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1.
In a two-year-study, the fish community of the Loosdrecht Lakes area was characterized with regard to the professional fishery and the forage base. The lakes are shallow (mean depth 2 m) and eutrophic to hypertrophic. The bream,Abramis brama, dominates the fish biomass. The pikeperch,Stizostedion lucioperca, is the main predator.Bream up to 30 cm have a slow growth rate and are in a bad condition. A faster growth rate and a better condition are shown by bream of 30 cm and more. The small bream feeds on chironomid larvae, benthic cladocerans and zooplankton. The better condition of bream over 30 cm is explained by the more efficient feeding of larger bream onChironomus plumosus larvae. Pikeperch show a fast growth rate and a good condition. Recruitment is limited by the low densities of smelt,Osmerus eperlanus, leaving cannibalism as the most important way for the 0+ pikeperch to become piscivorous and to manifest a fast growth.The impact of the professional gillnet fishery on bream and pikeperch is small because the mesh sizes in use are as large as 75–100 mm bar mesh.The planktivorous 0+ pikeperch consumes mainly the carnivorous zooplanktersLeptodora kindtii and cyclopoids. The zooplankton community lacks large herbivorous species likeDaphnia hyalina, capable of consuming bluegreens. A possible experiment in biomanipulation with a view to find out whether the development ofD.hyalina is depressed by the small planktivorous cyprinids, is predator enhancement with the aid of a stocking programme for indoor-raised 0+ pikeperch in early summer. 相似文献
2.
A J van Zonneveld H Veerman M E MacDonald J A van Mourik H Pannekoek 《Journal of cellular biochemistry》1986,32(3):169-178
Full-length tissue-type plasminogen activator (t-PA) cDNA served to construct deletion mutants within the N-terminal "heavy" (H)-chain of the t-PA molecule. The H-chain cDNA consists of an array of structural domains homologous to domains present on other plasma proteins ("finger," "epidermal growth factor," "kringles"). These structural domains have been located on an exon or a set of exons. The endpoints of the deletions nearly coincide with exon-intron junctions of the chromosomal t-PA gene. Recombinant t-PA deletion mutant proteins were obtained after transient expression in mouse Ltk- cells, transfected with SV40-pBR322-derived t-PA cDNA plasmids. It is demonstrated that the serine protease moiety of t-PA and its substrate specificity for plasminogen is entirely contained within the C-terminal "light" (L)-chain of the protein. The presence of cDNA, encoding the t-PA signal peptide preceding the remaining portion of t-PA, suffices to achieve secretion of (mutant) t-PA into the medium. The stimulatory effect of fibrin on the plasminogen activator activity of t-PA was shown to be mediated by the kringle K2 domain and, to a lesser extent, by the finger domain. The other domains on the H-chain, kringle K1, and the epidermal growth-factor-like domain, do not contribute to this property of t-PA. These findings correlate well with the fibrin-binding properties of the rt-PA deletion-mutant proteins, indicating that stimulation of the activity is based on aligning of the substrate plasminogen and its enzyme t-PA on the fibrin matrix. The primary target for endothelial plasminogen activator inhibitor (PAI) is located within the L-chain of t-PA. Deleting specific segments of t-PA H-chain cDNA and subsequent transient expression in mouse Ltk- cells of t-PA deletion-mutant proteins did not affect the formation of a stable complex between mutant t-PA and PAI. 相似文献
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5.
Interaction of the salivary low-molecular-weight mucin (MG2) with Actinobacillus actinomycetemcomitans 总被引:2,自引:0,他引:2
J. Groenink A. J. M. Ligtenberg E. C. I. Veerman J. G. M. Bolscher A. V. Nieuw Amerongen 《Antonie van Leeuwenhoek》1996,70(1):79-87
Periodontitis is associated with the presence of certain Gram-negative bacteria in the oral cavity, among these Actinobacillus actinomycetemcomitans. In order to determine which types of salivary components interact with A. actinomycetemcomitans two strains (HG 1175 and FDC Y4) were incubated with whole saliva and individual glandular secretions, viz. parotid, submandibular, and sublingual saliva. Immunochemical analysis by immunoblotting of bacteria-bound salivary proteins showed that IgA, the low-molecular mucin MG2, parotid agglutinin, and a 300 kDa sublingual and submandibular glycoprotein, were bound to the bacterial strains tested. In addition, adherence of A. actinomycetemcomitans to salivary proteins in a solid-phase was studied. After electrophoresis and transfer of salivary proteins to nitrocellulose membranes A. actinomycetemcomitans adhered only to MG2. In this assay periodate treatment, mild acid hydrolysis or neuraminidase digestion of the saliva glycoproteins abolished binding of two clinical isolates (HG 1175 and NY 664), suggesting that sialic acid residues on MG2 are involved in the binding. In contrast, adherence of the smooth laboratory strain Y4 was not affected by removal of sialic acid residues or even periodate treatment of MG2.Abbreviations S-IgA
Secretory IgA
- MG1
high-molecular-weight mucin
- MG2
low-molecular-weight mucin
- EP-GP
extra parotid-glycoprotein
- PRPs
proline-rich proteins
- SNA
Sambucus nigra agglutinin
- MAA
Maackia amurensis agglutinin
- PNA
peanut agglutinin
- UEA
Ulex europaeus agglutinin 相似文献
6.
Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews
(genus Sorex) for the region between the tRNA(Pro) and the conserved
sequence block-F revealed variable numbers of 79-bp tandem repeats. These
repeats were found in all 19 individuals sequenced, representing three
subspecies and one closely related species of the masked shrew group (Sorex
cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an
outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an
adjacent 76-bp imperfect copy of the tandem repeats. One individual was
heteroplasmic for length variants consisting of five and seven copies of
the 79-bp tandem repeat. The sequence of the repeats is conducive to the
formation of secondary structure. A termination-associated sequence is
present in each of the repeats and in a unique sequence region 5' to the
tandem array as well. Mean genetic distance between the masked shrew taxa
and the pygmy shrew was calculated separately for the unique sequence
region, one of the tandem repeats, the imperfect repeat, and these three
regions combined. The unique sequence region evolved more rapidly than the
tandem repeats or the imperfect repeat. The small genetic distance between
pairs of tandem repeats within an individual is consistent with a model of
concerted evolution. Repeats are apparently duplicated and lost at a high
rate, which tends to homogenize the tandem array. The rate of D- loop
sequence divergence between the masked and pygmy shrews is estimated to be
15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid
sequence evolution in shrews may be due either to their high metabolic rate
and short generation time or to the presence of variable numbers of tandem
repeats.
相似文献
7.
8.
大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
9.
Yvonne M. van Houten Pam van Stratum Jan Bruin Alfred Veerman 《Entomologia Experimentalis et Applicata》1995,77(3):289-295
In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially
applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites
is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive
diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report
on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter
diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential
of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence
on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of
predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition
were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait
in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause
line ofA. cucumeris established successfully under diapause-inducing short-day conditions. 相似文献
10.
To explain photoperiodic induction of diapause in the spider mite Tetranychus urticae a new theoretical model was developed which took into account both the hourglass and rhythmic elements shown to be present in the photoperiodic reaction of these mites. It is emphasized that photoperiodic induction is the result of time measurement as well as the summation and integration of a number of successive photoperiodic cycles: the model, therefore, consists of separate ‘clock’ and ‘counter’ mechanisms. In current views involvement of the circadian system in photoperiodism is interpreted in terms of the hypothesis that the photoperiodic clock itself is based on one or more circadian oscillators. Here a different approach has been chosen as regards the role of the circadian system in photoperiodism: the possibility, previously put forward by other authors, that some aspect of the photoperiodic induction mechanism other than the clock is controlled by the circadian system was investigated by assuming a circadian influence on the photoperiodic counter mechanism. The derivation of this ‘hourglass timer oscillator counter’ model of photoperiodic induction in T. urticae is described and its operation demonstrated on the basis of a number of diel and nondiel photoperiods, with and without light interruptions. 相似文献