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961.
Amor BB Shaw SL Oldroyd GE Maillet F Penmetsa RV Cook D Long SR Dénarié J Gough C 《The Plant journal : for cell and molecular biology》2003,34(4):495-506
Establishment of the Rhizobium-legume symbiosis depends on a molecular dialogue, in which rhizobial nodulation (Nod) factors act as symbiotic signals, playing a key role in the control of specificity of infection and nodule formation. Using nodulation-defective (Nod-) mutants of Medicago truncatula to study the mechanisms controlling Nod factor perception and signalling, we have previously identified five genes that control components of a Nod factor-activated signal transduction pathway. Characterisation of a new M. truncatula Nod- mutant led to the identification of the Nod Factor Perception (NFP) locus. The nfp mutant has a novel phenotype among Nod- mutants of M. truncatula, as it does not respond to Nod factors by any of the responses tested. The nfp mutant thus shows no rapid calcium flux, the earliest detectable Nod factor response of wild-type plants, and no root hair deformation. The nfp mutant is also deficient in Nod factor-induced calcium spiking and early nodulin gene expression. While certain genes controlling Nod factor signal transduction also control the establishment of an arbuscular mycorrhizal symbiosis, the nfp mutant shows a wild-type mycorrhizal phenotype. These data indicate that the NFP locus controls an early step of Nod factor signal transduction, upstream of previously identified genes and specific to nodulation. 相似文献
962.
963.
Alkylation of manganese(II) tetraphenylporphyrin by antimalarial fluorinated artemisinin derivatives
Rodriguez M Bonnet-Delpon D Bégué JP Robert A Meunier B 《Bioorganic & medicinal chemistry letters》2003,13(6):1059-1062
The alkylating properties of two artemisinin derivatives bearing a trifluoromethyl substituent at C10 were evaluated toward manganese(II) tetraphenylporphyrin, considered as a heme model. Chlorin-type covalent adducts were obtained by alkylation of the porphyrin ring by C-centered radicals derived from reductive activation of the peroxide function of the drugs. 相似文献
964.
Heat shock proteins play an important role in bacterial survival and response to environmental stress. We cloned the Prevotella loescheii HSP70 homolog (dnaK) and characterized the coding sequence, regulatory regions, and evolutionary relationships to other bacteria. Predicted proteins
encoded by the P. loescheii dnaK homolog (open reading frame ORF-1) and two downstream coding regions, ORF-2 and ORF-3, are highly homologous to the proteins
encoded by ORF-4 (dnaK), ORF-5, and ORF-6 from the dnaK region of Porphyromonas gingivalis. The dnaK promoter resembles other HSP (heat shock protein) promoters. Alignment of the predicted protein encoded by ORF-2 showed significant
homology to the Bacteroides fragilis tnpA gene from the transposon Tn4555, whereas the ORF-3 protein showed homology to B. fragilis transposase (Tn5220) and integrase (Tn4555) proteins. This suggests a transposition-like event may be responsible for transfer
of these genes between Porphyromonas and Prevotella.
Received: 8 June 2000 / Accepted: 11 August 2000 相似文献
965.
While the effects of interleukin-3 (IL-3) and granulocyte macrophage-colony stimulating factor (GM-CSF) on microglia are well documented, very little is known about the effects of a related cytokine, interleukin-5 (IL-5). We therefore undertook studies to determine how IL-5 alters various aspects of microglial functioning. Treatment of microglia with IL-5 resulted in the induction of proliferation at levels similar to those induced by GM-CSF. IL-5 also increased cellular metabolism of microglial cells. To determine whether increased metabolism correlated with activation of microglia, we measured levels of nitrite, a breakdown product of nitric oxide. Treatment of microglial cultures with IL-5 increased nitrite levels, while GM-CSF treatment had no effect. Treatment of microglia with IL-5 did not cause activation of the signal transduction pathways linked to the classical IL-5 receptor, STAT5A/5B and ERK1 and ERK2. It is therefore likely that the effects of IL-5 on microglia are not mediated via the classical IL-5 receptor, but rather via a novel receptor. 相似文献
966.
967.
The dynamics of the "Etang de Berre", a brackish lagoon situated close to the French Mediterranean sea coast, is strongly disturbed by freshwater inputs coming from an hydroelectric power station. The system dynamics has been described as a sequence of daily typical states from a set of physicochemical variables such as temperature, salinity and dissolved oxygen rates collected over three years by an automatic sampling station. Each daily pattern summarizes the evolution, hour by hour of the physicochemical variables. This article presents results of forecasts of the states of the system subjected to the simultaneous effects of meteorological conditions and freshwater releases. We recall the main step of the classification tree method used to build up the predictive model (Classification and Regression Trees, Breiman et al., 1984) and we propose a transfer procedure in order to test the stability of the model. Results obtained on the Etang de Berre data set allow us to describe and predict the effects of the environmental variables on the system dynamics with a margin of error. The transfer procedure applied after the tree building process gives a maximum gain in prediction accuracy of about 15%. 相似文献
968.
Thirty-one Listeria strains were tested for sensitivity to four class IIa bacteriocins, namely, enterocin A, mesentericin Y105, divercin V41,
and pediocin AcH, and to nisin A. Class IIa bacteriocins displayed surprisingly similar antimicrobial patterns ranging from
highly susceptible to fully resistant strains, whereas nisin A showed a different pattern in which all Listeria strains were inhibited. Particularly, it was observed that the strain Listeria monocytogenes V7 could not be inhibited by any of the class IIa bacteriocins tested. These observations suggest that Listeria strains resistant to the whole range of class IIa bacteriocins may occur in natural environments, which could be of great
concern with regard to the use of these peptides as food preservatives.
Received: 22 October 1999 / Accepted: 15 December 1999 相似文献
969.
970.
New collections allow us to describe some new algae forming: a) centimetric, unorganized, masses (Toutinella bifurcata from the Middle Triassic of Provence); b) large, decimetric masses (Zarramanella menorica from the ‘Buntsandstein’ of Minorca, Balearic Islands) and c) interesting, plurispecific biocenosis, laminated and silicified, from the French Massif Central: Lower Stephanian of Saint-Étienne basin (with Hankerpella minima, Baltzerella stephaniense, Ponsinella undulata) and Lower Autunian of Bourbon-l'Archambault basin (Hanskerpella pustulata, Baltzerella stephaniense, Ponsinella multifrons, Sarfatigirella intricata). Other forms are badly preserved, one is possibly a Broutinella sp. and another may be a coccoid form of cyanobacteria or chlorophyceae. Silicified biocenoses macroscopically occur in the form of regular laminations, exhibiting vertical, planar joints (1–2 cm wide) and horizontal, planar joints, 5 mm to 3 cm thick, with various sedimentary infillings. These facies represent early and late silicifications of biological felts (mats), probably previously partly calcified and affected by desiccation cracks partly infilled before the silicification. There is no evidence for an early silicification of living filaments and trichomes. The silicification also affects other types of sediments (petites, sandstones, conglomerates, breccias) associated with the algal formations. Macroscopically, these laminated formations do not show domes or hemispheres; on the other hand, these features clearly appear under the microscope, and these formations are true stromatolites. The basins of Saint-Étienne and Bourbon-l'Archambault contain volcanic rocks; the siliceous series, very localized in the basins, represent an impregnation of various primary materials by silica of hydrothermal origin. The present study is voluntarily limited to the palaeontological and palaeoecological appearances; algal laminations formed in ephemeral pools and small lakes, under very particular conditions, ‘hydrothermal’ sensu lato, are still to be stated more precisely.