全文获取类型
收费全文 | 182篇 |
免费 | 14篇 |
专业分类
196篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 13篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1964年 | 1篇 |
1960年 | 1篇 |
1955年 | 1篇 |
1926年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有196条查询结果,搜索用时 15 毫秒
1.
2.
J. De Las Rivas B. Crystall P. J. Booth J. R. Durrant S. Özer G. Porter D. R. Klug J. Barber 《Photosynthesis research》1992,34(3):419-431
A Photosystem two (PS II) core preparation containing the chlorophyll a binding proteins CP 47, CP 43, D1 and D2, and the non-chlorophyll binding cytochrome-b559 and 33 kDA polypeptides, has been isolated from PS II-enriched membranes of peas using the non-ionic detergent heptylthioglucopyranoside and elevated ionic strengths. The primary radical pair state, P680+Pheo-, was studied by time-resolved absorption and fluorescence spectroscopy, under conditions where quinone reduction and water-splitting activities were inhibited. Charge recombination of the primary radical pair in PS II cores was found to have lifetimes of 17.5 ns measured by fluorescence and 21 ns measured by transient decay kinetics under anaerobic conditions. Transient absorption spectroscopy demonstrated that the activity of the particles, based on primary radical pair formation, was in excess of 70% (depending on the choice of kinetic model), while time-resolved fluorescence spectroscopy indicated that the particles were 91% active. These estimates of activity were further supported by steady-state measurements which quantified the amount of photoreducible pheophytin. It is concluded that the PS II core preparation we have isolated is ideal for studying primary radical pair formation and recombination as demonstrated by the correlation of our absorption and fluorescence transient data, which is the first of its kind to be reported in the literature for isolated PS II core complexes from higher plants.Abbreviations CP 43 and CP 47
chlorophyll binding proteins of PS II having apparent molecular weights on SDS-PAGE of 43 kDa and 47 kDa, respectively
- D1 and D2 polypeptides
PS II reaction centre polypeptides encoded by the psbA and psbD genes, respectively
- HPLC
high performance liquid chromatography
- PS II
Photosystem two
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
- P680
primary electron donor of PS II
- Pheo
phenophytin a
- SPC
single photon counting
- PBQ
phenyl-p-benzoquinone
- DPC
1,5-diphenylcarbazide
AFRC Photosynthesis Research Group, Department of Biochemistry 相似文献
3.
Estrus in a 10-yr-old brown hyena was described by monitoring urinary steroid metabolites. These studies were repeated the succeeding year and combined with ultrasonography, vaginal cytology, and laparoscopy to further aid in identifying natural and induced estrus. Collection of semen from a 14-yr-old male brown hyena was accomplished by electroejaculation. Use of frozen semen once during natural estrus and again during estrus induced with follicle stimulating hormone (FSH) did not result in pregnancy. Further studies with this animal indicate that stimulation with gonadotropin releasing hormone (GNRH), rather than FSH, may be the more appropriate treatment for stimulating ovulation in canids or related species. While this study did not result in conception, a significant step toward that end was realized by utilizing urinary estrogen to monitor the estrus cycle. 相似文献
4.
Mark A. Faist Safa Shoaee Sachetan Tuladhar George F. A. Dibb Samuel Foster Wei Gong Thomas Kirchartz Donal D. C. Bradley James R. Durrant Jenny Nelson 《Liver Transplantation》2013,3(6):744-752
The use of fullerenes with two or more adducts as acceptors has been recently shown to enhance the performance of bulk‐heterojunction solar cells using poly(3‐hexylthiophene) (P3HT) as the donor. The enhancement is caused by a substantial increase in the open‐circuit voltage due to a rise in the fullerene lowest unoccupied molecular orbital (LUMO) level when going from monoadducts to multiadducts. While the increase in the open‐circuit voltage is obtained with many different polymers, most polymers other than P3HT show a substantially reduced photocurrent when blended with fullerene multiadducts like bis‐PCBM (bis adduct of Phenyl‐C61‐butyric acid methyl ester) or the indene C60 bis‐adduct ICBA. Here we investigate the reasons for this decrease in photocurrent. We find that it can be attributed partly to a loss in charge generation efficiency that may be related to the LUMO‐LUMO and HOMO‐HOMO (highest occupied molecular orbital) offsets at the donor‐acceptor heterojunction, and partly to reduced charge carrier collection efficiencies. We show that the P3HT exhibits efficient collection due to high hole and electron mobilities with mono‐ and multiadduct fullerenes. In contrast the less crystalline polymer Poly[[9‐(1‐octylnonyl)‐9H‐carbazole‐2,7‐diyl]‐2,5‐thiophenediyl‐2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl (PCDTBT) shows inefficient charge carrier collection, assigned to low hole mobility in the polymer and low electron mobility when blended with multiadduct fullerenes. 相似文献
5.
Joel Luke Emily M. Speller Andrew Wadsworth Mark F. Wyatt Stoichko Dimitrov Harrison K. H. Lee Zhe Li Wing C. Tsoi Iain McCulloch Diego Bagnis James R. Durrant Ji‐Seon Kim 《Liver Transplantation》2019,9(15)
Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long‐lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O‐IDTBR and nonplanar O‐IDFBR. A three‐phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo‐oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3‐hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs. 相似文献
6.
M. R. Price M. Sekowski G. -Y. Yang L. G. Durrant R. A. Robins R. W. Baldwin 《Cancer immunology, immunotherapy : CII》1991,33(2):80-84
Summary A murine anti-(human gastric carcinoma) monoclonal antibody, GL-013 (IgG1), which reacts with a high-molecular-mass glycoprotein from colorectal tumour tissue [Yang and Price (1989) Anticancer Res 9: 1707], was examined for reactivity against a panel of purified and partially purified antigens associated with tumours of the gastrointestinal tract. These included carcinoembryonic antigen (CEA), normal cross-reacting antigen, Y-hapten glycoproteins, and perchloric acid extracts and glycolipid preparations from colorectal tumours. While the GL-013 antibody failed to bind to these antigens, it was found to react strongly with synthetic peptides with sequences based upon that reported for the protein core of a human gastrointestinal mucin [Barnd et al. (1989) Proc Natl Acad Sci USA 86: 7159; Gum et al. (1989) J Biol Chem 264: 6480]. In control tests, a series of other anti-(colorectal tumour) antibodies (IgG1 and IgG3), with broad reactivity towards gastrointestinal carcinomas, as well as an anti-CEA antibody, (IgG1) failed to react with the synthetic peptides. It is concluded that the anti-(gastric carcinoma) monoclonal antibody GL-013 binds to a threonine-rich peptide epitope expressed within the protein core of gastrointestinal mucins.
Present address: Cancer Research Institute, China Medical University, Shenyang, Liaoning, People's Republic of China 相似文献
7.
Steven A. Hawks Florent Deledalle Jizhong Yao Dylan G. Rebois Gang Li Jenny Nelson Yang Yang Thomas Kirchartz James R. Durrant 《Liver Transplantation》2013,3(9):1201-1209
We explore the interrelation between density of states, recombination kinetics, and device performance in efficient poly[4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl‐alt‐4‐(2‐ethylhexyloxy‐1‐one)thieno[3,4‐b]thiophene‐2,6‐diyl]:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PBDTTT‐C:PC71BM) bulk‐heterojunction organic solar cells. We modulate the active‐layer density of states by varying the polymer:fullerene composition over a small range around the ratio that leads to the maximum solar cell efficiency (50–67 wt% PC71BM). Using transient and steady‐state techniques, we find that nongeminate recombination limits the device efficiency and, moreover, that increasing the PC71BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a significant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents significant progress in understanding what limits these high‐efficiency polymer:fullerene systems. 相似文献
8.
High avidity cytotoxic T lymphocytes (CTL) are important in viral clearance and anti-tumor immunity, however, mechanisms for their optimal generation and maintenance in vivo remain unclear. Immunizing mice with an antibody-DNA vaccine encoding a single CTL epitope, induces a 100 fold higher avidity response than peptide vaccination with the identical epitope. The high avidity response is retained into memory and can be efficiently reactivated with an antibody-DNA boost. In contrast, reactivation of high avidity CTL with peptide, stimulated responses with a significant drop in avidity, suggesting loss or conversion of the high avidity CTL to lower avidity. Similarly, high avidity T cells maintained ex vivo were exquisitely sensitive to signaling with low doses of peptide (1 ng/ml) giving optimal TCR stimulation and resulting in retained avidity, proliferation and ability to kill specific targets. In contrast, high avidity T cells maintained ex vivo with supraoptimal TCR stimulation (10 μg/ml peptide) resulted in reduced avidity and failure to kill tumor cells. They also failed to proliferate, showed a significant increase in apoptosis and expressed high levels of the exhaustion marker programmed death-1 (PD-1) and low levels of the lymphocyte-activation gene 3 (LAG-3). This suggests high avidity T cells are recruited to the memory pool but can be lost by supraoptimal stimulation in vitro and in vivo. This is characterized by loss of function and an increase in cell death. The remaining CTL, exhibit low functional avidity that is reflected in reduced anti-tumor activity. This could contribute to failure of the immune system to control the growth of tumors and has implications for vaccination strategies and adoptive transfer of T cells. 相似文献
9.
Christopher J. Durrant Trevor J. C. Beebee Frank Greenaway David A. Hill 《Conservation Genetics》2009,10(2):489-496
We investigated the population genetics of seven maternity roosts of Bechstein’s bats widely distributed across the south
of England. Across all of the populations sampled, two mitochondrial DNA microsatellite loci were fixed for single haplotypes.
Genetic diversity across eight nuclear microsatellite loci was similar in all seven populations, with a mean He of 0.727. However, six of the populations showed substantial homozygote excess, with F
IS estimates greater than zero, indicative of recent inbreeding. Bottleneck tests also implied that six of the populations have
experienced recent declines. Genetic differentiation among the populations was low, with a mean intersite F
ST estimate of 0.041. There was no significant isolation by distance using allele frequency-based criteria (F
ST and genetic distances), however, a weak correlation was found using the allele size-based R
ST criterion. Assignment tests were unable to distinguish the seven sampling sites as distinct clusters. Mean intra-roost relatedness
(r) was 0.079, indicative of recent inbreeding relative to German populations. All but one of the bats had one or more half
or full siblings in its maternity roost. In addition, family relationships of individuals within a colony were significantly
commoner than family relationships among four proximal roosts <8 km apart. The results are discussed in the context of conservation
requirements for this rare British bat. 相似文献
10.
Therésa M. Jones Joanna Durrant Ellie B. Michaelides Mark P. Green 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1667)
The mechanisms underpinning the ecological impacts of the presence of artificial night lighting remain elusive. One suspected underlying cause is that the presence of light at night (LAN) supresses nocturnal production of melatonin, a key driver of biological rhythm and a potent antioxidant with a proposed role in immune function. Here, we briefly review the evidence for melatonin as the link between LAN and changes in behaviour and physiology. We then present preliminary data supporting the potential for melatonin to act as a recovery agent mitigating the negative effects of LAN in an invertebrate. Adult crickets (Teleogryllus commodus), exposed to constant illumination, were provided with dietary melatonin (concentrations: 0, 10 or 100 µg ml−1) in their drinking water. We then compared survival, lifetime fecundity and, over a 4-week period, immune function (haemocyte concentration, lysozyme-like and phenoloxidase (PO) activity). Melatonin supplementation was able only partially to mitigate the detrimental effects of LAN: it did not improve survival or fecundity or PO activity, but it had a largely dose-dependent positive effect on haemocyte concentration and lysozyme-like activity. We discuss the implications of these relationships, as well as the usefulness of invertebrates as model species for future studies that explore the effects of LAN. 相似文献