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   2154篇
  免费   59篇
  国内免费   41篇
  2023年   18篇
  2022年   31篇
  2021年   37篇
  2020年   33篇
  2019年   35篇
  2018年   27篇
  2017年   34篇
  2016年   18篇
  2015年   32篇
  2014年   65篇
  2013年   93篇
  2012年   39篇
  2011年   102篇
  2010年   78篇
  2009年   128篇
  2008年   116篇
  2007年   143篇
  2006年   103篇
  2005年   102篇
  2004年   85篇
  2003年   84篇
  2002年   60篇
  2001年   46篇
  2000年   31篇
  1999年   42篇
  1998年   38篇
  1997年   55篇
  1996年   42篇
  1995年   45篇
  1994年   40篇
  1993年   41篇
  1992年   40篇
  1991年   34篇
  1990年   33篇
  1989年   37篇
  1988年   21篇
  1987年   31篇
  1986年   21篇
  1985年   19篇
  1984年   22篇
  1983年   14篇
  1982年   26篇
  1981年   14篇
  1980年   14篇
  1979年   12篇
  1978年   12篇
  1976年   16篇
  1975年   10篇
  1973年   8篇
  1972年   9篇
排序方式: 共有2254条查询结果,搜索用时 15 毫秒
111.
Bipolar disorder seasonality has been documented previously, though information on the effect of demographic and clinical variables on seasonal patterns is scant. This study examined effects of age, sex, index admission, and predominant polarity on bipolar disorder seasonality in a nationwide population. An inpatient cohort admitted to hospital exclusively for mental illness was derived from the Taiwan National Health Insurance Research Database for 2002–2007. The authors identified 9619 inpatients with bipolar disorder, who had generated 15 078 acute admission records. An empirical mode decomposition method was used to identify seasonal oscillations in bipolar admission data, and regression and cross-correlation analyses were used to quantify the degree and timing of bipolar admission seasonality. Results for seasonality timing found that manic or mixed episodes peak in spring or summer, and depressive episodes peak in winter. Analysis for degree of seasonality revealed that (1) the polarity of patients' index admission predicted the seasonality of relapse admissions; (2) seasonality was significant in female admissions for depressive episodes and in male admissions for manic episodes; (3) young adults displayed a higher degree of seasonality for acute admissions than middle-aged adults; and (4) patients with predominantly depressive admissions displayed a higher degree of seasonality than patients with predominantly manic admissions. Demographic and clinical variables were found to affect the seasonality of acute admissions for bipolar disorders. These findings highlight the need for research on identification and management of seasonal features in bipolar patients. (Author correspondence: )  相似文献   
112.
Recent studies in fruit flies have imposed dietary restriction (DR) by diluting yeast and have reported increased lifespan as the yeast-to-sugar ratio decreased. In this study, the effects of DR on the lifespan of Bactrocera dorsalis were investigated using constant-feeding diets with different yeast:sugar ratios and an intermittent-feeding diet in which flies ate every sixth day. Antioxidant enzyme activities and the malondialdehyde concentration were also measured in virgin females under constant-feeding DR protocols to investigate their relationships with lifespan. The results showed that B. dorsalis lifespan was significantly extended by DR, and carbohydrate-enriched diet may be important for lifespan-extension. Female flies lived significantly longer than males at all dietary levels under both feeding regimes, indicating no interaction between diet and sex in determining lifespan. Antioxidant enzyme activities increased with the amount of yeast increased in the diets (0–4.76%) between starvation and DR treatments, indicating that the antioxidants may have influences in determining lifespan in B. dorsalis under starvation and DR treatments. However, antioxidants cannot keep up with increased oxidative damage induced by the high yeast diet (25%). These results revealed that the extension of lifespan by DR is evolutionarily conserved in B. dorsalis and that yeast:sugar ratios significantly modulate lifespan in this species.  相似文献   
113.
Disulfated and trisulfated steroids have been synthesized from cholesterol and their acetylcholinesterase inhibitory activity has been evaluated. In our studies we have found that the activity was not only dependent on the location of the sulfate groups but on their configurations. 2β,3α,6α-trihydroxy-5α-cholestan-6-one trisulfate (18) was the most active steroid with an IC50 value of 15.48 μM comparable to that of 2β,3α-dihydroxy-5α-cholestan-6-one disulfate (1). Both compounds were found to be less active than the reference compound eserine. The butyrylcholinesterase activity of 1 and 18 was one magnitude lower than that against acetylcholinesterase revealing a selective inhibitor profile.  相似文献   
114.
Growth hormone (GH) and anabolic androgenic steroids (AAS) are commonly used in sports communities. Several studies have suggested an association between GH and AAS. We have investigated the impact of GH in rats treated with nandrolone decanoate (ND). Male Wistar rats received ND (15 mg/kg) every third day during three weeks and were subsequently treated with recombinant human GH (1.0 IU/kg) for ten consecutive days. Plasma samples were collected and peripheral organs (i.e. heart, liver, testis and thymus) were dissected and weighed. Concentration of thirteen endogenous steroids was measured in the rat plasma samples using high specificity LC–MS/MS methods. Seven steroids were detected and quantified, and concentrations of estrone, testosterone, and androstenedione were significantly different among the groups, while concentrations of pregnenolone, DHEA, 17-hydroxyprogesterone and corticosterone were not altered. Administration of rhGH alone altered the plasma steroid distribution, and the results demonstrated significantly increased concentrations of plasma estrone as well as decreased concentrations of testosterone and androstenedione in the ND-treated rats. Administration of rhGH to ND-pretreated rats did not reverse the alteration of the steroid distribution induced by ND. Administration of ND decreased the weight of the thymus, and addition of rhGH did not reverse this reduction. However, rhGH administration induced an enlargement of thymus. Taken together, the plasma steroid profile differed in the four groups, i.e. control, AAS, rhGH and the combination of AAS and rhGH treatment.  相似文献   
115.
116.
117.
Although hormones are key regulators of many fitness and life history traits, the causes of individual level variation in hormones, particularly in wild systems, remain understudied. Whilst we know that androgen and glucocorticoid levels vary within and among individuals in mammalian populations, how this relates to key reproductive processes such as gestation and lactation, and their effects on a female''s measurable hormone levels are poorly understood in wild systems. Using fecal samples collected from females in a wild red deer population between 2001 and 2013, we explore how fecal androgen (FAM) and cortisol (FCM) metabolite concentrations change with age and season, and how individual differences relate to variation in reproductive state. Both FAM and FCM levels increase toward parturition, although this only affects FCM levels in older females. FCM levels are also higher when females suckle a male rather than a female calf, possibly due to the higher energetic costs of raising a son. This illustrates the importance of accounting for a female''s life history and current reproductive status, as well as temporal variation, when examining individual differences in hormone levels. We discuss these findings in relation to other studies of mammalian systems and in particular to the relatively scarce information on variation in natural levels of hormones in wild populations.  相似文献   
118.
鱼类性别决定和分化机制极为复杂,通过性腺组织切片鉴定得出黄河鲤从未分化性腺发育为Ⅱ期精巢、卵巢的时间为受精后第40天到第80天。选取一些可能参与黄河鲤性别决定分化相关的基因(amh、ar、cyp19a、cyp19b、dax1、dmrt1、er、foxl2、nobox、sox9a、sox9b、zp2)进行实时荧光定量PCR分析各个基因在受精后40d、45d、50d、55d、65d和80d的表达情况。结果显示性别决定相关基因在50d都有高表达,推测45-50 d为性别决定的关键时间。ar、amh、dax1、dmrt1、sox9a、sox9b六个基因在80d雄性表达量升高,且雄性明显高于雌性,推测这些基因参与精巢分化发育过程。cyp19a、cyp19b、foxl2、nobox、zp2五个基因在80d雌性表达升高,且高于雄性,推测其可能参与卵巢分化发育。  相似文献   
119.
BackgroundSex steroid hormones have been reported to induce inflammation causing dysregulation of cytokines in prostate cancer cells. However, the underlying epigenetic mechanism has not well been studied. The objective of this study was to evaluate the effect of sex steroid hormones on epigenetic DNA methylation changes in prostate cancer cells using a signature PCR methylation array panel that correspond to 96 genes with biological function in the human inflammatory and autoimmune signals in prostate cancer. Of the 96-gene panel, 32 genes showed at least 10% differentially methylation level in response to hormonal treatment when compared to untreated cells. Genes that were hypomethylated included CXCL12, CXCL5, CCL25, IL1F8, IL13RAI, STAT5A, CXCR4 and TLR5; and genes that were hypermethylated included ELA2, TOLLIP, LAG3, CD276 and MALT1. Quantitative RT-PCR analysis of select genes represented in a cytokine expression array panel showed inverse association between DNA methylation and gene expression for TOLLIP, CXCL5, CCL18 and IL5 genes and treatment of prostate cancer cells with 5′-aza-2′-deoxycytidine with or without trichostatin A induced up-regulation of TOLLIP expression. Further analysis of relative gene expression of matched prostate cancer tissues when compared to benign tissues from individual patients with prostate cancer showed increased and significant expression for CCL18 (2.6-fold; p < 0.001), a modest yet significant increase in IL5 expression (1.17-fold; p = 0.015), and a modest increase in CXCL5 expression (1.4-fold; p = 0.25). In conclusion, our studies demonstrate that sex steroid hormones can induce aberrant gene expression via differential methylation changes in prostate carcinogenesis.  相似文献   
120.
The study was conducted to explore the mechanisms of sex differences in the response to chronic hepatitis B(CHB) in terms of DNA methylation, SNP genotype, and gene expression. Genomic DNA was isolated from peripheral blood mononuclear cells(PBMCs) of CHB patients and healthy controls and evaluated using the Human Methylation 450 K Assay. The DNA methylation level at hg37 chromosome(CHR) X: 7810800 was further validated using pyrosequencing.SNP genotypes, VCX m RNA expression of PBMCs, and plasma VCX protein concentration were further examined using SNaPshot, RT-qPCR, and Western blot, respectively. Results showed that a total of 5529 CpG loci were differentially methylated between male and female CHB patients. DNA methylation level and CC+CT frequency at CHR X: 7810800,VCX mRNA expression of PBMCs, and plasma VCX protein concentration were higher in female than in male CHB patients. The CHR X: 7810800 locus was hypermethylated in CHB patients with CC+CT genotypes in comparison with those with the TT genotype. In cases of CC+CT genotypes, VCX mRNA expression was negatively correlated with the DNA methylation level. CHB patients with higher levels of HBV DNA, AST, and GGT or higher GPRI scores exhibited lower VCX expression. In conclusion, SNPs and DNA methylation at the CHR X: 7810800 locus cooperatively regulate VCX expression in CHB. The upregulated VCX expression in female CHB patients might represent a mechanism of protection from more severe liver dysfunction and extensive fibrosis, as observed in male CHB patients.  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