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951.
Barbara S Bregman 《Current opinion in neurobiology》1998,8(6):800-807
Important advances have been made in our understanding of conditions that influence the intrinsic capacity of mature CNS neurons to initiate and maintain a regrowth response. The combination of exogenous neurotrophic support with strategies to alter the terrain at the injury site itself suggests that there are important interactions between them that lead to increased axonal regeneration. The ability of chronically injured neurons to initiate a regeneration response is unexpected. Our view of the role that inhibitors play in restricting axonal growth has also expanded. The findings indicate that the windows of opportunity for enhancing growth after spinal cord injury may be more numerous than previously thought. 相似文献
952.
Christopher S. Cobbett Mike J. May Ross Howden Barbara Rolls 《The Plant journal : for cell and molecular biology》1998,16(1):73-78
This paper reports that the glutathione (GSH)-deficient mutant, cad2–1 , of Arabidopsis is deficient in the first enzyme in the pathway of GSH biosynthesis, γ-glutamylcysteine synthetase (GCS). The mutant accumulates a substrate of GCS, cysteine, and is deficient in the product, γ-glutamylcysteine. In vitro enzyme assays showed that the cad2–1 mutant has 40% of wild-type levels of GCS activity but is unchanged in the activity of the second enzyme in the pathway, GSH synthetase. The CAD2 locus maps to chromosome 4 and is tightly linked to a gene, GSHA , identified by a previously isolated cDNA. A genomic clone of GSHA complements both the phenotypic and biochemical deficiencies of the cad2–1 mutant. The nucleotide sequence of the gene has been determined and, in the mutant, this gene contains a 6 bp deletion within an exon. These data demonstrate that the CAD2 gene encodes GCS. The cad2–1 mutation is close to the conserved cysteine which is believed to bind the substrate glutamate and the specific inhibitor L-buthionine-[S,R] sulfoximine (BSO). Both root growth and GCS activity of the cad2–1 mutant was less sensitive than the wild-type to inhibition by BSO, indicating that the mutation may alter the affinity of the inhibitor binding site. 相似文献
953.
Regulation of Adherence and Virulence by the Entamoeba histolytica Lectin Cytoplasmic Domain, Which Contains a β2 Integrin Motif 下载免费PDF全文
Richard R. Vines Girija Ramakrishnan Joshua B. Rogers Lauren A. Lockhart Barbara J. Mann William A. Petri Jr. 《Molecular biology of the cell》1998,9(8):2069-2079
Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the β2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin’s role in virulence. 相似文献
954.
955.
John M. Andersland David C. Dixon Robert W. Seagull Barbara A. Triplett 《In vitro cellular & developmental biology. Plant》1998,34(3):173-180
Summary Over the last 25 yr, success in characterizing the individual protein components of animal cytoskeletons was possible, in
part, due to technical advances in the isolation and purification of anucleate cytoskeletons from animal cells. As a step
towards characterizing protein components of the plant cytoskeleton, we have isolated cytoskeletons from cytoplasts (anucleate
protoplasts) prepared from cotton fiber cells grown in ovule culture. Cytoplasts isolated into a hypertonic, Ca2+-free medium at pH 6.8 retained internal structures after extraction with the detergent, Triton X-100. These structures were
shown to include microtubule and microfilament arrays by immunofluorescence and electron microscopy. Actin and tubulin were
the only abundant proteins in these preparations, suggesting that microfilaments and microtubules were the major cytoskeleta
elements in the isolated cytoskeletons. The absence of additional, relatively abundant proteins suggests that (a) other cytoskeletal
arrays potentially present in fiber cells (e.g., intermediate filaments) were either lost during detergent extraction or were
minor components of the fiber cell cytoskeleton; and (b) high ratios of individual cytoskeletal-associated proteins relative
to actin and tubulin were not required to maintain microtubules and microfilaments in organized structures. 相似文献
956.
Barbara M. Reed Jeanine Denoma Jie Luo Yongjian Chang Leigh Towill 《In vitro cellular & developmental biology. Plant》1998,34(3):256-260
Summary Germplasm collections of vegetatively propagated crops are usually maintained as plants in fields or potted in greenhouses
or screened enclosures. Safety duplication of these collections, as duplicate plants or separate collections, is costly and
requires large amounts of space. Cryopreservation techniques which were recently developed for long-term storage of pear germalasm
may offer an efficient alternative to conventional germplasm collection maintenance. Pear (Pyrus L.) germplasm may now be stored as seeds (species), dormant buds or pollen from field-grown trees, or shoot tips fromin vitro-grown plants (cultivars). Pear germplasm may now be cryopreserved and stored for long periods (> 100 yr) utilizing slow-freezing
or vitrification ofin vitro-grown shoot-tips. Dormant bud freezing, pollen, and seed cryopreservation of other lines are being developed to complete
the base collection forPyrus. This cryopreserved collection provides base (long-term) storage for the field-grown pear germplasm collection at the National
Clonal Germplasm Repository, Corvallis, Oregon.
Based on a presentation at the 1997 Congress on In Vitro Biology held in Washington, D.C., June 14–18, 1997. 相似文献
957.
Lumenal and Transmembrane Domains Play a Role in Sorting Type I Membrane Proteins on Endocytic Pathways 总被引:4,自引:3,他引:1 下载免费PDF全文
Previous studies have shown that when the cytosolic domains of the type I membrane proteins TGN38 and lysosomal glycoprotein 120 (lgp120) are added to a variety of reporter molecules, the resultant chimeric molecules are localized to the trans-Golgi network (TGN) and to lysosomes, respectively. In the present study we expressed chimeric constructs of rat TGN38 and rat lgp120 in HeLa cells. We found that targeting information in the cytosolic domain of TGN38 could be overridden by the presence of the lumenal and transmembrane domains of lgp120. In contrast, the presence of the transmembrane and cytosolic domains of TGN38 was sufficient to deliver the lumenal domain of lgp120 to the trans-Golgi network. On the basis of steady-state localization of the various chimeras and antibody uptake experiments, we propose that there is a hierarchy of targeting information in each molecule contributing to sorting within the endocytic pathway. The lumenal and cytosolic domains of lgp120 contribute to sorting and delivery to lysosomes, whereas the transmembrane and cytosolic domains of TGN38 contribute to sorting and delivery to the trans-Golgi network. 相似文献
958.
The Activity of Differentiation Factors Induces Apoptosis in Polyomavirus Large T-Expressing Myoblasts 总被引:2,自引:0,他引:2 下载免费PDF全文
Gian Maria Fimia Vanesa Gottifredi Barbara Bellei Maria Rosaria Ricciardi Agostino Tafuri Paolo Amati Rossella Maione 《Molecular biology of the cell》1998,9(6):1449-1463
It is commonly accepted that pathways that regulate proliferation/differentiation processes, if altered in their normal interplay, can lead to the induction of programmed cell death. In a previous work we reported that Polyoma virus Large Tumor antigen (PyLT) interferes with in vitro terminal differentiation of skeletal myoblasts by binding and inactivating the retinoblastoma antioncogene product. This inhibition occurs after the activation of some early steps of the myogenic program. In the present work we report that myoblasts expressing wild-type PyLT, when subjected to differentiation stimuli, undergo cell death and that this cell death can be defined as apoptosis. Apoptosis in PyLT-expressing myoblasts starts after growth factors removal, is promoted by cell confluence, and is temporally correlated with the expression of early markers of myogenic differentiation. The block of the initial events of myogenesis by transforming growth factor β or basic fibroblast growth factor prevents PyLT-induced apoptosis, while the acceleration of this process by the overexpression of the muscle-regulatory factor MyoD further increases cell death in this system. MyoD can induce PyLT-expressing myoblasts to accumulate RB, p21, and muscle- specific genes but is unable to induce G00 arrest. Several markers of different phases of the cell cycle, such as cyclin A, cdk-2, and cdc-2, fail to be down-regulated, indicating the occurrence of cell cycle progression. It has been frequently suggested that apoptosis can result from an unbalanced cell cycle progression in the presence of a contrasting signal, such as growth factor deprivation. Our data involve differentiation pathways, as a further contrasting signal, in the generation of this conflict during myoblast cell apoptosis. 相似文献
959.
Serologic Detection of CagA Positive Helicobacter pylori Infection in a Northern Italian Population: Its Association with Peptic Ulcer Disease 总被引:2,自引:0,他引:2
960.
Joshua T. Cohen Barbara D. Beck Teresa S. Bowers Robert L. Bornschein Edward J. Calabrese 《人类与生态风险评估》1998,4(2):341-377
This paper describes development of a multi-pathway arsenic exposure model. The model uses information on arsenic concentrations in food, water, soil, and dust, combined with estimates of intake and medium-specific absorption. Urinary arsenic is predicted assuming that 60% of absorbed arsenic is excreted in urine under steady state conditions. Fecal arsenic is predicted assuming all unabsorbed arsenic is excreted in feces. We applied this model at a former copper smelter site. Site specific distributions were available for the following parameters: soil and dust arsenic concentration (geometric mean approximately 100 to 200?ppm and 50 to 100?ppm, respectively); the combined childhood soil and dust ingestion rate (geometric mean of 20?mg/d); soil and dust arsenic relative bioavailability (geometric mean 0.20 and 0.28, respectively); exposure duration; water arsenic concentration; air arsenic concentration; and total arsenic in food. Monte Carlo simulation was used to predict daily arsenic uptake and excretion in urine and feces for children. Predicted urine arsenic levels were less than measured levels (73% to 88% of measured values, depending on region of site). On the other hand, predicted fecal arsenic levels exceeded measured levels by a factor of 1.7 to 4.6. We were able to improve the correspondence between predicted and measured arsenic excretion rates by decreasing the assumed value of the combined soil and dust ingestion rate, and increasing the assumed bioavailability of arsenic in soil and dust. 相似文献