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   2349843篇
  免费   171610篇
  国内免费   3331篇
耳鼻咽喉   32051篇
儿科学   75895篇
妇产科学   62686篇
基础医学   348177篇
口腔科学   63638篇
临床医学   211347篇
内科学   457281篇
皮肤病学   51730篇
神经病学   185269篇
特种医学   88011篇
外国民族医学   489篇
外科学   353869篇
综合类   47509篇
现状与发展   12篇
一般理论   848篇
预防医学   182746篇
眼科学   54326篇
药学   175103篇
  11篇
中国医学   4575篇
肿瘤学   129211篇
  2021年   18984篇
  2019年   19537篇
  2018年   27057篇
  2017年   20358篇
  2016年   22746篇
  2015年   25638篇
  2014年   36098篇
  2013年   53960篇
  2012年   74675篇
  2011年   79412篇
  2010年   47058篇
  2009年   44569篇
  2008年   74612篇
  2007年   79481篇
  2006年   80301篇
  2005年   77785篇
  2004年   74368篇
  2003年   71691篇
  2002年   69365篇
  2001年   108741篇
  2000年   111451篇
  1999年   93496篇
  1998年   26991篇
  1997年   23659篇
  1996年   24055篇
  1995年   22715篇
  1994年   20894篇
  1993年   19712篇
  1992年   72000篇
  1991年   70070篇
  1990年   68391篇
  1989年   65663篇
  1988年   60302篇
  1987年   59125篇
  1986年   55217篇
  1985年   53004篇
  1984年   39311篇
  1983年   33396篇
  1982年   19858篇
  1979年   35866篇
  1978年   25651篇
  1977年   21230篇
  1976年   20332篇
  1975年   21816篇
  1974年   26149篇
  1973年   24802篇
  1972年   23200篇
  1971年   22037篇
  1970年   20247篇
  1969年   19315篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
192.
OBJECTIVE: To describe Ontario emergency physicians' knowledge of colleagues' sexual involvement with patients and former patients, their own personal experience of such involvement, and their attitudes toward postvisit relationships. DESIGN: Mailed survey. SETTING: Ontario. PARTICIPANTS: Emergency physicians practising in Ontario. RESULTS: Of 974 eligible mailed surveys, 599 (61.5%) were returned. Of these respondents, 52 (8.7%) reported being aware of a colleague in emergency practice who had been sexually involved with a patient or former patient. When describing their own behaviour, 37 respondents (6.2%) reported sexual involvement with a former patient. However, of this group, only 9 (25.0%) had met the patient in an emergency department. Thus, of the total number of respondents, only 1.5% (9/599) reported sexual involvement arising out of an emergency department visit. Most respondents (82.4%) agreed that it is inappropriate behaviour to ask a patient for a date after an emergency assessment and before the patient's departure, and 66.4% felt that it is inappropriate to contact the patient after discharge. However, only 10.6% believed it to be unacceptable to request a social meeting after encountering a patient previously cared for in the emergency department in a nonprofessional setting. Most respondents (96.5%) did not believe that sexual involvement could ever be therapeutic for the patient. However, only 66% felt that it was always an abuse of power and 62.4% supported zero tolerance of all sexual involvement between physicians and patients. CONCLUSIONS: Vague regulatory guidelines currently in place have failed to dispel confusion regarding what is acceptable social behaviour for physicians providing emergency care. Our results support the need for clarification, and suggest a basis for guidelines that would be acceptable to the emergency medical community: that an emergency visit should not form the basis for the initiation of personal or sexual relationships, yet neither should it preclude their development in nonmedical settings.  相似文献   
193.
With pulsed X-ray cinematography we have analysed the angular excursions of the distal hindlimb joints (proximal interphalangeal, PIP; metatarsophalangeal, MTP; ankle) in cats walking on a treadmill. These distal joints transmit the body weight and the dynamic forces onto the ground. We have included the knee and hip joints in the analysis to relate the angular excursions of the proximal and distal joints and to verify the data previously obtained with external markers on the kinematics of the proximal joints. At the beginning of the stance phase the PIP joints flexed rapidly, the MTP joints extended slowly and the ankle and knee yielded under body weight. Whereas the PIP joints maintained a rather constant angular position of −75° throughout the stance phase, extension continued in the MTP joints from −230° at touch-down to −270° at the end of the stance phase. Around 50 ms before lift-off the MTP joints flexed rapidly. Early (−30 ms) after lift-off this flexion changed into a slow extension. The PIP joints extended swiftly at the stance-swing transition and moderately at the end of the swing phase. During the middle part of the swing phase they flexed slowly. Small rotatory movements around the long axis of the foot took place in the last 100 ms of the swing phase. The results of this study on the distal joints are discussed in relation to the placing of the paw, to the translation of forward propulsion into a MTP movement and to the lifting of the paw (conventionally described as toe curling). They show a differentiated mechanical interaction between the different distal limb joints during these different phases, which must be known in detail to interpret the corresponding electromyographic data and to understand how the hip is moved forward over the MTP joints which serve as the final pivot during stance.  相似文献   
194.
Piecewise constant incidence models were developed to estimate the force of infection in women from age-and time-specific antenatal or neonatal seroprevalence data. Differential inclusion of infected women in sero-surveys compared to uninfected women was taken into account, with respect to both changes in inclusion rate following infection, and changes in relative inclusion rate over calendar time. These models were applied to anonymous HIV seroprevalence data collected from neonates born to black and Hispanic women in New York City 1988-1992, with incidence and fertility parameters estimated by maximum likelihood. Estimates of inclusion rate parameters accorded well with what is known about the natural history of HIV. The data could not distinguish between additive and multiplicative combination of the effects of age and time on incidence. Incidence was strongly dependent on age with the highest incidence in women aged 20-34 years. There was strong evidence that incidence had been falling in Hispanic women since 1982-1984. The results illustrate the extent to which trends in incidence over time may be confounded by changes in the relative inclusion rate of infected and uninfected women.  相似文献   
195.
D J Jones  G M Braid    J A Wedzicha 《Thorax》1994,49(8):811-812
BACKGROUND--Nasal mask discomfort is a major factor in compliance with treatment by nasal intermittent positive pressure ventilation (NIPPV) and nasal continuous positive airway pressure (CPAP). METHODS--A study of skin complications resulting from mask usage, with particular reference to predisposing factors, was carried out in 66 patients by means of a postal questionnaire. An effective means of managing ulceration at the nasal bridge while continuing therapy is described. RESULTS--Some disruption of treatment due solely to mask discomfort was experienced by 35 patients (53%), consisting of broken skin or open sores in 11 cases (17%). CONCLUSIONS-Although complications resulting from nasal mask usage are common, early identification of patients at risk of developing such complications and appropriate intervention will result in improved patient compliance.  相似文献   
196.
A case illustrating the potentially fatal complication of endogenous Gram Negative Aerobic Bacillus (GNAB) septicaemia secondary to nosocomial pneumonia is presented along with current theories as to its aetiology. The technique of selective decontamination of the digestive tract is designed and advocated to prevent such occurrences; oral and maxillofacial surgeons should be aware of this approach. It may be, however, that by using much simpler manoeuvres such as changes in policy regarding gastric stress ulcer prophylaxis, the already small risk of such an occurrence will be further reduced. Awareness of this condition will allow a higher index of suspicion when presented with catastrophic septic complications on the ITU and aid in more rational planning of antimicrobial therapy.  相似文献   
197.
The effect of localized hyperthermia on blood flow and cis-diamminedichloroplatinum(II) (CDDP) pharmacokinetics in 7,12-dimethylbenz[a]anthracene-induced mammary adenocarcinomas was studied. Blood flow was determined in rat tumors and normal tissue immediately and 1, 2, and 3 h after local hyperthermia treatment (43 degrees C, 1 h) as well as in unheated tumors of rats. The rate of blood flow in the tumor was increased 1.9 times at the end of treatment relative to control values and returned to the control values by 3 h after hyperthermia. Similarly, the rate of blood flow in the peripheral skin around the tumor immediately after hyperthermia was 2.2 times greater than that of unheated skin and returned to near normal values by 3 h after heating. Tumor-bearing rats received CDDP 1 h before, at the beginning of, at the end of, and 1 h after hyperthermia administration. The CDDP plasma concentration versus time profiles for rats did not vary statistically between treatment groups. Two h after CDDP administration, the mean tumor CDDP concentration of the rats which received drug at the beginning of hyperthermia was statistically greater (P less than 0.05) than tumor CDDP concentrations in rats which received drug at the end of heat treatment. The latter group was given CDDP when tumor blood flow was the greatest; however, mean tumor drug concentration was lowest of all the groups. The mean drug concentration in tumor tissues of rats which received drug 1 h after hyperthermia was comparable to rats which received drug at the beginning of hyperthermia. This suggests that drug delivery or uptake in tumors may be altered when local hyperthermia is administered concurrently or sequentially.  相似文献   
198.
To study micrometastasis at its earliest stages, the bacterial lacZ marker gene was introduced into human EJ Ha-ras-transformed BALB/c 3T3 cells (LZEJ), followed by their intravenous injection into nude mice. Lung micrometastases were easily identified by blue staining of lacZ-tagged cells minutes/hours after injection, permitting effective evaluation of establishment/clearance mechanisms of LZEJ cells. Different treatments were used to disable LZEJ cells (fixation, irradiation, or mitomycin C) to determine modulation of these processes--although unable to divide, these cells stain for lacZ expression for days after treatment. Fixation-killed cells generated large microfoci (> 13-15 cells/focus) with well-rounded morphologies while live, irradiated, or mitomycin-treated cells generated smaller, irregularly shaped foci (3-7 cells/focus). Fixed-cell foci were cleared more slowly from lungs than the other three classes, even when prefiltered to remove large aggregates. All foci of disabled cells were eventually cleared while a basal level of live-cell foci persisted. Co-injection of fixed and live cells (or preinjection of fixed cells, followed by live cells) resulted in complete clearance of live-cell microfoci; in contrast, preinjection of live cells (then injection of fixed cells) led to survival of live-cell micrometastases. Therefore, altered deformability and/or cell surface interactions of tumor cells modulate the effectiveness of host-clearing mechanisms in the lung and in some situations these altered cells facilitate clearance of live tumor cells that are normally tumor-progressing.  相似文献   
199.
An increase in the number of cases of tuberculosis, especially in children, has been observed recently. Post-vaccination conversion rate in babies immunised with BCG was assessed. Sensitization was detected as early as 4 weeks after BCG inoculation. Although 84.2% had physical evidence of BCG inoculation only 69.8% had developed detectable sensitization to the tubercle bacilli as shown by the Mantoux test.  相似文献   
200.
Exposure to cadmium via the diet is known to depend to a large extent on the intake of cereal grains, particularly the high-fibre fractions of wheat. Subjects with low iron status absorb more cadmium than those with better iron status. The purpose of the present study was to determine to what extent cadmium accumulation in human placenta is affected by the intake of grain fibre and maternal iron status during pregnancy. Thirty-nine pregnant women participated in the study. In each trimester the women were requested to complete a dietary history and to allow blood samples to be taken for haemoglobin, serum ferritin and serum thiocyanate determinations, the latter as a marker for smoking. At delivery the whole placenta was taken for the determination of the cadmium concentration. The 32 women who had serum thiocyanate levels less than 70 mumol/l, who had completed at least one dietary history and from whom a blood sample was obtained in the third trimester, were included in the final statistical analyses. In the group of women who consumed less than the median intake of grain fibre and had more than 15 micrograms ferritin/l serum in the third trimester, the placenta cadmium concentration was nearly half that in the placentae of women who had consumed more grain fibre or had lower iron status in late pregnancy.  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