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   797篇
  免费   47篇
  国内免费   26篇
耳鼻咽喉   4篇
儿科学   50篇
妇产科学   9篇
基础医学   79篇
口腔科学   48篇
临床医学   76篇
内科学   189篇
皮肤病学   7篇
神经病学   35篇
特种医学   117篇
外科学   54篇
综合类   7篇
预防医学   54篇
眼科学   10篇
药学   97篇
肿瘤学   34篇
  2023年   5篇
  2022年   6篇
  2021年   20篇
  2020年   6篇
  2019年   12篇
  2018年   17篇
  2017年   5篇
  2016年   15篇
  2015年   12篇
  2014年   16篇
  2013年   23篇
  2012年   23篇
  2011年   21篇
  2010年   20篇
  2009年   22篇
  2008年   28篇
  2007年   43篇
  2006年   24篇
  2005年   28篇
  2004年   16篇
  2003年   19篇
  2002年   12篇
  2001年   21篇
  2000年   12篇
  1999年   16篇
  1998年   41篇
  1997年   46篇
  1996年   52篇
  1995年   40篇
  1994年   31篇
  1993年   31篇
  1992年   15篇
  1991年   12篇
  1990年   8篇
  1989年   19篇
  1988年   19篇
  1987年   16篇
  1986年   12篇
  1985年   13篇
  1984年   10篇
  1983年   6篇
  1982年   7篇
  1981年   5篇
  1980年   5篇
  1979年   6篇
  1978年   4篇
  1977年   7篇
  1976年   6篇
  1975年   9篇
  1969年   3篇
排序方式: 共有870条查询结果,搜索用时 15 毫秒
861.
Objective Suboptimal levels of 25‐hydroxyvitamin D (25OHD) are common in haemodialysis patients (Chronic Kidney disease‐5D: CKD‐5D) and may be associated with reduced muscle strength and increased falls risk. We tested the hypothesis that 25OHD levels may be independently associated with falls risk in CKD‐5D. Background Supplementation with calcium and cholecalciferol reduces hip and other nonvertebral fractures in elderly individuals, and this effect may in part be attributable to reduction in falls frequency. The relationship between 25OHD and falls risk has not been investigated in CKD‐5D. Design and Patients This is a cross‐sectional study of 25 CKD‐5D patients with predialysis 25OHD, 1,25‐dihydroxyvitamin D (1,25(OH)2D) and intact parathyroid hormone (iPTH) measurement. Falls risk was assessed by quadriceps muscle strength, FallsScreen© test (FST), Berg Balance Scale (BBS), timed ‘up and go’ (TUG) test, Modified Barthel Index (MBI) and Falls Efficacy Scale (FES). Results Mean age was 69·8 ± 12·1 years, and median time on dialysis was 3·1 years. Median 25OHD level was 55·3 nmol/l (range 20·8–125·8 nmol/l). Muscle strength was significantly positively correlated with 25OHD (P = 0·024) but not with 1,25(OH)2D (P = 0·477) or PTH (P = 0·461). Statistically significant correlation between 25OHD levels and FST (P = 0·028) plus MBI (P = 0·0046) was noted. No significant correlation was detected between falls risk and 1,25(OH)2D or PTH. Conclusions Suboptimal levels of 25OHD in CKD‐5D are associated with reduced quadriceps muscle strength and increased falls risk. 25OHD may be more important than the active renal metabolite 1,25(OH)2D for muscle strength with implications for vitamin D choice and goals of supplementation. Further investigation is required to examine effectiveness of calciferol supplementation on the incidence of falls in CKD‐5D.  相似文献   
862.
The Friend virus complex was used as a model to study the effects of merocyanine 540 (MC 540)-mediated photosensitization on enveloped viruses. Simultaneous exposure to the lipophilic dye MC 540 and white light inactivated cell-free virus, cell-associated virus, and virus- transformed cells. When used under experimental conditions that are known to preserve most mature blood cells, at least some coagulation factors, and a significant portion of the pluripotent hematopoietic stem cell compartment, MC 540-mediated photosensitization reduced virus titers by greater than or equal to 4 log and the concentration of in vitro clonogenic erythroleukemia cells by greater than or equal to 5 log. Animals that received a single intravenous injection of photosensitized virus were resistant to a subsequent challenge with live virus. High sensitivity to MC 540-mediated photosensitization appears to be a property that is shared by other enveloped viruses. Thus, photosensitization mediated by MC 540 may be of benefit in the sterilization of blood products (in particular, cellular products), the production of vaccines, and selected areas of antiviral therapy.  相似文献   
863.
背景:对于中晚期(FicatⅢ,Ⅳ期)股骨头缺血性坏死且髋臼基本完好的患者,单纯股骨头表面置换是一种较好的治疗方法。股骨假体位置、下沉影响全髋关节置换术的治疗效果,但假体位置、下沉对半髋表面置换术疗效的影响尚需进一步研究。目的:观察钴铬合金半髋表面置换对中晚期(FicatⅢ,Ⅳ期)股骨头缺血性坏死且髋臼基本完好患者髋关节功能的影响,并分析疗效与股骨假体柄干角、下沉的关系,评估计算机辅助X射平片分析对假体失败的预测价值。设计:病例分析。单位:广西医科大学第一附属医院脊柱骨病科。对象:选择1997-06/2002-07广西医科大学第一附属医院脊柱骨病科收治的中晚期(FicatⅢ,Ⅳ期)股骨头缺血性坏死行半髋表面置换患者41例(48髋),患者手术时的年龄29~49岁,平均(37±9)岁,其中男30例,女11例。其中FicatⅢ期35髋,FicatⅣ期13髋,髋臼均相对正常。所有患者病变部位病理检查均为股骨头缺血性坏死;且均签署知情同意书。方法:①于术前和随访时采用UCLA(UniversityofCaliforniaLosAnge-les)髋关节功能评分标准对患者手术前后疼痛、步行、功能、活动进行评分,每一项记分为1~10分,10分为最佳。优,35~40分,好29~34分,一般22~28分,差<22分。术后评分为随访时评分平均值。②运用计算机辅助的EBRA-FCA法,在术后骨盆的X射线平片上测量股骨假体的柄干角、下沉,并对半髋表面置换术治疗股骨头缺血性坏死的疗效与股骨假体的柄干角、下沉的关系进行分析。③采用复诊的方式进行随访,于术后2个月开始第1次随访,每年随访1次,共随访8年。④两组样本间均数比较采用独立样本t检验(并做方差齐性检验)。在对临床结果的析因分析(posthocanalysis)基础上,比值比(oddsratio)分析用来确定假体早期失败的相对危险性。主要观察指标:①纳入患者半髋表面置换术前后UCLA评分比较。②FicatⅢ期和Ⅳ期患者术后疗效比较。③不同疗效患者随访期间股骨假体柄干角和下沉程度比较。结果:全部病例均获随访,其中8例随访3年,8例随访4年,8例随访5年,7例随访6年,6例随访7年,4例8年。①UCLA髋关节功能评分:疼痛、步行、功能、活动评分别由术前的(3.1±1.2),(4.4±1.7),(5.8±2.3),(5.5±2.7)分提高到术后的(9.1±2.5),(9.2±2.9),(9.1±3.4),(7.1±3.1)分,差异明显(P<0.01)。②疗效:FicatⅢ期35髋术后的满意率为89%与FicatⅣ期13髋术后的满意率相近(69%,P>0.05),其中疗效差8髋为失败组,其余40髋为成功组。③计算机辅助的X射线平片检查结果:失败组6个髋的股骨假体有明显下沉(其柄干角小于130°),2个髋的髋臼有破坏(1个柄干角为128°,1个柄干角为136°)。成功组平均柄干角明显大于失败组,分别为139°±6.2°,127°±5.3°,差异明显(P<0.01)。失败组中,6髋假体头中心和假体柄尖的下沉分别为(5.02±1.3)mm和(4.85±1.1)mm明显大于成功组[(1.48±0.2)和(1.04±0.2)mm,P<0.05];小于130°的柄干角其发生不良后果的机会增加了7.1倍。④股骨假体下沉时间:计算机辅助的X线片分析显示股骨假体下沉超过2mm的时间为(19.5±3.2)个月,明显早于临床出现症状的时间和X射线平片异常的时间[(35.6±4.2),(24.8±2.5)个月,P<0.01]。结论:①钴铬合金半髋表面置换是一种可供选择的向全髋关节置换术过渡的较好的治疗方法,可以恢复中晚期(FicatⅢ,Ⅳ期)股骨头缺血性坏死的且髋臼基本完好的患者的髋关节功能。②假体的松动下沉与假体的位置有关。③用来评估假体柄在骨盆平片上的下沉程度的计算机辅助的平片分析可以预测假体的失败。  相似文献   
864.
Khan  KN; Kociba  GJ; Wellman  ML 《Blood》1993,81(10):2585-2590
Erythroid aplasia is induced in cats by feline leukemia virus (FeLV) of subgroup C but not by FeLV of subgroup A. In an investigation of the role of macrophages in FeLV-C-induced diseases, the concentrations of FeLV and tumor necrosis factor-alpha (TNF-alpha) were compared between feline peritoneal macrophages incubated with FeLV of subgroup A or C. FeLV of both subgroups infected macrophages, but expression of FeLV-C was 21-fold higher than FeLV-A in peritoneal macrophages (P = .004). The supernatants of FeLV-C-inoculated macrophage cultures contained significantly higher levels of TNF-alpha (70 +/- 14 U/mL) at 72 hours postincubation compared with FeLV-A-inoculated (38 +/- 8 U/mL) and uninoculated (31 +/- 8 U/mL) cultures. Moreover, a positive correlation was shown between cell-associated FeLV surface glycoprotein gp70 and TNF-alpha expression in FeLV-C-infected macrophages by immunofluorescence (r = .6; P = .001), measured with a computer- assisted, laser-based digital imaging system. The addition of TNF-alpha to a uniform population of FeLV-infected cells (feline embryonic fibroblasts) caused an enhancement of viral expression (P < .05). These results indicate that FeLV-C has tropism for macrophages, FeLV expression is positively correlated with TNF-alpha expression in macrophages, and TNF-alpha enhances FeLV replication in fibroblasts. We suggest that FeLV-C infection of macrophages and secretion of TNF-alpha may be important in hematopoietic suppression in FeLV-C-infected cats.  相似文献   
865.
Gailani  D; Broze  GJ Jr 《Blood》1993,82(3):813-819
Factor XI (FXI) may be activated in a purified system by thrombin and by autoactivation in the presence of negatively charged substances such as dextran sulfate or sulfatides. The current studies were performed to determine if these processes occur during the coagulation of plasma. FXII--deficient plasma was supplemented with 125I-FXI and clot formation was induced with tissue factor and/or sulfatides. Cleavage of FXI was studied by standard polyacrylamide gel electrophoresis and autoradiography. Activated FXI (FXIa) was detected after 20 minutes of incubation with sulfatides alone and this process was markedly accelerated by the addition of tissue factor (TF). The enhancing effect of TF was blocked by hirudin, which indicated thrombin involvement in FXI activation. The contribution of FXIa to FIX activation in this system was studied using a 3H-FIX activation peptide release assay. Sulfatides increased FIX activation about twofold in plasma induced to clot with TF but had no effect if the plasma was immunodepleted of FXI. FIX activation was also increased in plasma induced to clot with FXa if sulfatides were present. The enhanced generation of FIXa was dependent on FXI and was blocked by hirudin. Some activation was seen in the reactions with sulfatides and hirudin and is likely solely caused by FXI autoactivation. The data indicate that during the coagulation of plasma in the presence of sulfatides, FXI is activated by a mechanism that is thrombin dependent and does not require FXII.  相似文献   
866.
Percutaneous transluminal renal angioplasty in children and adolescents   总被引:3,自引:0,他引:3  
Percutaneous transluminal renal angioplasty (PTRA) was performed in 12 children and adolescents with renal artery stenosis. Patients were divided into three groups: those with a short stenosis in the middle or distal part of the renal artery (n = 5), those with a short stenosis at or near the origin of the renal artery (n = 3), and those with a long stenosis at or near the origin (n = 4). The patients in the first group responded to PTRA. Those in the second group had a poor clinical response, and dilation was unsuccessful in the patients in the third group, who remained hypertensive. The location and length of the renal artery stenosis and its underlying cause appear to be important in determining the results of PTRA.  相似文献   
867.
Normal quantitative circumferential profile limits were established for a 30 degrees bilateral rotating slant-hole (RSH) collimator tomographic system. This system's value in detecting segmental coronary artery disease was assessed in a study evaluating 196 patients by thallium 201 myocardial scintigraphy and coronary arteriography. Profile curves were calculated from images of 20 healthy patients and used to identify significant coronary artery disease (greater than or equal to 70% diameter narrowing) in the left anterior descending (LAD), the right, and the left circumflex (LCx) coronary arteries. In a group of 86 patients, an abnormality on the apical or middle plane optimally identified segmental coronary artery disease. When such abnormalities were prospectively evaluated in a test group of 110 patients, the sensitivity and specificity were 79% and 93% for LAD, 90% and 90% for right, and 83% and 83% for LCx coronary artery disease. Compared with qualitative interpretation of the planar and tomographic images, quantitative tomography significantly improved the sensitivity of T1-201 imaging in detecting LAD, right, and LCx coronary artery disease (P less than .001) in patients with or without previous myocardial infarction.  相似文献   
868.
869.
Hepatic malignancies: improved treatment with intraarterial Y-90   总被引:4,自引:0,他引:4  
An improved treatment method for hepatic malignancies with yttrium-90 incorporated into the matrix of glass microspheres was evaluated prospectively. Fifteen patients with 12 metastatic colorectal cancers, one carcinoid, one islet cell tumor, and one hepatoma were treated with three dose levels: 5,000 cGy (5,000 rad), ten patients; 7,500 cGy (7,500 rad), three patients; and 10,000 cGy (10,000 rad), two patients. Mean follow-up was 7 months (range, 2-12 months). Stable disease in the liver was seen in ten patients, four of whom had concurrent progression of extrahepatic disease, which resulted in two deaths. Two additional deaths were not directly related to the malignant process. Progression of liver disease was found in five patients, with three deaths occurring at 7-8 months. No procedural, hematologic, or pulmonary complications occurred. Late gastroduodenal ulceration occurred at 6-8 weeks in three patients who had histories of chronic alcohol abuse. This method of therapy seems to be feasible and efficient. Caution is necessary with high doses or with patients with a history of or predisposition to gastroduodenal ulcers.  相似文献   
870.
蛇床子中一新的角型呋喃香豆素   总被引:6,自引:0,他引:6  
从辽宁新民产蛇床Cnidium monnieri 果实中分离鉴定8个化合物,分别为欧山芹素(oroselone,Ⅰ),β谷舀醇(Ⅱ),哥伦比亚内酯(columbianadin,Ⅲ),佛手柑内醋(bergapten,Ⅳ),O-乙酰哥伦比亚甙贰元(O-acetycolumbianetin,v),O-乙酰异蛇床素(cniforinA,Ⅵ),爱得尔庭(edultin,Ⅶ)和'-乙酰白芷素(2'-acetylangelicin,Ⅷ)。其中化合物Ⅷ为一新化合物,化合物Ⅰ系首次从该植物中分得。  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