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   678篇
  免费   24篇
  国内免费   22篇
耳鼻咽喉   1篇
儿科学   3篇
妇产科学   4篇
基础医学   139篇
口腔科学   4篇
临床医学   43篇
内科学   134篇
皮肤病学   9篇
神经病学   66篇
特种医学   13篇
外科学   27篇
综合类   40篇
预防医学   24篇
眼科学   15篇
药学   161篇
中国医学   26篇
肿瘤学   15篇
  2023年   14篇
  2022年   18篇
  2021年   25篇
  2020年   26篇
  2019年   30篇
  2018年   17篇
  2017年   17篇
  2016年   12篇
  2015年   11篇
  2014年   54篇
  2013年   38篇
  2012年   44篇
  2011年   56篇
  2010年   38篇
  2009年   38篇
  2008年   29篇
  2007年   27篇
  2006年   22篇
  2005年   16篇
  2004年   13篇
  2003年   25篇
  2002年   16篇
  2001年   3篇
  2000年   5篇
  1999年   9篇
  1998年   13篇
  1997年   10篇
  1996年   7篇
  1995年   4篇
  1994年   4篇
  1993年   6篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1989年   3篇
  1988年   1篇
  1986年   1篇
  1985年   3篇
  1984年   9篇
  1983年   6篇
  1982年   8篇
  1981年   10篇
  1980年   8篇
  1979年   5篇
  1978年   5篇
  1977年   1篇
  1976年   4篇
  1975年   4篇
  1974年   2篇
  1973年   1篇
排序方式: 共有724条查询结果,搜索用时 15 毫秒
1.
胃癌D17S261和D17S799位点二核苷酸重复序列不稳定性的意义   总被引:2,自引:2,他引:0  
目的研究二核苷酸重复序列不稳定性〔DRSI〕在胃癌发生中的作用及其临床意义.方法采用PCR方法检测了D17S261和D17S799位点二核苷酸重复序列不稳定性.结果胃癌总DRSI发生率为34%(17/50),其中高中分化腺癌DRSI阳性率(667%,10/15)显著高于低分化癌(194%,6/31,P<001);肠型胃癌DRSI阳性率(556%,10/18)显著高于胃型胃癌(20%,6/30,P<005),DRSI与胃癌部位、大小、浸润、分期、淋巴结转移无显著相关.结论DRSI在胃癌的发生中可能起重要作用.  相似文献   
2.
BACKGROUND: Mutations in the human SLC4A1 (AE1/band 3) gene are associated with hereditary spherocytic anaemia and with distal renal tubular acidosis (dRTA). The molecular diagnosis of AE1 mutations has been complicated by the absence of highly polymorphic genetic markers, and the pathogenic mechanisms of some dRTA-associated AE1 mutations remain unclear. Here, we characterized a polymorphic dinucleotide repeat close to the human AE1 gene and performed an immunocytochemical study of kidney tissue from a patient with inherited dRTA with a defined AE1 mutation. METHODS: One CA repeat region was identified in a phage P1-derived artificial chromosome (PAC) clone containing most of the human AE1 gene and the upstream flanking region. We determined its heterozygosity value in multiple populations by PCR analysis. Genotyping of one family with dominant dRTA identified the AE1 R589H mutation, and family member genotypes were compared with the CA repeat length. AE1 and vH(+)-ATPase polypeptides in kidney tissue from an AE1 R589H patient were examined by immunocytochemistry for the first time. RESULTS: This CA repeat, previously reported as D17S1183, is approximately 90 kb upstream of the AE1 gene and displayed considerable length polymorphism, with small racial differences, and a heterozygosity value of 0.56. The allele-specific length of this repeat confirmed co-segregation of the AE1 R589H mutation with the disease phenotype in a family with dominant dRTA. Immunostaining of the kidney cortex from one affected member with superimposed chronic pyelonephritis revealed vH(+)-ATPase-positive intercalated cells in which AE1 was undetectable, and proximal tubular epithelial cells with apparently enhanced apical vH(+)-ATPase staining. CONCLUSIONS: The highly polymorphic dinucleotide repeat adjacent to the human AE1 gene may be useful for future studies of disease association and haplotype analysis. Intercalated cells persist in the end-stage kidney of a patient with familial autosomal dominant dRTA associated with the AE1 R589H mutation. The absence of detectable AE1 polypeptide in those intercalated cells supports the genetic prediction that the AE1 R589H mutation indeed causes dominant dRTA.  相似文献   
3.
Abstract Nitric oxide (NO) plays an important physiological role in regulating gastrointestinal motility. Involvement of endogenous NO was evaluated in the response to non-adrenergic, non-cholinergic (NANC) nerve stimulation of the dog sphincter muscle of Oddi. Transmural electrical stimulation (TES), nicotine (10?5M) and K+ (10 mM) produced only a relaxation in the sphincter muscle strips contracted with substance P, which was not potentiated by atropine. The TES-induced relaxation was abolished by tetrodotoxin (3 times 10?7 M) and oxyhaemoglobin (1.6 times 10?5 M), but not affected by atropine (10?7 M), propranolol (10?7 M), phentolamine (10?7 M), indomethacin (10?6 M), chole-cystokinin (CCK, 10?8 M) and vasoactive intestinal polypeptide (VIP, 10?8 M). The relaxation was also abolished by treatment with NG-nitro-L-arginine (L-NA, 10?5 M), an NO synthase inhibitor. Nicotine produced a transient relaxation, which was abolished by tetrodotoxin, hexamethonium (10?5 M) and L-NA, but not affected by atropine and NG-nitro-D-arginine (D-NA, 10?5 M). The addition of K+ elicited a transient relaxation, which was abolished by tetrodotoxin and L-NA. The inhibitory effects of L-NA were antagonized by L-arginine (10?3 M). The presence of neurons containing nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase was histochemically demonstrated in the sphincter of Oddi. These findings may indicate that TES, nicotine and K+ liberate NO from NANC inhibitory nerve which is involved in the relaxation of the dog sphincter of Oddi. The muscular tone does not seem to be regulated by cholinergic nerves under the experimental conditions used.  相似文献   
4.
Summary The coenzyme nicotinamide adenine dinucleotide (NADH) has been used in an open label trial as novel medication in 34 patients with Parkinson's disease, using an intravenous administration technique. In all patients a beneficial clinical effect was observed. 21 patients (61.7%) showed a very good (better than 30%) improvement of disability, 13 patients (38.3%) a moderate (up to 30%) improvement. Concomitant with the improvement of the disability the urine level of homovanillic acid (HVA) increased significantly in all patients (in some patients by more than a 100%). The daily on phases of the patients could be increased from 2 up to 9 hours in the individual patients by NADH administration.  相似文献   
5.
Matrix Gla protein (MGP) is an 84-residue, vitamin K-dependent protein expressed by chondrocytes and vascular smooth muscle cells, and is a potent regulator of calcium deposition in cartilage and arterial wall. We isolated a polymorphic dinucleotide CA repeat marker from a genomic clone containing the human MGP gene. This polymorphism will be useful in genetic studies of arteriosclerosis and osteoporosis. Received: November 5, 1997 / Accepted November 27, 1997  相似文献   
6.
采用套式聚合酶链反应结合变性聚丙烯酰胺凝胶电泳和银染技术,并构建载脂蛋白CII(ApoCII)基因二核苷酸串联重复序列(TG)n(AG)m及(AG)m序列等位基因梯阶标准;检测正常汉族人群基因型和等位基因频率分布,检出36种(TG)n(AG)m序列基因型、12种等位基因。等位基因为17、18、26-35,其频率分别为0.061、0.011、0.002、0.002、0.054、0.255、0.372、0.084、0.026、0.039、0.052、0.041。检出7种(AG)m序列基因型、4种等位基因。等位基因为6、7、8、9,其频率分别为0.002、0.152、0.812、0.034。与欧洲白种人比较,ApoCII基因二核苷酸串联重复序列(TG)n(AG)m及(AG)m序列等位基因频率分布均具有明显的种族差异性(P<0.01,P<0.01)。  相似文献   
7.
8.

Aims

We explored the effect of remote ischaemic conditioning (RIC) on endothelial function and on circulating mediators.

Methods and results

In 20 healthy male volunteers (mean age 31?±?10 years), flow-mediated dilation (FMD) was measured before and after 20?min of arm ischaemia, followed by reperfusion. Remote ischaemic conditioning (RIC) was performed by applying 3 cycles of 5?min of ischaemia of the leg at the onset of index arm ischaemia. Each volunteer underwent the IR-induced vascular injury protocol with and without RIC in a crossover study design.In the control group, IR significantly reduced FMD (5.9?±?2.9% before IR vs. 2.2?±?3.7% after IR; p?<?0.001). This effect was significantly attenuated by performing RIC (FMD of 5.5?±?3.1% before IR vs. 4.0?±?3.4% % after IR; p for interaction?=?0.01). Serum levels of SOD and ADMA increased significantly whereas MCP-1 and VEGF levels decreased significantly.Only changes in SOD levels were significantly related to the degree of RIC induced protection (r²?=?0.34; p?=?0.018).

Conclusion

RIC has protective effects against endothelial IR injury. Our biomarker study suggests that anti-oxidative stress mediators, such as SOD, seem to be more involved in the pathogenesis of RIC-induced protection in humans than angiogenesis factors or chemo-attractant cytokines.  相似文献   
9.
The presence of nitric oxide synthase (NOS) in neuronal elements expressing the calcium-binding proteins calretinin (CR) and parvalbumin (PV) was studied in the rat main olfactory bulb. CR and PV were detected by using immunocytochemistry and the nitric oxide (NO) -synthesizing cells were identified by means of the reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) direct histochemical method. The possible coexistence of NADPH-diaphorase and each calcium-binding protein marker was determined by sequential histochemical-immunohistochemical double-labeling of the same sections. Specific neuronal populations were positive for these three markers. A subpopulation of olfactory fibers and olfactory glomeruli were positive for either NADPH-diaphorase or CR. In the most superficial layers, groups of juxtaglomerular cells, superficial short-axon cells and Van Gehuchten cells demonstrated staining for all three markers. In the deep regions, abundant granule cells were NADPH-diaphorase- and CR-positive and a few were PV-immunoreactive. Scarce deep short-axon cells demonstrated either CR-, PV-, or NADPH-diaphorase staining. Among all these labeled elements, no neuron expressing CR or PV colocalized NADPH-diaphorase staining. The present data contribute to a more detailed classification of the chemically- and morphologically-defined neuronal types in the rodent olfactory bulb. The neurochemical differences support the existence of physiologically distinct groups within morphologically homogeneous populations. Each of these groups would be involved in different modulatory mechanisms of the olfactory information. In addition, the absence of CR and PV in neuronal groups displaying NADPH-diaphorase, which moreover are calmodulin-negative, indicate that the regulation of NOS activity in calmodulin-negative neurons of the rat olfactory bulb is not mediated by CR or PV.  相似文献   
10.
Calcium-sensing receptor (CASR) in parathyroid gland regulates calcium homeostasis by sensing decreases in extracellular calcium levels and effecting an increase in secretion of parathyroid hormone. A polymorphic dinucleotide (CA) sequence was isolated from a genomic clone containing the human CASR gene and was mapped to 3q13.3–q21. This polymorphism will be useful in the genetic study of disorders affecting calcium metabolism, such as hypercalcemia, hypocalcemia, osteoporosis, hyperparathyroidism, and hypoparathyroidism. Received: June 2, 1998 / Accepted: June 24, 1998  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