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   4916篇
  免费   1294篇
  国内免费   19篇
耳鼻咽喉   88篇
儿科学   158篇
妇产科学   109篇
基础医学   1017篇
口腔科学   91篇
临床医学   565篇
内科学   1156篇
皮肤病学   61篇
神经病学   395篇
特种医学   232篇
外科学   851篇
综合类   78篇
一般理论   2篇
预防医学   531篇
眼科学   88篇
药学   456篇
中国医学   8篇
肿瘤学   343篇
  2021年   69篇
  2020年   64篇
  2019年   102篇
  2018年   102篇
  2017年   93篇
  2016年   97篇
  2015年   94篇
  2014年   125篇
  2013年   167篇
  2012年   204篇
  2011年   187篇
  2010年   106篇
  2009年   103篇
  2008年   173篇
  2007年   212篇
  2006年   167篇
  2005年   184篇
  2004年   194篇
  2003年   190篇
  2002年   157篇
  2001年   145篇
  2000年   168篇
  1999年   178篇
  1998年   98篇
  1997年   107篇
  1996年   137篇
  1995年   126篇
  1994年   132篇
  1993年   105篇
  1992年   170篇
  1991年   144篇
  1990年   166篇
  1989年   170篇
  1988年   136篇
  1987年   121篇
  1986年   144篇
  1985年   107篇
  1984年   108篇
  1983年   81篇
  1982年   56篇
  1981年   57篇
  1980年   65篇
  1979年   78篇
  1978年   52篇
  1977年   56篇
  1976年   45篇
  1975年   61篇
  1974年   40篇
  1971年   44篇
  1970年   44篇
排序方式: 共有6229条查询结果,搜索用时 15 毫秒
51.
The survival of grafted embryonic striatal tissue, dissected from the lateral ganglionic eminence, depends on the status of the host striatum. We found significantly larger volumes of surviving graft tissue and of striatal-like tissue (P-zone) within the graft, when the host striatum had been subjected to an excitotoxic lesion prior to transplantation surgery. Concomitantly the numbers of surviving grafted cells, assessed in both cresyl violet-stained sections and in sections stained with an immunohistochemical marker for striatal neurons, increased as compared to when graft tissue was placed in an intact unlesioned striatum. Finally, we examined the impact of treatment of the donor tissue with ciliary neurotrophic factor (CNTF) on graft survival. CNTF has previously been shown to protect striatal neurons against excitotoxic insults both in vitro and in vivo, but it did not improve striatal graft survival when added to the cell suspension prior to implantation.  相似文献   
52.
Background: Increased demands for psychiatric services and increased rates of sickness absence for depression have raised the question of the occurrence of psychiatric disorders in Norway, and whether there is in fact a rising incidence rate. Methods: Between 1989–1991, 2015 and 617 persons participated in a two-phase population study. Phase I comprised screening by the Hopkins Symptom Check List 25 items (HSCL-25), and phase II a diagnostic interview by the Composite International Diagnostic Interview (CIDI), including report of date (year) of the first occurrence of any symptoms, and any consequent diagnosis: Results: A symptom score of 1.75 or more was found in 19.8% of the women and 9.3% of the men by the HSCL-25. Depression, anxiety or somatoform disorder by CIDI was found in 21.5% of the women and 11.5% of the men. The incidence rate increased significantly from 3.3 to 12.8 per 1000 person years from 1930 to 1991. The incidence rate in the year before the interview was 42.6 per 1000 person years. Age of onset became lower. More women became ill, but the illness seemed to last longer in men. A major problem in comparing results between studies is the different concepts and operationalisations of psychiatric illness, and the varying time periods given for estimates. Conclusion: The findings provide evidence of psychiatric illness being a rising and major health problem, but the role of recall bias must be further investigated. Accepted: 19 August 1999  相似文献   
53.
Manipulations of plasma catecholamine concentrations influence outcome from ischemic brain insults. It has been suggested that these effects are mediated by influences on brain catecholamine concentrations. This study examined whether major changes in brain norepinephrine concentrations can alter outcome from severe forebrain ischemia. Sprague-Dawley rats were administered 50 mg/kg i. p. N-(chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) or were left untreated (control). One week later, these rats were subjected to either 7 or 8 min of normothermic forebrain ischemia (bilateral carotid occlusion and MABP=30 mmHg) and allowed to recover for 4 days. Histologic damage was then evaluated. In other control and DSP-4-treated animals, hippocampal microdialysate norepinephrine concentrations were measured before, during and after 8 min of forebrain ischemia. Norepinephrine concentrations were also determined in brain homogenates from non-ischemic DSP-treated and control rats. A 95% depletion of norepinephrine was observed in brain homogenates from non-ischemic DSP-4-treated rats compared with control. During ischemia, microdialysate norepinephrine concentrations increased in control but not in DSP-4-treated rats (P=0.002). For plasma, intra-ischemic epinephrine concentrations increased 8-10-fold and returned to baseline values post-ischemia with no differences between groups. Plasma norepinephrine values remained unchanged in both groups. Histologic damage resulting from either 7 or 8 min of ischemia in hippocampal structures, caudoputamen, and neocortex was similar between DSP-4-treated and control groups. This study could not identify any effect of major changes in brain norepinephrine concentrations on ischemic brain damage. These data indicate that peripheral catecholamine effects on near-complete forebrain ischemic outcome are unlikely to be mediated by effects on central catecholamine concentrations.  相似文献   
54.
OBJECTIVES: Retrospective exposure assessments are often performed in epidemiologic studies. The presence of an eventual misclassification, both nondifferential and differential, is debated but can rarely be investigated. The aim of this study was to compare self-reported information on the same physical and psychosocial work exposures with 25 years' difference. METHODS: In 1969-1970 a survey of randomly chosen men and women in Stockholm county, concerning, among other things, work exposures, was undertaken. During 1993-1994, 280 subjects participated in a reexamination, regarding psychosocial and physical factors at work and musculoskeletal disorders. The questions were all formulated in the same way as in 1969-1970. RESULTS: When self-reported information on work exposures, collected with a 25-year interval, was compared, acceptable, although not high, agreement was found for 3 out of 4 physical factors and for 4 out of 10 physical environmental factors. Questions measuring psychosocial load had somewhat lower agreement. Current exposure status influenced the memory of past exposures. Study subjects who reported low-back disorders at the reexamination tended to show a better agreement in their assessments of retrospective exposures than those without current symptoms. When relative risks from original and retrospective data were calculated, hardly any influence on the estimates due to that differential misclassification could be found. For persons with and without neck or shoulder symptoms no apparent differences in assessments were found. CONCLUSIONS: Retrospective assessments of exposures at the workplace showed misclassifications to a certain degree. However, the influence of the misclassifications on the risk estimates was limited.  相似文献   
55.
The effect of thiopental on glutamate metabolism was studied by 13C magnetic resonance spectroscopy. Cerebral cortical astrocytes were incubated with 0.5 mM [U-13C]glutamate for 2 hr in the presence of 0.5 or 1 mM thiopental. Labeled glutamate, glutamine, aspartate, and glutathione were observed in cell extracts, and glutamine, aspartate, and lactate in the medium. Not only present in the medium was uniformly labeled glutamate, but also glutamate derived from the tricarboxylic acid (TCA) cycle, and thus glutamate release could be detected. The amounts of [U-13C]glutamate and unlabeled glucose taken up by astrocytes were unchanged in the presence of 0.5 mM thiopental and decreased to about 50% and 80%, respectively when the concentration was increased to 1 mM. The amounts of most metabolites synthesized from [U-13C]glutamate were unchanged in the presence of 0.5 mM thiopental, but decreased [U-13C]glutamine, [U-13C]aspartate, and [U-13C]lactate were observed in the 1 mM group. Surprisingly, the amounts of [1,2,3-13C]glutamate, [2,3-13C]aspartate, and [3,4-13C]aspartate (2nd turn via the TCA cycle) were unchanged. However, this was not the case for [1,2-13C]lactate and [2,3-13C]lactate. Such variations indicate cellular compartmentation, possibly caused by a heterogeneous glutamate concentration within the cells affecting TCA cycle turnover rates differently.  相似文献   
56.
We report a case of Takayasu's disease with severe renovascular hypertension in a girl from Eritrea. In the "burn-out" phase after the erythrocyte sedimentation rate had normalized, reconstructive vascular surgery was performed as further progression of the disease seemed unlikely. However, probably due to her growth, the graft rotated and a second operation was successfully performed.  相似文献   
57.
BACKGROUND: The aim was to evaluate the use of clevidipine, a new vascular selective, ultra-short-acting calcium antagonist for blood pressure control after coronary artery bypass grafting (CABG). METHODS: The effects of clevidipine on central hemodynamics, myocardial blood flow and metabolism were studied at two different phases after CABG. In phase 1 (n=13), the hypertensive phase, the effects of clevidipine were compared to those of sodium nitroprusside (SNP) when used to control postoperative hypertension. In phase 2 (n=9), the normotensive phase, a clevidipine dose-response relationship was established. RESULTS: At a target mean arterial pressure (MAP) of 75 mmHg, systemic vascular resistance (SVR) and heart rate (HR) were lower, preload, stroke volume (SV) and pulmonary vascular resistance (PVR) were higher, while there were no differences in myocardial lactate metabolism or oxygen extraction with clevidipine compared to SNP. In the normotensive phase, clevidipine induced a dose-dependent decrease in MAP (-19%), SVR (-27%) and PVR (-15%), accompanied by an increase in SV (10%), but no reflex increase in HR or changes in cardiac preload. Clevidipine caused a direct coronary vasodilation, as indicated by a decrease in myocardial oxygen extraction from 54% to 45%. Myocardial lactate metabolism was unaffected by clevidipine. The blood clearance of clevidipine was 0.05 l x min(-1) x kg(-1), the volume of distribution at steady state was 0.08 l x kg(-1) and the initial and terminal half-lives were <1 min and 4 min, respectively. CONCLUSIONS: Clevidipine rapidly reduced MAP and induced a systemic, pulmonary and coronary vasodilation with no effect on venous capacitance vessels or HR. Clevidipine caused no adverse effects on myocardial lactate metabolism. Clevidipine thus appears suitable to control blood pressure after CABG.  相似文献   
58.
OBJECTIVE: The aims of the study were to determine whether the caregivers of discharged patients with schizophrenia were satisfied with their situation in general and with psychiatric services in particular and to examine the factors associated with caregiver satisfaction. METHODS: The data were drawn from a national project designed to study the treatment and life situation of deinstitutionalized schizophrenia patients in Finland. The patients were discharged from psychiatric hospitals in 1986, and both the patients (N=775) and their caregivers (N=545) were interviewed after a three-year follow-up. RESULTS: One-fifth of the caregivers were dissatisfied with the situation in general, and one-third were dissatisfied with the psychiatric services the patient received. Caregivers were more likely to be dissatisfied with the situation if they lived with the patient and if the patient's functional state was poor or the patient's use of services, particularly medication and rehabilitation, was low. Caregivers were likely to be dissatisfied with the psychiatric services if the patient had severe psychotic symptoms and poor "maintenance of grip on life" or if the patient was given less psychiatric care and rehabilitation or used more social services. CONCLUSIONS: The satisfaction of caregivers of persons with mental illness appears to have two dimensions. First, caregivers need to be accepted and treated as active partners in the patients' care and rehabilitation. Second, the burden on the families of persons with mental illness can be alleviated with long-term rehabilitation and care to help patients gain as high a functional state as possible.  相似文献   
59.
Background: Sickness absence with psychiatric disorders is a major public health problem with serious consequences for the individual, the employer and society. The aim was to assess the occurrence of psychiatric sickness absence with special focus on sex differences. Methods: A nationwide sickness insurance register was used. Population at risk was defined as all individuals entitled to sickness benefits in 1994 (N = 1,978,030). Those who were sick-listed for more than 14 consecutive days with a psychiatric diagnosis (n = 28,799) were selected as cases. Results: Of the population under study, 1.46% had at least one psychiatric sickness absence episode. Women had twice the male cumulative incidence of sickness absence for a psychiatric diagnosis. Cumulative incidence was highest among those aged 45–59 years. Men had more sickness absence days. Depression was the most common diagnosis among both women and men. Conclusion: Increased efforts are needed to recognise, treat and rehabilitate individuals with a lowered work capacity due to sickness absence. The increased risk of long sick-leave spells among men needs further attention. Accepted: 22 March 2000  相似文献   
60.
BACKGROUND: Although reduction of cerebral metabolic rate is thought to contribute to anesthetic neuroprotection, histologic evidence to support this concept has not been provided. In this study, histologic outcome was evaluated in rats subjected to different durations of severe forebrain ischemia while anesthetized with volatile anesthetics that have substantially different effects on cerebral metabolic rate. METHODS: Normothermic rats that underwent fasting were anesthetized with 0.75 minimum alveolar concentration (MAC) isoflurane-60% nitrous oxide (N2O) or 0.75 MAC halothane-60% N2O. Ischemia was induced with use of a combination of bilateral carotid occlusion and controlled hypotension. Rats in the isoflurane group were subjected to 6.5 min or 8.0 min ischemia, whereas the halothane group received 6.5 min ischemia. Histologic damage was assessed 4 days later. RESULTS: With 6.5 min ischemia, mean +/- SD, hippocampal CA1 percent of dead (% dead) neurons was reduced with isoflurane-N2O (45 +/- 18) versus halothane-N2O (60 +/- 23, P = 0. 023). Eight minutes of ischemia increased % dead neurons in the isoflurane-N2O group (60 +/- 17, P = 0.017). There was no difference between the isoflurane 8.0-min and halothane 6.5-min groups (P = 0. 935). A similar pattern was observed in hippocampal CA4 and the neocortex. Striatal damage was not affected by anesthetic or ischemic duration. CONCLUSIONS: At 6.5 min ischemia, isoflurane provided improved outcome versus halothane. Previous research has shown that 0.75 MAC isoflurane-N2O increases the time to onset of ischemic depolarization by 1.5 min and reduces cerebral metabolic rate by 42% versus 0.75 MAC halothane-N2O. In the current study, when the duration of ischemia was increased by 1.5 min in the isoflurane-N2O group, histologic outcome became similar to that in halothane-N2O-anesthetized rats. These results provide evidence that cerebral metabolic rate reduction has an advantageous effect on outcome from severe brain ischemia, but also suggest that such benefit is likely to be small.  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