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951.
Periplasmic phosphorylation of lipid A is linked to the synthesis of undecaprenyl phosphate 总被引:2,自引:0,他引:2
One-third of the lipid A found in the Escherichia coli outer membrane contains an unsubstituted diphosphate unit at position 1 (lipid A 1-diphosphate). We now report an inner membrane enzyme, LpxT (YeiU), which specifically transfers a phosphate group to lipid A, forming the 1-diphosphate species. (32)P-labelled lipid A obtained from lpxT mutants do not produce lipid A 1-diphosphate. In vitro assays with Kdo(2)-[4'-(32)P]lipid A as the acceptor shows that LpxT uses undecaprenyl pyrophosphate as the substrate donor. Inhibition of lipid A 1-diphosphate formation in wild-type bacteria was demonstrated by sequestering undecaprenyl pyrophosphate with the cyclic polypeptide antibiotic bacitracin, providing evidence that undecaprenyl pyrophosphate serves as the donor substrate within whole bacteria. LpxT-catalysed phosphorylation is dependent upon transport of lipid A across the inner membrane by MsbA, a lipid A flippase, indicating a periplasmic active site. In conclusion, we demonstrate a novel pathway in the periplasmic modification of lipid A that is directly linked to the synthesis of undecaprenyl phosphate, an essential carrier lipid required for the synthesis of various bacterial polymers, such as peptidoglycan. 相似文献
952.
953.
Can salinity-induced mortality explain larval vertical distribution with respect to a halocline? 总被引:2,自引:0,他引:2
For the larvae of two echinoderm species that coexist in Atlantic Canada (bipinnaria of the sea star Asterias rubens and 4- and 6-arm echinoplutei of the sea urchin Strongylocentrotus droebachiensis), we examined the effect of short- and long-term exposure to salinity (ranging from 18 to 35) on the probability of larval survival in laboratory experiments. We also related larval vertical distributions in response to sharp haloclines generated in the laboratory to survival probability in the salinity of different layers in the water column. For both species and developmental stages, survival probability decreased with decreasing salinity, and a salinity range of 24-27 emerged as the critical threshold for larval tolerance. The relationship between the proportion of larvae that crossed a halocline into the top water layer and the survival probability of larvae in the salinity of that layer was significant for both species. Interestingly, the shape of this response was species-specific but not stage-specific for S. droebachiensis. Our findings suggest that larval avoidance of low-salinity water layers may be an adaptive behavior that increases survival and indirectly influences larval distribution. 相似文献
954.
Meendering JR Torgrimson BN Miller NP Kaplan PF Minson CT 《American journal of physiology. Heart and circulatory physiology》2008,294(4):H1630-H1637
Medroxyprogesterone acetate (MPA) is widely known for its use in combination hormone therapy for postmenopausal women. However, MPA is also commonly used in young women for contraception and treatment of a number of gynecological conditions. Despite its widespread use, the cardiovascular effects of MPA in young women are unclear. Therefore, the purpose of this study was to determine the acute effects of MPA when used in combination with estradiol on markers of cardiovascular risk in young women. We suppressed endogenous estrogens and progesterone in 10 premenopausal women using a gonadotropin-releasing hormone antagonist (GnRHa) for 10 days. On day 4 of GnRHa subjects received 0.1 mg of estradiol (GnRHa+E(2)), and on day 7 5 mg of MPA was added (GnRHa+E(2)+MPA). Endothelium-dependent vasodilation and endothelium-independent vasodilation of the brachial artery, lipids, homocysteine, high-sensitivity C-reactive protein, and endothelin-1 were assessed during treatment with GnRHa, GnRHa+E(2), and GnRHa+E(2)+MPA. Four additional subjects were tested to validate the efficacy of the GnRHa model and confirm the findings. Endothelium-dependent vasodilation was greater during GnRHa+E(2) than during GnRHa or GnRHa+E(2)+MPA (P = 0.006). Endothelin-1 was lower during GnRHa+E(2) than GnRHa alone (P = 0.039). Endothelin-1 increased with the addition of MPA and was not significantly different from GnRHa alone. There were no differences in the other markers of cardiovascular risk between hormone treatment days. These data suggest that acute MPA administration negates the beneficial effects of estradiol on endothelium-dependent vasodilation in young women. In addition, these data suggest that estradiol decreases endothelin-1 concentrations and the addition of MPA may counteract the effect of estradiol on endothelin-1. 相似文献
955.
Deciduous lower premolars (milk teeth) of the Eocene artiodactyl family Cebochoeridae possess accessory denticles and are
remarkably similar to both deciduous and adult teeth of the cetacean family Basilosauridae, suggesting that morphological
characters of juvenile dentitions are important to understanding the phylogenetic origin of whales and morphological transitions
in the cetartiodactyl lineage. Incorporation of these new characters into a larger phylogenetic analysis of morphological
characters of artiodactyls, mesonychids, and basal and recent whales supports a monophyletic Cetartiodactyla, but does not
directly support a whale–hippo relationship. However, the presence of accessory denticles on some artiodactyl dentitions weakens
the morphological support for a monophyletic Artiodactyla, suggesting either that whales and cebochoerids may be more closely
related than had been thought, or that cebochoerids share a developmental pathway with cetaceans. 相似文献
956.
957.
Mohamed Mohideen Quwailid Alison Hugill Neil Dear Lucie Vizor Sara Wells Emma Horner Shelly Fuller Jessica Weedon Hamish McMath Paul Woodman David Edwards David Campbell Susan Rodger Joanne Carey Ann Roberts Pete Glenister Zuzanna Lalanne Nick Parkinson Emma L. Coghill Richard McKeone Sam Cox John Willan Andy Greenfield David Keays Saffron Brady Nigel Spurr Ian Gray Jackie Hunter Steve D.M. Brown Roger D. Cox 《Mammalian genome》2004,15(8):585-591
N-ethyl-N-nitrosourea (ENU) introduces mutations throughout the mouse genome at relatively high efficiency. Successful high-throughput phenotype screens have been reported and alternative screens using sequence-based approaches have been proposed. For the purpose of generating an allelic series in selected genes by a sequence-based approach, we have constructed an archive of over 4000 DNA samples from individual F1 ENU-mutagenized mice paralleled by frozen sperm samples. Together with our previously reported archive, the total size now exceeds 6000 individuals. A gene-based screen of 27.4 Mbp of DNA, carried out using denaturing high-performance liquid chromatography (DHPLC), found a mutation rate of 1 in 1.01 Mbp of which 1 in 1.82 Mbp were potentially functional. Screening of whole or selected regions of genes on subsets of the archive has allowed us to identify 15 new alleles from 9 genes out of 15 tested. This is a powerful adjunct to conventional mutagenesis strategies and has the advantage of generating a variety of alleles with potentially different phenotypic outcomes that facilitate the investigation of gene function. It is now available to academic collaborators as a community resource. 相似文献
958.
959.
Arsenite-Oxidizing Hydrogenobaculum Strain Isolated from an Acid-Sulfate-Chloride Geothermal Spring in Yellowstone National Park 总被引:1,自引:0,他引:1 下载免费PDF全文
Jessica Donahoe-Christiansen Seth D''Imperio Colin R. Jackson William P. Inskeep Timothy R. McDermott 《Applied microbiology》2004,70(3):1865-1868
An arsenite-oxidizing Hydrogenobaculum strain was isolated from a geothermal spring in Yellowstone National Park, Wyo., that was previously shown to contain microbial populations engaged in arsenite oxidation. The isolate was sensitive to both arsenite and arsenate and behaved as an obligate chemolithoautotroph that used H2 as its sole energy source and had an optimum temperature of 55 to 60°C and an optimum pH of 3.0. The arsenite oxidation in this organism displayed saturation kinetics and was strongly inhibited by H2S. 相似文献
960.
No Evidence for a Difference in Neuropsychological Profile among Carriers and Noncarriers of the FMR1 Premutation in Adults under the Age of 50 下载免费PDF全文
Jessica Ezzell Hunter Emily Graves Allen Ann Abramowitz Michele Rusin Mary Leslie Gloria Novak Debra Hamilton Lisa Shubeck Krista Charen Stephanie L. Sherman 《American journal of human genetics》2008,83(6):692-702
The 5′ untranslated region of the fragile X mental retardation gene, FMR1, contains a polymorphic CGG repeat. Expansions of this repeat are associated with a spectrum of disorders. Full mutation alleles, repeats ≥ 200, are associated with fragile X syndrome. Premutation alleles, repeats of ~55–199, are associated with a tremor-ataxia syndrome most commonly in older males and primary ovarian insufficiency in females. However, the neuropsychological impact of carrying a premutation allele is presently unclear in younger adults. In this study, we analyzed neuropsychological scores for 138 males and 506 females ascertained from the general population and from families with a history of fragile X syndrome. Subjects were age 18–50 years and had varying repeat lengths. Neuropsychological scores were obtained from measures of general intelligence, memory, and executive functioning, including attention. Principal component analysis followed by varimax rotation was used to create independent factors for analysis. These factors were modeled for males and females separately via a general linear model that accounted for correlation among related subjects. All models were adjusted for potential confounders, including age at testing, ethnicity, and household income. Among males, no repeat length associations were detected for any factor. Among females, only a significant association with repeat length and self-report attention (p < 0.01) was detected, with premutation carriers self-reporting significantly more attention-related problems compared to noncarriers. No significant interactions between repeat length and age were detected. Overall, these results indicate the lack of a global neuropsychological impact of carrying a premutation allele among adults under the age of 50. 相似文献