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   6925篇
  免费   309篇
  国内免费   74篇
耳鼻咽喉   111篇
儿科学   125篇
妇产科学   261篇
基础医学   523篇
口腔科学   136篇
临床医学   609篇
内科学   1945篇
皮肤病学   86篇
神经病学   382篇
特种医学   290篇
外科学   1393篇
综合类   26篇
预防医学   309篇
眼科学   148篇
药学   311篇
中国医学   3篇
肿瘤学   650篇
  2024年   3篇
  2023年   48篇
  2022年   134篇
  2021年   246篇
  2020年   135篇
  2019年   199篇
  2018年   213篇
  2017年   149篇
  2016年   165篇
  2015年   167篇
  2014年   301篇
  2013年   335篇
  2012年   597篇
  2011年   607篇
  2010年   367篇
  2009年   333篇
  2008年   573篇
  2007年   587篇
  2006年   483篇
  2005年   406篇
  2004年   350篇
  2003年   314篇
  2002年   260篇
  2001年   37篇
  2000年   13篇
  1999年   32篇
  1998年   52篇
  1997年   26篇
  1996年   31篇
  1995年   23篇
  1994年   18篇
  1993年   11篇
  1992年   10篇
  1991年   8篇
  1990年   11篇
  1989年   7篇
  1988年   5篇
  1987年   4篇
  1986年   5篇
  1984年   3篇
  1983年   4篇
  1982年   14篇
  1981年   4篇
  1980年   3篇
  1976年   2篇
  1975年   1篇
  1974年   4篇
  1973年   3篇
  1972年   1篇
  1969年   1篇
排序方式: 共有7308条查询结果,搜索用时 0 毫秒
21.
SUMMARY: We studied the effect of haemodialysis on the serum levels of tumour markers in 78 patients, 49 men and 29 women with a mean age of 61 ± 2 years, who had been undergoing haemodialysis for 39 ± 10 months. No patient had any clinical evidence of malignancy. Serum values of carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), squamous-cell-carcinoma-related antigen (SCC), neuron-specific enolase (NSE), tissue polypeptide antigen (TPA), CA 15-3, CA 19–9, and among males prostate-specific antigen (PSA) were determined before and after dialysis. Postdialysis values, after being corrected for haemoconcentration, were compared with predialysis values. A significant increase of 32% was observed in NSE levels ( P <0.001) and of 21% in CA 15-3 ( P <0.001) after haemodialysis. A lesser, but still statistically significant, increase (8-12%) was observed in SCC, AFP and CEA levels ( P <0.05), while the values of the remaining three markers remained unchanged. In conclusion, an increase in some tumour markers was found in our patients after dialysis, a finding which requires further investigation.  相似文献   
22.
Breast carcinoma is a genetically and phenotypically heterogeneous disease and is frequently associated with nonrandom chromosomal alterations. The aim of this study was to investigate the numerical aberrations of chromosome 20 in breast cancer. The observed chromosome-specific numerical abnormalities were evaluated along with the established clinicopathological parameters, the immunohistochemical expression of ER, PR, p53, c-erbB-2, Ki-67 and patients' survival. Nonisotopic in situ hybridization was applied to interphase cell nuclei on paraffin embedded tissue sections. Polysomy of chromosome 20 was the prevalent alteration in 45 of 50 (90%), monosomy in 2 of 50 (4%) and disomy in 3 of 50 (6%) cases. Invasive ductal carcinomas displayed a higher percentage of polysomy than lobular ones. A statistical significant association was demonstrated between Ki-67 immunohistochemical expression and polysomy of chromosome 20. Disomy was inversely correlated with Ki-67, while monosomy was suggestively associated with PR positive expression. Among the patients, those with the highest levels of polysomy showed the worst survival. In conclusion, the gain of chromosome 20 is the prevalent aberration in patients with breast carcinomas and may be useful prognostic marker in breast cancer.  相似文献   
23.
24.
In this study, we tested the paired-pulse transcranial magnetic stimulation (ppTMS) protocol – a conditioning stimulus (CS) given at variable intervals prior to a test stimulus (TS) – for visually evoked single-unit activity in cat primary visual cortex. We defined the TS as being supra-threshold when it caused a significant increase or decrease in the visually evoked activity. By systematically varying the interstimulus interval (ISI) between 2 and 30 ms and the strength of CS within the range 15–130% of TS, we found a clear dependence of the ppTMS effect on CS strength but little relation to ISI. The CS effect was strongest with an ISI of 3 ms and steadily declined for longer ISIs. A switch from enhancement of intracortical inhibition at short ISIs (2–5 ms, SICI) to intracortical facilitation (ICF) at longer ISIs (7–30 ms), as demonstrated for human motor cortex, was not evident. Whether the CS caused facilitation or suppression of the TS effect mainly depended on the strength of CS and the polarity of the TS effect: within a range of 60–130% a positive correlation between ppTMS and TS effect was evident, resulting in a stronger facilitation if the TS caused facilitation of visual activity, and more suppression if the TS was suppressive by itself. The correlation inverted when CS was reduced to 15–30%. The ppTMS effect was not simply the sum of the CS and TS effect, it was much smaller at weak CS strength (15–50%) but stronger than the sum of CS and TS effects at CS strength 60–100%. Differences in the physiological state between sensory and motor cortices and the interactions of paired synaptic inputs are discussed as possible reasons for the partly different effects of ppTMS in cat visual cortex and human motor cortex.  相似文献   
25.
The September 2002 COM. A 24-year-old female presented with a history of 3 generalized seizures, the first of which had occurred 6 months before admission. Her neurological examination was normal, but upon admission her MRI showed a small cystic lesion in the left parieto-occipital region. The lesion was hyper-intense on T-2 weighted images and did not show contrast enhancment. At surgery, the tumor was found to be deep to the cortex and was a cyst with amber fluid surrounded by gliotic brain. Microscopically, the tumor was well-demarcated from the surrounding tissues, which showed reactive changes, including Rosenthal fibers. The tumor was composed of GFAP-positive glial cells, which were arranged in a pseudopapillary fashion around blood vessels. In between, the tumor cells were positive for neuronal markers. The diagnosis was papillary glioneuronal tumor (PGNT), a relatively recently described lesion that may be a variant of ganglioglioma. The current literature on PGNTs is reviewed.  相似文献   
26.
27.
The co-segregation in one pedigree of bipolar affective disorder with Darier's disease whose gene is on chromosome 12q23-q24.1, and findings from linkage and association studies with the neighbouring gene of phospholipase A2 (PLA2) indicate that PLA2 may be considered as a candidate gene for affective disorders. All relevant genetic association studies, however, were conducted on bipolar patients. In the present study, the possible association between the PLA2 gene and unipolar affective disorder was examined on 321 unipolar patients and 604 controls (all personally interviewed), recruited from six countries (Belgium, Bulgaria, Croatia, Germany, Greece, and Italy) participating in the European Collaborative Project on Affective Disorders. After controlling for population group and gender, one of the eight alleles of the investigated marker (allele 7) was found to be more frequent among unipolar patients with more than three major depressive episodes than among controls (P<0.01); genotypic association was also observed, under the dominant model of genetic transmission (P<0.02). In addition, presence of allele 7 was correlated with a higher frequency of depressive episodes (P<0.02). These findings suggest that structural variations at the PLA2 gene or the chromosomal region around it may confer susceptibility for unipolar affective disorder.  相似文献   
28.
Objectives: The investigation of the effect of time and type of menopause on bone mineral density (BMD) at different ages. Methods: Five hundred and fourteen women, who had never received any hormonal substitution were studied in a cross-sectional design: 177 with normal (NMP), 210 with surgical (SUMP) and 127 with premature natural (EMP) menopause. Age at menopause was 49.1±3.9, 38.3±4.7 and 38.1±4.2 years (mean±1 S.D.), respectively. BMD was measured at L2–L4 vertebrae and proximal femur by the DEXA method. Results: EMP women presented significantly lower vertebral BMD than NMP women in the 45–55-years segments (P<0.001), but did not differ from SUMP women. This group exhibited lower vertebral BMD than NMP between 45 and 50 years (P<0.001). Regarding femoral neck, EMP women exhibited lower values than SUMP in the 45–50 and 55–65 age segments (P<0.001) whereas SUMP women presented significantly higher BMD values than NMP women after 55 years of age (P<0.001). The percentages of women with vertebral BMD (T-score values) in the osteoporotic range were significantly greater in EMP compared with either NMP or SUMP groups (both P<0.001) whereas in femoral neck lower in SUMP than the other two categories. Conclusions: Women with either natural or surgical premature menopause exhibit lower BMD of trabecular bone compared with normal menopause women at the age segments 45–55 and 45–50, respectively. However, surgical menopause women exceed normal menopause women in their mixed bone BMD values after 60 years as well as premature natural menopause women at almost all age segments.  相似文献   
29.
Results of a high-resolution genome screen of 437 Alzheimer's disease families   总被引:13,自引:0,他引:13  
Alzheimer's disease (AD) is a devastating neurodegenerative disorder of late life with complex inheritance. Mutations in three known genes lead to the rare early-onset autosomal dominant form of AD, while a common polymorphism (epsilon 4) in the gene encoding apolipoprotein E (APOE ) is a risk factor for more typical late-onset (>60 years) AD. A recent study concluded that there are up to four additional genes with an equal or greater contribution to the disease. We performed a 9 cM genome screen of 437 families with AD, the full National Institute of Mental Health (NIMH) sample, which has been carefully ascertained, evaluated and followed by our group over the last decade. Performing standard parametric and non-parametric linkage analyses, we observed a 'highly significant' linkage peak by Lander and Kruglyak criteria on chromosome 19q13, which probably represents APOE. Twelve additional locations-on 1q23, 3p26, 4q32, 5p14, 6p21, 6q27, 9q22, 10q24, 11q25, 14q22, 15q26 and 21q22-met criteria for 'suggestive' linkage [i.e. two-point lod score (TLS) >/=1.9 and/or multipoint lod score (MLS) >/=2.2] in at least one of our analyses. Although some of these will surely prove to be false positives, these linkage signals should provide a valuable framework for future studies aimed at identifying additional susceptibility genes for late-onset AD.  相似文献   
30.
Aspergillus isolates (n = 103) collected from cancer patients were screened to determine the taxonomic distribution and quantity of gliotoxin production. Gliotoxin was detected in 93% of Aspergillus fumigatus, 75% of A. niger, 25% of A. terreus, and 4% of A. flavus cultures. Gliotoxin concentrations were highest in cultures of A. fumigatus.  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