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   6860篇
  免费   218篇
  国内免费   38篇
耳鼻咽喉   240篇
儿科学   136篇
妇产科学   294篇
基础医学   836篇
口腔科学   49篇
临床医学   441篇
内科学   1808篇
皮肤病学   128篇
神经病学   611篇
特种医学   113篇
外科学   739篇
综合类   59篇
一般理论   10篇
预防医学   322篇
眼科学   199篇
药学   733篇
中国医学   4篇
肿瘤学   394篇
  2023年   19篇
  2022年   140篇
  2021年   260篇
  2020年   72篇
  2019年   135篇
  2018年   151篇
  2017年   113篇
  2016年   124篇
  2015年   164篇
  2014年   210篇
  2013年   323篇
  2012年   448篇
  2011年   568篇
  2010年   277篇
  2009年   185篇
  2008年   448篇
  2007年   544篇
  2006年   496篇
  2005年   534篇
  2004年   521篇
  2003年   453篇
  2002年   397篇
  2001年   27篇
  2000年   30篇
  1999年   32篇
  1998年   30篇
  1997年   18篇
  1996年   24篇
  1995年   33篇
  1994年   21篇
  1993年   18篇
  1992年   15篇
  1991年   21篇
  1990年   10篇
  1989年   14篇
  1988年   10篇
  1987年   18篇
  1986年   11篇
  1985年   15篇
  1984年   23篇
  1983年   19篇
  1982年   25篇
  1981年   12篇
  1980年   13篇
  1979年   21篇
  1978年   12篇
  1977年   8篇
  1975年   6篇
  1974年   8篇
  1973年   8篇
排序方式: 共有7116条查询结果,搜索用时 31 毫秒
41.
42.
Bronchoalveolar lavage (BAL) or induced sputum (IS) techniques may provide leukocytes for the evaluation of airway inflammatory response in bronchial asthma. The aim of the present study was to compare features of leukocyte populations obtained by the two different methods regarding the cell types and their activity in patients with bronchial asthma. The nitric oxide (NO) level released from the cells was measured as a marker of their activity. Pulmonary leukocytes were obtained from the BAL and IS of 11 asthmatic patients in stable condition at the time of the study. The BAL and IS leukocyte populations varied in cell count and NO production. Macrophages were the predominant leukocyte population in BAL (median (Me) = 83.0%, range 67.9-88.4%), whereas sputum sediments were found to consist mainly of neutrophils (Me = 55.7%, range 29.0-64.9%). The IS leukocytes released much more NO (p = 0.0022) than the BAL leukocytes. In spite of these quantitative differences, a similar pattern of NO production was observed in BAL and in IS cells. Both BAL and IS leukocyte populations produced almost the same amounts of NO before and after lipopolysaccharide stimulation (p = 0.9063, p = 0.4801, respectively). Furthermore, a slight positive correlation Spearman's rank (RS) = 0.5578, p = 0.0594) was noticed between the neutrophil percentages and NO levels produced by BAL cells, whereas in IS a statistically significant correlation between the percentage of neutrophils and the levels of NO (RS = 0.6643, p = 0.0184) was observed. In conclusion, the BAL and IS leukocyte populations are different in cell type, their size and activity. Depending on the asthma severity and the type of cells needed in a study, either BAL or IS specimens may be chosen as a source of pulmonary leukocytes. The use of IS as a noninvasive technique is supposed to be potential value particularly in the study of the airway inflammatory response mediated mainly by neutrophils, i.e. during and/or after exacerbation of the disease. Based on our results, a possible contribution of neutrophils in the production of NO in the airways of asthmatic patients can be proposed apart from other cells such as macrophages.  相似文献   
43.
44.
Magnetic Resonance Diffusion Tensor Imaging (DTI) of the control and traumatic injured spinal cord of a rat in vitro is reported. Experiments were performed on excised spinal cords from 10 Wistar rats, using a home-built 6.4 T MR microscope. MRI and histopathological results were compared. Presented results show that DTI of the spinal cord, perfused with formalin 10 minutes after the injury, can detect changes in water diffusion in white matter (WM) and in gray matter (GM), in areas extending well beyond the region of direct impact. Histology of neurons of the GM shows changes that can be attributed to ischemia. This is in agreement with the observed decrease of diffusion in the injured regions, which may be attributed to the cytotoxic edema due to ischemia. However, the diffusion changes in highly anisotropic WM seem to be caused by a direct action of mechanical force of impact, which significantly distorts the nerve fibers.  相似文献   
45.
Nucleolar organizer regions (NORs) are segments of DNA, encoding for ribosomal RNA. They are associated with argyrophilic proteins and, thus, they can be localized through silver staining. A correlation has been shown between the number, the size, or the intranuclear localization of AgNORs, and the proliferative activity of cells. The aim of this study was to examine numerous features of AgNORs in pituitary adenomas and to relate them to immunohistochemical typing of tumor. Histologic slides from 32 pituitary tumors and one normal pituitary were silver-stained and analyzed with a computerized system for microscopic image analysis, supported by an AgNORmeter95 program. All the tumors were also immunocyto chemically characterized. We have found that gonadotropinomas, when compared with plurihormonal adenomas, revealed a lower proportion of nuclei with a single AgNOR and a higher percentage of marginal dots. Recurrent adenomas, when compared with primary adenomas, showed a higher proportion of nuclei with three AgNOR dots, a larger total area of dots in the nuclei, and a higher standard deviation of the AgNOR dot area in the nucleus. Adenomas immunopositive for prolactin, when compared with immunonegative ones, showed a larger mean area of the AgNOR dot, a larger area of the biggest dot in the nucleus, and a higher proportion of nuclei within a single dot. These results suggest that the estimated parameters of AgNOR dots differ according to tumor aggressiveness and to the hormone immunopositivity of pituitary adenomas.  相似文献   
46.
Many data suggest involvement of inflammation in neurodegeneration. However, the exact mechanisms of this cooperation are poorly understood. We have previously shown that induction of inflammatory reaction, both before and after injury of the striatum, affects regeneration of dopaminergic neurons. In the present research we studied the role of inflammatory reaction in non-injured striatum. We used myelin oligodendrocyte glycoprotein (MOG) 35-55 in complete Freund's adjuvant (CFA) to elicit experimental autoimmune encephalomyelitis (EAE) mice model. As determined by HPLC, striatal dopamine (DA) and serotonin levels in mice treated with either MOG 35-55 in CFA or CFA alone were significantly higher compared to vehicle-treated controls on 13th day after induction. The ratio of homovanilic acid/dopamine (HVA/DA) and 3, 4 dihydroxyphenylacetic acid/dopamine (DOPAC/DA) were significantly lower in the MOG and CFA groups on 13th day, indicating decreased DA metabolism. Noradrenaline (NA) concentration did not differ between groups. Moreover, the striatal mRNA IL-1beta and TNF-alpha levels were elevated during induction phase of EAE in both groups, as determined by RT-PCR. Our data indicate regulatory connection between dopaminergic and immune systems.  相似文献   
47.
Moon WS  Tarnawski AS 《Human pathology》2003,34(11):1119-1126
Survivin is a recently described anti-apoptosis protein and regulator of cell division. Its expression and localization in hepatocellular carcinoma (HCC) and in normal liver tissue has not been fully elucidated. We examined the expression of survivin, Fas, proliferating cell nuclear antigen (PCNA), and apoptosis in 47 specimens of hepatocellular carcinoma (HCC) and surrounding nonmalignant hepatic tissues. To further determine the relationship between survivin expression and cell proliferation and apoptosis, we performed double immunostaining for survivin and PCNA TUNEL staining in the same HCC specimens. Positive immunostaining for survivin was present in 35 of 47 (74%) HCCs. Twenty-two of 35 survivin-positive HCCs (63%) showed punctate nuclear staining in HCC cells, and the remaining 13 showed predominant cytoplasmic staining. In contrast, nonmalignant hepatocytes showed only cytoplasmic staining. HCC cells had significantly higher PCNA-labeling and apoptotic indices compared with the case of nonmalignant hepatic tissue (P<0.001). Furthermore, nucleus-positive HCC specimens for survivin showed the highest PCNA labeling index. The nuclear localization of survivin in HCC cells correlated with tumor cell de-differentiation with the exception of the HepG2 cell line. Survivin expression was inversely associated with apoptosis and was strongly associated with Fas expression (P=0.01). All 4 HCC cell lines examined showed survivin expression and punctate nuclear localization. Our results indicate that survivin is localized to the cytoplasm in quiescent nonmalignant liver cells to suppress apoptosis and translocates into the nucleus in HCC cells. In conclusion, translocation of survivin from the cytoplasm to the nucleus may constitute an important regulatory mechanism for cell proliferation and differentiation in HCC.  相似文献   
48.
The telechelics 1 from methyl methacrylate and 1,1,2,2-tetraphenyl-1,2-diphenoxyethane, can be separated by adsorption chromatography. The structure of the dimers and trimers was identified by 1H NMR-spectroscopy. The free radical oligomerization is a process in which the syndiotactic structure is favoured above the isotactic one.  相似文献   
49.
Well-defined poly(4,4′-isopropylidenediphenyl carbonate)-block-polystyrene multiblock copolymers, PC-b-PS, were prepared by condensation of PC prepolymers having chloroformyl end-groups with PS prepolymers having hydroxyl end-groups. Both prepolymers had narrow molecular weight distribution (PC prepolymer: M?w/M?n ≤ 1,31, PS prepolymer: M?w/M?n ≤ 1,03). The course of the polycondensation reaction depends on the molecular weight of the prepolymers used as substrates. After fractionation, the obtained multiblock copolymers are homogeneous in chemical composition and have a narrow molecular weight distribution. The mechanical properties of the copolymers depend on the weight fraction of the PS blocks. All copolymers exhibit two glass transition temperatures, close to those of the parent homopolymers.  相似文献   
50.
Analysis of the 1H NMR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document} /β-propiolactone and of the model systems \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/(CH3)2O and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/CH3COOCH3 in liquid SO2 in the temperature region ?70 to ?20°C revealed that the reaction of the acetylium cation with β-propiolactone leads to the cyclic six-membered oxonium ion 4 , participating as an intermediate in the initial stage of polymerization.  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