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41.
Brutlag Douglas L.; Galper Adam R.; Millis David H. 《Bioinformatics (Oxford, England)》1991,7(1):9-19
We have developed a knowledge-based simulation of DNA metabolismthat accurately predicts the actions of enzymes on DNA undera large number of environmental conditions. Previous simulationsof enzyme systems rely predominantly on mathematical models.We use a frame-based representation to model enzymes, substratesand conditions. Interactions between these objects are expressedusing production rules and an underlying truth maintenance system.The system performs rapid inference and can explain its reasoning.A graphical interface provides access to all elements of thesimulation, including object representations and explanationgraphs. Predicting enzyme action is the first step in the developmentof a large knowledge base to envision the metabolic pathwaysof DNA replication and repair.
Received on February 1, 1990; accepted on October 2, 1990 相似文献
42.
Seismic and auditory tuning curves from bullfrog saccular and amphibian papular axons 总被引:1,自引:0,他引:1
Xiaolong Yu Edwin R. Lewis David Feld 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,169(2):241-248
We present seismic and auditory frequency tuning curves of individual bullfrog, Rana catesbeiana, saccular and amphibian papilla axons that responded to both seismic and auditory stimuli. In this study we found: 1) most saccular axons respond well to auditory stimuli with moderate signal strength (50-70 dB SPL) as well as to seismic stimuli; 2) most amphibian papilla axons respond well to seismic stimuli as well as to auditory stimuli, and their seismic sensitivities are comparable to those of saccular axons (responding to sinusoidal stimuli with peak accelerations in the range 0.001 to 0.1 cm/S2); 3) the responses to both seismic and auditory stimuli from both saccule and amphibian papilla are tuned, i.e. the strength of the response varies with the frequency of the stimulus; and this tuning is clearly not the result of second order resonance; 4) in individual axons the tuning properties for seismic stimuli often are not the same as those for auditory stimuli, a fact that may provide clues about how the stimulus signal energy is transferred to the hair cells in each case. 相似文献
43.
Summary Paleozoic carbonate ramp sedimentation has generally been described in terms of downlapping clinoforms composed of allochthonous
sediment derived from shallower environments. However, during transgressive episodes when carbonate sediment production is
low and down slope sediment transport by gravity becomes inactive, autochthonous carbonate sediment accumulates in vertical
stacks of essentially in situ sediment. Autochthonous outer ramp deposition is probably a part of many Paleozoic ramp strata,
but has heretofore not been recognized because of the general absence of adequate exposures.
Evidence of autochthonous, in situ deposition and preservation of sediments in a starved setting is well displayed in the
Alamogordo Member of the Lake Valley Formation in south central New Mexico. This evidence includes: 1) beds and bed sets that
are individually continuous and traceable along ramp slope for 32 km, 2) down-ramp sequential distributions of depth-sensitive
organisms and assemblages but patchy distribution of rock types, 3) lack of sedimentary structures indicative of transport,
4) well preserved, unabraded fossils, 5) the common occurrence of fossils in life position, 6) beds traceable into and through
mounds 7) bed thickness trends ascribed to biotic productivity, and 8) geopetal structures in original position.
Integrated paleontologic, sedimentologic, and stratigraphic data provide information about depositional processes and setting.
The depositional slope was approximately 0.5o based on the distribution of fossil algae; this is comparable to dips reported for other Mississippian homoclinal ramps.
An oxygen minimum zone may have impinged on the ramp during a major flooding event. Shifts in biotic gradients from bed to
bed reveal transgressive-regressive patterns that would not be resolvable without detailed paleontological evidence.
The Alamogordo Member formed as a result of transgressive and early highstand starved carbonate sedimentation along a narrow,
homoclinal outer ramp. The surface of maximum flooding and the boundary between the TST and HST are within the Alamogordo
Member. 相似文献
44.
David L. Lentz Maria Luisa Reyna de Aguilar Raul Villacorta Helen Marini 《Economic botany》1996,50(1):108-114
Paleoethnobotanical studies in the Zapotitdn Valley of north-central El Salvador revealed that a species of grass,Trachypogon plumosus, was in common use as a thatch material at the Ceren site, a small mesoamerican farming community inundated by volcanic ash circaa.d. 590. Although the grass must have been common in Precolumbian times, repeated attempts to collect fresh specimens from the modern valley were unsuccessful. A survey of the major herbaria with collections from El Salvador likewise demonstrated a lack of modern specimens from the Zapotitdn Valley. The elimination of theT. plumosus from this area and its characteristic savanna habitat probably occurred as a result of the introduction of competing Old World grasses and excessive herbivory. This finding demonstrates why conservationists working in the tropics should be concerned not only with the extinction of rain forest habitats, but with the elimination of other habitats as well. 相似文献
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49.
James N. Hislop Tarin A. Islam Ioanna Eleftheriadou David C. J. Carpentier Antonio Trabalza Michael Parkinson Giampietro Schiavo Nicholas D. Mazarakis 《The Journal of biological chemistry》2014,289(23):16148-16163
Rabies pseudotyped lentiviral vectors have great potential in gene therapy, not least because of their ability to transduce neurons following their distal axonal application. However, very little is known about the molecular processes that underlie their retrograde transport and cell transduction. Using multiple labeling techniques and confocal microscopy, we demonstrated that pseudotyping with rabies virus envelope glycoprotein (RV-G) enabled the axonal retrograde transport of two distinct subtypes of lentiviral vector in motor neuron cultures. Analysis of this process revealed that these vectors trafficked through Rab5-positive endosomes and accumulated within a non-acidic Rab7 compartment. RV-G pseudotyped vectors were co-transported with both the tetanus neurotoxin-binding fragment and the membrane proteins thought to mediate rabies virus endocytosis (neural cell adhesion molecule, nicotinic acetylcholine receptor, and p75 neurotrophin receptor), thus demonstrating that pseudotyping with RV-G targets lentiviral vectors for transport along the same pathway exploited by several toxins and viruses. Using motor neurons cultured in compartmentalized chambers, we demonstrated that axonal retrograde transport of these vectors was rapid and efficient; however, it was not able to transduce the targeted neurons efficiently, suggesting that impairment in processes occurring after arrival of the viral vector in the soma is responsible for the low transduction efficiency seen in vivo, which suggests a novel area for improvement of gene therapy vectors. 相似文献
50.
Hermógenes Fernández-Marín David R. Nash Sarah Higginbotham Catalina Estrada Jelle S. van Zweden Patrizia d'Ettorre William T. Wcislo Jacobus J. Boomsma 《Proceedings. Biological sciences / The Royal Society》2015,282(1807)
Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens. 相似文献