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991.
992.
An increase in the flux of nitrogen from the Mississippi river during the latter half of the twentieth century has caused eutrophication and chronic seasonal hypoxia in the shallow waters of the Louisiana shelf in the northern Gulf of Mexico. This has led to reductions in species diversity, mortality of benthic communities and stress in fishery resources. There is evidence for a predominantly anthropogenic origin of the increased nitrogen flux, but the location of the most significant sources in the Mississippi basin responsible for the delivery of nitrogen to the Gulf of Mexico have not been clearly identified, because the parameters influencing nitrogen-loss rates in rivers are not well known. Here we present an analysis of data from 374 US monitor ing stations, including 123 along the six largest tributaries to the Mississippi, that shows a rapid decline in the average first-order rate of nitrogen loss with channel size--from 0.45 day (-1) in small streams to 0.005 day (-1) in the Mississippi river. Using stream depth as an explanatory variable, our estimates of nitrogen-loss rates agreed with values from earlier studies. We conclude that the proximity of sources to large streams and rivers is an important determinant of nitrogen delivery to the estuary in the Mississippi basin, and possibly also in other large river basins. 相似文献
993.
Mutations in ATP6N1B, encoding a new kidney vacuolar proton pump 116-kD subunit, cause recessive distal renal tubular acidosis with preserved hearing 总被引:10,自引:0,他引:10
Smith AN Skaug J Choate KA Nayir A Bakkaloglu A Ozen S Hulton SA Sanjad SA Al-Sabban EA Lifton RP Scherer SW Karet FE 《Nature genetics》2000,26(1):71-75
The multi-subunit H+-ATPase pump is present at particularly high density on the apical (luminal) surface of -intercalated cells of the cortical collecting duct of the distal nephron, where vectorial proton transport is required for urinary acidification. The complete subunit composition of the apical ATPase, however, has not been fully agreed upon. Functional failure of -intercalated cells results in a group of disorders, the distal renal tubular acidoses (dRTA), whose features include metabolic acidosis accompanied by disturbances of potassium balance, urinary calcium solubility, bone physiology and growth. Mutations in the gene encoding the B-subunit of the apical pump (ATP6B1) cause dRTA accompanied by deafness. We previously localized a gene for dRTA with preserved hearing to 7q33-34 (ref. 4). We report here the identification of this gene, ATP6N1B, which encodes an 840 amino acid novel kidney-specific isoform of ATP6N1A, the 116-kD non-catalytic accessory subunit of the proton pump. Northern-blot analysis demonstrated ATP6N1B expression in kidney but not other main organs. Immunofluorescence studies in human kidney cortex revealed that ATP6N1B localizes almost exclusively to the apical surface of -intercalated cells. We screened nine dRTA kindreds with normal audiometry that linked to the ATP6N1B locus, and identified different homozygous mutations in ATP6N1B in eight. These include nonsense, deletion and splice-site changes, all of which will truncate the protein. Our findings identify a new kidney-specific proton pump 116-kD accessory subunit that is highly expressed in proton-secreting cells in the distal nephron, and illustrate its essential role in normal vectorial acid transport into the urine by the kidney. 相似文献
994.
Mutations in AXIN2 cause colorectal cancer with defective mismatch repair by activating beta-catenin/TCF signalling 总被引:12,自引:0,他引:12
995.
Role for the p53 homologue p73 in E2F-1-induced apoptosis 总被引:20,自引:0,他引:20
996.
Warm-coding deficits and aberrant inflammatory pain in mice lacking P2X3 receptors 总被引:25,自引:0,他引:25
Souslova V Cesare P Ding Y Akopian AN Stanfa L Suzuki R Carpenter K Dickenson A Boyce S Hill R Nebenuis-Oosthuizen D Smith AJ Kidd EJ Wood JN 《Nature》2000,407(6807):1015-1017
ATP activates damage-sensing neurons (nociceptors) and can evoke a sensation of pain. The ATP receptor P2X3 is selectively expressed by nociceptors and is one of seven ATP-gated, cation-selective ion channels. Here we demonstrate that ablation of the P2X3 gene results in the loss of rapidly desensitizing ATP-gated cation currents in dorsal root ganglion neurons, and that the responses of nodose ganglion neurons to ATP show altered kinetics and pharmacology resulting from the loss of expression of P2X(2/3) heteromultimers. Null mutants have normal sensorimotor function. Behavioural responses to noxious mechanical and thermal stimuli are also normal, although formalin-induced pain behaviour is reduced. In contrast, deletion of the P2X3 receptor causes enhanced thermal hyperalgesia in chronic inflammation. Notably, although dorsal-horn neuronal responses to mechanical and noxious heat application are normal, P2X3-null mice are unable to code the intensity of non-noxious 'warming' stimuli. 相似文献
997.
D O Morgan J C Edman D N Standring V A Fried M C Smith R A Roth W J Rutter 《Nature》1987,329(6137):301-307
The primary structure of human insulin-like growth factor II receptor, predicted from the complementary DNA sequence, reveals a transmembrane receptor molecule with a large extracellular domain made up of fifteen repeat sequences and a small region homologous to the collagen-binding domain of fibronectin. The structural and biochemical features of the IGF-II receptor appear identical to those of the cation-independent mannose-6-phosphate receptor. 相似文献
998.
Deletion of genes on chromosome 1 in endocrine neoplasia 总被引:22,自引:0,他引:22
C G Mathew B A Smith K Thorpe Z Wong N J Royle A J Jeffreys B A Ponder 《Nature》1987,328(6130):524-526
Recent studies have identified normal cellular DNA sequences which are lost in the development of embryonal and adult tumours. These tumours are thought to arise after a primary mutation in one allele of such a sequence is followed by loss of its normal homologue. In familial cases, the primary mutation is transmitted in the germ line. The secondary mutation may involve a substantial loss of chromosomal material and thus lead to identification of the site of the inherited mutation. We have examined constitutional and tumour genotypes of medullary thyroid carcinomas and phaeochromocytomas which develop in the dominantly inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2) to locate the predisposing gene in this syndrome. We observed deletion of a hypervariable region of DNA on the short arm of chromosome 1 in seven out of fourteen tumours. Analysis of the parental origin of the deleted allele in two families showed that it was derived from the affected parent in one case, which suggests that the deletion does not reflect the site of the inherited mutation in MEN2. The deleted region is distal to the breakpoint commonly detected in neuroblastomas, which share with the tumours of MEN2 embryological origin from neuroectoderm. 相似文献
999.
Mutations in COL11A2 cause non-syndromic hearing loss (DFNA13) 总被引:13,自引:0,他引:13
McGuirt WT Prasad SD Griffith AJ Kunst HP Green GE Shpargel KB Runge C Huybrechts C Mueller RF Lynch E King MC Brunner HG Cremers CW Takanosu M Li SW Arita M Mayne R Prockop DJ Van Camp G Smith RJ 《Nature genetics》1999,23(4):413-419
We report that mutation of COL11A2 causes deafness previously mapped to the DFNA13 locus on chromosome 6p. We found two families (one American and one Dutch) with autosomal dominant, non-syndromic hearing loss to have mutations in COL11A2 that are predicted to affect the triple-helix domain of the collagen protein. In both families, deafness is non-progressive and predominantly affects middle frequencies. Mice with a targeted disruption of Col11a2 also were shown to have hearing loss. Electron microscopy of the tectorial membrane of these mice revealed loss of organization of the collagen fibrils. Our findings revealed a unique ultrastructural malformation of inner-ear architecture associated with non-syndromic hearing loss, and suggest that tectorial membrane abnormalities may be one aetiology of sensorineural hearing loss primarily affecting the mid-frequencies. 相似文献
1000.
Conservation of a sex-determining gene 总被引:34,自引:0,他引:34