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241.
Effect of decapacitation factor on the oxygen uptake of rabbit spermatozoa recovered from the uterus 总被引:2,自引:0,他引:2
I. G. White J. C. Rodger Dr. R. N. Murdoch W. L. Williams T. O. Abney 《Cellular and molecular life sciences : CMLS》1975,31(1):80-81
Résumé L'addition d'un facteur de décapacitation préparé à partir du plasma séminal de lapin et de taureau a généralement produit une augmentation supplémentaire de l'absorption d'oxygène, quand il a été ajouté à la suspension de spermatozoïdes enlevée de l'utérus. Le facteur de décapacitation n'a exercé aucun effet stimulant similaire sur les spermatozoïdes de lapin avant l'incubation dans l'utérus et n'a montré lui-même aucune absorption d'oxygène appréciable.
Dr.I. G. White is indebted to the Population Council for a fellowship and to the Australian Research Grants Committee for financial support. The authors are indebted to ProfessorC. W. Emmens for his interest and advice. 相似文献
Dr.I. G. White is indebted to the Population Council for a fellowship and to the Australian Research Grants Committee for financial support. The authors are indebted to ProfessorC. W. Emmens for his interest and advice. 相似文献
242.
243.
Hessa T Kim H Bihlmaier K Lundin C Boekel J Andersson H Nilsson I White SH von Heijne G 《Nature》2005,433(7024):377-381
Membrane proteins depend on complex translocation machineries for insertion into target membranes. Although it has long been known that an abundance of nonpolar residues in transmembrane helices is the principal criterion for membrane insertion, the specific sequence-coding for transmembrane helices has not been identified. By challenging the endoplasmic reticulum Sec61 translocon with an extensive set of designed polypeptide segments, we have determined the basic features of this code, including a 'biological' hydrophobicity scale. We find that membrane insertion depends strongly on the position of polar residues within transmembrane segments, adding a new dimension to the problem of predicting transmembrane helices from amino acid sequences. Our results indicate that direct protein-lipid interactions are critical during translocon-mediated membrane insertion. 相似文献
244.
Vestrand WT Wozniak PR Wren JA Fenimore EE Sakamoto T White RR Casperson D Davis H Evans S Galassi M McGowan KE Schier JA Asa JW Barthelmy SD Cummings JR Gehrels N Hullinger D Krimm HA Markwardt CB McLean K Palmer D Parsons A Tueller J 《Nature》2005,435(7039):178-180
The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium. 相似文献
245.
246.
R gene expression induced by a type-III effector triggers disease resistance in rice 总被引:10,自引:0,他引:10
Gu K Yang B Tian D Wu L Wang D Sreekala C Yang F Chu Z Wang GL White FF Yin Z 《Nature》2005,435(7045):1122-1125
Disease resistance (R) genes in plants encode products that specifically recognise incompatible pathogens and trigger a cascade of events leading to disease resistance in the host plant. R-gene specificity is dictated by both host R genes and cognate avirulence (avr) genes in pathogens. However, the basis of gene-for-gene specificity is not well understood. Here, we report the cloning of the R gene Xa27 from rice and the cognate avr gene avrXa27 from Xanthomonas oryzae pv. oryzae. Resistant and susceptible alleles of Xa27 encode identical proteins. However, expression of only the resistant allele occurs when a rice plant is challenged by bacteria harbouring avrXa27, whose product is a nuclear localized type-III effector. Induction of Xa27 occurs only in the immediate vicinity of infected tissue, whereas ectopic expression of Xa27 resulted in resistance to otherwise compatible strains of the pathogen. Thus Xa27 specificity towards incompatible pathogens involves the differential expression of the R gene in the presence of the AvrXa27 effector. 相似文献
247.
Matthew?GortonEmail author John?White Mikhail?Dumitrashko 《Systemic Practice and Action Research》2005,18(1):35-52
Enterprises in the Former Soviet Union (FSU) have had to fundamentally reform how they are managed and operate to cope with the switch from central planning to a more market based economy. In understanding these challenges and how firms are reacting to them, the clinical inquiry approach, a variant of action research, is deemed particularly appropriate. Research following this approach was conducted with a case study enterprise drawn from the Moldovan wine industry. The process encouraged self-diagnosis and intervention and a PSEFI (Problems, Strategies, Evaluations, and Future Issues) matrix was drawn to guide and assess the companys evolution. Reflections on the benefits of the clinical inquiry approach in transitional economies, compared to more conventional business support and research methods are discussed. 相似文献
248.
Theologis A Ecker JR Palm CJ Federspiel NA Kaul S White O Alonso J Altafi H Araujo R Bowman CL Brooks SY Buehler E Chan A Chao Q Chen H Cheuk RF Chin CW Chung MK Conn L Conway AB Conway AR Creasy TH Dewar K Dunn P Etgu P Feldblyum TV Feng J Fong B Fujii CY Gill JE Goldsmith AD Haas B Hansen NF Hughes B Huizar L Hunter JL Jenkins J Johnson-Hopson C Khan S Khaykin E Kim CJ Koo HL Kremenetskaia I Kurtz DB Kwan A Lam B Langin-Hooper S Lee A Lee JM Lenz CA Li JH Li Y Lin X Liu SX Liu ZA Luros JS 《Nature》2000,408(6814):816-820
The genome of the flowering plant Arabidopsis thaliana has five chromosomes. Here we report the sequence of the largest, chromosome 1, in two contigs of around 14.2 and 14.6 megabases. The contigs extend from the telomeres to the centromeric borders, regions rich in transposons, retrotransposons and repetitive elements such as the 180-base-pair repeat. The chromosome represents 25% of the genome and contains about 6,850 open reading frames, 236 transfer RNAs (tRNAs) and 12 small nuclear RNAs. There are two clusters of tRNA genes at different places on the chromosome. One consists of 27 tRNA(Pro) genes and the other contains 27 tandem repeats of tRNA(Tyr)-tRNA(Tyr)-tRNA(Ser) genes. Chromosome 1 contains about 300 gene families with clustered duplications. There are also many repeat elements, representing 8% of the sequence. 相似文献
249.
The neuropeptide somatostatin inhibits secretion from electrically excitable cells in the pituitary, pancreas, gut and brain. In mammalian pituitary tumour cells somatostatin inhibits secretion through two distinct pertussis toxin-sensitive mechanisms. One involves inhibition of adenylyl cyclase, the other an unidentified cyclic AMP-independent mechanism that reduces Ca2+ influx by increasing membrane conductance to potassium. Here we demonstrate that the predominant electrophysiological effect of somatostatin on metabolically intact pituitary tumour cells is a large, sustained increase in the activity of the large-conductance Ca(2+)- and voltage-activated K+ channels (BK). This action of somatostatin does not involve direct effects of Ca2+, cAMP or G proteins on the channels. Our results indicate instead that somatostatin stimulates BK channel activity through protein dephosphorylation. 相似文献
250.
Understanding the process whereby the ribosome translates the genetic code into protein molecules will ultimately require high-resolution structural information, and we report here the first crystal structure of a protein from the small ribosomal subunit. This protein, S5, has a molecular mass of 17,500 and is highly conserved in all lifeforms. The molecule contains two distinct alpha/beta domains that have structural similarities to several other proteins that are components of ribonucleoprotein complexes. Mutations in S5 result in several phenotypes which suggest that S5 may have a role in translational fidelity and translocation. These include ribosome ambiguity or ram, reversion from streptomycin dependence and resistance to spectinomycin. Also, a cold-sensitive, spectinomycin-resistant mutant of S5 has been identified which is defective in initiation. Here we show that these mutations map to two distinct regions of the molecule which seem to be sites of interaction with ribosomal RNA. A structure/function analysis of the molecule reveals discrepancies with current models of the 30S subunit. 相似文献