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   2148篇
  免费   142篇
  国内免费   4篇
耳鼻咽喉   31篇
儿科学   152篇
妇产科学   116篇
基础医学   224篇
口腔科学   165篇
临床医学   193篇
内科学   539篇
皮肤病学   21篇
神经病学   250篇
特种医学   89篇
外科学   165篇
综合类   6篇
预防医学   97篇
眼科学   36篇
药学   128篇
肿瘤学   82篇
  2023年   20篇
  2022年   34篇
  2021年   57篇
  2020年   39篇
  2019年   70篇
  2018年   83篇
  2017年   52篇
  2016年   68篇
  2015年   60篇
  2014年   89篇
  2013年   106篇
  2012年   160篇
  2011年   139篇
  2010年   81篇
  2009年   78篇
  2008年   134篇
  2007年   112篇
  2006年   125篇
  2005年   112篇
  2004年   101篇
  2003年   69篇
  2002年   68篇
  2001年   22篇
  2000年   36篇
  1999年   30篇
  1998年   9篇
  1997年   7篇
  1996年   11篇
  1995年   9篇
  1994年   11篇
  1993年   6篇
  1992年   25篇
  1991年   25篇
  1990年   25篇
  1989年   19篇
  1988年   24篇
  1987年   24篇
  1986年   25篇
  1985年   23篇
  1984年   25篇
  1983年   12篇
  1982年   6篇
  1981年   7篇
  1980年   5篇
  1979年   5篇
  1978年   8篇
  1977年   6篇
  1974年   6篇
  1973年   3篇
  1965年   3篇
排序方式: 共有2294条查询结果,搜索用时 15 毫秒
11.
Paracentric inversion of Xq and ovarian dysfunction   总被引:1,自引:0,他引:1  
We report on a paracentric inversion X(q13 q24) in a 20-year-old woman with ovarian dysfunction. The findings add evidence on the role of breakpoints in Xq13 and Xq24 in causing ovarian dysfunction. A review of the published data on paracentric inversion of chromosome X is included.  相似文献   
12.
STUDY OBJECTIVE: To characterize the function and quality of sleep in patients with irritable bowel syndrome (IBS). DESIGN: A prospective study with a historic comparison group. SETTING: A regional hospital that also serves as a tertiary referral center. PATIENTS: Eighteen patients with IBS and a comparison group of 20 matched adults with mild benign snoring. INTERVENTIONS: A polysomnography study and a wrist actigraphy study. MEASUREMENTS: All subjects underwent sleep studies and completed self-report questionnaires (IBS severity, psychosocial variables, sleep function, and Epworth Sleepiness Scale). Fourteen IBS and 11 comparison patients underwent actigraphy. RESULTS: The IBS patients had more than 70% less slow-wave stage sleep (4.5 +/- 7.3% vs 19.3 +/- 12.9%; P = 0.006), compensated by increased stage 2 sleep (72.2 +/- 6.6% vs 60.1 +/- 16.8%; P = 0.01). The IBS group had significant sleep fragmentation with a significantly higher arousal and awakening index (P < 0.001), a longer wake period after sleep onset (P = 0.02), and more downward shifts to lighter sleep stages (P = 0.01). The 4-night actigraphy study supported the polysomnography findings. The sleep fragmentation index was significantly higher (P = 0.008) in the IBS group. The IBS patients reported greater daytime sleepiness (9.0 +/- 4.8 vs 6.4 +/- 4.8, Epworth Sleepiness Scale score, P < 0.01) and greater impairment in quality of life, which correlated significantly with the sleep fragmentation indexes. The difference between the groups was not due to differences in baseline anxiety/depression levels. CONCLUSIONS: Patients with IBS have impaired sleep quality, reduced slow-wave sleep activity, and significant sleep fragmentation. The cause-and-effect relationship of these findings with patients' daytime symptoms should be studied further.  相似文献   
13.
14.
The aim of this study is to report our 3years experience with the screening of congenital disorders of glycosylation. A common isoelectric focusing method with immunofixation was used for analysis of serum transferrin and alpha1-antitrypsin, apart from several other procedures. A group of about 1000 individuals, both healthy controls and patients, mostly with signs of a metabolic disease were examined. Here we present an overview of (1) hypoglycosylation findings, (2) distribution of protein variants, (3) misguiding rare Tf variants found in our set, and (4) association of some phenotypes with various diseases.  相似文献   
15.
Acetylcholinesterase (AChE) plays a crucial physiological role in termination of impulse transmission at cholinergic synapses through rapid hydrolysis of acetylcholine. It is a highly conserved molecule, and only a few naturally occurring genetic polymorphisms have been reported in the human gene. The goal of the present study was to make a systematic effort to identify natural single nucleotide polymorphisms (SNPs) in the human ACHE gene. To this end, the genomic coding sequences for acetylcholinesterase of 96 unrelated control individuals from three distinct ethnic groups were analyzed. A total of 13 ACHE SNPs were identified, 10 of which are newly described, and five that should produce amino acid substitutions [c.101G>A (p.Arg34Gln), c.169G>A (p.Gly57Arg), c.1031A>G (p.Glu344Gly), c.1057C>A (p.His353Asn), and c.1775C>G (p.Pro592Arg)]. Population frequencies of 11 of the 13 SNPs were established in four different populations: African Americans, Ashkenazi Jews, Sephardic Jews, and Israeli Arabs; 15 haplotypes and five ethnospecific alleles were identified. The low number of SNPs identified until now in the ACHE gene is ascribed to technical hurdles arising from the high GC content and the presence of numerous repeat sequences, and does not reflect its intrinsic heterozygosity. Among the SNPs resulting in an amino acid substitution, three are within the mature protein, mapping on its external surface: they are thus unlikely to affect its catalytic properties, yet could have antigenic consequences or affect putative protein-protein interactions. Furthermore, the newly identified SNPs open the door to a study of the possible association of AChE with deleterious phenotypes-such as adverse drug responses to AChE inhibitors employed in treatment of Alzheimer patients and hypersensitivity to pesticides.  相似文献   
16.
The present study assessed the effects of amount of practice and length of delay on the learning and retention of a timed motor sequence task. Participants learned to reproduce ten-element visual sequences by tapping in synchrony with the stimulus. Participants were randomly assigned to a varied-practice condition or a varied-delay condition. In the varied-practice condition, participants received either one, three, or six blocks of practice followed by a fixed 4-week delayed-recall. In the varied-delay condition, participants received three blocks of practice followed by a varied delay of either 3 days, or 2, 4, or 8 weeks. Learning was assessed by changes in accuracy, response variance, and percent response asynchrony. Our results showed that amount of practice per se did not affect learning and retention of the task. Rather, distribution of practice over several days was the most important factor affecting learning and retention. We hypothesize that passage of time is essential for a maximum benefit of practice to be gained, as the time delay may allow for consolidation of learning, possibly reflecting plastic changes in motor cortical representations of the skill. With regards to delay, our findings suggest that explicit and motoric components of a motor sequence are likely to be learned and maintained in separate but interacting systems. First, only the longest delay group showed decrements in percent correct, indicating that longer lengths of delay might hinder retrieval of explicit aspects of the task. Second, all groups showed a decrement in percent response asynchrony, suggesting that synchronization may be a more difficult parameter to maintain because it relies heavily on sensorimotor integration.  相似文献   
17.
为研究胸腺微环境在T细胞发育中的作用,我室在体外建立了7株小鼠胸腺基质细胞系,命名为MTECI~MTEC7。通过初步分离得到裸鼠骨髓富含干细胞的细胞群,表面CD4及CD8分子均为阴性。将分离的骨髓干细胞与胸腺基质细胞共育3天后,经双色荧光抗体染色,FACS分析发现胸腺基质细胞可诱导裸鼠骨髓干细胞表达CD4CD8分子。MTSC-SN及MTSC主要诱导的是CD4+CD8-细胞,部分CD4+CD8+细胞,而CD4-CD8+细胞极少,这种诱导特点可能和基质细胞系的类型有关。  相似文献   
18.
This study analyzes tooth loss and retention in 500 dry maxillae of adult South African Bantu-speaking blacks. The tribe, sex, and stated age at death were available. Specimens were equally distributed over the third to the seventh decades of life. The presence of dental units was recorded and analyzed between and within age groups. A total of 5063 dental units was recorded. Reduction of the frequency of dental units was mild and not significant between the third and fourth decades of life and between the sixth and seventh. Severe and significant tooth loss was recorded between the fourth and the fifth, and between the fifth and the sixth decades of life. Specimens from younger individuals (from 21 to 30 years of age) retained more teeth in the anterior region; after the third decade of life, there was a clear and significant persistence of canines with tendency toward loss of teeth anterior and posterior to them. Based upon the present observations and previous studies in this population, it is suggested that: (a) in most teeth, tooth retention pattern is indirectly related to periodontal bone loss (In the canines, however, the long roots rather than "resistance" to periodontitis may be the cause for the relatively high longevity rate); and (b) caries may have been the main cause for tooth loss until the fourth decade of life--later, periodontal disease may have become the predominant reason.  相似文献   
19.
Tal B  Rokem JS  Goldberg I 《Planta medica》1984,50(3):239-241
Cycloheximide and compactin were added to cell suspension cultures of DIOSCOREA DELTOIDEA. Cycloheximide inhibited growth and diosgenin biosynthesis completely at 40 mg/l when added during the growth phase. Compactin partially inhibited growth and diosgenin production at 100 microg/l when added during the growth phase. [1- (14)C]-Acetate incorporation into diosgenin was about 20-fold higher when added during the early stages of growth as compared to addition in the stationary phase. Incorporation of [1- (14)C]-acetate into diosgenin was inhibited by compactin only during the early stages of growth. These results indicate the formation of an accumulating intermediary metabolite during the early stages of growth which is transformed into diosgenin when D. DELTOIDEA cells are in the stationary phase.  相似文献   
20.
Background: The aim of this study was to examine the anti-inflammatory and anti-apoptotic patterns of omega-3 polyunsaturated fatty acids (n-3 PUFAs) during methotrexate (MTX) induced intestinal damage in cell culture and in a rat model. Methods: Non-treated and treated with MTX HT 29 and HCT116cells were exposed to increasing doses of n-3 PUFAs and cell viability was evaluated using PrestoBlue® assay. Male Sprague-Dawley rats were divided into 4 experimental groups: Control rats, CONTR+n-3 PUFA rats that were treated with oral n-3 PUFA, MTX rats were treated with MTX given IP, and MTX+n-3 PUFA rats were treated with oral n-3 PUFA before and following injection of MTX. Intestinal mucosal parameters and mucosal inflammation, enterocyte proliferation and apoptosis, TNF-α in mucosal tissue and plasma (ELISA), NF-κB, COX-2, TNF-α, Fas, FasL, Fadd, Bid, Bax and Bcl-2gene and protein levels were determined 72 h following MTX injection. Results: Exposure of HT 29 and HCT116cells to n-3 PUFA attenuated inhibiting effects of MTX on cell viability. MTX-n-3 PUFA rats demonstrated a lower intestinal injury score and enhanced intestinal repair. A significant decrease in enterocyte apoptosis in MTX+n-3 PUFA rats was accompanied by decreased TNF-α, FAS, FasL, FADD and BID mRNA levels. Decreased NF-κB, COX-2 and TNF-α levels in mucosa was accompanied by a decreased number of IELs and macrophages. Conclusions: n-3 PUFAs inhibit NF-κB/COX-2 induced production of pro-inflammatory cytokines and inhibit cell apoptosis mainly by extrinsic pathway in rats with MTX-induced intestinal damage.  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