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   5556777篇
  免费   424099篇
  国内免费   17324篇
耳鼻咽喉   79282篇
儿科学   175614篇
妇产科学   147479篇
基础医学   816581篇
口腔科学   159897篇
临床医学   512349篇
内科学   1013356篇
皮肤病学   127341篇
神经病学   459508篇
特种医学   217778篇
外国民族医学   1321篇
外科学   833891篇
综合类   162259篇
现状与发展   24篇
一般理论   3013篇
预防医学   469650篇
眼科学   134463篇
药学   396812篇
  30篇
中国医学   14594篇
肿瘤学   272958篇
  2021年   57601篇
  2019年   60016篇
  2018年   78002篇
  2017年   59709篇
  2016年   66587篇
  2015年   78617篇
  2014年   113705篇
  2013年   179599篇
  2012年   156637篇
  2011年   167527篇
  2010年   136149篇
  2009年   134356篇
  2008年   152496篇
  2007年   164868篇
  2006年   170775篇
  2005年   165723篇
  2004年   165768篇
  2003年   154848篇
  2002年   143959篇
  2001年   223489篇
  2000年   222542篇
  1999年   196955篇
  1998年   80463篇
  1997年   73934篇
  1996年   71696篇
  1995年   67580篇
  1994年   61618篇
  1993年   56994篇
  1992年   148904篇
  1991年   143979篇
  1990年   138580篇
  1989年   134352篇
  1988年   124377篇
  1987年   122377篇
  1986年   115947篇
  1985年   112835篇
  1984年   90241篇
  1983年   78969篇
  1982年   56342篇
  1981年   51936篇
  1980年   48752篇
  1979年   81364篇
  1978年   62088篇
  1977年   54150篇
  1976年   50552篇
  1975年   51684篇
  1974年   60133篇
  1973年   57837篇
  1972年   54381篇
  1971年   50132篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Rapidly advancing health technology poses problems for managers. Although clear conceptual frameworks exist for economic evaluation, in practice severe problems remain in carrying out timely research that is locally appropriate to the needs of managers. This paper explores some of these problems in the context of the policy analysis interface between economic research and the management of technology. In the light of experience gained from recent evaluation research it indicates how researchers and managers can each contribute to the provision of a stronger empirical basis for policy making and policy management. An earlier version of this paper was presented at the joint meeting of the Health Economists Study Group and Institute of Health Service Management, University of York, 6-8 July 1987. The author would like to thank Christopher Spry and Mike Drummond for helpful comments.  相似文献   
992.
The relationship between energy expenditure and body composition, in terms of fat and fat-free masses, has previously been described by a variety of predictive regression equations with parameters devoid of physiological content. We present here results obtained by calculating the specific energy expenditure, ie, the energy expenditure per unit of mass, of fat and fat-free tissue on the basis of measurements of the total energy expenditure (EE), the masses of fat (FM), and fat-free (FFM) tissue using the following simple model: EE = k1.FM + k2.FFM where k1 and k2 are the specific energy expenditures of fat and fat-free tissue, respectively. The results of observations on 104 women at rest yielded values for k1 and k2 of 0.31 and 1.35 watts/kg of fat and fat-free mass, respectively, with standard errors of estimate of 0.074 and 0.052 watts/kg, respectively. Analysis of several series of measurements, from other sources and on smaller samples of subjects, yielded similar values at rest but with larger standard errors of estimate. Data from subjects performing varying amounts of work in 24-h measurements showed, as expected, larger values for both tissues. The results explain to a very large extent the well-established relation between resting metabolic rate and body weight, ie, a linear relation with a non-zero intercept. The results also offer a clear-cut explanation for the well known difference in energy expenditure between men and women with the same body weight.  相似文献   
993.
The origin and nature of osteoclast-like multinucleated giant cells (OMGCs), in extraskeletal neoplasms, is uncertain. The ultrastructure, antigenic phenotype and function of OMGCsm in a breast carcinoma were studied in order to clarify the relationship between OMGCs, osteoclasts and other cells of the mononuclear phagocyte system (MPS). OMGCs resorbed cortical bone in a manner similar to osteoclasts. However, unlike osteoclasts, OMGCs did not possess a ruffled border or clear zone, and expressed HLA-DR and Fc receptors and CD14, CD16, CD18 and CD11 (p150,95) antigens. In addition, OMGCs failed to respond morphologically to calcitonin and were directly stimulated by parathyroid hormone (PTH) to increase bone resorption. These findings suggest that OMGCs are a specific type of macrophage polykaryon distinct from both osteoclasts and other types of inflammatory polykaryon. Occasional smaller (20-25 microns) macrophage-like cells were also associated with resorption pits. Bone resorption by OMGCs isolated from the breast indicates that a cell of the MPS can be transplanted to a new tissue location and perform a highly specialised function appropriate to an MPS cell of that tissue (i.e. the osteoclast). PTH stimulation of bone resorption by OMGCs suggests that PTH or a PTH-like protein, may be involved in the bone resorption and consequent hypercalcaemia associated with metastatic breast cancer.  相似文献   
994.
995.
Risedronate treatment reduces the risk of vertebral fracture in women with existing vertebral fractures, but its efficacy in prevention of the first vertebral fracture in women with osteoporosis but without vertebral fractures has not been determined. We examined the risk of first vertebral fracture in postmenopausal women who were enrolled in four placebo-controlled clinical trials of risedronate and who had low lumbar spine bone mineral density (BMD) (mean T-score =–3.3) and no vertebral fractures at baseline. Subjects received risedronate 5 mg (n= 328) or placebo (n= 312) daily for up to 3 years; all subjects were given calcium (1000 mg daily), as well as vitamin D supplementation (up to 500 IU daily) if baseline serum 25-hydroxyvitamin D levels were low. The incidence of first vertebral fracture was 9.4% in the women treated with placebo and 2.6% in those treated with risedronate 5 mg (risk reduction of 75%, 95% confidence interval 37% to 90%; P= 0.002). The number of patients who would need to be treated to prevent one new vertebral fracture is 15. When subjects were stratified by age, similar significant reductions were observed in patients with a mean age of 64 years (risk reduction of 70%, 95% CI 8% to 90%; P= 0.030) and in those with a mean age of 76 years (risk reduction of 80%, 95% CI 7% to 96%; P= 0.024). Risedronate treatment therefore significantly reduces the risk of first vertebral fracture in postmenopausal women with osteoporosis, with a similar magnitude of effect early and late after the menopause. Received: 12 September 2001 / Accepted: 11 December 2001  相似文献   
996.
Introduction   QT interval prolongation may cause the potentially lethal tachyarrhythmia torsades de pointes ( 1 ). The cause of the QT interval prolongation may be a congenital mutation in genes encoding cardiac potassium and sodium channels ( 2 ) or be acquired following drug administration ( 3 ) or metabolic disorders ( 4 ). Among a few other drugs volatile anaesthetics prolong the QT interval. During the last few years sevoflurane has become the most used volatile anaesthetic for the induction of anaesthesia in infants.
Methods   This investigation, on infants aged from 1 to 6 months, was approved by the institutional ethic committee. Thirty-six otherwise healthy infants due to elective surgery were included in our study The patients were randomly assigned to one of two treatment groups. Group S ( n  = 24) was anaesthetised with sevoflurane, Group H was anaesthetised with halothane. ECG recordings were taken before the anaesthesia onset, 15 min after the first contact with the volatile anaesthetic and 60 min after the ending of the volatile gas exposition. QTc interval was calculated using the Bazett's formula ( 5 ).
Results   QTc interval was significantly ( P < 0.0002) (Table 1) lengthened 15 min after anaesthesia induction with sevoflurane as well as 60 min ( P < 0.01) after the ending of the gas exposition without any difference in age and gender. The QTc interval in patients anaesthetised with halothane did not show any significant change.  

  Table 1  相似文献   

997.
This study examined the immunoregulatory role of recombinant interleukin 4 (IL-4), also known as B-cell stimulating factor 1, on the generation of cytotoxic effector cells from normal and leukaemic human blood mononuclear cells. When tested on cells from normal individuals, the addition of IL-4 to mixed lymphocyte cultures led to a dose-dependent proliferation of T-helper cells (CD3, 4 positive) with a concomitant decrease in phenotypic and functional cytotoxic T cells and natural killer (NK) cells. IL-4 also inhibited the interleukin-2 (IL-2)-induced generation of lymphokine-activated killer (LAK) activity when added at the beginning of mixed lymphocyte culture. When tested on mature leukaemic NK cells, IL-4 also inhibited the ability of IL-2 to induce LAK function using a short-term culture system. These results show that IL-4 acts on both normal and leukaemic cells and suggests that it acts at more than one level during the development of LAK function.  相似文献   
998.
非脱垂子宫经腹、阴式全切除术临床比较   总被引:1,自引:0,他引:1  
目的 探讨非脱垂子宫经阴道与经腹全切术的临床比较。方法 2000年5月~2001年1月对阴式子宫全切术 (TVH)28例及腹式子宫全切术 (TAH)35例分为两组进行手术 ,对临床指标进行观察比较。结果 28例TVH手术均成功。平均重量255g(120~510g)。与TAH手术比较 ,其术后病率、肛门排气时间及术后住院天数有显著性差异 ( p<0.001及 p<0.05) ,但其手术时间及术中出血量无显著性差异 ( p>0.05)。结论 随着微创手术的开展 ,利用阴道天然孔道 ,经阴道切除较大的子宫是有效和安全的 ,手术的成功与术者经验、技术及子宫活动度有关 ,有合适器械也是手术成功的因素。  相似文献   
999.
目的 评价单克隆IgH基因重排检测在恶性淋巴瘤 (B NHL)临床中的应用价值。方法 用半巢式PCR检测单克隆IgH基因重排。病例组为B NHL ,包括 6 9例石蜡包埋组织切片、治疗前 16例骨髓和 2 9例外周血、阳性者治疗后复查骨髓和外周血 ;对照组为 10例慢性淋巴结炎、3例T NHL和 2例HD。结果 对照组均阴性。病例组 :切片中单克隆IgH基因重排阳性率为 6 3.8% (44 / 6 9) ;骨髓和外周血阳性率分别为 43 .8%(7/ 16 )和 41.4% (12 / 2 9) ,细胞形态学检查未见异常细胞者阳性率分别为 33 .3% (3/ 9)和 31.3% (5 / 16 )。 16例同时采集骨髓和外周血者 ,阳性率分别为 43 .8% (7/ 16 )和 37.5 % (6 / 16 ) ,两者无统计学差异。治疗前单克隆IgH重排阳性者 ,6例完全缓解 (CR)后转阴 ,处于持续缓解状态 ,1例临床缓解后 13个月仍阳性 ,现在继续随访中 ,另 1例CR后持续阳性者 ,6个月后复发。结论 切片、骨髓和外周血中检测单克隆IgH基因重排可以作为B NHL诊断和随访微小残留病灶的辅助手段  相似文献   
1000.
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