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191.
Structure and evolution of a human erythroid transcription factor 总被引:44,自引:0,他引:44
192.
Crystal structure of the RNA-binding domain of the U1 small nuclear ribonucleoprotein A 总被引:100,自引:0,他引:100
The crystal structure of the RNA binding domain of the U1 small nuclear ribonucleoprotein A, which forms part of the ribonucleoprotein complex involved in the excision of introns, has been solved. It contains a four-stranded beta sheet and two alpha helices. The highly conserved segments designated RNP1 and RNP2 lie side by side on the middle two beta strands. U1 RNA binding studies of mutant proteins suggest that the RNA binds to the four-stranded beta sheet and to the flexible loops on one end. 相似文献
193.
194.
195.
Proline isomerism in staphylococcal nuclease characterized by NMR and site-directed mutagenesis 总被引:2,自引:0,他引:2
Nuclear magnetic resonance (NMR) studies have shown that two distinct folded conformations of staphylococcal nuclease coexist in solution and that these two states can interconvert directly without passing through an unfolded state. These experiments have also revealed that the two forms have very different folding kinetics, although the possibility that one component is an obligatory intermediate for the folding of the other form could be discounted. Here we report NMR data which show that alternative unfolded states are also distinguishable. These observations led us to hypothesize that cis/trans isomerism at a single peptide bond between a proline and its preceding residue might be the origin of the conformational multiplicity. Proline 117 was identified as a likely candidate for the site concerned and a mutant protein, in which Pro 117 was replaced by Gly, was constructed in order to test this. Alternative conformations are not observed in the spectrum of this mutant, lending powerful support to this hypothesis. 相似文献
196.
Postcopulatory sperm competition is a key aspect of sexual selection and is believed to drive the rapid evolution of both reproductive physiology and reproduction-related genes. It is well-established that mating behavior determines the intensity of sperm competition, with polyandry (i.e., female promiscuity) leading to fiercer sperm competition than monandry. Studies in mammals, particularly primates, showed that, owing to greater sperm competition, polyandrous taxa generally have physiological traits that make them better adapted for fertilization than monandrous species, including bigger testes, larger seminal vesicles, higher sperm counts, richer mitochondrial loading in sperm and more prominent semen coagulation. Here, we show that the degree of polyandry can also impact the dynamics of molecular evolution. Specifically, we show that the evolution of SEMG2, the gene encoding semenogelin II, a main structural component of semen coagulum, is accelerated in polyandrous primates relative to monandrous primates. Our study showcases the intimate relationship between sexual selection and the molecular evolution of reproductive genes. 相似文献
197.
Role of CO2 in the formation of gold deposits 总被引:6,自引:0,他引:6
Much of global gold production has come from deposits with uneconomic concentrations of base metals, such as copper, lead and zinc. These 'gold-only' deposits are thought to have formed from hot, aqueous fluids rich in carbon dioxide, but only minor significance has been attached to the role of the CO2 in the process of gold transport. This is because chemical bonding between gold ions and CO2 species is not strong, and so it is unlikely that CO2 has a direct role in gold transport. An alternative indirect role for CO2 as a weak acid that buffers pH has also appeared unlikely, because previously inferred pH values for such gold-bearing fluids are variable. Here we show that such calculated pH values are unlikely to record conditions of gold transport, and propose that CO2 may play a critical role during gold transport by buffering the fluid in a pH range where elevated gold concentration can be maintained by complexation with reduced sulphur. Our conclusions, which are supported by geochemical modelling, may provide a platform for new gold exploration methods. 相似文献
198.
199.
The mammalian inner ear contains organs for the detection of sound and acceleration, the cochlea and the vestibule, respectively. Mechanosensory hair cells within the neuroepithelia of these organs transduce mechanical force generated by sound waves or head movements into neuronal signals. Defects in hair cells lead to deafness and balance defects. Hair cells have stereocilia that are indispensable for mechanosensation, but the molecular mechanisms regulating stereocilia formation are poorly understood. We show here that integrin alpha8beta1, its ligand fibronectin and the integrin-regulated focal adhesion kinase (FAK) co-localize to the apical hair-cell surface where stereocilia are forming. In mice homozygous for a targeted mutation of Itga8 (encoding the alphabeta8 subunit), this co-localization is perturbed and hair cells in the utricle, a vestibular subcompartment, lack stereocilia or contain malformed stereocilia. Most integrin alpha-8beta1-deficient mice die soon after birth due to kidney defects. Many of the survivors have difficulty balancing, consistent with the structural defects of the inner ear. Our data suggest that integrin alpha8beta1, and potentially other integrins, regulates hair-cell differentiation and stereocilia maturation. Mutations affecting matrix molecules cause inherited forms of inner ear disease and integrins may mediate some effects of matrix molecules in the ear; thus, mutations in integrin genes may lead to inner-ear diseases as well. 相似文献
200.
Reduced vas deferens contraction and male infertility in mice lacking P2X1 receptors 总被引:10,自引:0,他引:10
Mulryan K Gitterman DP Lewis CJ Vial C Leckie BJ Cobb AL Brown JE Conley EC Buell G Pritchard CA Evans RJ 《Nature》2000,403(6765):86-89
P2X1 receptors for ATP are ligand-gated cation channels, present on many excitable cells including vas deferens smooth muscle cells. A substantial component of the contractile response of the vas deferens to sympathetic nerve stimulation, which propels sperm into the ejaculate, is mediated through P2X receptors. Here we show that male fertility is reduced by approximately 90% in mice with a targeted deletion of the P2X1 receptor gene. Male mice copulate normally--reduced fertility results from a reduction of sperm in the ejaculate and not from sperm dysfunction. Female mice and heterozygote mice are unaffected. In P2X1-receptor-deficient mice, contraction of the vas deferens to sympathetic nerve stimulation is reduced by up to 60% and responses to P2X receptor agonists are abolished. These results show that P2X1 receptors are essential for normal male reproductive function and suggest that the development of selective P2X1 receptor antagonists may provide an effective non-hormonal male contraceptive pill. Also, agents that potentiate the actions of ATP at P2X1 receptors may be useful in the treatment of male infertility. 相似文献