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161.
Twelve neutral free amino acids, i. e., serine, threonine, glutamine, asparagine, alanine, proline, methionine, tyrosine, valine, leucine, isoleucine and phenylalanine, were surveyed for the presence of D-enantiomers in plasma samples from patients with renal diseases and from normal subjects. D-serine, D-alanine and D-proline were found in the patient's plasma. The highest concentrations (D/L ratio) of D-serine, D-alanine and D-proline were 0.2362, 0.2087 and 0.0986, respectively. The sum of the contents of the three D-amino acids in a plasma sample correlated with the serum creatinine level of the subject. No D-amino acid was shown to be present in the plasma proteins. 相似文献
162.
The strategy presented here to identify unequivocally cryptic chromosomal rearrangements has relevance to both prenatal and postnatal cytogenetic analysis as well as the analysis of tumour-associated chromosome rearrangements. Microdissection and in vitro amplification of specific chromosomal regions are performed, followed by labelling for fluorescent in situ hybridization (FISH) to normal metaphase chromosomes (Micro-FISH). Micro-FISH probes have been used successfully to determine the derivation of chromosome segments unidentifiable by standard chromosome banding analysis. Micro-FISH probes (created in less than 24 hours) now make it possible to identify explicitly the chromosome constitution of virtually all cytologically visible chromosome rearrangements. 相似文献
163.
164.
Protein kinase C reduces Mg2+ block of NMDA-receptor channels as a mechanism of modulation. 总被引:42,自引:0,他引:42
The roles of N-methyl-D-aspartate (NMDA) receptors and protein kinase C (PKC) are critical in generating and maintaining a variety of sustained neuronal responses. In the nociceptive (pain-sensing) system, tissue injury or repetitive stimulation of small-diameter afferent fibres triggers a dramatic increase in discharge (wind-up) or prolonged depolarization of spinal cord neurons. This central sensitization can neither be induced nor maintained when NMDA receptor channels are blocked. In the trigeminal subnucleus caudalis (a centre for processing nociceptive information from the orofacial areas), a mu-opioid receptor agonist causes a sustained increase in NMDA-activated currents by activating intracellular PKC. There is also evidence that PKC enhances NMDA-receptor-mediated glutamate responses and regulates long-term potentiation of synaptic transmission. Despite the importance of NMDA-receptors and PKC, the mechanism by which PKC alters the NMDA response has remained unclear. Here we examine the actions of intracellularly applied PKC on NMDA-activated currents in isolated trigeminal neurons. We find that PKC potentiates the NMDA response by increasing the probability of channel openings and by reducing the voltage-dependent Mg2+ block of NMDA-receptor channels. 相似文献
165.
Elongation factor-1 alpha (EF-1 alpha), an essential component of the eukaryotic translational apparatus, is a GTP-binding protein that catalyses the binding of aminoacyl-transfer RNAs to the ribosome. Expression of the EF-1 alpha gene decreases towards the end of the lifespans of mouse and human fibroblasts, but forced expression of EF-1 alpha prolongs the lifespan of Drosophila melanogaster. Eukaryotic initiation factor-4E, another component of the translational machinery, is mitogenic or oncogenic when constitutively expressed in some mammalian cells. Thus, components of the protein synthesis apparatus seem to be involved in the control of cell proliferation. Using expression cloning, we have isolated a complementary DNA clone from a BALB/c 3T3 mouse fibroblast variant, A31-I-13 (ref. 10), which specifies a factor determining the susceptibility of BALB/c3T3 to chemically and physically induced transformation. Here we report that the factor is EF-1 alpha and that its constitutive expression causes BALB/c 3T3 A31-I-1 (ref. 10), C3H10T1/2 (ref. 11) and Syrian hamster SHOK fibroblasts to become highly susceptible to transformation induced by 3-methylcholanthrene and ultraviolet light. EF-1 alpha messenger RNA is also constitutively expressed in a quiescent culture of the highly susceptible variant A31-I-13. We conclude that the removal of regulation of the expression of these components of the translational machinery may predispose cells to become more susceptible to malignant transformation. 相似文献
166.
Mutation of the beta-amyloid precursor protein in familial Alzheimer's disease increases beta-protein production. 总被引:41,自引:0,他引:41
M Citron T Oltersdorf C Haass L McConlogue A Y Hung P Seubert C Vigo-Pelfrey I Lieberburg D J Selkoe 《Nature》1992,360(6405):672-674
Progressive cerebral deposition of the 39-43-amino-acid amyloid beta-protein (A beta) is an invariant feature of Alzheimer's disease which precedes symptoms of dementia by years or decades. The only specific molecular defects that cause Alzheimer's disease which have been identified so far are missense mutations in the gene encoding the beta-amyloid precursor protein (beta-APP) in certain families with an autosomal dominant form of the disease (familial Alzheimer's disease, or FAD). These mutations are located within or immediately flanking the A beta region of beta-APP, but the mechanism by which they cause the pathological phenotype of early and accelerated A beta deposition is unknown. Here we report that cultured cells which express a beta-APP complementary DNA bearing a double mutation (Lys to Asn at residue 595 plus Met to Leu at position 596) found in a Swedish FAD family produce approximately 6-8-fold more A beta than cells expressing normal beta-APP. The Met 596 to Leu mutation is principally responsible for the increase. These data establish a direct link between a FAD genotype and the clinicopathological phenotype. Further, they confirm the relevance of the continuous A beta production by cultured cells for elucidating the fundamental mechanism of Alzheimer's disease. 相似文献
167.
由于交流电晕电流正、负半波特性的不对称性,在采用交流电晕放电式消电法时.会出现逆带电及消电不完全的现象.通过串联电容,使交流电晕电流正、负半波特性对称,亦即使电晕电流中直流分量为零,从而实现无逆带电的交流电晕放电式消电. 相似文献
168.
It is usually assumed that, after construction of basic network architecture in embryos, immature networks undergo progressive maturation to acquire their adult properties. We examine this assumption in the context of the lobster stomatogastric nervous system. In the lobster, the neuronal population that will form this system is at first orgnanized into a single embryonic network that generates a single rhythmic pattern. The system then splits into different functional adult networks controlled by central descending systems; these adult networks produce multiple motor programmes, distinctively different from the single output of the embryonic network. We show here that the single embryonic network can produce multiple adult-like programmes. This occurs after the embryonic network is silenced by removal of central inputs, then pharmacologically stimulated to restore rhythmicity. Furthermore, restoration of the flow of descending information reversed the adult-like pattern to an embryonic pattern. This indicates that the embryonic network possesses the ability to express adult-like network characteristics, but descending information prevents it from doing so. Functional adult networks may therefore not necessarily be derived from progressive ontogenetic changes in networks themselves, but may result from maturation of descending systems that unmask preexisting adult networks in an embryonic system. 相似文献
169.
Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana 总被引:21,自引:0,他引:21
Lin X Kaul S Rounsley S Shea TP Benito MI Town CD Fujii CY Mason T Bowman CL Barnstead M Feldblyum TV Buell CR Ketchum KA Lee J Ronning CM Koo HL Moffat KS Cronin LA Shen M Pai G Van Aken S Umayam L Tallon LJ Gill JE Adams MD Carrera AJ Creasy TH Goodman HM Somerville CR Copenhaver GP Preuss D Nierman WC White O Eisen JA Salzberg SL Fraser CM Venter JC 《Nature》1999,402(6763):761-768
Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2. 相似文献
170.
Roles of postsynaptic density-95/synapse-associated protein 90 and its interacting proteins in the organization of synapses 总被引:5,自引:0,他引:5
Synapses are central stages for neurotransmission. Neurotransmitters are released from the presynaptic membrane of one neuron, and bind to the receptors accumulated at the postsynaptic membrane, followed by the activation of the other neuron. The strength of a synapse is modified depending on the history of the previous neurotransmissions. This property is called synaptic plasticity and is implicated in learning and memory. Synapses contain not only the components essential for neurotransmission but also the signalling molecules involved in synaptic plasticity. The elucidation of the molecular structures of synapses is one of the key steps to understand the mechanism of learning and memory. Recent studies have revealed postsynaptic density (PSD)-95/synapse-associated protein (SAP) 90 as a core component in the architecture of synapses. In this review, we summarize up-to-date information about PSD-95/SAP90 and its interacting proteins, and the organization of synapses orchestrated 相似文献