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   5185篇
  免费   297篇
  国内免费   40篇
耳鼻咽喉   81篇
儿科学   203篇
妇产科学   90篇
基础医学   566篇
口腔科学   41篇
临床医学   352篇
内科学   1297篇
皮肤病学   43篇
神经病学   398篇
特种医学   210篇
外科学   1137篇
综合类   47篇
预防医学   227篇
眼科学   85篇
药学   341篇
中国医学   12篇
肿瘤学   392篇
  2023年   25篇
  2022年   84篇
  2021年   139篇
  2020年   75篇
  2019年   106篇
  2018年   145篇
  2017年   117篇
  2016年   131篇
  2015年   145篇
  2014年   177篇
  2013年   218篇
  2012年   311篇
  2011年   343篇
  2010年   190篇
  2009年   165篇
  2008年   238篇
  2007年   242篇
  2006年   244篇
  2005年   262篇
  2004年   236篇
  2003年   213篇
  2002年   174篇
  2001年   144篇
  2000年   138篇
  1999年   110篇
  1998年   40篇
  1997年   31篇
  1996年   32篇
  1995年   33篇
  1994年   25篇
  1992年   72篇
  1991年   67篇
  1990年   65篇
  1989年   55篇
  1988年   58篇
  1987年   58篇
  1986年   43篇
  1985年   62篇
  1984年   41篇
  1983年   42篇
  1982年   26篇
  1980年   26篇
  1979年   53篇
  1978年   31篇
  1977年   28篇
  1976年   24篇
  1974年   30篇
  1973年   35篇
  1972年   30篇
  1971年   29篇
排序方式: 共有5522条查询结果,搜索用时 31 毫秒
61.
Estrogens, whether natural or synthetic, clearly influence reproductive development, senescence, and carcinogenesis. Pyrethroid insecticides are now the most widely used agents for indoor pest control, providing potential for human exposure. Using the MCF-7 human breast carcinoma cell line, we studied the estrogenic potential of several synthetic pyrethroid compounds in vitro using pS2 mRNA levels as the end point. We tested sumithrin, fenvalerate, d-trans allethrin, and permethrin. Nanomolar concentrations of either sumithrin or fenvalerate were sufficient to increase pS2 expression slightly above basal levels. At micromolar concentrations, these two pyrethroid compounds induced pS2 expression to levels comparable to those elicited by 10 nM 17ss-estradiol (fivefold). The estrogenic activity of sumithrin was abolished with co-treatment with an antiestrogen (ICI 164,384), whereas estrogenic activity of fenvalerate was not significantly diminished with antiestrogen co-treatment. In addition, both sumithrin and fenvalerate were able to induce cell proliferation of MCF-7 cells in a dose-response fashion. Neither permethrin nor d-trans allethrin affected pS2 expression. Permethrin had a noticeable effect on cell proliferation at 100 microM, whereas d-trans allethrin slightly induced MCF-7 cell proliferation at 10 microM, but was toxic at higher concentrations. Overall, our studies imply that each pyrethroid compound is unique in its ability to influence several cellular pathways. These findings suggest that pyrethroids should be considered to be hormone disruptors, and their potential to affect endocrine function in humans and wildlife should be investigated.  相似文献   
62.
BACKGROUND/PURPOSE: Hepatic fibrosis can progress in biliary atresia (BA) and is associated with capillarization of hepatic sinusoids. The significance of serum hyaluronic acid (HA) as a noninvasive indicator of histological sinusoidal endothelial cell (SEC) damage and hepatic fibrosis in BA, is investigated. METHODS: A total of 28 postoperative BA patients (mean age, 11.0+/-3.7 years) and 20 normal controls (mean age, 10.5+/-2.8 years) were studied. BA patients were divided into group I, good liver function (n = 8); group II, moderate liver dysfunction (n = 10); and group III, severe liver dysfunction (n = 10). Serum HA was determined using a one-step sandwich enzyme immunoassay, and liver histological damage was confirmed immunohistochemically using an antibody against factor VIII-related antigen (FVIIIRAg), which is specific for detecting damaged SEC. RESULTS: Serum HA was significantly higher (P < .0001) in group III (84.6+/-36.5 ng/mL) than in group I (15.9+/-6.9 ng/mL) or group 11 (28.7+/-10.7 ng/mL). Although immunoreactive products of FVIIIRAg were abundant in group III, they were not detected in SEC from group II. CONCLUSION: Serum HA may be of value for monitoring postoperative BA patients as a noninvasive indicator of SEC damage and progressive hepatic fibrosis.  相似文献   
63.
PURPOSE: The aim of this study was to determine whether chemokines such as serum IP-10 levels in patients with biliary atresia (BA) correlate with liver function and histology and assess its value as a medium to long-term prediction of prognosis in postoperative BA patients. METHODS: Thirty postoperative BA patients (mean age, 10.8+/-3.5 years) and eight normal controls (mean age, 10.3+/-3.3 years) were studied. The BA patients were divided into three groups according to liver function. Group I (n = 8) was jaundice free, had normal liver function and no evidence of severe cholangitis or portal hypertension. Group II (n = 12) had moderate liver dysfunction. Group III (n = 10), had severe liver dysfunction. Hepatic histology was assessed using conventional needle biopsy. Serum IP-10 levels were determined using a specific enzyme-linked immunosorbent assay (ELISA). RESULTS: Serum levels of IP-10 in group III (458.0+/-240.0 pg/mL) were significantly higher than those in group II (233.6+/-126.9 pg/mL; P < .0001). Levels in group II were also significantly higher than those in group I (144.8+/-23.4 pg/mL; P < .05), but there was no significant difference between group I and controls (107.9+/-34.0 pg/mL). Liver biopsy findings showed a progression of fibrosis and mononuclear cell infiltration from group I to group III. There was intimal hyperplasia and swelling of endothelial cells of branches of the hepatic artery in the portal area in group III. CONCLUSION: Because IP-10 levels correlate closely with histological findings in postoperative BA patients, it would appear to play a specific role in hepatocyte death and hepatic artery changes, thus providing important information about progressive fibrosis in BA patients that facilitates treatment decision making and prediction of prognosis.  相似文献   
64.
65.
The objective of this study was to investigate whether nitric oxide (NO) inhalation might be an alternative strategy as a chemical assist for the circulation in patients showing a deterioration in oxygen delivery. Twelve adult patients whose oxygen delivery indices (DO2I) were less than 400 ml/min/m2 after cardiovascular surgery were included in this study. NO was administered via a premixing system or a side stream system at doses between 1 and 10 (5.1+/-2.4) ppm. Data obtained before and during a 120 min NO inhalation were compared using the paired Student's t-test. The increase in PaO2/FiO2 resulting from NO inhalation was significant (from 162 to 251 mm Hg). DO2I increased significantly from 326 to 417 ml/min/m2 concomitantly with significant increases in both arterial oxygen content (CaO2) and cardiac index (CI) (from 14.1 to 15.4 vol% and from 2.31 to 2.71 L/min/m2 , respectively). The increase in SvO2 during NO inhalation was significant (from 55.2 to 62.6%). Among the other hemodynamic parameters, both total pulmonary resistance and systolic pulmonary arterial pressure (SPAP) showed significant decreases during NO inhalation, but right atrial pressure did not change significantly. There was a close relationship between the baseline SPAP level (bSPAP) and the decrease in SPAP during NO inhalation (dSPAP) (r = -0.88). However, negative correlations were observed between bSPAP and percentage increase in CI (%CI) (r = -0.61) and between bSPAP and percentage increase in DO2I (%DO2I) (r = -0.48). Moreover, positive relationships were observed between dSPAP and %CI (r = 0.62) and between dSPAP and %DO2I (r = 0.45). Hemoglobin (Hb) increased significantly from 11.0 to 11.4 g/dl. There were no significant changes in Fio2, pH, PacO2, or base excess (BE) during NO inhalation. The level of methemoglobin measured during the study period remained within the normal range (0.86+/-0.23%). In conclusion, NO inhalation could be an efficient and alternative assist for the circulation in patients whose oxygen delivery deteriorates after cardiovascular surgery.  相似文献   
66.
67.
68.
69.
1110 neonates, from 30 to 42 of estimated gestational age (EGA) were measured on the 1st day of life to estimate upper mid-arm circumference (MAC) and head circumference (HC). Individual MAC/HC ratio was calculated. MAC/HC ratio was used to estimate gestational age and nutritional status of the newborns. We proved that MAC/HC ratio increased linearly between 30 and 38 week of pregnancy and it stabilized between 38-42 week. We compared MAC/HC ratio with birth weight, skin fold score, and ponderal index. We concluded that this ratio may be very useful to estimate gestational age and to include the neonates to "the group of risk".  相似文献   
70.
In this paper attempts were made towards the optimalization and the control of some parameters of the RIA reaction.Basing on the law mass action, as well as on the Scatchard's and Sips's equations, the equilibrium constants for the reversible reaction: insulin-125I-antibody for different incubation temperatures were calculated. Moreover a characteristic of the antiinsulin antibody by means of the heterogeneity coefficient was done, as well as the values of the thermodynamic function increments were calculated, which made possible to point out explicitly the optimal shape of the standard curve.  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