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981.
982.
983.
To interpret visual scenes, visual systems need to segment or integrate multiple moving features into distinct objects or surfaces. Previous studies have found that the perceived direction separation between two transparently moving random-dot stimuli is wider than the actual direction separation. This perceptual “direction repulsion” is useful for segmenting overlapping motion vectors. Here we investigate the effects of motion noise on the directional interaction between overlapping moving stimuli. Human subjects viewed two overlapping random-dot patches moving in different directions and judged the direction separation between the two motion vectors. We found that the perceived direction separation progressively changed from wide to narrow as the level of motion noise in the stimuli was increased, showing a switch from direction repulsion to attraction (i.e. smaller than the veridical direction separation). We also found that direction attraction occurred at a wider range of direction separations than direction repulsion. The normalized effects of both direction repulsion and attraction were the strongest near the direction separation of ∼25° and declined as the direction separation further increased. These results support the idea that motion noise prompts motion integration to overcome stimulus ambiguity. Our findings provide new constraints on neural models of motion transparency and segmentation. 相似文献
984.
The incertae sedis Carpathoporella Dragastan, 1995, reported from the Lower Cretaceous of the Western Tethyan domain, is usually interpreted as remains of calcareous algae
(Dasycladales or Characeae). New thin-section material from the Aptian of Albania sheds light not only on its biogenic nature
but also on the morphological variability of this taxon. In fact, Carpathoporella represents the debris of colonial, bushy, most likely gorgonid octocorals with tuberculated spheroids that may be fused at
least near the basal root-like holdfast. Colony branching originates from longitudinally grooved calcareous branches or internodes.
Possible relationships to other Upper Cretaceous to Palaeogene genera are discussed and a revised critical inventory of Cretaceous
octocorals is presented. Due to the evidenced morphological features, Carpathoporella could either represent an ancestral isidid octocoral of the order Alcyonacea such as Moltkia Steenstrup or, due to the likely primary aragonitic skeletal mineralogy, a representative of Epiphaxum Lonsdale of the order Helioporacea. Due to morphological analogies, the new combination Carpathoporella elliotti (Radoičić) is proposed. In any case, the Lower Cretaceous record from Tethyan peri-reefal shallow-water carbonates is highlighted
since numerous skeletal findings of fossil gorgonid Octocorallia were so far only known from Upper Cretaceous and younger
strata of outer shelf environments of the boreal realm. The origin of deep-water Upper Cretaceous octocorals from Lower Cretaceous
shallow-water taxa such as Carpathoporella is proposed as a possible further example of onshore/offshore evolutionary pattern. 相似文献
985.
Plasmonic nanorods and their clusters are the fundamental units in plasmonic nanoantenna engineering. A theory that can predict the resonance of single nanorod already exists but is in lack for a heterodimer. Here, we propose a model combining the effective circuit theory for the response of spherical nanoparticles together with standard transmission line theory for hemispherically capped nanorod antennas. The resonances of multiple orders are predictable by defining the reflection phase at the terminals of such antennas, in both symmetric and asymmetric coupled nanorods. The theoretical results compare favorably with full-wave finite element numerical calculations. By the analytical formula, it is easy to control the length of the antennas for regulating the cooperative resonant properties and consequently the radiation characteristics of a nearby electric dipole. Consequently, we obtain both commensurate and incommensurate resonance features in such nanorod-based heterodimer antennas, showing respectively cumulative and selective responses from the individual nanorods. 相似文献
986.
RICHARD M. WEINSHILBOUM RICHARD KVETNANSKY JULIUS AXELROD IRWIN J. KOPIN 《Nature: New biology》1971,230(17):287-288
THE formation of the neurotransmitter noradrenaline from 3,4-dihydroxyphenylethylamine (dopamine) is catalysed by the enzyme dopamine-β-hydroxylase (DBH)1. This enzyme is associated both with the catecholamine-containing chromaffin granules in the adrenal medulla2,3 and with the vesicular structures in sympathetic nerve terminals which contain catecholamines4. Furthermore, DBH activity is released with catecholamines into the perfusate after stimulation of either the isolated perfused adrenal gland5 or the isolated perfused spleen6–8. DBH activity has been reported in the serum of both man and the rat9,10. This activity is similar to adrenal and sympathetic nerve DBH activity with regard to cofactor requirements, oxygen requirement and kinetic characteristics9,10. It has been suggested that serum DBH activity might be present as a result of release of enzyme with catecholamines from the adrenal glands and sympathetic nerves. If this is the case, serum DBH activity might be a useful and convenient index of sympathetic-adrenal activity. The work described here was undertaken to investigate both the source of the serum DBH and the effect on this activity of forced immobilization, a procedure which has been used as a model of stress and which has been shown to release catecholamines from the adrenal gland and increase catecholamine excretion11. 相似文献
987.
Protein is one of the three main storage chemical components in maize grains, and is negatively correlated with starch concentration
(SC). Our objective was to analyse the influence of genetic backgrounds on QTL detection for protein concentration (PC) and
to reveal the molecular genetic associations between PC and both SC and grain weight (GWP). Two hundred and eighty-four (Pop1)
and 265 (Pop2) F2:3 families were developed from two crosses between one high-oil maize inbred GY220 and two normal maize inbreds 8984 and 8622
respectively, and were genotyped with 185 and 173 pairs of SSR markers. PC, SC and GWP were evaluated under two environments.
Composite interval mapping (CIM) and multiple interval mapping (MIM) methods were used to detect single-trait QTL for PC,
and multiple-trait QTL for PC with both SC and GWP. No common QTL were shared between the two populations for their four and
one PC QTL. Common QTL with opposite signs of effects for PC and SC/GWP were detected on three marker intervals at bins 6.07–6.08,
8.03 and 8.03–8.04. Multiple-traits QTL mapping showed that tightly-linked QTL, pleiotropic QTL and QTL having effects with
opposite directions for PC and SC/GWP were all observed in Pop1, while all QTL reflected opposite effects in Pop2. 相似文献
988.
989.
T H Huang 《The Journal of biological chemistry》1979,254(22):11467-11474
NMR was used to study the quaternary structure of nitrosyl- and methemoglobin, the kinetics and equilibrium behavior of nitric oxide binding, and the oxidation of hemoglobin. The -9.6 ppm (from H2O) resonance was used as a measure of nitrosylhemoglobin molecules in the T quaternary structure. We found that stripped nitrosylhemoglobin is 70% in the T state below pH 6.4, and is in the R state above. Inositol hexaphosphate (IHP) raises this transition point to pH 7.5. For stripped aquomethemoglobin, the T marker at -10 ppm is absent. In IHP, at pH 6.5 all of the molecules are in the T state. At both higher and lower pH they shift to the R state. The intensity decreases to half of its maximum at pH 5.5 and 7.4. The relative affinity of nitric oxide binding to the alpha and beta subunits was inferred from the intensities of the resonances at -12 and -18 ppm. Under conditions in which nitrosylhemoglobin exists in the T state, NO binds to the alpha subunit 10 times more strongly than it does to the beta subunit. The kinetic experiments reveal that it binds to the two subunits at the same rate and that it dissociates at 5 x 10(-3) s-1 from the beta subunit and at 5 x 10(-4) s-1 from alpha subunit. At high pH, the two subunits are ligated at the same rate. Potassium ferricyanide oxidation, at pH 6.0 in the absence of IHP, is about 3 times more favorable for the alpha than the beta subunit. Addition of IHP raises this preferential oxidation slightly. At pH 8.44, both alpha and beta subunits were oxidized at the same rate. 相似文献
990.