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   14359篇
  免费   743篇
  国内免费   4篇
  2021年   78篇
  2020年   65篇
  2019年   90篇
  2018年   144篇
  2017年   154篇
  2016年   252篇
  2015年   394篇
  2014年   453篇
  2013年   1175篇
  2012年   803篇
  2011年   852篇
  2010年   504篇
  2009年   477篇
  2008年   806篇
  2007年   893篇
  2006年   892篇
  2005年   918篇
  2004年   994篇
  2003年   925篇
  2002年   888篇
  2001年   169篇
  2000年   128篇
  1999年   167篇
  1998年   217篇
  1997年   206篇
  1996年   162篇
  1995年   150篇
  1994年   117篇
  1993年   157篇
  1992年   142篇
  1991年   113篇
  1990年   103篇
  1989年   104篇
  1988年   96篇
  1987年   73篇
  1986年   83篇
  1985年   100篇
  1984年   107篇
  1983年   94篇
  1982年   111篇
  1981年   99篇
  1980年   91篇
  1979年   52篇
  1978年   54篇
  1977年   45篇
  1976年   55篇
  1975年   33篇
  1974年   43篇
  1973年   44篇
  1972年   30篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
An excess of cholesterol and/or oxysterols induces apoptosis in macrophages, contributing to the development of advanced atherosclerotic lesions. In foam cells, these sterols are stored in esterified forms, which are hydrolyzed by two enzymes: neutral cholesterol ester hydrolase 1 (Nceh1) and hormone-sensitive lipase (Lipe). A deficiency in either enzyme leads to accelerated growth of atherosclerotic lesions in mice. However, it is poorly understood how the esterification and hydrolysis of sterols are linked to apoptosis. Remarkably, Nceh1-deficient thioglycollate-elicited peritoneal macrophages (TGEMs), but not Lipe-deficient TGEMs, were more susceptible to apoptosis induced by oxysterols, particularly 25-hydroxycholesterol (25-HC), and incubation with 25-HC caused massive accumulation of 25-HC ester in the endoplasmic reticulum (ER) due to its defective hydrolysis, thereby activating ER stress signaling such as induction of CCAAT/enhancer-binding protein-homologous protein (CHOP). These changes were nearly reversed by inhibition of ACAT1. In conclusion, deficiency of Nceh1 augments 25-HC-induced ER stress and subsequent apoptosis in TGEMs. In addition to reducing the cholesteryl ester content of foam cells, Nceh1 may protect against the pro-apoptotic effect of oxysterols and modulate the development of atherosclerosis.  相似文献   
2.
Epstein-Barr virus (EBV) is a gammaherpesvirus, associated with infectious mononucleosis and various types of malignancy. We focused here on the BDLF4 gene of EBV and identified it as a lytic gene, expressed with early kinetics. Viral late gene expression of the BDLF4 knockout strain was severely restricted; this could be restored by an exogenous supply of BDLF4. These results indicate that BDLF4 is important for the EBV lytic replication cycle, especially in late gene expression.  相似文献   
3.
ADP-ribosylation factor (Arf) 1 is thought to affect the morphologies of organelles, such as the Golgi apparatus, and regulate protein trafficking pathways. Mice have six Arf isoforms. In knockdown experiments with HeLa cells, no single Arf isoform among Arf1–5 is required for organelle morphologies or any membrane trafficking step. This suggests that the cooperation of two or more Arfs is a general feature. Although many cell biological and biochemical analyses have proven the importance of Arf1, the physiological roles of Arf1 in mice remain unknown. To investigate the activity of Arf1 in vivo, we established Arf1-deficient mice. Arf−/− blastocysts were identified at the expected Mendelian ratio. The appearance of these blastocysts was indistinguishable from that of wild-type and Arf+/− blastocysts, and they grew normally in an in vitro culture system. However, Arf−/− embryos were degenerated at E5.5, and none survived to E12.5, suggesting that they died soon after implantation. These data establish for the first time that the Arf1 gene is indispensable for mouse embryonic development after implantation.  相似文献   
4.
5.
Homologous recombination technologies enable high-throughput cloning and the seamless insertion of any DNA fragment into expression vectors. Additionally, retroviral vectors offer a fast and efficient method for transducing and expressing genes in mammalian cells, including lymphocytes. However, homologous recombination cannot be used to insert DNA fragments into retroviral vectors; retroviral vectors contain two homologous regions, the 5′- and 3′-long terminal repeats, between which homologous recombination occurs preferentially. In this study, we have modified a retroviral vector to enable the cloning of DNA fragments through homologous recombination. To this end, we inserted a bacterial selection marker in a region adjacent to the gene insertion site. We used the modified retroviral vector and homologous recombination to clone T-cell receptors (TCRs) from single Epstein Barr virus-specific human T cells in a high-throughput and comprehensive manner and to efficiently evaluate their function by transducing the TCRs into a murine T-cell line through retroviral infection. In conclusion, the modified retroviral vectors, in combination with the homologous recombination method, are powerful tools for the high-throughput cloning of cDNAs and their efficient functional analysis.  相似文献   
6.
Lipid nanoparticles (LNP) modified with cell-penetrating peptides (CPP) were prepared for the delivery of small interfering RNA (siRNA) into cells. Lipid derivatives of CPP derived from protamine were newly synthesized and used to prepare CPP-decorated LNP (CPP-LNP). Encapsulation of siRNA into CPP-LNP improved the stability of the siRNA in serum. Fluorescence-labeled siRNA formulated in CPP-LNP was efficiently internalized into B16F10 murine melanoma cells in a time-dependent manner, although that in LNP without CPP was hardly internalized into these cells. In cells transfected with siRNA in CPP-LNP, most of the siRNA was distributed in the cytoplasm of these cells and did not localize in the lysosomes. Analysis of the endocytotic pathway indicated that CPP-LNP were mainly internalized via macropinocytosis and heparan sulfate-mediated endocytosis. CPP-LNP encapsulating siRNA effectively induced RNA interference-mediated silencing of reporter genes in B16F10 cells expressing luciferase and in HT1080 human fibrosarcoma cells expressing enhanced green fluorescent protein. These data suggest that modification of LNP with the protamine-derived CPP was effective to facilitate internalization of siRNA in the cytoplasm and thereby to enhance gene silencing.  相似文献   
7.
8.
9.
Epidemiologic studies have shown that low-density lipoprotein cholesterol (LDL-C) is a strong risk factor, whilst high-density lipoprotein cholesterol (HDL-C) reduces the risk of coronary heart disease (CHD). Therefore, strategies to manage dyslipidemia in an effort to prevent or treat CHD have primarily attempted at decreasing LDL-C and raising HDL-C levels. Cholesteryl ester transfer protein (CETP) mediates the exchange of cholesteryl ester for triglycerides between HDL and VLDL and LDL. We have published the first report indicating that a group of Japanese patients who were lacking CETP had extremely high HDL-C levels, low LDL-C levels and a low incidence of CHD. Animal studies, as well as clinical and epidemiologic evidences, have suggested that inhibition of CETP provides an effective strategy to raise HDL-C and reduce LDL-C levels. Four CETP inhibitors have substantially increased HDL-C levels in dyslipidemic patients. This review will discuss the current status and future prospects of CETP inhibitors in the treatment of CHD. At present anacetrapib by Merck and evacetrapib by Eli Lilly are under development. By 100mg of anacetrapib HDL-C increased by 138%, and LDL-C decreased by 40%. Evacetrapib 500 mg also showed dramatic 132% increase of HDL-C, while LDL-C decreased by 40%. If larger, long-term, randomized, clinical end point trials could corroborate other findings in reducing atherosclerosis, CETP inhibitors could have a significant impact in the management of dyslipidemic CHD patients. Inhibition of CETP synthesis by antisense oligonucleotide or small molecules will produce more similar conditions to human CETP deficiency and may be effective in reducing atherosclerosis and cardiovascular events. We are expecting the final data of prospective clinical trials by CETP inhibitors in 2015.  相似文献   
10.
Obesity-related complications are associated with the development of age-related hearing impairment. β-Conglycinin (β-CG), one of the main storage proteins in soy, offers multiple health benefits, including anti-obesity and anti-atherosclerotic effects. Here, to elucidate the potential therapeutic application of β-CG, we investigated the effect of β-CG on age-related hearing impairment. Male wild-type mice (age 6 months) were randomly divided into β-CG-fed and control groups. Six months later, the body weight was significantly lower in β-CG-fed mice than in the controls. Consumption of β-CG rescued the hearing impairment observed in control mice. Cochlear blood flow also increased in β-CG-fed mice, as did the expression of eNOS in the stria vascularis (SV), which protects vasculature. β-CG consumption also ameliorated oxidative status as assessed by 4-HNE staining. In the SV, lipofuscin granules of marginal cells and vacuolar degeneration of microvascular pericytes were decreased in β-CG-fed mice, as shown by transmission electron microscopy. β-CG consumption prevented loss of spiral ganglion cells and reduced the frequencies of lipofuscin granules, nuclear invaginations, and myelin vacuolation. Our observations indicate that β-CG ameliorates age-related hearing impairment by preserving cochlear blood flow and suppressing oxidative stress.  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