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   4112篇
  免费   285篇
  国内免费   18篇
耳鼻咽喉   9篇
儿科学   155篇
妇产科学   91篇
基础医学   737篇
口腔科学   17篇
临床医学   397篇
内科学   930篇
皮肤病学   96篇
神经病学   448篇
特种医学   82篇
外科学   389篇
综合类   25篇
一般理论   1篇
预防医学   337篇
眼科学   75篇
药学   260篇
中国医学   3篇
肿瘤学   363篇
  2023年   28篇
  2022年   50篇
  2021年   101篇
  2020年   64篇
  2019年   108篇
  2018年   99篇
  2017年   65篇
  2016年   86篇
  2015年   116篇
  2014年   138篇
  2013年   209篇
  2012年   339篇
  2011年   349篇
  2010年   175篇
  2009年   161篇
  2008年   266篇
  2007年   287篇
  2006年   274篇
  2005年   268篇
  2004年   265篇
  2003年   276篇
  2002年   216篇
  2001年   41篇
  2000年   24篇
  1999年   48篇
  1998年   49篇
  1997年   43篇
  1996年   32篇
  1995年   35篇
  1994年   19篇
  1993年   19篇
  1992年   16篇
  1991年   18篇
  1990年   16篇
  1989年   11篇
  1988年   10篇
  1987年   12篇
  1986年   5篇
  1985年   5篇
  1984年   10篇
  1983年   4篇
  1982年   8篇
  1979年   8篇
  1977年   4篇
  1973年   2篇
  1972年   6篇
  1971年   2篇
  1970年   4篇
  1968年   6篇
  1966年   2篇
排序方式: 共有4415条查询结果,搜索用时 31 毫秒
21.
Modification of collagen matrices for enhancing angiogenesis   总被引:3,自引:0,他引:3  
The vascularization of engineered tissues in many cases does not keep up with the ingrowth of cells. Nutrient and oxygen supply are not sufficient, which ultimately leads to the death of the invading cells. The enhancement of the angiogenic capabilities of engineered tissues therefore represents a major challenge in the field of tissue engineering. The immobilization of angiogenic growth factors may be useful for enhancing angiogenesis. The most potent angiogenic growth factor specific to endothelial cells, vascular endothelial growth factor (VEGF), occurs in several splice variants. The variant with 165 amino acids both has a high angiogenic activity and a high affinity for heparin. We therefore incorporated heparin molecules into collagen matrices by covalently cross-linking them to amino functions on the collagen. Physical binding of VEGF to the heparin may then prevent a rapid clearance from the implant, while the release rate may become coupled to the degradation of the collagen matrix. The modified matrices were characterized by determination of the extent of the heparin immobilization, the in vitro degradation rate by collagenase. For testing the angiogenic properties, non-modified and heparinized collagen specimens were--either loaded with VEGF or non-loaded--subcutaneously implanted on the back of rats. Specimens were explanted after varying periods of implantation, the dry weights and the hemoglobin contents, as well as immunostained histological sections were evaluated: heparinized collagen matrices loaded with VEGF are vascularized to a substantially higher extent as compared to non-modified matrices.  相似文献   
22.
The present study describes the use of the automated BACTEC 9240 blood culture system, the Serum Separator Tube (SST), and the BD PHOENIX Automated Microbiology System in combination for the direct identification and antimicrobial susceptibility testing (AST) of gram-negative rods (GNRs) from positive blood cultures (BCs) without subculture. The study was conducted in three phases: (i) the recovery yield of Escherichia coli ATCC 25922 was determined with the SST between 0 and 8 h after spiked BC bottles turned positive; (ii) the identifications and susceptibility testing results obtained with the PHOENIX system for nine American Type Culture Collection strains of GNRs processed by the SST procedure and for colonies from agar medium were compared; and (iii) the procedure with the BACTEC system, SSTs, and the PHOENIX system was applied to positive cultures of blood from 309 patients during a 3-month period. The SST procedure with E. coli yielded sufficient numbers of cells to perform direct inoculation at any time between 0 and 8 h after a BC bottle turned positive. By using the identities obtained from pure cultures with the PHOENIX system and other biochemical identification systems as reference methods, the agreement between the reference methods and the PHOENIX system tested directly by using cultures of blood from patients was 92.9%. The 7.1% discrepant results were due to 6.5% incorrect identifications with the PHOENIX system with BC samples and 0.6% incorrect identifications with the PHOENIX system with samples from agar cultures. By AST the overall categorical accuracy was 99.0%, with 0.1% very major errors, 0.1% major errors, and 0.8% minor errors. In conclusion, use of the combination of the BACTEC system, SSTs, and the PHOENIX system has the potential to allow the agar isolation step to be skipped and the procedures for rapid direct identification and susceptibility testing of GNRs from positive BCs to be improved both in hospital-based and in central non-hospital-based laboratories.  相似文献   
23.
Compilation of published comparative genomic hybridization studies   总被引:6,自引:0,他引:6  
The power of comparative genomic hybridization (CGH) has been clearly proven since the first paper appeared in 1992 as a tool to characterize chromosomal imbalances in neoplasias. This review summarizes the chromosomal imbalances detected by CGH in solid tumors and in hemopathies. In May of 2001, we took a census of 430 articles providing information on 11,984 cases of human solid tumors or hematologic malignancies. Comparative generic hybridization has detected a number of recurrent regions of amplification or deletion that allows for identification of new chromosomal loci (oncogenes, tumor suppressor genes, or other genes) involved in the development, progression, and clonal evolution of tumors. When CGH data from different studies are combined, a pattern of nonrandom genetic aberrations appears. As expected, some of these gains and losses are common to different types of pathologies, while others are more tumor-specific.  相似文献   
24.
Outer membrane protein A (OmpA) is a class of bacterial cell wall protein that is immunogenic without adjuvant. As specific immune responses are initiated in the lymph nodes (LN, we analyzed the effect of the OmpA from Klebsiella pneumoniae (KpOmpA) onchemokine/ chemokine receptor expression by APC and on cell migration to the LN. Upon contact with KpOmpA, human immature DC and macrophages acquire CCR7 expression and responsiveness to CCL21. In parallel, CCR1 and CCR5 expression is down-regulated and CXCL8, CCL2, CCL3 and CCL5 production is up-regulated. Mice injected subcutaneously with KpOmpA present a transient inflammatory reaction at the site of injection accompanied by an enlargement of the draining LN with a higher proportion of DC and macrophages. Lastly, when exposed to KpOmpA prior injection, DC but not macrophages migrate to the draining LN. In conclusion, KpOmpA confers a migratory phenotype to DC and triggers their migration to the regional LN. This property contributes to explain how innate cells initiate adaptive immune response upon recognition of conserved bacterial components and also why OmpA is immunogenic in the absence of adjuvant.  相似文献   
25.
Intercellular contacts, mediated by E-cadherin, are essential for germ cell migration and maturation. Furthermore, it has been suggested that decrease or loss of E-cadherin correlates with tumour progression and invasive behaviour. beta-catenin is involved in a number of different processes, including cell--cell interaction when bound to cadherins, and determination of cell fate in pluripotent cells when activated via the Wnt signal-transduction pathway. To shed more light on the role of these factors in normal fetal germ cell development and the pathogenesis of germ cell tumours (GCTs), the present study investigated the presence and localization of E-cadherin and beta-catenin by immunohistochemistry. E-cadherin was only weakly expressed in or absent from fetal germ cells of the second and third trimesters, and was not expressed in carcinoma in situ/intratubular germ cell neoplasia unclassified (CIS/ITGCNU) and gonadoblastoma, the precursor of an invasive GCT in dysgenetic gonads. In GCTs, it was generally not expressed in seminoma and dysgerminoma, but was found in the vast majority of non-seminoma cells. beta-catenin was found in the cytoplasm of fetal germ cells at all gestational ages and in spermatogenesis in post-pubertal testes. It was also present in CIS/ITGCNU and gonadoblastoma. Whereas seminomas and dysgerminoma were negative, non-seminoma cells were frequently found to express beta-catenin. Expression of both factors therefore reflects the degree of differentiation of these tumours. No differences for either E-cadherin or beta-catenin were observed between samples of tumours resistant or sensitive to chemotherapy, and E-cadherin expression did not correlate with vascular invasion. E-cadherin and beta-catenin therefore play a role in both normal and malignant germ cell development and differentiation that warrants further investigation, but they seem to be of limited value as predictive or prognostic factors in GCTs.  相似文献   
26.
Summary The hemangiogenic potencies of initially avascular intra-embryonic mesoderm were studied in chick and quail embryos and in chick-quail chimeras. The prechordal mesoderm, primitive streak and primitive node of quail embryos were heterospecifically grafted into limb buds of chick embryos. Hemangiopoietic quail cells in the host limb were detected by immunohistological staining with the monoclonal anti-MB-1 antibody after 3–6 days of re-incubation. The antibody is specifically directed against quail hemangiopoietic cells and their derivatives. Quail endothelial cells were found in pure quail and in chimeric vessels, inside as well as outside the graft. The main artery of the limb and the vessels inside the graft were connected by chimeric arteries. Proximal to the graft, quail endothelial cells were located predominantly within the lining of the main artery, while distally they were found mainly in the veins and the marginal sinus. The results show that, as early as stage 3 (according to Hamburger and Hamilton 1951, HH) all parts of the avascular intraembryonic mesoderm tested, give rise to endothelial cells. Both mechanisms, angiogenesis and vasculogenesis, contribute to the vascularization of the limb. Immunocytological and scanning electron microscopic studies indicate that centrifugal and centripetal migration of angiogenic cells occurs outside the vessels as well as on the inner surface of the endothelium.Supported by the Deutsche Forschungsgemeinschaft (CH 44/9-1)  相似文献   
27.
Chemokines are a superfamily of small chemotactic proteins. While increased levels of interleukin-8 have been measured in serum and urine during urinary tract infection, little is known about other chemokines in this condition. Monocyte chemoattractant protein (MCP)–1, macrophage inflammatory protein (MIP)–1, MIP-1 and interferon- inducible protein (IP)–10 were measured in 30 patients with culture-proven urosepsis during a 3-day follow-up and in 11 healthy humans after intravenous injection of endotoxin (4 ng/kg). Urine and serum levels of MCP-1, MIP-1, and IP-10, but not of MIP-1, were elevated in patients on admission, and decreased after initiation of antibiotic treatment. Endotoxin administration to healthy subjects induced increases in plasma and urine concentrations of all four chemokines. These data indicate that clinical and experimental gram-negative infection in humans is associated with enhanced production of chemokines that act mainly on mononuclear cells and that these chemokines are at least in part locally produced.  相似文献   
28.
29.
Mitochondrial translation is essential for the biogenesis of the mitochondrial oxidative phosphorylation system (OXPHOS) that synthesizes the bulk of ATP for the cell. Hypomorphic and loss-of-function variants in either mitochondrial DNA or in nuclear genes that encode mitochondrial translation factors can result in impaired OXPHOS biogenesis and mitochondrial diseases with variable clinical presentations. Compound heterozygous or homozygous missense and frameshift variants in the FARS2 gene, that encodes the mitochondrial phenylalanyl-tRNA synthetase, are commonly linked to either early-onset epileptic mitochondrial encephalopathy or spastic paraplegia. Here, we expand the genetic spectrum of FARS2-linked disease with three patients carrying novel compound heterozygous variants in the FARS2 gene and presenting with spastic tetraparesis, axial hypotonia and myoclonic epilepsy in two cases.Subject terms: Metabolic disorders, Mutation  相似文献   
30.
An analysis of 691 French clinical Legionella isolates showed that the endemic L. pneumophila serogroup 1 strain Paris was responsible for 12.2% of all cases of legionellosis and had a specific pulsed-field gel electrophoresis pattern. We also demonstrated the presence of this endemic clone throughout Europe.  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