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   25039篇
  免费   2172篇
  国内免费   1385篇
耳鼻咽喉   365篇
儿科学   472篇
妇产科学   235篇
基础医学   2090篇
口腔科学   476篇
临床医学   2676篇
内科学   2487篇
皮肤病学   320篇
神经病学   958篇
特种医学   1095篇
外国民族医学   1篇
外科学   2220篇
综合类   5798篇
现状与发展   8篇
预防医学   3002篇
眼科学   325篇
药学   2847篇
  35篇
中国医学   1995篇
肿瘤学   1191篇
  2024年   133篇
  2023年   291篇
  2022年   718篇
  2021年   919篇
  2020年   776篇
  2019年   441篇
  2018年   461篇
  2017年   561篇
  2016年   498篇
  2015年   792篇
  2014年   1015篇
  2013年   1408篇
  2012年   2145篇
  2011年   2207篇
  2010年   2012篇
  2009年   1695篇
  2008年   1864篇
  2007年   1796篇
  2006年   1618篇
  2005年   1318篇
  2004年   1006篇
  2003年   847篇
  2002年   670篇
  2001年   677篇
  2000年   578篇
  1999年   280篇
  1998年   106篇
  1997年   97篇
  1996年   75篇
  1995年   72篇
  1994年   51篇
  1993年   41篇
  1992年   87篇
  1991年   90篇
  1990年   103篇
  1989年   99篇
  1988年   75篇
  1987年   74篇
  1986年   77篇
  1985年   91篇
  1984年   56篇
  1983年   64篇
  1979年   67篇
  1978年   35篇
  1977年   34篇
  1975年   32篇
  1974年   36篇
  1972年   33篇
  1971年   33篇
  1969年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Separation and measurement of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), adenine-adenosine, lipid phosphates (lipid-P), RNA and DNA, furthermore, separation of Mg2+-dependent, total (Mg2+-dependent plus Na+--K+-dependent or Mg2+--Na+--K+-dependent) and Na+--K+-dependent ATPases and measured of their activities were carried out in tissue samples obtained from "ulcerated antral mucosa", from "non-ulcerated antral mucosa" and the muscular layer beneath the examined mucosa specimens, of patients with antral ulcer. It has been found that (1) the tissue levels of ATP, ADP and AMP, of the sum ATP + ADP + AMP, adenine-adenosine, lipid-P, RNA all calculated for 1.0 mg DNA content, further, the activities of Mg2+-dependent, total (Mg2+-dependent plus Na+--K+-dependent) and Na+--K+-dependent ATPase were significantly higher in the ulcerated antral mucosa than those in the control antral mucosa; (2) no significant biochemical alterations were found in the muscles under the ulcerated and non-ulcerated antral mucosa of patients with antral ulcer; (3) the extents of increases in the substrate levels of ulcerated antral mucosa depended on their original levels in the control antral mucosa. The results indicate a cellular hyperfunction in the ulcerated antral mucosa, in comparison with the control one. No circulatory injury could be demonstrated in the ulcerated antral mucosa.  相似文献   
102.
目的 探讨一氧化氮 (NO)在缺氧复氧诱导神经细胞凋亡中的作用及中药银杏叶提取物的保护机制。方法 实验使用胎龄 16~ 17日Wistar大鼠的大脑皮层神经细胞进行原代分离培养 ;采用Wright Giemsa染色 ,光镜、透射电子显微镜观察 ;原位末端标记法确立缺氧复氧神经细胞凋亡病理模型 ;应用NADPH d组织化学方法检测神经细胞一氧化氮合酶 (NOS)的表达并用计算机图像分析系统进行定量检测。 结果 缺氧复氧可以使大鼠大脑皮层神经细胞发生凋亡 ,随缺氧时间的延长 ,凋亡细胞数渐多 ,至缺氧 8h复氧 18h达高峰 ;在缺氧 2h(H2 R0 组 )和缺氧 8h复氧 18h(R8R1 8)组中神经细胞NOS表达均显著增高 ,与正常对照组比有显著性差异 (P <0 0 1;P <0 0 5 )。EGB能显著抑制此双时相NOS活性的增强 ,并明显降低神经细胞凋亡率。 结论 缺氧复氧损伤可诱导培养的大鼠大脑皮层神经细胞发生凋亡。NOS表达增强从而使NO产生增加可能是缺氧复氧诱导神经细胞凋亡的机制之一。银杏叶提取物 (EGB)经下调NOS表达活性 ,抑制NO的产生保护培养的大鼠大脑皮层神经细胞免于凋亡。  相似文献   
103.
苦瓜提取物对实验性Ⅱ型糖尿病大鼠的血糖的影响   总被引:2,自引:0,他引:2  
目的:观察苦瓜提取物对链脲霉素引起的Ⅱ型糖尿病大鼠模型的血糖、血清胰岛素及血脂的影响。方法:大鼠尾静脉注射小剂量链脲霉素25mg·kg-1,同时喂以高糖高脂饲料复制Ⅱ型糖尿病大鼠模型.然后给予苦瓜提取物14,28,56mg·kg-1,连续灌胃给药4周后,测定血糖、血清胰岛素及血脂。结果:苦瓜提取物14,28,56mg·kg-1能降低实验性Ⅱ型糖尿病大鼠血糖及血清胰岛素水平,能升高HDL-C含量,而对血脂其它指标无明显影响。结论:苦瓜提取物对Ⅱ型糖尿病大鼠有治疗作用。  相似文献   
104.
小鼠胃癌MAGE3抗原H-2K~k限制性抗原肽的筛选   总被引:1,自引:0,他引:1  
本研究对小鼠胃癌MAGE3抗原H 2Kk 限制性的抗原肽进行了筛选。用CTL表位预测的基序法对易与H 2Kk 结合的多肽序列进行了预测并人工合成了 4个多肽。在体外检测了各多肽刺激H 2Kk 型小鼠T细胞增殖和分泌IFN γ的能力 ,同时测定了各多肽诱导出的CTL对小鼠前胃癌细胞株MFC细胞的杀伤活性。结果显示 ,抗原肽MAGE31 3 0 1 3 7可有效地刺激特异性T细胞的增殖和分泌细胞因子IFN γ ,其诱导出的CTL细胞对MFC细胞也有较高的杀伤活性。这些实验结果证实抗原肽MAGE31 3 0 1 3 7可以作为多肽疫苗来对表达MAGE3抗原的H 2Kk 型小鼠胃癌进行免疫治疗。  相似文献   
105.
目的:制备戊型肝炎病毒(HEV)缅甸株和墨西哥株ORF2重组蛋白(p166Bur和p166Mex)的单克隆抗体(McAbs),用于分析HEV不同基因型B细胞抗原表位的特点。方法:将免疫BALB/C小鼠脾细胞与SP2/0骨髓瘤细胞融合,获得分泌抗-p166Bur和抗-p166Mex McAbs的杂交瘤细胞株,然后采用ELISA和免疫印迹法测定McAbs与不同基因型HEV ORF2编码蛋白p166的免疫反应性。结果:获得4株杂交瘤细胞株,即分泌抗-p166Bur McAbs的2G2、2B1以及分泌抗-p166Mex McAbs的D8G10和E5E12,其中2B1分泌的McAb仅能与第Ⅰ、Ⅱ基因型编码的重组蛋白结合,而其余3株分泌的McAbs既能与Ⅰ、Ⅱ基因型HEV的p166重组蛋白发生反应,也能与Ⅲ、Ⅳ基因型的p166蛋白反应。结论:HEV第Ⅰ、Ⅱ基因型与Ⅲ、Ⅳ基因型ORF2编码蛋白既有共同又有不同的B细胞抗原表位。  相似文献   
106.
Merkel cell carcinoma was diagnosed in a 79-year-old Caucasian woman. The tumour was localised to the upper lip and was in stage T2. After successful cryosurgery and a 7-year tumour-free period, a new tumour developed in her palatine tonsil. Histologically and immunohistochemically, this resembled the tumour in the lip. The regional lymph nodes were devoid of metastasis. The paraffin-embedded material of the two tumours and the unaffected lymphatic tissue were analysed with DNA microarrays for comparative genomic hybridisation to assess the genetic relationship of the tumours. In both tumours, regions on 2p and 10p were commonly over-represented, while 41 regions on chromosomes 1–4, 6, 8–9, 11 and 14–22 were commonly under-represented. Chromosomes 1, 3, 4, 16–18 and X were most frequently involved in the DNA losses. In gene copy numbers in the two tumours, 31 chromosome locations were found to be differently affected. The partly similar and partly different molecular patterns indicated a genetic relationship between the tumours and excluded the possibility that the tonsillar tumour was a metastasis. The findings suggest that a genetically altered field was the reason for the development of the tonsillar cancer; thus, it can be regarded pathogenetically as a second field tumour.  相似文献   
107.
目的:探讨细菌脂多糖(LPS)对小鼠树突状细胞(DC)系DC2.4 TLR7蛋白表达的诱导作用.方法:用RPMIl640完全培养液培养DC2.4细胞,光学显微镜观察LPS刺激前后的细胞形态特征,RT-PCR和Western blot分别测定TLR7 mRNA和蛋白表达.结果:LPS刺激前后,细胞中均有TLR7 mRNA转录.LPS刺激前,细胞较小而透亮,树突较少,无,TLR7蛋白表达;LPS刺激后,细胞体积增大,树突增粗增多,刺激后12 h、24 h、48 h,TLR7蛋白均有表达,且在3个时间点的表达量基本一致.结论:LPS可诱导DC2.4中TLR7蛋白的表达.  相似文献   
108.
The endogenous ligand, anandamide activates at least two receptors on nociceptors; the excitatory vanilloid type 1 transient receptor potential receptor, the activity of which is indispensable for the development and maintenance of inflammatory heat hyperalgesia, and the inhibitory cannabinoid 1 receptor, the activity of which reduces that pathological pain sensation. Recent data are equivocal on whether increasing anandamide levels at the peripheral terminals of nociceptors in pathological conditions increases or decreases inflammatory heat hyperalgesia. Here, by using the cobalt-uptake technique we examined whether vanilloid type 1 transient receptor potential receptor activity evoked by 10 nM-100 microM anandamide is increased or decreased in inflammatory conditions. An inflammatory milieu for cultured rat primary sensory neurons was established by incubating the cells in the presence of the inflammatory mediators, bradykinin and prostaglandin E2. Anandamide, similarly to the archetypical vanilloid type 1 transient receptor potential receptor agonist, capsaicin induced concentration-dependent cobalt-uptake in a proportion of neurons. However, the potency of anandamide was significantly lower than that of capsaicin. While pre-incubation of cultures with bradykinin and prostaglandin E2 alone did not evoke cobalt-entry, the inflammatory mediators potentiated the effect of both capsaicin and anandamide. Application of the competitive vanilloid type 1 transient receptor potential receptor antagonist, capsazepine, or inhibitors of protein kinase A, protein kinase C or phospholipase C inhibited the anandamide-evoked cobalt-uptake both in the presence and absence of bradykinin and prostaglandin E2. These findings show that inflammatory mediators significantly increase the excitatory potency and efficacy of anandamide on vanilloid type 1 transient receptor potential receptor, thus, increasing the anandamide concentration in, or around the peripheral terminals of nociceptors might rather evoke than decrease inflammatory heat hyperalgesia.  相似文献   
109.
Yersinia pestis, the etiologic agent of plague is a highly invasive organism being able to invade non-phagocytic epithelial cells. Its plasminogen activator (Pla), encoded by the pPCP1 plasmid plays a pivotal role in internalisation of bacteria by HeLa cells. The aim of this study was to analyse the intracellular signalling processes and cytoskeletal rearrangement events associated with invasion. Wortmannin caused a 50% decrease of invasiveness at 50nM concentration pointing to the involvement of phosphatidyl-inosinol-4 kinase (PtINs4). Pre-treatment with staurosporin, a potent inhibitor of protein kinases (PKs) and with genistein, a specific tyrosine kinase inhibitor decreased the number of internalised bacteria about seven-fold and two-fold, respectively, indicating the involvement of PKs including tyrosine kinases in Pla-mediated internalisation. Cytochalasin D, an actin polymerisation inhibitor, C3 exoenzyme of Clostridium botulinum, a specific inhibitor of small GTPase Rho, and NDGA, a 5-lipoxygenase inhibitor also involved in Rho activation strongly reduced the number of internalised bacteria revealing the role of cytoskeletal events in the invasion process. All the tested inhibitors changed the invasion but not the adhesion pattern of the Pla producing recombinant strain. Actin rearrangement could also be visualised also with rhodamin-phalloidin staining.  相似文献   
110.
The cells of origin of a neocortical cholinergic afferent projection have been identified by anterograde and retrograde methods in the rat. Horseradish peroxidase injected into neocortex labelled large, acetylcholinesterase-rich neurons in the ventromedial extremity of the globus pallidus. This same group of neurons underwent retrograde degeneration following cortical ablations. The region in which cell depletion occurred also showed significant decreases in the activities of choline acetyltransferase and acetylcholinesterase. Discrete electrolytic and kainic acid lesions restricted to the medial part of the globus pallidus each resulted in significant depletions of neocortical choline acetyltransferase and acetylcholinesterase. Hemitransections caudal to this cell group did not result in such depletions. Taken together these observations suggest that the acetylcholinesterase-rich neurons lying in the ventromedial extremity of the globus pallidus, as mapped in this study, constitute the origin of a major subcortical cholinergic projection to the neocortex. The utility of acetylcholinesterase histochemistry in animals pretreated with di-isopropylphosphorofluoridate in identifying cholinergic neurons is discussed in the light of this example; specifically, it is proposed that high acetylcholinesterase activity 4–8 h after this pretreatment is a necessary, but not sufficient, criterion for the identification of cholinergic perikarya.The neurons in question appear to be homologous to the nucleus basalis of the substantia innominata of primates, and are thus termed ‘nucleus basalis magnocellularis’ in the rat. No evidence was obtained to support the hypothesis that nucleus of the diagonal band projects to neocortex. However, striking similarities in size and acetylcholinesterase activity were observed among the putative cholinergic perikarya of the nucleus basalis magnocellularis, the nucleus of the diagonal band, and the medial septal nucleus.Kainic acid lesions of the neocortex produced uniform and complete destruction of neuronal perikarya. These lesions decreased neocortical glutamic acid decar?ylase activity, suggesting that there are GABAergic perikarya in the neocortex. However, the same lesions did not affect neocortical choline acetyltransferase. This observation suggests that there are no cholinergic perikarya in the neocortex, a conclusion that is consistent with the absence of intensely acetylcholinesterase-reactive neurons in the neocortex.  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