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排序方式: 共有211条查询结果,搜索用时 15 毫秒
151.
Collins N Poot RA Kukimoto I García-Jiménez C Dellaire G Varga-Weisz PD 《Nature genetics》2002,32(4):627-632
The mechanism by which the eukaryotic DNA-replication machinery penetrates condensed chromatin structures to replicate the underlying DNA is poorly understood. Here we provide evidence that an ACF1-ISWI chromatin-remodeling complex is required for replication through heterochromatin in mammalian cells. ACF1 (ATP-utilizing chromatin assembly and remodeling factor 1) and an ISWI isoform, SNF2H (sucrose nonfermenting-2 homolog), become specifically enriched in replicating pericentromeric heterochromatin. RNAi-mediated depletion of ACF1 specifically impairs the replication of pericentromeric heterochromatin. Accordingly, depletion of ACF1 causes a delay in cell-cycle progression through the late stages of S phase. In vivo depletion of SNF2H slows the progression of DNA replication throughout S phase, indicating a functional overlap with ACF1. Decondensing the heterochromatin with 5-aza-2-deoxycytidine reverses the effects of ACF1 and SNF2H depletion. Expression of an ACF1 mutant that cannot interact with SNF2H also interferes with replication of condensed chromatin. Our data suggest that an ACF1-SNF2H complex is part of a dedicated mechanism that enables DNA replication through highly condensed regions of chromatin. 相似文献
152.
A palaeontological solution to the arthropod head problem 总被引:9,自引:0,他引:9
The composition of the arthropod head has been one of the most controversial topics in zoology, with a large number of theories being proposed to account for it over the last century. Although fossils have been recognized as being of potential importance in resolving the issue, a lack of consensus over their systematics has obscured their contribution. Here, I show that a group of previously problematic Cambrian arthropods from the Burgess Shale and Chengjiang faunas form a clade close to crown-group euarthropods, the group containing myriapods, chelicerates, insects and crustaceans. They are characterized by modified or even absent endopods, and two pre-oral appendages. Comparison with reconstructions of the crown-group euarthropod ground plan and recent investigations into onychophorans demonstrates that these two appendages are the first antenna (of extant crustaceans) and a more anterior appendage associated with an ocular segment. The latter appendage has been reduced in all crown-group euarthropods. Its most likely relic is as a component of the labrum. These fossils thus tie together results from disparate living groups (onychophorans and euarthropods). 相似文献
153.
The population vector hypothesis was introduced almost twenty years ago to illustrate that a population vector constructed from neural activity in primary motor cortex (MI) of non-human primates could predict the direction of hand movement during reaching. Alternative explanations for this population signal have been suggested but could not be tested experimentally owing to movement complexity in the standard reaching model. We re-examined this issue by recording the activity of neurons in contralateral MI of monkeys while they made reaching movements with their right arms oriented in the horizontal plane-where the mechanics of limb motion are measurable and anisotropic. Here we found systematic biases between the population vector and the direction of hand movement. These errors were attributed to a non-uniform distribution of preferred directions of neurons and the non-uniformity covaried with peak joint power at the shoulder and elbow. These observations contradict the population vector hypothesis and show that non-human primates are capable of generating reaching movements to spatial targets even though population vectors based on MI activity do not point in the direction of hand motion. 相似文献
154.
Georgraphic differences in phytoplankton sensitivity to PCBs 总被引:1,自引:0,他引:1
155.
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157.
Allen JT Brown L Sanders R Moore CM Mustard A Fielding S Lucas M Rixen M Savidge G Henson S Mayor D 《Nature》2005,437(7059):728-732
Diatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the 'biological pump' than they have previously been attributed, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate, but northern Atlantic waters are richer in nitrate than silicate. Following the spring stratification, diatoms are the first phytoplankton to bloom. Once silicate is exhausted, diatom blooms subside in a major export event. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by 'mining' deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere. 相似文献
158.
Aligianis IA Johnson CA Gissen P Chen D Hampshire D Hoffmann K Maina EN Morgan NV Tee L Morton J Ainsworth JR Horn D Rosser E Cole TR Stolte-Dijkstra I Fieggen K Clayton-Smith J Mégarbané A Shield JP Newbury-Ecob R Dobyns WB Graham JM Kjaer KW Warburg M Bond J Trembath RC Harris LW Takai Y Mundlos S Tannahill D Woods CG Maher ER 《Nature genetics》2005,37(3):221-223
Warburg Micro syndrome (WARBM1) is a severe autosomal recessive disorder characterized by developmental abnormalities of the eye and central nervous system and by microgenitalia. We identified homozygous inactivating mutations in RAB3GAP, encoding RAB3 GTPase activating protein, a key regulator of the Rab3 pathway implicated in exocytic release of neurotransmitters and hormones, in 12 families with Micro syndrome. We hypothesize that the underlying pathogenesis of Micro syndrome is a failure of exocytic release of ocular and neurodevelopmental trophic factors. 相似文献
159.
Gibbs RA Weinstock GM Metzker ML Muzny DM Sodergren EJ Scherer S Scott G Steffen D Worley KC Burch PE Okwuonu G Hines S Lewis L DeRamo C Delgado O Dugan-Rocha S Miner G Morgan M Hawes A Gill R Celera Holt RA Adams MD Amanatides PG Baden-Tillson H Barnstead M Chin S Evans CA Ferriera S Fosler C Glodek A Gu Z Jennings D Kraft CL Nguyen T Pfannkoch CM Sitter C Sutton GG Venter JC Woodage T Smith D Lee HM Gustafson E Cahill P Kana A Doucette-Stamm L Weinstock K Fechtel K Weiss RB Dunn DM Green ED 《Nature》2004,428(6982):493-521
The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution. 相似文献
160.
B Weber O Riess G Wolff S Andrew C Collins R Graham J Theilmann M R Hayden 《Nature genetics》1992,2(3):216-222
No detectable rearrangements involving chromosome 4p16.3 have been observed in patients with Huntington's disease (HD). New mutations for HD could involve structural alterations which might aid the localization of the defective gene. We have reinvestigated a well documented sporadic case of HD. DNA haplotyping with markers between D4S10 and the telomeric locus D4S141 reveals a recombination event in one chromosome of the sporadic HD patient. The site of recombination maps within a 50 kilobase (kb) region, about 700 kb from the 4p telomere. Based on the extremely low HD mutation rate and significantly decreased recombination in the distal region of 4p, we hypothesize a direct link between the site of the recombination and HD in this patient. 相似文献