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41.
The tradeoff between colonization and competitive ability has been proposed as a mechanism for ecological succession, and this tradeoff has been demonstrated in multiple successional communities. The tradeoff between competitive ability and predation resistance is also a widely-described phenomenon; however, this tradeoff is not usually postulated as a cause of ecological succession. Early successional species that arrive before predator colonization could be either (1) less vulnerable to predation than their successors, by virtue of being poor competitors (direct competition-predation tradeoff); or (2) equally or more vulnerable to predation, because they normally colonize ahead of predators in succession and therefore are not evolutionarily adapted to avoid predators that they rarely encounter (no competition–predation tradeoff). To test these alternative hypotheses, we established water-filled containers in an oak–hickory forest. We allowed half of the containers to be naturally colonized by early-successional Culex mosquitoes, mid-successional Aedes mosquitoes, and the mosquito predator Toxorhynchites rutilus. In the other half of the containers, we prevented Aedes colonization via systematic removal of Aedes eggs, but allowed Culex and T. rutilus to colonize. The numbers of mature Culex larvae and pupae, and later the total number of Culex, were significantly greater in containers where Aedes had been removed, which suggests that Culex are competitively suppressed by Aedes. Toxorhynchites rutilus abundance and colonization rate were unaffected by the removal of Aedes, and densities of both Culex and Aedes decreased significantly with T. rutilus abundance in both treatments. In-laboratory bioassays showed that Culex were significantly more vulnerable to predation by T. rutilus than were Aedes. These data are consistent with the hypothesis that Culex and Aedes demonstrate a direct colonization–competition tradeoff, and are inconsistent with the hypothesis of a direct competition–predation tradeoff. 相似文献
42.
We interact with the world through the assessment of available, but sometimes imperfect, sensory information. However, little is known about how variance in the quality of sensory information affects the regulation of controlled actions. In a series of three experiments, comprising a total of seven behavioral studies, we examined how different types of spatial frequency information affect underlying processes of response inhibition and selection. Participants underwent a stop-signal task, a two choice speed/accuracy balance experiment, and a variant of both these tasks where prior information was given about the nature of stimuli. In all experiments, stimuli were either intact, or contained only high-, or low- spatial frequencies. Overall, drift diffusion model analysis showed a decreased rate of information processing when spatial frequencies were removed, whereas the criterion for information accumulation was lowered. When spatial frequency information was intact, the cost of response inhibition increased (longer SSRT), while a correct response was produced faster (shorter reaction times) and with more certainty (decreased errors). When we manipulated the motivation to respond with a deadline (i.e., be fast or accurate), removal of spatial frequency information slowed response times only when instructions emphasized accuracy. However, the slowing of response times did not improve error rates, when compared to fast instruction trials. These behavioral studies suggest that the removal of spatial frequency information differentially affects the speed of response initiation, inhibition, and the efficiency to balance fast or accurate responses. More generally, the present results indicate a task-independent influence of basic sensory information on strategic adjustments in action control. 相似文献
43.
Seshi R. Sompuram Kodela Vani Brian Tracey Debra A. Kamstock Steven A. Bogen 《The journal of histochemistry and cytochemistry》2015,63(9):681-690
A new standardized immunohistochemistry (IHC) control for breast cancer testing comprises formalin-fixed human epidermal growth factor receptor 2, estrogen receptor, or progesterone receptor peptide antigens covalently attached to 8-µm glass beads. The antigen-coated beads are suspended in a liquid matrix that hardens upon pipetting onto a glass microscope slide. The antigen-coated beads remain in place through deparaffinization, antigen retrieval, and immunostaining. The intensity of the beads’ stain provides feedback regarding the efficacy of both antigen retrieval and immunostaining. As a first report, we tested the sensitivity and specificity of the new IHC controls (“IHControls”). To evaluate sensitivity, various staining problems were simulated. IHControls detected primary and secondary reagent degradation similarly to tissue controls. This first group of IHControls behaved similarly to tissue controls expressing high concentrations of the antigen. The IHControls were also able to detect aberrations in antigen retrieval, as simulated by sub-optimal times or temperatures. Specificity testing revealed that each antigen-coated bead was specific for its cognate IHC test antibody. The data support the conclusion that, like tissue controls, IHControls are capable of verifying the analytic components of an immunohistochemical stain. Unlike tissue controls, IHControls are prepared in large bulk lots, fostering day-to-day reproducibility that can be standardized across laboratories. 相似文献
44.
The magnitudes of inter-chromophore interactions in bacterial photosynthetic reaction centers are investigated by measuring absorption and Stark spectra of reaction centers in which monomeric chromophores are modified and in a novel triplet mutant which lacks the special pair. The circular dichroism spectrum of the triple mutant reaction center was also measured. Only small changes in the spectroscopic properties are observed, as has also been found for several types of reaction centers in which the absorption or chemical properties of a chromophore are altered by site-specific mutations. We conclude that the electronic absorption, circular dichroism and Stark features of the special pair and the monomeric chromophores in the reaction center are relatively insensitive to inter-chromophore interactions. 相似文献
45.
Marion S. R?der Mark E. Sorrells Steven D. Tanksley 《Molecular & general genetics : MGG》1992,232(2):215-220
Summary The long-range structure of 5S rRNA gene clusters has been investigated in wheat (Triticum aestivum L.) by means of pulsed field gel electrophoresis. Using aneuploid stocks, 5S rRNA gene clusters were assigned to sites on chromosomes 1B, 1D, 513 and 5D. Cluster sizes were evaluated and the copy number of 5S DNA repeats was estimated at 4700-5200 copies for the short repeating unit (410 bp) and about 3100 copies for the long repeat (500 bp) per haploid genome. A comparison of wheat cultivars revealed extremely high levels of polymorphism in the 5S rRNA gene clusters. With one restriction enzyme digest all varieties tested gave unique banding patterns and, on a per fragment basis, 21-fold more polymorphism was detected among cultivars for 5S DNA compared to standard restriction fragment length polymorphisms (RFLPs) detected with single copy clones. Experiments with aneuploid stocks suggest that the 5S rRNA gene clusters at several chromosomal sites contribute to this polymorphism. A number of previous reports have shown that wheat cultivars are not easily distinguished by isozymes or RFLPs. The high level of variation detected in 5S rRNA gene clusters therefore offers the possibility of a sensitive fingerprinting method for wheat. 5S DNA and other macro-satellite sequences may also serve as hypervariable Mendelian markers for genetic and breeding experiments in wheat. 相似文献
46.
C. Steven McDaniel Taghi Manshouri M. Zouhair Atassi 《Journal of Protein Chemistry》1987,6(5):455-461
A peptide corresponding to residues 26–41 of α-bungarotoxin, and closed by a disulfide bond between two cysteine residues
at the amino and C terminal ends of the peptide, was synthesized and the monomeric form was purified. The peptide, which represents
the exposed part of the long central loop of the toxin molecule, was examined for binding to acetylcholine receptor. The peptide
was shown by radiometric titrations to bind radiolabeled receptor, and radiolabeled peptide was bound by receptor. The specificity
of the binding was confirmed by inhibition with the parent toxin. A synthetic analog of the peptide in which Trp-28 was replaced
by glycine had very little (10%) of the original activity. Succinylation of the amino groups of the peptide resulted in virtually
complete (98%) loss of the binding activity. These results indicate that a shortened loop peptide corresponding to the region
26–41 of α-bungarotoxin exhibits binding activities mimicking those of the parent molecule. In this region, Trp-28, and one
or both of Lys-26 and Lys-38, are essential contact residues in the binding to receptor. 相似文献
47.
48.
Cross-comparisons of nectar production data are complicated because different workers use bags made of various materials to exclude animal visitors. Using clonal populations of Asclepias syriaca and A. exaltata in northern Virginia, we carefully measured the effects of four bagging treatments (bridal veil, pellon, paper, plastic) on microenvironment (temperature, relative humidity) and nectar production (volume, concentration, sucrose amount) over the course of a day. In general, bridal veil bags changed the microenvironment least relative to unbagged controls. Plastic bags resulted in higher temperatures and constantly higher relative humidities. Temperature and relative humidity were also elevated, though less dramatically, in paper and pellon bags. Under more humid conditions, flowers contained larger volumes of more dilute nectar. Therefore, researchers who wish to obtain nectar production data that reflect natural field conditions should use bridal veil, or a material with similar properties, to bag inflorescences. We also performed a watering experiment, involving the addition of the equivalent of a 10-cm rain to the A. syriaca plot. After watering, nectar volumes and sucrose amounts were increased approximately twofold. 相似文献
49.
Hanafi H. Russell Richard J. Jackson David P. Spath Steven A. Book 《The Western journal of medicine》1987,147(5):615-622
Drinking water contamination by toxic chemicals has become widely recognized as a public health concern since the discovery of 1,2-dibromo-3-chloropropane in California''s Central Valley in 1979. Increased monitoring since then has shown that other pesticides and industrial chemicals are present in drinking water. Contaminants of drinking water also include naturally occurring substances such as asbestos and even the by-products of water chlorination. Public water systems, commercially bottled and vended water and mineral water are regulated, and California is also taking measures to prevent water pollution by chemicals through various new laws and programs. 相似文献
50.
Big Moose Basin: simulation of response to acidic deposition 总被引:2,自引:1,他引:1
George F. Davis John J. Whipple Steven A. Gherini Carl W. Chen Robert A. Goldstein Arland H. Johannes Peter W.H Chan Ronald K. Munson 《Biogeochemistry》1987,3(1-3):141-161
The ILWAS model has been enhanced for application to multiple-lake hydrologic basins. This version of the model has been applied to the Big Moose basin, which includes Big Moose Lake and its tributary streams, lakes, and watersheds. The basin, as defined, includes an area of 96 km2, with over 20 lakes and ponds, and 70 km of streams. Hydrologic and chemical calibrations have been made using data from seven sampling stations. When total atmospheric sulfur loading to the basin is halved, the model predicts, after four years of simulation, a decreasing sulfate concentration and to a lesser extent a rising alkalinity at Big Moose Lake outlet. At the end of four years, the results show an increase in pH of 0.1 to 0.5 pH units depending upon season. 相似文献