首页 | 官方网站   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   4315篇
  免费   154篇
  国内免费   5篇
医药卫生   4474篇
  2021年   44篇
  2020年   25篇
  2019年   40篇
  2018年   31篇
  2017年   34篇
  2016年   58篇
  2015年   49篇
  2014年   77篇
  2013年   116篇
  2012年   183篇
  2011年   179篇
  2010年   120篇
  2009年   104篇
  2008年   200篇
  2007年   208篇
  2006年   182篇
  2005年   210篇
  2004年   206篇
  2003年   190篇
  2002年   186篇
  2001年   27篇
  2000年   25篇
  1999年   31篇
  1998年   29篇
  1997年   24篇
  1984年   20篇
  1980年   23篇
  1955年   21篇
  1940年   24篇
  1939年   36篇
  1938年   25篇
  1937年   32篇
  1936年   52篇
  1935年   33篇
  1934年   33篇
  1933年   71篇
  1932年   50篇
  1931年   71篇
  1930年   90篇
  1929年   80篇
  1928年   65篇
  1927年   71篇
  1926年   70篇
  1925年   68篇
  1924年   72篇
  1923年   56篇
  1922年   51篇
  1921年   25篇
  1914年   18篇
  1913年   21篇
排序方式: 共有4474条查询结果,搜索用时 46 毫秒
31.
32.
Summary The microgamogony of Eimeria ferrisi from experimentally infected mice was investigated with the electron microscope. Microgamonts were recognizable by the presence of peripherally arranged nuclei and the presence of single or paired centrioles between each nucleus and the limiting membrane of the parasite. Often an intranuclear centrocone directed toward the centriole was present. Differentiation of the microgamete began when elevations of the limiting membrane, which indicated the commencement of flagellar development, appeared above the centrioles. This event was accompanied by the segregation of nuclear content into a dense osmiophilic portion and an electron-pale portion. Then followed a gradual protrusion of the dense portion of the nucleus and developing flagella into the parasitophorous vacuole. A dense ring developed at the base of the differentiating microgamete, resulting in the formation of a stalk which was occupied by the residual portion of the nucleus. Fully developed microgametes became detached and occupied the parasitophorous vacuole along with the residual cytoplasm. Microgametes had an anterior perforatorium, a dense elongate nucleus, with an anteriorly positioned mitochondrion in a small groove of the nucleus. Usually two flagella were present but one microgamete appeared to have three. Polysaccharide first appeared when differentiation was in progress and increased until large numbers of granules were present in the microgamont cytoplasm.Abbreviations AM Amylopectin - B Basal Body of Flagellum - CC Centrocone - CE Centriole - DR Dense Ring - ER Endoplasmic Reticulum - F Flagellum - HC Host Cell - HN Host Cell Nucleus - MI Mitochondrion - MN Microneme - MP Micropore - MT Microtubule - N Nucleus - P Perforatorium - PL Osmiophilic Plate - PV Parasitophorous Vacuole - RN Residual Nucleus Supported in part by the Deutsche Forschungsgemeinschaft1, the Alexander von Humboldt Foundation2 and a Faculty Development Grant to Andrews University by the Merck Foundation, Rahway, New Jersey, USA  相似文献   
33.
P H Groeneveld  T Erich    G Kraal 《Immunology》1986,58(2):285-290
In the present study, the effect of LPS on different splenic non-lymphoid cells was investigated. Marginal zone (MZ) macrophages, marginal metallophils and interdigitating cells (IDC) were demonstrated using specific monoclonal antibodies in a two-step immunoperoxidase procedure in combination with enzyme histochemistry. The results indicate that the number of marginal zone macrophages decreases markedly after LPS treatment, but is followed by a rapid repopulation as observed by monoclonal antibody staining and selective uptake of FITC-Ficoll. Marginal metallophils are normally located at the inner border of the marginal sinus and can specifically be identified by the monoclonal antibody MOMA-1. Following LPS stimulation, many MOMA-1-positive cells were present in the corona and central parts of the follicles, with decreasing numbers near the marginal sinus. These findings strongly suggest that LPS induces a migration of marginal metallophils towards the follicle centres. Most of the tangible body macrophages in the follicle centres appeared to be slightly MOMA-1-positive, which indicates that marginal metallophils may, at least under certain circumstances, differentiate into tangible body macrophages. In the inner PALS, many interdigitating cells, NLDC-145-positive cells, can be found. The number of NLDC-145-positive cells was shown to be severely decreased at later time-intervals after LPS administration, resulting in an almost unstained inner PALS at 2 days. In contrast to the above-mentioned splenic non-lymphoid cells, the red pulp macrophages are only minimally affected by LPS.  相似文献   
34.
In 1942, Jaffe and Lichtenstein introduced the term aneurysmal bone cyst (ABC). Primary ABC is characterized by the presence of spongy or multi-cameral cystic tissue filled with blood. The process is benign, but it is locally destructive and has a high propensity for recurrence. In this paper, we present the third case of multiple metachronous primary ABCs as a rare variant of ABC. We describe the 10-year history of a 12-year-old boy with metachronous multiple primary ABCs at five different sites (right proximal humerus, right ulna, bilateral distal radius and right lateral clavicle). Furthermore, our patient suffered from vascular malformations, such as aortic isthmus stenosis, hypoplastic thoraco-abdominal aorta and bilateral renal artery stenosis. To date, in contrast to solitary ABC, the multiple lesions have been found more frequently in male individuals. Using interphase cytogenetics, we analyzed three of five of the patients ABCs and one of these was also analyzed by GTG-banding. No chromosomal abnormalities were found. Significantly, we excluded the missense mutation of codon 201 in guanine nucleotide-binding protein 1 gene consistently found in McCune-Albright syndrome (MAS) and in non-MAS cases of polyostotic fibrous dysplasia of bone with or without secondary ABC.  相似文献   
35.
Poly[2-(methylsulfinyl)ethyl acrylate] ( 1 ) was synthesized as well as derivatives 14C-labelled in side groups ( 6 ) or 14C-labelled in the main chain ( 11 ). Polymer 11 with the 14C-labelled main chain was fractionated by precipitation. The η-M-relation determined by measurements of unlabelled polymers in the ultracentrifuge for comparison was used to establish the viscosimetrically determined molecular weights of the labelled fractions. After intravenous application of aqueous solutions of the polymer in rats the excretion rate up to 72 h after treatment was ascertained to ca. 50%; the concentration in the blood serum was found to be strikingly high. A tendency to reinforced storage in organs of high phagocytose activity by growing molecular weight was observed. The tumor affinity was — if at all — low.  相似文献   
36.
A newly developed enzyme immunoassay (EIA) was used to detect the presence of pneumococcal teichoic and lipoteichoic acids in cerebrospinal fluid (CSF) from patients with Streptococcus pneumoniae meningitis who were being treated with antibiotics. All initial CSF samples, which on culture grew S. pneumoniae, were positive in the EIA. A total of 14 subsequent culture-negative samples gave clear signals in the EIA up to day 15 after the onset of antibiotic treatment. For 11 CSF specimens, culture, microscopy, and latex agglutination were negative while the EIA detected pneumococcal antigens. The EIA did not react either with CSF of patients with meningitis caused by bacteria other than S. pneumoniae or by viral pathogens. In conclusion, this EIA can be a valuable tool for the diagnosis of S. pneumoniae meningitis from CSF samples in cases in which prior antimicrobial therapy minimizes the usefulness of culture or other antigen detection tests.  相似文献   
37.
p73 and p63 are recently cloned genes that share considerable structural and functional homologies with the p53 tumor suppressor gene. These genes, unlike p53, express multiple mRNA isoforms with variable biologic functions, and their suppressor nature has yet to be confirmed. To determine the interrelationship between these genes in the tumorigenesis of head and neck squamous carcinoma (HNSC), we performed immunohistochemical analyses of their protein products and compared the data with clinicopathologic parameters in 38 patients. In histologically normal epithelium, p53 and p73 showed similar basal and/or parabasal expression, but that of p53 was weaker and discontinuous. p63 staining was noted in more suprabasal cellular layers and was stronger. In dysplasias, all three markers manifested variable but gradual increase in extent and intensity of cellular expression with histologic progression. In carcinomas, p63 was the most frequently expressed (94.7%), followed by p73 (68.4%) and p53 (52.6%). Significant statistical correlation was noted only between p63 and p73 expressions (P =.04). Although no statistical correlation was found between p53 and p63 or p73, p53-negative tumors overexpressed either p63 or p73. p73 expression was associated with distant metastasis and perineural/vascular invasion. Our study indicates that (1) p63 and p73 expression may represent an early event in HNSC tumorigenesis, (2) the lack of correlation between p73 or p63 and p53 expression suggests an independent and/or compensatory functional role, (3) p73 expression may play a part in HNSC progression, and (4) p73 and p63 may function as oncogenes in the development of these tumors.  相似文献   
38.
39.
Summary By means of electron microscopy a study has been made of different developmental stages of Eimeria callospermophili, E. falciformis, Toxoplasma gondii, Frenkelia spec. (= M-organism), Babesia bigemina, and B. ovis. Major emphasis was given to the analysis of some characteristic organelles of the motile stages of the sporozoans. These organelles were the paired organelle, the micronemes and the micropores.Supported by the Deutsche Forschungsgemeinschaft.  相似文献   
40.
Summary Light and electron microscope studies on the Sarcocystis of Rattus fuscipes showed that sarcocysts of two types occurred in this rat. These types could be distinguished from each other on the morphology of their cyst walls, on the size and micromorphology of their zoites, as well as by the changes they induced in the host cell. On the basis of these differences, it was concluded that the two sarcocyst types belonged to distinct Sarcocystis species. The possible life histories of the infections occurring in the rats were considered.Abbreviations A Amylopectin - C Conoid - CF Connected Tissue Fibres - CP Capillary - CW Cyst Wall - DC Daughter Cell - DCA Daughter Cell Anlagen - E Erythrocyte - FE Fibrillar Elements - GA Golgi Adjunct - GO Golgi Apparatus - GS Ground Substance - HC Host Cell - HCN Host Cell Nucleus - I Invagination - M Metrocyte - ME Merozoite - MI Mitochondrion - MIH Host Cell Mitochondrion - MN Micronemes - N Nucleus - NE Nucleus of Endothelial Cell - NR Neck Region - NU Nucleolus - OG Osmiophilic Granules - P Papilla - PI Pellicular Invagination - PR Projections - PW Primary Wall - RH Rhoptries - S Septum - SP Sarcoplasm - TS Thread-like Structures - Z Zoites Visiting DAAD Research Fellow from the Department of Parasitology, University of Queensland, AustraliaSupported by the Deutsche Forschungsgemeinschaft  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-23

京公网安备 11010802026262号