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   110617篇
  免费   8221篇
  国内免费   3806篇
耳鼻咽喉   578篇
儿科学   1703篇
妇产科学   1437篇
基础医学   18445篇
口腔科学   1513篇
临床医学   5973篇
内科学   16346篇
皮肤病学   2030篇
神经病学   14309篇
特种医学   1448篇
外国民族医学   22篇
外科学   7988篇
综合类   11625篇
现状与发展   9篇
预防医学   3642篇
眼科学   1135篇
药学   21267篇
  11篇
中国医学   2996篇
肿瘤学   10167篇
  2024年   146篇
  2023年   1612篇
  2022年   2149篇
  2021年   3904篇
  2020年   3194篇
  2019年   3601篇
  2018年   3502篇
  2017年   3389篇
  2016年   3151篇
  2015年   3684篇
  2014年   5835篇
  2013年   7543篇
  2012年   5704篇
  2011年   6739篇
  2010年   5678篇
  2009年   5677篇
  2008年   5981篇
  2007年   5490篇
  2006年   4891篇
  2005年   4149篇
  2004年   3929篇
  2003年   3598篇
  2002年   2768篇
  2001年   2301篇
  2000年   2213篇
  1999年   1920篇
  1998年   2078篇
  1997年   1917篇
  1996年   1712篇
  1995年   1434篇
  1994年   1292篇
  1993年   1181篇
  1992年   964篇
  1991年   889篇
  1990年   701篇
  1989年   624篇
  1988年   523篇
  1987年   504篇
  1986年   504篇
  1985年   813篇
  1984年   861篇
  1983年   556篇
  1982年   669篇
  1981年   580篇
  1980年   467篇
  1979年   396篇
  1978年   325篇
  1977年   224篇
  1976年   196篇
  1975年   159篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
992.
To clarify the role of IP-10 in autoimmune liver diseases, we studied the serum levels of IP-10 in 14 patients with autoimmune hepatitis (AIH), 23 patients with primary biliary cirrhosis (PBC), and 65 patients with chronic viral hepatitis (20 type B and 45 type C). The hepatic expression of IP-10 mRNA and the correlation between the serum levels of IP-10 and clinical parameters were also evaluated. In addition to 20 healthy controls, 16 rheumatoid arthritis (RA) patients were included as an extrahepatic inflammatory disease. The serum level of IP-10 was significantly (P < 0.02) higher in patients with AIH, PBC, and chronic hepatitis B and C than in healthy controls, and it was significantly correlated (P < 0.05) with the serum levels of aspartate aminotransferase and alanine aminotransferase in patients with AIH, PBC, and chronic hepatitis B and C. The serum level of IP-10 was not elevated in RA patients. After successful treatment of AIH and chronic hepatitis C, the serum level of IP-10 decreased to the same level as in healthy volunteers. As we previously showed in cases with chronic hepatitis B or C, in situ hybridization in both AIH and PBC cases demonstrated the expression of IP-10 mRNA in hepatocytes around focal or lobular necrosis surrounded by infiltrating mononuclear cells, whereas IP-10 mRNA was not expressed in areas around the damaged bile ducts in PBC cases. The present results suggest that IP-10 is specifically produced by hepatocytes in inflammatory areas irrespective of the aetiology of hepatitis, and that IP-10 may help to recruit T cells to the hepatic lesions in autoimmune liver diseases as well as in chronic viral hepatitis.  相似文献   
993.
The N-methyl-D-aspartate (NMDA) receptor, a subtype of ionotropic glutamate receptors, plays an important role in the regulation of neuronal development, learning and memory, and neurodegenerative diseases. NMDA receptor blockade enhances neurogenesis in the hippocampal dentate gyrus in vivo. The effect of NMDA receptor antagonist on proliferation of neural progenitor cells, however, remains to be determined. We investigated changes in the diameter and number of neurospheres derived from the embryonic rat brain after NMDA receptor blockade. Cortical progenitor cells were isolated from gestational day 18 fetal rats according to the Percoll density gradient method. Cultured spheres expressed neural progenitor markers, musashi-1 and nestin. Immunohistochemical analysis demonstrated that cells in Dulbecco's modified Eagle medium/F12 containing 1% fetal bovine serum on day 8 differentiated to MAP-2-positive neurons and GFAP-positive astrocytes. The expression of NR1 and NR2B subunits of the NMDA receptor in neurospheres was detected. Neither brief nor sustained exposure to NMDA altered the diameter and number of neurospheres. Brief exposure to 30 μM MK-801, an NMDA receptor antagonist, decreased the diameter of neurospheres. Sustained exposure to 30 μM MK-801 decreased the diameter and number of neurospheres. Our results provide evidence that MK-801 directly decreased proliferation of neural progenitor cells.  相似文献   
994.
995.

Background

An association between Tako-Tsubo cardiomyopathy (TTC) and underlying malignancies has been observed, suggesting that TTC might be the consequence of paraneoplastic phenomena. This study investigates the presence of autoantibodies against cardiomyocytes as well as adrenergic (β1, β2) and muscarinic (M2) receptors in patients with TTC.

Methods and results

Serum from 20 TTC patients and 20 controls with ischemic heart disease was obtained. Indirect immunofluorescence testing for intracellular autoantibodies against cardiomyocytes showed a homogenous distribution, as in both groups 9 of 20 sera displayed a characteristic binding pattern of antibodies including vascular walls and intracellular structures. Flow cytometry analysis revealed no difference between TTC and controls in the binding of autoantibodies to the surface antigens of cardiomyocyte HL-1 cells (p?=?0.569, t-test). Flow cytometry analysis of nontransfected wild type cells (p?=?0.633, t-test), M2 receptor-transfected cells (p?=?0.687, t-test), β1 receptor-transfected cells (p?=?0.444, t-test) and β2 receptor-transfected cells (p?=?0.632, t-test) showed similar results for control and TTC sera. Likewise, the binding pattern of TTC patients with a history of neoplasia compared to those without or to controls did not differ significantly (p?>?0.05, u-test).

Conclusion

Findings suggest that the presumed paraneoplastic etiology of TTC cannot be attributed to the formation of these antibodies.  相似文献   
996.
997.
为了观察同种异体NK细胞对不同肿瘤细胞的体外杀伤活性,并初步探讨其分子机制。以K562细胞为对照,应用LDH释放法检测不同效靶比时同种异体NK细胞杀伤CNE2、KG1a和U251细胞的活性。应用RT-PCR和流式细胞仪分别检测4种细胞MHCI类链相关分子(MICA/B)和人巨细胞病毒糖蛋白UL16结合蛋白(ULBP1~3)基因和分子的表达情况。效靶比20∶1时用AMO-1、BMO-1、M295、M310和M551单抗分别阻断肿瘤细胞表面MICA、MICB、ULBP1、ULBP2和ULBP3分子,观察NK细胞对其杀伤活性的变化。结果:NK细胞对K562、CNE2和KG1a细胞均有杀伤活性,对U251细胞无杀伤活性。在mRNA水平4种细胞均表达MICA/B和ULBP1~3基因。K562细胞表达MICA/B和ULBP1~3全部分子;KG1a和U251细胞均不表达5种分子;CNE2细胞表达MICA/B和ULBP2,不表达ULBP1和ULBP3。CNE2、KG1a和U251细胞均高表达HLAI分子,而K562细胞不表达。用单抗分别阻断靶细胞表面相应的NKG2D配体分子,NK细胞对KG1a和U251细胞的杀伤活性无变化。NK细胞对K562和CNE2细胞的杀伤活性可部分被封闭。同种异体NK细胞在体外对不同肿瘤细胞的杀伤活性不同,其杀伤机制也不完全相同。  相似文献   
998.
We investigated the effects of a single bacterial lipopolysaccharide (LPS) injection in vivo on the gene expression of tumor necrosis factor-α (TNF) and its receptors: TNF receptor type I (TNF-R 55 kDa or TNF-R1) and TNF receptor type II (TNF-R 75 kDa or TNF-R2) in various tissues and white blood cells. While TNF mRNA rapidly accumulated in most tissues, TNF-R1 and TNF-R2 mRNA levels were found to be differentially regulated in lung, spleen, lymph nodes and white blood cells. In most cases, TNF-R mRNA levels did not parallel TNF mRNA levels. These observations indicate that TNF-R of both types are capable of modulating the host response to LPS, not only by shedding of their extracellular domains, but also by strict regulation of their gene expression.  相似文献   
999.
妊娠17~37周胎儿可溶性白介素2受体和NK细胞含量的变化   总被引:1,自引:0,他引:1  
杜涛  方群 《中国免疫学杂志》2005,21(10):768-771
目的:探讨妊娠17~37周正常和宫内感染时胎儿外周血可溶性白介素2受体(Soluble interleuldn-2 receptor,sIL-2R)和自然杀伤细胞(Natural killer,NK)含量的变化。方法:超声引导下行脐带穿刺术,收集129例胎儿外周血,包括97例正常对照组胎儿血,32例宫内感染组(单纯疱疹病毒感染、弓形虫感染、风疹病毒感染)胎儿血,采用双色免疫荧光标记流式细胞仪技术测定胎JLPF周血NK细胞百分率,双抗体夹心酶联免疫吸附试验测定胎JLPF周血中sIL-2R的含量,分析生理状态下胎儿外周血NK细胞、sIL-2R的状况和宫内感染时NK细胞和sIL-2R含量的变化。结果:妊娠17—37周胎儿外周血NK细胞、sIL-2R含量不随孕周改变,r(NK)=-0.03,P〉0.05;r(sIL-2R)=0.167,P〉0.05,宫内感染时NK细胞含量减少,sIL-2R含量增多,与正常对照组相比差异有显著意义;t(NK)=4.29,P〈0.01;t(sIL-2R)=-5.833,P〈0.01。结论:妊娠17—37周胎儿外周血有一定量的NK细胞和sIL-2R存在,但机体免疫功能仍不完善,宫内感染时机体容易出现免疫抑制状态。  相似文献   
1000.
Lee LF  Cui X  Cui Z  Gimeno I  Lupiani B  Reddy SM 《Virus genes》2005,31(1):73-80
Marek’s disease virus (MDV), a highly cell-associated oncogenic chicken herpesvirus, causes Marek’s disease in domestic chickens. A unique phosphoprotein of MDV, pp38, has previously been associated with the maintenance of transformation in MDV-induced tumor cell lines. However, recently, the biological properties of a deletion mutant virus (rMd5Δpp38) revealed that pp38 is involved in early cytolytic infection in lymphocytes but not in the induction of tumors. Thus, pp38 is important for early cytolytic infection and not for transformation. The pp38 protein of the MDV serotype 1 vaccine strain CVI988/Rispens differs by one amino acid when compared to the pathogenic strains of MDV. Monoclonal antibody, H19, recognizes all serotype 1 MDV strains except CVI988/Rispens. Previous studies have also shown that the unique pp38 epitope in CVI988/Rispens induced high antibody response. In order to study the role of this epitope in the protective properties of CVI988/Rispens, we generated a mutant rMd5 virus in which the wild type pp38 gene has been substituted with that of CVI988/Rispens (rMd5/pp38CVI). The replication properties of rMd5/pp38CVI, both in vitro and in vivo, and tumor induction were examined. We found that the biological properties of rMd5/pp38CVI were similar to the wild type rMd5 virus with regards to in vivo replication, antibody response and tumor induction. This shows that the pp38 derived from CVI988/Rispens is not involved in protective properties as was previously suggested.  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