全文获取类型
收费全文 | 7940篇 |
免费 | 371篇 |
国内免费 | 12篇 |
出版年
2023年 | 40篇 |
2022年 | 43篇 |
2021年 | 89篇 |
2020年 | 58篇 |
2019年 | 77篇 |
2018年 | 245篇 |
2017年 | 210篇 |
2016年 | 240篇 |
2015年 | 209篇 |
2014年 | 224篇 |
2013年 | 396篇 |
2012年 | 615篇 |
2011年 | 861篇 |
2010年 | 461篇 |
2009年 | 218篇 |
2008年 | 543篇 |
2007年 | 505篇 |
2006年 | 449篇 |
2005年 | 444篇 |
2004年 | 361篇 |
2003年 | 338篇 |
2002年 | 231篇 |
2001年 | 96篇 |
2000年 | 190篇 |
1999年 | 100篇 |
1998年 | 74篇 |
1997年 | 44篇 |
1996年 | 52篇 |
1995年 | 36篇 |
1994年 | 31篇 |
1993年 | 32篇 |
1992年 | 41篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 41篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 26篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 29篇 |
1976年 | 29篇 |
1975年 | 19篇 |
1974年 | 22篇 |
1973年 | 19篇 |
排序方式: 共有8323条查询结果,搜索用时 906 毫秒
991.
Lajnert V Pavičić DK Gržić R Kovač Z Pahor D Kuis D Simonić-Kocijan S Antonić R Bakarčić D 《Gerodontology》2012,29(2):e674-e679
doi: 10.1111/j.1741‐2358.2011.00543.x Influences of age and maxillary anterior teeth status on patient’s satisfaction with dental appearance and tooth colour Objectives: To study the impact of age, gender, tooth colour and maxillary anterior teeth status on patient’s satisfaction with their dental appearance. Material and methods: A total of 259 Caucasian subjects participated in the study (119 men, mean age 56 years; 140 women, mean age 61 years) divided into three age groups (young <35 age; middle aged 35–54 age; old ≥55 age). Their maxillary anterior teeth status was classified into three groups: (1) natural teeth (NTG) group; (2) composite filling group (CFG) and (3) porcelain‐fused‐to‐metal fixed prosthodontic restoration group (FPDG). The participants judged appearance and tooth colour using a scale with three categories: completely dissatisfied, moderately dissatisfied and completely satisfied. Results: Almost half of the participants were completely satisfied with their dental appearance and tooth colour. Half of the ‘young’ and ‘middle‐aged’ participants with natural maxillary anterior teeth were completely satisfied and half of the ‘old’ participants were moderately satisfied with their dental appearance and tooth colour. The majority of participants with composite restorations (45–51%) were moderately satisfied with their dental appearance, one‐third of ‘young’ and ‘middle‐aged’ participants were moderately satisfied or dissatisfied with their tooth colour and more than 70% of older participants were dissatisfied with their tooth colour (p > 0.05). Conclusions: Satisfaction with the appearance of the maxillary anterior teeth differed both between individuals of different age and different dental status. 相似文献
992.
Loughran NB Hinde S McCormick-Hill S Leidal KG Bloomberg S Loughran ST O'Connor B O'Fágáin C Nauseef WM O'Connell MJ 《Molecular biology and evolution》2012,29(8):2039-2046
Myeloperoxidase (MPO) is a member of the mammalian heme peroxidase (MHP) multigene family. Whereas all MHPs oxidize specific halides to generate the corresponding hypohalous acid, MPO is unique in its capacity to oxidize chloride at physiologic pH to produce hypochlorous acid (HOCl), a potent microbicide that contributes to neutrophil-mediated host defense against infection. We have previously resolved the evolutionary relationships in this functionally diverse multigene family and predicted in silico that positive Darwinian selection played a major role in the observed functional diversities (Loughran NB, O'Connor B, O'Fagain C, O'Connell MJ. 2008. The phylogeny of the mammalian heme peroxidases and the evolution of their diverse functions. BMC Evol Biol. 8:101). In this work, we have replaced positively selected residues asparagine 496 (N496), tyrosine 500 (Y500), and leucine 504 (L504) with the amino acids present in the ancestral MHP and have examined the effects on the structure, biosynthesis, and activity of MPO. Analysis in silico predicted that N496F, Y500F, or L504T would perturb hydrogen bonding in the heme pocket of MPO and thus disrupt the structural integrity of the enzyme. Biosynthesis of the mutants stably expressed in human embryonic kidney 293 cells yielded apoproMPO, the heme-free, enzymatically inactive precursor of MPO, that failed to undergo normal maturation or proteolytic processing. As a consequence of the maturational arrest at the apoproMPO stage of development, cells expressing MPO with mutations N496F, Y500F, L504T, individually or in combination, lacked normal peroxidase or chlorinating activity. Taken together, our data provide further support for the in silico predictions of positive selection and highlight the correlation between positive selection and functional divergence. Our data demonstrate that directly probing the functional importance of positive selection can provide important insights into understanding protein evolution. 相似文献
993.
Brondello JM Prieur A Philipot D Lemaitre JM Lenaers G Piette J Dulić V 《Médecine sciences : M/S》2012,28(3):288-296
Cellular senescence is, essentially, a permanent proliferation arrest induced by various cellular stresses or inappropriate stimuli. This arrest, which is associated with dramatic changes in cell morphology, metabolism and gene expression, involves a complex signalling network aiming at stable inactivation of CDKs, major cell cycle regulators. Notably, several tumour suppressors, such as p53, pRb or p16(Ink4a), play key roles both in the initiation of the senescence program and in its maintenance, which often involves epigenetic changes. While having widely recognized roles in tumour suppression and wound healing, senescence, like the roman god Janus, recently revealed another darker face. Mostly due to altered secretion phenotype favouring inflammation, senescent cells strongly influence surrounding tissue contributing to the development of age-related pathologies, including cancer. 相似文献
994.
995.
Skarlandtová H Bičíková M Neužil P Mlček M Hrachovina V Svoboda T Medová E Kudlička J Dohnalová A Havránek S Kazihnítková H Máčová L Vařejková E Kittnar O 《Physiological research / Academia Scientiarum Bohemoslovaca》2012,61(1):25-34
Glucocorticoids (GCs) are steroid hormones produced by the adrenal cortex in reaction to stress stimuli. GCs production is not stable over a 24-hour period; the plasma concentration peaks in the morning (approximately upon awakening) and then the plasma levels decrease, reaching the nadir in the evening. In our experiments, the levels of cortisol, cortisone, DHEA and DHEAS were tested in young female pigs (n=23) during heart catheterization at two different day times (in the morning and in the afternoon). The non-parametric Mann-Whitney test for statistical analysis was used. We found only minimal statistical differences in studied markers between the morning and afternoon group (p>0.05). The absence of circadian variation in GCs levels could originate either at an early age of our experimental pigs, or in stressful conditions on the experiment day, or most likely the day before (e.g. social isolation, fasting, transport, and catheterization), respectively. We can conclude there is no difference in the stress load between morning and afternoon experiments, and therefore we can assume the stress load is not a limiting factor for the timing when catheterization should be preferably performed. 相似文献
996.
Background and Aims
In the genus Anemone two small groups of taxa occur with the highest ploidy levels 2n = 6x = 48, belonging to the closely related clades: the montane/alpine Baldensis clade and the more temperate Multifida clade. To understand the formation of polyploids within these groups, the evolution of allohexaploid A. baldensis (AABBDD, 2n = 6x = 48) from Europe and allotetraploid Anemone multifida (BBDD, 2n = 4x = 32) from America was analysed.Methods
Internal transcribed spacer and non-transcribed spacer sequences were used as molecular markers for phylogenetic analyses. Cytogenetic studies, including genomic in situ hybridization with genomic DNA of potential parental species as probe, fluorescence in situ hybridization with 5S and 18S rDNA as probes and 18S rDNA restriction analyses, were used to identify the parental origin of chromosomes and to study genomic changes following polyploidization.Key Results
This study shows that A. multifida (BBDD, 2n= 4x = 32) and A. baldensis (AABBDD, 2n = 6x = 48) are allopolyploids originating from the crosses of diploid members of the Multifida (donor of the A and B subgenomes) and Baldensis groups (donor of the D subgenome). The A and B subgenomes are closely related to the genomes of A. sylvestris, A. virginiana and A. cylindrica, indicating that these species or their progeny might be the ancestral donors of the B subgenome of A. multifida and A and B subgenomes of A. baldensis. Both polyploids have undergone genomic changes such as interchromosomal translocation affecting B and D subgenomes and changes at rDNA sites. Anemone multifida has lost the 35S rDNA loci characteristic of the maternal donor (B subgenome) and maintained only the rDNA loci of the paternal donor (D subgenome).Conclusions
It is proposed that A. multifida and A. baldensis probably had a common ancestor and their evolution was facilitated by vegetation changes during the Quaternary, resulting in their present disjunctive distribution. 相似文献997.
Anita Ljubičić Ćalušić Mladinić MarinVarnai Veda Marija Petrinec BrankoMacan Jelena Kopjar NevenkaLucić Vrdoljak Ana Želježić Davor 《Journal of thermal biology》2012
Flashover phenomenon occurs when surfaces exposed to thermal radiation reach the ignition temperature, and the fire rapidly spreads in enclosed area. Flashover training (FOT) performed by firefighters is a simulation of flashover phenomenon under controlled conditions. The study aimed to test thermal and physical strain in male firefighters and instructors attending FOT and its influence on DNA damage, exhaled breath condensate (EBC) pH, and fraction of exhaled nitric oxide (FeNO). DNA damage markers were analyzed in 51 attendees and 7 instructors, and EBC pH and FeNO in 40 respiratory healthy non-smoking subjects (34 attendees and 6 instructors).The average body temperature and pulse increase was 1.1 °C and 30 beats per minute, respectively. A prominent increase in the alkali-labile sites' level has been observed in instructors' peripheral leukocytes compared to first-time attendees (tail length p=0.050, % of DNA in tail p=0.005). FOT was related only to physiological FVC and FEV1 increase (by 4% and 2.7% on average), and FeNO dropped after the exercise by 2 ppb in comparison with basal values (P=0.034). EBC pH did not change during FOT, but FeNO was inversely correlated to EBC pH after the exercise (Spearman's rho=−0.66, P=0.013). With respect to the thermal and physical strain, FOT is considered to be a safe training procedure for healthy firefighters. The increase rate in primary DNA damage found in the instructors' peripheral leukocytes requires further examination in a larger sample size. 相似文献
998.
Alcohol consumption is traditionally part of most human cultures, and with the onset of industrial revolution it was recognized as a health and social problem. The aim of this article is to investigate cumulative incidence of alcohol consumption in Croatia. Data were obtained from the Croatian Adult health Survey in 2003 followed by 2008. The cohort consisted of 3229 participants. Questions regarding alcohol consumption were calculated into two factors describing existence or non-existence of risk behavior. Results revealed higher incidence of risk alcohol consumption in man than in women and highest in the 35-65, age group. Due to the some study limitations results might be underestimated. Present problem of alcohol is alarming, even more so, in women's population it might be only the tip of the iceberg. Cultural and regional differences should be taken into account when educational programs are constructed, especially due to the different type of alcohol consumed. 相似文献
999.
The aim of this article was to identify parameters that determinate PCS and MCS values, and analyze 5-year changes in those values according to the age, sex and geographic region. Cohort of 3229 participants was obtained from the CAHS 2003-2008. Results revealed no statistically significant differences between same age group, sex, and different region regarding PCS and MCS. When chronic conditions were in the model difference was present, PCS being more influenced by all conditions but bronchial asthma. The strongest influence comes from musculoskeletal conditions; followed by weak heart. Values for PSC and MSC decreased in 2008 compared with 2003, but only in few cases decrease was statistically significant. Values of PCS and MCS are higher in men in all regions, but they show higher variability than woman. Our results support the findings that data obtained through SF-36 could be the useful for public health interventions regarding chronic diseases. 相似文献
1000.
Milanović SM Ivanković D Uhernik AI Fister K Peternel R Vuletić S 《Collegium antropologicum》2012,36(Z1):113-116
The aim of this study was to examine the association of weight gain and life expectancy at birth in Croatia. Mean body mass index was based on the data from the Croatian Adult Health Survey 2003. Birth rate and mortality data needed for life expectancy calculation were supplied by the Central Bureau of Statistics. The results suggest that the increase in mean body mass index value (1.31 kg m(-2) for women and 1.41 kg m(-2) for men) will shorten life expectancy at birth for one year. Obesity, if unchecked, might have a negative effect on life expectancy in Croatia. Despite widespread knowledge about how to reduce the severity of the problem, observed trends in obesity in Croatia continue to worsen. These trends threaten to diminish the health and life expectancy of current and future generations. 相似文献