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   432738篇
  免费   294499篇
  国内免费   49002篇
耳鼻咽喉   3995篇
儿科学   6064篇
妇产科学   3875篇
基础医学   109791篇
口腔科学   5669篇
临床医学   83820篇
内科学   120643篇
皮肤病学   6617篇
神经病学   31126篇
特种医学   15545篇
外国民族医学   135篇
外科学   61606篇
综合类   87283篇
现状与发展   60篇
一般理论   13篇
预防医学   54529篇
眼科学   22127篇
药学   77045篇
  169篇
中国医学   56444篇
肿瘤学   29683篇
  2023年   5311篇
  2022年   10986篇
  2021年   13232篇
  2020年   13378篇
  2019年   18881篇
  2018年   19612篇
  2017年   19911篇
  2016年   18134篇
  2015年   21149篇
  2014年   22982篇
  2013年   22002篇
  2012年   27007篇
  2011年   29950篇
  2010年   26881篇
  2009年   32615篇
  2008年   22527篇
  2007年   18886篇
  2006年   18084篇
  2005年   17809篇
  2004年   16290篇
  2003年   15071篇
  2002年   14336篇
  2001年   15577篇
  2000年   11292篇
  1999年   16673篇
  1998年   16463篇
  1997年   16355篇
  1996年   16689篇
  1995年   16763篇
  1994年   16360篇
  1993年   14464篇
  1992年   14067篇
  1991年   13142篇
  1990年   11999篇
  1989年   11743篇
  1988年   11192篇
  1987年   10453篇
  1986年   9903篇
  1985年   8893篇
  1984年   6741篇
  1983年   6702篇
  1982年   7690篇
  1981年   7219篇
  1980年   6846篇
  1979年   6708篇
  1978年   5828篇
  1977年   6132篇
  1976年   5746篇
  1975年   5487篇
  1974年   5041篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
奥曲肽对肝动脉栓塞治疗大鼠肝癌影响的实验研究   总被引:2,自引:1,他引:1  
目的 观察奥曲肽(octreotide)降低肝动脉栓塞(HAE)促进肿瘤新生血管生长的作用以及抑瘤作用。方法 采用大鼠肝内种植Walker 256瘤株制作肝癌模型,分为对照组、Octreotide组、HAE组和HAE+octreotide组共四组。定期切取肿瘤标本测量肿瘤体积,检测标本中的血管内皮生长因子(VEGF)的表达及微血管密度(MVD)。结果 各干预组肿瘤体积均小于对照组(P<0.01), HAE+octreotide组肿瘤体积也小于 HAE组(P<0.05); HAE+octrotide组 VEGF表达低于HAE组(P<0.05);Octreotide组、HAE+octreotide组 MVD表达低于对照组(P<0.05)。结论 在对大鼠肝癌的治疗中,行肝动脉栓塞时联用奥曲肽,可降低单纯肝动脉栓塞引起的癌组织 VEGF高表达,减少肿瘤新生血管形成,加强其抑瘤作用。  相似文献   
982.
983.
包皮过长和包茎组织中触觉小体观察   总被引:5,自引:2,他引:3  
目的观察包茎和包皮过长组织中触觉小体差异情况。方法收集21~25岁年龄组包皮标本44例,按包皮解剖形态分为:①包茎组21例;②包皮过长组23例。用免疫组化方法对两组包皮标本中的触觉小体进行染色,在放大100倍的视野下观察和统计两组包皮标本中触觉小体总数以及视野的总数,并用卡方检验对两组间的差异进行统计学分析。结果两组标本中,分别有8个(8/21包茎组)和10个(10/23包皮过长组)标本中未发现触觉小体,其差异无显著性(P=0.717)。包茎组和包皮过长组中触觉小体的密度分别为33.1%和21.1%,差异具显著性(P=0.022)。结论包茎中触觉小体密度较包皮过长明显升高可能是一种生理性代偿机制,而两种包皮组织中触觉小体的消失可能遵循同一规律。  相似文献   
984.
985.
The prevalence of asthma and allergic disease has increased in many countries, and there has been speculation that immunization promotes allergic sensitization. Bordetella pertussis infection exacerbates allergic asthmatic responses. We investigated whether acellular pertussis vaccine (Pa) enhanced or prevented B. pertussis-induced exacerbation of allergic asthma. Groups of mice were immunized with Pa, infected with B. pertussis, and/or sensitized to ovalbumin. Immunological, pathological, and physiological changes were measured to assess the impact of immunization on immune deviation and airway function. We demonstrate that immunization did not enhance ovalbumin-specific serum immunoglobulin E production. Histopathological examination revealed that immunization reduced the severity of airway pathology associated with sensitization in the context of infection and decreased bronchial hyperreactivity upon methacholine exposure of infected and sensitized mice. These data demonstrate unequivocally the benefit of Pa immunization to health and justify selection of Pa in mass vaccination protocols. In the absence of infection, the Pa used in this study enhanced the interleukin-10 (IL-10) and IL-13 responses and influenced airway hyperresponsiveness to sensitizing antigen; however, these data do not suggest that Pa contributes to childhood asthma overall. On the contrary, wild-type virulent B. pertussis is still circulating in most countries, and our data suggest that the major influence of Pa is to protect against the powerful exacerbation of asthma-like pathology induced by B. pertussis.  相似文献   
986.
The activities of azithromycin, erythromycin, and ciprofloxacin against 21 Legionella isolates were measured by an agar dilution method and in macrophages. The MICs for 90% of strains tested were 2.0, 1.0, and 0.5 micrograms/ml for azithromycin, erythromycin, and ciprofloxacin, respectively. Azithromycin and ciprofloxacin were both bactericidal in the macrophage system, but erythromycin was bacteriostatic.  相似文献   
987.
All nine exons of the ADH2(3) allele, which encodes the human alcohol dehydrogenase beta 3 subunit, have been cloned and sequenced. Comparison of this sequence to the ADH2(1) nucleotide sequence revealed only a single difference that results in an amino acid change, thus proving that the significant kinetic differences between these two isozymes is due to the Cys for Arg substitution at position 369. There are also two silent polymorphisms, and two changes in noncoding regions.  相似文献   
988.
Since 1982, when the World Federation of Hemophilia first published a document on the state of the art of hemophilia diagnosis and care, there have been lights and shadows in this field. Although the widespread infection of hemophiliacs with the human immunodeficiency virus (HIV) contaminating clotting factor concentrates is still a threatening and formidable shadow, the gloomy picture brought about by the AIDS epidemic is partially lightened by spectacular improvements in therapy and diagnosis. Carrier detection and first-trimester prenatal diagnosis can now be performed accurately in most kindreds by analysis of DNA of the factor VIII or IX genes. An important step forward towards the elimination of the risk of blood-borne infections transmitted by plasma products was recently made through the application of virucidal methods to clotting factor concentrates. Since HIV appears more vulnerable to such methods than the hepatitis viruses, currently available concentrates can be considered substantially free from the risk of transmitting HIV infection. Even though transmission of hepatitis is much reduced but not totally abolished, virucidal methods are continuously being improved, so that it can be foreseen that concentrates will become safer and safer. Finally, factor VIII produced by recombinant DNA technology is undergoing the first clinical trials in hemophiliacs. Hopefully, it will free from the risk of transmitting infections and will be available in sufficiently large amounts to meet the need of hemophiliacs worldwide. In 1982, the World Federation of Hemophilia published a message on the status of diagnosis and treatment of hemophilia. Since then, hemophilia care has been complicated by widespread infection of hemophiliacs with human immunodeficiency virus (HIV).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
989.
The effects of size and hydrophobicity of small (molecular weights below 2,000) polypeptides on their predominantly hydrophobic interactions with a neutral phospholipid monolayer were studied. The changes in surface pressure were determined when various concentrations of Gly, Gly-Gly-Gly, -Ala, -Ala- -Ala- -Ala, -Ala-Gly-Gly-Gly-Gly, -Phe- -Leu- -Glu- -Glu- -Leu, adrenocorticotropic hormone fragments 1–10 (ACTH-(1–10)), porcine β-lipotropin, -endorphin and human fibrinopeptide A were injected under dimyristoylphosphatidylcholine (DMPC) monolayers at an initial surface pressure of 10 dyne/cm. In all cases, when peptides with the same number of residues are compared, the concentration needed to increase the surface pressure of the film by 1 dyne/cm was inversely related to its hydrophobicity. A reasonably good correlation was found to exist between the calculated free energy of transfer of a polypeptide from ethanol to water (a measure of its hydrophobicity) and its ability to increase the surface pressure of the DMPC film (a measure of the extent of its interaction with the neutral lipid monolayer).  相似文献   
990.
1. KCl, carbachol, neurokinin A and endothelin produced concentration-dependent contractions of mucosa-free muscle strips from the dome of the human urinary bladder. The maximal response to carbachol or neurokinin A exceeded that to KCl, while the maximal response to endothelin approached that to KCl. 2. Nifedipine (1 microM) abolished the response to KCl, reduced the response to carbachol or neurokinin A but had no effect on the response to endothelin. Bay K 8644 (1 microM) markedly potentiated the response to KCl but had little or no effect on the response produced by the other stimulants. 3. Superfusion of the strips with a nominally calcium (Ca)-free medium containing EDTA (1 mM) for 30 min markedly reduced the response to carbachol, neurokinin A and endothelin, although a small response was still evident at high concentrations. Likewise, after a prolonged (60 min) superfusion of the strips with a high K (80 mM) Ca-free medium plus EDTA (1 mM) these three agonists still produced a small contractile response. 4. The nifedipine (1 microM) resistant response to carbachol, neurokinin A or endothelin was markedly depressed by LaCl3 (1 mM). In contrast, the nifedipine-(1 microM) resistant response to carbachol was not modified by NiCl2 (0.1 mM) or omega-conotoxin (0.1 microM). 5. Caffeine produced divergent effects depending upon the temperature of incubation: a relaxation at 37 degrees C and a concentration-dependent (2.5-20 mM) contraction at 25 degrees C. The latter was markedly inhibited by procaine (3 mM) but unaffected by nifedipine (1 microM). 6. After a prolonged (60 min) superfusion with a high K, Ca-free medium containing EDTA the response to carbachol (100 microM) was abolished by previous exposure to procaine (3 mM). Conversely, the response to endothelin (1 microM) was unaffected by procaine. The response to endothelin in these experimental conditions was also resistant to LaCl3 (1 mM). 7. These findings indicate that multiple sources of Ca are mobilized for contraction of the human bladder muscle by different stimulants. Dihydropyridine- and voltage-sensitive Ca channels provide the major if not the sole source of Ca for the response to KCl, play some role in the response to muscarinic (carbachol) or NK-2 tachykinin receptor stimulation but are not involved in the response to endothelin. Carbachol, neurokinin A and endothelin all mobilize a Ca pool (either extracellular or located at membrane level) which is LaCl3-sensitive but nifedipine-resistant. Neither T- nor N-type channels appear to be involved in the response to carbachol.(ABSTRACT TRUNCATED AT 400 WORDS)  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