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   52606篇
  免费   3886篇
  国内免费   131篇
耳鼻咽喉   659篇
儿科学   1368篇
妇产科学   1241篇
基础医学   6775篇
口腔科学   1597篇
临床医学   6124篇
内科学   10236篇
皮肤病学   806篇
神经病学   4680篇
特种医学   1993篇
外国民族医学   2篇
外科学   6600篇
综合类   665篇
一般理论   44篇
预防医学   5121篇
眼科学   1157篇
药学   3999篇
  3篇
中国医学   102篇
肿瘤学   3451篇
  2022年   287篇
  2021年   647篇
  2020年   462篇
  2019年   731篇
  2018年   866篇
  2017年   671篇
  2016年   729篇
  2015年   876篇
  2014年   1334篇
  2013年   2091篇
  2012年   2991篇
  2011年   3221篇
  2010年   1770篇
  2009年   1696篇
  2008年   2954篇
  2007年   3211篇
  2006年   3239篇
  2005年   3054篇
  2004年   3140篇
  2003年   2958篇
  2002年   2785篇
  2001年   1052篇
  2000年   879篇
  1999年   975篇
  1998年   708篇
  1997年   579篇
  1996年   547篇
  1995年   501篇
  1994年   461篇
  1993年   446篇
  1992年   672篇
  1991年   691篇
  1990年   589篇
  1989年   639篇
  1988年   599篇
  1987年   588篇
  1986年   551篇
  1985年   626篇
  1984年   524篇
  1983年   436篇
  1982年   432篇
  1981年   412篇
  1980年   356篇
  1979年   365篇
  1978年   301篇
  1977年   266篇
  1976年   258篇
  1975年   224篇
  1974年   253篇
  1973年   238篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Glucose is provided to cells by a family of glucose transport facilitators known as GLUTs. These transporters are expressed in a tissue specific manner and are overexpressed in many primary tumors of these tissues. Regulation of glucose transport facilitator expression has been demonstrated in endometrial tissue and endometrial adenocarcinoma. The following experiments were conducted to quantify and localize the expression of GLUT1 and GLUT8 in benign endometrium and compare this expression to endometrial cancer. Endometrial tissue samples were obtained from random hysterectomy specimens of patients with benign indications for surgery and endometrial cancer. Immunoblot and immunolocatization studies were performed using GLUT1 and GLUT8 specific antisera. Endometrial samples from 65 women who had undergone hysterectomy were examined (n=38 benign, n=27 malignant). A 44 and a 35.4 kDa immunoreacive species was demonstrated in endometrium and endometrial cancer for GLUT1 and GLUT8, respectively. Upregulation of GLUT1 expression was demonstrated with increasing grade of tumors (P<0.002). GLUT8 expression was increased in all tumor subtypes compared to atrophic endometrium (P<0.001). Apical localization by GLUT1 and GLUT8 was demonstrated in endometrial glands. GLUT1 and GLUT8 demonstrated diffuse intracellular localization in the cancer subtypes. GLUT1 and GLUT8 are expressed in both human endometrium and endometrial cancer. There appears to be a step-wise progression in GLUT1 and GLUT8 expression as tumor histopathology worsens. GLUT1 and GLUT8 may be important markers in tumor differentiation, as well as providing energy to rapidly dividing tumor cells.  相似文献   
82.
Background. The National Heart, Lung, and Blood Institute (NHLBI) guidelines recommend that patients receive a follow-up outpatient asthma visit after being discharged from an emergency department (ED) for asthma. Objective. To measure the frequency of follow-up outpatient asthma visits and its association with repeat ED asthma visit. Design. We conducted a retrospective cohort study of children with asthma using claims data from a university-based managed care organization from 01 1998 to 10 2000. We performed a multivariate survival analysis using Cox proportional hazards model to determine the effect of follow-up outpatient asthma visits on the likelihood of a repeat ED asthma visit, after controlling for severity of illness, patient age, gender, insurance, and the specialty of the primary care provider. Results: A total of 561 children had 780 ED asthma visits. Of these, 103 (17%) had a repeat ED asthma visit within 1 year. Almost two-thirds of children (66%) did not receive outpatient follow-up for asthma within 30 days of an ED asthma visit. Outpatient asthma visits within 30 days of an ED asthma visit are associated with an increased likelihood (relative risk = 1.80; 95% confidence interval 1.19, 2.72) for repeat ED asthma visits within 1 year. Conclusions. Most patients do not have outpatient follow-up after an ED asthma visit. However, those patients that present for outpatient follow-up have an increased likelihood for repeat ED asthma visits. For the primary care provider, these outpatient follow-up visits signal an increased risk that a patient will return to the ED for asthma and are a key opportunity to prevent future ED asthma visits.  相似文献   
83.
Pulmonary diffusing capacity for carbon monoxide (DLCO) and pulmonary capillary blood flow (Qp) were measured on exercise in patients with a low DLCO with the aim of predicting, from the overall DL/Qp ratio, diffusion limitation for oxygen and relating it to the fall in arterial oxygen saturation actually observed. Five patients with cryptogenic fibrosing alveolitis (DLCO ranging from 20-54% predicted normal) exercised for 5 min at a work load equal to 60% of their maximum (45 to 90 watts). At 5 min (and previously at rest) they rebreathed rapidly for 15 sec from a 1.0 L bag containing helium (He), sulphur hexafluoride (SF6) and freon-22, 30% oxygen in argon and less than 1 ppm 11C-labelled carbon monoxide. Pulmonary capillary blood flow (Qp) and diffusing capacity (DLCO) were measured from flow-weighted breath-by-breath concentrations of freon-22 and 11CO, after correction for gas mixing delays (using He and SF6). Oxygen saturation (SaO2) (ear oximetry), MO2 and MCO2 and cardiac frequency were measured. PAO2 (ideal) was derived and mixed venous O2 saturation and content were calculated (Fick); PaO2 and PVO2 were derived from standard dissociation curves. For comparison, DLCO and Qp were measured in a similar fashion in five normal subjects exercising at 60 watts. Mean DLCO in patients with fibrosis was 9.62 (SD 2.88) ml.min-1, mm Hg-1 on exercise and mean Qp was 10.48 (SD 1.79) L.min-1 giving mean DLCO/Q ratios of 0.92 (SD 0.28). At 60 watts mean DLCO/Qp in normal subjects was 2.54 (SD 0.3), 2.76-times greater than in patients. SaO2% fell in patients by 3-15% on exercise. Predictions of alveolar-end capillary PO2 gradients from these overall DL/Q gradients showed that diffusion limitation accounted for 99% of the alveolar-arterial PO2 gradient on exercise in fibrosing alveolitis. Hughes (1991 Respir. Physiol. 83:167-178) [corrected] suggests that this simple approach overestimates the contribution of diffusion limitation by about 30%.  相似文献   
84.
BACKGROUND AND METHODS. Rapid changes in cardiac output (CO) and organ perfusion occur with hemorrhagic shock and fluid resuscitation. To assess regional alterations of flow, 40 Sprague-Dawley male rats were subjected to hemorrhagic shock and crystalloid resuscitation under halothane anesthesia. Polyethylene microspheres were injected before and after hemorrhage and after resuscitation. At sacrifice, brain, lungs, heart, liver, intestine, spleen and kidneys were harvested, weighed and radioactivity counted. Changes in mean arterial pressure, oxygen consumption, organ flow and CO were also measured. RESULTS: Cardiac output decreased during hemorrhage (P less than 0.01), it increased with resuscitation but did not return to baseline even with infusion of fluid volumes of three times the blood loss. Flow decreased during hemorrhage in all organs, but the difference was not statistically significant in the liver (P greater than 0.05), since a larger percentage of CO was maintained as hepatic perfusion. During resuscitation, flow to brain and kidneys increased over the percentage values expected by increased CO (P less than 0.01), but flow to the liver did not increase significantly. Flow to small bowel remained depressed (P less than 0.005). CONCLUSIONS: Following hemorrhage there is hypoperfusion of all splanchnic organs; however, flow to the liver decreases least. Crystalloid resuscitation in our model failed to return CO to baseline. Blood supply to intestine remained depressed in disproportion to CO both after hemorrhage and resuscitation and hepatic blood flow remained decreased after resuscitation.  相似文献   
85.
86.
87.
High-frequency ventilation: issues of strategy   总被引:1,自引:0,他引:1  
Although each high-frequency ventilator has functional characteristics that are design related, it now appears that when used with similar treatment strategies and within their functional limitations, similar clinical outcomes can be realized. Optimized treatment protocols must vary depending on the pulmonary disease to be treated, with strategies during treatment for pulmonary injury different from those used in pulmonary injury prevention. It is still unclear whether any one particular high-frequency ventilator will have specific disadvantages that cannot be overcome by device modification and that are inherent in a particular HFV methodology. Experimental and clinical data suggest that HFV will contribute significantly in reducing neonatal pulmonary morbidity and aid in the prevention of chronic pulmonary disease.  相似文献   
88.
The intrauterine position occupied by a rodent fetus influences the amount of testosterone to which it is exposed before birth. Animals that are gestated between two male fetuses (2M) are exposed to higher circulating levels of testosterone than are animals positioned between two female fetuses (2F) and there are reliable differences in the reproductive physiology and behavior of 2M and 2F animals when adult. To determine whether intrauterine position modifies development of the central nervous system, we examined the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) in male and female gerbils from known intrauterine positions. We found that adult 2M female gerbils had 16% more SNB motoneurons than did 2F females. 2M males did not differ from 2F males in SNB motoneuron number, but the bulbocavernosus muscle, which is innervated by SNB motoneurons, was approximately 50% larger in 2M than in 2F males. These data indicate that intrauterine position can influence the morphology of the sexually dimorphic SNB neuromuscular system.  相似文献   
89.
Reports of an 18-fold higher incidence of schizophrenia among second-generation Afro-Caribbeans, and especially Jamaican migrants in the United Kingdom were soon called “an epidemic of schizophrenia,” with the inference that a novel virus, likely to be perinatally transmitted, was a possible etiological agent. This intriguing observation led us to explore a possible link with human T-cell lymphotropic virus type one (HTLV-I), because it is a virus that is endemic in the Caribbean Islands, is perinatally transmitted, known to be neuropathogenic, and the cause of a chronic myelopathy (tropical spastic paraparesis/ HTLV-I associated myelopathy). We therefore examined inpatients at the Bellevue Mental Hospital, Kingston, Jamaica and did standard serological tests for retroviruses HTLV-I and HTLV-II and HIV-I and HIV-II on 201 inpatients who fulfilled ICD-9 and DSM III-R criteria for schizophrenia. Our results produced important negative data, since the seropositivity rates for HTLV-I, the most likely pathogen, were no greater than the seropositivity range for HTLV-I carriers in this island population, indicating that HTLV-I and the other retroviruses tested do not play a primary etiological role in Jamaican schizophrenics.  相似文献   
90.
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