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   24178篇
  免费   1752篇
  国内免费   617篇
耳鼻咽喉   93篇
儿科学   400篇
妇产科学   434篇
基础医学   6339篇
口腔科学   512篇
临床医学   1380篇
内科学   3110篇
皮肤病学   776篇
神经病学   1122篇
特种医学   290篇
外国民族医学   5篇
外科学   1494篇
综合类   3680篇
现状与发展   1篇
预防医学   925篇
眼科学   251篇
药学   2850篇
  7篇
中国医学   1495篇
肿瘤学   1383篇
  2024年   58篇
  2023年   326篇
  2022年   481篇
  2021年   845篇
  2020年   913篇
  2019年   754篇
  2018年   699篇
  2017年   877篇
  2016年   909篇
  2015年   941篇
  2014年   1608篇
  2013年   1901篇
  2012年   1560篇
  2011年   1893篇
  2010年   1457篇
  2009年   1403篇
  2008年   1265篇
  2007年   1110篇
  2006年   997篇
  2005年   775篇
  2004年   735篇
  2003年   662篇
  2002年   512篇
  2001年   396篇
  2000年   398篇
  1999年   335篇
  1998年   371篇
  1997年   283篇
  1996年   282篇
  1995年   288篇
  1994年   254篇
  1993年   204篇
  1992年   173篇
  1991年   119篇
  1990年   87篇
  1989年   56篇
  1988年   43篇
  1987年   36篇
  1986年   33篇
  1985年   76篇
  1984年   83篇
  1983年   55篇
  1982年   59篇
  1981年   48篇
  1980年   39篇
  1979年   34篇
  1978年   20篇
  1977年   22篇
  1976年   22篇
  1975年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
In search of potential drugs for the treatment of estrogen- and androgen-dependent cancer as well as the prophylaxis of metastases, tetralones, tetralins, and dihydronaphthalenes bearing a OCH3 substituent at the benzene nucleus and an imidazol-4-yl, imidazol-1-yl, or 1,2,4-triazol-1-yl substituent in 2-position were synthesized with and without C1-spacer between the rings (compounds 2 – 26 ). The compounds were tested in vitro for inhibition of the three target enzymes P450 arom (human placental microsomes), P450 17 (rat testicular microsomes), and P450 TxA2 (citrated human whole blood). To examine selectivity, some compounds were further tested in vitro for inhibition of P450 18 (bovine adrenal mitochondria), P450 see (bovine adrenal mitochondria) and corticoid formation (aldosterone, corticosterone; ACTH stimulated rat adrenal tissue). In vivo, selected compounds were examined in Sprague Dawley rats regarding P450 TxA2 inhibition, reduction of plasma testosterone concentration, antiuterotrophic activity (inhibition of the uterotrophic activity of androstenedione), reduction of plasma estradiol concentration (pregnant mares' serum gonadotropin-primed rats), and mammary tumor inhibiting activity (dimethylbenzanthracene-induced tumor; pre- and postmenopausal model). In the series of imidazol-4-yl compounds, which represent a novelty in the field of azole inhibitors of steroidogenic P450 enzymes, strong inhibitors of P450 arom and/or P450 17 were found: 7-OCH3-2-(imidazol-4-ylmethylene)-1-tetralone ( 4 ) and 7-OCH3-2-(imidazol-4-ylmethyl)-tetralin ( 12 ) are among the most potent inhibitors of P450 arom in vitro known so far. Compound 4 is a selective inhibitor, whereas 12 shows in addition strong inhibition of P450 17. In contrast to 12 , the 6-OCH3 derivative (compound 11 ) is a selective inhibitor of P450 17, being 50 times more potent than ketoconazole. Some imidazol-1-yl compounds show a marked inhibition of P450 TxA2: 2-(imidazol-1-ylmethyl)-1-tetralone ( 13 ) is a selective inhibitor of P450 TxA2, whereas 7-OCH3-2-(imidazol-1-ylmethyl)-tetralin ( 17 ) as well as 2-(imidazol-1-ylmethyl)-tetralin ( 16 ) and 7-OCH3-2-imidazol-1-yl-3,4-dihydronaphthalene ( 25 ) additionally show strong inhibition of P450 arom and P450 17. Regarding the other steroidogenic P450 enzymes as well as corticosterone formation, the compounds show only little inhibitory activity. Aldosterone formation, however, is inhibited at low concentrations. Nevertheless, 4 and 12 are more selective, i.e. inhibit aldosterone synthesis less than the well known inhibitor of P450 arom fadrozole. The compounds show activity in the aforementioned in vivo tests.  相似文献   
42.
Gingival crevicular fluid (GCF) IL-8 and IL-1,1β levels were determined by sandwich enzyme-linked immunosorbent assays. Associations between IL-8 and IL-1β GCF levels, and between these cytokines and patient estrogen status were evaluated. IL-8 and IL-1β were detected more frequently and in higher amounts/30 s GCF sample in estrogen-deficient patients than in estrogensufficient patients. IL-8 and IL-1β GCF levels were significantly correlated. These lindings suggest that GCF IL-8 levels are associated with patient estrogen status and local IL-1β concentrations.  相似文献   
43.
目的研究IFN-γ,IL-4水平对血透患者外周血淋巴细胞(PBLC)凋亡调控蛋白Fas,Bcl-2表达的影响.方法采用流式细胞术的间接免疫荧光素标记法和双抗体夹心ELISA法,分别检测30例HD患者PBLC Fas,Bcl-2的表达水平和血清IFN-γ,IL-4水平.结果H-D患者血清IFN-γ水平明显低于健康对照组,IL-4浓度显著高于对照组(P均<0.01);其外周血PBLC的Fas表达水平明显高于健康对照组,而Bcl-2水平则明显低于健康对照组(P均<0.01).经相关分析发现:Fas表达水平与血清IFN-γ水平呈负相关,而与血清IL-4水平呈正相关(P均<0.01);Bcl-2表达水平与血清IFN-γ水平呈正相关,而与血清IL-4水平呈负相关(P均<0.01).结论HD患者PBLC存在异常凋亡现象;并与Th1型细胞因子分泌低下,以及TTh2型细胞因子分泌增加之间有一定的相关性,上述改变可能在HD患者的免疫功能紊乱中起着重要作用.  相似文献   
44.
BACKGROUND: Interleukin-6 (IL-6) is a multifunctional cytokine which regulates immune responses and host defence mechanisms. IL-6 has been found to be increased in certain inflammatory conditions of the kidney, in which tubular epithelial cells play a pivotal role. Human renal tubular cells express IL-6. Until now no data about the effect of the immunosuppressant drug mycophenolic acid (MPA) on IL-6 expression were available. METHODS: Proximal and distal tubular epithelial cells (PTC/DTC) have been isolated immunomagnetically. Confluent monolayers were stimulated with interleukin-1beta (IL-1beta; 25 U/ml), IL-1beta+ MPA (0.25-50 micro M) or MPA alone for 48 h. Release of IL-6 protein into the supernatant was evaluated with an enzyme immunoassay, IL-6 mRNA expression was evaluated using the Quantikine mRNA kit. RESULTS: After IL-1beta stimulation, a highly significant 2.6- (PTC) and 3.8-fold (DTC) upregulation of IL-6 expression was detectable. IL-6 mRNA was upregulated by IL-1beta [1.57- (PTC) and 2.03-fold (DTC)]. MPA inhibited this cytokine-induced IL-6 expression in a dose-dependent manner. Incubation with the lowest MPA concentration had no effect on the stimulated upregulation, whereas all higher doses significantly decreased IL-6 expression. Dexamethasone significantly inhibited the cytokine-induced IL-6 protein release in PTC, but not in DTC. CONCLUSIONS: In this study we demonstrated for the first time an inhibitory effect of MPA on the stimulated IL-6 expression of renal tubular epithelial cells. In contrast to older data, which showed a synergistic upregulation of the expression of a CC-chemokine by a combination of cytokines and MPA, in the present study we could demonstrate an immunosuppressive effect of MPA on the expression of an important cytokine.  相似文献   
45.
Early multiple organ dysfunction syndrome appears to be facilitated with bacterial translocation in severely burn injury, yet the mechanisms of bacterial translocation remains in dispute. The aim of this study was to investigate the potential role of intestinal bifidobacteria in the pathogenesis of gut-derived bacteria/endotoxin translocation following burns and the effects of bifidobacterial supplement on gut barrier. Methods: Wistar rats were randomly divided into burn group (Burn, n=60),sham burn group (SB, n=10) in experiment Ⅰ , and burn + saline group (BS, n=30), burn + bifidobacteria group (BB, n=30), and sham-burn + saline group (SS, n= 10) in experiment Ⅱ. Animals in BB group were fed bifidobacterial preparation (5 × 109 CFU/ml) after burns, 1.5ml,twice daily. Animals in BS and SS were fed saline. Samples were taken on days 1, 3, and 5 in burn groups, and on day 3 in sham-burn groups. The incidence of bacteria/endotoxin translocation and counts of Bifidobacterium, Fungi and Escherichia coli in gut mucosa were determined with standard methods. The levels of sIgA in mucus of small intestine were measured by RIA. The positive sIgA expression in lamina propria and ileum mucosal injury was evaluated light microscopically by blinded examiners. Results: Our results showed that the incidence of bacterial translocation was increased after burns, which was accompanied by significant decrease in number of bifidobacteria but significant increase in E. coli and fungi in gut mucosa, and elevation of levels of plasma endotoxin and IL-6 (P<0. 001).The incidence of bacterial translocation was markedly reduced after 3- and 5-day supplementation of bifidobacteria compared with control group (P<0.05). The counts of mucosal bifidobacteria were increased by 4- to 40-fold,while E. coli and fungi were decreased by 2- to 30-fold and 10- to 150-fold, respectively, after bifidobacterial supplementation in contrast to control group. The damage of mucosa tended to be less pronounced after 3-day bifidobacteria-supplemented formula compared with control group [grade 2(0-6) vs. grade 4(3-6), P<0.05]. Moreover, the expression and release of sIgA was markedly augmented after 3-day bifidobacteria-supplementation formula and it returned to normal range on day 5. Conclusion: The decrease in counts and proportion of bifidobacteria in mucous membrane flora may play an important role in the development of bacteria/endotoxin translocation following thermal injury. The supplement of exogenous bifidobacteria could per se improve gut barriers, and attenuate bacteria/endotoxin translocation secondary to major burns.  相似文献   
46.
目的 研究在IL 2和IL 4作用下 ,趋化性细胞因子受体CCR3在人生发中心 (germinalcenter,GC)B细胞上的表达及其功能特性。方法 采用流式细胞术检测人GCB细胞上CCR3表达和在CCR3配体eotaxin作用下B细胞的凋亡 ,实时定量RT PCR和Northernblot法检测GCB细胞内CCR3mRNA的表达 ,淋巴细胞趋化和黏附试验检测B细胞的趋化和黏附能力。结果 人GCB细胞极低表达趋化性细胞因子受体CCR3,经IL 2和IL 4作用后 ,GCB细胞高表达CCR3,但此时CCR3不能在其配体作用下诱导GCB细胞的趋化和黏附功能 ,而是诱导GCB细胞凋亡。结论 IL 2和IL 4联合诱导人GCB细胞CCR3表达 ,CCR3可能具有死亡受体的功能。  相似文献   
47.
胃癌是最常见的癌肿之一,应用原位杂交技术检测胃癌组织中IL—6及其受体mRNA的表达情况,具有灵敏度高、特异性强的特点,而且较直观地在组织原位和转录水平对标本中IL—6及其受体进行研究,这使得形态学观察与功能学检测相结合,更能反映胃粘膜不同病变细胞分泌IL—6及其受体的情况。  相似文献   
48.
目的:探讨血清中白细胞介素4(IL-4)和白细胞介素13(IL-13)在支气管哮喘发病中的作用.方法:本研究对临床确诊的支气管哮喘46例,与正常对照组46例,分别抽取血清采用 ELISA 法测定其 IL-4、IL-13的含量.结果:支气管哮喘急性发作期病人和对照组正常人血清中的 IL-4水平分别为(460.84±27.11)和(132.97±24.66) ng/L,二组经 t 检验后 P<0.001.两组 IL-13 的水平分别为(23.76±5.44)和(12.61±2.49) ng/L,二组经 t 检验后 P<0.001.结论:哮喘病人 IL-4、IL-13 明显高于对照组,提示 IL-4、IL-13 对哮喘发病有一定的调控作用,对支气管哮喘气道非特异性炎症和局部免疫反应起重要作用.  相似文献   
49.
肺挫伤致肺水肿患者血浆中E-SLT,IL-8,TNF-α和ET-1的变化   总被引:1,自引:1,他引:0  
目的本研究观察胸部外伤所致肺水肿病人血中E-选择素、TNF、白细胞介素-8和内皮素的变化.方法用固相双夹心酶联免疫吸附法和放免技术共测定了24例胸部外伤病人在治疗前后血中E-选择素、肿瘤坏死因子、白细胞介素-8和内皮素浓度.结果临床肺水肿病人血中E-选择素、肿瘤坏死因子、白细胞介素-8和内皮素的浓度在发病时明显升高,与正常对照组比较,差异有显著性(P<0.001).治愈后恢复正常,治疗后各项指标与正常对照组比较差异无显著性(P>0.05),但治疗前后差异有显著性(P<0.001).结论E-选择素、肿瘤坏死因子、白细胞介素-8和内皮素在肺水肿发病机制中起着重要,随着这些因子的升高出现肺水肿并逐渐加重,这些因子降低后肺水肿逐步消失.因此对这些因子的检测有助于估计病情和评价疗效.  相似文献   
50.
目的 探讨白细胞介素 (IL) 2和B7 1双免疫基因转染肝癌细胞瘤苗免疫小鼠后获得的脾淋巴细胞经mIL 12基因修饰后治疗小鼠肝癌的可行性和疗效。方法 用 2 0 0PFU 细胞滴度的重组腺病毒载体 (Adv)将人IL 2和B7 1基因共同转染小鼠肝癌Hepal 6细胞株 ,经 80mg L丝裂霉素 (MMC)处理制备成肝癌细胞瘤苗 ,免疫同系小鼠后分离其脾淋巴细胞 (SLC) ,转染mIL 12基因 (Adv滴度 2 0 0PFU 细胞 )后注射入直径 1cm的小鼠皮下移植肝癌内 ,观察抗瘤效果。结果 转mIL 12基因SLC治疗组小鼠瘤体增加值最小 ( 0 .0 8± 0 .0 5 )cm3,与各对照组比差异有显著性 [(转染BGFP基因SLC、未转染SLC和生理盐水注射组分别为 ( 3 .46± 0 .15 ) ,( 3 .5 6± 0 .2 3)和( 8.12± 0 .5 4)cm3,P <0 .0 5 ]。结论 IL 2和B7 1双基因修饰肝癌瘤苗诱导小鼠产生的免疫脾淋巴细胞可能成为一种新的过继免疫治疗效应细胞及携带IL 12基因的载体细胞 ;基因治疗、特异性主动免疫和过继性细胞免疫治疗结合将有更优越的抗瘤效果。  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