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   24498篇
  免费   1338篇
  国内免费   703篇
耳鼻咽喉   156篇
儿科学   473篇
妇产科学   260篇
基础医学   3301篇
口腔科学   199篇
临床医学   1664篇
内科学   4317篇
皮肤病学   259篇
神经病学   2327篇
特种医学   681篇
外国民族医学   2篇
外科学   1832篇
综合类   2079篇
现状与发展   2篇
一般理论   4篇
预防医学   2823篇
眼科学   316篇
药学   3672篇
  2篇
中国医学   946篇
肿瘤学   1224篇
  2023年   216篇
  2022年   431篇
  2021年   559篇
  2020年   435篇
  2019年   944篇
  2018年   1027篇
  2017年   625篇
  2016年   522篇
  2015年   692篇
  2014年   1037篇
  2013年   1256篇
  2012年   1205篇
  2011年   1769篇
  2010年   1587篇
  2009年   978篇
  2008年   781篇
  2007年   776篇
  2006年   687篇
  2005年   569篇
  2004年   482篇
  2003年   447篇
  2002年   406篇
  2001年   377篇
  2000年   314篇
  1999年   294篇
  1998年   248篇
  1997年   252篇
  1996年   205篇
  1995年   178篇
  1994年   175篇
  1993年   141篇
  1992年   130篇
  1991年   108篇
  1990年   102篇
  1989年   96篇
  1988年   84篇
  1987年   84篇
  1985年   580篇
  1984年   798篇
  1983年   634篇
  1982年   688篇
  1981年   724篇
  1980年   590篇
  1979年   527篇
  1978年   356篇
  1977年   310篇
  1976年   374篇
  1975年   251篇
  1974年   189篇
  1973年   161篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
心室成纤维细胞条件培养液促进成纤维细胞增殖   总被引:2,自引:0,他引:2  
目的:探讨心室成纤维细胞条件培养液成纤维细胞自身增殖作用。方法:利用成纤维细胞培养、同位素掺入率测定和RT-PCR方法。结果:心室成纤维细胞条件培养液能显增加细胞自身的[^3H]-胸腺嘧啶核苷的掺入率,并具有剂量依赖性,促进细胞自身的c-fos基因的表达,刺激后1h达高峰。ETA受体拮抗剂BQ123能部分阻断条件培养液增加成纤维细胞增殖的作用,而AT1受体拮抗剂CV11974和(α-肾上腺素受体拮抗剂regitin无此效果。结论:心室成纤维细胞能自分泌内皮素等生物活性物质,促进成纤维细胞增殖。  相似文献   
112.
Parasitic nematodes infect more than 1 billion people in the global south. The development of effective antihelminthic vaccines is a crucial tool for their future elimination. Protective immune responses to nematodes depend on Gata3+ Th2 cells, which can also be induced by nematode-released products. Whether these nematode products induce antigen-specific long-lived memory T cells and thereby confer protection against a challenge infection is not known yet. Hence, we set out to characterize the formation of memory Th2 cells induced by immunization with Heligmosomoides polygyrus excretory-secretory (HES) products, infection-induced versus immunization-induced recall responses to a challenge infection, and whether HES-induced memory T cells show protective properties following adoptive transfer. Our results show that 8 weeks postimmunization, HES induces long-lived functional memory Th2 cells at the site of immunization in the peritoneal cavity. Following a H. polygyrus challenge infection, HES-immunized mice display MHC-II-dependent antigen-specific Th2 cytokine responses in the gut-draining lymph nodes, comparable to those induced by a prior natural infection. Moreover, adoptive transfer of sorted memory CD4+ T cells from HES-immunized donors reduces female worm fecundity following a challenge H. polygyrus infection in recipient mice, highlighting a protective role for immunization-induced memory T cells.  相似文献   
113.
Quinolin-2-one represents an important and valuable chemical motif that possesses a wide variety of biological activities; however, the anti-influenza activities of quinolin-2-one-containing compounds were rarely reported. Herein, we describe the screening and identification of 3-aryl-quinolin-2-one derivatives as a novel class of antiviral agents. The 3-aryl-quinolinone derivatives were synthesized via an efficient copper-catalyzed reaction cascade that we previously developed. Using this synthetic method, preliminary structure–activity relationships of this scaffold against the influenza A virus infection were systematically explored. The most potent compound 34 displayed IC50 values of 2.14 and 4.88 μM against the replication of H3N2 (A/HK/8/68) and H1N1 (A/WSN/33) strains, respectively, without apparent cytotoxicity on MDCK cells. We further demonstrated that 27 and 34 potently inhibited the plaque formation of the IAV, rendering this scaffold attractive for pursuing novel anti-influenza agents.  相似文献   
114.
兔体外循环对胃泌素及其受体的影响   总被引:8,自引:0,他引:8  
徐鹏  易定华 《医学争鸣》2000,21(4):502-504
目的 研究体外循环 (CPB)过程中胃泌素及胃泌素受体的释放对胃液 p H值的影响 .方法 采用兔 CPB模型 ,分别测定 CPB过程中胃液的 p H值 ,胃液及血清中胃泌素质量浓度 ,并通过原位杂交的方法检测胃泌素受体 m RNA在胃肠道粘膜中的表达 .结果  CPB过程中胃液的 p H值 (2 .2 1±0 .2 2 )与血液的 p H值 (7.40± 0 .15 )呈明显相关性 (P<0 .0 1) ,而且胃液的 p H值随 CPB时间增加 ,CPB组 (2 .2 1±0 .2 2 )较对照组明显降低 (5 .30± 0 .17,P<0 .0 1) .胃液及血清中胃泌素质量浓度随体外循环时间延长较对照组明显增高 .胃泌素受体 m RNA的表达量 (0 .43± 0 .0 4) %随 CPB时间增加较对照组明显增加 (0 .2 7± 0 .0 8) % ,(P<0 .0 1) .结论  CPB过程中随时间延长 ,胃液及血清中胃泌素浓度增高 ,胃液 p H值降低及胃泌素受体 m RNA的表达量增高使胃粘膜处于高酸环境中 ,是 CPB术后发生胃肠道并发症的潜在的危险因素  相似文献   
115.
乙型肝炎病毒核糖核酸酶H基因表达及鉴定   总被引:6,自引:1,他引:5  
张惠中  程虹 《医学争鸣》2000,21(3):385-387
目的 乙型肝炎病毒核糖核酸酶 H (HBV- RNase H)为该病毒生活周期中负链 DNA合成所必需 ,获取该基因片段及其表达蛋白 ,为进一步的基础研究及应用研究创造条件 .方法 以 HBV全基因片段为模板 ,PCR方法定位扩增 HBV-RNase H特异性片段 ,连接于 p T7Blue克隆载体 ,酶切鉴定并测序后克隆于 p GSTag载体进行原核表达 .PAGE电泳及Western杂交鉴定表达产物 .结果 DNA测序结果显示 PCR扩增产物及载体中插入片段与已知序列相同 ;Western杂交结果表明 ,所表达产物为 GST与 RNase H的融合蛋白 .结论  HBV- RNase H基因的成功克隆及表达为进一步研究 HBV感染的早期诊断及乙肝患者的治疗奠定了基础  相似文献   
116.
  1. 8-Iso prostaglandin F (8-iso PGF) is one of a series of prostanoids formed independently of the cyclo-oxygenase pathway. It has been shown to be upregulated in many conditions of oxidant stress where its formation is induced by free radical-catalysed actions on arachidonic acid. As 8-iso PGF is formed in vivo in diseases in which oxidant stress is high such as septic shock, we have assessed the relative potency and efficacy of this compound in pulmonary arteries from control and lipopolysaccharide (LPS)-treated rats.
  2. Several studies have characterized the contractile actions of 8-iso PGF on various smooth muscle preparations, but its potential dilator actions have not been addressed. Thus these studies examined both the contractile and dilator actions of 8-iso PGF in rat pulmonary artery rings. The thromboxane mimetic U46619, PGE2 sodium nitroprusside (SNP) and acetyl choline (ACh) were used for comparison. Each prostanoid had to be dissolved in ethanol to a maximum concentration of 1×10−2M. At high concentrations, ethanol directly contracted pulmonary vessels. We were therefore limited by the actions of the vehicle such that we were unable to add prostanoids at concentrations higher than 1×10−4M. In some cases this meant that maximum responses were not achieved and in these cases the Emax and pD2 values are apparent estimates.
  3. The following rank order of potency was obtained from contractile studies; U46619>8-iso PGF>PGE2, each prostanoid producing concentration-dependent contractions (10−103×10−4M, 10−910−4M, 10−810−4M, respectively). As has been shown previously for other smooth muscle preparations, the thromboxane receptor (TP) antagonist ICI 192605, (1×10−6, 1×10−5 and 1×10−4M), inhibited the contractions of 8-iso PGF in a concentration-dependent fashion.
  4. The nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 1×10−4M), enhanced the contractile function of both 8-iso PGF and PGE2, but had no effect on that caused by U46619. Similarly, L-NAME inhibited the dilator function of all agents tested except the exogenous nitric oxide (NO) donor SNP, indicating that PGE2 and 8-iso PGF like ACh, act through the release of NO. The specificity of the effects of L-NAME were confirmed in studies with the inactive enantiomer D-NAME (1×10−4M), which did not affect the contractile or the dilator actions of 8-iso PGF. Furthermore, ICI 192605 enhanced the dilator actions of 8-iso PGF, suggesting that the dilator component of 8-iso PGF was achieved via activation of a non-TP receptor.
  5. Isoprostanes may modulate vascular tone by a direct action on TP receptors to cause contraction and via a distinct receptor leading to the release of NO to cause dilatation.
  相似文献   
117.
Bias in somatic hypermutation of human VH genes   总被引:3,自引:1,他引:2  
Translationally silent mutations, which are not antigen selected,of human VH6 Ig gene rearrangements isolated from human spleenwere analyzed for bias to gain insight into intrinsic featuresof the mutation process. Sixty-three clones representing 38VH6DJ rearrangements had an overall mutation frequency of 4.5%,a replacement/silent (R/S) mutation ratio of 2.1 and 167 uniquesilent mutations. The silent mutations showed bias in: (I) targetingto CDR1 and CDR2, (II) an increased frequency of mutations ofA compared to T nucleotide bases on the coding strand, and (III)an increased frequency of transitions versus transvereions.Bias of CG over CA, of GC over GT and of AC over AT transvereionswas also present. Hot spots of mutation were observed, somewhich corresponded to potential sites of stem - loop formation.The results suggest that the somatic mutation process in manmay be targeted to the complementarity determining region forsome V genes, exhibits specific base substitutions favoringtransitions and specific types of transversions, and may beoccurring on only one DNA strand.  相似文献   
118.
Opioids have been shown to produce analgesia and to be reinforcing during the first week of life in the rat. Opioids also have analgesic actions in both the infant and adult, but can be aversive in the mature animal. We examined the aversive effects of the opioid agonist U50,488 during the first postnatal week in the rat pup in three ways. In the first experiment, U50,488, injected peripherally (1.0–30.0 mg/kg), was paired with an odor and pups were tested 8 h later for positional preference for avoidance of that odor. This task is similar to conditioned preference/aversion tests used with adult animals. Both 3- and 7-day-old pups learned to avoid the odor adulterated side at the two higher doses. When exposed to odors previously associated with U50,488, pups at both ages decreased locomotor activity. In a second experiment, acute treatment with U50,488 increased ultrasonic distress vocalizations (USV) equally at 3 and 7 days of age, increased locomotor activity, and decreased rectal temperature. Neither of the latter two effects was correlated with the increase in USV production. The third experiment showed that conditioned odor cues increased USV 8 h later in 3- and 7-day-old pups at 1.0–10.0 mg/kg without changes in activity or rectal temperature. The results from these studies suggest that U50,488 can produce aversions in the neonatal rat pup as it does in the adult.Supported by U.S.P.H.S. grant DA-06600  相似文献   
119.
5-Fu佐剂包裹物的抗肿瘤作用的实验研究   总被引:3,自引:0,他引:3  
本文作了福氏完全佐剂(Freund’scompleteadjuvant,FCA)包裹5-Fu的抗肿瘤作用的实验研究。在对小鼠S180肿瘤(腹水型),EAC肿瘤(腹水型)及H22肝癌(腹水型)荷瘤鼠的治疗实验中,一次性腹腔注射2mg~6mg的5-Fu(相当于70公斤人给予778~2334mg的剂量)均不能显著延长荷瘤鼠的存活期,盐水FCA亦无治疗作用,而5-FuFCA却显示出显著的治疗效果。4次实验,5-FU-FCA治疗组荷瘤鼠平均存活期30.6天~48.3天,均显著长于同次实验的各对照组,且每次实验都有2/8至3/8的荷瘤鼠可完全治愈。  相似文献   
120.
We perform systematically amino acid analysis of the CSF before and after strong acid hydrolysis in children with unexplained neurological disease. By comparing the amino acid pattern before and after hydrolysis, defects can be traced in the metabolism not only of amino acids but also of purines, peptides, N-acetylated amino acids and peptides, and probably other compounds. This method has yielded important information such as the identification of two new diseases, GABA transaminase deficiency and adenylosuccinase deficiency, and the discovery of a peculiar, acid-labile double peak in the CSF of patients with the transient neonatal hyperammonaemia syndrome and with urea cycle defects. This substance was subsequently identified by others as -glutamylglutamine. As a consequence, we strongly recommend incorporating of this approach in the investigation of all children with unclear neurological disease.  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