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   93865篇
  免费   5906篇
  国内免费   733篇
耳鼻咽喉   1089篇
儿科学   2926篇
妇产科学   2298篇
基础医学   12593篇
口腔科学   2152篇
临床医学   7649篇
内科学   20505篇
皮肤病学   1954篇
神经病学   8649篇
特种医学   3816篇
外国民族医学   23篇
外科学   13219篇
综合类   1675篇
一般理论   47篇
预防医学   5391篇
眼科学   1548篇
药学   7624篇
  3篇
中国医学   518篇
肿瘤学   6825篇
  2023年   380篇
  2022年   930篇
  2021年   1687篇
  2020年   1099篇
  2019年   1556篇
  2018年   1971篇
  2017年   1527篇
  2016年   1582篇
  2015年   1843篇
  2014年   2408篇
  2013年   3584篇
  2012年   4699篇
  2011年   4886篇
  2010年   3239篇
  2009年   2834篇
  2008年   4346篇
  2007年   4522篇
  2006年   4312篇
  2005年   4117篇
  2004年   4454篇
  2003年   4326篇
  2002年   4374篇
  2001年   3719篇
  2000年   3664篇
  1999年   2955篇
  1998年   1177篇
  1997年   922篇
  1996年   857篇
  1995年   828篇
  1994年   713篇
  1993年   701篇
  1992年   1791篇
  1991年   1776篇
  1990年   1512篇
  1989年   1453篇
  1988年   1347篇
  1987年   1200篇
  1986年   1183篇
  1985年   1040篇
  1984年   772篇
  1983年   707篇
  1982年   447篇
  1981年   396篇
  1979年   565篇
  1978年   416篇
  1975年   430篇
  1974年   479篇
  1973年   461篇
  1972年   421篇
  1971年   393篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Ultrasound of femoral head cartilage: a new method of assessing bone age   总被引:4,自引:0,他引:4  
This paper analyses the relationship between the thickness of the anterior femoral head cartilage (FHC), as measured by ultrasound, and some anthropometric parameters, such as height, weight, skeletal and chronological age. In addition, it provides standard norms for FHC thickness in a paediatric population. Both hips were examined in 213 consecutive subjects (99 boys and 114 girls), aged 1.9–14 years. Seventy-four subjects underwent hand and wrist X-rays for skeletal maturation: 32 of these were dropped from the study because a discrepancy as high as two standard deviations was found between their skeletal and their chronological age. The thickness of FHC correlated strongly with skeletal and chronological age, standing height and body weight. A side difference of 0.2 mm in FHC was considered to be abnormal. The study population was divided into 13 groups according to chronological age and values of FHC for boys and girls are provided for each group. It is suggested that the magnitude of hyaline FHC is a valuable feature in the evaluation of skeletal maturation in children.  相似文献   
992.
Summary In 810 schoolchildren (aged 5–14 years) the prevalence of a grade 1–3/6 vibratory innocent heart murmur (VIHM) is 41%. Restricted to a grade 2 or 3 VIHM, the prevalence is 14%, decreasing from 21% in the age-class 5–6 years to 8% for children 13–14 years of age. The prevalence of a grade 3 VIHM is 1%. Together with a matched control, 84 children with a grade 2 or 3 VIHM underwent further cardiologic examination including electrocardiography, phonocardiography, and Doppler echocardiography. A positive correlation was found between the presence of a VIHM and higher left ventricular voltages on the ECG, but within the normal range; lower heart rate; smaller diameter of the ascending aorta (AAO); and higher blood flow velocity and higher maximal acceleration of the blood flow in the LVOT and the AAO. In 40% of the children with a VIHM, a systolic aortic valve vibration was seen with a frequency 100 Hz and an amplitude 1 mm, whereas this type of vibration was present in only one case control. No significant difference was found concerning the prevalence of false tendons in the left ventricle, systolic and diastolic diameter of the left ventricle, systolic time intervals, and shortening fraction of the left ventricle. The VIHM is strongly associated with a smaller AAO, with higher velocity and acceleration of the blood flow in the LVOT and AAO, and with a vibratory phenomenon of the aortic valve, pointing towards the LVOT-aortic valve region as the site of origin of the VIHM.  相似文献   
993.

Purpose

Treatment of aged human oocytes by puromycin allows a high rate of parthenogenetic activation and development until the first cleavage division. This technique was used for the study of the chromosome complement of oocytes which remained unfertilized after in vitro fertilization. Three hundred four unfertilized oocytes were treated with 10 Μg/ml puromycin for 6–8 hr and further cultured for 12–15 hr.

Results

Activation occurred in 90.5% of the oocytes. Heterozygous diploids with two pronuclei predominated (61%), which is in contrast to the mouse, where the majority of oocytes activated by puromycin are uniform haploids (89%).

Conclusions

Therefore we conclude that puromycin treatment induces retention of the second polar body in human oocytes, unlike in mouse oocytes treated in the same way. Chromosome analysis performed on 182 oocytes suggested a nondisjunction (ND) rate for the second meiotic division of 12.7%. This is a low figure considering the fact that puromycin itself has been reported to induce nondisjunction. For the first meiotic division a ND rate of only 5.6% was found. This rate is lower than the one found in metaphase II arrested oocytes and we believe that this difference is due to the technical differences between the study of meiotic and that of mitotic chromosomes.  相似文献   
994.
一氧化氮,抗氧化剂,抗氧化酶与矽肺关系的研究   总被引:11,自引:1,他引:10  
目的 探讨一氧化氮、抗氧化剂、抗氧化酶与矽肺的关系。方法 检测73例矽肺患者和60例健康对照者的血浆一氧化氮(P-NO)、维生素C(P-VC)、维生素E(P-VE)、β-胡萝卜素(P-β-CAR)含量及红细胞超氧化物歧化酶(E-SOD)、过氧化氢酶(E-CAT)、谷胱甘肽过氧化物酶(E-GSH-Px)活性。结果 与对照组比较,患者组的P-NO平均值显著升高(P〈0.001),P-VC、P-VE、P  相似文献   
995.
996.
Purpose: To describe the service utilization patterns of homeless and runaway youth in a “service-rich” area of Los Angeles, California; identify demographic and other correlates of utilization; and contextualize the findings with qualitative data.

Method: During Phase 1 of this study, survey data were collected from an ethnically diverse sample of 296 youth aged 13–23 years, recruited from both service and natural “hang-out” sites using systematic sampling methods. During Phase 2, qualitative data were collected from 46 youth of varying ethnicities and lengths of time homeless.

Results: Drop-in centers and shelters were the most commonly used services (reported by 78% and 40%, respectively). Other services were used less frequently [e.g., medical services (28%), substance abuse treatment (10%) and mental health services (9%)]. Utilization rates differed by ethnicity, length of time in Los Angeles, and city of first homeless episode (Los Angeles versus all others). Shelter use was strongly associated with use of all other services. Despite youths’ generally positive reactions to services, barriers were described including rules perceived to be restrictive, and concerns youth had about confidentiality and mandated reporting. Youth suggested improvements including more targeted services, more long-term services, revised age restrictions, and more and/or better job training and transitional services to get them off the streets.

Conclusions: Because shelters and drop-in centers act as gateways to other services and offer intervention potential for these hard-to-reach youth, it is vital that we understand the perceived barriers to service utilization.  相似文献   

997.
PURPOSE: To describe the service utilization patterns of homeless and runaway youth in a "service-rich" area (Los Angeles, California); identify demographic and other correlates of utilization; and contextualize the findings with qualitative data. METHOD: During Phase 1 of this study, survey data were collected from an ethnically diverse sample of 296 youth aged 13-23 years, recruited from both service and natural "hang-out" sites using systematic sampling methods. During Phase 2, qualitative data were collected from 46 youth of varying ethnicities and lengths of time homeless. RESULTS: Drop-in centers and shelters were the most commonly used services (reported by 78% and 40%, respectively). Other services were used less frequently [e.g., medical services (28%) and substance abuse treatment (10%) and mental health services (9%)]. Utilization rates differed by ethnicity, length of time in Los Angeles, and city of first homeless episode (Los Angeles vs. all others). Shelter use was strongly associated with use of all other services. Despite youths' generally positive reactions to services, barriers were described including restrictive rules, confidentiality and reporting problems, and negative interactions with staff members. Youth suggested improvements including more targeted services, more long-term services, revised age restrictions, and more and/or better job training and transitional services to get them off the streets. CONCLUSIONS: Because shelters and drop-in centers act as gateways to other services and offer intervention potential for these hard-to-reach youth, it is vital that barriers to use of these services are eliminated.  相似文献   
998.
The dramatic appearance of managed care organizations (MCOs) on the U.S. health scene has generated tremendous anxiety among health care providers and patients. These fears are based on the belief that managed care techniques pose greater risks of under treatment than do fee-for-service modes of payment. In addition, many physicians and patients resent the limits placed on clinical autonomy by the MCO model and the stresses that it places on the traditional physician-patient relationship. These misgivings have been exacerbated by the mostly negative response to MCOs in the media and academia. Legislatures have responded to these claims and public fears with a wave of regulatory initiatives. Some of these regulations are attempts to protect patients. Others, however, are motivated primarily by antipathy toward the concept of managed care itself. This essay is an attempt to develop a social ethic of regulation and argues that the sole reason that private enterprise may be justifiably limited is when it presents a risk of harm to others or society. While some regulation and proposed regulation of MCOs meet this standard, much legislation represents an unjustified attempt to limit or handicap otherwise legal behavior merely because a segment of the population and medical profession find it aesthetically unpleasing and oppose its approach to the delivery of health services.  相似文献   
999.
Plasma homocysteine concentration in a Belgian school-age population   总被引:2,自引:0,他引:2  
BACKGROUND: Total plasma homocysteine (tHcy) is an independent risk factor for cardiovascular disease in adults. Data for children and adolescents are lacking. OBJECTIVE: The aim of this study was to provide a reference range for tHcy and to explore the relation between tHcy and nutritional indexes in a Belgian pediatric population. DESIGN: tHcy, folate, and vitamin B-12 were measured in 647 healthy children (353 girls and 294 boys) aged 5-19 y. RESULTS: The tHcy distribution was, as in adults, skewed to the right [geometric mean (-1 SD, +1 SD): 7.41 micromol/L (5.51, 9.96)]. Concentrations were lowest in younger children and increased with age. After the tHcy distribution was examined according to age, 3 age ranges were distinguished: 5-9 y [6.21 micromol/L (5.14, 7.50)], 10-14 y [7.09 micromol/L (5.69, 8.84)], and 15-19 y [8.84 micromol/L (6.36, 12.29)]. We observed no significant differences in tHcy values between girls and boys in children aged < 15 y; in postpubertal children, however, concentrations were higher in boys than in girls. In the 3 age groups, folate was inversely correlated with tHcy; the negative relation between tHcy and vitamin B-12 was less strong. Familial cardiovascular disease was more frequent in children who had hyperhomocysteinemia. CONCLUSIONS: These observations suggest that in children, as in adults, genetic, nutritional, and endocrine factors are determinants of the metabolism of homocysteine. The significance of tHcy values in childhood and young adulthood in terms of predicting cardiovascular risk in adulthood should be investigated.  相似文献   
1000.
Background. Prior studies of recall accuracy for screening mammogram behavior have examined relatively homogeneous groups. Data are limited on possible systematic group differences, so we evaluated women's recall accuracy in two separate care systems in one city.Methods. Women 50 to 70 years old with and without screening mammograms 10 to 14 months prior were identified from fiscal, clinic, and radiology records at a military care system (MCS) and a county-funded system (CFS) for indigents. Mammogram status was verified through radiology records. Women were excluded if mammograms were diagnostic, done for other than annual screening, or had abnormal results. Interview ers blinded to mammogram status surveyed randomly selected eligible women.Results. For 62 screened/31 unscreened MCS women and 78 screened/61 unscreened CFS women, specificity was similar, at 65 and 62%, respectively. In contrast, sensitivity varied significantly: 95% versus 79% (P = 0.011). Primary ethonocultural groups were Euro-American (MCS—60%) and Mexican American (CFS—85%). Although not different in specificity of recall (67% versus 61%), these major subgroups significantly differed in sensitivity (97% versus 80%, P = 0.017), proportion of true negatives due to never having a mammogram (35% versus 57%, P = 0.003), and proportion with ≥high school education (78% versus 19%, P < 0.00001).Conclusion. Systematic differences in recall validity may exist and compromise the accuracy of intergroup comparisons.  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