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   8179篇
  免费   1037篇
  国内免费   168篇
耳鼻咽喉   23篇
儿科学   246篇
妇产科学   267篇
基础医学   1498篇
口腔科学   186篇
临床医学   750篇
内科学   1598篇
皮肤病学   55篇
神经病学   651篇
特种医学   203篇
外国民族医学   1篇
外科学   707篇
综合类   580篇
现状与发展   4篇
一般理论   1篇
预防医学   818篇
眼科学   88篇
药学   599篇
  1篇
中国医学   119篇
肿瘤学   989篇
  2024年   82篇
  2023年   392篇
  2022年   631篇
  2021年   706篇
  2020年   475篇
  2019年   451篇
  2018年   332篇
  2017年   352篇
  2016年   325篇
  2015年   362篇
  2014年   532篇
  2013年   611篇
  2012年   366篇
  2011年   383篇
  2010年   301篇
  2009年   353篇
  2008年   318篇
  2007年   291篇
  2006年   255篇
  2005年   231篇
  2004年   183篇
  2003年   160篇
  2002年   160篇
  2001年   141篇
  2000年   108篇
  1999年   104篇
  1998年   95篇
  1997年   77篇
  1996年   75篇
  1995年   64篇
  1994年   50篇
  1993年   69篇
  1992年   49篇
  1991年   53篇
  1990年   39篇
  1989年   30篇
  1988年   37篇
  1987年   20篇
  1986年   21篇
  1985年   18篇
  1984年   26篇
  1983年   8篇
  1982年   19篇
  1981年   5篇
  1980年   10篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1971年   1篇
  1968年   1篇
排序方式: 共有9384条查询结果,搜索用时 15 毫秒
21.
In this longitudinal study of a random sample of North Carolinians over the age of 65 and living in their homes, 325 blacks and 280 whites were examined and interviewed 18 months after baseline examinations. Coronal caries incidence was greater among whites than blacks. The increment due to teeth becoming root fragments were similar for both races; however, there were more newly crowned teeth among whites. Newly crowned surfaces were not used as part of the caries increment in logistic regression models to investigate potential risk predictors. For blacks, caries development over the 18-month period was associated with a higher lactobacillus score and more coronal caries at baseline, more previously filled coronal surfaces, and lack of active membership in clubs or other groups. For whites, having no self-reported tooth sensitivity, having a lower socioeconomic index score, taking antihistamine medications at baseline, and having the perception of more problems after the age of 40 than before were all associated with the development of coronal caries.  相似文献   
22.
Standardised epidemiological caries assessments used in oral health surveys have been shown to be poor at predicting whether a tooth surface will be treated restoratively when a patient visits a dentist. However, it has been argued that oral health surveys may be more relevant in determining needs at the level of an individual or groups of individuals. The objective of this study was to determine the discriminatory power of visual caries assessments at two thresholds (D1 & D3) in adolescents of average age 12.1 years to predict experience of dentinal caries 3 years later or the experience of restorative treatment (not re‐treatment) during the 3‐year period. The data was derived from a prospective 3‐year longitudinal study in which the dental care provided by 41 dentists for 403 adolescents was monitored. Dental caries experience was monitored by annual standardised assessments of caries undertaken by a single trained examiner. ROC analysis showed that caries assessed visually at the D1 threshold in 12‐year‐olds was a better predictor (P < 0.001) of experiencing some dentinal caries after 3 years (Az = 0.781) than was caries assessed visually at D3 threshold in 12‐year‐olds (Az = 0.670). Assessing caries visually at either the D1 or the D3 threshold had no discriminatory power for predicting whether an individual would experience some restorative treatment during the ensuing 3‐year period (Az for D1 = 0.507; Az for D3 = 0.518).  相似文献   
23.
Acute subdural hematoma: Outcome and outcome prediction   总被引:3,自引:0,他引:3  
Patients with traumatic acute subdural hematoma were studied to determine the factors influencing outcome.Between January 1986 and August 1995, we collected 113 patients who underwent craniotomy for traumatic acute subdural hematoma. The relationship between initial clinical signs and the outcome 3 months after admission was studied retrospectively.Functional recovery was achieved in 38% of patients and the mortality was 60%. 91% of patients with a high Glasgow Coma Scale (GCS) score (9–15) and 23% of patients with a low GCS score (3–8) achieved functional recovery. All of 14 patients with a GCS score of 3 died. The mortality of patients with GCS scores of 4 and 5 was 95% to 75%, respectively. Patients over 61 years old had a mortality of 73% compared to 64% mortality for those aged 21–40 years. 97% of patients with bilateral unreactive pupil and 81% of patients with unilateral unreactive pupil died. The mortality rates of associated intracranial lesions were 91% in intracerebral hematoma, 87% in subarachnoid hemorrhage, 75% in contusion.Time from injury to surgical evacuation and type of surgical intervention did not affect mortality. Age and associated intracranial lesions were related to outcome. Severity of injury and pupillary response were the most important factors for predicting outcome.  相似文献   
24.
The aim of this study was to identify predictors of torsades de pointes (TdP) in patients with atrial fibrillation (AF) or flutter exposed to the Class III antiarrhythmic drug almokalant. TdP can be caused by drugs that prolong myocardial repolarization. One hundred patients received almokalant infusion during AF (infusion 1) and 62 of the patients during sinus rhythm (SR) on the following day (infusion 2). Thirty-two patients converted to SR. Six patients developed TdP. During AF, T wave alternans was more common prior to infusion (baseline) in patients developing TdP (50% vs 4%, P < 0.01). After 30 minutes of infusion 1, the TdP patients exhibited a longer QT interval (493 ± 114 vs 443 ± 54 ms [mean ± SD], P < 0.01), a larger precordial QT dispersion (50 ± 74 vs 27 ± 26 ms, P < 0.05), and a lower T wave amplitude (0.12 ± 0.22 vs 0.24 ± 0.16 mV. P < 0.01). After 30 minutes of infusion 2, they exhibited a longer QT interval (672 ± 26 vs 489 ± 74 ms, P < 0.001), a larger QT dispersion in precordial (82 ± 7 vs 54 ± 52 ms, P < 0.01) and extremity leads (163 ± 0 vs 40 ± 34 ms, P < 0.001), and T wave alternans was more common (100% vs 0%, P < 0.001). Risk factors for development of TdP were at baseline: female gender, ventricular extrasystoles, and treatment with diuretics; and, after 30 minutes of infusion: sequential bilateral bundle branch block, ventricular extrasystoles in bigeminy, and a biphasic T wave. Patients developing TdP exhibited early during almokalant infusion a pronounced QT prolongation, increased QT dispersion, and marked morphological T wave changes.  相似文献   
25.
Two hundred forty-two patients referred for various gastrointestinal complaints were evaluated for clinical parameters that would predict findings of lactose malabsorption. Breath hydrogen and blood glucose lactose tests were performed after ingestion of 50 g lactose. Presenting complaints, duration of symptoms, and patient demographics such as age, sex, and ethnic heritage were not different between lactose malabsorbers and absorbers as defined by the breath hydrogen lactose test. Foodrelated symptoms in general and after specific foods such as milk, ice cream, cheese, and yogurt were also similar between groups. Prior to testing, 30% of malabsorbers (N=161) and 36% of absorbers (N=81) reported lactoserelated symptoms (P=NS). The blood glucose response to lactose was abnormal in 60% of malabsorbers and 15% of absorbers. This study confirmed our impression that it is difficult to predict lactose absorption status by clinical parameters. The majority of our lactose malabsorber patients were unaware of lactose-associated symptoms. Furthermore, symptom assessment, demographics, food history, and blood glucose testing did not predict abnormal hydrogen responses to lactose.The opinions and assertations expressed herein are those of the authors and are not to be construed as reflecting opinions of the United States Air Force or the Department of Defense.This work has been presented in part at the Annual Scientific Session of the American Gastroenterological Association, San Francisco, California, May 19, 1986, and published as an abstract (Gastroenterology 90:1562, 1986).  相似文献   
26.
Zinc(II) phthalocyanine is the active component of the liposomal formulation CGP 55847 which showed a high activity in photodynamic therapy in a variety of animal tumours. The photophysical properties of zinc(II) phthalocyanine have been studied in detail and compared to those of Photofrin, the only sensitizing agent approved so far for phase III/IV clinical trials. Since the efficacy of photodynamic therapy intrinsically depends on the spectroscopic features of the sensitizer, quantum chemical methods have proven to be an efficient means for optimizing chemical structures. As will be shown, a simple modification of the time-honoured INDO model of Pople allows a prediction of the singlet and triplet state properties of molecules of the size of zinc(II) phthalocyanine with an rms error of ≤ 1000 cm−1.  相似文献   
27.
Objective:  This study determined the clinical predictors of suicidal behavior during a 2-year follow-up of patients with bipolar disorder presenting with a major depressive episode (MDE).
Method:  Sixty four patients with DSM-III-R bipolar disorder were assessed at presentation for treatment of an MDE. Correlates of past suicidal behavior were determined by comparing patients with and without a history of suicide attempts using a t -test, Wilcoxon test or chi-squared test of independence on individual explanatory variables. Putative predictors of attempts during the follow-up period were tested separately using Cox proportional hazards regression analysis.
Results:  Twelve of 64 patients had at least one suicide attempt in the follow-up period, five of them attempted in the first 2 months and seven around or shortly after the 1-year follow-up visit. All attempters had a history of past suicide attempts. Most predictors of future suicidal behavior were correlates of past suicidal behavior. Family history of suicide acts and comorbid borderline personality disorder predicted early attempts, while younger age, high hostility scores, number of past attempts, subjective pessimism as reflected in depression and suicidal ideation, and few reported reasons for living predicted suicidal acts during the whole period.
Conclusion:  In this data set of bipolar patients we noted an intriguing picture of two clusters of suicide attempts. Hostility was the strongest risk factor. These findings may have implications in both the identification of at-risk patients and the timing of clinical interventions including aggressive pharmacotherapeutic prophylaxis to prevent relapse or recurrence of depressive symptomatology.  相似文献   
28.
The purpose of the study was to examine the relationship between the longitudinal development of incisal tooth wear and periodontal conditions in 51 persons. Stone casts obtained at the ages of 15 and 27 yr were used to assess incisal wear according to a graded scale, the Incisal wear Index (Iwl). The wear increase after 12 yr, ΔIwI, was related to the various health index scores at the age of 15 yr, including the Plaque Index (PII) and Gingival Index (GI) systems. The chi-square tests showed a statistically significant association between AIwI and periodontal condition in 15-yr-olds. Thus, relatively low P1I and GI values were accompanied by relatively high AIwI values. It was concluded that in 15-yr-olds, P1I and GI levels are clinical predictors of future wear (ΔIwI) of maxillary and mandibular central incisors. Pocket depth (PD) was a less valuable clinical predictor of such wear.  相似文献   
29.
The purpose of this study was to identify factors which will predict the risk of severe postoperative complications in individual patients in a neurosurgical unit. Eleven risk factors were investigated in 363 neurosurgical patients, of whom 40 (11%) developed postoperative complications requiring mechanical ventilation for more than 24 h in an intensive care unit, 16 were found to be severely disabled or in a vegetative state at follow-up 1 month after admission, and 28 patients died. By applying stepwise, logistic regression analysis to the patient's data, we were able to select two significant risk variables, i.e. the Glasgow Coma Scale (GCS) 8 or less preoperatively and emergency anaesthesia. The presence of GCS 8 or less on the consciousness scale was associated with postoperative complications in approximately 40% of the cases. Emergency patients with severe neurological damage had the greatest risk of postoperative complications (93%). Fatal outcome for patients with postoperative complications was seen in 40% of the cases.  相似文献   
30.
A feedforward network is used to recognize short, digitized, isolated utterances. A high, multispeaker recognition rate is achieved with a small vocabulary with a single training utterance. This approach makes use of the pattern recognition property of the network architecture to classify different temporal patterns in the multidimensional feature space. The network recognizes the utterances without the need of segmentation, phoneme identification, or time alignment. We train the network with four words spoken by one single speaker. The network is then able to recognize 20 tokens spoken by 5 other speakers. We repeat the above training and testing procedure using a different speaker's utterances for training each time. The overall accuracy is 97.5%. We compare this approach to the traditional dynamic programming (DP) approach, and find that DP with slope constraints of 0 and 1 achieve 98.5% and 85% accuracies respectively. Finally we validate out statistics by training and testing the network of a four-word subset of the Texas Instruments (Tl) isolated word database. The accuracy with this vocabulary exceeds 96%. By doubling the size of the training set, the accuracy is raised to 98%. Using a suitable threshold, we are able to raise the accuracy of one network from 87% to 98.5%. Thresholding applied to all networks would then raise the overall accuracy to well over 99%.

This technique is especially promising because of the low overhead and computational requirements, which make it suitable for a low cost, portable, command recognition type of application.  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