首页 | 官方网站   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   5413382篇
  免费   408974篇
  国内免费   16122篇
医药卫生   5838478篇
  2021年   57379篇
  2019年   59627篇
  2018年   77455篇
  2017年   59497篇
  2016年   65927篇
  2015年   78009篇
  2014年   112590篇
  2013年   178356篇
  2012年   154244篇
  2011年   165101篇
  2010年   135247篇
  2009年   133743篇
  2008年   150211篇
  2007年   162341篇
  2006年   168299篇
  2005年   162853篇
  2004年   163076篇
  2003年   152484篇
  2002年   141082篇
  2001年   215621篇
  2000年   213516篇
  1999年   189911篇
  1998年   78257篇
  1997年   72268篇
  1996年   70515篇
  1995年   66047篇
  1994年   59959篇
  1993年   55607篇
  1992年   142398篇
  1991年   137562篇
  1990年   132962篇
  1989年   128881篇
  1988年   119153篇
  1987年   117063篇
  1986年   110779篇
  1985年   107644篇
  1984年   86221篇
  1983年   75673篇
  1982年   54684篇
  1981年   50342篇
  1980年   47303篇
  1979年   77130篇
  1978年   59494篇
  1977年   51880篇
  1976年   48205篇
  1975年   49947篇
  1974年   56873篇
  1973年   54916篇
  1972年   51581篇
  1971年   47854篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This article reports on a longitudinal qualitative study ofthe psychosocial factors influencing women's experience of breastfeeding.The findings illustrate the complex web of factors, both personaland environmental, that influence breastfeeding behaviour. Thesignificance of breastfeeding derives from the fact that it,in concert with the arrival of a new baby, heralds significantchanges in a woman's day-to-day life. Three major areas of change,in part precipitated by breastfeeding, were critical. Theseinclude changes in the amount of time available to the motherand the nature of the activities that fill this time, changesin a woman's body due to pregnancy and breastfeeding, and changesin the nature of a woman's personal needs. These changes constitutea substantial and often disconcerting shift in lifestyle. Thearticle examines the potential consequences of these changesfor the mother and the host of mediating factors that influenceher response to them and hence to breastfeeding. The mediatingfactors include the personal and psychological factors relatedto the attitudes, values and character traits of the mother,baby, and those close to them. Others are structural factorssuch as the absence or presence of formal and informal supportsystems that range from paid maternity leave to community drop-incentres, educational programmes, and community parks. They alsoinclude the host of cultural factors that influence the waysin which individuals and society view breastfeeding.  相似文献   
992.
Segregation analysis of leprosy in families of northern Thailand   总被引:4,自引:0,他引:4  
Sixty-three families with multiple instances of leprosy were identified through a major leprosy treatment center in northern Thailand. Complex segregation analyses for single major genes or polygenic inheritance were performed using the maximum-likelihood routine POINTER to determine the most likely etiologic model of genetic susceptibility. Liability differences between men and women were considered in these models. When individuals were considered to be affected because they had any form of leprosy, a generalized major gene model with nearly dominant parameters on the liability scale, but additive penetrances, was found to be the most likely. When only those individuals who had tuberculoid forms of leprosy were considered to be affected, a recessive model was found to be the most likely; however, the discrimination between various models was poor. Further analyses are necessary to delineate genetic mechanisms to explain these apparently divergent results. In particular, methods of testing two locus models should be considered.  相似文献   
993.
Oil-emulsified (OE) and aqueous (Aq) vaccines were prepared with the same batch of inactivated A24 8345 foot and mouth disease virus (FMDV). Calves born to vaccinated dams did not respond to the Aq vaccine 30 or 90 days post partum. When the OE vaccine was used on a similar group of calves, no responses were elicited up to 21 days post partum. However, calves 30 or more days old responded like adult cattle to the OE vaccine. When the OE vaccine was used in colostral antibody-free calves 3-30 days old, all animals showed good antibody responses but, in calves vaccinated 3 or 7 days post partum, antibodies were detectable only after a considerable period of time. Our results show that both passively acquired colostral antibodies and age are important in the response of very young calves to FMDV oil vaccines. From a practical point of view, in endemic areas where adult cattle are periodically vaccinated, vaccination of calves between 30 and 60 days post partum with OE vaccines would lead to high levels of herd protection.  相似文献   
994.
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   
995.
L A Rodriguez  M Prados  P Silver  V A Levin 《Cancer》1989,64(12):2420-2423
Ninety-nine patients with primary recurrent malignant tumors of the central nervous system were treated with procarbazine as a single agent. Procarbazine was not given as a specified protocol, but for patients who were ineligible or refused other protocols. All patients had been treated previously with radiotherapy and 96 patients had also received previous chemotherapy. Twenty-five patients were treated at the first progression of their tumor, 47 were treated at the second progression, and 27 were treated at the third progression of their tumor. For the aggregate, the response plus stabilization rate was 27% for glioblastoma multiforme with median time to tumor progression of 30 weeks, and 28% for other anaplastic gliomas with a median time to tumor progression of 49 weeks. With respect to the percent of patients who responded or stabilized to treatment, these results are inferior to those reported previously for patients treated with procarbazine at recurrence. With respect to duration of response and stabilization, the data are comparable.  相似文献   
996.
During recent decades there has been a controversial discussion if comparable plasma level profiles which are rather constant or those which show a high peak are more efficient for the cure of gonorrhoea. So far, investigations in this field were not based on the Grasso apparatus. Although the findings with cefotiam and ceftizoxime do not allow to formulate a general hypothesis without any restriction, it can be stated that on the basis of an identical area under the antibiotic level time curve, 'peak concentration' profiles are more favourable.  相似文献   
997.
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   
998.
999.
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   
1000.
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   

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-23

京公网安备 11010802026262号