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31.
Influence of femB on methicillin resistance and peptidoglycan metabolism in Staphylococcus aureus. 总被引:12,自引:6,他引:6 下载免费PDF全文
The inactivation of FemB by insertion of Tn551 in the central part of the femB open reading frame was shown to increase susceptibility of methicillin-resistant Staphylococcus aureus strains toward beta-lactam antibiotics to the same extent as did inactivation of femA. Strains carrying the methicillin resistance determinant (mec) and expressing PBP 2' were affected to the same extent as were strains selected for in vitro resistance, which did not express PBP 2'. Both femA and femB, which form an operon, are involved in a yet unknown manner in the glycine interpeptide bridge formation of the S. aureus peptidoglycan. FemB inactivation was shown to reduce the glycine content of peptidoglycan by approximately 40%, depending on the S. aureus strain. The reduction of the interpeptide bridge glycine content led to significant reduction in peptidoglycan cross-linking, as measured by gel permeation high-pressure liquid chromatography of muramidase-digested cell walls. Maximum peptide chain length was reduced by approximately 40%. It is shown that the complete pentaglycine interpeptide bridge is important for the sensitivity against beta-lactam antibiotics and for the undisturbed activity of the staphylococcal cell wall-synthesizing and hydrolyzing enzymes, as was also apparent from electron microscopic examinations, which revealed aberrant placement of cross walls and retarded cell separation, leading to a pseudomulticellular phenotype of the cells for both femA and femB mutants. 相似文献
32.
Summary In asexual reproduction of the water mold,Saprolegnia ferax, four distinct and sequentially produced spores are involved in dispersal, two of which are motile and two of which are nonmotile. Composition of cell surface glycoproteins may be important in dispersal strategies for each of these stages. Binding patterns of fluorescently labelled lectins were investigated to identify differences in glycoproteins of asexually produced dispersal stages. The pattern of lectin binding to zoospores was diverse. FITC-Con A bound to surfaces of zoospores and membranes of the water expulsion vacuole system, indicating the prescence of mannosyl and glucosyl residues. In zoospores incubated for more than 30 min in FITC-WGA and FITC-GS II. which bind N-acetyl glucosamine, fluorescence was sometimes localized in peripheral, intracellular patches. In shorter incubations, secondary zoospores bound these lectins along the groove region where K-bodies were located. Surfaces of cystospores typically bound FITC-WGA, but not FITC-GS II. FITC-GS II, however, bound to empty cystospore walls, probably because reactive sugars were available at the inner surface of the wall. Germ tubes emerging from cystospores bound labelled WGA and GS II, but not Con A. The same lectin binding pattern was found along discharge papilla of primary cystospores, indicating that modifications in cystospore walls associated with direct germination and zoospore discharge were similar. Thus, glycoproteins involved in early establishment of the hyphal system differ from those forming the cell surface of cystospores. Differences in the binding pattern of lectins to zoospores and cystospores highlight differences between cell surface carbohydrates of motile and nonmotile asexual stages.Abbreviations BPA
lectin fromBauhinia purpurea
- C1
primary cystospore
- C2
secondary cystospore
- Con A
concanavalin A, lectin fromCanavalia ensiformis
- DBA
lectin fromDolichos biflorus
- DIC
Nomarski differential interference contrast optics
- DS
dilute salts
- FITC
fluorescein isothiocyanate
- FUC
fucose
- Gal
galactose
- GalNAc
N-acetyl galactosamine
- Glc
glucose
- GlcNAc
N-acetyl glucosamine
- GS I
Griffonia simplicifolia lectin I
- GS II
G. simplicifolia lectin II
- Man
mannose
- MPA
lectin fromMaclura pomifera
- PC
phase contrast optics
- PNA
lectin fromArachis hypogaea
- SBA
soybean agglutinin, lectin fromGlycine max
- UEA-1
lectin fromUlex europaeus
- WGA
wheat germ agglutinin fromTriticum vulgare
- WV
water expulsion vacuole 相似文献
33.
Sarah M. Nour John R. Lawrence Hong Zhu George D. W. Swerhone Martha Welsh Tom W. Welacky Edward Topp 《Applied microbiology》2003,69(1):607-615
The soybean cyst nematode (SCN), Heterodera glycines, causes economically significant damage to soybeans (Glycine max) in many parts of the world. The cysts of this nematode can remain quiescent in soils for many years as a reservoir of infection for future crops. To investigate bacterial communities associated with SCN cysts, cysts were obtained from eight SCN-infested farms in southern Ontario, Canada, and analyzed by culture-dependent and -independent means. Confocal laser scanning microscopy observations of cyst contents revealed a microbial flora located on the cyst exterior, within a polymer plug region and within the cyst. Microscopic counts using 5-(4,6-dichlorotriazine-2-yl)aminofluorescein staining and in situ hybridization (EUB 338) indicated that the cysts contained (2.6 ± 0.5) × 105 bacteria (mean ± standard deviation) with various cellular morphologies. Filamentous fungi were also observed. Live-dead staining indicated that the majority of cyst bacteria were viable. The probe Nile red also bound to the interior polymer, indicating that it is lipid rich in nature. Bacterial community profiles determined by denaturing gradient gel electrophoresis analysis were simple in composition. Bands shared by all eight samples included the actinobacterium genera Actinomadura and Streptomyces. A collection of 290 bacteria were obtained by plating macerated surface-sterilized cysts onto nutrient broth yeast extract agar or on actinomycete medium. These were clustered into groups of siblings by repetitive extragenic palindromic PCR fingerprinting, and representative isolates were tentatively identified on the basis of 16S rRNA gene sequence. Thirty phylotypes were detected, with the collection dominated by Lysobacter and Variovorax spp. This study has revealed the cysts of this important plant pathogen to be rich in a variety of bacteria, some of which could presumably play a role in the ecology of SCN or have potential as biocontrol agents. 相似文献
34.
In 1976, Crump, Hoel, Langley, and Peto described how almost any dose‐response relationship for carcinogens becomes linear at low doses when background cancers are taken into account. This has been used, by the U.S. Environmental Protection Agency, USEPA, as partial justification for a regulatory posture that assumes low‐dose linearity, as is illustrated by a discussion of regulation of benzene as a carcinogen. The argument depends critically on the assumption that the pollutant and the background proceed by the same biological mechanism. In this paper we show that the same argument applies to noncancer end points also. We discuss the application to a number of situations: reduction in lung function and consequent increase in death rate due to (particulate) air pollution; reduction in IQ and hence (in extreme cases) mental deficiency due to radiation in utero; reduction of sperm count and hence increase in male infertility due to DBCP exposure. We conclude that, although the biological basis for the health effect response is different, in each case low‐dose linearity might arise from the same mathematical effect discussed by Crump et al. (1976). We then examine other situations and toxic end points where low‐dose linearity might apply by the same argument. We urge that biologists and chemists should concentrate efforts on comparing the biological and pharmacokinetic processes that apply to the pollutant and the background. Finally, we discuss some public policy implications of the possibility that low dose linearity may be the rule rather than the exception for environmental exposures. 相似文献
35.
Ulrich Nowitzki Ralf Wyrich Peter Westhoff Katrin Henze Claus Schnarrenberger William Martin 《Plant molecular biology》1995,29(6):1279-1291
Exploiting the differential expression of genes for Calvin cycle enzymes in bundle-sheath and mesophyll cells of the C4 plant Sorghum bicolor L., we isolated via subtractive hybridization a molecular probe for the Calvin cycle enzyme d-ribulose-5-phosphate 3-epimerase (R5P3E) (EC 5.1.3.1), with the help of which several full-size cDNAs were isolated from spinach. Functional identity of the encoded mature subunit was shown by R5P3E activity found in affinity-purified glutatione S-transferase fusions expressed in Escherichia coli and by three-fold increase of R5P3E activity upon induction of E. coli overexpressing the spinach subunit under the control of the bacteriophage T7 promoter, demonstrating that we have cloned the first functional ribulose-5-phosphate 3-epimerase from any eukaryotic source. The chloroplast enzyme from spinach shares about 50% amino acid identity with its homologues from the Calvin cycle operons of the autotrophic purple bacteria Alcaligenes eutrophus and Rhodospirillum rubrum. A R5P3E-related eubacterial gene family was identified which arose through ancient duplications in prokaryotic chromosomes, three R5P3E-related genes of yet unknown function have persisted to the present within the E. coli genome. A gene phylogeny reveals that spinach R5P3E is more similar to eubacterial homologues than to the yeast sequence, suggesting a eubacterial origin for this plant nuclear gene.Abbreviations R5P3E
d-ribulose-5-phosphate 3-epimerase
- RPI
ribose-5-phosphate isomerase
- TKL
transketolase
- PRK
phosphoribulokinase
- GAPDH
glyceraldehyde-3-phosphate dehydrogenase
- FBP
fructose-1,6-bisphophatase
- FBP
fructose 1,6-bisphosphate
- G6PDH
glucose-6-phosphate dehydrogenase
- 6PGDH
6-phosphogluconate dehydrogenase
- OPPP
oxidative pentose phosphate pathway
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- FBA
fructose-1,6-bisphophate aldolase
- IPTG
isopropyl -d-thiogalactoside
- GST
glutathione S-tranferase
- PBS
phosphate-buffered saline
- TPI
triosephosphate isomerase 相似文献
36.
Selenoprotein P associates with endothelial cells in rat tissues 总被引:11,自引:0,他引:11
R. F. Burk Kristina E. Hill Martha E. Boeglin Ford F. Ebner Harold S. Chittum 《Histochemistry and cell biology》1997,108(1):11-15
Selenoprotein P is an extracellular heparin-binding protein that has been implicated in protecting the liver against oxidant
injury. Its location in liver, kidney, and brain was determined by conventional immunohistochemistry and confocal microscopy
using a polyclonal antiserum. Selenoprotein P is associated with endothelial cells in the liver and is more abundant in central
regions than in portal regions. It is also present in kidney glomeruli associated with capillary endothelial cells. Staining
of selenoprotein P in the brain is also confined to vascular endothelial cells. The heparin-binding properties of selenoprotein
P could be the basis for its binding to tissue. Its localization to the vicinity of endothelial cells is potentially relevant
to its oxidant defense function.
Accepted: 6 March 1997 相似文献
37.
The purpose of this investigation was to determine whether Madurella mycetomatis, the most frequent agent of eumycotic mycetomas, produces siderophores and synthesizes new outer membrane proteins under iron-starvation conditions. Siderophore production, only of the hydroxamate type, was demonstrated in all nine strains tested. It was regulated by extracellular iron concentrations. Under iron-restricted conditions, M. mycetomatis expressed various outer membrane iron-regulated proteins, particularly of 24-kilodalton, that may participate in iron metabolism. 相似文献
38.
39.
Summary Sixteen patients with unusual heteromorphisms involving alterations of the length and/or position of centromeric heterochromatin are described. Family studies showed that the heteromorphisms were present in other relatives and segregated in the expected 1:1 ratio. There was a significantly greater frequency of unusual heteromorphisms among Orientals than in other races studied. 相似文献
40.
Crayfish (Cambarus bartoni) were tested individually in an electronic shuttlebox thermoregulatory device which allowed them to control water temperature, and thereby their body temperature, by their movements.Crayfish which initially selected 22.1°C water increased their preferred temperature by 1.8°C following injection of killed bacteria (Aeromonas hydrophila) into the gill cavity.This behavioral fever appears similar to that of vertebrates, and may enhance host defense reactions against pathogens. 相似文献