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   19781篇
  免费   1468篇
  国内免费   78篇
耳鼻咽喉   170篇
儿科学   389篇
妇产科学   284篇
基础医学   2669篇
口腔科学   527篇
临床医学   2019篇
内科学   4017篇
皮肤病学   285篇
神经病学   1829篇
特种医学   1190篇
外国民族医学   1篇
外科学   3115篇
综合类   205篇
一般理论   16篇
预防医学   1294篇
眼科学   550篇
药学   1193篇
中国医学   18篇
肿瘤学   1556篇
  2023年   138篇
  2022年   255篇
  2021年   547篇
  2020年   332篇
  2019年   443篇
  2018年   516篇
  2017年   397篇
  2016年   446篇
  2015年   550篇
  2014年   743篇
  2013年   891篇
  2012年   1443篇
  2011年   1457篇
  2010年   838篇
  2009年   803篇
  2008年   1215篇
  2007年   1274篇
  2006年   1128篇
  2005年   1066篇
  2004年   1000篇
  2003年   892篇
  2002年   732篇
  2001年   372篇
  2000年   350篇
  1999年   301篇
  1998年   178篇
  1997年   140篇
  1996年   109篇
  1995年   87篇
  1994年   77篇
  1993年   71篇
  1992年   161篇
  1991年   164篇
  1990年   159篇
  1989年   133篇
  1988年   121篇
  1987年   129篇
  1986年   117篇
  1985年   115篇
  1984年   128篇
  1983年   75篇
  1982年   76篇
  1981年   64篇
  1980年   58篇
  1979年   108篇
  1978年   81篇
  1977年   70篇
  1976年   62篇
  1973年   58篇
  1972年   54篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
BACKGROUND: Although soluble mediators released by basophils in tissue sites contribute to the chronic injury that occurs in hypersensitivity diseases, only limited information is available about how circulating basophils are recruited to tissues. In particular, the interaction of basophils with endothelium under conditions that mimic physiologic flow has not been explored. OBJECTIVE: We sought to identify adhesion molecules regulating the attachment of human basophils to IL-4-activated human umbilical vein endothelial cells (HUVECs) under flow conditions. METHODS: A parallel-plate flow chamber and blocking mAbs were used to define the adhesion molecules involved in the interactions of peripheral blood basophils (PBBs) and cord blood-derived basophils (CBDBs) with IL-4-activated HUVECs and with Chinese hamster ovary (CHO) cell transfectants expressing specific adhesion molecules. A fluorescent ligand specific for very late antigen 4 (VLA-4) was used to directly examine the VLA-4 affinity state of basophils. RESULTS: Flowing PBBs and CBDBs attached to activated HUVECs and to CHO cells expressing P- or E-selectin. However, only CBDBs attached to vascular cell adhesion molecule 1 (VCAM-1)-transfected CHO cells under flow conditions. The attachment of CBDBs to CHO cells was blocked by mAbs directed against E-selectin, P-selectin, and VCAM-1, whereas attachment of PBBs was blocked by E-selectin and P-selectin mAbs. Activating VLA-4 with Mn(2+) on PBBs resulted in adhesion to the VCAM-1-transfected CHO cells, indicating that VLA-4 activity on PBBs can be regulated, at least in part, through affinity changes. The Mn(2+)-induced upregulation of basophil VLA-4 affinity was demonstrated directly by using a fluorescent ligand for VLA-4 and flow cytometry. CONCLUSIONS: The interaction of human CBDBs and PBBs with endothelium under flow conditions is mediated in part by both P- and E-selectin. VLA-4 additionally contributes to the adhesion of flowing CBDBs. However, the affinity of VLA-4 is too low to support the adhesion under flow conditions of unstimulated PBBs.  相似文献   
72.
73.
The acylphloroglucinol hyperforin, a constituent of the herb Hypericum perforatum (St. John's wort), was recently identified as potent and direct inhibitor of 5-lipoxygenase (5-LO), the key enzyme in the biosynthesis of proinflammatory leukotrienes. In this study, naturally occurring analogues of hyperforin, isolated from H. perforatum, as well as a series of synthetic derivatives obtained by chemical modification of hyperforin by acylation, alkylation or oxidation, were analysed for the inhibition of 5-LO. The efficacies of these compounds were evaluated in intact human polymorphonuclear leukocytes, but also the inhibitory effects on isolated recombinant human 5-LO were investigated. Our data show that some of the oxidised hyperforin derivatives possess even improved efficacy, whereas alkylation and acylation have detrimental effects.  相似文献   
74.
Microdeletion syndromes are commonly transmitted as dominant traits and are frequently associated with variably expressed pleiotropic phenotypes. Nonlethal homozygous microdeletions, on the other hand, are very rare. Here, we delineate the fifth and so far largest homozygous microdeletion in nonmalignancies of approximately 400 kb on chromosome 4q11-q12 in a large consanguineous East-Anatolian family with six affected patients. The deleted region contains the beta-sarcoglycan gene (SGCB), the predicted gene SPATA18 (spermatogenesis associated 18 homolog) and several expressed sequence tags. Patients presented with a severe and progressive Duchenne-like muscular dystrophy phenotype, a combination of hyperlaxity and joint contractures, chest pain, palpitations, and dyspnea.  相似文献   
75.
Siderophore production by Vibrio vulnificus   总被引:13,自引:9,他引:13       下载免费PDF全文
Previous studies in our laboratory, as well as clinical evidence, have suggested that increased iron levels in the host may be important in infections caused by the halophilic pathogen Vibrio vulnificus. To study iron acquisition, we induced siderophore production by growth in a low-iron medium, and biochemical testing indicated the production of both hydroxamate- and phenolate-type siderophores. The siderophores were extracted from growth filtrates with ethyl acetate (for phenolates) and phenol-chloroform-ether (for hydroxamates). These extracts enhanced the growth of V. vulnificus when the bacterium was grown in iron-limited medium. The ability of these siderophores to stimulate the growth of Salmonella typhimurium LT-2 enb-7 (a mutant deficient in the biosynthesis of enterochelin) and Arthrobacter flavescens JG-9 (a hydroxamate auxotroph) supported the conclusion that V. vulnificus produces both hydroxamate- and phenolate-type siderophores.  相似文献   
76.
Two hundred forty-eight human immunodeficiency virus (HIV)-positive and 496 HIV-negative subjects in Uganda were tested by HerpeSelect herpes simplex virus type 2 enzyme-linked immunosorbent assay (ELISA) and Western blotting to optimize the ELISA for use in this population. A higher index cutoff value was required for optimal sensitivity and specificity, and overall performance of the assay was not affected by HIV status.  相似文献   
77.
78.
The cytological features of testicular germ cell tumours were established in smears from 15 freshly resected tumours. These features were applied to the fine needle aspiration cytology diagnosis of metastases in 27 patients referred for chemotherapy. There were 16 positive reports in 32 aspirates of which 13 were taken before chemotherapy and three in patients with residual or new masses after chemotherapy. Teratomas and typical seminomas showed certain characteristic morphological features in cytological preparations which when present in fine needle aspiration cytology material enabled tumour types to be diagnosed. Spermatocytic and anaplastic seminoma were not represented in this series. It is unlikely that these could be distinguished from malignant teratoma undifferentiated (MTU) in the fine needle aspiration cytology material. Metastases from carcinomatous areas in MTU and malignant teratoma intermediate (MTI) may not be distinguishable in fine needle aspiration cytology material from metastatic adenocarcinoma or undifferentiated carcinoma from a different primary site. Positive cytological findings are of value to the oncologist in the management of patients with metastases from testicular germ cell tumours; negative cytology does not exclude the presence of viable tumour. The sampling of small foci of viable tumour in large necrotic masses persisting after chemotherapy is a problem for radiologists, cytologists, and histopathologists. This paper does not advocate the use of fine needle aspiration cytology for the diagnosis of primary testicular tumour.  相似文献   
79.
The Chediak-Higashi Syndrome (CHS) is a rare inherited disorder occurring in man and several animal homologs including the beige mouse; it is characterized by pigmentary dilution, susceptibility to pyogenic infections, and the presence of enlarged lysosomes in many cell types. Beige mice 6 months of age and older were found to have darkened livers, kidneys, and spleens, accompanied by splenomegaly. A fluorescence microscopic survey of tissues from beige mice revealed marked accumulations of a microscopic survey of tissues from beige mice revealed marked accumulations of a yellow autofluorescent pigment inhepatocytes, renal proximal tubule cells, and splenic macrophages. Additionally, large amounts of hemosiderin were present in the spleen. In beige mice, the pigment was noted in animals as young as 1 to 2 weeks of age and gradually increased in amount as the animals aged. A histochemical investigation of the pigment showed that it was ceroid-like in nature and contained in lysosomes. Ultrastructurally, the pigment was composed of lipid-like droplets embedded in a dense matrix and surrounded by a limiting membrane. The accumulation of ceroid-like material in beige mice may be a reflection of the metabolic disturbance which underlies CHS.  相似文献   
80.
The beige mouse is considered to be a homologue of Chediak-Higashi syndrome (CHS). Cytochemical and electron microscopic studies have revealed an inherited lesion in the kidneys of these mice. The alteration was confined to the distal segments (S3) of the proximal tubules and was characterized by the accumulation of numerous massive polysaccharide-rich granules. These granules were reactive for acid phosphatase and β-glucuronidase activities and were therefore considered to be lysosomes. Small numbers of lymphocytes were also observed in the perivascular spaces and within the tubules of the S3 segment. The fine structure of S3 cells was also markedly altered. In addition to the massive lysosomes, dense material was found associated with the brush border and was present in pinocytotic vesicles at the base of the brush border and between basal invaginations of the plasma membranes. Despite these changes, reabsorption of exogeneous peroxidase by S3 cells appeared to be normal. The presence of a congenital defect in the kidney of the beige mouse appears to provide a useful model for studying the morphology and function of the S3 region of the nephron.  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