全文获取类型
收费全文 | 134篇 |
免费 | 11篇 |
出版年
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 2篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 9篇 |
2009年 | 15篇 |
2008年 | 7篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1997年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 468 毫秒
111.
THOMAS DENK FRIÐGEIR GRÍMSSON ZLATKO KVAEK 《Botanical journal of the Linnean Society. Linnean Society of London》2005,149(4):369-417
A large number of plant macrofossils from several Middle to Upper Miocene localities from Iceland have been studied. The fossil material includes four ferns and fern allies, seven conifers, and about 40 species of flowering plants. Betula islandica and Salix gruberi are described as new species. Coniferous twigs previously ascribed to the genus Sequoia are shown to belong to Cryptomeria based on macro‐morphological and epidermal features. Fossil plants from Iceland are compared with coeval fossil taxa from Europe and North America and with living plants. The main finding is that the Miocene flora of Iceland belongs to a widespread Neogene northern hemispheric floral type including plants whose representatives are restricted to East Asia, North America and to western Eurasia at the present time. Previously inferred conspicuous similarities to North American modern equivalents appear to be misleading. The type of vegetation in four plant‐bearing sedimentary formations from the late Mid Miocene to Late Miocene, the 12 Ma Brjánslækur‐Seljá Formation, the 10 Ma Tröllatunga‐Gautshamar Formation, the 9–8 Ma Skarðsströnd‐Mókollsdalur Formation, and the 7–6 Ma Hreðavatn‐Stafholt Formation, corresponds to a humid temperate broadleaved (deciduous)–coniferous mixed forest dominated by Betulaceae, Fagaceae and Acer. Changes in species composition in the sedimentary formations reflect a shift from warm temperate (Cfa climate) to cool temperate (Cfb climate) conditions from the late Mid Miocene to the latest Miocene. This shift was connected to repeated phases of extinction and colonization. Specifically, one set of thermophilic taxa including Magnolia, Liriodendron, Sassafras and Comptonia went extinct between 12 and 10 Ma, and appears to have been replaced by another set of thermophilic taxa in the 10 Ma formation (Juglandaceae aff. Pterocarya/Cyclocarya, Rhododendron ponticum type). The 9–8 and 7–6 Ma formations are characterized by taxa that migrated to Iceland from Europe, such as Fagus gussonii, Betula cristata and Pterocarya fraxinifolia type. Although there is convincing evidence that plants colonized Iceland both from North America and Europe until 12 Ma, migration in the younger formations (9–8, 7–6 Ma) is suggested to have occurred mainly from Europe. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 149 , 369–417. 相似文献
112.
David EK Ferrier 《BMC biology》2011,9(1):3
The phylum to which humans belong, Chordata, takes its name from one of the major shared derived features of the group, the
notochord. All chordates have a notochord, at least during embryogenesis, and there is little doubt about notochord homology
at the morphological level. A study in BMC Evolutionary Biology now shows that there is greater variability in the molecular genetics underlying notochord development than previously appreciated. 相似文献
113.
Available techniques of X-ray detection have been under development due to specific shortcomings such as finite lifetime, low sensitivity, and post-processing requirements. Here we report on the fabrication of an X-ray sensor based on bacteriorhodopsin (BR) with a radius of r=3mm as the sensing area on a flexible substrate. The flexible X-ray detector can be placed on the targeted area for real-time monitoring of radiation dosage. We show that BR sensor is a potential candidate for such a powerful sensing device. For this purpose, we measure the electrical current generated by the BR sensor under different radiation dosages, energies and dose rates. This averaged current is in the range of nanoampere and is proportional to the dose rate of the received X-ray. The current also increases with the increase of radiation energy. BR radiation sensor can be readily miniaturized and is relatively easy to fabricate. The capability for real-time data collection and reusability are other advantages of this radiation sensor. 相似文献
114.
J. Matthijs Biesbroek Nick A. Weaver Saima Hilal Hugo J. Kuijf Mohammad Kamran Ikram Xin Xu Boon Yeow Tan Narayanaswamy Venketasubramanian Albert Postma Geert Jan Biessels Christopher P. L. H. Chen 《PloS one》2016,11(11)
MethodsA total of 167 patients with SVD were recruited from memory clinics. Assumption-free region of interest-based analyses based on major white matter tracts and voxel-wise analyses were used to determine the association between WMH location and executive functioning, visuomotor speed and memory.ResultsRegion of interest-based analyses showed that WMHs located particularly within the anterior thalamic radiation and forceps minor were inversely associated with both executive functioning and visuomotor speed, independent of total WMH volume. Memory was significantly associated with WMH volume in the forceps minor, independent of total WMH volume. An independent assumption-free voxel-wise analysis identified strategic voxels in these same tracts. Region of interest-based analyses showed that WMH volume within the anterior thalamic radiation explained 6.8% of variance in executive functioning, compared to 3.9% for total WMH volume; WMH volume within the forceps minor explained 4.6% of variance in visuomotor speed and 4.2% of variance in memory, compared to 1.8% and 1.3% respectively for total WMH volume.ConclusionsOur findings identify the anterior thalamic radiation and forceps minor as strategic white matter tracts in which WMHs are most strongly associated with cognitive impairment in memory clinic patients with SVD. WMH volumes in individual tracts explained more variance in cognition than total WMH burden, emphasizing the importance of lesion location when addressing the functional consequences of WMHs. 相似文献
115.
Revisiting Coptotermes (Isoptera: Rhinotermitidae): a global taxonomic road map for species validity and distribution of an economically important subterranean termite genus
下载免费PDF全文
![点击此处可从《Systematic Entomology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
THOMAS CHOUVENC HOU‐FENG LI JAMES AUSTIN CHRISTIAN BORDEREAU THOMAS BOURGUIGNON STEPHEN L. CAMERON ELIANA M. CANCELLO REGINALDO CONSTANTINO ANA MARIA COSTA‐LEONARDO PAUL EGGLETON THEODORE A. EVANS BRIAN FORSCHLER J. KENNETH GRACE CLAUDIA HUSSENEDER JAN KŘEČEK CHOW‐YANG LEE TIMOTHY LEE NATHAN LO MATTHEW MESSENGER AARON MULLINS ALAIN ROBERT YVES ROISIN RUDOLF H. SCHEFFRAHN DAVID SILLAM‐DUSSÈS JAN ŠOBOTNÍK ALLEN SZALANSKI YOKO TAKEMATSU EDWARD L. VARGO AKINORI YAMADA TSUYOSHI YOSHIMURA NAN‐YAO SU 《Systematic Entomology》2016,41(2):299-306
116.
PHYTOALEXIN DEFICIENT 4 affects reactive oxygen species metabolism,cell wall and wood properties in hybrid aspen (Populus tremula L. × tremuloides)
下载免费PDF全文
![点击此处可从《Plant, cell & environment》网站下载免费的PDF全文](/ch/ext_images/free.gif)
IRENEUSZ ŚLESAK MAGDALENA SZECHYŃSKA‐HEBDA HALINA FEDAK NATALIA SIDORUK JOANNA DĄBROWSKA‐BRONK DAMIAN WITOŃ ANNA RUSACZONEK ANDRZEJ ANTCZAK MICHAŁ DROŻDŻEK BARBARA KARPIŃSKA STANISŁAW KARPIŃSKI 《Plant, cell & environment》2015,38(7):1275-1284
The PHYTOALEXIN DEFICIENT 4 (PAD4) gene in Arabidopsis thaliana (AtPAD4) is involved in the regulation of plant – pathogen interactions. The role of PAD4 in woody plants is not known; therefore, we characterized its function in hybrid aspen and its role in reactive oxygen species (ROS)‐dependent signalling and wood development. Three independent transgenic lines with different suppression levels of poplar PAD expression were generated. All these lines displayed deregulated ROS metabolism, which was manifested by an increased H2O2 level in the leaves and shoots, and higher activities of manganese superoxide dismutase (MnSOD) and catalase (CAT) in the leaves in comparison to the wild‐type plants. However, no changes in non‐photochemical quenching (NPQ) between the transgenic lines and wild type were observed in the leaves. Moreover, changes in the ROS metabolism in the pad4 transgenic lines positively correlated with wood formation. A higher rate of cell division, decreased tracheid average size and numbers, and increased cell wall thickness were observed. The results presented here suggest that the Populus tremula × tremuloides PAD gene might be involved in the regulation of cellular ROS homeostasis and in the cell division – cell death balance that is associated with wood development. 相似文献
117.
Reddy RM Yeow WS Chua A Nguyen DM Baras A Ziauddin MF Shamimi-Noori SM Maxhimer JB Schrump DS Nguyen DM 《Apoptosis : an international journal on programmed cell death》2007,12(1):55-71
Apo2L/TRAIL is actively investigated as a novel targeted agent to directly induce apoptosis of susceptible cancer cells. Apo2L/TRAIL-refractory
cells can be sensitized to the cytotoxic effect of this ligand by cytotoxic chemotherapeutics. The aim of this study was to
evaluate the in vitro tumoricidal activity of the Apo2L/TRAIL + Trichostatin A in cultured thoracic cancer cells and to elucidate the molecular
basis of the synergistic cytotoxicity of this combination. Concurrent exposure of cultured cancer cells to sublethal concentrations
of Apo2L/TRAIL and Trichostatin A resulted in profound enhancement of Apo2L/TRAIL-mediated cytotoxicity in all cell lines
regardless of their intrinsic susceptibility to this ligand. This combination was not toxic to primary normal cells. While
Apo2L/TRAIL alone or Trichostatin A alone mediated < 20% cell death, 60 to 90% of cancer cells were apoptotic following treatment
with TSA + Apo2L/TRAIL combinations. Complete translocation of Bax from the cytosol to the mitochondria compartment was mainly
observed in combination-treated cells and this was correlated with robust elevation of caspase 9 proteolytic activity indicative
of activation of the mitochondria apoptogenic effect. Profound TSA + Apo2L/TRAIL–mediated cytotoxicity and apoptosis were
completely abrogated by either Bcl2 over-expression or by the selective caspase 9 inhibitor, highlighting the essential role
of mitochondria-dependent apoptosis signaling cascade in this process. Moreover, increased caspase 8 activity observed in
cells treated with the TSA + Apo2L/TRAIL combination was completely suppressed by Bcl-2 over-expression or by the selective
caspase 9 inhibitor indicating that the elevated caspase 8 activity in combination-treated cells was secondary to a mitochondria-mediated
amplification feedback loop of caspase activation. These finding form the basis for further development of HDAC inhibitors
+ Apo2L/TRAIL combination as novel targeted therapy for thoracic malignancies.
R.M. Reddy and W.-S. Yeow contributed equally to this work.
This research was supported by the Intramural Research Program of the National Cancer Institute, NIH. 相似文献
118.
Variegin, a novel fast and tight binding thrombin inhibitor from the tropical bont tick 总被引:1,自引:0,他引:1
Koh CY Kazimirova M Trimnell A Takac P Labuda M Nuttall PA Kini RM 《The Journal of biological chemistry》2007,282(40):29101-29113
Tick saliva contains potent antihemostatic molecules that help ticks obtain their enormous blood meal during prolonged feeding. We isolated thrombin inhibitors present in the salivary gland extract from partially fed female Amblyomma variegatum, the tropical bont tick, and characterized the most potent, variegin, one of the smallest (32 residues) thrombin inhibitors found in nature. Full-length variegin and two truncated variants were chemically synthesized. Despite its small size and flexible structure, variegin binds thrombin with strong affinity (K(i) approximately 10.4 pM) and high specificity. Results using the truncated variants indicated that the seven residues at the N terminus affected the binding kinetics; when removed, the binding characteristics changed from fast to slow. Further, the thrombin active site binding moiety of variegin is in the region of residues 8-14, and the exosite-I binding moiety is within residues 15-32. Our results show that variegin is structurally and functionally similar to the rationally designed thrombin inhibitor, hirulog. However, compared with hirulog, variegin is a more potent inhibitor, and its inhibitory activity is largely retained after cleavage by thrombin. 相似文献
119.
Ibrahim Ben Daya Albert I. H. Chen Mohammad Javad Shafiee Alexander Wong John T. W. Yeow 《PloS one》2015,10(12)
3-D ultrasound imaging offers unique opportunities in the field of non destructive testing that cannot be easily found in A-mode and B-mode images. To acquire a 3-D ultrasound image without a mechanically moving transducer, a 2-D array can be used. The row column technique is preferred over a fully addressed 2-D array as it requires a significantly lower number of interconnections. Recent advances in 3-D row-column ultrasound imaging systems were largely focused on sensor design. However, these imaging systems face three intrinsic challenges that cannot be addressed by improving sensor design alone: speckle noise, sparsity of data in the imaged volume, and the spatially dependent point spread function of the imaging system. In this paper, we propose a compensated row-column ultrasound image reconstruction system using Fisher-Tippett multilayered conditional random field model. Tests carried out on both simulated and real row-column ultrasound images show the effectiveness of our proposed system as opposed to other published systems. Visual assessment of the results show our proposed system’s potential at preserving detail and reducing speckle. Quantitative analysis shows that our proposed system outperforms previously published systems when evaluated with metrics such as Peak Signal to Noise Ratio, Coefficient of Correlation, and Effective Number of Looks. These results show the potential of our proposed system as an effective tool for enhancing 3-D row-column imaging. 相似文献
120.
PHYLOGENY OF THE HEXAPODA AND OVARIAN METAMERISM 总被引:3,自引:0,他引:3