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71.
The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era. 相似文献
72.
We have isolated a complementary DNA clone by screening a rat brain cDNA library for expression of kainate-gated ion channels in Xenopus oocytes. The cDNA encodes a single protein of relative molecular mass (Mr) 99,800 which on expression in oocytes forms a functional ion channel possessing the electrophysiological and pharmacological properties of the kainate subtype of the glutamate receptor family in the mammalian central nervous system. 相似文献
73.
Activated CD8 binding to class I protein mediated by the T-cell receptor results in signalling 总被引:7,自引:0,他引:7
The CD8 glycoprotein of T cells bind nonpolymorphic regions of class I major histocompatibility complex proteins on target cells and these interactions promote antigen recognition and signalling by the T-cell receptor. Studies using artificial membranes indicated that effective CD8/class I interaction is critical for response by alloantigen-specific cytotoxic T lymphocytes when class I protein is the only ligand on the antigen-bearing surface. But significant CD8-mediated binding of cytotoxic T lymphocytes to non-antigenic class I protein could not be detected in the absence of the alloantigen. These apparently contradictory findings indicate that CD8 binding to class I protein might be activated through the T-cell receptor and the results reported here demonstrate that this is the case. Treatment of cytotoxic T lymphocytes with soluble anti-T-cell receptor antibody activates adhesion of the cytotoxic T lymphocytes to class I, but not class II proteins. The specificity of this binding implies that it is mediated by CD8 and blocking by anti-CD8 antibodies confirmed this. Furthermore, binding of CD8 to class I protein resulted in generation of an additional signal(s) necessary to initiate response at low T-cell receptor occupancy levels. 相似文献
74.
G. R. Pettit L. E. Houghton N. H. Rogers R. M. Coomes D. F. Berger P. R. Reucroft J. F. Day J. L. Hartwell H. B. Wood Jr. 《Cellular and molecular life sciences : CMLS》1972,28(4):381-382
Zusammenfassung Eine Voruntersuchung der Insektengruppe Lepidoptera auf anti-tumor-aktive Stoffe führte zu einer detaillierten chemischen Prüfung der aus Asien stammenden SchmetterlingeCatopsilia crocale Cramer (Pieridae) undPieris rapae cruavora. Ein bedeutender Teil der Anti-Tumor-Aktivität scheint ihren Ursprung in der chemischen Substanz Isoxanthopterin zu besitzen.
The present contribution represents Part XXVII of the series Antineoplastic Agents. For Part XXVI refer toG. R. Pettit, J. F. Day, J. L. Hartwell andH. B. Wood, Nature, Lond.227, 962 (1970).
This investigation was supported by Public Health Service Research Grants No. CA-10612-01 to No. CA-10612-04 from the National Cancer Institute, and was presented in part at the American Chemical Society Meeting, Washington, D.C., September 1971. We are also grateful to the National Science Foundation for financial assistance (Grant numbers GB-4939 and GB-6979) used in obtaining the Atlas CH-4B and SM-1B mass spectrometers employed in this study. 相似文献
The present contribution represents Part XXVII of the series Antineoplastic Agents. For Part XXVI refer toG. R. Pettit, J. F. Day, J. L. Hartwell andH. B. Wood, Nature, Lond.227, 962 (1970).
This investigation was supported by Public Health Service Research Grants No. CA-10612-01 to No. CA-10612-04 from the National Cancer Institute, and was presented in part at the American Chemical Society Meeting, Washington, D.C., September 1971. We are also grateful to the National Science Foundation for financial assistance (Grant numbers GB-4939 and GB-6979) used in obtaining the Atlas CH-4B and SM-1B mass spectrometers employed in this study. 相似文献
75.
Testosterone, search behaviour and persistence 总被引:4,自引:0,他引:4
76.
Adams DJ Biggs PJ Cox T Davies R van der Weyden L Jonkers J Smith J Plumb B Taylor R Nishijima I Yu Y Rogers J Bradley A 《Nature genetics》2004,36(8):867-871
Embryonic stem cell technology revolutionized biology by providing a means to assess mammalian gene function in vivo. Although it is now routine to generate mice from embryonic stem cells, one of the principal methods used to create mutations, gene targeting, is a cumbersome process. Here we describe the indexing of 93,960 ready-made insertional targeting vectors from two libraries. 5,925 of these vectors can be used directly to inactivate genes with an average targeting efficiency of 28%. Combinations of vectors from the two libraries can be used to disrupt both alleles of a gene or engineer larger genomic changes such as deletions, duplications, translocations or inversions. These indexed vectors constitute a public resource (Mutagenic Insertion and Chromosome Engineering Resource; MICER) for high-throughput, targeted manipulation of the mouse genome. 相似文献
77.
Muscular dystrophies are among the most common human genetic diseases and are characterized by progressive muscle degeneration. Muscular dystrophies result from genetic defects in components of the dystrophin-glycoprotein complex (DGC), a multimeric complex found in the muscle cell plasma membrane. The DGC links the intracellular cytoskeleton to the extracellular matrix and is thought to be important for maintaining the mechanical integrity of muscles and organizing signalling molecules. The exact role of the DGC in the pathogenesis of disease has, however, remained uncertain. Mutations in Caenorhabditis elegans DGC genes lead to specific defects in coordinated movement and can also cause muscle degeneration. Here we show that mutations in the gene snf-6 result in phenotypes indistinguishable from those of the DGC mutants, and that snf-6 encodes a novel acetylcholine/choline transporter. SNF-6 mediates the uptake of acetylcholine at neuromuscular junctions during periods of increased synaptic activity. SNF-6 also interacts with the DGC, and mutations in DGC genes cause a loss of SNF-6 at neuromuscular junctions. Improper clearing of acetylcholine and prolonged excitation of muscles might contribute to the pathogenesis of muscular dystrophies. 相似文献
78.
Rogers GC Rogers SL Schwimmer TA Ems-McClung SC Walczak CE Vale RD Scholey JM Sharp DJ 《Nature》2004,427(6972):364-370
During anaphase identical sister chromatids separate and move towards opposite poles of the mitotic spindle. In the spindle, kinetochore microtubules have their plus ends embedded in the kinetochore and their minus ends at the spindle pole. Two models have been proposed to account for the movement of chromatids during anaphase. In the 'Pac-Man' model, kinetochores induce the depolymerization of kinetochore microtubules at their plus ends, which allows chromatids to move towards the pole by 'chewing up' microtubule tracks. In the 'poleward flux' model, kinetochores anchor kinetochore microtubules and chromatids are pulled towards the poles through the depolymerization of kinetochore microtubules at the minus ends. Here, we show that two functionally distinct microtubule-destabilizing KinI kinesin enzymes (so named because they possess a kinesin-like ATPase domain positioned internally within the polypeptide) are responsible for normal chromatid-to-pole motion in Drosophila. One of them, KLP59C, is required to depolymerize kinetochore microtubules at their kinetochore-associated plus ends, thereby contributing to chromatid motility through a Pac-Man-based mechanism. The other, KLP10A, is required to depolymerize microtubules at their pole-associated minus ends, thereby moving chromatids by means of poleward flux. 相似文献
79.
Schmutz J Wheeler J Grimwood J Dickson M Yang J Caoile C Bajorek E Black S Chan YM Denys M Escobar J Flowers D Fotopulos D Garcia C Gomez M Gonzales E Haydu L Lopez F Ramirez L Retterer J Rodriguez A Rogers S Salazar A Tsai M Myers RM 《Nature》2004,429(6990):365-368
As the final sequencing of the human genome has now been completed, we present the results of the largest examination of the quality of the finished DNA sequence. The completed study covers the major contributing sequencing centres and is based on a rigorous combination of laboratory experiments and computational analysis. 相似文献
80.
Vanilloid receptor-1 is essential for inflammatory thermal hyperalgesia 总被引:83,自引:0,他引:83
Davis JB Gray J Gunthorpe MJ Hatcher JP Davey PT Overend P Harries MH Latcham J Clapham C Atkinson K Hughes SA Rance K Grau E Harper AJ Pugh PL Rogers DC Bingham S Randall A Sheardown SA 《Nature》2000,405(6783):183-187
The vanilloid receptor-1 (VR1) is a ligand-gated, non-selective cation channel expressed predominantly by sensory neurons. VR1 responds to noxious stimuli including capsaicin, the pungent component of chilli peppers, heat and extracellular acidification, and it is able to integrate simultaneous exposure to these stimuli. These findings and research linking capsaicin with nociceptive behaviours (that is, responses to painful stimuli in animals have led to VR1 being considered as important for pain sensation. Here we have disrupted the mouse VR1 gene using standard gene targeting techniques. Small diameter dorsal root ganglion neurons isolated from VR1-null mice lacked many of the capsaicin-, acid- and heat-gated responses that have been previously well characterized in small diameter dorsal root ganglion neurons from various species. Furthermore, although the VR1-null mice appeared normal in a wide range of behavioural tests, including responses to acute noxious thermal stimuli, their ability to develop carrageenan-induced thermal hyperalgesia was completely absent. We conclude that VR1 is required for inflammatory sensitization to noxious thermal stimuli but also that alternative mechanisms are sufficient for normal sensation of noxious heat. 相似文献