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91.
Y Stefan C Dufour S Falkmer 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(13):1073-1075
When antisera specific against bovine PP (BPP) were used, immunoreactive parenchymal cells were observed in the endocrine pancreas and in the gastro-intestinal tract of the teleost bony fish Cottus scorpius, as well as in the pancreas of the elasmobranchian cartilaginous fish Squalus acanthias. Of the two principal islets of Cottus, PP-cells were located selectively to that in the pyloric region. 相似文献
92.
Drosophila odorant receptors are both ligand-gated and cyclic-nucleotide-activated cation channels 总被引:5,自引:0,他引:5
Wicher D Schäfer R Bauernfeind R Stensmyr MC Heller R Heinemann SH Hansson BS 《Nature》2008,452(7190):1007-1011
From worm to man, many odorant signals are perceived by the binding of volatile ligands to odorant receptors that belong to the G-protein-coupled receptor (GPCR) family. They couple to heterotrimeric G-proteins, most of which induce cAMP production. This second messenger then activates cyclic-nucleotide-gated ion channels to depolarize the olfactory receptor neuron, thus providing a signal for further neuronal processing. Recent findings, however, have challenged this concept of odorant signal transduction in insects, because their odorant receptors, which lack any sequence similarity to other GPCRs, are composed of conventional odorant receptors (for example, Or22a), dimerized with a ubiquitously expressed chaperone protein, such as Or83b in Drosophila. Or83b has a structure akin to GPCRs, but has an inverted orientation in the plasma membrane. However, G proteins are expressed in insect olfactory receptor neurons, and olfactory perception is modified by mutations affecting the cAMP transduction pathway. Here we show that application of odorants to mammalian cells co-expressing Or22a and Or83b results in non-selective cation currents activated by means of an ionotropic and a metabotropic pathway, and a subsequent increase in the intracellular Ca(2+) concentration. Expression of Or83b alone leads to functional ion channels not directly responding to odorants, but being directly activated by intracellular cAMP or cGMP. Insect odorant receptors thus form ligand-gated channels as well as complexes of odorant-sensing units and cyclic-nucleotide-activated non-selective cation channels. Thereby, they provide rapid and transient as well as sensitive and prolonged odorant signalling. 相似文献
93.
94.
Chapman HN Hau-Riege SP Bogan MJ Bajt S Barty A Boutet S Marchesini S Frank M Woods BW Benner WH London RA Rohner U Szöke A Spiller E Möller T Bostedt C Shapiro DA Kuhlmann M Treusch R Plönjes E Burmeister F Bergh M Caleman C Huldt G Seibert MM Hajdu J 《Nature》2007,448(7154):676-679
Extremely intense and ultrafast X-ray pulses from free-electron lasers offer unique opportunities to study fundamental aspects of complex transient phenomena in materials. Ultrafast time-resolved methods usually require highly synchronized pulses to initiate a transition and then probe it after a precisely defined time delay. In the X-ray regime, these methods are challenging because they require complex optical systems and diagnostics. Here we propose and apply a simple holographic measurement scheme, inspired by Newton's 'dusty mirror' experiment, to monitor the X-ray-induced explosion of microscopic objects. The sample is placed near an X-ray mirror; after the pulse traverses the sample, triggering the reaction, it is reflected back onto the sample by the mirror to probe this reaction. The delay is encoded in the resulting diffraction pattern to an accuracy of one femtosecond, and the structural change is holographically recorded with high resolution. We apply the technique to monitor the dynamics of polystyrene spheres in intense free-electron-laser pulses, and observe an explosion occurring well after the initial pulse. Our results support the notion that X-ray flash imaging can be used to achieve high resolution, beyond radiation damage limits for biological samples. With upcoming ultrafast X-ray sources we will be able to explore the three-dimensional dynamics of materials at the timescale of atomic motion. 相似文献
95.
Stefan Michal Wasilewski 《Systemic Practice and Action Research》2009,22(4):345-349
‘I made a mistake’: Alan Greenspan (Financial Times: Alan Beattie and James Politi: Washington, 23rd October 2008). Such are
the words of great men, for even in troubled times their self-effacing manner provides useful guidance. Whilst Mr Greenspan
may feel this way, he is a product of his environment, one that has seen the cumulative development of financial instruments
and strategies that have not been thought through as to their impact on a complex economy. Mainly this is because risk is
thought to be discrete and the methods used to price it are flawed. To an engineer the control of a machine is built-in. Although
the economy is not a machine, but an intensely connected complex of ever emerging businesses, the process of control needs
to be structured in a similar manner. Pricing investment risk in this environment should never have been left to opaque institutions,
or processes that do not recognise the co-dependencies of business and systemic functionality. To do so is to ignore the correlation
of events in a highly connected world. These events are dynamic and conditional, whose outturns are unknowable. This does
not mean unmanageable, but that the control process be built-in to businesses and government in a consistent manner, transparent
yet using different parameters. Transparent means that data, assumptions and processes need to be monitored and published
in timely manner. As far as accounting for results is concerned it should be recognised that budgeting and reporting to investors
is founded on dynamic processes that are therefore changeable; usually out of date; and co-dependent upon others within a
complex dynamic network that is both internal and external to the business. The works of Stafford Beer (Brain of the Firm,
Heart of the Enterprise, Diagnosing the System) Fredrick Vestor (The Art of Interconnected Thinking) and others are examples
of how to manage the internal dynamics of a business and point to a methodology that synthesises the approaches of investors
such as Warren Buffett so that extreme outcomes such as the Credit-Crunch 2008 can be reduced in frequency but investors are
free to ‘take their risks’. This research aims to compare two extreme events in the financial arena, the ‘Reinsurance Spiral
of the late 1980s’ and the ‘2008 Credit-Crunch’, show their commonalities and propose methods that supply liquidity in all
but gross systemic failure and allow investment risk to be more ably assessed and priced. It is not meant to be an exhaustive
analysis but one focused on how ignoring the proper relationship of time, functions and processes brought about the current
problem in both insurance and the capital markets and how a solution may be found. This research note offers an overview on
the ongoing PhD research on the topic.
相似文献
Stefan Michal WasilewskiEmail: |
96.
Zhang J Ding L Holmfeldt L Wu G Heatley SL Payne-Turner D Easton J Chen X Wang J Rusch M Lu C Chen SC Wei L Collins-Underwood JR Ma J Roberts KG Pounds SB Ulyanov A Becksfort J Gupta P Huether R Kriwacki RW Parker M McGoldrick DJ Zhao D Alford D Espy S Bobba KC Song G Pei D Cheng C Roberts S Barbato MI Campana D Coustan-Smith E Shurtleff SA Raimondi SC Kleppe M Cools J Shimano KA Hermiston ML Doulatov S Eppert K Laurenti E Notta F Dick JE Basso G Hunger SP Loh ML Devidas M Wood B Winter S 《Nature》2012,481(7380):157-163
97.
T Hashimoto T Perlot A Rehman J Trichereau H Ishiguro M Paolino V Sigl T Hanada R Hanada S Lipinski B Wild SM Camargo D Singer A Richter K Kuba A Fukamizu S Schreiber H Clevers F Verrey P Rosenstiel JM Penninger 《Nature》2012,487(7408):477-481
Malnutrition affects up to one billion people in the world and is a major cause of mortality. In many cases, malnutrition is associated with diarrhoea and intestinal inflammation, further contributing to morbidity and death. The mechanisms by which unbalanced dietary nutrients affect intestinal homeostasis are largely unknown. Here we report that deficiency in murine angiotensin I converting enzyme (peptidyl-dipeptidase A) 2 (Ace2), which encodes a key regulatory enzyme of the renin-angiotensin system (RAS), results in highly increased susceptibility to intestinal inflammation induced by epithelial damage. The RAS is known to be involved in acute lung failure, cardiovascular functions and SARS infections. Mechanistically, ACE2 has a RAS-independent function, regulating intestinal amino acid homeostasis, expression of antimicrobial peptides, and the ecology of the gut microbiome. Transplantation of the altered microbiota from Ace2 mutant mice into germ-free wild-type hosts was able to transmit the increased propensity to develop severe colitis. ACE2-dependent changes in epithelial immunity and the gut microbiota can be directly regulated by the dietary amino acid tryptophan. Our results identify ACE2 as a key regulator of dietary amino acid homeostasis, innate immunity, gut microbial ecology, and transmissible susceptibility to colitis. These results provide a molecular explanation for how amino acid malnutrition can cause intestinal inflammation and diarrhoea. 相似文献
98.
Cheneau M Barmettler P Poletti D Endres M Schauss P Fukuhara T Gross C Bloch I Kollath C Kuhr S 《Nature》2012,481(7382):484-487
In relativistic quantum field theory, information propagation is bounded by the speed of light. No such limit exists in the non-relativistic case, although in real physical systems, short-range interactions may be expected to restrict the propagation of information to finite velocities. The question of how fast correlations can spread in quantum many-body systems has been long studied. The existence of a maximal velocity, known as the Lieb-Robinson bound, has been shown theoretically to exist in several interacting many-body systems (for example, spins on a lattice)--such systems can be regarded as exhibiting an effective light cone that bounds the propagation speed of correlations. The existence of such a 'speed of light' has profound implications for condensed matter physics and quantum information, but has not been observed experimentally. Here we report the time-resolved detection of propagating correlations in an interacting quantum many-body system. By quenching a one-dimensional quantum gas in an optical lattice, we reveal how quasiparticle pairs transport correlations with a finite velocity across the system, resulting in an effective light cone for the quantum dynamics. Our results open perspectives for understanding the relaxation of closed quantum systems far from equilibrium, and for engineering the efficient quantum channels necessary for fast quantum computations. 相似文献
99.
Rohringer N Ryan D London RA Purvis M Albert F Dunn J Bozek JD Bostedt C Graf A Hill R Hau-Riege SP Rocca JJ 《Nature》2012,481(7382):488-491
Since the invention of the laser more than 50 years ago, scientists have striven to achieve amplification on atomic transitions of increasingly shorter wavelength. The introduction of X-ray free-electron lasers makes it possible to pump new atomic X-ray lasers with ultrashort pulse duration, extreme spectral brightness and full temporal coherence. Here we describe the implementation of an X-ray laser in the kiloelectronvolt energy regime, based on atomic population inversion and driven by rapid K-shell photo-ionization using pulses from an X-ray free-electron laser. We established a population inversion of the Kα transition in singly ionized neon at 1.46 nanometres (corresponding to a photon energy of 849 electronvolts) in an elongated plasma column created by irradiation of a gas medium. We observed strong amplified spontaneous emission from the end of the excited plasma. This resulted in femtosecond-duration, high-intensity X-ray pulses of much shorter wavelength and greater brilliance than achieved with previous atomic X-ray lasers. Moreover, this scheme provides greatly increased wavelength stability, monochromaticity and improved temporal coherence by comparison with present-day X-ray free-electron lasers. The atomic X-ray lasers realized here may be useful for high-resolution spectroscopy and nonlinear X-ray studies. 相似文献
100.