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   8417篇
  免费   342篇
  国内免费   28篇
耳鼻咽喉   122篇
儿科学   81篇
妇产科学   164篇
基础医学   1133篇
口腔科学   241篇
临床医学   468篇
内科学   1636篇
皮肤病学   94篇
神经病学   694篇
特种医学   244篇
外科学   1765篇
综合类   37篇
预防医学   268篇
眼科学   403篇
药学   672篇
中国医学   13篇
肿瘤学   752篇
  2023年   35篇
  2022年   55篇
  2021年   111篇
  2020年   70篇
  2019年   88篇
  2018年   121篇
  2017年   102篇
  2016年   113篇
  2015年   100篇
  2014年   176篇
  2013年   255篇
  2012年   385篇
  2011年   443篇
  2010年   228篇
  2009年   253篇
  2008年   387篇
  2007年   445篇
  2006年   439篇
  2005年   506篇
  2004年   454篇
  2003年   501篇
  2002年   435篇
  2001年   274篇
  2000年   290篇
  1999年   255篇
  1998年   124篇
  1997年   95篇
  1996年   93篇
  1995年   72篇
  1994年   72篇
  1993年   51篇
  1992年   174篇
  1991年   159篇
  1990年   141篇
  1989年   149篇
  1988年   136篇
  1987年   135篇
  1986年   133篇
  1985年   128篇
  1984年   89篇
  1983年   53篇
  1982年   33篇
  1980年   28篇
  1979年   42篇
  1978年   35篇
  1977年   31篇
  1974年   34篇
  1973年   26篇
  1972年   32篇
  1969年   27篇
排序方式: 共有8787条查询结果,搜索用时 15 毫秒
1.
2.
Although many single nucleotide polymorphism (SNP) studies have reported an association of atopy, allergic diseases and total serum immunoglobulin E (IgE) levels, almost all of these studies sought risk factors for the onset of these allergic diseases. Furthermore, many studies have analyzed a single gene and hardly any have analyzed environmental factors. In these analyses, the results could be masked and the effects of other genes and environmental factors may be decreased. Here, we described the correlation between four genes [interleukin (IL)-4 (C-590T), IL-4 receptor (A1652G), FCER1B (G6842A) and STAT6 (G2964A)] in connection with IgE production; the role of IL-10 (C-627A) as a regulatory cytokine of allergy; and the severity of food allergy (FA) and atopic eczema (AE) in 220 Japanese allergic children. In addition to these SNPs, environmental factors, i.e., patient's attitude, indoor environment, and so on, were also investigated in this study. Our study was retrospective, and the correlation was analyzed by our defined clinical scores divided into three terms: worst symptoms, recent symptoms and general amelioration at the most recent examination during the disease course. Our results indicated that IL-10 AA, the genotype with lower IL-10 production, is associated with higher IgE levels in the serum (p < 0.0001, estimate; 0.912). Marginal liver abnormalities were observed in the subject group with both FA and AE (p < 0.1191, estimate; 0.1490). Our defined clinical scores enabled evaluation of various aspects of disease severity. Based on the scores, while no single SNP selected in this study determined severity, the combination of the SNP with laboratory data and environmental factors appeared to determine severity.  相似文献   
3.
Antipsychotic drugs are classified as typical and atypical based on extrapyramidal effects. However, since the frontal cortex is one of the most important regions for antipsychotic actions, this study attempted to classify antipsychotic drugs based on gene expression in the frontal cortex. Chlorpromazine and thioridazine were selected as typical antipsychotics, and olanzapine and quetiapine as atypical antipsychotics. Since these drugs have similar chemical structures, the effect of the basic structure on gene expression can be eliminated. Cluster analysis of microarray experiments separated 4-drug-administered mice into chlorpromazine-quetiapine and thioridazine-olanzapine groups. This classification scheme is different from that which is based on criteria currently used to group the typical and atypical drugs and suggests that antipsychotic drugs can be further separated into multiple groups.  相似文献   
4.
Iron deficiency (ID) is one of the most commonly known forms of nutritional deficiencies. Low body iron is thought to induce neurologic defects but may also play a protective role against cancer development by cell growth arrest. Thus, ID may affect cellular pathways controlling cell growth and proliferation, the mechanism of which is still not fully understood. The serine/threonine protein kinase Akt and its downstream target, the mammalian Target of Rapamycin (mTOR), is known to play a crucial role in the regulation of cell growth and survival. Therefore, we hypothesized that Akt/mTOR pathway could be influenced by ID. Three-week-old male Wistar-strain rats were divided into 3 groups and the 2 groups had free access to a control diet (C group) or an iron-deficient diet (D group). The third group (PF group) were pair-fed the control diet to the mean intake of the D group. After 4 weeks, rats were killed and their brains were sampled. In separate experiments, COS-1 cells were cultured with or without the iron chelator deferoxamine. Western blots of brain samples and COS-1 lysates were used to analyze the expression and phosphorylation state of Akt, TSC2, mTOR, and S6 kinase proteins implicated in the Akt/mTOR pathway. Using 2 different ID models, we show for the first time that iron deficiency depresses Akt activity in rats and in COS-1 cells, leading to a decrease in mTOR activity.  相似文献   
5.
The aim of this study was to clarify and compare the temporal course of bone mineral density (BMD) between fast bone losers and normal residents in Miyama Village, a rural Japanese community. BMD was measured over a 10-year period in a cohort study in Miyama Village, Wakayama Prefecture, Japan, to provide information on rate of bone loss in the mature and elderly population. Subjects (n=400) were selected by sex and age stratum from the full list of residents born in 1910–1949, with 50 men and 50 women in each age decade. Baseline BMD of the lumbar spine and proximal femur was measured using dual energy X-ray absorptiometry in 1990, 1993, 1997 and 2000. In the cohort, 171 men and 189 women completed the follow-up survey performed in 1993. After calculating the rate of bone loss between 1990 and 1993, the greatest tertile from the distribution of bone loss was categorized as fast bone losers, with the remainder considered as normal subjects. Changes in BMD were compared between normal subjects and fast bone losers over the 10-year period. Mean rate of change for BMD at both lumbar spine and femoral neck in fast bone losers recovered to levels similar to those in normal subjects over 7 years of observation. By contrast, BMD at the lumbar spine and femoral neck decreased steeply over the 10-year period in both groups, and mean BMD for fast bone losers was significantly lower than that of normal subjects (P<0.05). These differences were apparent only at the lumbar spine in both men and women, even after adjusting for age. These results indicate that fast bone loss is a transient phenomenon rather than a fixed status, although individuals who have been categorized as fast bone losers at some stage continue to display low BMD in the lumbar spine.  相似文献   
6.
A case of a branchial cyst with a high amylase activity of the cyst fluid was found in a 58-year-old female. The literature on branchial cysts with high amylase activity is reviewed. Amylase that showed high activity in the cystic fluid was revealed to be due to the salivary isoenzymes (S3 and S4) which migrated more to the anodic side on electrophoresis.  相似文献   
7.
Bradykinin-stimulated prostacyclin synthesis in porcine aortic endothelial cells was enhanced by pretreatment of the cells with pertussis toxin or islet-activating protein (IAP) for 5 hr or longer. Although ADP-ribosylation of a protein with a molecular weight of 41–42 kD in the cell membranes was completed by 3 hr after the addition of IAP into the incubation medium, there was good correlation between enhancement of bradykinin-induced prostacyclin synthesis and ADP-ribosylation of the IAP substrate over a wide range of IAP concentrations. Furthermore, even if IAP was removed from the incubation medium at 3 hr, bradykinin-induced prostaglandin synthesis at 24 hr was still potentiated. Cycloheximide and actinomycin D enhanced bradykinin-induced prostacyclin synthesis and apparently blocked the effect of IAP. Since this result suggested the involvement of an inhibitor protein(s) of prostacyclin synthesis in the IAP effect, we studied the effect of IAP on the level of lipocortin I which is known to inhibit phospholipase A2. Western and Northern blot analyses revealed that IAP decreased the amounts of protein and mRNA of lipocortin I. These results suggest that the enhancement of bradykinin-induced prostacyclin synthesis by IAP is associated with a decrease in the level of lipocortin I.  相似文献   
8.
9.
Hepatocyte regeneration has been widely investigated, with the mitotic index and the incorporation of [3H]thymidine being used as regeneration markers. We focused on the induction of DNA replication enzymes, particularly DNA polymerases (pol) α, δ, and ε. Using rat models, we have shown that the activity of pol α in crude liver extract well represents the regenerating capacity of hepatocytes. Using pol α as an indicator, we analyzed liver regeneration in rat models under various conditions: obstructive jaundice, external or internal biliary drainage, and the obstruction of portal vein branches. It has been revealed that the ligation of the common bile duct alone induces a certain amount of hepatocyte proliferation. It was striking that external biliary drainage suppressed regeneration capacity in cholestatic rat liver after partial hepatectomy. The strong regeneration in nonligated lobes induced by portal branch ligation was similar to the liver regeneration seen after partial hepatectomy with respect to the induction of DNA polymerases. Taken together, the aspects of DNA replication, particularly the induction of DNA polymerases, may contribute to shedding new light on the regeneration of human liver. This work was supported in part by a Grant-in-Aid for General Scientific Research and for Cancer Research from the Ministry of Education, Science and Culture, Japan, and by grants from the Uehara Memorial Foundation  相似文献   
10.
Phenotype, donor-specific cytolytic activity, and helper activity to release cytokines of cells infiltrating within renal allografts of hosts rendered unresponsive by perioperative administration of donor lymphocytes via the portal vein (p.v.) were investigated in order to analyze the mechanism of prolongation of allograft survival. Graft-infiltrating cells (GIC) were obtained from Lewis (LEW, RT-1l) hosts inoculated perioperatively with 1 x 10(8) donor Brown-Norway (BN, RT-1n) lymphocytes p.v., a group that displays prolonged renal allograft survival (MST: 22.2 +/- 5.3 days, n = 10) compared with an uninoculated control group (MST: 7.8 +/- 0.6 days, n = 10, P less than 0.01). The percentages of cytotoxic/suppressor T cells (OX-8+) and Ia-positive cells (OX-6+) in GIC (23.1 +/- 4.4% and 9.0 +/- 2.0%, respectively) and in spleen cells (7.5 +/- 2.6% and 8.5 +/- 1.1%, respectively) from p.v.-inoculated LEW hosts on day 6 postgrafting were significantly lower than those of uninoculated control recipients (GIC: OX-8; 39.4 +/- 8.2%, OX-6; 23.0 +/- 1.9%. SP cell: OX-8; 21.6 +/- 9.9%, OX-6; 12.7 +/- 0.4%, P less than 0.05). Cytolytic activity of GIC from tolerant hosts on day 6 postgrafting toward donor blastoid lymphocytes was significantly decreased (19.0 +/- 1.2% at E/T = 50), compared with that from control allografts during ongoing rejection (51.5 +/- 5.3%, P less than 0.01). The amounts of in vitro cytokine production of GIC from tolerant hosts after mitogen stimulation were remarkably decreased (IL-2: 8.7 +/- 1.4 U/ml, IL-3: 15.4 +/- 0.6 U/ml, and BSF-2: 24.6 +/- 3.5 U/ml) than those of uninoculated control hosts during ongoing rejection (IL-2: 19.6 +/- 2.9 U/ml, IL-3: 22.2 +/- 2.7 U/ml, and BSF-2: 67.5 +/- 13.2 U/ml, P less than 0.05). These results demonstrated that activation of both Tc cells and Th cells was inhibited in the spleen and in situ in renal allografts following administration of donor lymphocytes through the portal vein.  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