全文获取类型
收费全文 | 503篇 |
免费 | 37篇 |
出版年
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 21篇 |
2013年 | 16篇 |
2012年 | 17篇 |
2011年 | 27篇 |
2010年 | 18篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 30篇 |
2006年 | 33篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有540条查询结果,搜索用时 62 毫秒
471.
Host specificity testing to predict host range is one of the key steps to predicting the risk a biological control agent will present to non-target organisms in the new environment. When host specificity testing data contain discrepancies, or unacceptable levels of uncertainty, it can be difficult for decision-makers to adequately address this uncertainty. To better understand the uncertainty in host specificity testing, we used a range of statistical tools to examine a data set associated with the leaf weevil Cleopus japonicus (Curculionidae), a biological control agent for the weed Buddleja davidii (Buddlejaceae) in New Zealand. Significant uncertainty arose during the early stages of host specificity testing when one C. japonicus larva reared to pupation on a culturally important native plant. Further trials were conducted to evaluate the suitability of C. japonicus as a biological control agent, and despite the uncertainty, C. japonicus was released in New Zealand in 2006, and has since established populations at each release site. However, the possibility of larvae completing their life cycle on the native plant initiated this evaluation of the statistics associated with testing biological control agents. We present results from analyses of the C. japonicus survival data using confidence intervals, equivalence testing, power analyses and survival curves to highlight the appropriateness of each of these tools for interpreting host specificity tests in biological control. 相似文献
472.
Krupa JC Shaya D Chi L Linhardt RJ Cygler M Withers SG Mort JS 《Analytical biochemistry》2007,361(2):218-225
A rapid, continuous, and convenient three-enzyme coupled UV absorption assay was developed to quantitate the glucuronic acid and N-acetylglucosamine transferase activities of hyaluronan synthase from Pasteurella multocida (PmHAS). Activity was measured by coupling the UDP produced from the PmHAS-catalyzed transfer of UDP-GlcNAc and UDP-GlcUA to a hyaluronic acid tetrasaccharide primer with the oxidation of NADH. Using a fluorescently labeled primer, the products were characterized by gel electrophoresis. Our results show that a truncated soluble form of recombinant PmHAS (residues 1-703) can catalyze the glycosyl transfers in a time- and concentration-dependent manner. The assay can be used to determine kinetic parameters, inhibition constants, and mechanistic aspects of this enzyme. In addition, it can be used to quantify PmHAS during purification of the enzyme from culture media. 相似文献
473.
Neganova I Al-Qassab H Heffron H Selman C Choudhury AI Lingard SJ Diakonov I Patterson M Ghatei M Bloom SR Franks S Huhtaniemi I Hardy K Withers DJ 《Biology of reproduction》2007,76(6):1045-1053
Insulin receptor signaling regulates female reproductive function acting in the central nervous system and ovary. Female mice that globally lack insulin receptor substrate (IRS) 2, which is a key mediator of insulin receptor action, are infertile with defects in hypothalamic and ovarian functions. To unravel the tissue-specific roles of IRS2, we examined reproductive function in female mice that lack Irs2 only in the neurons. Surprisingly, these animals had minimal defects in pituitary and ovarian hormone levels, ovarian anatomy and function, and breeding performance, which indicates that the central nervous system IRS2 is not an obligatory signaling component for the regulation of reproductive function. Therefore, we undertook a detailed analysis of ovarian function in a novel Irs2 global null mouse line. Comparative morphometric analysis showed reduced follicle size, increased numbers of atretic follicles, as well as impaired oocyte growth and antral cavity development in Irs2 null ovaries. Granulosa cell proliferation was also defective in the Irs2 null ovaries. Furthermore, the insulin- and eCG-stimulated phosphoinositide-3-OH kinase signaling events, which included phosphorylation of Akt/protein kinase B and glycogen synthase kinase 3-beta, were impaired, whereas mitogen-activated protein kinase signaling was preserved in Irs2 null ovaries. These abnormalities were associated with reduced expression of cyclin D2 and increased CDKN1B levels, which indicates dysregulation of key components of the cell cycle apparatus implicated in ovarian function. Our data suggest that ovarian rather than central nervous system IRS2 signaling is important in the regulation of female reproductive function. 相似文献
474.
To investigate patterns of thermoregulation in free-ranging and captive southern brown bandicoots Isoodon obesulus, we measured abdominal body temperature (Tb) of five free-ranging bandicoots over 42 days using implanted data loggers and Tb of three captive bandicoots over 3 months using implanted temperature-sensitive radio transmitters. Bandicoots in the wild had a mean Tb of 36.5±1.0 °C (range 33.4–39.8 °C) and showed a pronounced nychthemeral pattern with two distinct temperature phases. Tb increased at 13:30±2.6 h each day and remained high for 10.65±2.07 h, suggesting a crepuscular and early evening activity pattern. Daily Tb variation of I. obesulus would save considerable energy by reducing daytime thermoregulatory costs in the wild. Captive bandicoots had a similar mean body temperature (36.9±0.2°C) and range (33.0–39.9°C) as free-ranging bandicoots. However, the nychthemeral Tb pattern of captive bandicoots was different from free-ranging bandicoots, with a less pronounced daily cycle and the nocturnal rise in Tb occurring mainly at sunset and the daily decline occurring mainly at dawn. 相似文献
475.
Larcombe AN Withers PC 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(2):229-236
Thermoneutral metabolic and ventilatory parameters were measured every 3 months over 2 years for southern brown bandicoots
held in captivity, and from a nearby reserve. Captive bandicoots were 130 g (9.9%) heavier than wild bandicoots. Long-term
captivity had no effect on body temperature, basal metabolic rate (oxygen consumption), thermal conductance or respiratory
ventilation, but there was an effect on carbon dioxide production, respiratory exchange ratio and total evaporative water
loss (values were between 15 and 25% higher for captive than for wild bandicoots). Diet may be influencing these aspects of
captive bandicoot physiology; the diet of captive bandicoots would be considerably different to that of wild bandicoots. Water
availability seems to have a minimal effect. This study has important implications regarding physiological measurement for
captive and wild mammals. For bandicoots at least, captive animals are equivalent to wild animals for some physiological parameters
at thermoneutrality (body temperature, resting metabolic rate and thermal conductance), but not others. 相似文献
476.
Biosynthesis and engineering of isoprenoid small molecules 总被引:9,自引:0,他引:9
Isoprenoid secondary metabolites are a rich source of commercial products that have not been fully explored. At present, there
are isoprenoid products used in cancer therapy, the treatment of infectious diseases, and crop protection. All isoprenoids
share universal prenyl diphosphate precursors synthesized via two distinct pathways. From these universal precursors, the
biosynthetic pathways to specific isoprenoids diverge resulting in a staggering array of products. Taking advantage of this
diversity has been the focus of much effort in metabolic engineering heterologous hosts. In addition, the engineering of the
mevalonate pathway has increased levels of the universal precursors available for heterologous production. Finally, we will
describe the efforts to produce to commercial terpenoids, paclitaxel and artemisinin. 相似文献
477.
Toni M. Withers Geoff R. Allen Christine L. Todoroki Andrew R. Pugh Belinda A. Gresham 《Entomologia Experimentalis et Applicata》2021,169(1):97-110
The solitary larval endoparasitoid Eadya daenerys Ridenbaugh (Hymenoptera: Braconidae) is a proposed biocontrol agent of Paropsis charybdis Stål (Coleoptera: Chrysomelidae, Chrysomelinae), a pest of eucalypts in New Zealand. Eadya daenerys oviposition behaviour was examined in two assay types during host range testing, with the aim of improving ecological host range prediction. No‐choice sequential and two‐choice behavioural observations were undertaken against nine closely related species of New Zealand non‐target beetle larvae, including a native beetle, introduced weed biocontrol agents, and invasive paropsine beetles. No behavioural measure was significantly different between no‐choice and two‐choice tests. In sequential no‐choice assays the order of first presentation (target–non‐target) had no significant effect on the median number of attacks or the attack rate while on the plant. Beetle species was the most important factor. Parasitoids expressed significantly lower on‐plant attack rates against non‐targets compared to target P. charybdis larvae. The median number of attacks was always higher towards target larvae than towards non‐target larvae, except for the phylogenetically closest related non‐target Trachymela sloanei (Blackburn) (Coleoptera: Chrysomelidae, Chrysomelinae). Most non‐target larvae were disregarded upon contact, which suggests that the infrequent attack behaviour observed by two individual E. daenerys against Allocharis nr. tarsalis larvae in two‐choice tests and the frass of Chrysolina abchasica (Weise) was probably abnormal host selection behaviour. Results indicate that E. daenerys is unlikely to attack non‐target species apart from Eucalyptus‐feeding invasive paropsines (Chrysomelinae). Non‐lethal negative impacts upon less preferred non‐target larvae are possible if E. daenerys does attack them in the field; however, this is likely to be rare. 相似文献
478.
479.
Batteries: Lithiation‐Induced Dilation Mapping in a Lithium‐Ion Battery Electrode by 3D X‐Ray Microscopy and Digital Volume Correlation (Adv. Energy Mater. 4/2014)
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
480.
Pseudomonas aeruginosa is a Gram-negative, environmental bacterium with versatile metabolic capabilities. P. aeruginosa is an opportunistic bacterial pathogen which establishes chronic pulmonary infections in patients with cystic fibrosis (CF). The overproduction of a capsular polysaccharide called alginate, also known as mucoidy, promotes the formation of mucoid biofilms which are more resistant than planktonic cells to antibiotic chemotherapy and host defenses. Additionally, the conversion from the nonmucoid to mucoid phenotype is a clinical marker for the onset of chronic infection in CF. Alginate overproduction by P. aeruginosa is an endergonic process which heavily taxes cellular energy. Therefore, alginate production is highly regulated in P. aeruginosa. To better understand alginate regulation, we describe a protocol using the mini-himar1 transposon mutagenesis for the identification of novel alginate regulators in a prototypic strain PAO1. The procedure consists of two basic steps. First, we transferred the mini-himar1 transposon (pFAC) from host E. coli SM10/λpir into recipient P. aeruginosa PAO1 via biparental conjugation to create a high-density insertion mutant library, which were selected on Pseudomonas isolation agar plates supplemented with gentamycin. Secondly, we screened and isolated the mucoid colonies to map the insertion site through inverse PCR using DNA primers pointing outward from the gentamycin cassette and DNA sequencing. Using this protocol, we have identified two novel alginate regulators, mucE (PA4033) and kinB (PA5484), in strain PAO1 with a wild-type mucA encoding the anti-sigma factor MucA for the master alginate regulator AlgU (AlgT, σ22). This high-throughput mutagenesis protocol can be modified for the identification of other virulence-related genes causing change in colony morphology. 相似文献