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   3308篇
  免费   192篇
  国内免费   119篇
耳鼻咽喉   49篇
儿科学   52篇
妇产科学   25篇
基础医学   397篇
口腔科学   75篇
临床医学   304篇
内科学   649篇
皮肤病学   38篇
神经病学   76篇
特种医学   134篇
外科学   122篇
综合类   565篇
现状与发展   1篇
预防医学   198篇
眼科学   21篇
药学   411篇
中国医学   146篇
肿瘤学   356篇
  2023年   17篇
  2022年   53篇
  2021年   44篇
  2020年   38篇
  2019年   89篇
  2018年   82篇
  2017年   59篇
  2016年   53篇
  2015年   67篇
  2014年   234篇
  2013年   156篇
  2012年   129篇
  2011年   167篇
  2010年   134篇
  2009年   172篇
  2008年   242篇
  2007年   300篇
  2006年   166篇
  2005年   198篇
  2004年   167篇
  2003年   143篇
  2002年   98篇
  2001年   88篇
  2000年   89篇
  1999年   102篇
  1998年   63篇
  1997年   49篇
  1996年   63篇
  1995年   26篇
  1994年   31篇
  1993年   31篇
  1992年   29篇
  1991年   29篇
  1990年   16篇
  1989年   19篇
  1988年   17篇
  1987年   9篇
  1986年   10篇
  1985年   17篇
  1984年   24篇
  1983年   17篇
  1982年   10篇
  1981年   17篇
  1980年   6篇
  1979年   9篇
  1978年   9篇
  1977年   7篇
  1976年   6篇
  1975年   10篇
  1974年   5篇
排序方式: 共有3619条查询结果,搜索用时 15 毫秒
51.
Summary In a phase I study a cytotoxic activity in the serum of a tumor patient given infusions of synthetic alkyl-lysophospholipid has been demonstrated. Serum samples collected after ALP infusions inhibited 3H-thymidine incorporation by human leukemic cells to an extent that correlated to the dose of ALP administered. Serum taken after the highest dose of ALP given (50 mg/kg body weight) led to complete cell destruction after 72 h in vitro. Whereas cells from the HL60 line were very sensitive to the serum cytotoxicity, K562 cells were much less affected. Cytotoxic activity was found to be cleared from the circulation in a biphasic manner; more than 50% disappeared within 6–8 h but 20–30% was still present after 4 days.Supported by DFG An 111/2  相似文献   
52.
Granulocyte colony-stimulating factor (G-CSF)-induced alteration of phosphoprotein during differentiation of HL-60 cells was studied. From the two-dimensional gel electrophoresis analysis of phosphoproteins, a 45 kD phosphoprotein in the cytosolic fraction of DMSO-pretreated HL-60 cells was rapidly dephosphorylated by the addition of G-CSF. This 45 kD phosphoprotein migrated into four or five spots between 4.5 and 5.5 pI. The dephosphorylation of 45 kD protein was observed within at least 10 min and reached a maximum at 60 min. Phosphoamino acid analysis showed that only serine residue of 45 kD phosphoprotein was phosphorylated, suggesting that G-CSF induced an activation of serine phosphatase. Furthermore, Staurosporine and calphostin C inhibited the phosphorylation of 45 kD protein, suggesting that protein kinase C or its downstream kinase(s) is involved in the phosphorylation of 45 kD protein. These results indicate that G-CSF causes dephosphorylation of a 45 kD cytosolic phosphoprotein which may play a role in signal transduction of G-CSF.  相似文献   
53.
ABSTRACT: The low level of amphotropic retrovirus mediated gene transfer into human hematopoietic stem cells (HSC) has been an impediment to gene therapy for hematopoietic diseases (1). We have previously shown that mouse and human HSC have low levels of the mRNA encoding PiT-2, the amphotropic retrovirus receptor. We hypothesized that the low level of PiT-2 mRNA was responsible for the low frequency of transduction of HSC by amphotropic retroviral vectors (2). In this study we compared the level of PiT-2 and PiT-1, the Gibbon Ape Leukemia Virus receptor (GaLV), in 5 human tissue culture cell lines. PiT-2 and PiT-1 mRNA levels were highest in K562 cells and lowest in HL60 cells. In hematopoietic cell lines, the level of PiT-2 or PiT-1 mRNA correlated directly with retrovirus binding and transduction with the appropriate (amphotropic or GaLV) retrovirus vector. The level of expression of PiT-2 and PiT-1 mRNA could be increased by treatment of HL60 cells with either PMA or Interleukin-1α. The increase in the level of PiT-2 and PiT-1 mRNA correlated with increased transduction with both amphotropic and GaLV retroviral vectors. We conclude that the improved transduction was a direct effect of the increased levels of receptor mRNA and unrelated to changes in the cell cycle status.  相似文献   
54.
Summary. In an attempt to mimic clinical conditions for the treatment of leukaemia, the HL60 promyelocytic cell line was treated for 18 h with low, clinically relevant, levels of the anthracycline epirubicin and the Vinca alkaloid vinblastine. The resulting drug-resistant sublines not only expressed P-glycoprotein and the MDR phenotype but were also cross-resistant to chlorambucil, methotrexate but were also cross-resistant to chlorambucil, methotrexate and cisplatinum, and had increased resistance to radiation. Development of resistance was associatted with an aberrant differentiation phenotype with decreased expression of myeloid antigens and expression of glycophorin A. an antigen normally associated with erythroid differentiation. The ability of HL60 cells to terminally differentiate in response to all- trans -retinoic acid (vitamin A acid) was lost in the sublines. These results suggest that either a single novel mechanism is responsible for multiple drug resistance or the initial response to drug treatment is the co-induction of multiple mechanisms. These cells and the method by which they were generated therefore provide a clinically relevant model for the study of the initial events in the development of not only multidrug resistance but also the extended multiple drug resistance usually encountered in the treatment of leukaemia.  相似文献   
55.
目的 探讨 1,6-二磷酸果糖 (FDP)减轻体外循环 (CPB)术后全身炎症反应的临床效果。方法 将 3 8例心脏直视手术患者随机分为实验组 2 0例 ,对照组 18例。实验组在常规 CPB预充液中加入 FDP2 0 0 m g/kg,对照组不用 FDP。于手术开始前 (T0 )、 CPB结束后即刻 (T1)、CPB结束后 3小时 (T2 )、 6小时 (T3)及 2 4小时 (T4)分别抽取桡动脉血 ,采用 EL ISA法测定血浆肿瘤坏死因子 (TNF-α)、白介素 -6(IL-6)、白介素 -8(IL-8) ,用硫代巴比妥酸比色法测定血浆丙二醛 (MDA)。结果 两组术前血浆 TNF-α、IL-6、IL-8、MDA浓度无差异 ,CPB结束后均已明显升高 (P <0 .0 5) ,CPB后 3小时 TNF-α、 IL -6、 IL -8达高峰 ,6小时开始下降 ,MDA在 6小时达高峰 ,2 4小时 TNF-α、 MDA恢复到接近术前水平 (P >0 .0 5) ,IL -6、 IL -8仍高于术前 (P <0 .0 5)。实验组血浆 TNF-α、 IL -6、 IL -8浓度在 T1、 T2 、 T3均明显低于对照组 (P <0 .0 1) ,MDA浓度在 T1、 T2 (P <0 .0 5)和 T3 (P <0 .0 1)均明显低于对照组 ,血浆 IL -6、 IL -8在 T4也均低于对照组 (P <0 .0 1,P <0 .0 5)。结论  CPB术后血浆 TNF-α、IL-6、IL-8、MDA浓度明显升高 ,在 CPB预充液中加入 FDP可明显降低 CPB术后TNF-α、 IL-6、 IL-8及 MDA的浓度 ,  相似文献   
56.
BACKGROUND: Patent foramen ovale (PFO) with or without atrial septal aneurysm (ASA) is highly associated with cerebral ischemic events in young patients. The prevalence of PFO and ASA in elderly patients with cerebral ischemic events is not well described. OBJECTIVE: Our study is to evaluate the frequencies of PFO with right-to-left shunt (RLS) and ASA in elderly patients and to determine whether age is a predictor of flow-reversed PFO with RLS in cerebral ischemic events. METHODS: A prospective registry for all consecutive patients with cerebral ischemic events who were evaluated by transesophageal echocardiography (TEE) for the detection of possible cardiac source of embolization was established and maintained in a university hospital. Patients' demographics including age, gender, ethnic origin, cerebrovascular risk factors, and all positive TEE data were collected from July 2000 to August 2001 for statistical analysis. A univariate and multivariate stepwise logistic regression analysis was performed. RESULTS: In older patients the prevalence of PFO with RLS, PFO, and ASA was 25/118 (20%), 28/118 (24%), and 38/118 (32%), respectively, as opposed to younger patients, in whom it was 35/119 (30%), 39/119 (33%), and 38/119 (32%), respectively. Older patients had higher frequencies of hypertension (59; 69%), CAD (25; 21%), and prior history of stroke (23; 20%) as opposed to younger patients. Younger age (<60 years), gender, smoking history, hypertension, hyperlipidemia, CAD, and prior history of stroke were not associated with higher prevalence of PFO with RLS. Patent foramen ovale was associated with ASA (P < 0.001) and LVH (P < 0.019) in patients with TIA and stroke. In multivariate analysis only ASA (P < 0.001) remained significant with PFO, with RLS controlling for age, gender, and LVH. CONCLUSIONS: PFO with RLS and ASA are frequently present in elderly stroke and/or TIA patients and age is not a predictor for PFO. Transesophageal echocardiography should be considered for all stroke and/or TIA patients irrespective of their age.  相似文献   
57.
The endothelium of the vessel wall as a barrier between blood and the subendothelial matrix proteins is essential for preventing thrombus formation and subsequent atherosclerosis development. Atherosclerosis is an inflammatory disease in which immune and autoimmune mechanisms are involved. Recently, it was demonstrated that endothelial cells in the vessel wall can be damaged not only by classic risk factors, such as hyperlipidemia, smoking and disturbed blood flow, but also (auto)immune reactions to autoantigens present in the cell surface, among which heat shock protein 60 (HSP60) was mostly studied. HSP60 normally located in mitochondria can be translocated into the cell member in response to stress stimuli. Meanwhile, autoantibodies against HSP60 are present in most subjects, especially patients with heart attack and stroke. These autoantibodies may bind to HSP60 expressed in endothelial cells resulting in the cell damage, subsequently initiating the formation of atherosclerotic lesions. Based on the recent progress in the research field, the present review will update the mechanisms of immune response to endothelial cells by which cell damage can initiate the development of atherosclerosis.  相似文献   
58.
Mineo TC  Ambrogi V  Mineo D  Fabbri A  Fabbrini E  Massoud R 《Chest》2005,127(6):1960-1966
BACKGROUND: In patients with severe emphysema, bone mineral density (BMD) is reduced and the risk of osteoporosis is increased. STUDY OBJECTIVES: To identify the impact of lung volume reduction surgery on BMD. DESIGN: Prospective cohort study. SETTING: University hospital. PATIENTS AND INTERVENTIONS: Forty emphysematous patients, all receiving oral steroid therapy, underwent bilateral lung volume reduction surgery. Thirty similar patients, who refused the operation, followed a standard respiratory rehabilitation program. MEASUREMENTS: All subjects were evaluated pretreatment and 12 months posttreatment for respiratory function, nutritional status, and bone-related biochemical parameters. BMD was assessed by dual-energy radiograph absorptiometry. RESULTS: After surgery, we observed significant improvements in respiratory function (FEV1, + 18.8% [p < 0.01]; residual volume [RV], -29.6% [p < 0.001]; diffusing capacity of the lung for carbon monoxide [Dlco], + 21.6% [p < 0.01]) nutritional parameters (fat-free mass, + 6.0% [p < 0.01]), levels of bone-related hormones (free-testosterone, + 20.5% [p < 0.01]; parathormone, -11.2% [p < 0.01]), bone turnover markers (osteocalcin, -12.7% [p < 0.05]; bone-alkaline-phosphatase, -14.0% [p < 0.05]; beta-crosslaps, -33.6% [p < 0.001]), BMD (lumbar, + 8.8% [p < 0.01]; femoral, + 5.5% [p < 0.01]), and T-score (lumbar, + 21.0% [p < 0.01]; femoral, + 12.4% [p < 0.01]) with reduction in osteoporosis rate (50 to 25%). Nineteen patients who had undergone surgery were able to discontinue treatment with oral steroids. These subjects showed a more significant improvement in BMD (lumbar, + 9.6%; femoral, + 6.8%; p < 0.001) and T-score (lumbar, + 27.3%; femoral, + 14.3%; p < 0.001). The remaining 21 patients who had undergone surgery experienced significant improvement compared to respiratory rehabilitation subjects despite continued therapy with oral steroids (BMD: lumbar, + 4.5% vs -0.7%, respectively [p < 0.01]; femoral, + 2.7% vs -1.1%, respectively [p < 0.05]; T-score: lumbar, + 14 vs -2.1, respectively [p < 0.01]; femoral, + 7.4 vs -2.7, respectively [p < 0.01]). The increase in lumbar BMD was correlated with the surgical reduction of RV (p = 0.02) and with the increase in Dlco (p = 0.01) and fat-free mass (p = 0.01). CONCLUSIONS: Lung volume reduction surgery significantly improves BMD compared to respiratory rehabilitation therapy, even in patients requiring oral steroids. The increase in BMD correlates with RV, Dlco, and fat-free mass, suggesting that the restoration of respiratory dynamics, gas exchange, and nutritional status induces improvement in bone metabolism and mineral content.  相似文献   
59.
60.
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