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   459篇
  免费   43篇
  2023年   3篇
  2022年   8篇
  2021年   7篇
  2020年   3篇
  2019年   4篇
  2018年   13篇
  2017年   5篇
  2016年   6篇
  2015年   26篇
  2014年   17篇
  2013年   25篇
  2012年   36篇
  2011年   38篇
  2010年   26篇
  2009年   21篇
  2008年   26篇
  2007年   24篇
  2006年   31篇
  2005年   31篇
  2004年   25篇
  2003年   11篇
  2002年   17篇
  2001年   9篇
  2000年   11篇
  1999年   3篇
  1998年   7篇
  1992年   2篇
  1991年   3篇
  1989年   2篇
  1988年   3篇
  1987年   4篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1977年   1篇
  1976年   2篇
  1975年   2篇
  1974年   1篇
  1973年   1篇
  1972年   3篇
  1971年   1篇
  1970年   6篇
  1969年   5篇
  1968年   4篇
  1967年   1篇
  1966年   3篇
  1965年   4篇
  1964年   5篇
  1960年   1篇
排序方式: 共有502条查询结果,搜索用时 15 毫秒
31.
Telocytes (TCs) are a distinct type of interstitial cells, which are featured with a small cellular body and long and thin elongations called telopodes (Tps). TCs have been widely identified in lots of tissues and organs including heart. Double staining for CD34/PDGFR‐β (Platelet‐derived growth factor receptor β) or CD34/Vimentin is considered to be critical for TC phenotyping. It has recently been proposed that CD34/PDGFR‐α (Platelet‐derived growth factor receptor α) is actually a specific marker for TCs including cardiac TCs although the direct evidence is still lacking. Here, we showed that cardiac TCs were double positive for CD34/PDGFR‐α in primary culture. CD34/PDGFR‐α positive cells (putative cardiac TCs) also existed in mice ventricle and human cardiac valves including mitral valve, tricuspid valve and aortic valve. Over 87% of cells in a TC‐enriched culture of rat cardiac interstitial cells were positive for PDGFR‐α, while CD34/PDGFR‐α double positive cells accounted for 30.25% of the whole cell population. We show that cardiac TCs are double positive for CD34/PDGFR‐α. Better understanding of the immunocytochemical phenotypes of cardiac TCs might help using cardiac TCs as a novel source in cardiac repair.  相似文献   
32.
The criteria used for defining life are influenced by various philosophical visions about life, ranging from holism to reductionism and from mechanistic-reductionism to vitalism. Using different scenarios about the origin and evolution of life as well as properties of energy-dissipative systems, artificial life simulations and basic tenets of xenobiology, guidelines can be established for formulating a definition of life. A definition of life is proposed that is parametric, non-Earth-centric, quantitative and capable of discriminating ‘living entities’ from ‘life’. Living entities are defined as self-maintained systems, capable of adaptive evolution individually, collectively or as a line of descend. Life is a broader concept indicating that the capacity to express these attributes is either virtual or actual. At least four major phase transitions can be recognized during the origin of life (reflexive activity; self-regulated homeostasis; the advent of informatons and the origin of adaptive evolution); these make the origin and evolution of early life an example of ‘punctuated gradualism’. Such phase transitions can be used to identify a boundary in early evolution where life began. This contribution identifies the step in the evolution of a dynamic system when digital control of the system’s state becomes dominant over analogical control, and genetic information is irreversibly used for adaptive evolution, as the boundary between non-living and living systems.  相似文献   
33.
34.
Mycotoxins are fungal secondary metabolites that elicit a wide spectrum of toxicological effects, including the alteration of normal immune function. In the present study we investigated the independent effect of four mycotoxins, aflatoxin B1 (AFB1), fumonisin B1 (FB1), deoxynivalenol (DON) and nivalenol (NIV), on lymphocyte proliferation using human and porcine lymphocytes. Human and porcine peripheral blood mononuclear cells and porcine splenocytes were cultured with increasing concentrations of mycotoxins for 72 hours and labelled in the last 24 hours with [methyl-3H]-thymidine. The results showed that increased concentrations of AFB1, DON and NIV affected the [methyl-3H]-thymidine cellular proliferation following mitogen stimulation in both species and cell types. Lower concentrations of mycotoxins enhanced cellular proliferation, which was more pronounced in human than in porcine cells, while higher concentrations caused a dose-dependent decrease. DON and NIV were the most potent mycotoxin in both species and both cell types. Based on the results of this in vitro study, high correlations were found between proliferation of human and porcine lymphocytes after mycotoxin exposure, especially for DON and NIV.  相似文献   
35.
Two outlines for mixed model based approaches to quantitative trait locus (QTL) mapping in existing maize hybrid selection programs are presented: a restricted maximum likelihood (REML) and a Bayesian Markov Chain Monte Carlo (MCMC) approach. The methods use the in-silico-mapping procedure developed by Parisseaux and Bernardo (2004) as a starting point. The original single-point approach is extended to a multi-point approach that facilitates interval mapping procedures. For computational and conceptual reasons, we partition the full set of relationships from founders to parents of hybrids into two types of relations by defining so-called intermediate founders. QTL effects are defined in terms of those intermediate founders. Marker based identity by descent relationships between intermediate founders define structuring matrices for the QTL effects that change along the genome. The dimension of the vector of QTL effects is reduced by the fact that there are fewer intermediate founders than parents. Furthermore, additional reduction in the number of QTL effects follows from the identification of founder groups by various algorithms. As a result, we obtain a powerful mixed model based statistical framework to identify QTLs in genetic backgrounds relevant to the elite germplasm of a commercial breeding program. The identification of such QTLs will provide the foundation for effective marker assisted and genome wide selection strategies. Analyses of an example data set show that QTLs are primarily identified in different heterotic groups and point to complementation of additive QTL effects as an important factor in hybrid performance.  相似文献   
36.
Our previous studies have shown that diabetes in the male streptozotocin (STZ)-induced diabetic rat is characterized by a decrease in circulating testosterone and concomitant increase in estradiol levels. Interestingly, this increase in estradiol levels persists even after castration, suggesting extra-testicular origins of estradiol in diabetes. The aim of the present study was to examine whether other target organs of diabetes may be sources of estradiol. The study was performed in male Sprague–Dawley non-diabetic (ND), STZ-induced diabetic (D) and STZ-induced diabetic castrated (Dcas) rats (n = 8–9/group). 14 weeks of diabetes was associated with decreased testicular (ND, 26.3 ± 4.19; D, 18.4 ± 1.54; P < 0.05), but increased renal (ND, 1.83 ± 0.92; D, 7.85 ± 1.38; P < 0.05) and ocular (D, 23.4 ± 3.66; D, 87.1 ± 28.1; P < 0.05) aromatase activity. This increase in renal (Dcas, 6.30 ± 1.25) and ocular (Dcas, 62.7 ± 11.9) aromatase activity persisted after castration. The diabetic kidney also had increased levels of tissue estrogen (ND, 0.31 ± 0.01; D, 0.51 ± 0.11; Dcas, 0.45 ± 0.08) as well as estrogen receptor alpha protein expression (ND, 0.63 ± 0.09; D, 1.62 ± 0.28; Dcas, 1.38 ± 0.20). These data suggest that in male STZ-induced diabetic rats, tissues other than the testis may become sources of estradiol. In particular, the diabetic kidney appears to produce estradiol following castration, a state that is associated with a high degree or renal injury. Overall, our data provides evidence for the extra-testicular source of estradiol that in males, through an intracrine mechanism, may contribute to the development and/or progression of end-organ damage associated with diabetes.  相似文献   
37.
38.
Ferryl (Fe(IV)=O) species are involved in key enzymatic processes with direct biomedical relevance; among others, the uncontrolled reactivities of ferryl Mb (myoglobin) and Hb (haemoglobin) have been reported to be central to the pathology of rhabdomyolysis and subarachnoid haemorrhage. Rapid-scan stopped-flow methods have been used to monitor the spectra of the ferryl species in Mb and Hb as a function of pH. The ferryl forms of both proteins display an optical transition with pK approximately 4.7, and this is assigned to protonation of the ferryl species itself. We also demonstrate for the first time a direct correlation between Hb/Mb ferryl reactivity and ferryl protonation status, simultaneously informing on chemical mechanism and toxicity and with broader biochemical implications.  相似文献   
39.
40.
Novel substituted 5,7-diaryl-2,3-dihydro-1,4-diazepines and 4,6-diaryl-2-aminopyrimidines were synthesized and tested for their antiproliferative activity. Title compounds were obtained by cyclocondensation of a substituted flavone with ethylenediamine and guanidine respectively. The cytotoxicity in vitro against various human leukemic cancer cell lines viz., Jurkat, HL60, MOLT3, NCEB-1, K562 was determined.  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