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   33757篇
  免费   1552篇
  国内免费   140篇
耳鼻咽喉   252篇
儿科学   514篇
妇产科学   417篇
基础医学   4500篇
口腔科学   1010篇
临床医学   2311篇
内科学   8524篇
皮肤病学   750篇
神经病学   2411篇
特种医学   1282篇
外科学   5471篇
综合类   137篇
一般理论   1篇
预防医学   1185篇
眼科学   619篇
药学   2339篇
中国医学   65篇
肿瘤学   3661篇
  2022年   330篇
  2021年   582篇
  2020年   282篇
  2019年   395篇
  2018年   541篇
  2017年   435篇
  2016年   513篇
  2015年   515篇
  2014年   712篇
  2013年   874篇
  2012年   1383篇
  2011年   1578篇
  2010年   831篇
  2009年   781篇
  2008年   1378篇
  2007年   1493篇
  2006年   1550篇
  2005年   1535篇
  2004年   1426篇
  2003年   1513篇
  2002年   1567篇
  2001年   1447篇
  2000年   1447篇
  1999年   1247篇
  1998年   462篇
  1997年   336篇
  1996年   308篇
  1995年   260篇
  1994年   234篇
  1993年   226篇
  1992年   911篇
  1991年   806篇
  1990年   729篇
  1989年   742篇
  1988年   676篇
  1987年   686篇
  1986年   602篇
  1985年   570篇
  1984年   366篇
  1983年   310篇
  1982年   162篇
  1979年   243篇
  1978年   183篇
  1977年   153篇
  1975年   154篇
  1974年   157篇
  1973年   169篇
  1970年   151篇
  1969年   154篇
  1967年   155篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
D2-40 antibody is raised against an oncofetal antigen, the M2A antigen. It has been used as a marker for lymphatic endothelium as well as mesothelioma and cerebellar hemangioblastoma. We demonstrate here that positive D2-40 immunoreactivity was found in the developing cerebrum, particularly in the germinal matrix layer, immature ependyma, choroid plexus and meninges. In the developing cerebellum, positive D2-40 immunoreactivity was found in the external granular layer particularly of the outer portion and the Purkinje cell layer as well as meninges. Some brain tumors such as anaplastic ependymoma, some medulloblastomas, glioblastoma, pineal germinoma, craniopharyngioma, choroid plexus papilloma, choroid plexus carcinoma, and meningioma showed positive immunoreactivity with D2-40. Therefore, D2-40 antibody is considered a useful marker for research on developing brain and diagnosis of brain tumors, differentiation between choroid plexus carcinoma and metastatic carcinoma. In addition, on cultured human neural cells, D2-40 immunoreactivity was found in nestin-positive neural stem/progenitor cells and neuronal lineage cells. As D2-40 antibody recognizes cell surface antigen M2A, it might be a candidate cell surface marker for isolation of human neural stem cells/neuronal lineage cells in the fluorescence-activated cell sorting technique.  相似文献   
992.
Ohsaki K  Nakamura S 《Neuroscience》2006,141(4):1899-1908
The central patterning mechanism of neuronal circuits is an important issue in developmental neuroscience. We report here the role of a peripheral whisker pattern for the patterning of the trigeminal projection at the brainstem and thalamus in the mouse somatosensory system. The whisker pattern was manipulated by infecting the embryonic epidermis with adenovirus harboring Shh. The ectopic expression of Shh led to the induction of extra whiskers and displacement of whiskers, where these whiskers were histologically normal. The altered whisker pattern was isomorphically represented in the brainstem (barrelette: subnuclei principalis and subnuclei interpolaris), thalamus (barreloid) and cortex (barrel) as revealed by cytochrome oxidase staining. The barrelette-like pattern of the parvalbumin became discernible by immunostaining at P7 in subnuclei principalis and at P4 in subnuclei interpolaris in normal mice. These are the barrelette neurons projecting to the thalamus and the local circuit within the barrelette. The barrelette-like parvalbumin pattern also exhibits the altered whisker pattern induced by the adenovirus harboring Shh. These results highlight the role the peripheral whisker pattern for the central patterning of the brainstem, thalamus, and cortex in the mouse somatosensory system.  相似文献   
993.
Cellular responses to DNA damage involve the relocalization of checkpoint proteins to DNA double-strand breaks (DSBs). The fission yeast checkpoint mediator protein Crb2, a homolog of mammalian 53BP1, forms ionizing radiation-induced nuclear foci (IRIF). The IRIF formation by Crb2 requires histone H2A C-terminal phosphorylation and H4-K20 methylation. However, the relevance of Crb2 relocalization is uncertain, because neither histone modification is required for a checkpoint response. Here we show that these histone modifications cooperate in the same Crb2 recruitment pathway, which also requires the Tudor and BRCT motifs in Crb2. In the absence of these histone modifications, an alternative recruitment pathway is sufficient for checkpoint activation and accumulation of Crb2 at a persistent DSB generated by HO endonuclease. This parallel pathway requires a cyclin-dependent kinase phosphorylation site in Crb2 that mediates an association with another BRCT protein Cut5 (the TopBP1 homolog), which also accumulates at HO-induced DSBs. We propose that such dual recruitment mechanisms may be a common feature of DNA damage checkpoint mediators.  相似文献   
994.
995.
Recent reports indicate that copy number variations (CNVs) within the human genome contribute to nucleotide diversity to a larger extent than single nucleotide polymorphisms (SNPs). In addition, the contribution of CNVs to human disease susceptibility may be greater than previously expected, although a complete understanding of the phenotypic consequences of CNVs is incomplete. We have recently reported a comprehensive view of CNVs among 270 HapMap samples using high-density SNP genotyping arrays and BAC array CGH. In this report, we describe a novel algorithm using Affymetrix GeneChip Human Mapping 500K Early Access (500K EA) arrays that identified 1203 CNVs ranging in size from 960 bp to 3.4 Mb. The algorithm consists of three steps: (1) Intensity pre-processing to improve the resolution between pairwise comparisons by directly estimating the allele-specific affinity as well as to reduce signal noise by incorporating probe and target sequence characteristics via an improved version of the Genomic Imbalance Map (GIM) algorithm; (2) CNV extraction using an adapted SW-ARRAY procedure to automatically and robustly detect candidate CNV regions; and (3) copy number inference in which all pairwise comparisons are summarized to more precisely define CNV boundaries and accurately estimate CNV copy number. Independent testing of a subset of CNVs by quantitative PCR and mass spectrometry demonstrated a >90% verification rate. The use of high-resolution oligonucleotide arrays relative to other methods may allow more precise boundary information to be extracted, thereby enabling a more accurate analysis of the relationship between CNVs and other genomic features.  相似文献   
996.
The aim of the present study was to examine the clinicopathological presentations of follicular lymphomas (FL) of the salivary glands, as compared to mucosa-associated lymphoid tissue (MALT) lymphomas. A total of 27 primary salivary gland lymphomas were examined: 6 FL (five, grade 1; one, grade 2); 19 MALT lymphomas; and two diffuse large B-cell lymphomas. The FL patients ranged in age from 24 to 73 years, with a mean of 49 years, which was younger than that of MALT patients (mean: 64 years; P < 0.05). Four of the six FL arose from the submandibular gland, which was the origin of only five out of a total of 19 MALT lymphomas. One FL patient was in clinical stage (CS) IE, two in CS IIE, and two in CS III and IV. As regards the MALT lymphoma patients, 13 (68%) were in CS IE and five (26%) in CS IIE. None of the FL patients had clinical diagnosis of autoimmune disease but eight MALT lymphoma patients had autoimmune disease. The present study found a relatively high incidence of FL in the salivary glands. The observed differences in age of onset, background of autoimmune disease, and lesion site suggests that the pathogenesis of FL may differ from that of MALT lymphoma.  相似文献   
997.
Preoptic mechanism for cold-defensive responses to skin cooling   总被引:1,自引:0,他引:1  
We recently identified a somatosensory pathway that transmits temperature information from the skin to a median subregion of the preoptic area (POA), a thermoregulatory centre. Here, we investigated in vivo the local neuronal circuit in the rat POA that processes the thermosensory information and outputs thermoregulatory effector signals. Skin cooling-evoked increases in sympathetic thermogenesis in brown adipose tissue, in metabolism and in heart rate were reversed by inhibition of neurons in the median preoptic nucleus (MnPO). Glutamatergic stimulation or disinhibition of MnPO neurons evoked thermogenic, metabolic and cardiac responses that mimicked the cold-defensive responses to skin cooling and were reversed by antagonizing GABAA receptors in the medial preoptic area (MPO), which is thought to contain neurons providing thermoregulatory output to effectors. These results suggest that GABA inhibition of output neurons in the MPO by MnPO neurons that are activated by cool sensory signals from the skin is a core thermoregulatory mechanism within the POA that is essential for the feedforward defence of body temperature against cold challenges in the environment.  相似文献   
998.
Macrophage recognition of Salmonella enterica serovar Typhimurium leads to a cascade of signaling events, including the activation of Src family and Syk kinases and the production of reactive oxygen species (ROS), which are critical for host innate defense during early stages of bacterial infection. ROS production depends on the NADPH oxidase, but little is known about the innate immune receptors and proximal adapters that regulate Salmonella-induced ROS. Herein, we demonstrate that serovar Typhimurium induces ROS through a pathway that requires both triggering receptor expressed on myeloid cells 2 (TREM2) and DAP12. This pathway is highly analogous to the pathways utilized by Fc receptors and integrins to regulate ROS production. Oral infection of mice with serovar Typhimurium demonstrates that the DAP12-dependent pathway regulates cecal colonization during early stages of Salmonella infection. Thus, DAP12 is an important regulator of Salmonella-induced ROS production in macrophages, and TREM2 is essential for linking DAP12 to the innate response to serovar Typhimurium.  相似文献   
999.
A completely infarcted lymph node is an unusual event. However, lymph node infarction should alert the pathologist to the considerable likelihood of malignant lymphoma. We report two unusual cases of acute myeloid leukemia presenting with granulocytic sarcoma at disease onset with a lymph node lesion exhibiting extensive lymph node infarction. The infarcted tissue contained numerous eosinophilic cell ghosts. There were some islands of degenerated, pyknotic medium-sized nuclei resembling lymphoblasts present in the necrotic area. By immunohistochemistry, these medium sized cells were CD3-, CD20-, CD34+, CD43+, CD45RO-, CD68-, CD79a- and myeloperoxidase+ in both cases. Differentiation of granulocytic sarcoma from malignant lymphomas is important for adequate therapy. The present cases indicate that granulocytic sarcoma should be added to the list of differential diagnoses for lymph node infarction.  相似文献   
1000.
The examination of rheumatoid factor (RF), one of the diagnostic marker of rheumatoid arthritis (RA), showed negative about 25% of patients with RA. We analyzed a matrix metalloproteinase-3 (MMP-3) and a carbohydrate in rheumatoid factor (CA.RF) for diagnosis of RA: the former is used the kit "Panaclear MMP-3[Plate]" and the latter is used the kit "Picolumi CA.RF". The basic study of these reagents showed satisfactory results. In 73.3% of seronegative RA showed positive on both MMP-3 and CA.RF levels in serum, respectively. We found that these examinations might be useful for diagnosis of RA, especially during seronegative RA.  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