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   1841篇
  免费   63篇
  国内免费   20篇
耳鼻咽喉   75篇
儿科学   113篇
妇产科学   67篇
基础医学   242篇
口腔科学   12篇
临床医学   87篇
内科学   390篇
皮肤病学   18篇
神经病学   193篇
特种医学   9篇
外科学   112篇
综合类   12篇
预防医学   187篇
眼科学   57篇
药学   219篇
中国医学   2篇
肿瘤学   129篇
  2023年   4篇
  2022年   23篇
  2021年   48篇
  2020年   13篇
  2019年   21篇
  2018年   30篇
  2017年   13篇
  2016年   30篇
  2015年   23篇
  2014年   30篇
  2013年   45篇
  2012年   101篇
  2011年   110篇
  2010年   59篇
  2009年   44篇
  2008年   123篇
  2007年   173篇
  2006年   174篇
  2005年   175篇
  2004年   193篇
  2003年   187篇
  2002年   138篇
  2001年   9篇
  2000年   9篇
  1999年   14篇
  1998年   13篇
  1997年   10篇
  1996年   9篇
  1995年   3篇
  1994年   5篇
  1993年   7篇
  1992年   2篇
  1991年   7篇
  1990年   4篇
  1989年   10篇
  1988年   9篇
  1987年   5篇
  1986年   7篇
  1985年   2篇
  1983年   2篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   6篇
  1974年   3篇
  1973年   3篇
  1972年   7篇
  1971年   2篇
  1970年   2篇
  1961年   1篇
排序方式: 共有1924条查询结果,搜索用时 15 毫秒
51.
52.
53.

Background/purpose

Endoscopic variceal ligation (EVL) is effective in controlling rebleeding from esophageal varices in children, but there is no data on the use of EVL to prevent initial bleeding. The objective of this study was to prospectively evaluate the efficacy of EVL in preventing the first hemorrhage from esophageal varices in children.

Methods

Thirty-seven children with portal hypertension (22 liver cirrhosis, 15 portal vein thrombosis), aged 4 to 17 years (M = 9.5 ± 4.4 years) were included in the study. The criteria for inclusion were (1) no previous variceal bleeding; (2) the presence of esophageal varices classified grade II or more, and (3) their enlargement by at least I grade after 6 months of observation without endoscopic treatment or appearance of endoscopic signs of high bleeding risk. A Multi-Band Ligator was used, and 2 to 6 bands were fixed under general anesthesia during one procedure depending on the number and size of varices. Follow-up examinations were performed every 3 months, repeating the procedure if necessary. In total, 75 procedures of EVL were performed, from one to 5 in each patient

Results

Four patients underwent liver transplantation before eradication of varices. Two others were excluded from the observation because of lack of compliance to the protocol. Of the remaining 31 patients, eradication of varices was achieved in 28 children (90.3%) after 2.0 EVL sessions performed at 3-month intervals. The average time of follow-up after cessation of treatment is 16 months. No bleeding from varices occurred in any child during or after treatment. There were no differences in results between children with liver cirrhosis and portal vein thrombosis. Development of hypertensive gastropathy was observed in 2 children with one episode of bleeding. Recurrence of varices without bleeding occurred in 3 children after 12, 13, and 28 months from eradication.

Conclusions

The study results confirmed that endoscopic variceal ligation is a safe and highly effective procedure in children with portal hypertension, regardless of its etiology. Eradication of esophageal varices was followed by 16 months free of bleeding. Prolonged observation is mandatory to conclude if preventive EVL influences the natural history of disease and diminishes the risk of first bleeding onset.  相似文献   
54.
T cells are involved in the pathogenesis of nephrotic syndrome (NS). The aim of the study was to determine whether the activity of T-helper-1 (Th1) and T-helper-2 (Th2) cells and the distribution of the lymphocyte subsets, namely CD45RA+CD4+ (”naive” helper T cells, suppressor-inducer), CD45RA+CD8+ (”naive” suppressor T cells, suppressor-effector), CD45RO+CD4+ (”memory” helper T cells), are predictive for steroid sensitivity in children with primary NS. These parameters were assessed at the onset of disease, before initiation of steroid therapy. Two groups of NS children were retrospectively formed according to steroid sensitivity (SS) or resistance (SR). The activity of Th1 and Th2 cells was defined by the production of interleukin-2 (IL-2), interferon-γ, IL-4, and IL-10 in the supernatants of CD4+ T cell cultures activated with autologous monocytes presenting tetanus toxoid (TT). Peripheral lymphocyte subsets were determined using double- or triple-color flow cytometry. In SS children with NS we found a decreased proliferative response of CD4+ T cells to TT stimulation, cytokine synthesis indicating the predominance of Th2 activity, and an increased percentage of activated suppressor-inducer (CD45RA+ CD4+CD25+, 5.18±0.8, P<0.001) and suppressor-effector (CD45RA+CD8+CD25+, 2.05±0.6, P<0.01) cells, with the concomitant reduction of activated memory cells (CD45RO+CD4+CD25+, 0.2±0.1, P<0.001). In children with SRNS we found an increased proliferative response of CD4+ T cells to TT, a rise in activated memory (CD45RO+CD4+CD25+, 3.82±0.7, P<0.01) and suppressor-inducer peripheral T cells (CD45RA+ CD4+CD25+, 3.85±0.6, P<0.01), but a low percentage of activated suppressor-effector (CD45RA+CD8+ CD25+, 0.5±0.2, P<0.05) T cells. We conclude that prior to treatment the distribution of lymphocyte subpopulations in peripheral blood together with Th1 and Th2 cell activity provides a useful tool for evaluating the likelihood of steroid sensitivity in patients with primary NS. Received: 3 November 1998 / Revised: 1 September 1999 / Accepted: 8 September 1999  相似文献   
55.
Prostate-specific antigen (PSA) screening has led to a dramatic increase in prostate cancer detection with a concurrent stage migration. Although the test has revolutionized prostate cancer detection by identifying disease that is potentially curable in the majority of men, only 25% of men receiving test results of PSA > 4 ng/ml will have prostate cancer and many men receiving a normal PSA will have disease, including high-grade disease. There is a need for improved biomarkers for detecting prostate cancer. One such method of cancer detection is surface-enhanced laser desorption and ionization (SELDI). The Early Detection Research Network (EDRN) validation study for SELDI for prostate cancer is described. In a three-stage study, the portability and reproducibility of the technique will be determined; the predictive algorithm will be refined in a multi-institutional case-control population; followed by ultimate validation in the context of a prospective trial with complete disease ascertainment. The unique aspect of the EDRN SELDI validation study is the novel use of two groups of cancer cases: those cases with higher-risk disease (Gleason > or = 7) and those cases with lower-risk disease (Gleason < or = 6). This study will allow the first evaluation of a predictive algorithm that includes prognosis in disease screening. The EDRN SELDI prostate cancer biomarker validation study is a rigorous evaluation of a new detection method for prostate cancer. The methodologies used for this evaluation will prove useful for guiding future biomarker studies in this challenging disease.  相似文献   
56.
Women who are born with constitutional heterozygous mutations of the BRCA1 gene face greatly increased risks of breast and ovarian cancer. The product of the BRCA1 gene is involved in the repair of double-stranded DNA breaks and it is believed that increased susceptibility to DNA breakage contributes to the cancer phenotype. It is hoped therefore that preventive strategies designed to reduce chromosome damage will also reduce the rate of cancer in these women. To test for increased mutagenicity of cells from BRCA1 carriers, the frequency of chromosome breaks was measured in cultured blood lymphocytes following in vitro exposure to bleomycin in female BRCA1 carriers and was compared with noncarrier relatives. The frequency of chromosome breaks was also measured in BRCA1 carriers following oral selenium supplementation. Carriers of BRCA1 mutations showed significantly greater mean frequencies of induced chromosome breaks per cell than did healthy noncarrier relatives (0.58 versus 0.39; P < 10(-4)). The frequency of chromosome breaks was greatly reduced following 1 to 3 months of oral selenium supplementation (mean, 0.63 breaks per cell versus 0.40; P < 10(-10)). The mean level of chromosome breaks in carriers following supplementation was similar to that of the noncarrier controls (0.40 versus 0.39). Oral selenium is a good candidate for chemoprevention in women who carry a mutation in the BRCA1 gene.  相似文献   
57.
58.
The influence of felbamate (200 mg/kg or 50 mg/kg) on antinociceptive effect of morphine (10 mg/kg), metamizol (500 mg/kg) and indomethacin (10 mg/kg or 1.4 mg/kg) was investigated in a mouse model using the hot-plate test. All drugs were injected intraperitoneally. Felbamate was administered to mice 30 min before applying the analgesic drugs. Measurement of nociception was performed within 2 h after felbamate administration. The research studies were further conducted with a multiple (10 days) drug dosage. Felbamate in the dose of 200 mg/kg significantly increases the analgesic effect of morphine and weakens the effect of metamizol and indomethacin. Multiple administration of felbamate does not affect the activity of morphine and metamizol, but decreases analgesic effect of indomethacin.  相似文献   
59.
Sonogashira coupling of (E)-6'-iodohomovinyl nucleosides 1 with (trimethylsilyl)acetylene gave the conjugated 8'-(trimethylsilyl)enyne derivatives of the adenosine 2a and uridine 2b with expected E-stereochemistry. Desilylation of 2a,b with tetrabutylammonium fluoride followed by treatment with N-iodosuccinimide/AgNO(3) afforded 8'-iodoenynes 4a,b. Analogous coupling of (Z)-6'-iodohomovinyl nucleosides 7a,b produced (Z)-8'-(trimethylsilyl)enynes 8a,b, which were deprotected with aqueous trifluoroacetic acid to give the Z-enynes 9a,b. Stereoselective coupling of the adenosine 4'-acetylenic 11 and ethyl (Z)-3-bromoacrylate followed by deprotection gave the conjugated enyne system attached in the reverse orientation at C4' 13. Because of their diverse stereochemical attributes, deprotected enyne analogues 5a, 6a, 9a, and 13 derived from adenosine require a different vicinity for binding with S-adenosyl-l-homocysteine (AdoHcy) hydrolase and/or addition of enzyme-bound water across the conjugated enyne system. Enyne 5a and 8'-iodoenyne 6a produced time-dependent and concentration-dependent inhibition of AdoHcy hydrolase (K(i), 0.55 and 118.5 microM, respectively). No reduction in NAD(+) content of the enzyme and no iodide ion released were observed upon incubation of 6a with the enzyme, while incubation of 5a produced 30% reduction in the NAD(+) content of the enzyme. No specific antiviral activity was noted for 5a,b, 6a,b, 9a,b, and 13 against any of the viruses tested; the E-iodoenynes 6a and 6b inhibited HIV-1 virus (IC(50), 1.1 and 1.8 microM; selectivity index, 7 and 3, respectively). The E-enyne 5a showed activity against cytomegalovirus at a concentration (EC(50), 30 microM) that was 3- to 10-fold lower than the cytotoxic concentration.  相似文献   
60.
The authors would like to present the difficulties in differentiation of diabetes mellitus type 1 and type 2 in adolescence on the basis of two 17 years-old patients. In both patients' cases the following symptoms: polydipsia, polyuria and weight loss with hyperglycemia and glycosuria have been observed for a few months. During laboratory studies some additional abnormalities were observed: elevated HbA1c, dyslipidemia and high level of liver enzymes. Normal level of insulin as well as C-peptide lack of ketonuria and negative parameters of autoimmunologic reaction the supported diagnosis of diabetes mellitus type 2. Due to insulin therapy and metformin a correct level of glycemia was achieved. CONCLUSION: Decompensated diabetes mellitus type 2 in adolescents may be difficult to differentiate with type 1.  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