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   70815篇
  免费   7339篇
  国内免费   1843篇
耳鼻咽喉   446篇
儿科学   1627篇
妇产科学   1399篇
基础医学   4801篇
口腔科学   1604篇
临床医学   8103篇
内科学   10446篇
皮肤病学   2489篇
神经病学   4126篇
特种医学   1037篇
外国民族医学   7篇
外科学   5942篇
综合类   10212篇
现状与发展   8篇
一般理论   2篇
预防医学   15671篇
眼科学   1136篇
药学   4461篇
  57篇
中国医学   1714篇
肿瘤学   4709篇
  2024年   277篇
  2023年   1325篇
  2022年   2679篇
  2021年   3517篇
  2020年   3502篇
  2019年   2649篇
  2018年   2600篇
  2017年   2740篇
  2016年   3089篇
  2015年   2768篇
  2014年   5044篇
  2013年   6143篇
  2012年   4605篇
  2011年   4735篇
  2010年   3676篇
  2009年   3352篇
  2008年   3227篇
  2007年   3145篇
  2006年   2820篇
  2005年   2434篇
  2004年   1976篇
  2003年   1723篇
  2002年   1471篇
  2001年   1359篇
  2000年   1065篇
  1999年   896篇
  1998年   884篇
  1997年   800篇
  1996年   687篇
  1995年   633篇
  1994年   571篇
  1993年   438篇
  1992年   479篇
  1991年   449篇
  1990年   323篇
  1989年   319篇
  1988年   283篇
  1987年   191篇
  1986年   185篇
  1985年   184篇
  1984年   159篇
  1983年   102篇
  1982年   113篇
  1981年   82篇
  1980年   74篇
  1979年   57篇
  1978年   37篇
  1977年   33篇
  1976年   39篇
  1975年   29篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
In a two-wave longitudinal study of third and sixth graders ( N = 617), we obtained self-reports of depression and peer, teacher, parent, and self-reports of competence in five domains: academic, social, attractiveness, conduct, and athletic. Competency evaluations by others predicted change in self-perceived competence over time for girls, but not for boys. Depression predicted change in self-perceived competence over time for boys but not for girls. Among girls, the relative importance of parent, teacher, and peer appraisals shifted from third to sixth grade. For both boys and girls, self-perceptions of competence predicted change in depression scores over time. Furthermore, self-perceived competencies mediated the relation between competency appraisals by others and children's self-reported depression. Results are interpreted in light of a competency-based model of child depression.  相似文献   
202.
To determine the risk factors associated with mortality in very low birthweight (VLBW) infants admitted to the neonatal intensive care units (NIUC) in Malaysia.

Method:


A prospective observational study of outcome of all VLBW infants born between 1 January 1993 and 30 June 1993 and admitted to the NICU.

Results:


Data of 868 VLBW neonates from 18 centres in Malaysia were collected. Their mean birthweight was 1223 g (95% confidence intervals: 1208–1238 g). Thirty-seven point four per cent (325/868) of these infants died before discharge. After exclusion of all infants with congenital anomalies ( n =66, and nine of them also had incomplete records) and incomplete records ( n =82), stepwise logistic regression analysis of the remaining 720 infants showed that the risk factors that were significantly associated with increased mortality before discharge were: delivery in district hospitals, Chinese race, lower birthweight, lower gestation age, persistent pulmonary hypertension of the newborn, pulmonary airleak, necrotizing enterocolitis of stage 2 or 3, confirmed sepsis, hypotension, hypothermia, acute renal failure, intermittent positive pressure ventilation, and umbilical arterial catheterization. Factors that were significantly associated with lower risk of mortality were: use of antenatal steroid, oxygen therapy, surfactant therapy and blood transfusion.

Conclusion:


The mortality of VLBW infants admitted to the Malaysian NICU was high and was also associated with a number of preventable risk factors.  相似文献   
203.
In a series of 227 cases of endometrial carcinomas in FIGO stages I–IV, treated during the years 1984–89, immunohistochemical staining for the protein products of the two tumor suppressor genes p53 and retinoblastoma (Rb) were evaluated as prognostic factors with regard to tumor stage, FIGO grade, nuclear grade, morphometric nuclear parameters, DNA ploidy and S-phase fraction. Long-term survival analyses were endpoints and the Cox multivariate technique was used to evaluate the prognostic factors. In 20% of the cases p53 was positive. This was a genuine high-risk group associated with primary advanced carcinoma, nonendometrioid histology, poorly differentiated tumors, severe nuclear atypia, DNA aneuploidy, primary persistent tumors, recurrent tumors and a poor long-term survival rate (37% 5-year survival). In patients dying of their disease, 54% of the tumors stained positive for p53, compared with only 10% of the tumors not killing their hosts. Positive p53 staining was more common in older women. A pathologic Rb status (negative staining) was recorded in 6% of the cases. The Rb factor had only a minor influence on long-term survival and was not significant in multivariate analyses. The p53 staining status was the second most important prognostic factor after the nuclear grade in Cox multivariate analyses, after correcting for stage and age. Immunohistochemical staining for p53 protein should be included among previous available and important prognostic factors in endometrial carcinoma.  相似文献   
204.
During 1996 and 1997 a panel of European haematologists, oncologists, and neonatologists developed specific paediatric guidelines for the use of colony stimulating factors based on published literature and the clinical experience of these specialists within each of 13 countries. Well established indications for use comprise intervention in patients with life-threatening infection, adjunctive therapy post autologous bone marrow transplantation (BMT), mobilization of peripheral blood progenitor cells for autologous BMT, patients with acquired aplastic anaemia on anti-lymphocyte globulin and cyclosporin regimen, and severe congenital neutropenia. Less clear indications include primary prophylaxis to support dose intensification in children with high risk/advanced malignancies, secondary prophylaxis to prevent neutropenia in patients with a history of severe neutropenia, support therapy in cases of poor marrow function following BMT and for deteriorating marrow function following successful BMT, in neonatal sepsis and non infectious neonatal neutropenia, in drug induced neutropenia and in HIV-positive patients. Treatment is generally well tolerated and granulocyte colony stimulating factor appears better tolerated than granulocyte and macrophage colony stimulating factor. Economically colony stimulating factors have not been shown to induce excessive costs for a given patient. Conclusion In general the adult guidelines are applicable to children but additional considerations (aggressive or very progressive childhood neoplasms, specific indications, neonatal use, congenital disorders) must be taken into account. Received: 21 October 1997 and in revised form: 30 April 1998 /Accepted: 5 May 1998  相似文献   
205.
Voice endurance tests are often used to evaluate vocal fatigue or to test the suitability of an individual for voice demands. It is assumed that these tests help to identify subjects with laryngeal or vocal fatigue out of a population of persons with complaints of discomfort in the throat, recurrent hoarseness and decreased voice power. In this study we evaluated the Voice Interval Test with respect to its discriminative power by comparison of voice performances in 20 patients with a history of vocal fatigue with that in 12 healthy subjects. Voice performance was studied during the Voice Interval Test as well as during regular use of the voice on a working day by electroglottography (EGG), acoustic analysis and a self-rating scale for pain and fatigue. Despite the number of tests the data did not reveal any significant difference between the patients and the healthy subjects. Voice fatigue could therefore not be identified and the clinical relevance of the Voice Interval Test appears to be questionable.  相似文献   
206.
We investigated colonization with Ureaplasma urealyticum (Uu) in infants <30 weeks gestation and assessed the relationship to other risk factors influencing respiratory morbidity, plus the effect of treatment with erythromycin. Ventilated preterm infants [ n = 155; median GA 26 (23–29) weeks] were cultured for Uu in endotracheal aspirate and nasopharynx. Colonized infants were randomly assigned to treatment with erythromycin 40mg/kg/d, intravenously or orally. The rate of colonization was 29/155 (19%) and the Uu-colonized infants had lower mean gestational ages than the culture-negative infants (25 vs 26 weeks). For the colonized infants PROM (48% vs12%), chorioamnionitis in the mother (46% vs 17%) and vaginal delivery (71% vs 29%) were more common. More colonized infants needed supplemental oxygen at 36 weeks'postconceptual age ( p < 0:05). Erythromycin treatment was effective in reducing colonization with negative control cultures in 12/14 (86%) of treated infants. No significant differences were found between the colonized treated infants ( n = 14) and those not treated ( n = 14) in time with supplemental oxygen. Oxygen requirement at 36 weeks was related to lower gestational age, late appearance of PDA, late onset sepsis and signs of chorioamnionitis in the mother. We conclude that the Uu colonization is related to increasing immaturity, the presence of prolonged rupture of membranes, signs of chorioamnionitis and vaginal delivery. Treatment with erythromycin reduced colonization but did not significantly alter length of time with supplemental oxygen.  相似文献   
207.
Effects of Pediatric Chronic Physical Disorders on Child and Family Adjustment   总被引:26,自引:0,他引:26  
Research conducted primarily over the past 5–8 years on the psychosocial effects of pediatric chronic physical disorders on children and their families is reviewed. A large body of studies show that both children and their mothers, as groups, are at increased risk for psychosocial adjustment problems compared to peers, but that there is considerable individual variation in outcome. Since the last review on this topic (Eiser, 1990a), many studies have been conducted to identify risk and resistance factors associated with differences in adjustment among these children and their mothers. Improvements are noted in the theoretical basis for this work, programmatic nature of some of the research, and efforts at producing clinically relevant information. Evaluations of interventions, however, are lagging. Critical issues and future directions regarding developmental approaches, theory, method, measurement and intervention are discussed.  相似文献   
208.
Purpose and Methods: We performed multiple comparisons between available amino acid (aa) sequences of homeodomain(HOM)-containing proteins from a wide spectrum of animals to create an evolutionary classification of the proteins. Results: Based on results of statistical and special computational analyses of over 500 homeodomain aa sequences (HOMs) a novel system of concepts describing complex structural correlations between homologous proteins is proposed. This system includes such notions as differentiated isofunctionality of aa, chemotype, stereotype, local functional motifs, gradual conservativeness of aa positions, and group-specific domain patterns, as well as major categories of the evolutionary classification of HOMs (Division, Type, Branch, Class, Family, Series, Variety, Sort). Using this approach, a complete structural systematics of HOMs belonging to proteomes of eukaryotic animals is proposed. Conclusions: The proposed structural classification of HOMs is in full agreement with the bulk of experimental data revealing complex functional similarities and differences among HOMs in terms of their expression patterns in developing embryos. It turn, this classification can provide answers regarding homology among homeodomains when experimental data are conflicting.  相似文献   
209.
BACKGROUND: So far there are three different scores to predict postoperative vomiting (PV: Apfel et al., 1998) or postoperative nausea and vomiting (PONV: Koivuranta et al., 1997; Palazzo and Evans, 1993). All three scores used logistic regression analysis to identify and create weights for the risk factors for PV or PONV. In short, these were sex, age, history of previous PONV, motion sickness, duration of anaesthesia, and use of postoperative opioids. However, an external evaluation and a comparison of these scores has not been performed so far. METHODS: Patients undergoing a variety of surgical procedures under general anaesthesia were studied prospectively. Preoperatively, they completed a questionnaire concerning potential risk factors for the occurrence of PV or PONV implemented in the three risk scores. Balanced anaesthesia (induction agent, nondepolarising neuromuscular blocker, opioid, and inhalation agent in nitrous oxide/oxygen) was performed. No intravenous anaesthesia or any antiemetic prophylaxis was applied. Postoperatively, the patients were observed in the recovery room for the occurrence of PV and PONV and were visited twice on the ward within the 24-h observation period. Both the patients and the nursing staff were asked whether PV or PONV was present. The severity of PONV was categorised using a standardised scoring algorithm. A total of 1,444 patients was finally included into the analysis. Using information of the predicted risk for the individual patients and the actual occurrence of PV or PONV, Receiver Operator Characteristics (ROC-curves) were drawn. The area under each ROC-curve was calculated as a means of the predictive properties of each score and was compared for statistical differences. RESULTS: For prediction of PONV (any severity) the AUC-values (AUC=area under the curve) and the corresponding 95%-confidence intervals were: Apfel: 0.70 (0.67-0.72); Koivuranta: 0.71 (0.69-0.73); Palazzo: 0.68 (0.65-0.70). For prediction of PV: Apfel: 0.73 (0.71-0.75); Koivuranta: 0.73 (0.70-0.75); Palazzo: 0.68 (0.65-0.70). Thus, all three scores appeared to have a moderate accuracy as measured by the AUC. The score of Koivuranta predicts PONV (P=0.007) and also PV (P=0.002) significantly better than Palazzo's score. Furthermore, for predicting of PV the score of Apfel was also superior to Palazzo's score (P=0.005). All three scores predict PV with the same accuracy as PONV. CONCLUSION: The occurrence of PV and PONV in patients undergoing surgery under balanced anaesthesia can be predicted with moderate but acceptable accuracy using one of the available risk scores, regardless of local surgical or anaesthesiological circumstances. For clinical practice, we recommend the score published by Koivuranta, since its calculation is very simple.  相似文献   
210.
PURPOSE: We performed a prospective study to determine the incidence and spectrum of metabolic abnormalities predisposing to stone formation in patients with ureteropelvic junction obstruction and renal calculi. MATERIALS AND METHODS: A total of 47 consecutive patients with congenital ureteropelvic junction obstruction underwent metabolic evaluation of stone risk factors. Of these patients 21 had associated stones (study group), while 26 did not (control group). Logistical regression, Wilcoxon rank sum and Fisher's exact tests were performed to determine whether there was a significant difference between these groups in regard to the presence of metabolic risk factors. RESULTS: Demographically and symptomatically the 2 groups were equivalent except that the study patients were older. The 24-hour urinary excretion of calcium was significantly higher in study than in the control patients (p = 0.007). While the incidence of hypercalciuria and hyperuricosuria was also higher in the study population, these differences were not significant (p = 0.08 and 0.07, respectively). CONCLUSIONS: Metabolic abnormalities predisposing to stone formation are present more frequently in patients with ureteropelvic junction obstruction who have associated stones compared to those who do not. As such, urinary stasis alone does not explain stone formation in these cases. Rather, the local physiological environment of urine likely has a predisposing role. In addition to restoring unobstructed urinary flow, consideration should be given to metabolic evaluation and prophylactic treatment for affected patients.  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