全文获取类型
收费全文 | 62篇 |
免费 | 0篇 |
专业分类
系统科学 | 1篇 |
理论与方法论 | 2篇 |
现状及发展 | 26篇 |
研究方法 | 3篇 |
综合类 | 30篇 |
出版年
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 1篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1970年 | 4篇 |
1966年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有62条查询结果,搜索用时 375 毫秒
21.
22.
23.
Noeggerathiales are an extinct group of sporebearing plants of uncertain systematic position that are known from Carboniferous and Permian age Euramerican and Cathaysian floras that occurred in presentday Europe, North America, and East Asia. The order Noeggerathiales includes over 50 species of more than 20 fossil genera, but their paleoecology is not well understood yet. Previously this group had been found only in extrabasinal floras or those inhabiting clastic wetlands. Noeggerathiales have never been recorded in coal ball floras. Thus, it is up to now uncertain whether this group has contributed to the formation of coal. Recent investigations of an Early Permian peatforming flora of the Taiyuan Formation near Wuda, Inner Mongolia, which was preserved in a volcanic ash fall has provided evidence that noeggerathialean plants not only existed in the peatforming vegetation but could even be the dominant group in some areas of the coal swamp. The Noeggerathiales in this particular peatforming forest include Tingia unita, Paratingia wudensis, and a new species of Paratingia. Exceptionally well-preserved specimens indicate that these noeggerathialean plants are small trees with a canopy of compound leaves and strobili near the top of an unbranched (monocaulous) stem. 相似文献
24.
Activation of nitric oxide synthase in endothelial cells by Akt-dependent phosphorylation. 总被引:97,自引:0,他引:97
Nitric oxide (NO) produced by the endothelial NO synthase (eNOS) is a fundamental determinant of cardiovascular homesotasis: it regulates systemic blood pressure, vascular remodelling and angiogenesis. Physiologically, the most important stimulus for the continuous formation of NO is the viscous drag (shear stress) generated by the streaming blood on the endothelial layer. Although shear-stress-mediated phosphorylation of eNOS is thought to regulate enzyme activity, the mechanism of activation of eNOS is not yet known. Here we demonstrate that the serine/threonine protein kinase Akt/PKB mediates the activation of eNOS, leading to increased NO production. Inhibition of the phosphatidylinositol-3-OH kinase/Akt pathway or mutation of the Akt site on eNOS protein (at serine 1177) attenuates the serine phosphorylation and prevents the activation of eNOS. Mimicking the phosphorylation of Ser 1177 directly enhances enzyme activity and alters the sensitivity of the enzyme to Ca2+, rendering its activity maximal at sub-physiological concentrations of Ca2+. Thus, phosphorylation of eNOS by Akt represents a novel Ca2+-independent regulatory mechanism for activation of eNOS. 相似文献
25.
Hermann JC Marti-Arbona R Fedorov AA Fedorov E Almo SC Shoichet BK Raushel FM 《Nature》2007,448(7155):775-779
With many genomes sequenced, a pressing challenge in biology is predicting the function of the proteins that the genes encode. When proteins are unrelated to others of known activity, bioinformatics inference for function becomes problematic. It would thus be useful to interrogate protein structures for function directly. Here, we predict the function of an enzyme of unknown activity, Tm0936 from Thermotoga maritima, by docking high-energy intermediate forms of thousands of candidate metabolites. The docking hit list was dominated by adenine analogues, which appeared to undergo C6-deamination. Four of these, including 5-methylthioadenosine and S-adenosylhomocysteine (SAH), were tested as substrates, and three had substantial catalytic rate constants (10(5) M(-1 )s(-1)). The X-ray crystal structure of the complex between Tm0936 and the product resulting from the deamination of SAH, S-inosylhomocysteine, was determined, and it corresponded closely to the predicted structure. The deaminated products can be further metabolized by T. maritima in a previously uncharacterized SAH degradation pathway. Structure-based docking with high-energy forms of potential substrates may be a useful tool to annotate enzymes for function. 相似文献
26.
Lisa Seipold Hermann Altmeppen Tomas Koudelka Andreas Tholey Petr Kasparek Radislav Sedlacek Michaela Schweizer Julia Bär Marina Mikhaylova Markus Glatzel Paul Saftig 《Cellular and molecular life sciences : CMLS》2018,75(17):3251-3267
A disintegrin and metalloproteinase 10 (ADAM10) plays a major role in the ectodomain shedding of important surface molecules with physiological and pathological relevance including the amyloid precursor protein (APP), the cellular prion protein, and different cadherins. Despite its therapeutic potential, there is still a considerable lack of knowledge how this protease is regulated. We have previously identified tetraspanin15 (Tspan15) as a member of the TspanC8 family to specifically associate with ADAM10. Cell-based overexpression experiments revealed that this binding affected the maturation process and surface expression of the protease. Our current study shows that Tspan15 is abundantly expressed in mouse brain, where it specifically interacts with endogenous ADAM10. Tspan15 knockout mice did not reveal an overt phenotype but showed a pronounced decrease of the active and mature form of ADAM10, an effect which augmented with aging. The decreased expression of active ADAM10 correlated with an age-dependent reduced shedding of neuronal (N)-cadherin and the cellular prion protein. APP α-secretase cleavage and the expression of Notch-dependent genes were not affected by the loss of Tspan15, which is consistent with the hypothesis that different TspanC8s cause ADAM10 to preferentially cleave particular substrates. Analyzing spine morphology revealed no obvious differences between Tspan15 knockout and wild-type mice. However, Tspan15 expression was elevated in brains of an Alzheimer’s disease mouse model and of patients, suggesting that upregulation of Tspan15 expression reflects a cellular response in a disease state. In conclusion, our data show that Tspan15 and most likely also other members of the TspanC8 family are central modulators of ADAM10-mediated ectodomain shedding in vivo. 相似文献
27.
Aharonian F Akhperjanian AG Bazer-Bachi AR Beilicke M Benbow W Berge D Bernlöhr K Boisson C Bolz O Borrel V Braun I Breitling F Brown AM Chadwick PM Chounet LM Cornils R Costamante L Degrange B Dickinson HJ Djannati-Ataï A Drury LO Dubus G Emmanoulopoulos D Espigat P Feinstein F Fontaine G Fuchs Y Funk S Gallant YA Giebels B Gillessen S Glicenstein JF Goret P Hadjichristidis C Hauser D Hauser M Heinzelmann G Henri G Hermann G Hinton JA Hofmann W Holleran M Horns D Jacholkowska A de Jager OC 《Nature》2006,440(7087):1018-1021
The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought. 相似文献
28.
Eva C. Schwarz Christina Backes Arne Knörck Nicole Ludwig Petra Leidinger Cora Hoxha Gertrud Schwär Thomas Grossmann Sabine C. Müller Martin Hart Jan Haas Valentina Galata Isabelle Müller Tobias Fehlmann Hermann Eichler Andre Franke Benjamin Meder Eckart Meese Markus Hoth Andreas Keller 《Cellular and molecular life sciences : CMLS》2016,73(16):3169-3181
29.
30.
Hermann G. W. Burchard 《Foundations of Science》2011,16(1):67-99
Impressions, energy radiated by phenomena in the momentary environmental scene, enter sensory neurons, creating in afferent
nerves a data stream. Following Kant, by our inner sense the mind perceives its own thoughts as it ties together sense data
into an internalized scene. The mind, residing in the brain, logically a Language Machine, processes and stores items as coded
grammatical entities. Kantian synthetic unity in the linguistic brain is able to deliver our experience of the scene as we
appear to see it. Uniquely, the brain records its own history, synthesizing a Movie-in-the-Brain, called the Noumenal Cosmos.
Attempting thereby to represent the actual Universe, this makes for a sovereign brain that governs itself. The brain is domicile
of an Ego, with its selfhood at stake at all times. Yet, it can know itself only by its actions, in which it appears as an
actor in its own movie. Phenomena enter garbled, as confused apparitions, and must be put in good form using top–down feedback
control by Ego, so that each movie frame makes rational sense within the overall context of the Noumenal Cosmos. A stack of
frames is processed typically in 40 Hz rhythm with 300 ms process time each, for about 12 in the stack at any time. Successive
neural centers are processing the stack in the brain assembly line, based on data from increasingly global receptive fields.
Ego stitches together the movie frames, but only the top frame is in consciousness for 25 ms. The top frame contains the whole
scene where the Ego makes an appearance as the actor that imposes Kantian synthetic unity on the scene, merely an assembly
of grammatical texts, in a system-internal coded process language, fitting the scene into the Noumenal Cosmos. But Ego observes
Ego only to the extent permitted by the objectivity rule, only what it does and thinks, not its true face. From the Noumenal
Cosmos, the Ego receives grammatical messages in the internal sense code. They are integrated into a whole in the reaction
of the Ego to the momentary scene. The voluntary nature of Ego’s decisions is explained, based on its ability to code in advance
its own actions sequentially in time, as it sees fit with a view to an orderly Noumenal Cosmos, records of code being arranged
spatially in neural structures. 相似文献