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   9219篇
  免费   983篇
  国内免费   16篇
耳鼻咽喉   70篇
儿科学   207篇
妇产科学   293篇
基础医学   1361篇
口腔科学   238篇
临床医学   861篇
内科学   1549篇
皮肤病学   195篇
神经病学   655篇
特种医学   655篇
外科学   1502篇
综合类   254篇
一般理论   7篇
预防医学   968篇
眼科学   207篇
药学   567篇
  1篇
中国医学   2篇
肿瘤学   626篇
  2021年   127篇
  2020年   76篇
  2019年   163篇
  2018年   162篇
  2017年   120篇
  2016年   120篇
  2015年   137篇
  2014年   179篇
  2013年   274篇
  2012年   383篇
  2011年   401篇
  2010年   227篇
  2009年   266篇
  2008年   417篇
  2007年   400篇
  2006年   433篇
  2005年   400篇
  2004年   352篇
  2003年   324篇
  2002年   314篇
  2001年   296篇
  2000年   298篇
  1999年   258篇
  1998年   130篇
  1997年   125篇
  1996年   144篇
  1995年   139篇
  1994年   119篇
  1993年   107篇
  1992年   224篇
  1991年   203篇
  1990年   190篇
  1989年   226篇
  1988年   165篇
  1987年   205篇
  1986年   176篇
  1985年   186篇
  1984年   147篇
  1983年   127篇
  1982年   105篇
  1981年   66篇
  1980年   75篇
  1979年   119篇
  1978年   69篇
  1977年   77篇
  1976年   69篇
  1975年   58篇
  1974年   74篇
  1973年   70篇
  1968年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
进一步研究了抗三尖杉酯碱的HL-60细胞(HR20)抗细胞凋亡的机制及该抗性和抗药性的关系。结果表明,环孢菌素A(CsA)20,10μg·ml ̄(-1)诱导HL-60细胞发生凋亡,而阻断HR20细胞于G_1期,就不能诱导细胞发生凋亡。低浓度的CsA明显增加柔红霉素在HR20细胞内的积聚,其逆转抗药性作用与阻断细胞周期运行无关。CsA10μg·ml ̄(-1)处理HR20细胞,可引起50kDa的蛋白质高度磷酸化。结果提示:环孢菌素A阻断抗三尖杉酯碱的HL-60细胞于G_1期,而诱导敏感的HL-60细胞发生凋亡,其阻断作用与抗药性无关  相似文献   
83.
Carcinoma of the esophagus shows a strong male predominance and other epidemiologic differences from cancers arising at other sites. In this study, the prevalence of Y chromosome loss in 29 carcinomas of the esophagus and 53 carcinomas arising elsewhere in the aerodigestive tract was assessed by in situ hybridization of formalin-fixed paraffin-embedded tissue sections. Absence of the Y chromosome was defined as (1) negative staining for Y in neoplastic cells with positive staining for Y in immediately adjacent nonneoplastic epithelial and stromal cells, (2) positive staining of neoplastic cells with control probes for chromosomes X and 17, and (3) similar results at different stringencies and levels of protein digestion. According to these criteria, absence of the Y chromosome was observed in 13 of 14 (93%) adenocarcinomas of the esophagus, 8 of 13 (62%) squamous cell carcinomas of the esophagus, and 5 of 53 (9%) carcinomas arising in other sites. For the neoplasms examined, Y chromosome deletion was strongly and selectively associated with carcinomas, particularly adenocarcinomas, of the esophagus (P < .0001). These findings suggest that Y chromosome loss may be pathogenetically significant in these neoplasms. © 1993 Wiley-Liss, Inc.  相似文献   
84.
Aboriginal suicide has become an issue receiving national attention because of the association with "deaths in custody". To date little systematic work has been directed to the investigation of suicide among a non-incarcerated Aboriginal population. This paper focuses on deaths by suicide within one geographical area. It identifies two factors, alcoholism and disruption of interpersonal attachments, which may play a causal role in male Aboriginal suicide. The sudden emergence of suicide in this partial descent population, in concert with suicides among incarcerated and non-incarcerated Aborigines elsewhere, suggests that socio-historical forces must be examined to further clarify the phenomenon.  相似文献   
85.
The use of food frequency questionnaires for measuring dietary intake has become widespread in epidemiologic studies. It has been suggested that inquiring about a person's usual serving size of each food, in addition to the frequency of consumption, will improve the accuracy of this method. This approach implies that individuals characteristically eat a specific amount of any particular food, and that this amount can be reported with reasonable accuracy. To investigate the variability of portion sizes, the authors analyzed data for 68 commonly consumed foods, based on four one-week weighed diet histories recorded by 194 Boston-area women aged 34-59 years during 1980 and 1981. For each food, total population variance in portion size was partitioned into within-person (intraindividual) and between-person (interindividual) components. For all but seven food items (yogurt, liver, mixed vegetables, watermelon, pancakes/waffles, cold cereal, and cooked cereal) the within-person variance in portion size exceeded the between-person variance. The mean of the within-person to between-person variance ratios, after exclusion of two outlying foods, was 3.4 for untransformed portion sizes, and 3.2 after portion sizes were loge-transformed. Foods with a high within-person variance also tended to have a high between-person variance. The dominance of within-person variance in portion sizes suggests that the concept of usual portion size is complex, and that subjects may experience substantial difficulty in specifying their "usual" portion size. The smaller contribution of between-person variance to the total variance in portion size suggests that specification of a standard portion size by the investigator may not introduce a large error in the estimation of food and nutrient intake.  相似文献   
86.
Clinical applications of electrical stimulation for effecting change in the damaged or disabled nervous system are in their infancy. This technique is extremely powerful, because any neural structure that is electrically excitable can potentially be affected. Although early attempts to apply electrical stimulation were limited by insufficient physiological knowledge and undeveloped technology, developments over the past two decades now provide a strong base for clinical applications. Clinical systems for bladder control and respiration have been in use for many years. Some applications of FES to restore hand function and walking are in multicenter testing, whereas many others are being studied for clinical feasibility at single sites. Applications are focusing on safety and efficacy, as well as on clinical outcome measures to address the issues posed by the regulatory and reimbursement processes. As clinical systems become more routine, issues of multiple system applications will need to be addressed. Present and future applications of functional electrical stimulation may be expected to significantly enhance independence and improve the quality of life for individuals with central nervous system dysfunction.  相似文献   
87.
The clinical course and outcome of 111 patients with tricuspid atresia, seen during 1972-1982, were reviewed. All clinical and investigation data, progress and management were analysed. The mean age at presentation was 21.9 +/- 8.8 days. Patients with reduced pulmonary blood flow presented earlier. Patients with normal or increased pulmonary blood flow usually presented in heart failure. "True" natural history was observed in 13 unoperated patients. Six of these died at the age of 7 days to 8 months (mean 32.2 days). Seven patients survived without surgery for 11 months to 24 years, the older ones developing pulmonary vascular obstructive disease. The overall mortality in the whole series was 32.4% (36/111), the mean age at death was 3.1 years (range 3 days-48 years). The mortality rate within the first year of life was 22.5%. The mean age of survivors at follow-up was 10.7 +/- 0.9 years (range 11 months-27 years).  相似文献   
88.
This study investigated the effect of dehydration on measurements of body composition by hydrostatic weighing (HW) and bioelectric impedance analysis (BIA). Ten endurance-trained male athletes between the ages of 18 and 42 years performed an endurance training session consisting of running until body weight was reduced by approximately 3%. Body composition was determined prior to exercise and immediately after exercise by HW and BIA techniques. A high correlation existed between pre- and postdehydration for both HW and BIA. Validity coefficients between HW and BIA were moderate (predehydration 0.85 and postdehydration 0.82). In addition, BIA percent fat was 3.5% higher than HW percent fat. The BIA revealed a mean loss of 2.1% fat BIA and only 0.9% fat HW after approximately 45 minutes of exercise. BIA also showed an increase in percent body water (mean = 2.6%) in all 10 subjects after dehydration. There are indications that BIA, with its present equational configuration, is measuring something other than lean body weight. J Orthop Sports Phys Ther 1989;10(11):451-455.  相似文献   
89.
Optic nerve pseudomeningioma secondary to localized amyloidosis   总被引:1,自引:0,他引:1  
A 55-year-old woman presented with a mass of the optic nerve sheath suggestive of a meningioma. On excision, this proved to be amyloid. No systemic involvement could be found. Although amyloid may arise as a solitary lesion of the orbit or extraocular muscle, this "pseudomeningiomatous" pattern has not been previously noted. A magnetic resonance scan was helpful because the amyloid imaged at a density similar to vitreous and cerebral white matter, unlike meningiomas, which appear more like bone. The diagnosis of localized amyloidosis, however, still remains dependent on histopathology and cannot be made on a clinical basis.  相似文献   
90.
Sperm-agglutinating antibodies were present in three (2-6%) of 117 fertile men and in 19 (33-9%) of 56 men who had been vasectomized. Twenty-four of the 56 vasectomized men had been studied before vasectomy; sperm-agglutinating antibodies were present in one (4-3%) compared with eight (33-3%) after vasectomy. No sperm-immobilizing antibodies were detected before vasectomy but were present in 10 (17-9%) of the 56 men after vasectomy.  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