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In order to study gravity effects on plant structure and function, it may become necessary to remove the g-stimulus. On Earth, various instruments such as clinostats have been used by biologists in an attempt to neutralize the effects
of gravity. In this study, the position of amyloplasts was assayed in columella cells in the roots of Arabidopsisthaliana (L.) Heynh. seedlings grown in the following conditions: on Earth, on a two-dimensional clinostat at 1 rpm, on a three-dimensional
clinostat (also called a random-positioning machine, or an RPM), and in space (true microgravity). In addition, the effects
of these gravity treatments on columella cell area and plastid area also were measured. In terms of the parameters measured,
only amyloplast position was affected by the gravity treatments. Plastid position was not significantly different between
spaceflight and RPM conditions but was significantly different between spaceflight and the classical two-dimensional clinostat
treatments. Flanking columella cells showed a greater susceptibility to changes in gravity compared to the central columella
cells. In addition, columella cells of seedlings that were grown on the RPM did not exhibit deleterious effects in terms of
their ultrastructure as has been reported previously for seedlings grown on a two-dimensional clinostat. This study supports
the hypothesis that the RPM provides a useful simulation of weightlessness.
Received: 5 January 2000 / Accepted: 22 February 2000 相似文献
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Irene Mittermann Jacquelyn S. Fetrow Diana L. Schaak Steven C. Almo Dietrich Kraft Erwin Heberle-Bors R. Valenta 《Sexual plant reproduction》1998,11(4):183-191
Profilins are structurally well conserved low molecular weight (12–15 kDa) eukaryotic proteins which interact with a variety
of physiological ligands: (1) cytoskeletal components, e.g., actin; (2) polyphosphoinositides, e.g., phosphatidylinositol-4,5-bisphosphate;
(3) proline-rich proteins, e.g., formin homology proteins and vasodilatator-stimulated phosphoprotein. Profilins may thus
link the microfilament system with signal transduction pathways. Plant profilins have recently been shown to be highly crossreactive
allergens which bind to IgE antibodies of allergic patients and thus cause symptoms of type I allergy. We expressed and purified
from Escherichia coli profilins from birch pollen (Betula verrucosa), humans (Homo sapiens) and yeast (Schizosaccharomyces pombe) and demonstrated that each of these profilins is able to form stable homo- and heteropolymers via disulphide bonds in vitro.
Circular dichroism analysis of oxidized (polymeric) and reduced (monomeric) birch pollen profilin indicates that the two states
have similar secondary structures. Using 125I-labeled birch pollen, yeast and human profilin in overlay experiments, we showed that disulphide bond formation between
profilins can be disrupted under reducing conditions, while reduced as well as oxidized profilin states bind to actin and
profilin-specific antibodies. Exposure of profilin to oxidizing conditions, such as when pollen profilins are liberated on
the surface of the mucosa of atopic patients, may lead to profilin polymerization and thus contribute to the sensitization
capacity of profilin as an allergen.
Received: 25 February 1998 / Revision accepted: 12 May 1998 相似文献
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The choice for specific parameter estimation methods is often more dependent on its availability than its performance. We developed SPOTPY (Statistical Parameter Optimization Tool), an open source python package containing a comprehensive set of methods typically used to calibrate, analyze and optimize parameters for a wide range of ecological models. SPOTPY currently contains eight widely used algorithms, 11 objective functions, and can sample from eight parameter distributions. SPOTPY has a model-independent structure and can be run in parallel from the workstation to large computation clusters using the Message Passing Interface (MPI). We tested SPOTPY in five different case studies to parameterize the Rosenbrock, Griewank and Ackley functions, a one-dimensional physically based soil moisture routine, where we searched for parameters of the van Genuchten-Mualem function and a calibration of a biogeochemistry model with different objective functions. The case studies reveal that the implemented SPOTPY methods can be used for any model with just a minimal amount of code for maximal power of parameter optimization. They further show the benefit of having one package at hand that includes number of well performing parameter search methods, since not every case study can be solved sufficiently with every algorithm or every objective function. 相似文献
59.
Hugues Aschard Bjarni?J. Vilhjálmsson Nicolas Greliche Pierre-Emmanuel Morange David-Alexandre Trégou?t Peter Kraft 《American journal of human genetics》2014,94(5):662-676
Many human traits are highly correlated. This correlation can be leveraged to improve the power of genetic association tests to identify markers associated with one or more of the traits. Principal component analysis (PCA) is a useful tool that has been widely used for the multivariate analysis of correlated variables. PCA is usually applied as a dimension reduction method: the few top principal components (PCs) explaining most of total trait variance are tested for association with a predictor of interest, and the remaining components are not analyzed. In this study we review the theoretical basis of PCA and describe the behavior of PCA when testing for association between a SNP and correlated traits. We then use simulation to compare the power of various PCA-based strategies when analyzing up to 100 correlated traits. We show that contrary to widespread practice, testing only the top PCs often has low power, whereas combining signal across all PCs can have greater power. This power gain is primarily due to increased power to detect genetic variants with opposite effects on positively correlated traits and variants that are exclusively associated with a single trait. Relative to other methods, the combined-PC approach has close to optimal power in all scenarios considered while offering more flexibility and more robustness to potential confounders. Finally, we apply the proposed PCA strategy to the genome-wide association study of five correlated coagulation traits where we identify two candidate SNPs that were not found by the standard approach. 相似文献
60.
John C O'LearyIII Qingyou Li Paul Marinec Laura J Blair Erin E Congdon Amelia G Johnson Umesh K Jinwal John KorenIII Jeffrey R Jones Clara Kraft Melinda Peters Jose F Abisambra Karen E Duff Edwin J Weeber Jason E Gestwicki Chad A Dickey 《Molecular neurodegeneration》2010,5(1):45