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971.
972.
Jennifer B. Glass Si Chen Katherine S. Dawson Damian R. Horton Stefan Vogt Ellery D. Ingall 《Geomicrobiology journal》2018,35(1):81-89
Metal cofactors are required for many enzymes in anaerobic microbial respiration. This study examined iron, cobalt, nickel, copper, and zinc in cellular and abiotic phases at the single-cell scale for a sulfate-reducing bacterium (Desulfococcus multivorans) and a methanogenic archaeon (Methanosarcina acetivorans) using synchrotron X-ray fluorescence microscopy. Relative abundances of cellular metals were also measured by inductively coupled plasma mass spectrometry. For both species, zinc and iron were consistently the most abundant cellular metals. M. acetivorans contained higher nickel and cobalt content than D. multivorans, likely due to elevated metal requirements for methylotrophic methanogenesis. Cocultures contained spheroid zinc sulfides and cobalt/copper sulfides. 相似文献
973.
The nucleotide sequence of a genomic fragment from Halobacterium salinarium containing an open reading frame encoding a protein with a calculated molecular mass of 71 kDa was determined. Database searches
revealed that this protein, Hp71, has similarities to eukaryotic cytoskeletal proteins. Heterologous production of Hp71 in
Escherichia coli allowed the isolation of anti-Hp71 antibodies. The antibodies were used (1) to verify the production of Hp71 in H. salinarium and (2) to determine its cytoplasmic localization by immune electron microscopy. Homologous overproduction of Hp71 in H. salinarium and heterologous production in Haloferax volcanii resulted in modifications of cell morphology from rods to extended rods, and from pleiomorphic cells to rods, respectively.
Structure prediction methods indicated that Hp71 has a head-rod-tail configuration, including an N-terminal domain with a
nucleotide binding motif (P-loop), and an extended discontinuous coiled-coil domain of 330 amino acids. To identify related
proteins, the complete genomes of Haemophilus influenzae, Mycoplasma genitalium, and Methanococcus jannaschii were searched for deduced proteins with extended coiled-coil domains. Only one or two proteins were found for each organism,
showing that Hp71 is one of only a few prokaryotic intracellular proteins with extended coiled-coil domains. The phenotype
upon overproduction and the similarity of Hp71 to the SMC superfamily of P-loop head-rod-tail proteins (named after SMC1,
which is involved in the “stability of minichromosomes” in yeast) indicate that Hp71 might be involved in cytoskeleton formation
and/or chromosome partitioning in H. salinarium.
Received: 25 March 1997 / Accepted: 11 August 1997 相似文献
974.
Rapid reactions comprising efflux of K+ and Cl−, phosphorylation of a 63-kDa protein (pp63), extracellular alkalinization and synthesis of H2O2 are equally induced in cells of Picea abies (L.) Karst. by chitotetraose, colloidal chitin and cell wall elicitors from the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) Quél. an ectomycorrhizal partner of spruce. Cleavage of fungal cell wall elicitors and of artificial chitin
elicitors to monomeric and dimeric fragments by apoplasmic spruce chitinases (36-kDa class I chitinase, pI 8.0, and 28-kDa
chitinase, pI 8.7; EC 3.2.1.14) equally prevented induction of these rapid reactions. Also, N-acetylglucosamine oligomers
and elicitors from the fungal cell walls showed a similar dependence of their activity on the degree of polymerisation. From
these results it is suggested that, during ectomycorrhiza formation, only some of the chitin-derived elicitors reach their
receptors at the plant plasma membrane, initiating reactions of the hypersensitive response in the host cells. The remaining
fungal elicitors will be degraded to varying extents by wall-localized chitinases of the host root, reducing the defence reactions
of the plant and allowing symbiotic interactions of both organisms.
Received: 6 January 1997 / Accepted: 14 March 1997 相似文献
975.
Flavonol-deficient petunia pollen [conditionally male fertile (CMF) pollen] is unable to germinate but application of nanomolar
concentrations of flavonol aglycones completely restores function (Mo et al. 1992). In this study a chemically synthesized
radioactive flavonol, [4′-O-14C]kaempferide, was used as a model compound to study the metabolism of flavonols during the first few hours of pollen germination.
[4′-O-14C] Kaempferide was as efficient at inducing CMF pollen germination as kaempferol and quercetin, the aglycone form of the endogenous
flavonols in petunia pollen. Analysis by high-performance liquid chromatography (HPLC) of extracts from both in-vitro-germinated
pollen and the germination medium showed that more than 95% of the applied radioactivity was recovered as three kaempferide
3-O-glycosides and unmetabolized kaempferide; no flavonol catabolites were detected. Only HPLC fractions that contained the aglycone, or produced
it upon acid hydrolysis, could induce CMF pollen germination in vitro. Structurally diverse flavonols could be classified
according to how efficiently the aglycone was internalized and glycosylated during pollen germination. The ability of an individual
flavonol to restore germination correlated with the total uptake of flavonols but not with the amount of glycoside formed
in the pollen. Thus this study reinforces the conclusion that flavonol aglycones are the active compound for inducing pollen
germination.
Received: 4 November 1996/Accepted: 4 December 1996 相似文献
976.
Predation impact of Cyclops vicinus on the rotifer community in Lake Constance in spring 总被引:1,自引:0,他引:1
The predation impact of Cyclops vicinus on rotifers was studiedunder near-natural conditions in small enclosures to evaluatewhether copepod predation is responsible for the decline ofrotifers in Lake Constance in spring. Cyclops vicinus fed selectivelyon Synchaeta spp.; Keratella and Polyarthra spp. were not selectedfor. Predation rates increased with prey density up to a maximumof 37 Synchueta day1 at a density of 1.6 x 106 Synchaetam2, i.e. at -1200 Synchaeta l1. Calculation ofcropping rates suggests that Cyclops alone can control the abundanceof Synchaeta in spring, i.e. that mainly Cyclops is responsiblefor the decline of Synchaeta species in Lake Constance in May. 相似文献
977.
978.
Erika van Wyk Henk Bouwman Herman van der Bank Gerhard H Verdoorn Dieter Hofmann 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2001,129(3):243-264
Gaschromatography was used to establish the presence of quantifiable residues of 14 persistent chlorinated hydrocarbon pollutants in whole blood, clotted blood, heart, kidney, liver and muscle samples obtained from individual African whitebacked (Pseudogyps africanus), Cape griffon (Gyps coprotheres) and Lappetfaced (Torgos tracheliotos) vultures from different localities in South Africa. The levels of pesticides measured in whole blood samples of live specimens were compared between nestlings from two natural breeding colonies, adults from a wildlife area and birds held in captivity. Statistically significant (P<0.05) differences between populations were detected in geometric means calculated for γ-BHC (lindane), α(cis)-chlordane and α-endosulfan. Five of the organochlorine contaminants displayed significant variations between concentrations detected in the clotted blood, organs and muscles excised from vulture carcasses. This includes residues of γ-BHC, α-chlordane, dieldrin, β-endosulfan and heptachlor epoxide. Values of the respective biocides measured in vulture samples were generally low in comparison to results documented for a number of avian species. Although no threat is posed by any of the organochloride pesticides, continual monitoring of especially breeding colonies is recommended. Furthermore, the suitability of African whitebacked vulture nestlings as basic bioindicators is highly advocated. 相似文献
979.
T Muehlberger H H Homann A L Dellon P M Vogt 《Plastic and reconstructive surgery》2001,108(7):2080-2085
Augustus V. Waller's name is associated eponymously with the regressive changes in transected nerves. This article intends to present the many other aspects of Waller's scientific ventures. Apart from pioneering intravital microscopy, Waller made significant contributions to the understanding of the process of tissue inflammation. In addition to his observations of the degenerative changes in severed nerve fibers, he developed a concept of trophic dependence that is relevant for the management of the regeneration of peripheral nerves in plastic surgery. 相似文献
980.