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   7490篇
  免费   289篇
  国内免费   41篇
耳鼻咽喉   70篇
儿科学   189篇
妇产科学   115篇
基础医学   835篇
口腔科学   113篇
临床医学   385篇
内科学   1820篇
皮肤病学   94篇
神经病学   581篇
特种医学   506篇
外科学   1106篇
综合类   26篇
预防医学   212篇
眼科学   125篇
药学   476篇
  1篇
中国医学   11篇
肿瘤学   1155篇
  2023年   34篇
  2022年   69篇
  2021年   121篇
  2020年   82篇
  2019年   94篇
  2018年   91篇
  2017年   91篇
  2016年   132篇
  2015年   132篇
  2014年   141篇
  2013年   207篇
  2012年   315篇
  2011年   356篇
  2010年   201篇
  2009年   162篇
  2008年   270篇
  2007年   318篇
  2006年   316篇
  2005年   305篇
  2004年   343篇
  2003年   375篇
  2002年   370篇
  2001年   187篇
  2000年   240篇
  1999年   238篇
  1998年   106篇
  1997年   106篇
  1996年   107篇
  1995年   95篇
  1994年   88篇
  1993年   89篇
  1992年   200篇
  1991年   198篇
  1990年   216篇
  1989年   190篇
  1988年   185篇
  1987年   136篇
  1986年   133篇
  1985年   116篇
  1984年   94篇
  1983年   74篇
  1982年   52篇
  1981年   27篇
  1980年   30篇
  1979年   53篇
  1978年   39篇
  1977年   35篇
  1975年   34篇
  1974年   38篇
  1969年   25篇
排序方式: 共有7820条查询结果,搜索用时 15 毫秒
71.
Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is a secreted protein which may play a pivotal role in tumor-associated microvascular angiogenesis and hyperpermeability. The expression of mRNA for VEGF was examined in eight gastric carcinoma cell lines and 30 gastric carcinoma tissues as well as corresponding normal mucosa. All the cell lines expressed VEGF mRNA at various levels that correlated well with the amounts of VEGF secreted into the condition medium. The expression of VEGF mRNA by TMK-1 cells was increased by the treatment of epidermal growth factor (EGF) or interleukin-1α (IL-1α), whereas it was decreased by the treatment of interferon-β (IFN-β). In gastric carcinoma tissues, the level of VEGF mRNA in primary tumors was higher than that in the corresponding normal mucosas in six (46%) of 13 well-differentiated adenocarcinomas and in two (12%) of 17 poorly differentiated adenocarcinomas, respectively. Vessel counts in well-differentiated adenocarcinomas had a tendency to be higher than those in poorly differentiated adenocarcinomas. In well-differentiated adenocarcinomas, the levels of VEGF mRNA expression tended to be higher in carcinomas of advanced stage than in early stage carcinomas. Both in situ mRNA hybridization and immunohistochemistry demonstrated the presence of VEGF expression within the tumor cells. These results suggest that VEGF may confer angiogenesis and progression of human gastric carcinomas, especially of the well-differentiated type.  相似文献   
72.
The Trk family of tyrosine protein kinase receptors plays a significant role in the development and maintenance of neural tissues. It has been recently shown that Trk receptors are also expressed by a wide range of normal non-neuronal tissues in humans in a cell type-specific manner. In the present study, the expression patterns of TrkA in 337 non-neuronal invasive carcinomas of 15 different human tissues were investigated immunohistochemically. Overall, 133 (39%), 101 (30%) and 103 (31%) tumors exhibited strong, moderate and no TrkA Immunoreactivity, respectively. Esophageal and thyroid carcinomas expressed high levels of TrkA, whereas the levels in gastric and colon cancers were low. TrkA expression was detected not only in carcinomas originating from TrkA-positive normal counterpart tissues, Including the esophagus, breast, lung and uterus, but also in those from TrkA-negative tissues/cells of the thyroid, liver and ovary. Immunostaining for nerve growth factor-β, the specific ligand for TrkA, in esophageal and breast carcinomas demonstrated its immunoreactivity in stromal fibroblasts and some TrkA-expressing tumor cells. These results suggest that paracrine/autocrine regulation via stromal/tumoral NGF-tumoral TrkA interaction may be involved In the growth of certain non-neuronal carcinomas.  相似文献   
73.
Electron microscopic study was made on precancerous and cancerous lesions in glandular stomach of rats induced by MNNG. Three types of lesions, were found; regenerative glandular hyperplasia, adenomatous hyperplasia and adenocarcinoma. These were compared with the fine structure of similar lesions produced by X-irradiation in the glandular stomach of mice. The precancerous lesion in the present study demonstrated formation of adenomatous hyperplasia by epithelial cells which included mucoid cells characterized by sparce surface microvilli, a few erratic terminal webs, small number of mucous granules, many small mitochondria, and a bizarre nucleus. The development of these mucoid cells seems to be related with the growth of gastric carcinoma. The ultrastructure of adenocarcinomas revealed many structural variations or abnormalities of cellular differentiation. They were classified into 1) surface and pit mucous cell type, 2) pyloric gland cell type, 3) goblet cell type, 4) paneth cell type, 5) intestinal epithelial cell type, 6) endocrine cell type, 7) oncocyte type, 8) filament-rich cell type, and 9) anaplastic cell type involving intracellular microcyst cells. Filament-rich cells were found in poorly differentiated adenocarcinoma or scirrhous carcinoma and may be derived from metaplasia of tumor cell.  相似文献   
74.
A 36-year-old nulliparous woman developed multiple extra-uterine fibroids in the pelvic cavity years after laparoscopic myomectomy. Molecular genetic analysis by methylation-specific polymerase chain reaction (MSPCR) of the human X-linked androgen receptor gene and loss of heterozygosity (LOH) analysis at 5 microsatellite loci was performed on the tumors. All tumors showed an identical non-random X-chromosome inactivation pattern by MSPCR and an identical pattern of LOH was found in all the tumors by LOH analysis. This demonstrated that 3 fibroids resected 2 years later and 14 fibroids resected 6 years later were all metastatic tumors originating from the uterine leiomyoma found during the initial surgery, suggesting that morcellation before removal of the leiomyoma nodule during laparoscopic myomectomy may have been associated with the pathogenesis of this case.  相似文献   
75.
76.
This study regards the urinary protein of patients with renal diseases. Analysis was done by micro-vertical-electrophoresis using polyacrylamide gel with sodium dodecyl sulfate (SDS-PAGE). This method was an easy, reliable and rapid method for the estimation of low molecular weight proteinuria, which are present in renal tubular dysfunction. We found 6 patients with renal tubular dysfunction in 214 patients with renal diseases by the use of this method. Thus, the present method is considered to be useful for mass-screening of children with proteinuria.  相似文献   
77.
Guinea pig cochleas were exposed to either broad-band noise at intensities between 95 and 115 dBA or octave-band noise centered at 380 Hz or 4.2 kHz at intensities between 115 and 125 dB SPL. Cochlear microphonics (CM), summating potentials (SP) and action potentials (AP) were recorded from differential electrodes in the perilymphatic scalae between successive 20-min periods of noise exposure. The endocochlear potential (EP) and endolymph potassium concentration [Kendo+] were recorded continuously from scala media using double-barreled potassium-sensitive electrodes. It was found that the initial exposure to noise at 115 dBA produced considerable suppression of the CM and AP, while the EP and [Kendo+] were elevated above their normal values. When animals previously treated with kanamycin were subjected to the same level of noise exposure no systematic increase in either EP ro [Kendo+] was observed. After prolonged exposure to 380 Hz octave-band noise at 125 dB SPL, a slow decline of EP and [Kendo+] was observed. The relationships between the changes in EP, [Kendo+] and CM are discussed.  相似文献   
78.
The effect of nitric oxide on retinal blood flow during hypoxia in cats   总被引:4,自引:0,他引:4  
PURPOSE: To investigate how nitric oxide (NO) contributes to the regulation of retinal circulation during rest and hypoxia in cats. METHODS: N(G)-nitro-L-arginine-methyl ester (L-NAME; n = 7), an NO synthase inhibitor; N(G)-nitro-D-arginine methyl ester (D-NAME; n = 6), the inactive isomer; or phosphate-buffered saline (PBS; n = 7) was injected intravitreously. Hypoxia was induced in the cats by the administration of 10% oxygen. Vessel diameter and blood velocity were measured simultaneously in the anesthetized cats with a laser Doppler velocimetry system, and the retinal blood flow (RBF) and wall shear rate (WSR) were calculated as an index of shear stress on the retinal vessel wall. RESULTS: After intravitreous injection of L-NAME, the vessel diameter (-8.1% +/- 2.0%, P < 0.01), velocity (-17.0% +/- 3.7%, P < 0.01), and RBF (-29.4% +/- 4.6%, P < 0.01) significantly decreased compared with the preinjection level. In the PBS group, maximum increases above the prehypoxia diameter (13.7% +/- 3.5%, P < 0.01), velocity (39.5% +/- 8.6%, P < 0.01), RBF (73.9% +/- 10.6%, P < 0.01), and WSR (28.3% +/- 7.1%, P < 0.01) were observed during hypoxia. In the L-NAME group, those changes substantially decreased in response to hypoxia. D-NAME was inactive with regard to RBF during rest and hypoxia. CONCLUSIONS: These results suggest that NO may be continuously produced in the retina during rest and contributes to increased RBF during hypoxia. In addition, the increased WSR during hypoxia indicates that NO plays an important role in retinal hypoxic hyperemia through a flow-induced mechanism.  相似文献   
79.
Prospective, periodical sero-epidemiological surveillance on mumps was carried out in three different populations in Aichi prefecture. 1) In a newly developed residental quarter full of big apartment buildings, where heavy population density burst has been occurring, mumps has been observed as an endemic disease. Serologically, almost all the children under six years old has experienced mumps infection in such an area. 2) In an old city with stable population dynamics, mumps outbreaks have been taken place pediodically. The results of serosurvey suggested that the periodic outbreaks occurred when more than 60–70% of the children became susceptible, regardless of seasons. 3) In a relatively isolated small town, mumps epidemics has not been observed for many years and when the disease is introduced into the community however, large outbreak develops in the town.  相似文献   
80.
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