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   39749篇
  免费   3006篇
  国内免费   1419篇
耳鼻咽喉   331篇
儿科学   1155篇
妇产科学   228篇
基础医学   5242篇
口腔科学   2185篇
临床医学   3190篇
内科学   4356篇
皮肤病学   186篇
神经病学   1003篇
特种医学   2497篇
外国民族医学   3篇
外科学   12213篇
综合类   5225篇
现状与发展   1篇
预防医学   1115篇
眼科学   121篇
药学   1724篇
  12篇
中国医学   1020篇
肿瘤学   2367篇
  2024年   58篇
  2023年   406篇
  2022年   832篇
  2021年   997篇
  2020年   910篇
  2019年   865篇
  2018年   1060篇
  2017年   954篇
  2016年   1177篇
  2015年   1344篇
  2014年   2319篇
  2013年   2521篇
  2012年   1947篇
  2011年   2268篇
  2010年   1978篇
  2009年   2130篇
  2008年   2065篇
  2007年   2184篇
  2006年   2037篇
  2005年   2116篇
  2004年   1740篇
  2003年   1480篇
  2002年   1162篇
  2001年   994篇
  2000年   1009篇
  1999年   846篇
  1998年   676篇
  1997年   685篇
  1996年   592篇
  1995年   557篇
  1994年   525篇
  1993年   389篇
  1992年   368篇
  1991年   333篇
  1990年   274篇
  1989年   232篇
  1988年   232篇
  1987年   197篇
  1986年   199篇
  1985年   213篇
  1984年   169篇
  1983年   100篇
  1982年   142篇
  1981年   125篇
  1980年   118篇
  1979年   135篇
  1978年   117篇
  1977年   100篇
  1976年   69篇
  1973年   42篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
目的:研究健血升白冲剂对小鼠血液系统的影响。方法:以骨髓细胞计数,白细胞计数和血象为指标,观察健血升白冲剂对正常小鼠和化学及放射损伤小鼠的影响。结果:健血升白冲剂明显增加正常小鼠白细胞计数(P<001),显著改善环磷酰胺诱导小鼠白细胞和骨髓细胞的减少作用(分别为P<005,P<001),并能显著增加60Co放射损伤小鼠骨髓细胞(P<001)和白细胞(P<001)。结论:健血升白冲剂对化学及放射损伤小鼠血液系统有明显的保护及改善作用。是一个有开发价值的药物。  相似文献   
52.
Summary Previous studies of Alcian blue-induced birefringence in adult avian cortical bone showed that a short period of intermittent loading rapidly produces an increased level of orientation of proteoglycans within the bone tissue. In the absence of further loading, this persists for over 24 hours. We have proposed that this phenomenon could provide a means for “capturing” the effects of transient strains, and so provide a persistent, constantly updated strain-related influence on osteocyte populations related to the bones' averaged recent strain history, in effect, a “strain memory” in bone tissue. In our present study, we use the Alcian blue-induced birefringence technique to demonstrate that proteoglycan orientation also occurs after intermittent loading of both cortical and cancellous mammalian bonein vivo andin vitro. We also show that the change in birefringence is proportional to the magnitude of the applied strain, and that the reorientation occurs rapidly, reaching a maximal value after only 50 loading cycles. Examination of electron micrographs of bone tissue after staining with cupromeronic blue allows direct visualization and quantification of the change in proteoglycan orientation produced by loading. This shows that intermittent loading is associated with a realignment of the proteoglycan protein cores, bringing them some 5 degrees closer to the direction of collagen fibrils in the bone matrix.  相似文献   
53.
从1985年起,应用胫骨骨条植骨结合多根克氏针内固定治疗股骨颈骨折21例,经随访7个月—48个月,优17例、良3例、差1例。通过临床观察,用自体胫骨骨条植骨提供活的骨细胞及诱导成骨,能促进加速骨折愈合。本手术方法简单、安全  相似文献   
54.
This double-masked, placebo-controlled study was undertaken to determine the efficacy and safety of oral clodronate in the prevention of bone loss in early postmenopausal women with vertebral osteopenia. Altogether 610 women with a mean age of 53 years were recruited for the study. They were 1–5 years postmenopausal and their lumbar spine bone mineral density (BMD) was at least 1 standard deviation below the mean of premenopausal women (T-score ≤−1). The subjects were randomized into five study groups to receive either placebo, clodronate 65 mg, 400 mg or 800 mg daily, or intermittent clodronate in 3 month cycles with 400 mg daily for 15 days followed with no treatment for 75 days for 3 years. One hundred and eighty-seven of 509 women who completed the primary study continued in the extension study of 2 years in which previous placebo users were switched to clodronate 800 mg daily, while previous users of 400 mg or 800 mg of clodronate used either placebo or 800 mg of clodronate daily. In the primary study clodronate was administered in the evening, and in the extension 1 h before breakfast on an empty stomach. In the primary study mean changes in lumbar spine BMD were −3.4% in the placebo group and +0.4% in 800 mg clodronate group [difference between groups at 3 years 3.8% (95% CI 2.7% to 4.9%, p<0.0001)], and in the trochanter area BMD −1.1% in the placebo group, and + 0.4% in the 800 mg clodronate group [difference between groups at 3 years 1.5% (95% CI 0.05% to 2.9%)]. During the extension study mean changes in lumbar spine BMD were +1.5% in the clodronate group and −0.2 % in the placebo group [difference between groups 1.7% (CI 0.4% to 3.0%, p = 0.010)] and in trochanter BMD were +2.5% in the clodronate group and no change in the placebo group [difference between groups 2.1% (CI 0.3% to 3.9%, p = 0.007)]. No statistically significant differences between the placebo and 800 mg clodronate groups were found in the femoral neck BMD. In the primary study the urinary excretion of type I collagen aminoterminal telopeptide (NTX) decreased by 44% (p<0.0001 compared with placebo) and that of deoxypyridinoline by 18% (p<0.0001) in the clodronate 800 mg group. In the extension study urinary NTX decreased by 51% (p<0.0001) in those who were switched to 800 mg of clodronate and increased by 67% (p<0.0001) in those who stopped using that dose. There was no difference in the frequency of gastrointestinal complaints between clodronate- and placebo-treated patients in the primary study, but they were more common among women who received clodronate in the extension phase. Clodronate in daily doses of 400–800 mg caused a slight elevation of aminotransferase levels, usually within the reference range. In bone biopsies no defect in mineralization was found. In conclusion, clodronate in a daily dose of 800 mg prevents early postmenopausal bone loss at the sites of the skeleton in which cancellous bone predominates. It effectively reduces bone resorption and bone turnover rate. Antifracture efficacy of clodronate remains to be established by prospective, placebo-controlled trials. Received: 4 March 2002 / Accepted: 9 July 2002  相似文献   
55.
目的 评价和探讨修复骨外露及皮肤软组织缺损的各种方法 ,使其更好地用于临床。方法  3 5例不同部位的骨外露分别采用皮片移植、皮瓣及肌皮瓣转移、皮瓣及肌皮瓣游离移植等方法 ,覆盖外露的骨面。结果  3 1例全部存活 ,1例皮瓣部分坏死 ,2例创口延迟愈合 ,1例游离皮瓣失败。结论 对骨外露及皮肤软组织缺损应尽量在早期修复 ,最常用的方法是皮瓣及肌皮瓣的转移或移植。  相似文献   
56.
来源于骨髓和脐带血的基质细胞基本特性的比较   总被引:5,自引:0,他引:5  
目的比较骨髓与脐带血细胞体外培养基质细胞的基本特性,为基质细胞的选择应用提供依据.方法用Dexter长期培养体系培养骨髓和脐带血基质细胞,以细胞增殖、细胞形态、细胞化学染色、细胞表面及基质细胞支持另一骨髓细胞形成的鹅卵石造血区(CAFC),长期培养起始细胞(LTC-IC)为指标,比较两者的生长特性、成分及功能.结果①细胞生长特性:出现贴壁细胞时间,骨髓细胞为培养3d,脐带血细胞为培养5~6d;细胞融合成片时间,骨髓细胞为培养10~14d,脐带血细胞为培养12~18d;第21天细胞增殖数,骨髓比脐带血细胞增殖少;②细胞成分:21d培养后细胞成分,骨髓来源者以成纤维细胞为主,其次是巨噬细胞与内皮细胞,脂肪细胞最少;脐带血细胞来源者,以巨噬细胞为主,其次是内皮细胞、成纤维细胞,偶见脂肪细胞;细胞化学与上述结果基本一致;细胞表面抗原检测,CD14、CD45的表达骨髓细胞明显低于脐带血细胞;③细胞功能:骨髓来源的基质细胞较脐带血细胞的基质细胞支持另一骨髓细胞形成的CAFC和LTC-IC明显多.结论①生长特征:形成贴壁细胞时间骨髓较脐带血短,骨髓细胞比脐带血细胞有核细胞数增殖快、持续时间相对短;②细胞成分特性:骨髓来源形成的基质细胞以成纤维细胞为主,脐带血来源者以巨噬细胞为主;③细胞功能特性:骨髓细胞形成的贴壁细胞较脐带血细胞形成的贴壁细胞更利于CAFC、LTC-IC生长.  相似文献   
57.
通用型脊柱内固定系统椎弓根螺钉翻修作用的生物力学研究   总被引:25,自引:0,他引:25  
目的测试自行设计的通用型脊柱内固定系统(generalspinesystem,GSS)椎弓根螺钉以及SOCON、TSRH和Diapason螺钉置入椎体的拔出力及旋入力矩,评价GSS螺钉的翻修作用。方法将36个正常成人腰椎椎体标本随机分为三组,每组12个椎体(24侧椎弓根)。各组标本每个椎体的每侧椎弓根均先拧入CCD螺钉(直径6.0mm,长45mm),行螺钉拔出试验,测试并记录螺钉的最大旋入力矩和最大轴向拔出力。然后各组标本每个椎体均随机选择一侧椎弓根经原钉道拧入GSS螺钉(直径6.5mm,长45mm);第一组另一侧拧入SOCON螺钉(直径7.0mm,长45mm),第二组另一侧拧入TSRH螺钉(直径7.0mm,长45mm),第三组另一侧拧入Diapason螺钉(直径6.7mm,长45mm)。分别测试螺钉最大旋入力矩及最大轴向拔出力。结果第一组GSS螺钉最大轴向拔出力为CCD螺钉的114%,SOCON螺钉为CCD螺钉的108%;GSS螺钉最大轴向拔出力大于SOCON螺钉,差异无显著性(P>0.05);GSS螺钉最大旋入力矩小于SOCON螺钉,差异无显著性(P>0.05)。第二组GSS螺钉最大轴向拔出力为CCD螺钉的127%,TSRH螺钉为CCD螺钉的64%;GSS螺钉最大轴向拔出力大于TSRH螺钉,差异有显著性(P<0.01);GSS螺钉最大旋入力矩大于TSRH螺钉,差异有显著性(P<0.01)。第三组GSS螺钉最大轴向拔出力为CCD螺钉的122%,Diapason螺钉为CCD螺钉的8  相似文献   
58.
Reconstitution of the nasal scaffolding with maintainence of soft tissue proportions either following severe facial trauma or as a sequela to aesthetic rhinoplasty misadventures frequently is best achieved using the stability afforded by bone grafts. Split cranial bone grafts offer many advantages and may be the donor site of choice, and may even allow such surgery to be performed on an outpatient basis in some cases. The use of miniplate or screw osteosynthesis, now commonly accepted as a superior technique in craniomaxillofacial procedures, may simplify fixation of these calvarial nasal bone grafts with an apparent decrease in the risk of resorption.  相似文献   
59.
Intravenous administration of human bone marrow stromal cells (hMSCs) after middle cerebral artery occlusion (MCAo) in rats provides functional benefit. We tested the hypothesis that these functional benefits are derived in part from hMSC production of growth and trophic factors. Quantitative sandwich enzyme‐linked immunosorbent assay (ELISA) of hMSCs cultured with normal and MCAo brain extracts were performed. hMSCs cultured in supernatant derived from ischemic brain extracts increased production of brain‐derived neurotrophic factor (BDNF), nerve growth factor (NGF), vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF). These neurotrophins and angiogenic growth factors increased in a post‐ischemia time‐dependent manner. The hMSC capacity to increase expression of growth and trophic factors may be the key to the benefit provided by transplanted hMSCs in the ischemic brain.  相似文献   
60.
Platelet factor 4 ( PF4) is a negativehematopoietic factor.It can inhibit the prolifera-tion of endothelial cells and hematopoietic stem/progenitor cells,particularly megakaryoryocyticcells,reversibly[1] ,inhibit DNA synthesis,blockcell cycle progression during S phase and reducethe sensibility of normal hematopoietic stem/pro-genitor cells,but not some cancer or leukemia celllines,to cytotoxic drugs and ionizing radia-tion[2 - 3] ,and it also can cause a population in-crease of the stem cel…  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