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81.
Bicarbonate enhances synchronous division of the giant nuclei of sporophytes in<Emphasis Type="Italic"> Bryopsis plumosa</Emphasis> 总被引:1,自引:0,他引:1
A mature sporophyte of Bryopsis plumosa (Hudson) C. Agardh forms a huge number of zoospores in its cell continuum. Zoospore formation starts with the division of
a single giant nucleus and subsequent repeated mitosis. We found that an elevation of photosynthetic activity triggered the
division of a mature giant nucleus. Transfer to short-day conditions was not necessary. Giant nuclei did not divide in darkness
or in the presence of 1 μM DCMU. Giant nuclei of as many as 90% of sporophtyes started to divide following the addition of
5 mM NaHCO3 to the growth medium under continuous white light (6–12 W m−2). Frequency of nuclear division increased with increased light intensity. By combining those parameters that promoted the
division of giant nuclei, we developed the "two-step culture method" which is composed of preliminary and main cultures. This
new method guarantees that giant nuclei of more than 90% of all sporophytes synchronously divide between 72 and 96 h after
the transfer to the main culture (continuous white light of 12 W m−2 in PES medium supplemented with 5 mM NaHCO3). 相似文献
82.
83.
Otsuka M Kenmoku H Ogawa M Okada K Mitsuhashi W Sassa T Kamiya Y Toyomasu T Yamaguchi S 《Plant & cell physiology》2004,45(9):1129-1138
ent-Kaurene is a tetracyclic hydrocarbon precursor for gibberellins (GAs) in plants and fungi. To address whether fungal GA biosynthesis enzymes function in plants, we generated transgenic Arabidopsis plants overexpressing ent-kaurene synthase (GfCPS/KS) from a GA-producing fungus Gibberella fujikuroi. GfCPS/KS catalyzes a two-step reaction corresponding to ent-copalyl diphosphate synthase (CPS) and ent-kaurene synthase (KS) activities in plants. When GfCPS/KS was overexpressed and targeted to plastids, a range of GA-deficient phenotypes of the ga1-3 and ga2-1 mutants (defective in CPS and KS, respectively) were restored to wild type. Unexpectedly, the transgenic lines overproducing GfCPS/KS emitted the GA precursor ent-kaurene into the headspace besides its accumulation in the plant body. When co-cultivated with the ent-kaurene overproducers in a closed environment, the airborne ent-kaurene was able to fully complement the dwarf phenotype of ga1-3 and ga2-1 mutants, but not that of the ga3-1 mutant (defective in ent-kaurene oxidase). These results suggest that ent-kaurene may be efficiently metabolized into bioactive GAs in Arabidopsis when supplied as a volatile. We also provide evidence that ent-kaurene is released in the headspace of wild-type Chamaecyparis obtusa and Cryptomeria japonica plants, suggesting the occurrence of this hydrocarbon GA precursor as a volatile in nature. 相似文献
84.
85.
Intestinal IgA synthesis: regulation of front-line body defences 总被引:2,自引:0,他引:2
Immunoglobulin A is the most abundant immunoglobulin isotype in mucosal secretions. In this review, we summarize recent advances in our understanding of the sites, mechanisms and functions of intestinal IgA synthesis in mice. On the basis of these recent findings, we propose an updated model for the induction and regulation of IgA responses in the gut. In addition, we discuss new insights into the role of IgA in the maintenance of gut homeostasis and into the reciprocal interactions between gut B cells and the bacterial flora. 相似文献
86.
Essential role of NF-kappa B-inducing kinase in T cell activation through the TCR/CD3 pathway 总被引:1,自引:0,他引:1
Matsumoto M Yamada T Yoshinaga SK Boone T Horan T Fujita S Li Y Mitani T 《Journal of immunology (Baltimore, Md. : 1950)》2002,169(3):1151-1158
NF-kappa B-inducing kinase (NIK) is involved in lymphoid organogenesis in mice through lymphotoxin-beta receptor signaling. To clarify the roles of NIK in T cell activation through TCR/CD3 and costimulation pathways, we have studied the function of T cells from aly mice, a strain with mutant NIK. NIK mutant T cells showed impaired proliferation and IL-2 production in response to anti-CD3 stimulation, and these effects were caused by impaired NF-kappa B activity in both mature and immature T cells; the impaired NF-kappa B activity in mature T cells was also associated with the failure of maintenance of activated NF-kappa B. In contrast, responses to costimulatory signals were largely retained in aly mice, suggesting that NIK is not uniquely coupled to the costimulatory pathways. When NIK mutant T cells were stimulated in the presence of a protein kinase C (PKC) inhibitor, proliferative responses were abrogated more severely than in control mice, suggesting that both NIK and PKC control T cell activation in a cooperative manner. We also demonstrated that NIK and PKC are involved in distinct NF-kappa B activation pathways downstream of TCR/CD3. These results suggest critical roles for NIK in setting the threshold for T cell activation, and partly account for the immunodeficiency in aly mice. 相似文献
87.
Nobutoshi Yamazaki Hidemi Ishida Tasuku Kimura Morihiko Okada 《Journal of human evolution》1979,8(3):337-349
A computer simulation technique was applied to make clear the mechanical characteristics of primate bipedal walking. A primate body and the walking mechanism were modeled mathematically with a set of dynamic equations. Using a digital computer, the following were calculated from these equations by substituting measured displacements and morphological data of each segment of the primate: the acceleration, joint angle, center of gravity, foot force, joint moment, muscular force, transmitted force at the joint, electric activity of the muscle, generated power by the leg and energy expenditure in walking.The model was evaluated by comparing some of the calculated results with the experimental results such as foot force and electromyographic data, and improved in order to obtain the agreement between them.The level bipedal walking of man, chimpanzee and Japanese monkey and several types of synthesized walking were analyzed from the viewpoint of biomechanics.It is concluded that the bipedal walking of chimpanzee is nearer to that of man than to that of the Japanese monkey because of its propulsive mechanism, but it requires large muscular force for supporting the body weight. 相似文献
88.
89.
Oda K Kasahara S Yamagata Y Abe K Nakajima T 《Bioscience, biotechnology, and biochemistry》2002,66(7):1587-1590
A gene of exo-1,3-beta-D-glucanase (exgS) was cloned from a koji mold, Aspergillus saitoi, genomic DNA using PCR. The exgS has an ORF comprising 2832 bp, which contains one intron of 45 bp, and encodes 945 amino acids. The deduced amino acid sequences showed that the ExgS has a non-homologous linker region consisting of 180 amino acids, which encompassed highly conserved regions observed in Exg homologues from filamentous fungi. A recombinant protein (ExgS) has been recovered from the cultural filtrate of an Aspergillus oryzae strain that carried an expression vector containing full length of the exgS. The N-terminal amino acid sequences of the recombinant exo-1,3-beta-D-glucanase (ExgS) were identical to that of native ExgS from A. saitoi. 相似文献
90.
Plasmid-encoded asp operon confers a proton motive metabolic cycle catalyzed by an aspartate-alanine exchange reaction 下载免费PDF全文
Abe K Ohnishi F Yagi K Nakajima T Higuchi T Sano M Machida M Sarker RI Maloney PC 《Journal of bacteriology》2002,184(11):2906-2913
Tetragenococcus halophila D10 catalyzes the decarboxylation of L-aspartate with nearly stoichiometric release of L-alanine and CO(2). This trait is encoded on a 25-kb plasmid, pD1. We found in this plasmid a putative asp operon consisting of two genes, which we designated aspD and aspT, encoding an L-aspartate-beta-decarboxylase (AspD) and an aspartate-alanine antiporter (AspT), respectively, and determined the nucleotide sequences. The sequence analysis revealed that the genes of the asp operon in pD1 were in the following order: promoter --> aspD --> aspT. The deduced amino acid sequence of AspD showed similarity to the sequences of two known L-aspartate-beta-decarboxylases from Pseudomonas dacunhae and Alcaligenes faecalis. Hydropathy analyses suggested that the aspT gene product encodes a hydrophobic protein with multiple membrane-spanning regions. The operon was subcloned into the Escherichia coli expression vector pTrc99A, and the two genes were cotranscribed in the resulting plasmid, pTrcAsp. Expression of the asp operon in E. coli coincided with appearance of the capacity to catalyze the decarboxylation of aspartate to alanine. Histidine-tagged AspD (AspDHis) was also expressed in E. coli and purified from cell extracts. The purified AspDHis clearly exhibited activity of L-aspartate-beta-decarboxylase. Recombinant AspT was solubilized from E. coli membranes and reconstituted in proteoliposomes. The reconstituted AspT catalyzed self-exchange of aspartate and electrogenic heterologous exchange of aspartate with alanine. Thus, the asp operon confers a proton motive metabolic cycle consisting of the electrogenic aspartate-alanine antiporter and the aspartate decarboxylase, which keeps intracellular levels of alanine, the countersubstrate for aspartate, high. 相似文献