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   1250篇
  免费   107篇
  国内免费   3篇
耳鼻咽喉   6篇
儿科学   45篇
妇产科学   15篇
基础医学   209篇
口腔科学   4篇
临床医学   160篇
内科学   317篇
皮肤病学   7篇
神经病学   126篇
特种医学   40篇
外科学   199篇
综合类   11篇
预防医学   69篇
眼科学   9篇
药学   67篇
中国医学   7篇
肿瘤学   69篇
  2023年   13篇
  2022年   13篇
  2021年   35篇
  2020年   32篇
  2019年   42篇
  2018年   38篇
  2017年   25篇
  2016年   19篇
  2015年   36篇
  2014年   48篇
  2013年   76篇
  2012年   116篇
  2011年   96篇
  2010年   80篇
  2009年   69篇
  2008年   83篇
  2007年   56篇
  2006年   74篇
  2005年   58篇
  2004年   47篇
  2003年   68篇
  2002年   46篇
  2001年   8篇
  2000年   4篇
  1999年   8篇
  1998年   14篇
  1997年   9篇
  1996年   10篇
  1995年   11篇
  1994年   5篇
  1993年   4篇
  1992年   3篇
  1990年   5篇
  1986年   4篇
  1985年   5篇
  1984年   6篇
  1983年   4篇
  1982年   16篇
  1981年   7篇
  1980年   5篇
  1979年   5篇
  1978年   9篇
  1977年   3篇
  1976年   6篇
  1975年   3篇
  1974年   4篇
  1973年   5篇
  1970年   3篇
  1969年   3篇
  1965年   2篇
排序方式: 共有1360条查询结果,搜索用时 31 毫秒
81.
In humans, group 1 CD1 glycoproteins present foreign and self lipid and glycolipid antigens to T-cells. Homologues of these molecules are not found in mice or rats but are present in guinea pigs (GPs). We examined CD1 and MHC class II expression in the central nervous system (CNS) of GPs sensitized for experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. In normal GPs and the uninflamed CNS, low-level MHC class II (MHC II) immunoreactivity occurred on vascular elements, meningeal macrophages and parenchymal microglial cells, whereas immunoreactivity for CD1 was absent. In the inflamed CNS, the majority of infiltrating cells were MHC II+ and microglia showed increased expression. CD1 immunoreactivity was detected on astrocytes and subsets of inflammatory cells Including B cells and macrophages. Minimal CD1 and MHC II co-expression was noted on inflammatory cells or glia. We conclude that group 1 CD1 molecules are strongly upregulated in the inflamed CNS on subsets of cells distinct from the majority of MHC II bearing cells. The expression of CD1 proteins in such lesions broadens the potential repertoire of antigens recognized at these sites and highlights the value of the GP as a model for studies of the relevance of CD1 molecules in host defense and autoimmune diseases.  相似文献   
82.
Definitive neonatal diagnosis of congenital adrenal hyperplasia (CAH) is frequently complicated by normal 17-hydroxyprogesterone levels in 21-hydroxylase-deficient patients, residual maternal steroids, and other interfering substances in neonatal blood. In an effort to improve the diagnosis, we developed a gas chromatography/mass spectrometry method for simultaneous measurement of 15 urinary steroid metabolites as early as the first day of life. Furthermore, we developed 11 precursor/product ratios that diagnose and clearly differentiate the four enzymatic deficiencies that cause CAH. Random urine samples from 31 neonatal 21-hydroxylase-deficient patients and 59 age-matched normal newborns were used in the development. Additionally, samples from two 11 beta-hydroxylase-deficient patients and one patient each for 17 alpha-hydroxylase and 3 beta-hydroxysteroid dehydrogenase deficiencies were used. The throughput for one bench-top gas chromatography/mass spectrometry instrument is 20 samples per day. Thus, this method affords an accurate, rapid, noninvasive means for the differential diagnosis of CAH in the newborn period without the need for invasive testing and ACTH stimulation.  相似文献   
83.
The literature make it clear that lung cancer in women differs from that in men in several specific aspects. We conducted a retrospective study of the 967 consecutive recorded patients (696 men and 91 women after exclusions) diagnosed with small cell lung cancers (SCLC) between 1981 and 1994 in the Bas-Rhin population-based cancer registry to determine if such particularities could be observed in SCLC. Data included demographic and social characteristics, medical and smoking history, management (diagnosis and treatment), hospitalisation and survival. The end point for survival was 31 December 1998. Women were more frequently single, divorced, or widowed (P=0.007) and lived more often in urban areas (places with more than 10,000 inhabitants) (P=0.017). They differed significantly from men in their tobacco exposure (P=0.0001) and non-smoking rates (P=0.0003) but not in clinical presentation, except for more frequently elevated LDH levels (P=0.02). Bone marrow biopsies were more often performed in men (P=0.004), but management was otherwise comparable. The mean number of hospitalisations (for any reason) was comparable in both sexes but women tended to remain hospitalised longer (P=0.057). Overall survival did not differ, but women older than 70 years died sooner than their male counterparts (P=0.026). Our study confirms that some of gender differences reported in the lung cancer literature exist in SCLC. Sex-related differences in LDH levels have not previously been reported, to our knowledge. North American and European data concerning survival among women and men are discordant. Whether these gender differences are related to a real difference between the sexes or simply to differential exposure to carcinogens remains to be determined.  相似文献   
84.
PURPOSE: The action spectrum of ultraviolet radiation mainly responsible for melanoma induction is unknown, but evidence suggests it could be ultraviolet A (UVA), which has a different geographic distribution than ultraviolet B (UVB). This study assessed whether melanoma mortality rates are more closely related to the global distribution of UVA or UVB. METHODS: UVA and UVB radiation and age-adjusted melanoma mortality rates were obtained for all 45 countries reporting cancer data to the World Health Organization. Stratospheric ozone data were obtained from NASA satellites. Average population skin pigmentation was obtained from skin reflectometry measurements. RESULTS: Paradoxically, melanoma mortality rates decreased with increasing UVB in men (r = -0.48, p < 0.001), and women (r = -0.57, p < 0.001), and with increasing UVA in both sexes. By contrast, rates were positively associated with increasing UVA/UVB ratio in men (r = + 0.49, p < 0.001) and women (r = + 0.55, p < 0.001). After multiple adjustment that included controlling for skin pigmentation, only UVA was associated with melanoma mortality rates in men (p < 0.02) with a suggestive but non-significant trend present in women (p = 0.12). CONCLUSIONS: UVA radiation was associated with melanoma mortality rates after controlling for UVB and average pigmentation. The results require confirmation in observational studies.  相似文献   
85.
86.
Stereotactic Radiosurgery (SRS) has evolved as a unique discipline that combines aspects of both surgery and radiation oncology. Technological developments in the past few decades have provided a wide array of treatment techniques, including (i) the Gamma Knife; (ii) Linac-based stereotactic techniques using circular collimators or using micro multileaf collimators (mMLCs); (iii) the Cyber Knife, using an x-band linac mounted on a robotic arm; and (iv) serial and spiral tomotherapy. This paper provides a review of the treatment planning methods for stereotactic radiosurgery. Because of the differences in planning strategies used for each SRS technique, this paper will provide both a general review of the pre-requisites and common features of SRS treatment planning and the planning techniques specific to each of the SRS techniques.  相似文献   
87.
The actual incidence of true multicentric glioblastoma multiforme (GBM) varies between 2.4 and 4.9% of all GBMs. True multicentric tumors are described as widespread lesions in different lobes or hemispheres, which cannot be explained by spreading along the cerebrospinal fluid or blood pathways. We present here a case of multicentric GBM identified with positron emission tomography. CASE REPORT: A 73-year-old woman with sudden onset headaches, balance problems, and one episode of syncope was diagnosed as having an irregular, contrast-enhancing, space-occupying lesion in the left-temporal-parietal region on magnetic resonance imaging (MRI). The tissue diagnosis was confirmed as GBM, and she received stereotactic radiosurgery using the Leksell Gamma Knife (Elekta Instruments, Atlanta, GA). A 3-month, follow-up, MRI scan showed a remarkable decrease in the size of the contrast-enhancing area that was targeted during radiosurgery. A suspicious area of enhancement was detected on the right side, although no surrounding edema was evident. Fluorodeoxyglucose (FDG)-PET scanning revealed a large irregular neoplasm extending from the inferior left-temporal lobe into the deep parietal lobe with extremely intense FDG uptake, suggesting a very aggressive tumor. A smaller lesion was also discovered in the deep right-frontal lobe, representing a second neoplastic focus. The patient refused any further treatment. CONCLUSION: PET scans, in conjunction with MRI scans, allow for the best possible and most comprehensive diagnosis and treatment plans.  相似文献   
88.
The integrin VLA-4 has been shown to play a key role in the entry of antigen-specific T cells into the CNS during autoimmune demyelination. Treatment of animals with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, with antibodies to VLA-4 is known to suppress acute disease. In the present study, a synthetic antagonist of VLA-4 (TBC 3486) was injected subcutaneously into mice adoptively sensitized for chronic relapsing EAE. TBC 3486 was administered daily for 14 days at early (before acute signs) and late time points (during chronic disease). Early treatment led to marked delay in disease onset and reduction in clinical severity and demyelination. After termination of treatment, clinical severity remained lower than in controls for more than 1 week. TBC 3486-treated animals showing no clinical signs (at the height of disease in controls) displayed moderate levels of inflammation but little damage to myelin. Late administration of TBC 3486 to animals with chronic EAE had no effect clinically. Immunocytochemistry and Western blotting of CNS tissue from acutely treated animals supported a moderate shift toward a Th2-type cytokine profile after treatment. Thus, TBC 3486 effectively delayed and reduced the acute (but not chronic) phase of EAE, and this amelioration correlated with changes in the inflammatory molecule profile.  相似文献   
89.
90.
Cytoplasmic polyadenylation is a widespread mechanism to regulate mRNA translation that requires two sequences in the 3′ untranslated region (UTR) of vertebrate substrates: the polyadenylation hexanucleotide, and the cytoplasmic polyadenylation element (CPE). Using a cell-free Drosophila system, we show that these signals are not relevant for Toll polyadenylation but, instead, a “polyadenylation region” (PR) is necessary. Competition experiments indicate that PR-mediated polyadenylation is required for viability and is mechanistically distinct from the CPE/hexanucleotide-mediated process. These data indicate that Toll mRNA is polyadenylated by a noncanonical mechanism, and suggest that a novel machinery functions for cytoplasmic polyadenylation during Drosophila embryogenesis.  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