全文获取类型
收费全文 | 1226篇 |
免费 | 129篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 34篇 |
2015年 | 45篇 |
2014年 | 48篇 |
2013年 | 49篇 |
2012年 | 69篇 |
2011年 | 66篇 |
2010年 | 56篇 |
2009年 | 38篇 |
2008年 | 69篇 |
2007年 | 52篇 |
2006年 | 44篇 |
2005年 | 49篇 |
2004年 | 40篇 |
2003年 | 39篇 |
2002年 | 41篇 |
2001年 | 38篇 |
2000年 | 41篇 |
1999年 | 45篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 29篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 20篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有1355条查询结果,搜索用时 203 毫秒
61.
Summary A (13q21q) translocation was found in an infant with Down's syndrome. The 17-year-old mother and the grandmother carried the translocation 45,XX,t(13;21)(p12;q11). The great grandparents had normal karyotypes. Fluorescence marker studies suggested that the translocation originated in the great grandmother. The hypothesis was supported by satellite association studies which showed a significant excess of 13–21 and 13–15 associations in the great grandmother. 相似文献
62.
Renal reabsorption of urea was studied in 8 9-month old reindeer calves fed low protein (19–34 g crude protein, mostly lichens) and high protein (68–69 g crude protein, lichens + soybean meal) diets. Low protein diets fed for a 3-month period resulted in an average renal reabsorption of 93% of the filtered urea, while only 50 % was reabsorbed on the high protein ration. It was calculated that if the reabsorbed urea was used completely for protein synthesis in the rumen, 4 g crude protein could be made daily in the lichen fed animals. This amount would be a very significant contribution to the nitrogen economy of animals which are usually in a negative nitrogen balance when lichens are the main food consumed. 相似文献
63.
A translocation of a part of the long arm of a chromosome No. 1 onto the long arm of a chromosome No. 6 was observed in a 2 1/2-year-old boy with mental retardation, harelip, cleft palate and congenital glaucoma. Different banding methods revealed that the translocation t(1;6)(q23;q27) apparently was balanced. The conncection between the patients' symptoms and the chromosomal rearrangement might be fortuitous or produced by the chromosome aberration. 相似文献
64.
Roger Hillson Joel D. Alejandre Kathryn H. Jacobsen Rashid Ansumana Alfred S. Bockarie Umaru Bangura Joseph M. Lamin Anthony P. Malanoski David A. Stenger 《PloS one》2014,9(11)
This study demonstrates the use of bootstrap methods to estimate the total population of urban and periurban areas using satellite imagery and limited survey data. We conducted complete household surveys in 20 neighborhoods in the city of Bo, Sierra Leone, which collectively were home to 25,954 persons living in 1,979 residential structures. For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images. We used bootstrap statistical methods to estimate the total population of the pooled sections, including the associated uncertainty intervals, as a function of sample size. Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size. We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs. 相似文献
65.
Rebecca E. Williams Lisa Cottrell Matthew Jacobsen Lasantha R. Bandara Mike D. Kelly Sandy Kennedy 《Biomarkers》2013,18(6):472-490
N-Phenylanthranilic acid (NPAA) causes renal papillary necrosis (RPN) in the rat following repeated oral dosing. Non-invasive early detection of RPN is difficult, but a number of potential biomarkers have been investigated, including phospholipid and uronic acid excretion. This study used 1H-nuclear magnetic resonance (NMR) spectroscopic analysis of urine to investigate urinary metabolic perturbations occurring in the rat following exposure to NPAA. Male Alderley Park rats received NPAA (300, 500 or 700?mg?kg?1?day?1 orally) for 7?days, and urine was collected on days 7–8, 14–15, 21–22 and 28–29. In a separate study, urine was collected on days 1–2, 3–4, 5–6 and 7–8 from rats receiving 500?mg?kg?1?day?1. Samples were analysed by 1H NMR spectroscopy combined with multivariate data analysis and clinical chemistry. Histopathology and clinical chemistry analysis of terminal blood samples was carried out following termination on days 4, 6, 8 and 29 (4?week time course) and days 2, 4, 6 and 8 (8?day study). Urine analysis revealed a marked, though variable, excretion of β-hydroxybutyrate, acetoacetate and acetone (ketone bodies) seen on days 3–4, 5–6 and 7–8 of the study. It is postulated that the ketonuria might be secondary to an alteration in fatty acid metabolism due to inhibition of prostaglandin synthesis. In addition, an elevation in urinary ascorbate was observed during the first 8?days of the study. Ascorbate is considered to be a biomarker of hepatic response, probably reflecting an increased hepatic activity due to glucuronidation of NPAA. 相似文献
66.
67.
Differences in acidity of apples are probably mainly caused by a malic acid transporter gene on LG16
Sabaz Ali Khan Jules Beekwilder Jan G. Schaart Roland Mumm Jose Miguel Soriano Evert Jacobsen Henk J. Schouten 《Tree Genetics & Genomes》2013,9(2):475-487
Acidity has profound effects on the taste of apples (Malus × domestica). Malic acid is the predominant organic acid in apples. Differences in malic acid content are caused by differences in accumulation of malic acid in the vacuole. This accumulation may be caused by a gene that is responsible for transport of malic acid from the cytosol into the vacuole. Here, we provide evidence that a malic acid transporter gene at the top of chromosome 16 caused significant differences in malic acid concentration and pH of apples. The pH of apples in a segregating F1 population was mapped and at the pH locus (named henceforth Ma locus for malic acid), two putative malic acid transporter genes were detected. These genes show high homology to AtALMT genes that code for malate channel proteins located in vacuolar membrane in Arabidopsis. The expression of one of the candidate genes (Ma1) cosegregated clearly with malic acid content. The inheritance of at least one dominant allele of this gene sufficed for an increased expression level that likely caused the observed threefold increase of the malic acid concentration and the reduction of the pH from 4 to 3 in mature apples, compared to the presence of the recessive, lowly expressed allele only. Our results show that differences in fruit acidity were probably caused by differences in expression levels of alleles of a malic acid transporter gene. 相似文献
68.
Anne Thoustrup Saber Jacob Stuart Lamson Nicklas Raun Jacobsen Gitte Ravn-Haren Karin S?rig Hougaard Allen Njimeri Nyendi Pia Wahlberg Anne Mette Madsen Petra Jackson H?kan Wallin Ulla Vogel 《PloS one》2013,8(7)
Background
Particulate air pollution is associated with cardiovascular disease. Acute phase response is causally linked to cardiovascular disease. Here, we propose that particle-induced pulmonary acute phase response provides an underlying mechanism for particle-induced cardiovascular risk.Methods
We analysed the mRNA expression of Serum Amyloid A (Saa3) in lung tissue from female C57BL/6J mice exposed to different particles including nanomaterials (carbon black and titanium dioxide nanoparticles, multi- and single walled carbon nanotubes), diesel exhaust particles and airborne dust collected at a biofuel plant. Mice were exposed to single or multiple doses of particles by inhalation or intratracheal instillation and pulmonary mRNA expression of Saa3 was determined at different time points of up to 4 weeks after exposure. Also hepatic mRNA expression of Saa3, SAA3 protein levels in broncheoalveolar lavage fluid and in plasma and high density lipoprotein levels in plasma were determined in mice exposed to multiwalled carbon nanotubes.Results
Pulmonary exposure to particles strongly increased Saa3 mRNA levels in lung tissue and elevated SAA3 protein levels in broncheoalveolar lavage fluid and plasma, whereas hepatic Saa3 levels were much less affected. Pulmonary Saa3 expression correlated with the number of neutrophils in BAL across different dosing regimens, doses and time points.Conclusions
Pulmonary acute phase response may constitute a direct link between particle inhalation and risk of cardiovascular disease. We propose that the particle-induced pulmonary acute phase response may predict risk for cardiovascular disease. 相似文献69.
70.
Jef Faridi Katrine E. Nielsen Paul C. Stein Jens Peter Jacobsen 《Journal of biomolecular structure & dynamics》2013,31(2):321-332
Abstract We have used one and two dimensional exchange 1H NMR spectroscopy to characterize the dynamics of the binding of a homodimeric thiazole orange dye, 1,1′-(4,4,8,8-tetramethyl-4,8-diaza-undecamethylene)-bis-4-(3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene)-quinolinium tetraiodide (TOTO), to double stranded DNA (dsDNA). The double stranded oligonucleotides used were d-(CGCTAGCG)2 ( 1 ) and d(CGCTAGCTAGCG)2 ( 2 ). TOTO binds preferentially to the (5′-CTAG-3′)2 sites and forms mixtures of 1:1 and 1:2 dsDNA-TOTO complexes with 2 in ratios dependent on the relative amount of TOTO and the oligonucleotide in the sample. The dynamic exchange between preferential binding sites in the case of a 2:1 1 -TOTO mixture is an intermolecular exchange process between two binding sites on different oligonucleotides. In the case of the 1:1 2 -TOTO complex an intramolecular exchange process occur between two different binding sites on the same strand. Both processes were studied. The results demonstrate the ability of TOTO to migrate along a dsDNA strand in an intramolecular exchange process. The migration process (“creeping”) along the DNA strand is 6 times faster than the rate of intermolecular exchange between sites in two different oligonucleotides. 相似文献