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   6899篇
  免费   260篇
  国内免费   38篇
耳鼻咽喉   242篇
儿科学   139篇
妇产科学   296篇
基础医学   915篇
口腔科学   54篇
临床医学   442篇
内科学   1821篇
皮肤病学   144篇
神经病学   620篇
特种医学   113篇
外科学   741篇
综合类   60篇
一般理论   10篇
预防医学   324篇
眼科学   199篇
药学   676篇
中国医学   4篇
肿瘤学   397篇
  2023年   19篇
  2022年   140篇
  2021年   260篇
  2020年   72篇
  2019年   137篇
  2018年   151篇
  2017年   113篇
  2016年   125篇
  2015年   166篇
  2014年   212篇
  2013年   323篇
  2012年   450篇
  2011年   569篇
  2010年   280篇
  2009年   185篇
  2008年   452篇
  2007年   544篇
  2006年   501篇
  2005年   537篇
  2004年   524篇
  2003年   453篇
  2002年   398篇
  2001年   23篇
  2000年   24篇
  1999年   30篇
  1998年   31篇
  1997年   19篇
  1996年   26篇
  1995年   33篇
  1994年   21篇
  1993年   18篇
  1992年   21篇
  1991年   25篇
  1990年   11篇
  1989年   16篇
  1988年   9篇
  1987年   20篇
  1986年   14篇
  1985年   17篇
  1984年   27篇
  1983年   20篇
  1982年   26篇
  1981年   14篇
  1980年   14篇
  1979年   21篇
  1978年   14篇
  1977年   15篇
  1975年   9篇
  1974年   9篇
  1973年   10篇
排序方式: 共有7197条查询结果,搜索用时 31 毫秒
51.
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   
52.
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   
53.
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   
54.
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   
55.
Rats were subjected to 4 h continuous or intermittent exposure to vinyl chloride (VC) at different time-weighted average concentrations (15, 50, 150, 500 and 15,000 mg/m3). Hepatic non-protein sulfhydryl content (NPSH) and excretion of thiodiglycolic acid (TdGA) in urine were determined. VC at concentrations from 50 mg/m3 to 15,000 mg/m3 caused a dose-dependent depression of NPSH, but no difference in the magnitude of this depression induced by continuous or intermittent exposure at the same average concentration of VC was noted. At average concentrations of 50 mg/m3 and 150 mg/m3, the urinary excretion of TdGA under continuous exposure did not differ from that under intermittent exposure, whereas at VC concentrations of 500 mg/m3 and 15,000 mg/m3 it was higher following continuous exposure.  相似文献   
56.
The occurrence of childhood obesity is influenced by both genetic and epigenetic factors. FTO (FTO alpha-ketoglutarate dependent dioxygenase) is a gene of well-established connection with adiposity, while a protooncogene PLAG1 (PLAG1 zinc finger) has been only recently linked to this condition. We performed a cross-sectional study on a cohort of 16 obese (aged 6.6–17.7) and 10 healthy (aged 11.4–16.9) children. The aim was to evaluate the relationship between methylation and expression of the aforementioned genes and the presence of obesity as well as alterations in anthropometric measurements (including waist circumference (WC), body fat (BF_kg) and body fat percent (BF_%)), metabolic parameters (lipid profile, blood glucose and insulin levels, presence of insulin resistance) and blood pressure. Expression and methylation were measured in peripheral blood mononuclear cells using a microarray technique and a method based on restriction enzymes, respectively. Multiple regression models were constructed to adjust for the possible influence of age and sex on the investigated associations. We showed significantly increased expression of the FTO gene in obese children and in patients with documented insulin resistance. Higher FTO expression was also associated with an increase in WC, BF_kg, and BF_% as well as higher fasting concentration of free fatty acids (FFA). FTO methylation correlated positively with WC and BF_kg. Increase in PLAG1 expression was associated with higher BF%. Our results indicate that the FTO gene is likely to play an important role in the development of childhood adiposity together with coexisting impairment of glucose-lipid metabolism.  相似文献   
57.
PURPOSE: To describe a randomized trial of a cognitive behavioral intervention on reducing symptom severity among patients diagnosed with solid tumors and undergoing a first course of chemotherapy and to determine whether the intervention had an additive or interactive effect on symptom severity in the presence of supportive care medications. PATIENTS AND METHODS: Patients (N = 237) were accrued from comprehensive and community cancer centers, interviewed, and randomly assigned to either the experimental intervention (n = 118) or conventional care (n = 119). A symptom severity index, based on summed severity scores across 15 symptoms, was the primary outcome. Each patient's site of cancer, stage at diagnosis, chemotherapy protocols, and use of supportive medications were learned from medical records. RESULTS: Groups were equivalent at baseline, and attrition by characteristics by group was not different. The proportion of patients not receiving chemotherapy at 10 and 20 weeks did not differ by group. At the 10- and 20-week observations, there was a significant interaction between the experimental group and baseline symptom severity. Patients in the experimental group who entered the trial with higher symptom severity reported significantly lower severity at 10 and 20 weeks. Controlling for chemotherapy treatment status at follow-up and supportive care medications did not alter the effect of the experimental intervention. CONCLUSION: Compared with conventional care alone, the experimental intervention was effective among patients who entered the trial with higher levels of symptom severity. Age, sex, site or stage of cancer, and supportive medications did not modify the effect of this cognitive behavioral intervention on symptom severity.  相似文献   
58.
PURPOSE: Recent findings indicating that many genes related to cancer development are silenced by an aberrant DNA methylation suggest that inhibitors of this process may be effective cancer therapeutics. In this study we investigated the efficacy of low-dose 5-aza-2'-deoxycitydine (DAC), a methylation inhibitor, with interleukin (IL) 12, one of the most potent cytokines with antitumor activity. Experimental Design: Mice inoculated with L1210 leukemia cells or with B16F10 melanoma cells were treated with 7 daily injections of low-dose DAC (0.2 mg/kg) and/or 7 daily doses of IL-12 (100 ng/dose). Scid/scid mice as well as monoclonal antibodies against CD4, CD8, and NK1.1 were used to investigate the mechanisms of the antitumor effects of the combination treatment. The activity of murine lymphocytes was measured with enzyme-linked immunospot and (51)Cr release assays. RESULTS: Treatment with DAC or IL-12 given alone produced moderate antitumor effects. In both tumor models combined treatment resulted in potentiated antitumor effects and produced 70% long-term survivors among mice inoculated with L1210 cells. The antitumor efficacy of combined treatment was abrogated in scid/scid mice, and after depletion of CD4(+) and CD8(+) T cells. Mice inoculated with B16F10 melanoma cells had significantly delayed tumor growth after combined treatment with DAC and IL-12. Strong antitumor effect correlated with a significant activation of lymph node-derived CD8(+) and CD4(+) cells. Transient neutropenia was observed in mice under treatment of DAC alone, but remarkably this effect was not potentiated by IL-12. CONCLUSIONS: This study provides the first evidence that antitumor effects of DAC can be strongly potentiated by IL-12 and could be beneficial in an effective low-dose-based antitumor therapy.  相似文献   
59.
High cytoplasmic expression of maspin was described in ovarian cancers of shorter survival rates. Until now, no relationship has been described between expression of maspin and sensitivity to cisplatin in ovarian cancers. This study aimed at examining the relationship between expression of maspin, detected by immunohistochemistry and clinical response to cisplatin in ovarian cancer cases as well as the in vitro sensitivity to cisplatin of 11 ovarian cancer cell lines. The analyzes were performed on 73 samples of ovarian cancer and on A2780P, A2780RCIS, CAOV-3, EFO 21, EFO 27, ES-2, Mdah 2774, OAW 42, OVCAR-3, PA-1, and SKOV-3 ovarian cancer cells. Cytoplasmic maspin expression in studied cells significantly correlated with cisplatin sensitivity. A significantly shorter overall survival and progression-free survival was associated with lower cytoplasmic maspin expression at first-look laparotomies and nuclear maspin expression and secondary cytoreductions. Higher nuclear maspin at first-look laparotomies expression was specific for cases of complete response. In the study, the elevated expression of maspin was shown to be typical for cisplatin-sensitive ovarian cancers.  相似文献   
60.
Nogo‐B (Reticulon 4B) is considered to be a novel vascular marker, which may have a protective role in injury‐induced neointima formation and atherosclerosis. Nogo A/B is found to be crucial for monocyte/macrophage recruitment in acute inflammation and it is expressed in CD68 + macrophages. We hypothesize that macrophage infiltration in atherosclerosis is not dependent on Nogo‐B expression in arterial wall. We have assessed Nogo‐B expression and macrophage accumulation in the iliac arteries of healthy organ donors and organ donors with cardiovascular risk factors. Paraffin sections of 66 iliac arteries, from 44 deceased organ donors (17 women and 27 men), were studied. The healthy and cardiovascular risk (CVR) subgroups were created. With regard to staging of the atherosclerotic process, the thickness of arterial intima was measured in digitalized images of H+E stained tissue sections. Immunohistochemical reactions (Nogo‐B and CD68) were carried out in all arteries (66 samples). Western blotting (WB‐19 samples) and real‐time PCR (27 samples) were performed on selected arteries. Significantly higher Nogo‐B expression was demonstrated in the intima of the healthy subjects' subgroup, using immunohistochemistry. WB and real‐time PCR revealed a trend toward lower Nogo‐B expression in the adventitia of the CVR subgroup. Furthermore, the thickness of the intima was found to negatively correlate with the expression of Nogo‐B in the intima and media (r = ?0.32; p < 0.05; r = ?0.32; p < 0.05). Macrophage infiltrates were more prominent in intima of CVR subjects (0.65 vs 3.52 a.u.; p < 0.01). Macrophage density in intima increased with atherosclerosis progression (r = 0.37; p < 0.01). CD68 macrophages density in adventitia was lower in CVR arteries than in healthy arteries. The expression of Nogo‐B, in arterial intima, is impeded in the early stages of atherosclerosis. Accumulation of arterial intimal CD68 macrophages has been shown to progress; however, the overall macrophage density in the adventitia is reduced in arteries shown to have intimal thickening. Macrophage infiltration is not accompanied by Nogo‐B expression in atherosclerotic arteries.  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