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121.
A receptor selective linear hexapeptide tachykinin analog, senktide, is shown to be highly ordered in solution. The conformational restriction is attributed to steric and electrostatic interactions produced by N-methylation of the third amino acid residue in the sequence and the negatively charged N-terminus. The structure of senktide is described as a dynamic mixture of similar conformations where the predominant one is a distorted antiparallel hydrogen bonded beta-pleated sheet. The observed senktide-receptor specificity is suggested to result from a selection of this or a closely related conformation. 相似文献
122.
123.
Liu CJ Huhman D Sumner LW Dixon RA 《The Plant journal : for cell and molecular biology》2003,36(4):471-484
Mining of Medicago truncatula EST databases and screening of a root cDNA library led to the identification of three cytochrome p450 81E subfamily members. Two were functionally characterized by expression in yeast. The recombinant enzymes in yeast microsomes utilized the same isoflavone substrates, but produced different products hydroxylated at the 2' and/or 3' positions of the B-ring. When transiently expressed in alfalfa leaves, green fluorescent protein (GFP) fusions of the isoflavone 2'- and 3'-hydroxylases localized to the endoplasmic reticulum. The isoflavone 2'-hydroxylase was functional when expressed in Arabidopsis. Differential tissue-specific and biotic/abiotic stress-dependent expression patterns were observed for the isoflavone 2'-hydroxylase and 3'-hydroxylase genes, suggesting differential involvement of 2'- and 3'-hydroxylated isoflavonoids in pathogen defense and insect-induced responses, respectively, in Medicago. 相似文献
124.
125.
126.
Metabolic profiling of saponins in Medicago sativa and Medicago truncatula using HPLC coupled to an electrospray ion-trap mass spectrometer 总被引:5,自引:0,他引:5
Triterpene saponins isolated from Medicago sativa (alfalfa) and Medicago truncatula roots were separated, profiled and identified using an optimized, reversed-phase HPLC with on-line photodiode array detection and electrospray ionization mass spectrometry method (HPLC/PDA/ESI/MS). ESI source polarity and solvent conditions were compared. The effects of these parameters on mass spectral attributes were determined. Ion structures were confirmed using tandem mass spectrometry (MS/MS). Fifteen saponins were identified in alfalfa (cultivars Apollo, Radius, and Kleszczewska) based upon negative-ion HPLC/PDA/ESI/MS, HPLC/PDA/ESI/MS/MS and literature data. In addition, the identification of two new malonated saponins in alfalfa are proposed. Negative-ion HPLC/PDA/ESI/MS and HPLC/PDA/ESI/MS/MS spectra were utilized along with HPLC retention times to profile and identify 27 saponins in M. truncatula (cultivar Jemalong, A17). M. truncatula yielded a much more complex mixture of saponins than observed for alfalfa. The authors are not aware of any previous reports identifying saponin glycosides in M. truncatula. 相似文献
127.
Adrian T. Sumner 《Chromosoma》1998,107(6-7):486-490
Diplochromosomes, consisting of four chromatids lying side-by-side, instead of the normal two, are produced when cells go
through two rounds of DNA replication without separation of chromatids. They are thus an indication of the failure of the
normal chromosome separation mechanism. In the present experiments, induction of diplochromosomes by inhibitors of topoisomerase
II (Topo II) was used to provide further evidence that Topo II is required for separation of daughter chromosomes. Actively
growing cultures of CHO cells were treated with Colcemid, and separated into metaphase and interphase fractions, each of which
was treated for 2 h with the Topo II inhibitor being tested. The cells were then cultivated in fresh medium without inhibitor
for periods of between 18 and 44 h, and metaphase cells once again accumulated by treatment with Colcemid. Chromosome preparations
were made in the standard way and stained with Giemsa. Up to 2,000 metaphases were counted from each culture, and the proportion
with diplochromosomes calculated. At appropriate concentrations, the Topo II inhibitors etoposide and mitoxantrone induced
substantial levels of metaphases with diplochromosomes in cultures that had been treated when the cells were in interphase
(up to 30% and 11%, respectively). Amsacrine, however, only produced a smaller proportion (4.7%) of metaphases with diplochromosomes
after a much longer culture period following treatment. All the inhibitors caused severe chromosome damage. When used to treat
metaphase cells, mitoxantrone and amsacrine only induced diplochromosomes after prolonged culture, although a small number
of diplochromosomes were seen after etoposide treatment and a shorter period of culture. Results with cells treated in metaphase
might indicate that Topo II is, in fact, not required for anaphase chromosome separation, although it is clearly important
for segregation of newly replicated DNA.
Received: 8 August 1998 / Accepted: 13 September 1998 相似文献
128.
Nucleotide variation in the triosephosphate isomerase (Tpi) locus of Drosophila melanogaster and Drosophila simulans 总被引:3,自引:0,他引:3
Hasson E; Wang IN; Zeng LW; Kreitman M; Eanes WF 《Molecular biology and evolution》1998,15(6):756-769
DNA sequence variation in a 1.1-kb region including the coding portion of
the Tpi locus was examined in 25 homozygous third-chromosome lines of
Drosophila melanogaster, nine lines of Drosophila simulans, and one line of
Drosophila yakuba. Our data show that the widespread allozyme polymorphism
observed in cosmopolitan D. melanogaster is due to a glutamic acid
substitution occurring in a phylogenetically conserved lysine that has been
identified as part of the "hinged-lid" active site of the enzyme. This
observation suggests that the replacement polymorphism may have important
functional consequences. One replacement polymorphism was also observed in
D. simulans, although its functional relevance is more difficult to assess,
since it affects a site that is not strongly conserved. This amino acid
change in D. simulans is associated with a single lineage possessing seven
unique silent substitutions, which may be indicative of balancing selection
or population subdivision. The absence of fixed amino acid differences
between D. melanogaster and D. simulans and only a single difference with
D. yakuba suggests that triose phosphate isomerase is under strong
functional constraint. Silent variation is slightly higher for D.
melanogaster than for D. simulans. Finally, we outline the general lack of
evidence for old balanced polymorphisms at allozyme loci in D.
melanogaster.
相似文献
129.
We describe protocols for the fractionation of isolated hepatocytes into eight sub-populations using centrifugal elutriation. The distribution of fluorescein isothiocyanate and acridine orange in hepatocytes prepared from livers pre-perfused with one of these dyes is described and used as an indicator of acinar zone derivation for each population. The cytochrome P-450 content and response to induction by 3-methylcholanthrene and phenobarbitone; the distribution of lactate dehydrogenase, glucose-6-phosphatase, pyruvate kinase and tyrosine aminotransferase activities in the sub-populations is also reported. A marked asymmetry of distribution in all these activities was observed. On the basis of putative zone derivations (based on data of fluorescent dye distribution) of eight factors studied, the distributions of six were consistent with the sub-populations being derived from different acinar zones. Two major discrepancies were noted however, the distribution of pyruvate kinase activity and the response of the sub-populations to phenobarbitone. We conclude from this study that while a metabolic heterogeneity was revealed in the sub-populations generated, further characterisation is required to determine whether acinar zone separation has occurred and if so to what extent. 相似文献
130.
Okra was grown in field plots of Tifton loamy sand naturally infested with the nematodes Meloidogyne incognita and Criconemoides ornalus and the pathogenic fungi Fusarium oxysporum, F. solani, F. roseum, and Pythium spp. Plots were treated with various soil pesticides and left exposed or covered with biodegradable paper film mulch under trickle irrigation. Soil was assayed for nematodes and fungi, and plant roots were examined for root-rot and insect damage. Fewer nematodes and fungi generally were recovered from soil treated with DD-MENCS (with and without film mulch) or methyl bromide-chloropicrin (2:1) (MBC) and film mulch than from nontreated soil. Funfigation with DD-MENCS or MBC suppressed populations of M. incognita, C. ornatus, F. oxysporum, F. solani, F. roseum, and Pythium spp. Ethoprop (alone or combined with other pesticides), sodium azide, and chloroneb were less effective than DD-MENCS and MBC. Plant growth anti yield were greatest when nematodes and pathogenic fungi were controlled. Yield was increased 3-fold by DD-MENCS + film mulch or MBC + film mulch in comparison with the average yield of okra produced in Georgia. The root-knot nematode-Fusarium wilt complex was most severe in nonfuntigated soil. 相似文献