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   132029篇
  免费   13084篇
  国内免费   8752篇
耳鼻咽喉   1244篇
儿科学   1712篇
妇产科学   1092篇
基础医学   13198篇
口腔科学   2328篇
临床医学   17187篇
内科学   17321篇
皮肤病学   1448篇
神经病学   5436篇
特种医学   4565篇
外国民族医学   69篇
外科学   12556篇
综合类   26637篇
现状与发展   36篇
一般理论   24篇
预防医学   11730篇
眼科学   3384篇
药学   14489篇
  178篇
中国医学   9268篇
肿瘤学   9963篇
  2024年   556篇
  2023年   1999篇
  2022年   4992篇
  2021年   6536篇
  2020年   5126篇
  2019年   4125篇
  2018年   4176篇
  2017年   4270篇
  2016年   3872篇
  2015年   6107篇
  2014年   7690篇
  2013年   7556篇
  2012年   10558篇
  2011年   11555篇
  2010年   8737篇
  2009年   7157篇
  2008年   8019篇
  2007年   7884篇
  2006年   7471篇
  2005年   6704篇
  2004年   4891篇
  2003年   4535篇
  2002年   3773篇
  2001年   3016篇
  2000年   2428篇
  1999年   2036篇
  1998年   1255篇
  1997年   1228篇
  1996年   880篇
  1995年   864篇
  1994年   715篇
  1993年   445篇
  1992年   465篇
  1991年   419篇
  1990年   370篇
  1989年   331篇
  1988年   248篇
  1987年   243篇
  1986年   170篇
  1985年   147篇
  1984年   83篇
  1983年   58篇
  1982年   34篇
  1981年   36篇
  1980年   15篇
  1979年   39篇
  1978年   10篇
  1977年   11篇
  1976年   6篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
STUDY OBJECTIVE--The aim was to examine if there is an effect of fathers' age and of birth order on the occurrence of congenital heart disease. DESIGN--This was a hospital based case-referent study including use of birth defects surveillance data. SUBJECTS--Subjects were 497 cases of congenital heart disease aged between 3 months and 5 years, born in Beijing and Hebei Province, China; 6222 children without congenital heart disease serve as reference baseline. MEASUREMENTS AND MAIN RESULTS--With stratified analysis and logistic regression analyses, congenital heart disease was found to be associated with fathers' age less than 25 years (odds ratio 2.63), independent of mothers' age and of birth order. There was also evidence to show a higher birth order effect on the occurrence of congenital heart disease independent of parental ages. CONCLUSION--Higher birth order and fathers aged less than 25 years were both independently associated with some categories of congenital heart disease and with congenital heart disease overall.  相似文献   
82.
异体造血干细胞移植的重要并发症是移植物抗宿主病(GVHD),免疫抑制剂是有效防治GVHD的一类药物.在异体造血干细胞移植后应用免疫抑制剂,使得GVHD发生率下降,严重程度减轻.本文对几类主要的免疫抑制剂的作用机理以及在异体造血干细胞移植中作为预防和治疗GVHD的应用作一综述.  相似文献   
83.
法乐四联症右室心肌超微结构定量测量与临床的对比研究   总被引:3,自引:0,他引:3  
为探讨法乐四联症(F_4)右室心肌超微结构的不同表现与F_4术前各项临床检查及术后心功能的关系,作者对室间隔缺损组(Ⅰ组,11例),儿童F_4组(Ⅱ组,13例)和成人F_4组(Ⅲ组,13例)进行比较,用Systat计算机统计软件作多因素方差分析和Pearson相关研究。结果见Ⅱ、Ⅲ组病人的PO_2仅和核浆比有关,P_(RV)与细胞的核体密度、横径、核浆比及肥大肌细胞比率明显有关,肥大肌细胞比率与病人年龄及PaO_2明显相关。作者认为F_4病人右室心肌超微结构改变主要系右室压力增高所致,这种改变与年龄有关。  相似文献   
84.
85.
Abstract We previously demonstrated that epidermal growth factor (EGF) induces a several-fold increase in ornithine decarboxylase (ODC) activity and the steady-state level of ODC mRNA in cultured SV40-transformed human keratinocytes (1). Pretreatment of cell cultures with ultraviolet B (UVB) radiation resulted in a reduction of EGF-induced ODC activity. To determine whether UVB inhibits the accumulation of ODC mRNA by EGF, cells were pretreated with 20 mJ/cm2 UVB or sham-irradiated and then incubated with 100 ng/ml EGF. Northern blot analysis revealed that UVB irradiation entirely blocked the EGF induction of ODC mRNA. Since the binding of EGF to its plasma membrane receptor is the first step in initiating a biological response, the effect of UVB on EGF binding was evaluated. UVB treatment of cultured keratinocytes resulted in an immediate and dose-dependent reduction of EGF binding. Scatchard analysis revealed thai the reduction of EGF binding was due to a 52% decrease in the number of available receptors, from 6.2 × 104/cell to 3.0 × 104/cell. However, UVB decreased the EGF-binding affinity very little (Kd = 0.60 nM in control and Kd=0.75 nM in UVB-treated Z114 cells). In addition, UVB did not alter the rate of EGF internalization. These data suggest that UVB blocks the signal transduction pathway of EGF that is involved in regulation of ODC gene expression. Immunoblot analysis of extracts from irradiated cells showed that UVB induced tyro-sine phosphorylation of EGFR and that the quantity of EGFR protein was unaffected by UVB treatment. Phosphorylation of EGFR may be responsible for decreased binding of EGF to its receptor.  相似文献   
86.
87.
吡那地尔对高血压心脏结构和功能重构的影响   总被引:5,自引:0,他引:5  
在等降压剂量下吡那地尔和赖诺普利可使4月龄自发性高血压大鼠的血压下降6.0 ̄8.0kPa,并接近同种属正常血压大刀瓣血压水平。  相似文献   
88.
目的:探讨保留甲状软骨膜对全喉切除手术进程和病人术后恢复情况的影响。方法:在甲状软骨膜下游离甲状软骨并切断其上角。不结扎和切断舌骨下肌群和喉上动脉。保留之甲状软骨膜用以加强修复咽壁黏膜。结果:本组病例较经典全喉切除术手术时间缩短30min以上。手术中出血在100ml以下。患者术后第2d下床活动,第4d开始进食流质。手术创口均一期愈合。结论:全喉切除术中保留甲状软骨膜可有效地简化手术步骤,减少创伤和出血。利用甲状软骨膜加强咽壁黏膜缝合口,进一步减少了咽漏的发生.  相似文献   
89.
PROBLEM and METHOD: Early pregnancy factor (EPF), an Immunosuppressive substance, which appears in pregnant women's sera 48 h after fertilization, is a kind of pregnancy-specific protein. To determine whether the EPF activity could be a super early indicator of pregnancy, we used rosette inhibition assay to detect EPF activity in the sera, collected from 70 women 2–7 days after ovulation intending to conceive monitored by ultrasonography. Simultaneously we selected 40 non-pregnant sera and 12 early-pregnant sera as negative control and positive control, respectively. RESULTS: The results of this study demonstrated that EPF activity is detected in 35 women's sera out of 70 women within 2–7 days after ovulation, and 28 women out of the 35 were pregnant, which was known by follow-up, and 7 were not pregnant, possibly due to either false positive results or embryo loss because of preimplantation failure, thus causing no pregnancy. The other 35 out of 70 had no EPF activity and 34 of them were not pregnant, which was known by follow-up, but one case became pregnant, which was false negative result. Our study showed that diagnosis of the super early pregnancy could be made by detecting EPF activity in maternal serum within the time of preimplantation. The accuracy of pregnancy diagnosis by this method is 88.6%, with a false negative rate of 3.4% and a false positive rate of 17.1%. The β-HCG level was measured from the above 70 women's sera in order to contrast EPF activity. All of the sera collected 2–6 days following ovulation indicated that there were lower β-HCG values in very early pregnancy (≥a5 mIU/ml). On the seventh day after ovulation, EPF activity was detected in 11 out of 15 sera with only 2 of them with a b-HCG level that reached or slightly surpassed that of the early pregnancy diagnosis (5 mIU/ml and 5.4 mIU/ml, respectively). This demonstrated that β-HCG is not the earliest signal of pregnancy; otherwise the EPF activity is one that appears 2–6 days earlier than β-HCG appears. We measured the progesterone level of the 48 sera from the 70 collected above within 2–7 days postovulation and found most of them reached the level of progesterone in the luteal phase (7.5–98.3 nmol/L). This indicated that ovulation had taken place in these women, which was in accordance with observations by ultrasonography. CONCLUSIONS: Our study showed that diagnosis (of 88.6%) of super early pregnancy could be made with an accuracy of 88.6% by detecting EPF activity in maternal serum within 2-days after ovulation. This offers a basis for pregnancy diagnosis for the women who attempt to terminate their pregnancy safely or who conceive unexpectedly, and it contributes to family-planning.  相似文献   
90.
Pleomorphic xanthoastrocytoma (PXA) is a rare, low-grade astrocytic tumor found in the central nervous system. Histologically, the tumor is characterized by markedly pleomorphic and lipidized cells. Although most of the patients have a favorable prognosis, a small number of cases undergoing recurrence or progression to anaplastic astrocytoma were reported. Very few genetic studies have been performed on PXA because of its rarity and the pathogenesis of this neoplasm is largely unknown. In order to provide an overview of genetic alterations in PXA, we performed comparative genomic hybridization to identify chromosomal imbalances (DNA gains and losses) in three cases of PXA. Genetic imbalance was detected on at least one chromosome for each case. One case, which revealed multiple genetic alterations, showed a poor prognosis. DNA gain on chromosome 7 and loss on 8p were demonstrated in two of three cases, suggesting that the candidate gene(s) located on these regions may play a role in the development of PXA. Further studies are needed to identify the residing candidate genes that are involved in the tumorigenesis of PXA. In addition, the histopathological features and previous genetic studies on PXA are reviewed.  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