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   2036篇
  免费   128篇
  国内免费   18篇
耳鼻咽喉   7篇
儿科学   48篇
妇产科学   37篇
基础医学   231篇
口腔科学   37篇
临床医学   288篇
内科学   318篇
皮肤病学   29篇
神经病学   192篇
特种医学   207篇
外科学   286篇
综合类   19篇
一般理论   5篇
预防医学   195篇
眼科学   39篇
药学   131篇
中国医学   1篇
肿瘤学   112篇
  2021年   23篇
  2020年   14篇
  2019年   17篇
  2018年   26篇
  2017年   27篇
  2016年   24篇
  2015年   22篇
  2014年   41篇
  2013年   51篇
  2012年   72篇
  2011年   79篇
  2010年   37篇
  2009年   49篇
  2008年   75篇
  2007年   94篇
  2006年   77篇
  2005年   64篇
  2004年   81篇
  2003年   65篇
  2002年   69篇
  2001年   69篇
  2000年   79篇
  1999年   54篇
  1998年   40篇
  1997年   47篇
  1996年   43篇
  1995年   37篇
  1994年   36篇
  1993年   29篇
  1992年   54篇
  1991年   50篇
  1990年   41篇
  1989年   64篇
  1988年   47篇
  1987年   57篇
  1986年   59篇
  1985年   61篇
  1984年   36篇
  1983年   22篇
  1982年   23篇
  1981年   14篇
  1980年   14篇
  1979年   16篇
  1977年   17篇
  1976年   16篇
  1975年   15篇
  1972年   12篇
  1971年   17篇
  1970年   12篇
  1966年   11篇
排序方式: 共有2182条查询结果,搜索用时 93 毫秒
1.
Background Percutaneous abdominal aortic aneurysm(AAA) repair has been previously described using the "preclose"technique and general endotrachial anesthesia (GA).  相似文献   
2.
Porphyrin dimers 9 with either linkages and possible isomers bis[1-[6,7-bis[2-(methoxycarbonyl)ethyl]-1,3,5,8-tetramethyl-2- vinylporphin-4-yl]ethyl] ether (10) bis[1-[6,7-bis[2-(methoxycarbonyl)ethyl]-1,3,5,8-tetramethyl-4- vinylporphin-2-yl]ethyl] ether (11), and 1-[6,7-bis[2-(methoxycarbonyl)ethyl]-1,3,5,8-tetramethyl-2-vinylporph in- 4-yl]ethyl 1-[6,7-bis[2-(methoxycarbonyl)ethyl]-1,3,5,8-tetramethyl-4-vinylporph in- 2-yl]ethyl ether (12) were synthesized from the corresponding (1-hydroxyethyl)vinyldeuteroporphyrin IX dimethyl esters (Hvd). The pure Hvd isomers 2-(1-hydroxyethyl)-4-vinyldeuteroporphyrin IX dimethyl ester (7) and 4-(1-hydroxyethyl)-2-vinyldeuteroporphyrin IX dimethyl ester (8) were obtained from 2-acetyl-4-(1-hydroxyethyl) deuteroporphyrin IX dimethyl ester (3) and 4-acetyl-2-(1-hydroxyethyl)deuteroporphyrin IX dimethyl ester (4). Porphyrins 3 and 4 were prepared either by partial reduction of 2,4-diacetyldeuteroporphyrin IX dimethyl ester (2) or by oxidation of hematoporphyrin IX dimethyl ester (1) by using tetra-n-propylammonium perruthenate (Prn4N)(RuO4) with N-methylmorpholine N-oxide as an oxidizing agent. The in vivo photosensitizing ability and therapeutic ratios of dimers 9-12 were compared with that of Photofrin II in the SMT-F tumor growing subcutaneously in DBA/2 Ha mice. These dimers were found to have better tumoricidal activity than Photofrin II with reduced skin phototoxicity.  相似文献   
3.
Bonfanti  R; Furie  BC; Furie  B; Wagner  DD 《Blood》1989,73(5):1109-1112
PADGEM protein (PADGEM), also known as GMP140, is a platelet alpha- granule membrane protein that is translocated to the external membrane after platelet activation. Although the biosynthesis of this protein was originally thought to be confined to megakaryocytes, the synthesis of PADGEM in endothelial cells was recently demonstrated (McEver et al: Blood 70:1974a, 1987). We now describe the subcellular localization of this protein in endothelial cells. Immunofluorescence staining of permeabilized human umbilical vein endothelial cells with KC4, a well characterized monoclonal antibody to PADGEM, showed positively stained elongated structures similar in distribution and shape to Weibel-Palade bodies. Their identity as Weibel-Palade bodies was confirmed by double label immunofluorescence using KC4 and a polyclonal antiserum to von Willebrand factor (vWf), a protein known to be specifically stored in these organelles. All Weibel-Palade bodies were found to contain PADGEM. In contrast to strong perinuclear staining produced with anti- vWf antibodies, no significant perinuclear staining was obtained with KC4, indicating that relatively little PADGEM is present in the endoplasmic reticulum and in the Golgi apparatus. In endothelial cells treated with secretagogues that stimulate vWf release the elongated structures positive for PADGEM disappeared, further identifying these structures as Weibel-Palade bodies. This observation extends the parallels between Weibel-Palade bodies and alpha-granules and suggests a possible functional association between vWf and PADGEM.  相似文献   
4.
BACKGROUND: The dopamine transporter (DAT) is known to be a key regulator of dopamine, and recent studies of genetics, treatment, and imaging have highlighted the role of DAT in attention-deficit/hyperactivity disorder (ADHD). The findings of in vivo neuroimaging of DAT in ADHD have been somewhat discrepant, however. METHOD: Dopamine transporter binding was measured using a highly selective ligand (C-11 altropane) and positron emission tomography (PET). The sample consisted of 47 well-characterized, treatment-na?ve, nonsmoking, non-comorbid adults with and without ADHD. Additionally, control subjects had few symptoms of ADHD. RESULTS: Results showed significantly increased DAT binding in the right caudate in adults with ADHD compared with matched control subjects without this disorder. CONCLUSIONS: These results confirm abnormal DAT binding in the striatum of adults with ADHD and provide further support that dysregulation of DAT may be an important component of the pathophysiology of ADHD.  相似文献   
5.
Contact lens disinfection systems were evaluated for their effectiveness in killing Acanthamoeba castellanii and Acanthamoeba polyphaga trophozoites and cysts. Amoebae were inoculated into commercially available contact lens cleaning and soaking solutions. At intervals varying from 30 minutes to 24 hours, solutions were filtered. The filters were removed and cultured for Acanthamoeba organisms. Striking differences were observed in the abilities of the different disinfecting solutions to kill the organisms. Solutions containing chlorhexidine were effective at very short exposure times. Solutions containing benzalkonium chloride required slightly longer exposure times but were faster than solutions containing only thimerosal. Solutions containing sorbate, polyaminopropyl biguanide, or polyquaternium-1 were not effective at killing Acanthamoeba organisms in the time allotted for the experiment. Solutions containing hydrogen peroxide were quite effective if the agent was not prematurely catalyzed. A. polyphaga generally required longer exposure to disinfectants than did A. castellanii for complete inhibition to occur.  相似文献   
6.
Occurrence of the t(2;5)(p23;q35) in non-Hodgkin's lymphoma   总被引:9,自引:3,他引:6  
Primary CD30(Ki-1)-positive anaplastic large-cell lymphoma (ALCL) is considered by some to be a distinct clinicopathologic entity associated with the t(2;5) (p23;q35). However, the specificity of t(2;5) for ALCL has not been carefully studied. Therefore, we performed a detailed analysis of all cases of ALCL with abnormal cytogenetics results in the Nebraska Lymphoma Study Group registry, as well as all other cases of non-Hodgkin's lymphoma with t(2;5) in the registry. We found the t(2;5) in only five of 10 cases of ALCL, four of whom were young patients. However, we also found the t(2;5) in 11 other cases of nonanaplastic lymphoma, including eight children with typical peripheral T-cell lymphomas of various types. The t(2;5) was also found in three older adults with B-cell lymphomas of various types. Thus, the t(2;5) was not specific for CD30+ ALCL. However, t(2;5) may define a clinicopathologic entity in children and young adults characterized by variable morphologies with a T-cell or indeterminate phenotype, CD30-positivity, nodal disease with frequent extranodal involvement, advanced stage, and an excellent response to therapy, including bone marrow transplantation for relapsed disease. The clinical relevance of the t(2;5) in older patients requires further study.  相似文献   
7.
Urine drug testing has become an increasingly controversial issue in today's society. In this paper, several issues involved in urine drug testing are discussed. These include the limitations of the accuracy of urine testing, testing in schools, athletics, the military and industry, and the legalities of drug testing. Also discussed is background information about urine drug screening and key factors in obtaining specimens for testing. Conclusions about the role of urine drug testing in the battle against substance abuse are drawn.  相似文献   
8.
9.
The role of excitatory amino acids (EAAs) in the excitation of monkey spinothalamic tract (STT) neurons following activation of cutaneous primary afferent fibers by noxious and non-noxious stimuli was investigated. The responses of STT neurons to either NMDA or non-NMDA EAA ligands were blocked by infusion of specific antagonists through a microdialysis fiber into the region surrounding the cells. Our results show that blockade of non-NMDA receptors results in a nearly complete elimination of the responses of STT neurons to all stimuli. Blockade of NMDA receptors results in an attenuation of the responses to noxious stimuli but, in addition, prevents the development of the sensitization of STT neurons that is often observed after intradermal injection of capsaicin. These observations further support a role of EAAs in the transmission of sensory information from primary afferent fibers to dorsal horn neurons and a role for NMDA receptors in the generation of hyperalgesia.  相似文献   
10.
PURPOSE: Many behavioral studies have found impaired perception of dynamic visual stimuli in dyslexia and several neuroimaging studies have found reduced activation of the human motion area MT+ in dyslexia. These results are often interpreted as a magnocellular (MC) deficit in dyslexia. It has also been claimed that colored filters can help dyslexics to read. One defining feature of the MC-pathway is a greater weight for L-cone input than M-cone input, and at most very weak S-cone input. We measured the subjective speed matches between L-, M-, and S-cone isolating stimuli in good and poor readers. METHODS: Subjects performed a speed-matching task with drifting cone-isolating stimuli to find the point of subjective equality between two drifting patterns. Such a task is known to activate cortical area MT+, presumably via the MC-pathway. RESULTS: L- to M-cone speed-match ratios were negatively correlated with single-word (r=-0.46) and irregular-word reading (r=-0.56) but not with non-word reading. CONCLUSIONS: Results suggest that relative L-cone sensitivity within the MC-pathway may limit orthographic reading performance.  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