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排序方式: 共有644条查询结果,搜索用时 15 毫秒
91.
Nonadditive effects of consumption in an intertidal macroinvertebrate community are independent of food availability but driven by complementarity effects 下载免费PDF全文
Emily M. van Egmond Peter M. van Bodegom Jurgen R. van Hal Richard S. P. van Logtestijn Matty P. Berg Rien Aerts 《Ecology and evolution》2018,8(6):3086-3097
Suboptimal environmental conditions are ubiquitous in nature and commonly drive the outcome of biological interactions in community processes. Despite the importance of biological interactions for community processes, knowledge on how species interactions are affected by a limiting resource, for example, low food availability, remains limited. Here, we tested whether variation in food supply causes nonadditive consumption patterns, using the macroinvertebrate community of intertidal sandy beaches as a model system. We quantified isotopically labeled diatom consumption by three macroinvertebrate species (Bathyporeia pilosa, Haustorius arenarius, and Scolelepis squamata) kept in mesocosms in either monoculture or a three‐species community at a range of diatom densities. Our results show that B. pilosa was the most successful competitor in terms of consumption at both high and low diatom density, while H. arenarius and especially S. squamata consumed less in a community than in their respective monocultures. Nonadditive effects on consumption in this macroinvertebrate community were present and larger than mere additive effects, and similar across diatom densities. The underlying species interactions, however, did change with diatom density. Complementarity effects related to niche‐partitioning were the main driver of the net diversity effect on consumption, with a slightly increasing contribution of selection effects related to competition with decreasing diatom density. For the first time, we showed that nonadditive effects of consumption are independent of food availability in a macroinvertebrate community. This suggests that, in communities with functionally different, and thus complementary, species, nonadditive effects can arise even when food availability is low. Hence, at a range of environmental conditions, species interactions hold important potential to alter ecosystem functioning. 相似文献
92.
Jenny Christal & Hal Whitehead 《Ethology : formerly Zeitschrift fur Tierpsychologie》2001,107(4):323-340
We examined patterns of affiliation within groups of sperm whales ( Physeter macrocephalus ), particularly concentrating on how short-term spatio–temporal associations reflect long-term relationships. Female and immature sperm whales live in stable, and partially matrilineal, social units. Two or more social units may move together for periods of several days, forming a cohesive group of about 20 animals. We observed that sperm whales in the eastern tropical Pacific quite consistently associated with members of their own social unit more than they did with other animals in their group with whom they did not share a long-term relationship. There was little evidence for preferred, or avoided, affiliations within social units, except in two large and relatively unstable units. In two well-studied groups, individuals did not show consistently favoured positions in the foraging rank relative to other members of their social unit. These results indicate the importance of long-term relationships to female and immature sperm whales, but suggest that relationships are quite homogeneous within social units. 相似文献
93.
Valery Andrushchenko Zoya Leonenko David Cramb Hans van de Sande Hal Wieser 《Biopolymers》2002,61(4):243-260
The interaction of natural calf thymus DNA with Cr3+ ions was studied at room temperature by means of vibrational CD (VCD) and infrared absorption (ir) spectroscopy, and atomic force microscopy (AFM). Cr3+ ion binding mainly to N7 (G) and to phosphate groups was demonstrated. ψ‐Type VCD spectra resembling electronic CD (ECD) spectra, which appear during ψ‐type DNA condensation, were observed. These spectra are characterized mainly by an anomalous, severalfold increase of VCD intensity. Such anomalous VCD spectra were assigned to DNA condensation with formation of large and dense particles of a size comparable to the wavelength of the probing ir beam and possessing large‐scale helicity. Atomic force microscopy confirmed DNA condensation by Cr3+ ions and the formation of tight DNA particles responsible for the ψ‐type VCD spectra. Upon increasing the Cr3+ ion concentration the shape of the condensates changed from loose flower‐like structures to highly packed dense spheres. No DNA denaturation was seen even at the highest concentration of Cr3+ ions studied. The secondary structure of DNA remained in a B‐form before and after the condensation. VCD and ir as well as AFM proved to be an effective combination for investigating DNA condensation. In addition to the ability of VCD to determine DNA condensation, VCD and ir can in the same experiment provide unambiguous information about the secondary structure of DNA contained in the condensed particles. © 2002 Wiley Periodicals, Inc. Biopolymers 61: 243–260, 2002 相似文献
94.
L. Halás 《Biologia Plantarum》1974,16(5):348-354
The photosynthetic rate in leaf discs (P LD) ofPrunus laurocerasus L. plants taken up from leaves of various ages was measured under constant temperature (20±0.5°C) CO2 concentration in air (0.03%) complete water saturation and irradiance (71 W m2 PhAR). TheP LD is the highest in mature leaves of the current year. The extent of depression in the second and further years depends on the degree of habitat shading. In a slightly shaded habitat (60 to 73% daily sum of photosynthetically active radiation—PhAR) it decreases by almost 50% in the second year. In a deeply shaded habitat (22.5–28.2% daily sum PhAR) the depression amounts to 31.7% in the second year in the third and fourth years to 61.7 and 73.2% respectively. 相似文献
95.
96.
Patrick J. Babin Jan Bogerd Frank P. Kooiman Wil J. A. Van Marrewijk Dick J. Van der Horst 《Journal of molecular evolution》1999,49(1):150-160
Large lipid transfer proteins (LLTP) are nonexchangeable apolipoproteins and intracellular lipid-exchange proteins involved
in the assembly, secretion, and metabolism of lipoproteins. We have identified contiguous conserved sequence motifs in alignments
of insect apolipophorin II/I precursor (apoLp-II/I), human apolipoprotein B (apoB), invertebrate and vertebrate vitellogenins
(VTG), and the large subunit of mammalian microsomal triglyceride transfer protein (MTP). Conserved motifs present in the
N-terminal part of nonexchangeable apolipoproteins encompass almost completely the large subunit of MTP, suggesting a derivation
from a common ancestral functional unit, termed large lipid transfer (LLT) module. Divergence of LLTP from a common ancestor
is supported by (1) the statistical significance of the combined match scores obtained after motif-based database searches,
(2) the presence of several identical amino acid residues in all LLTP sequences currently available, (3) the conservation
of hydrophobic clusters in an α-helical domain, (4) the phylogenetic analysis of the conserved sequences related to the von
Willebrand factor D (VWD) module identified in nonexchangeable apolipoproteins, and (5) the presence of four and one ancestral
exon boundaries in the LLT and VWD modules, respectively. Our data indicate that the genes coding for apoLp-II/I, apoB, VTG,
and the MTP large subunit are members of the same multigene superfamily. LLTP have emerged from an ancestral molecule designed
to ensure a pivotal event in the intracellular and extracellular transfer of lipids and liposoluble substances.
Received: 8 June 1998 / Accepted: 15 February 1999 相似文献
97.
Phosphorylation and/or Presence of Serine 37 in the Movement Protein of Tomato Mosaic Tobamovirus Is Essential for Intracellular Localization and Stability In Vivo 下载免费PDF全文
Shigeki Kawakami Hal S. Padgett Daijiro Hosokawa Yoshimi Okada Roger N. Beachy Yuichiro Watanabe 《Journal of virology》1999,73(8):6831-6840
The P30 movement protein (MP) of tomato mosaic tobamovirus (ToMV) is synthesized in the early stages of infection and is phosphorylated in vivo. Here, we determined that serine 37 and serine 238 in the ToMV MP are sites of phosphorylation. MP mutants in which serine was replaced by alanine at positions 37 and 238 (LQ37A238A) or at position 37 only (LQ37A) were not phosphorylated, and mutant viruses did not infect tobacco or tomato plants. By contrast, mutation of serine 238 to alanine did not affect the infectivity of the virus (LQ238A). To investigate the subcellular localization of mutant MPs, we constructed viruses that expressed each mutant MP fused with the green fluorescent protein (GFP) of Aequorea victoria. Wild-type and mutant LQ238A MP fusion proteins showed distinct temporally regulated patterns of MP-GFP localization in protoplasts and formation of fluorescent ring-shaped infection sites on Nicotiana benthamiana. However mutant virus LQ37A MP-GFP did not show a distinct pattern of localization or formation of fluorescent rings. Pulse-chase experiments revealed that MP produced by mutant virus LQ37A was less stable than wild-type and LQ238A MPs. MP which contained threonine at position 37 was phosphorylated, but the stability of the MP in vivo was very low. These studies suggest that the presence of serine at position 37 or phosphorylation of serine 37 is essential for intracellular localization and stability of the MP, which is necessary for the protein to function. 相似文献
98.
99.
Repeated calls are part of the vocal repertoire of a diverse array of species, often presented in sequences that take time and effort on the part of the signal producer. Rhythmic repeated call sequences make up a significant portion of long-finned pilot whale (Globicephala melas) vocal production, yet the function of these sequences has not been investigated until now. In this study, we explored the relationship between behavioural context and the presence of these vocal sequences using recordings of a population of pilot whales found off Cape Breton, Nova Scotia, Canada. We used a binomial logit-link generalized linear model to look for possible predictors of the presence of repeated call sequences. They were more common in recordings of socializing whales than in those of whales in other behavioural states, and least common in resting whales. These vocal repetitions were also more common with larger group size. These results suggest that sequences function in maintaining contact and cohesion within this social species, possibly also serving in individual or group identification. The context of repeated call sequences indicate that they are not primarily mother–calf interactions, as they are heard just as commonly from groups without young. Future studies of pilot whale repeated call sequences should include individual-level behaviour and detailed acoustic calling context. 相似文献
100.