全文获取类型
收费全文 | 1214篇 |
免费 | 84篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 17篇 |
2016年 | 37篇 |
2015年 | 78篇 |
2014年 | 53篇 |
2013年 | 97篇 |
2012年 | 106篇 |
2011年 | 79篇 |
2010年 | 80篇 |
2009年 | 59篇 |
2008年 | 73篇 |
2007年 | 60篇 |
2006年 | 86篇 |
2005年 | 55篇 |
2004年 | 70篇 |
2003年 | 50篇 |
2002年 | 54篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 7篇 |
1998年 | 17篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1952年 | 1篇 |
排序方式: 共有1298条查询结果,搜索用时 31 毫秒
941.
Summary A 2.1-kb SStI fragment including the rp49 gene and the 3 end of the -serendipity gene has been cloned and sequenced in Drosophila pseudoobscura. rp49 maps at region 62 on the tip of chromosome II of this species. Both the coding and flanking regions have been aligned and compared with those of D. subobscura. There is no evidence for heterogeneity in the rate of silent substitution between the rp49 coding region and the rate of substitutions in flanking regions, the overall silent divergence per site being 0.19. Noncoding regions also differ between both species by different insertions/deletions, some of which are related to repeated sequences. The rp49 region of D. pseudoobscura shows a strong codon bias similar to those of D. subobscura and D. melanogaster. Comparison of the rates of silent (K
S
) and nonsilent (K
a
) substitutions of the rp49 gene and other genes completely sequenced in D. pseudoobscura and D. melanogaster confirms previous results indicating that rp49 is evolving slowly both at silent and nonsilent sites. According to the data for the rp49 region, D. pseudoobscura and D. subobscura lineages would have diverged some 9 Myr ago, if one assumes a divergence time of 30 Myr for the melanogaster and obscura groups.Offprint requests to: C. Segarra 相似文献
942.
Analysis of a maize α-tubulin gene promoter by transient expression and in transgenic tobacco plants 总被引:1,自引:0,他引:1
Joan Rigau Montserrat Capellades Lluis Montoliu Miguel Angel Torres Carme Romera José Antonio Martínez-Izquierdo Denis Tagu Pere Puigdomènech 《The Plant journal : for cell and molecular biology》1993,4(6):1043-1050
The pattern of expression directed by the promoter of the maize Tub α 1 gene was investigated by analysis of chloramphenicol acetyl transferase (CAT) and β-glucuronidase (GUS) activities in transient expression experiments of maize and tobacco protoplasts. The same promoter was also investigated by histochemical GUS analysis in transgenic tobacco plants containing promoter gene fusions. As determined by histochemical tests, the Tub α 1 promoter gene preferentially directs GUS expression in regenerating root tip meristems and pollen. This pattern corresponds to the distinctive features of natural expression of the gene in maize as determined by Northern analysis. However, no expression is observed in other meristematic tissues of the transgenic tobacco plants, as in shoot apex or in coleoptiles, which is weakly detected in maize. Analysis of the regulatory properties of 5' promoter deletions showed that the proximal region of the promoter, from positions −1410 or −449 to 15 bp upstream of the ATG, is sufficient to establish the qualitative pattern of expression in transgenic tobacco plants. Deletions to positions −352 or −117 abolished the expression in roots, but not in pollen, suggesting that upstream of these positions there are elements responsible for the pattern in root. Further deletions abolished all the promoter activity, suggesting that this promoter region contains the elements essential for expression in pollen. The different patterns and levels of transient and stable expression are discussed. 相似文献
943.
944.
Montserrat Capellades Raoul Lemeur Pierre Debergh 《Plant Cell, Tissue and Organ Culture》1991,25(1):21-26
Shootlets of Rosa multiflora L. cv. Montse were cultured in vitro with four different levels of sucrose (0, 1, 3 and 5%). Chloroplasts of shootlets grown in a medium without sucrose contained numerous, large plastoglobuli and were lacking in starch granules. The size and number of starch granules increased with the level of sucrose in the culture medium. Starch content in leaves of shootlets grown with 5% sucrose was higher (ca 1, 3%) than those grown with 3% (ca 0, 45%) and 1% sucrose (ca 0, 27%). Starch might be used by the in vitro shootlets during the acclimation period.Abbreviations BA
benzyladenine
- Pi
orthophosphate
- S
sucrose
- Rubisco
ribulose 1,5-bisphosphate carboxylase
- TEM
transmission electron microscopy 相似文献
945.
946.
AbstractCarnivores are the main biological agents identified in the Upper Pleistocene assemblage of Cova del Coll Verdaguer (NE Iberian Peninsula). At the site, ungulate bones were primarily accumulated and modified by hyenas, as shown by partly digested bones, coprolites and the pattern of damage on bones. However, other small- to medium-sized carnivores seemed to be involved in the accumulation, owing primarily to the presence of their bones and coprolites. Finally, other carnivores, including the brown bear, used the cave to hibernate and for birthing cubs. The combination of zooarchaeological and taphonomic studies, together with previous coprogenic analyses, at the site indicates that it is only by using these combined approaches that it is possible to identify the majority of the agents involved in an accumulation. 相似文献
947.
Lizet Aguirre-Güitrón Montserrat Calderón-Santoyo Rosa Isela Ortiz-Basurto Pedro Ulises Bautista-Rosales 《Biocontrol Science and Technology》2018,28(6):574-590
In this study, conditions of the spray-drying process of Meyerozyma caribbica were optimised using response surface methodology (RSM). The effect of three parameters (protective agent, inlet air temperature and protective agent concentration) on the cell viability of Meyerozyma caribbica was evaluated. Each parameter was evaluated at three levels. All of the evaluated factors presented an effect on the viability of the control agent. According to RSM, optimal conditions include the use of trehalose with a concentration of 7.75% (w/v) and inlet air temperature of 112.5°C. The validation of the optimal spray-drying conditions allows obtaining a formulation of M. caribbica with 95.41?±?0.93% viability, 5?±?0.37% humidity and aw of 0.33?±?0.11. Storage for six months at 4°C presented a 5% loss in cell viability. 相似文献
948.
949.
Montserrat Lázaro del Nogal Cesareo Férnandez Paloma Serrano Andrés Santiago Patricia Villavicencio Teresa Martin 《Revista espa?ola de geriatría y gerontología》2018,53(1):15-18
Objectives
The Hospital Clínico San Carlos Committee against violence established a protocol in 2012 in order to detect and follow-up violence against elderly persons. This article presents the experience after 3 years of its introduction, as well as an analysis comparing the differences between those younger and older than 65 years of age.Material and methods
All cases were collected during years 2013, 2014, and 2015, and were divided into two groups, A and B, according to age, younger or older than 65 years. Parameters studied were: gender, place of detection (emergency department, during hospital admission, or outpatient clinics), type of professional worker who detected each case (social workers, nurses, or physicians), previous history of violence, type of aggression (physical, psychological, financial), institutional procedures once aggression was confirmed, and deaths after one year of follow-up. The SPPS v.18.0 package was used for the statistical analysis.Results
A total of 172 cases were detected, of which 140 of them were included in group A (< 65 years), and 32 in group B (> 65 years, 22.8%). Gender: Group A: women: 93.5%. Group B: women: 78.1% (P = .014). Registration site: Group A: emergency department: 90.7%, hospital wards: 6.4%, outpatient wards: 3.0. Group B: emergency department: 65.6%, hospital wards: 31.6%, outpatient wards: 2.8% (P = .001). Notification: Group A: social worker: 25%, physician: 67.8%, nurse: 6.4%. Group B: social worker: 65.2%, physician: 28.1%, nurse: 6.2% (P < .001). Previous violence history: Group A: 62.1%. Group B: 68.7%. Type of abuse: Group A: physical: 56.4%, psychological: 2.8%, physical + psychological: 30.4%, physical + psychological + economic: 10.1%. Group B: physical: 31.1%, psychological: 5.1%, neglect: 18.7%, physical + psychological: 10.1, physical + psychological + economic: 9.8, economic: 25.1 (P < .0001). Resources employed and follow-up: Injuries: Group A: 63.5%. Group B: 31.2% (P = .001). Judicial protection measures: Group A: 12.8. Group B: 15.6 (P = .773). Removal order: Group A: 2.1. Group B: 6.25 (P = .235). More than one-third of patients in group B, and none of the patients in group A, died in the year of follow-up.Conclusions
There are more problems detected in the Emergency Department. There is a history of previous violence in more than half of the cases in both age groups. The profile of the victim is an elderly woman with significant physical and cognitive impairment. Economic abuse and neglect are more frequent in the elderly population. In our series, more than one-third of elderly patients who are victims of ill-treatment die each year. The hospital registry is fundamental for the detection and follow-up of abuse in the elderly. 相似文献950.
Molecular characteristics of a deficient pyrimidine 5'-nucleotidase (P5N) were studied in a partially purified red cell enzyme extract. The results showed a high Michaelis constant for uridine 5'-monophosphate, an acidic shift of the optimum pH and normal heat stability. Enzyme electrophoresis using a starch gel and histidine-citrate buffer pH 7.0 showed a single band with identical mobility to that of the 'minor' band of normal enzyme. This electrophoretic pattern supports the hypothesis that P5N deficiency is, at least in some cases, a consequence of the absence of a 'major' isoenzymatic band characteristically present in normal enzyme. 相似文献