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   5104篇
  免费   334篇
  国内免费   26篇
耳鼻咽喉   36篇
儿科学   120篇
妇产科学   73篇
基础医学   783篇
口腔科学   80篇
临床医学   348篇
内科学   1309篇
皮肤病学   274篇
神经病学   336篇
特种医学   109篇
外科学   482篇
综合类   22篇
一般理论   1篇
预防医学   258篇
眼科学   161篇
药学   382篇
中国医学   14篇
肿瘤学   676篇
  2024年   5篇
  2023年   31篇
  2022年   93篇
  2021年   157篇
  2020年   103篇
  2019年   96篇
  2018年   165篇
  2017年   128篇
  2016年   154篇
  2015年   127篇
  2014年   169篇
  2013年   252篇
  2012年   355篇
  2011年   375篇
  2010年   209篇
  2009年   195篇
  2008年   353篇
  2007年   376篇
  2006年   351篇
  2005年   329篇
  2004年   335篇
  2003年   300篇
  2002年   296篇
  2001年   54篇
  2000年   43篇
  1999年   51篇
  1998年   55篇
  1997年   54篇
  1996年   38篇
  1995年   30篇
  1994年   25篇
  1993年   28篇
  1992年   20篇
  1991年   10篇
  1990年   9篇
  1989年   21篇
  1988年   9篇
  1987年   5篇
  1986年   5篇
  1985年   9篇
  1984年   6篇
  1983年   5篇
  1982年   7篇
  1976年   3篇
  1975年   2篇
  1974年   3篇
  1972年   2篇
  1968年   2篇
  1967年   2篇
  1965年   3篇
排序方式: 共有5464条查询结果,搜索用时 31 毫秒
41.
It is generally accepted that phosphorylation plays a pivotal role in the cellular response of cell differentiation and proliferation. Immunohistochemical expression of classical protein kinase C (cPKC) subspecies (alpha, beta and gamma) in eight reactive lymphoid tissues, three normal spleens and 149 non-Hodgkin's lymphomas was examined. cPKC beta was observed primarily in the mantle zone B cells, but appeared as very faint staining in Ki-67 positive proliferated B cells in the germinal centers of secondary lymph follicles. In contrast to the reactive state, high levels of cPKC subspecies were recognized in the majority of 149 cases of non-Hodgkin's lymphoma, including those thought to have arisen from germinal center cells such as follicular lymphoma. The expression of cPKC alpha was found in higher frequency in T cell lymphomas than B cell lymphomas (P < 0.01) by the Chi-squared test. High levels of cPKC alpha were present only in high grade or highly aggressive lymphomas, showing the highest incidence in the small non-cleaved cell type, according to the International Working Formulation and National Cancer Institute (P < 0.01). cPKC gamma was not detected in normal lymphoid cells and was expressed in only four cases of non-Hodgkin's lymphomas. It is presumed that cPKC alpha and beta have a relationship to cell activation and proliferation of lymphoid cells of reactive and neoplastic states. It might be considered that the expression of cPKC alpha may have a relationship with aggressiveness in non-Hodgkin's lymphomas.  相似文献   
42.
Gastric motility in patients with recurrent gastric ulcers.   总被引:3,自引:0,他引:3  
The existence of abnormal gastric motility in gastric ulcer disease remains controversial. The aim of this study was to characterize gastric motility in patients with recurrent gastric ulcers. Studies were performed in 10 control subjects and in 24 patients with recurrent active gastric ulcer disease as diagnosed by gastrointestinal endoscopy. Gastric motility was evaluated by cutaneous electrogastrography (EGG) and by gastric semi-liquid meal emptying. The EGG was recorded before and after ingestion of a test meal containing 20 mg/kg of acetaminophen. Patients with a dominant EGG frequency of greater than 0.06 Hz were defined as tachygastria, while those with a frequency of less than 0.04 Hz were defined as bradygastria. A transient frequency decrease, called postprandial dip (PD), was identified visually. The degree of gastric emptying was determined from the serum acetaminophen concentration 45 minutes after the meal. Control subjects showed no irregularity in their dominant EGG frequency in tither fasting or postprandial states. PD was observed in 8 control subjects. In patients presenting with active gastric ulcers, abnormal patterns in the dominant EGG frequency (either as tachygastria or bradygastria) were observed in 14 of the 24 patients when fasting and in 15 of them in the postprandial state. After successful treatment, the number of patients with abnormal patterns in their dominant EGG frequency remained unchanged, while PD was observed in 11 patients. No significant difference was observed in the EGG power ratio as a result of successful treatment. Gastric emptying was significantly delayed compared with controls in both the active and healed stages. These findings suggest that abnormal gastric motility, including gastric electrical abnormalities and delayed gastric emptying, plays an important role in the pathophysiology of recurrent gastric ulcers.  相似文献   
43.
In this study, we isolated and characterized a murine counterpart of the human Arpp (hArpp) gene. Sequence analysis revealed that the murine Arpp (mArpp) gene is almost identical to the Ankrd2 gene, which has recently been isolated as a mouse gene induced in stretched skeletal muscle. The mArpp gene encodes a protein of 332 amino acids that contains four well-conserved ankyrin-repeat domains in the central portion of the protein. The amino acid sequence of mArpp protein (mArpp) is highly homologous to that of mouse cardiac-restricted ankyrin-repeat protein (Carp), which is proposed to be a putative genetic marker for cardiac hypertrophy. Immunohistochemical analysis revealed that mArpp is preferentially expressed in type 1 skeletal muscle fibers, and that mArpp is localized in both the nucleus and the sarcomeric I-band of muscle fibers, suggesting that Arpp may function as a nuclear and sarcomeric protein. Furthermore, mArpp was also expressed in neurons of the cerebellum and cerebrum, the islets of Langerhans in the pancreas, and the esophageal epithelium, suggesting that mArpp may play a functional physiologic role in brain, pancreas, and esophagus as well as in type 1 muscle fibers. Interestingly, although mArpp was localized in both nucleus and cytoplasm in neurons, its localization was restricted to nucleus in pancreas and esophagus, suggesting that intracellular localization of mArpp is regulated in a tissue-specific manner. Furthermore, we found that mArpp- and Carp-expression in skeletal muscle were markedly up-regulated after denervation. Although the elevated expression level of Carp was kept only for two weeks after denervation, that of Arpp was kept at least for 4 weeks, suggesting that mArpp and Carp may play distinct functional roles in denervated skeletal muscle.  相似文献   
44.
We report on a 6-year-old boy with de novo 46, XY, del(3)(q12q23) and bilateral blepharo-phimosis, ptosis, epicanthus inversus, in addition to multiple other anomalies. Since 4 previously reported cases of interstitial deletion of 3q involving 3q23 band are clinically similar, we propose this blepharophimosis sequence due to 3q23 deletion as a further “contiguous gene syndrome”.  相似文献   
45.
46.
Summary Marek's disease virus (MDV)-infected chickens show thymic atrophy during the acute phase of infection. We examined whether the thymic atrophy by MDV-infection was mediated by apoptosis. Apoptosis-specific DNA ladderings were clearly observed in thymocytes one week after MDV-infection. Histological and flow cytometry studies revealed that immature CD4+CD8+ thymocytes underwent apototic cell death. In addition, the expression level of CD8 molecules on both CD4CD8+ and CD4+CD8+ thymocyte populations was down-regulated in the infected chickens. These thymic changes might be involved in the pathogenesis of Marek's disease.  相似文献   
47.
Soluble human interleukin-6 receptor (sIL-6R) was measured in the serum of 30 healthy individuals, 32 individuals with monoclonal gammopathy of undetermined significance (MGUS), 20 patients with early multiple myeloma (MM) and 54 patients with overt MM. The serum activity recognized by an immunoradiometric assay was determined to be sIL-6R, because of its binding capacity to IL-6 and its molecular mass of 55 kDa. All sera of healthy individuals contained sIL-6R (mean value: 89 ng/ml, range 17-300 ng/ml). Serum sIL-6R levels were increased by 51% in patients with MGUS (mean value: 135 ng/ml, p<0.005), by 44% in patients with early myeloma (mean value: 128 ng/ml, p<0.001) and by 116 % in patients with overt MM (mean value: 193 ng/ml, p<0.001). In patients with MM, a complete lack of correlation (p>0.7) was found between serum sIL-6R levels and other previously recognized prognostic factors in this disease, particularly serum IL-6 levels and those factors related to tumor cell mass. The independence of serum sIL-6R levels on tumor cell mass was directly demonstrated by studying four patients with MM treated with autologous bone marrow transplantation for periods of between 320 and 760 days. These levels were found to be remarkably stable and constant, independent of whether patients relapsed or achieved complete remission. Finally, physiological concentrations of sIL-6R were found to increase by tenfold the sensitivity of human myeloma cell lines to IL-6. These observations suggest a high control of the sIL-6R level in vivo, and, possibly, an important functional role of this circulating protein in patients with monoclonal gammopathies.  相似文献   
48.
Free radicals are involved in the pathogenesis and/or progression of Parkinson's disease (PD). Several ergot derivative dopamine (DA) agonists have been reported to scavenge free radicals in vitro and to show a neuroprotective effect in vivo. We investigated the in vitro free radical scavenging and antioxidant activities of cabergoline, a long-acting ergot DA agonist, as well as its ability to activate glutathione (GSH), catalase (Cat) and superoxide dismutase (SOD) activating effects and its in vivo neuroprotective properties against 6-hydroxydopamine (6-OHDA) intracerebroventricularly (i.c.v.) in mice. The striatal DA turnover induced by i.c.v. injection of 6-OHDA was completely normalized by pretreatment with cabergoline. Moreover, cabergoline scavenged free radicals in vitro and significantly reduced lipid peroxidation in vitro and in vivo. Furthermore, daily administration of cabergoline to mice significantly increased striatal GSH levels by activation of RNA expressions of GSH-related enzymes, although striatal Cat and SOD activities did not change. In addition, our present results suggest that repeated administration of cabergoline attenuates both 6-OHDA-induced nigrostriatal DAergic dysfunction and DA neuronal cell death, since cabergoline also had a neuroprotective effect in the immunohistochemical experiment. In conclusion, our findings indicate that the multiple antioxidant mechanisms of cabergoline, such as activation of the GSH system and the direct free radical scavenging activity, may explain the neuroprotective effect of this ergot DA agonist.  相似文献   
49.
Three phases of neurogenesis can be recognized during Xenopus spinal cord development. An early peak during gastrulation/neurulation is followed by a phase of low level neurogenesis throughout the remaining embryonic stages and a later peak at early larval stages. We show here that several genes known to be essential for early neurogenesis (X-NGNR-1, XNeuroD, XMyT1, X-Delta-1) are also expressed during later phases of neurogenesis in the spinal cord, suggesting that they are involved in regulating spinal neurogenesis at later stages. However, additional neuronal determination genes may be important during larval stages, because X-NGNR-1 shows only scant expression in the spinal cord during larval stages. Thyroid hormone treatment of early larvae promotes neurogenesis in the spinal cord, where thyroid hormone receptor xTRalpha is expressed from early larval stages onward and results in precocious up-regulation of XNeuroD, XMyT1, and N-Tubulin expression. Similarly, thyroid hormone treatments of Xenopus embryos, which were coinjected with xTRalpha and the retinoid X receptor xRXRalpha, repeatedly resulted in increased numbers of neurons, whereas unliganded receptors repressed neurogenesis. Our findings show that thyroid hormones are sufficient to up-regulate neurogenesis in the Xenopus spinal cord.  相似文献   
50.
We compared morphological and morphometric data on various motor neurons in the human pyramidal system using the modified Klüver-Barrera staining method with extremely minimized shrinkage ratio and an image-analyzer. We classified motor neurons in the human pyramidal system into three groups according to the measurement data. This report may be of interest to better understand the process of nerve conduction in the human pyramidal system.  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