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Mimicry in vertebrates is usually a permanent state--mimics resemble and normally accompany their model throughout the life stages during which they act as mimics. Here we show that the bluestriped fangblenny fish (Plagiotremus rhinorhynchos), which aggressively attacks other coral-reef fish, can turn off the mimetic colours that disguise it as the benign bluestreak cleaner wrasse, Labroides dimidiatus, and assume a radically different appearance. This opportunistic facultative mimicry extends the fangblenny's scope by allowing it to blend into shoals of small reef fish as well as to remain inconspicuous at cleaning stations. 相似文献
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Techniques to facilitate controlled interactions between single photons and atoms are now being actively explored. These techniques are important for the practical realization of quantum networks, in which multiple memory nodes that utilize atoms for generation, storage and processing of quantum states are connected by single-photon transmission in optical fibres. One promising avenue for the realization of quantum networks involves the manipulation of quantum pulses of light in optically dense atomic ensembles using electromagnetically induced transparency (EIT, refs 8, 9). EIT is a coherent control technique that is widely used for controlling the propagation of classical, multi-photon light pulses in applications such as efficient nonlinear optics. Here we demonstrate the use of EIT for the controllable generation, transmission and storage of single photons with tunable frequency, timing and bandwidth. We study the interaction of single photons produced in a 'source' ensemble of 87Rb atoms at room temperature with another 'target' ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval. 相似文献
167.
Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas 总被引:1,自引:0,他引:1
Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas. Whether they are generated by the effervescent disruption of fast-rising bubbly melt or by the separate ascent of a bubble foam layer accumulated at depth still remains a matter of debate. No field measurement has yet allowed firm discrimination between these two models. A key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase. This composition should differ markedly depending on whether the magma degassing occurs before or during eruption. Here we report the analysis of magmatic gas during a powerful (250-600 m high) lava fountain, measured with Fourier transform infrared spectroscopy on Mount Etna, Sicily. The abundances of volcanic gas species, determined from absorption spectra of lava radiation, reveal a fountain gas having higher CO2/S and S/Cl ratios than other etnean emissions, and which cannot derive from syn-eruptive bulk degassing of Etna basalt. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater. 相似文献
168.
Sipkins DA Wei X Wu JW Runnels JM Côté D Means TK Luster AD Scadden DT Lin CP 《Nature》2005,435(7044):969-973
The organization of cellular niches is known to have a key role in regulating normal stem cell differentiation and regeneration, but relatively little is known about the architecture of microenvironments that support malignant metastasis. Using dynamic in vivo confocal imaging, here we show that murine bone marrow contains unique anatomic regions defined by specialized endothelium. This vasculature expresses the adhesion molecule E-selectin and the chemoattractant stromal-cell-derived factor 1 (SDF-1) in discrete, discontinuous areas that influence the homing of a variety of tumour cell lines. Disruption of the interactions between SDF-1 and its receptor CXCR4 inhibits the homing of Nalm-6 cells (an acute lymphoblastic leukaemia cell line) to these vessels. Further studies revealed that circulating leukaemic cells can engraft around these vessels, suggesting that this molecularly distinct vasculature demarcates a microenvironment for early metastatic tumour spread in bone marrow. Finally, purified haematopoietic stem/progenitor cells and lymphocytes also localize to the same microdomains, indicating that this vasculature might also function in benign states to demarcate specific portals for the entry of cells into the marrow space. Specialized vascular structures therefore appear to delineate a microenvironment with unique physiology that can be exploited by circulating malignant cells. 相似文献
169.
Israël G Szopa C Raulin F Cabane M Niemann HB Atreya SK Bauer SJ Brun JF Chassefière E Coll P Condé E Coscia D Hauchecorne A Millian P Nguyen MJ Owen T Riedler W Samuelson RE Siguier JM Steller M Sternberg R Vidal-Madjar C 《Nature》2005,438(7069):796-799
Aerosols in Titan's atmosphere play an important role in determining its thermal structure. They also serve as sinks for organic vapours and can act as condensation nuclei for the formation of clouds, where the condensation efficiency will depend on the chemical composition of the aerosols. So far, however, no direct information has been available on the chemical composition of these particles. Here we report an in situ chemical analysis of Titan's aerosols by pyrolysis at 600 degrees C. Ammonia (NH3) and hydrogen cyanide (HCN) have been identified as the main pyrolysis products. This clearly shows that the aerosol particles include a solid organic refractory core. NH3 and HCN are gaseous chemical fingerprints of the complex organics that constitute this core, and their presence demonstrates that carbon and nitrogen are in the aerosols. 相似文献
170.
In the embryo and in the adult, skeletal muscle growth is dependent on the proliferation and the differentiation of muscle progenitors present within muscle masses. Despite the importance of these progenitors, their embryonic origin is unclear. Here we use electroporation of green fluorescent protein in chick somites, video confocal microscopy analysis of cell movements, and quail-chick grafting experiments to show that the dorsal compartment of the somite, the dermomyotome, is the origin of a population of muscle progenitors that contribute to the growth of trunk muscles during embryonic and fetal life. Furthermore, long-term lineage analyses indicate that satellite cells, which are known progenitors of adult skeletal muscles, derive from the same dermomyotome cell population. We conclude that embryonic muscle progenitors and satellite cells share a common origin that can be traced back to the dermomyotome. 相似文献