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   46774篇
  免费   3631篇
  国内免费   3228篇
  2024年   104篇
  2023年   518篇
  2022年   1215篇
  2021年   2007篇
  2020年   1450篇
  2019年   1801篇
  2018年   1841篇
  2017年   1372篇
  2016年   2014篇
  2015年   2997篇
  2014年   3422篇
  2013年   3654篇
  2012年   4253篇
  2011年   3834篇
  2010年   2470篇
  2009年   2122篇
  2008年   2605篇
  2007年   2350篇
  2006年   2045篇
  2005年   1829篇
  2004年   1563篇
  2003年   1405篇
  2002年   1138篇
  2001年   811篇
  2000年   643篇
  1999年   639篇
  1998年   414篇
  1997年   400篇
  1996年   348篇
  1995年   283篇
  1994年   269篇
  1993年   189篇
  1992年   257篇
  1991年   218篇
  1990年   153篇
  1989年   132篇
  1988年   103篇
  1987年   121篇
  1986年   89篇
  1985年   80篇
  1984年   63篇
  1983年   46篇
  1982年   47篇
  1981年   34篇
  1980年   28篇
  1979年   34篇
  1978年   21篇
  1975年   24篇
  1974年   20篇
  1972年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
The dairy industry is a multi-billion dollar industry catering the nutritional needs of all age groups globally through the supply of milk. Clinical mastitis has a severe impact on udder tissue and is also an animal welfare issue. Moreover, it significantly reduces animal value and milk production. Mammary tissue damage reduces the number and activity of epithelial cells and consequently contributes to decreased milk production. The high incidence, low cure rate of this highly economic and sometimes deadly disease is an alarming for dairy sector as well as policy makers. Bovine mammary epithelial cells (MECs) and their stem cells are very important in milk production and bioengineering. The adult mammary epithelium consists of two main cell types; an inner layer of luminal epithelial cells, which produce the milk during lactation, and an outer layer of myoepithelial cells resting on a basement membrane, which are responsible for pushing the milk through the ductal network to the teat cistern. Inner layer of columner/luminal cells of bovine MECs, is characterized by cytokeratin18, 19 (CK18, CK19) and outer layer such as myoepithelial cells which are characterized by CK14, α-smooth muscle actin (α-SMA) and p63. Much work has been done in mouse and human, on mammary gland stem cell research, particularly in cancer therapy, but stem cell research in bovine is still in its infancy. Such stem/progenitor cell discoveries in human and mouse mammary gland bring some hope for application in bovines. These progenitors may be therapeutically adopted to correct the structural/cytological defects in the bovine udder due to mastitis. In the present review we focused on various kinds of stem/progenitor cells which can have therapeutic utility and their possibilities to use as a potential stem cell therapy in the management of bovine post-mastitis damage in orders to restore milk production. The possibilities of bovine mammary stem cell therapy offers significant potential for regeneration of tissues that can potentially replace/repair diseased and damaged tissue through differentiation into epithelial, myoepithelial and/or cuboidal/columnar cells in the udder with minimal risk of rejection and side effects.  相似文献   
862.
Stroke is a major cause of mortality and the leading cause of permanent disability. In this study, we adopted the classic middle cerebral artery occlusion(MCAO) stroke model to observe the therapeutic effects of coccomyxa gloeobotrydiformis(CGD) on ischemic stroke, and discuss the underlying mechanisms. Low dose (50 mg/kg.day) and high dose (100 mg/kg.day) concentrations of the drug CGD were intragastrically administrated separately for 8 weeks. Infarct volumes, neurologic deficits and degree of stroke-induced brain edema were measured 24 hours after reperfusion. Furthermore, oxidative stress related factors (SOD and MDA), mitochondrial membrane potential, and apoptosis regulatory factors (mitochondrial Cyt-C, Bcl-2, Bax, and caspase-3) were all investigated in this research. We found that CGD attenuated cerebral infarction, brain edema and neurologic deficits; CGD maintained the mitochondrial membrane potential and decreased mitochondrial swelling. It also prevented oxidative damage by reducing MDA and increasing SOD. In addition, CGD could effectively attenuate apoptosis by restoring the level of mitochondrial Cyt C and regulating the expression of Bcl-2, Bax and caspase 3. These results revealed that CGD has a therapeutic effect on ischemic stroke, possibly by inducing mitochondrial protection and anti-apoptotic mechanisms.  相似文献   
863.
The oral and intestinal host tissues both carry a heavy microbial burden. Although commensal bacteria contribute to healthy intestinal tissue structure and function, their contribution to oral health is poorly understood. A crucial component of periodontal health is the recruitment of neutrophils to periodontal tissue. To elucidate this process, gingival tissues of specific‐pathogen‐free and germ‐free wild‐type mice and CXCR2KO and MyD88KO mice were examined for quantitative analysis of neutrophils and CXCR2 chemoattractants (CXCL1, CXCL2). We show that the recruitment ofneutrophils to the gingival tissue does not require commensal bacterial colonization but is entirely dependent on CXCR2 expression. Strikingly, however, commensal bacteria selectively upregulate the expression of CXCL2, but not CXCL1, in a MyD88‐dependent way that correlates with increased neutrophil recruitment as compared with germ‐free conditions. This is the first evidence that the selective use of chemokine receptor ligands contributes to neutrophil homing to healthy periodontal tissue.  相似文献   
864.
Background aimsThe potential protective effects of mesenchymal stromal cells (MSCs) on some kidney diseases has been reported. However, the effect of MSCs on doxorubicin-induced nephropathy is still poorly understood.MethodsRats with doxorubicin-induced kidney injuries were treated with human cord-derived MSCs. Human MSCs were first labeled with 5-bromo-2′-deoxyuridine to track their homing in kidneys after infusion.ResultsAlleviation of proteinuria, decreased serum albumin, alleviation of lipid disorders and histologic alterations were found in rats 4 weeks after treatment with MSCs, particularly in rats that were given repeat doses. Decreases in serum levels of interleukin-6, tumor necrosis factor-α and prostaglandin E2 and decreases in messenger RNA levels of kidney tissue cylooxygenase-2 and EP4 were found in MSC-treated rats. MSC-treated rats also displayed an increase in serum interleukin-10 levels.ConclusionsThese results indicate that MSCs ameliorate doxorubicin-induced kidney injuries and inflammation, suggesting a potential clinical treatment for inflammatory kidney diseases.  相似文献   
865.
Background aimsMany rodent experiments and human studies on stem cell therapy have shown promising therapeutic approaches to liver diseases. We investigated the clinical outcomes of five patients with liver failure of various causes who received autologous CD34-depleted bone marrow-derived mononuclear cell (BM-MNC) transplantation, including mesenchymal stromal cells, through the hepatic artery.MethodsCD34-depleted BM-MNCs were obtained from five patients waiting for liver transplantation by bone marrow aspiration and using the CliniMACS CD34 Reagent System (Miltenyi Biotech, Bergisch Gladbach, Germany), and autologous hepatic artery infusion was performed. The causes of hepatic decompensation were hepatitis B virus (HBV), hepatitis C virus (HCV), propylthiouracil-induced toxic hepatitis and Wilson disease.ResultsSerum albumin levels improved 1 week after transplantation from 2.8 g/dL, 2.4 g/dL, 2.7 g/dL and 1.9 g/dL to 3.3 g/dL, 3.1 g/dL, 2.8 g/dL and 2.6 g/dL. Transient liver elastography data showed some change from 65 kPa, 33 kPa, 34.8 kPa and undetectable to 46.4 kPa, 19.8 kPa, 29.1 kPa and 67.8 kPa at 4 weeks after transplantation in a patient with Wilson disease, a patient with HCV, and two patients with HBV. Ascites decreased in two patients. One of the patients with HBV underwent liver transplantation 4 months after the infusion, and the hepatic progenitor markers (cytokeratin [CD]-7, CD-8, CD-9, CD-18, CD-19, c-Kit and epithelial cell adhesion molecule [EpCAM]) were highly expressed in the explanted liver.ConclusionsSerum albumin levels, liver stiffness, liver volume, subjective healthiness and quality of life improved in the study patients. Although these findings were observed in a small population, the results may suggest a promising future for autologous CD34-depleted BM-MNC transplantation as a bridge to liver transplantation in patients with liver failure.  相似文献   
866.
Detection of somatic variation using sequence from disease-control matched data sets is a critical first step. In many cases including cancer, however, it is hard to isolate pure disease tissue, and the impurity hinders accurate mutation analysis by disrupting overall allele frequencies. Here, we propose a new method, Virmid, that explicitly determines the level of impurity in the sample, and uses it for improved detection of somatic variation. Extensive tests on simulated and real sequencing data from breast cancer and hemimegalencephaly demonstrate the power of our model. A software implementation of our method is available at http://sourceforge.net/projects/virmid/.  相似文献   
867.
Producing gene fusions through genomic structural rearrangements is a major mechanism for tumor evolution. Therefore, accurately detecting gene fusions and the originating rearrangements is of great importance for personalized cancer diagnosis and targeted therapy. We present a tool, BreakTrans, that systematically maps predicted gene fusions to structural rearrangements. Thus, BreakTrans not only validates both types of predictions, but also provides mechanistic interpretations. BreakTrans effectively validates known fusions and discovers novel events in a breast cancer cell line. Applying BreakTrans to 43 breast cancer samples in The Cancer Genome Atlas identifies 90 genomically validated gene fusions. BreakTrans is available at http://bioinformatics.mdanderson.org/main/BreakTrans  相似文献   
868.
869.
870.
Multipotent mesenchymal stem/stromal cells (MSCs) are capable of differentiating into a variety of cell types from different germ layers. However, the molecular and biochemical mechanisms underlying the transdifferentiation of MSCs into specific cell types still need to be elucidated. In this study, we unexpectedly found that treatment of human adipose- and bone marrow-derived MSCs with cyclin-dependent kinase (CDK) inhibitor, in particular CDK4 inhibitor, selectively led to transdifferentiation into neural cells with a high frequency. Specifically, targeted inhibition of CDK4 expression using recombinant adenovial shRNA induced the neural transdifferentiation of human MSCs. However, the inhibition of CDK4 activity attenuated the syngenic differentiation of human adipose-derived MSCs. Importantly, the forced regulation of CDK4 activity showed reciprocal reversibility between neural differentiation and dedifferentiation of human MSCs. Together, these results provide novel molecular evidence underlying the neural transdifferentiation of human MSCs; in addition, CDK4 signaling appears to act as a molecular switch from syngenic differentiation to neural transdifferentiation of human MSCs.  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