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221.
222.
Matthews JM Kuschnig R Guenther DB Walker GA Moffat AF Rucinski SM Sasselov D Weiss WW Kusching R 《Nature》2004,430(6995):51-53
Pressure-driven (p-mode) oscillations at the surface of the Sun, resulting from sound waves travelling through the solar interior, are a powerful probe of solar structure, just as seismology can reveal details about the interior of the Earth. Astronomers have hoped to exploit p-mode asteroseismology in Sun-like stars to test detailed models of stellar structure and evolution, but the observations are extremely difficult. The bright star Procyon has been considered one of the best candidates for asteroseismology, on the basis of models and previous reports of p-modes detected in ground-based spectroscopy. Here we present a search for p-modes in 32 days of nearly continuous photometric satellite-based observations of Procyon. If there are p-modes in Procyon, they must have lifetimes less than 2-3 days and/or peak amplitudes <15 parts per million, which defy expectations from the Sun's oscillations and previous theoretical predictions. Target selection for future planned asteroseismology space missions may need to be reconsidered, as will the theory of stellar oscillations. 相似文献
223.
R Cramer G Meyer M Loche M Robert-Gero 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1980,291(7):633-636
BHK21 cells transformed by wild type or Ts3 mutant polyoma virus contain an inhibitor of polyoma virus replication when grown at permissive (36 degrees C) as well as non-permissive temperature (39 +/- 0.5 degrees C). Cells transformed by the Tsa mutant contain the inhibitor at the permissive but not at the non-permissive temperature. The inhibitor reappears in the latter cells however, upon shift from the non-permissive to the permissive temperature. If a reversible protein inhibitor (methionyl-adenylate, reversible inhibitor of the aminoacyl-t-RNA synthetase) is applied during the temperature shift experiments, the inhibitor does not reappear indicating that new protein synthesis is required for the recovery of its activity. 相似文献
224.
Meyer G Kim B van Golen C Feldman EL 《Cellular and molecular life sciences : CMLS》2005,62(4):461-470
Insulin-like growth factor I (IGF-I) is a potent stimulator of neuroblastoma cell motility. Cell motility requires lamellipodium extension at the leading edge of the cell through organized actin polymerization, and IGF-I stimulates lamellipodial elaboration in human neuroblastoma cells. Rac is a Rho GTPase that stimulates lamellipodial formation via the regulation of actin polymerization. In this study, we show that IGF-I-stimulated phosphatidylinositol 3-kinase (PI-3K) activity promotes rac activation and subsequent activation of the down- stream effectors LIM kinase and cofilin. Overexpression of wild-type LIM kinase and wild-type Xenopus ADF/cofilin (XAC) suppresses IGF-I-stimulated motility in SH-SY5Y cells, while expression of dominant negative LIM kinase and constitutively active XAC increases SH-SY5Y motility in the absence of IGF-I stimulation. These results suggest that regulation by cofilin of actin depolymerization is important in the process of neuroblastoma cell motility, and IGF-I regulates cofilin activity in part through PI-3K, rac, and LIM kinase.Received 18 October 2004; received after revision 3 December 2004; accepted 16 December 2004 相似文献
225.
Widespread aneuploidy revealed by DNA microarray expression profiling 总被引:22,自引:0,他引:22
Hughes TR Roberts CJ Dai H Jones AR Meyer MR Slade D Burchard J Dow S Ward TR Kidd MJ Friend SH Marton MJ 《Nature genetics》2000,25(3):333-337
Expression profiling using DNA microarrays holds great promise for a variety of research applications, including the systematic characterization of genes discovered by sequencing projects. To demonstrate the general usefulness of this approach, we recently obtained expression profiles for nearly 300 Saccharomyces cerevisiae deletion mutants. Approximately 8% of the mutants profiled exhibited chromosome-wide expression biases, leading to spurious correlations among profiles. Competitive hybridization of genomic DNA from the mutant strains and their isogenic parental wild-type strains showed they were aneuploid for whole chromosomes or chromosomal segments. Expression profile data published by several other laboratories also suggest the use of aneuploid strains. In five separate cases, the extra chromosome harboured a close homologue of the deleted gene; in two cases, a clear growth advantage for cells acquiring the extra chromosome was demonstrated. Our results have implications for interpreting whole-genome expression data, particularly from cells known to suffer genomic instability, such as malignant or immortalized cells. 相似文献
226.
Critical test of a sister chromatid exchange model for the immunoglobulin heavy-chain class switch 总被引:1,自引:0,他引:1
B lymphocytes may switch from producing an immunoglobulin heavy chain of the mu class to that of the gamma, epsilon or alpha class. To maintain the specificity, the new heavy chain must keep the original variable (V) region; this is achieved by deleting DNA sequences so that the V (consisting of joined VH, diversity (DH) and joining (JH) gene segments) and C (constant) gene segments coding for the new heavy chain are brought into close proximity (reviewed in ref. 5; we do not consider here the mu-delta situation). There are, in principle, three types of chromosomal rearrangements that yield a deletion: rearrangement within a chromatid; unequal sister chromatid exchange (as suggested by Obata et al.); and unequal recombination between chromosomal homologues. We have analysed the arrangement of C mu DNA in clones of the pre-B-cell line 18-81 that switches in vitro from mu to gamma 2b. The clones examined produce either mu, gamma 2b or no immunoglobulin chain. We report here that all the gamma 2b clones had lost at least one copy of C mu and no clones contained three copies of C mu. These findings formally exclude both unequal sister chromatid exchange and recombination between homologues as mechanisms for creating a gene encoding the gamma 2b chain. 相似文献
227.
Zusammenfassung Der Einbau von Aminosäuren wird durch DBC-Coenzym in vivo und in vitro beschleunigt. Mit Cyanocobalamin ist der Effekt nur an avitaminotischen Ratten zu beobachten. Die Resultate bestätigen die Hypothese, wonach der Cofaktor B12 an der Regulation der Eiweiss-Synthese mitwirkt. 相似文献
228.
229.
Heterologe Transplantation von Tumoren nach Vorbehandlung der Wirtstiere mit radioaktiven Isotopen 总被引:1,自引:0,他引:1
Summary The investigation deals with the successful heterologous transplantation of the Mouse Crocker-Sarcoma on young rats, that were pretreated with the radioactive isotopes P32 and Au198. The growth tendency of the tumours varies according to the character of the radioactive isotope, the mode of administration and the interval between the injection of the radioactive substance and the heterotransplantation. 相似文献