulted in similar survival (approximately 90% hatching) and pregnancy rates (17-25%). Three calves were born following vitrification and embryo transfer of these embryos; two from the PHA-treated group, and one from non-PHA control group. We concluded that PHA treatment significantly improved the fusion efficiency of somatic NT in cattle, and therefore, increased the development of cloned blastocysts. Furthermore, within a determined range of dose and duration, PHA had no detrimental effect on embryo survival post-vitrification, nor on pregnancy or calving rates following embryo transfer.  相似文献   
64.
选育出两株利用葡萄糖废母液生产酒精的菌株S_(995)和S_8。S_(095)用于70%母液和30%糖蜜混合连续酒精发酵,醪液中酒精份平均可达10.1%。S_8用于50%、70%母液和50%、30%玉米糖化醪混合生产酒精,醪液中酒精份可达12.37%(实验室数据)和10%(实际生产数据)。  相似文献   
65.
The ubiquitin proteasome system is a potent regulatory mechanism used to control protein stability in numerous cellular processes, including neural development. Many neurodegenerative diseases are featured by the accumulation of UPS-associated proteins, suggesting the UPS dysfunction may be crucial for pathogenesis. Recent experiments have highlighted the UPS as a key player during synaptic development. Here we summarize recent discoveries centered on the role of the UPS in synapse remodeling and draw attention to the potential link between the synaptic UPS dysfunction and the pathology of neurodegenerative diseases.  相似文献   
66.
Filamin-A cross-links actin filaments into dynamic orthogonal networks, and interacts with an array of proteins of diverse cellular functions. Because several filamin-A interaction partners are implicated in signaling of cell mobility regulation, we tested the hypothesis that filamin-A plays a role in cancer metastasis. Using four pairs of filamin-A proficient and deficient isogenic cell lines, we found that filamin-A deficiency in cancer cells significantly reduces their migration and invasion. Using a xenograft tumor model with subcutaneous and intracardiac injections of tumor cells, we found that the filamin-A deficiency causes significant reduction of lung, splenic and systemic metastasis in nude mice. We evaluated the expression of filamin-A in breast cancer tissues by immunohistochemical staining, and found that low levels of filamin-A expression in cancer cells of the tumor tissues are associated with a better distant metastasis-free survival than those with normal levels of filamin-A. These data not only validate filamin-A as a prognostic marker for cancer metastasis, but also suggest that inhibition of filamin-A in cancer cells may reduce metastasis and that filamin-A can be used as a therapeutic target for filamin-A positive cancer.  相似文献   
67.
Lipoxygenases (LOXs) are enzymes involved in lipid peroxidation. Here we reported the identification, molecular and functional characterization of the gene encoding rice (Oryza sativa L.) seed LOX3 (sLOX3). Via a map-based cloning strategy we identified Os03g0700400 as the candidate gene encoding sLOX3. Further functional complementary test and biochemical characterization of the recombinant Os03g0700400 protein verified the identification. The sLOX3 gene was highly expressed in roots, moderately in embryos and very weakly in leaves, leaf sheaths and stems. Transient expression experiment (in rice protoplasts) and subsequent laser confocal microscopic analysis demonstrated that the sLOX3 protein was localized into the cytosol. We next showed that overexpression of sLOX3 in a japonica sLOX3-normal rice cultivar, Wuyunjing 7 accelerated the decrease of seed germination ability when the seeds were routinely stored, which demonstrated that sLOX3 had a negative effect on seed longevity (storability). Meanwhile, an increased occurrence of embryo decay was observed in the same transgenic seeds, suggesting that sLOX3 might negatively affect seed longevity by facilitating colonization of particular seed pathogens. Our result forwarded the understanding of the effects of 9-LOX on rice seed longevity.  相似文献   
68.
Microbes are key components of the soil environment, playing an important role in maintaining soil health, sustainability, and productivity. The composition and structure of soil bacterial communities were examined in winter wheat–rice (WR) and winter wheat–maize (WM) cropping systems derived from five locations in the Low-Middle Yangtze River plain and the Huang-Huai-Hai plain by pyrosequencing of the 16S ribosomal RNA gene amplicons. A total of 102,367 high quality sequences were used for multivariate statistical analysis and to test for correlation between community structure and environmental variables such as crop rotations, soil properties, and locations. The most abundant phyla across all soil samples were Proteobacteria, Acidobacteria, and Bacteroidetes. Similar patterns of bacterial diversity and community structure were observed within the same cropping systems, and a higher relative abundance of anaerobic bacteria was found in WR compared to WM cropping systems. Variance partitioning analysis revealed complex relationships between bacterial community and environmental variables. The effect of crop rotations was low but significant, and interactions among soil properties, locations, and crop rotations accounted for most of the explained variation in the structure of bacterial communities. Soil properties such as pH, available P, and available K showed higher correlations (positive or negative) with the majority of the abundant taxa. Bacterial diversity (the Shannon index) and richness (Chao1 and ACE) were higher under WR than WM cropping systems.  相似文献   
69.
Human serum albumin (HSA) and human parathyroid hormone (1-34) [PTH (1-34)] fusion protein [HSA/PTH (1-34)] is a promising long-acting form of PTH (1-34) for osteoporosis treatment. Secretory expression of intact HSA/PTH (1-34) in Pichia pastoris GS115 was accompanied by two degradation fragments, with molecular weights around 66 kDa, in addition to the well-known ~45 kDa HSA-truncated fragment, resulting in a low yield of intact protein. In this study, two internal cleavage sites were identified in the PTH (1-34) portion of the fusion protein by Western Blot analysis. To minimize proteolytic cleavages, several protease genes including PEP4 (encoding proteinase A), PRB1 (proteinase B) and seven YPSs genes (yapsin family members) were knocked out respectively by disruption of the individual genes and the selective combinations. Reduced degradation was observed by single disruption of either PEP4 gene or YPS1 gene, and the lowest level of degradation was observed in a pep4yps1△ double disruptant. After 72 h of induction, more than 80 % of the HSA/PTH (1-34) secreted by the pep4yps1△ double disruptant remained intact, in comparison to only 30 % with the wild-type strain.  相似文献   
70.
Shen CI  Wang CH  Shen SC  Lee HC  Liao JW  Su HL 《PloS one》2011,6(5):e18894
Sialic acids (SAs) linked to galactose (Gal) in α2,3- and α2,6-configurations are the receptors for avian and human influenza viruses, respectively. We demonstrate that chicken tracheal ciliated cells express α2,3-linked SA, while goblet cells mainly express α2,6-linked SA. In addition, the plant lectin MAL-II, but not MAA/MAL-I, is bound to the surface of goblet cells, suggesting that SA2,3-linked oligosaccharides with Galβ1-3GalNAc subterminal residues are specifically present on the goblet cells. Moreover, both α2,3- and α2,6-linked SAs are detected on single tracheal basal cells. At a low multiplicity of infection (MOI) avian influenza virus H6N1 is exclusively detected in the ciliated cells, suggesting that the ciliated cell is the major target cell of the H6N1 virus. At a MOI of 1, ciliated, goblet and basal cells are all permissive to the AIV infection. This result clearly elucidates the receptor distribution for the avian influenza virus among chicken tracheal epithelial cells and illustrates a primary cell model for evaluating the cell tropisms of respiratory viruses in poultry.  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