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   1636篇
  免费   213篇
  国内免费   24篇
耳鼻咽喉   34篇
儿科学   97篇
妇产科学   24篇
基础医学   130篇
口腔科学   42篇
临床医学   235篇
内科学   357篇
皮肤病学   108篇
神经病学   62篇
特种医学   141篇
外科学   274篇
综合类   97篇
现状与发展   30篇
预防医学   69篇
眼科学   19篇
药学   64篇
中国医学   3篇
肿瘤学   87篇
  2024年   15篇
  2023年   181篇
  2022年   11篇
  2021年   21篇
  2020年   55篇
  2019年   22篇
  2018年   57篇
  2017年   52篇
  2016年   46篇
  2015年   59篇
  2014年   92篇
  2013年   74篇
  2012年   46篇
  2011年   43篇
  2010年   88篇
  2009年   100篇
  2008年   44篇
  2007年   69篇
  2006年   39篇
  2005年   42篇
  2004年   29篇
  2003年   29篇
  2002年   49篇
  2001年   35篇
  2000年   37篇
  1999年   44篇
  1998年   40篇
  1997年   51篇
  1996年   44篇
  1995年   38篇
  1994年   31篇
  1993年   37篇
  1992年   14篇
  1991年   12篇
  1990年   19篇
  1989年   31篇
  1988年   28篇
  1987年   22篇
  1986年   13篇
  1985年   17篇
  1984年   10篇
  1983年   4篇
  1982年   10篇
  1981年   10篇
  1980年   13篇
  1979年   4篇
  1978年   6篇
  1976年   14篇
  1975年   10篇
  1974年   3篇
排序方式: 共有1873条查询结果,搜索用时 375 毫秒
991.
Spontaneous integrin expression on CD4+, CD8+ and CD19+ lymphocytes at 6 months was significantly lower in breastfed than formula-fed infants ( p < 0.05). In another study of 59 formula-fed and 64 breastfed 12-month-old children blast transformation and cytokine production by lymphocytes, and T cell changes were measured before and after measles-mumps-rubella vaccination (MMR). Before vaccination, lymphocytes of breastfed children had lower levels of blast transformation without antigen ( p < 0.001), with tetanus toxoid ( p < 0.02) or Candida ( p < 0.04), and lower interferon-γ production ( p < 0.03). Fourteen days after the live viral vaccination, only the breastfed children had increased production of interferon-γ ( p < 0.02) and increased percentages of CD56+ ( p < 0.022) and CD8+ cells ( p < 0.004). These findings are consistent with a Thl type response by breastfed children, not evident in formula-fed children. Feeding mode has an important long-term immunomodulating effect on infants beyond weaning.  相似文献   
992.
Summary: The records of 738 women with low-grade cervical epithelial abnormalities were examined for changes in degree of cervical disease and lesion size, as well as sociodemographic and behavioural factors which influence the development of invasive cancer of the cervix. Survival analysis was used to determine the predictors and rates of progression and regression. The results suggest that about 80% of low-grade epithelial abnormalities of the cervix will not progress within 2 years. The only predictors of progression were a biopsy diagnosis of CIN 1 and die size of the lesion. Predictors of regression were older age, older age at first intercourse, greater parity, fewer sexual partners, and absence of a past history of genital herpes. Although progression rates of low-grade abnormalities of the cervix were very low, CIN 1 lesions were 2.4 times (95% CI: 1.6 to 3.7) more likely to progress than lower-grade lesions and large lesions (>l/2 ectocervix) were 2.0 times (95% CI: 1.2 to 3.3) more likely to progress than small ones (相似文献   
993.
Prostate cancer and benign tumors of the prostate are the two most common neoplastic diseases in men in the United States, however, research on their causes and treatment has been slow because of the difficulty in obtaining fresh samples of human tissue and a lack of well characterized cell lines which exhibit growth and differentiation characteristics of normal prostatic epithelium. Non-neoplastic adult human prostatic epithelial cells from a white male donor were immortalized with human papillomavirus 18 which resulted in the establishment of the RWPE-1 cell line. Cells from the RWPE-1 cell line were further transformed by v-Ki-ras to establish the RWPE-2 cell line. The objectives of this study were to: (1) establish the prostatic epithelial origin and androgen responsiveness of RWPE-1 and RWPE-2 cell lines; (2) examine their response to growth factors; and (3) establish the malignant characteristics of the RWPE-2 cell line. Immunoperoxidase staining showed that both RWPE-1 and RWPE-2 cells express cytokeratins 8 and 18, which are characteristic of luminal prostatic epithelial cells, but they also coexpress basal cell cytokeratins. These cell lines show growth stimulation and prostate specific antigen (PSA) and androgen receptor (AR) expression in response to the synthetic androgen mibolerone, which establishes their prostatic epithelial origin. Both cell lines also show a dose-dependent growth stimulation by EGF and bFGF and growth inhibition when exposed to TGF-beta, however, the transformed RWPE-2 cells are less responsive. RWPE-1 cells neither grow in agar nor form tumors when injected into nude mice with or without Matrigel. However, RWPE-2 cells form colonies in agar and tumors in nude mice. In the in vitro invasion assay, RWPE-1 cells are not invasive whereas RWPE-2 cells are invasive. Nuclear expression of p53 and Rb proteins was heterogeneous but detectable by immunostaining in both cell lines. The RWPE-1 cells, which show many normal cell characteristics, and the malignant RWPE-2 cells, provide useful cell culture models for studies on prostate growth regulation and carcinogenesis.   相似文献   
994.
Invasive prostatic carcinomas and prostatic intraepithelial neoplasia (PIN) are characterized by a loss of normal cell organization, cell polarity, and cell:cell and cell:basement membrane adhesion. The objective of this study was to establish in vitro three-dimensional (3- D) cell models which can be used to investigate mechanisms involved in acinar morphogenesis and differentiation in normal prostatic epithelium and their abnormalities in cancer cells. The process of acinar morphogenesis, including structural and functional differentiation, was investigated by culture on basement membrane gels (Matrigel). The human papillomavirus 18 immortalized, non-tumorigenic cell line RWPE-1, the v- Ki-ras transformed, tumorigenic RWPE-2 cell line derived from RWPE-1 cells (see previous paper pp. 1221-1229) and the human prostatic carcinoma cell line DU-145 were used. When cultured on Matrigel, RWPE-2 cells remain as single cells or form small aggregates and DU-145 cells form large amorphous cell aggregates without any organization or lumen. In contrast, RWPE-1 cells form acini of polarized epithelium with a distinct lumen, show a distinct laminin basement membrane, and express alpha6beta1 integrins at their basal end. Exposure to conditioned medium from NIH 3T3 cultures accelerates glandular morphogenesis. Parallel cultures maintained as monolayers on plastic remain as monolayers. In the presence of the synthetic androgen mibolerone, acinar cells express prostate specific antigen (PSA) as determined by immunostaining. We conclude that normal prostate cells can undergo acinar morphogenesis while tumorigenic cells have lost this ability. The 3-D cultures provide physiologically relevant in vitro models for elucidating regulation of growth, morphogenesis and differentiation in the normal human prostate, for defining heterotypic interactions in benign prostatic hyperplasia and for establishing the basis for the loss of normal cell organization in early neoplastic lesions such as PIN as well as during tumor progression in prostate cancer.   相似文献   
995.
996.
The communication development in 11 children with Angelman's syndrome is described. The clinical observation that these children appear to have a greater ability with receptive rather than expressive language is investigated and these skills assessed using published communication schedules. In addition the understanding and the use of nonverbal communication such as natural gesture was studied. The data collected highlight the fact that these children have developed very few words and have difficulty in using gestural or sign systems. This has implications for speech and language therapists and the children's remedial programmes. Possible future longitudinal studies are suggested.  相似文献   
997.
998.
Serial changes in plasma levels of calcium, phosphorus, magnesium, alkaline phosphatase, and total proteins have been investigated in 138 healthy, term Caucasian infants. Blood samples were obtained for each infant from cord blood and on day 1 and day 6. The infants were studied in three groups according to whether they were breast fed, received 'Ostermilk No. 1' or 'Cow and Gate V' formulas. Levels of calcium, phosphorus, magnesium, alkaline phosphatase, and total proteins did not differ between the groups at birth or on day 1. By day 6 calcium levels were higher and phosphorus levels lower in the breast-fed infants compared with either of the artificially-fed groups. Phosphorus levels were lower in the V Formula group compared with the Ostermilk group but the mean calcium levels of these two groups did not differ significantly. However, only 2-8% of the V Formula group developed hypocalcaemia compared with 18-2% of the Ostermilk group. The only infant developing clinical tetany belonged to the group fed Ostermilk. Evidence is also given which suggests that those infants with low calcium levels on day 1 who were fed the high-solute milk tended to show a fall in calcium by day 6. This did not apply to the two other groups. It is concluded that the use of adapted cows' milk preparations for infant feeding should lead to a reduction in the incidence of neonatal tetany.  相似文献   
999.
Six patients with hypergraphia and epilepsy are presented and their clinical features compared with other patients reported in the literature. It is suggested that hypergraphia occurs more frequently in patients with right-sided non-dominant temporal lobe lesions, in contrast for example to the schizophreniform presentation of left-sided lesions. Other features of psychopathology possibly associated with non-dominant lesions, including elation, hypereligiosity and déjà vu experiences, are also discussed.  相似文献   
1000.
Percutaneous management of renal cysts: results of a four-year study   总被引:3,自引:0,他引:3  
Raskin  MM; Poole  DO; Roen  SA; Viamonte  M  Jr 《Radiology》1975,115(3):551
  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