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991.
Harrison B Raju D Garmory HS Brett MM Titball RW Sarker MR 《Applied and environmental microbiology》2005,71(12):8362-8370
Clostridium perfringens type A food poisoning is caused by C. perfringens isolates carrying a chromosomal enterotoxin gene (cpe), while non-food-borne gastrointestinal (GI) diseases, such as antibiotic-associated diarrhea (AAD) and sporadic diarrhea (SD), are caused by C. perfringens plasmid cpe isolates. A recent study reported the association of beta2 toxin (CPB2) with human GI diseases, and particularly AAD/SD, by demonstrating that a large percentage of AAD/SD isolates, in contrast to a small percentage of food poisoning isolates, carry the beta2-toxin gene (cpb2). This putative relationship was further tested in the current study by characterizing 14 cpe+ C. perfringens fecal isolates associated with recent cases of human SD in England (referred to hereafter as SD isolates). These SD isolates were all classified as cpe+ type A, and 12 of the 14 cpe+ isolates carry their cpe gene on the plasmid and 2 carry it on the chromosome. Interestingly, cpb2 is present in only 12 plasmid cpe isolates; 11 isolates carry cpe and cpb2 on different plasmids, but cpe and cpb2 are located on the same plasmid in one isolate. C. perfringens enterotoxin is produced by all 14 cpe+ SD isolates. However, only 10 of the 12 cpe+/cpb2+ SD isolates produced CPB2, with significant variation in amounts. The levels of cpb2 mRNA in low- to high-CPB2-producing SD isolates differed to such an extent (30-fold) that this difference could be considered a major cause of the differential level of CPB2 production in vitro by SD isolates. Furthermore, no silent or atypical cpb2 was found in a CPB2 Western blot-negative isolate, 5422/94, suggesting that the lack of CPB2 production in 5422/94 was due to low expression of cpb2 mRNA. This received support from our observation that the recombinant plasmid carrying 5422/94 cpb2, which overexpressed cpb2 mRNA, restored CPB2 production in F4969 (a cpb2-negative isolate). Collectively, our present results suggest that CPB2 merits further study as an accessory toxin in C. perfringens-associated SD. 相似文献
992.
How to Bring the “Unseen” Proteome to the Limelight via Electrophoretic Pre-Fractionation Techniques
The present review reports a panoply of electrophoretic methods as pre-fractionation tools in proteomic investigations in
preparation for mass spectrometry or two-dimensional electrophoresis map analysis. Such electrophoretic pre-fractionation
protocols include all those electrokinetic methodologies which are performed in free solution, most of them relying on isoelectric
focusing steps (although some approaches based on gels and granulated media are also discussed). Devices associated with electrophoretic
separations are multi-chamber apparatuses, such as the multi-compartment electrolyzers equipped with either isoelectric membranes
or with isoelectric beads, Off-Gel electrophoresis in a multi-cup device and the Rotofor, an instrument also based on a multi-chamber
system but exploiting the conventional technique of carrier-ampholyte-focusing. Other free-flow systems, as well as miniaturized
chambers, are also described. 相似文献
993.
994.
995.
Modeling the simple epidemic with deterministic differential equations and random initial conditions
In a simple epidemic the only transition in the population is from susceptible to infected and the total population size is fixed for all time. This paper investigates the effect of random initial conditions on the deterministic model for the simple epidemic. By assuming a Beta distribution on the initial proportion of susceptibles, we define a distribution that describes the proportion of susceptibles in a population at any time during an epidemic. The mean and variance for this distribution are derived as hypergeometric functions, and the behavior of these functions is investigated. Lastly, we define a distribution to describe the time until a given proportion of the population remains susceptible. A method for finding the quantiles of this distribution is developed and used to make confidence statements regarding the time until a given proportion of the population is susceptible. 相似文献
996.
Fish track wastewater pollution to estuaries 总被引:1,自引:0,他引:1
Excess nitrogen is a forceful agent of ecological change in coastal waters, and wastewater is a prominent source of nitrogen.
In catchments where multiple sources of nitrogen pollution co-exist, biological indicators are needed to gauge the degree
to which wastewater-N can propagate through the receiving food webs. The purpose of this study was to test whether estuarine
fish are suitable as indicators of sewage-N pollution. Fish were analysed from three estuaries within a 100-km strip on the
Australian East Coast. The estuaries differ substantially in wastewater loading: (1) the Maroochy Estuary receives a large
fraction of the local shire’s treated sewage, (2) the Mooloolah Estuary has no licensed treated wastewater outfalls but marinas/harbours
and stormwater may contribute nitrogen, and (3) the Noosa Estuary which neither receives licensed discharges nor has suspected
wastewater loads. Sampling for fish included both high rainfall (‘wet’ season) and low rainfall (‘dry’ season) periods. Muscle-δ15N was the variable predicted to respond to treated wastewater loading, reflecting the relative enrichment in 15N resulting from the treatment process and distinguishing it from alternative N sources such as fertiliser and natural nitrogen
inputs (both 15N-depleted). Of the 19 fish species occurring in all three estuaries, those from the Maroochy Estuary had significantly elevated
δ15N values (up to 9.9‰), and inter-estuarine differences in fish-δ15N were consistent across seasons. Furthermore, not only did all fish from the estuary receiving treated wastewater carry a
very distinctive sewage-N tissue signal, but enriched muscle-δ15N was also evident in all species sampled from the one estuary in which sewage contamination was previously only suspected (i.e. the Mooloolah Estuary: 0.2–4.8‰ enrichment over fish from reference system). Thus, fish-δ15N is a suitable indicator of wastewater-N not only in systems that receive large loads, but also for the detection of more
subtle nitrogen inputs. Arguably, fish may be preferred indicators of sewage-N contamination because they: (1) integrate nitrogen
inputs over long time periods, (2) have an element of ‘ecological relevance’ because fish muscle-δ15N reflect movement of sewage-N through the food chain, and (3) pollution assessments can usually be based on evidence from
multiple species. 相似文献
997.
Frank RA Pratap JV Pei XY Perham RN Luisi BF 《Structure (London, England : 1993)》2005,13(8):1119-1130
The pyruvate dehydrogenase (PDH) multienzyme complex is central to oxidative metabolism. We present the first crystal structure of a complex between pyruvate decarboxylase (E1) and the peripheral subunit binding domain (PSBD) of the dihydrolipoyl acetyltransferase (E2). The interface is dominated by a "charge zipper" of networked salt bridges. Remarkably, the PSBD uses essentially the same zipper to alternately recognize the dihydrolipoyl dehydrogenase (E3) component of the PDH assembly. The PSBD achieves this dual recognition largely through the addition of a network of interfacial water molecules unique to the E1-PSBD complex. These structural comparisons illuminate our observations that the formation of this water-rich E1-E2 interface is largely enthalpy driven, whereas that of the E3-PSBD complex (from which water is excluded) is entropy driven. Interfacial water molecules thus diversify surface complementarity and contribute to avidity, enthalpically. Additionally, the E1-PSBD structure provides insight into the organization and active site coupling within the approximately 9 MDa PDH complex. 相似文献
998.
999.
Lopez-Vaamonde C Godfray HC West SA Hansson C Cook JM 《Journal of evolutionary biology》2005,18(4):1029-1041
We studied host selection and exploitation, two crucial aspects of parasite ecology, in Achrysocharoides parasitoid wasps, which show remarkable host specificity and unusual offspring sex allocation. We estimated a molecular phylogeny of 15 Achrysocharoides species and compared this with host (plant and insect) phylogenies. This tri-trophic phylogenetic comparison provides no evidence for cospeciation, but parasitoids do show phylogenetic conservation of the use of plant genera. Patterns of sequence divergence also suggest that the parasitoids radiated more recently (or evolved much faster) than their insect hosts. Three main categories of brood production occur in parasitoids: (1) solitary offspring, (2) mixed sex broods and (3) separate (split) sex broods. Split sex broods are very rare and virtually restricted to Achrysocharoides, while the other types occur very widely. Our phylogeny suggests that split sex broods have evolved twice and provides evidence for a transition from solitary to mixed sex broods, via split sex broods, as predicted by theory. 相似文献
1000.
Dissection of Arabidopsis ADP-RIBOSYLATION FACTOR 1 function in epidermal cell polarity 总被引:10,自引:0,他引:10 下载免费PDF全文
Vesicle trafficking is essential for the generation of asymmetries, which are central to multicellular development. Core components of the vesicle transport machinery, such as ADP-ribosylation factor (ARF) GTPases, have been studied primarily at the single-cell level. Here, we analyze developmental functions of the ARF1 subclass of the Arabidopsis thaliana multigene ARF family. Six virtually identical ARF1 genes are ubiquitously expressed, and single loss-of-function mutants in these genes reveal no obvious developmental phenotypes. Fluorescence colocalization studies reveal that ARF1 is localized to the Golgi apparatus and endocytic organelles in both onion (Allium cepa) and Arabidopsis cells. Apical-basal polarity of epidermal cells, reflected by the position of root hair outgrowth, is affected when ARF1 mutants are expressed at early stages of cell differentiation but after they exit mitosis. Genetic interactions during root hair tip growth and localization suggest that the ROP2 protein is a target of ARF1 action, but its localization is slowly affected upon ARF1 manipulation when compared with that of Golgi and endocytic markers. Localization of a second potential target of ARF1 action, PIN2, is also affected with slow kinetics. Although extreme redundancy precludes conventional genetic dissection of ARF1 functions, our approach separates different ARF1 downstream networks involved in local and specific aspects of cell polarity. 相似文献