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   2674篇
  免费   69篇
  国内免费   57篇
耳鼻咽喉   11篇
儿科学   47篇
妇产科学   29篇
基础医学   429篇
口腔科学   240篇
临床医学   121篇
内科学   393篇
皮肤病学   20篇
神经病学   318篇
特种医学   17篇
外科学   196篇
综合类   166篇
预防医学   67篇
眼科学   35篇
药学   623篇
中国医学   50篇
肿瘤学   38篇
  2022年   20篇
  2021年   42篇
  2020年   27篇
  2019年   32篇
  2018年   38篇
  2017年   50篇
  2016年   35篇
  2015年   34篇
  2014年   76篇
  2013年   98篇
  2012年   58篇
  2011年   106篇
  2010年   92篇
  2009年   87篇
  2008年   81篇
  2007年   66篇
  2006年   73篇
  2005年   100篇
  2004年   92篇
  2003年   56篇
  2002年   70篇
  2001年   71篇
  2000年   74篇
  1999年   82篇
  1998年   61篇
  1997年   52篇
  1996年   42篇
  1995年   48篇
  1994年   48篇
  1993年   51篇
  1992年   51篇
  1991年   51篇
  1990年   54篇
  1989年   47篇
  1988年   53篇
  1987年   47篇
  1986年   32篇
  1985年   58篇
  1984年   54篇
  1983年   42篇
  1982年   55篇
  1981年   62篇
  1980年   46篇
  1979年   45篇
  1978年   49篇
  1977年   51篇
  1976年   43篇
  1975年   23篇
  1974年   23篇
  1972年   14篇
排序方式: 共有2800条查询结果,搜索用时 31 毫秒
11.
用放射免疫分析法测定了28例偏头痛、10例慢性紧张型头痛患者和16例健康对照组血浆精氨酸加压素(AVP)、催产素(OT)、环磷酸腺苷(cAMP)及环磷酸鸟苷(cGMP)含量。结果表明,偏头痛发作期AVP含量下降、cAMP含量升高,偏头痛间歇期cGMP含量下降,血浆OT含量在发作期和间歇期均明显下降。慢性紧张型头痛患者血浆AVP、OT、cAMP和cGMP与对照组比较均无显著性差异。结果提示,血浆AVP和OT水平降低以及环核苷酸的代谢异常与偏头痛发病机制有关。  相似文献   
12.
The current U.K. trial protocol (UKALL XI) for childhood lymphoblastic leukaemia demands mercaptopurine (MP) dose escalation in children who tolerate daily 75  mg/m2 MP (100% dose) without cytopenias. The previous trial (UKALL X) did not. MP metabolism was studied in a group of UKALL XI children ( n =21) who tolerated 100% dosages and who were matched in this respect with a similar group of UKALL X children. Red blood cell MP derived thioguanine nucleotide (TGN) concentrations were measured in both groups under comparable conditions; at 75  mg/m2 MP there was no significant difference. MP dose escalation in the UKALL XI children produced higher TGN concentrations (TGNs at 100% vs 125% dosages, median difference 90  pmol/8×108 RBCs, 95% CI 25 to 165  pmol, P <0.02). Assayed at the time of cytopenia induced dose reduction, the UKALL XI children had accumulated significantly higher TGN concentrations than the UKALL X children (median difference 78  pmol/8×108 RBCs, 95% CI 20 to 144, P <0.02). These findings indicate that dose escalation in children tolerant of 100% MP dosages produces higher peak TGN concentrations.  相似文献   
13.
本文以腺苷酸为测定物,探讨了以国产自动平衡记录仪为高效液相色谱记录并定量分析结果的方法。结果表明,从自动平衡记录上得到峰形、计算结果均与原机所带积分仪的一致。其稳定性、灵敏度和线性响应均能达到高效液相色谱检测器的要求,是一种可以代替积分仪分析结果的经济、可靠的方法。  相似文献   
14.
In the brain, nitric oxide (NO) has been identified as a messenger molecule and a mediator of excitatory amino acid-induced neurotoxicity. In this study, the effects of NO on serum-induced mitogenesis and cell proliferation of the cerebellar glial cells were assessed. NO-generating agent, S-nitroso-N-acetylpenicillamine (SNAP) increased intracellular cyclic guanosine monophosphate (cGMP) levels. Furthermore, 2 chemically dissimilar NO-generating agents, SNAP and sodium nitroprusside (SNP) inhibited serum-induced thymidine incorporation and cell proliferation. The antimitogenic effect of NO was mimicked by 8-bromo-cGMP and blocked by hemoglobin, a known inhibitor of NO. The effect of NO was not cytotoxic, since the cells were not stained with Trypan blue and did not show increased release of lactate dehydrogenase in the culture supernatants. However, NO-treated cells showed decreased conversion of tetrazolium to blue formazan suggesting that NO inhibited mitochondrial activity in the glial cells. These results demonstrate that NO inhibits serum-induced mitogenesis and cell proliferation of cultured rat cerebellar glial cells.  相似文献   
15.
Purpose To report the occurrence of cyclic exotropia in a patient with retinitis pigmentosa. Methods A 31-year-old man presented with cyclic exotropia of the left eye of 4 years duration that alternated every 24 h. A detailed ophthalmologic examination was performed. Results The patient showed an orthotropia and a comitant left exotropia of 30 prism diopters at distance and 25 prism diopters at near in the primary position on an exotropic day with a cycle of 48 h. A fundoscopic examination showed bone spicule formation and arteriolar narrowing, and electroretinography showed no response in either eye. A Goldmann visual field examination showed a central island in both eyes. Conclusions Cyclic exotropia may occur in patients with retinitis pigmentosa, an association that to the best of our knowledge has not been previously reported in the English ophthalmic literature. Cyclic exotropia is an unusual association with retinitis pigmentosa.  相似文献   
16.
目的:评价^18氟-胸腺嘧啶核苷(^18F-FLT)正电子发射体层(PET)-CT显像对胸部肿瘤定性诊断的价值。方法:对17例做了^18氟-脱氧葡萄糖(^18F-FDG)PET-CT检查,但定性诊断困难的患者,在第2~3天进行了^18F-FLITPET-CT显像。分析病变在两种不同显像剂PET-CT上的表现,分别测量二者的最大标准摄取值(maxSUV)。结果:8例恶性病变(5例肺癌、1例纵隔淋巴瘤、1例胸椎恶性肿瘤、1例胸椎转移瘤),其中7例见FLT异常摄取,5例肺癌平均maxSUV为4.2(鳞癌2例、腺癌2例、肺泡癌1例);9例良性病变(5例肺结核、1例肺炎、3例纵隔淋巴结结核)无或轻度摄取FLT,其中6例肺内良性病变平均maxSUV为1.6;9例良性病变中8例见FDG异常浓聚,其中6例肺内良性病灶平均maxSUV为3.9,3例纵隔淋巴结结核也见FDG明显摄取,平均maxSUV为11.0。11例肺内病灶FDG和FLT显像的敏感性、特异性、准确性分别为100.0%(5/5)、16.7%(1/6)、54.5%(6/11)和80.0%(4/5)、66.7%(4/6)、72.7%(8/11)。结论:胸部肿瘤^18F-FLT显像的特异性较高,在^18F-FDG显像阳性,难以确定病变性质时,FLIT可以作为FDG的有益补充,二者联合显像有助于提高胸部肿瘤诊断的准确性。  相似文献   
17.
AIM To clone novel gastric cancer-associated genes and investigate their roles in gastric cancer occurrence.METHODS A method called differential display was used which allows the identification of differentially expressed genes by using PAGE to display PCR-amplified cDNA fragments between gastric cancer cells and normal gastric mucosa cells. These fragments were cloned into plasmid vector pUC18. Homology analysis was made after sequencing these fragments.RESULTS Two novel genes were identified compared with sequences from GenBank. One was registered with the AD number AF 051783. In situ hybridization showed that these two novel genes expressed specifically in gastric cancer tissues.CONCLUSION The two novel genes obtained by differential display were confirmed to be gastric cancer-associated genes using in situ hybridization.  相似文献   
18.
Neuronal regulation of smooth muscle tone in the female pig urethra has mainly been studied in vitro using electrical field stimulation (EFS) of nerves. Excitatory control is considered to be exerted by released noradrenaline, whereas inhibitory control is non-adrenergic non-cholinergic (NANC), and mediated by nitric oxide (NO), and an as yet unidentified agent. We investigated the functional and morphological effects of α-latrotoxin (αLTX), a spider neurotoxin believed to cause massive release of vesicle-stored neurotransmitters, on spontaneously developed urethral smooth muscle tone. The effects were compared to those of EFS and high potassium. In the presence of the NO-synthesis inhibitor Nω-nitro-L-arginine (L-NOARG: 0.3 mM) both αLTX and EFS evoked contractions. After treatment with scopolamine and phentolamine, no contraction was observed, and under these conditions αLTX and EFS induced relaxation. At low frequencies (<12 Hz), the EFS-induced relaxations were rapid, whereas at higher frequencies (>12 Hz), they were biphasic, consisting of a rapid first phase followed by a more long-lasting second phase. L-NOARG abolished the relaxations at low frequencies, as well as the first phase of the biphasic relaxation. The second phase was not affected by treatment with L-NOARG, but 0.1 μM ω-conotoxin GVIA, blocker of N-type voltage-operated calcium- channels (VOCCs), markedly reduced or abolished the response. In the presence of L-NOARG or ω-conotoxin GVIA, the αLTX-induced relaxation was significantly decreased, and the combination of L-NOARG and ω-conotoxin GVIA further reduced or abolished the relaxation. In preparationstreated with tetrodotoxin or scorpion venom, believed to inactivate nerves by acting on sodium channels, αLTX and EFS had no effects. αLTX-induced relaxation was not associated with changes in cyclic GMP or cyclic AMP content. High (80 mM) potassium solution induced a triphasic response of the preparation. A transient relaxation was followed by a restoration of tone, and then by a persistent relaxation. The persistent relaxation was slightly reduced by scorpion venom or L-NOARG, but reduced by 50% by a combination of L-NOARG and ω-conotoxin GVIA. Ultrastructural analysis of the urethral circular smooth muscle layer revealed a moderate amount of nerve profiles supplying the smooth muscle. In control preparations, the nerve profiles contained both small synaptic vesicles and large dense core vesicles. αLTX caused a major loss of both types of vesicle. The present data suggest that αLTX has the ability to release not only adrenergic and cholinergic transmitters, but also NANC mediators of relaxation, including NO, from nerve terminals in the urethra. Received: 13 January 1997 / Accepted: 17 April 1997  相似文献   
19.
In this article we present a patient with acute lymphoblastic leukemia (ALL) associated with eosinophilia, in which the eosinophilia preceded a meningeal and bone-marrow relapse of ALL. We analysed the purine and pyrimidine nucleotide content of the eosinophils (92% pure) and compared the nucleotide pattern with that of eosinophils from healthy donors and from patients with eosinophilia not associated with leukemia. The ratios of purine : pyrimidine and of uracil :cytosine nucleotides were decreased compared with those in eosinophils from healthy donors and from patients with eosinophilia with other aetiologies. The total nucleotide concentration was increased, especially the concentration of UDP-sugars and pyrimidine nucleotides.

The decrease in these ratios and the increase in concentration of the nucleotides and the UDPsugars were also detected in leukemic cells of patients with ALL (de Korte et al., Leukemia Res. 10, 389–396 (1986)) compared to normal lymphocytes. We suggest a malignant character of the eosinophils in our patient with ALL associated with eosinophilia, in contrast with the nonmalignant state suggested previously for these cells.  相似文献   

20.
Sixty-eight primary liver grafts were analyzed to see whether adenine nucleotides (AN: ATP, ADP, and AMP) or purine catabolites (PC: adenosine, inosine, hypoxanthine, and xanthine) of tissue or effluent can predict primary graft nonfunction. AN, PC, and nicotinamide adenine dinucleotide, oxidized form (NAD+) of the tissue before (pretransplant) and after graft reperfusion (post-transplant) and of the effluent were analyzed. The graft outcome was classified into two groups (group A: successful, n=64; group B: primary nonfunctioning, n=4). No significant differences were observed in pretransplant measurements between groups A and B, whereas ATP, ADP, total AN, total AN+total PC (T) and NAD+, in post-transplant tissues, were significantly higher in group A. Xanthine in the effluent was significantly higher in group B than in group A. ATP, ADP, total AN, T, and NAD+ in post-transplant tissue were significantly associated with primary graft nonfunction by logistic regression analysis.  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