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   3242篇
  免费   252篇
  国内免费   8篇
耳鼻咽喉   17篇
儿科学   80篇
妇产科学   41篇
基础医学   421篇
口腔科学   81篇
临床医学   248篇
内科学   763篇
皮肤病学   34篇
神经病学   421篇
特种医学   313篇
外科学   346篇
综合类   40篇
一般理论   3篇
预防医学   277篇
眼科学   20篇
药学   154篇
中国医学   3篇
肿瘤学   240篇
  2022年   28篇
  2021年   44篇
  2020年   29篇
  2019年   55篇
  2018年   51篇
  2017年   55篇
  2016年   50篇
  2015年   58篇
  2014年   85篇
  2013年   106篇
  2012年   143篇
  2011年   151篇
  2010年   119篇
  2009年   106篇
  2008年   161篇
  2007年   155篇
  2006年   134篇
  2005年   131篇
  2004年   114篇
  2003年   114篇
  2002年   128篇
  2001年   103篇
  2000年   101篇
  1999年   110篇
  1998年   56篇
  1997年   52篇
  1996年   48篇
  1995年   43篇
  1994年   38篇
  1993年   42篇
  1992年   81篇
  1991年   72篇
  1990年   83篇
  1989年   70篇
  1988年   60篇
  1987年   51篇
  1986年   43篇
  1985年   47篇
  1984年   37篇
  1983年   28篇
  1982年   18篇
  1981年   31篇
  1980年   22篇
  1979年   26篇
  1978年   20篇
  1975年   20篇
  1974年   27篇
  1973年   18篇
  1972年   17篇
  1971年   18篇
排序方式: 共有3502条查询结果,搜索用时 15 毫秒
51.
The Leiden Roster for Huntington's disease (HD) contained data on 2617 cases up to July 1988. The age at onset (AO) was known in 1084 cases and in 1020 of these both their AO and the sex of the affected parent was known. The mean AO was higher for females than for males and higher for maternal than for paternal cases. However, in the group born before 1925 only females with maternal inheritance had a higher mean AO. Data on influence of sex and line of inheritance were present for the grandparents as well as for the great grandparents. Influence of the line of inheritance from the grandparents was particularly present for the grandmother-father (MP) lineage; regarding the great grandparents a significant difference was found between the MPM and PMP lineage. The results obtained for juvenile HD cases were comparable to those previously published. In late onset cases (over 50 years) no maternal preponderance in inheritance was found.  相似文献   
52.
Thiel embalming is recommended as an alternative to formalin‐based embalming because it preserves tissue elasticity, color, and flexibility in the long term, with low infection and toxicity risk. The degree to which Thiel embalming preserves elasticity has so far been assessed mainly by subjective scoring, with little quantitative verification. The aim of this study is to quantify the effect of Thiel embalming on the elastic properties of human ankle tendons and ligament. Biomechanical tensile tests were carried out on six Thiel‐embalmed samples each of the peroneus longus, peroneus brevis, and calcaneal tendons, and the calcaneofibular ligament, with strain rates of 0.25%s?1, 2%s?1, and 8%s?1. The stress?strain relationship was calculated from the force‐extension response with cross‐sectional area and gauge length. Young's modulus was determined from the stress?strain curve. The results showed that the tendon and ligament elasticity were lower after Thiel embalming than the literature values for fresh nonembalmed tendons and ligament. The biomechanical tensile test showed that the measured elasticity of Thiel‐embalmed tendons and ligaments increased with the strain rate. The Thiel embalming method is useful for preserving human ankle tendons and ligaments for anatomy and surgery teaching and research, but users need to be aware of its softening effects. The method retains the mechanical strain rate effect on tendons and ligament. Clin. Anat. 28:917–924, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   
53.
54.
Histamine release (HR) after activation of human basophils with anti-IgE demonstrates a great variability among different donors. To elucidate the biochemical basis of this phenomenon, we studied the activation of purified basophils from donors that barely demonstrated HR (less than 7%) after stimulation by anti-IgE, although IgE was present on these cells and formyl-methionyl-leucyl-phenylalanine (fMLP)-induced HR was normal. Basophils from anti-IgE "nonreleasers" demonstrated, in contrast to cells from "releasers," hardly any changes in cytosolic-free Ca++ concentration after addition of anti-IgE. However, anti-IgE treatment of basophils from these anti-IgE nonreleasers resulted in at least two intracellular changes. First, a profound inhibition (54.2% +/- 4.2%) of a subsequent fMLP-induced HR was observed. This inhibition caused by anti-IgE was also observed in basophils from anti-IgE releasers treated with wortmannin, an inhibitor of the anti-IgE-induced HR. The time course of the inhibition induced by wortmannin plus anti-IgE on the fMLP-induced HR (half-life maximum, 4 minutes; time of maximum concentration, 10 minutes) was comparable to the time course of the anti-IgE-induced HR. Second, anti-IgE did induce homotypic aggregation in these anti-IgE-nonreleasing basophils, like in anti-IgE-releasing basophils. These studies indicate that basophils not responding to anti-IgE with HR or cytosolic-free Ca++ concentration changes do generate intracellular signals that inhibit the subsequent response to a heterologous stimulus and induce homotypic aggregation.  相似文献   
55.
Clonal cell lines producing corticotropin-releasing hormone (CRH) have been generated by transfection of the W2 rat medullary thyroid carcinoma (MTC) cell with a CRH-encoding CMV/ SV40 expression vector. Here, we report the morphological, immunohistochemical, and ultrastructural features of rat tumors derived by implantation of CRH-producing W2CRH-7 cells and compare them with non-CRH-producing W2 MTCs. Both types of tumors grew rapidly and consisted of sheets and nests of pleomorphic cells infiltrating adjacent adipose tissue. Immunohistochemistry revealed CRH in only W2CRH-7 tumors; scattered cells in these tumors also were immunoreactive for chromogranin and for vasoactive intestinal peptide. Otherwise, the two tumor types exhibited similar profiles of various neuroendocrine markers, including neuron-specific enolase, synaptophysin, calcitonin, and somatostatin. Ultrastructurally, the tumors contained abundant dilated rough endoplasmic reticulum, a prominent Golgi apparatus, and numerous lysosomes. Very few secretory granules were noted in the W2 tumors; by contrast, secretory granules, although still not numerous in the majority of W2CRH-7 cells, were more abundant in scattered cells of those tumors. The positive immunostaining for CRH is consistent with the observations of increased plasma CRH and pituitary-adrenal activation induced by these transplanted tumors. This system provides a valuable model for CRH excess mimicking tumoral CRH-dependent Cushing’s syndrome in human patients.  相似文献   
56.
Human granulosa cells were isolated from preovulatory folliclesduring cycles stimulated with HMG-HCG or clomiphene-HMG-HCGor from unstimulated cycles. The cells were cultwed for 6–8days in medium M199 containing fetal calf serum under 5% CO2in air. Highly purified human prolactin and human chorionicgonadotrophin were added alone or in combination to the cultures,and the content of steroids in the medium was measured everysecond day, utilizing conventional RIA techniques. In the presenceof HCG the formation of progesterone (P) increased 3–5-foldover the control level with maximal effect after 4 days. Incells derived from clomiphene-HMG-HCG stimulated cycles, prolactinper se did not influence basal P formation but reduced the stimulatoryeffect of HCG. This was only seen in granulosa cells from follicles< 20 mm in diameter. In experiments with Forskolin, an adenylatecyclase activator, P formation was stimulated and the stimulationwas counteracted by the concomitant presence of prolactin, indicatingthat prolactin did not interfere with the LH-HCG receptor. Incells from smaller follicles, or in cells from follicles aspiratedfrom the natural cycle prior to the endogenous LH peak, P formationwas stimulated by HCG but the addition of prolactin did notreduce this stimulatory effect. The results are discussed inrelation to earlier reports on prolactin effects in vitro bothon laboratory animals and human material.  相似文献   
57.
Objective:  Effects of pump treatment vs. four times daily injections were explored in children with diabetes with regard to quality of life and impact of disease as well as adverse effects and parameters of metabolic control.
Methods:  An open, parallel, randomized controlled prospective comparative study lasting 14 months was completed by 38 type 1 children with diabetes (age 4–16 yr) following a 3.5-months run-in phase. Standardized quality-of-life Pediatric Quality of life Inventory (PedsQL) and impact of disease scores were obtained every 3.5 months as well as regular medical parameters. Parallel treatment group data and longitudinal within-patient data were analysed for each treatment modality.
Results:  Within-patient comparisons of the two treatment modalities showed significant improvement in PedsQL and impact scores after pump treatment. Treatment group comparisons did not show significant improvement. Pump treatment resulted in decreased symptomatic hypoglycaemia and lowered haemoglobin A1c by 0.22% after run in.
Conclusions:  Within-patient comparison suggests that metabolic control, frequency of severe hypoglycaemia (a threefold decrease), quality of life and impact of disease scores are improved by pump treatment in comparison to regular treatment with four daily insulin injections.  相似文献   
58.

Introduction

MED13L-related intellectual disability is characterized by moderate intellectual disability (ID), speech impairment, and dysmorphic facial features. We present 8 patients with MED13L-related intellectual disability and review the literature for phenotypical and genetic aspects of previously described patients.

Materials and methods

In the search for genetic aberrations in individuals with ID, two of the patients were identified by chromosomal microarray analysis, and five by exome sequencing. One of the individuals, suspected of MED13L-related intellectual disability, based on clinical features, was identified by Sanger sequencing.

Results

All 8 individuals had de novo MED13L aberrations, including two intragenic microdeletions, two frameshift, three nonsense variants, and one missense variant. Phenotypically, they all had intellectual disability, speech and motor delay, and features of the mouth (open mouth appearance, macroglossia, and/or macrostomia). Two individuals were diagnosed with autism, and one had autistic features. One had complex congenital heart defect, and one had persistent foramen ovale. The literature was reviewed with respect to clinical and dysmorphic features, and genetic aberrations.

Conclusions

Even if most clinical features of MED13L-related intellectual disability are rather non-specific, the syndrome may be suspected in some individuals based on the association of developmental delay, speech impairment, bulbous nasal tip, and macroglossia, macrostomia, or open mouth appearance.  相似文献   
59.
Secondary lymphoid-tissue chemokine, SLC, also known as exodus-2 and 6Ckine, is a novel CC chemokine with selectivity for T lymphocytes and preferential expression in lymphoid tissues. We have studied its production, receptor usage and biological activities. High levels of SLC mRNA were detected in lymph nodes, the gastrointestinal tract and several gland tissues, but no expression was found by Northern blot analysis in freshly isolated or stimulated blood monocytes and lymphocytes, or neutrophils and eosinophils. In situ hybridization revealed constitutive expression of SLC in the T cell areas and the marginal zone of follicles in lymph nodes and the mucosa-associated lymphoid tissue, but not in B cell areas or sinuses. Comparison with immunocytochemical staining showed similarity between the in situ expression of SLC and the distribution of interdigitating dendritic cells but not with sinus-lining dendritic cells, macrophages or T lymphocytes. SLC induced chemotaxis of T lymphocytes and its activity increased considerably when the cells were conditioned with IL-2 or phytohemagglutinin (PHA). Under optimal conditions SLC had unusually high efficacy and induced the migration of up to 50 % of input T lymphocytes. SLC also induced Ca2+ mobilization in these cells. Similar responses were obtained with EBI1 ligand chemokine (ELC), and sequential stimulation with both chemokines led to cross-desensitization, suggesting that SLC acts via the ELC receptor, CCR7. This was confirmed using murine pre-B cells stably transfected with CCR7 which bound SLC with high affinity and showed chemotaxis and Ca2+ mobilization in response to both SLC and ELC. In T lymphocytes PHA and IL-2, which enhanced chemotactic responsiveness, also markedly enhanced CCR7 expression. In contrast to all known chemokine receptors, up-regulation of CCR7 by IL-2 was transient. A maximum was reached in 2 – 3 days and expression returned to initial levels within 8 – 10 days. The present study shows that SLC is constitutively produced within the T cell areas of secondary lymphoid organs and attracts T lymphocytes via CCR7.  相似文献   
60.
Placental superoxide is increased in pre-eclampsia   总被引:3,自引:0,他引:3  
One of the current hypotheses on the pathophysiology of pre-eclampsia (PE) states that the placenta secretes one or more cytotoxic factors resulting in maternal endothelial dysfunction. Among the candidate factors are the products of increased oxidative stress. Although there is circumstantial evidence of such an increase, direct evidence is still lacking. Electron paramagnetic spin trap resonance (EPR), the most direct method to detect free radicals in tissues, was used to measure superoxide levels in placentae from normal pregnancies (n=13) and pregnancies complicated by PE (n=10). The superoxide level was significantly increased in the placental tissue of pre-eclamptic women. Moreover, upon inhibition of Cu-Zn superoxide dismutase (SOD) activity the relative increase of the superoxide levels was significantly smaller in the placentae from the PE patients, implying decreased basal Cu-Zn SOD activity. These findings lend direct support to the hypothesis that oxidative stress in placental tissue is increased in PE.  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