全文获取类型
收费全文 | 31354篇 |
免费 | 2763篇 |
国内免费 | 25篇 |
专业分类
34142篇 |
出版年
2023年 | 161篇 |
2022年 | 367篇 |
2021年 | 776篇 |
2020年 | 415篇 |
2019年 | 549篇 |
2018年 | 654篇 |
2017年 | 537篇 |
2016年 | 966篇 |
2015年 | 1631篇 |
2014年 | 1709篇 |
2013年 | 2000篇 |
2012年 | 2633篇 |
2011年 | 2679篇 |
2010年 | 1632篇 |
2009年 | 1353篇 |
2008年 | 2009篇 |
2007年 | 1985篇 |
2006年 | 1930篇 |
2005年 | 1655篇 |
2004年 | 1679篇 |
2003年 | 1476篇 |
2002年 | 1439篇 |
2001年 | 275篇 |
2000年 | 201篇 |
1999年 | 264篇 |
1998年 | 298篇 |
1997年 | 214篇 |
1996年 | 197篇 |
1995年 | 167篇 |
1994年 | 149篇 |
1993年 | 143篇 |
1992年 | 114篇 |
1991年 | 140篇 |
1990年 | 102篇 |
1989年 | 92篇 |
1988年 | 82篇 |
1987年 | 66篇 |
1986年 | 82篇 |
1985年 | 89篇 |
1984年 | 92篇 |
1983年 | 92篇 |
1982年 | 111篇 |
1981年 | 110篇 |
1980年 | 87篇 |
1979年 | 60篇 |
1978年 | 45篇 |
1977年 | 45篇 |
1976年 | 47篇 |
1975年 | 46篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The electron donor (component B) to the methyl coenzyme M methylreductase system from Methanosarcina thermophila was isolated as the 7-methyl derivative and characterized. Gas chromatography-mass spectrometry and 1H NMR analyses identified this derivative as 7-methylthioheptanoylthreonine phosphate (CH3-S-HTP), indicating that the original component B had the same structure (HS-HTP) as previously determined for component B from Methanobacterium thermoautotrophicum. The heterodisulfide of HS-HTP and coenzyme M (HS-CoM, 2-mercaptoethanesulfonate) was enzymatically reduced in cell extracts using electrons supplied by either H2 or CO, confirming that HS-HTP was a functional molecule in M. thermophila. 相似文献
102.
John S. Beck Anne E. Kwitek Phillip H. Cogen Andrew K. Metzger Geoffrey M. Duyk Val C. Sheffield 《Human genetics》1993,91(1):25-30
p53 is a tumor suppressor gene located on 17p, a region of the human genome frequently deleted in tumors. Mutation of the p53 gene is an important step leading to development of many forms of human cancer. To simplify the analysis of tumors for p53 point mutations, we describe a GC-clamped denaturing gradient gel assay for detecting single-base substitutions within highly conserved regions of the p53 gene. This assay alows for efficient screening of tumors for single-base substitutions within the p53 gene and can be used to facilitate sequence analysis of p53 point mutations. 相似文献
103.
Andrew R. J. Curtis Sophie Headland Susan Lindsay Nicholas S. T. Thomas Eileen Boye Smaragda Kamakari Paul Roustan Maria Anvret Jan Wahlstrom Gillian McCarthy Angus J. Clarke Shomi Bhattacharya 《Human genetics》1993,90(5):551-555
Four families, each with two individuals affectecd by Rett Syndrome (RS), were analysed using restriction fragment lenght polymorphisms and microsatellite markers from the X chromosome. In two of the families, X-linked dominant inheritance of the RS defect from a germinally mosaic mother could be assumed. Therefore, maternal X chromosome markers showing discordant inheritance were used to exclude regions of the X chromosome as locations of the RS gene. Much of the short arm could be excluded, including regions containing three candidate genes, OTC, synapsin 1 and synaptophysin. Although most of the long arm was inherited in common it was possible to exclude a centromeric region. Inheritance of X chromosome markers is also presented for two families with affected aunt-niece pairs, one of which has not been previously studied at the DNA level. 相似文献
104.
Nick S. Fradgley James Bacon Alison R. Bentley Germano Costa-Neto Andrew Cottrell Jose Crossa Jaime Cuevas Matthew Kerton Edward Pope Stéphanie M. Swarbreck Keith A. Gardner 《Global Change Biology》2023,29(5):1296-1313
Wheat is a major crop worldwide, mainly cultivated for human consumption and animal feed. Grain quality is paramount in determining its value and downstream use. While we know that climate change threatens global crop yields, a better understanding of impacts on wheat end-use quality is also critical. Combining quantitative genetics with climate model outputs, we investigated UK-wide trends in genotypic adaptation for wheat quality traits. In our approach, we augmented genomic prediction models with environmental characterisation of field trials to predict trait values and climate effects in historical field trial data between 2001 and 2020. Addition of environmental covariates, such as temperature and rainfall, successfully enabled prediction of genotype by environment interactions (G × E), and increased prediction accuracy of most traits for new genotypes in new year cross validation. We then extended predictions from these models to much larger numbers of simulated environments using climate scenarios projected under Representative Concentration Pathways 8.5 for 2050–2069. We found geographically varying climate change impacts on wheat quality due to contrasting associations between specific weather covariables and quality traits across the UK. Notably, negative impacts on quality traits were predicted in the East of the UK due to increased summer temperatures while the climate in the North and South-west may become more favourable with increased summer temperatures. Furthermore, by projecting 167,040 simulated future genotype–environment combinations, we found only limited potential for breeding to exploit predictable G × E to mitigate year-to-year environmental variability for most traits except Hagberg falling number. This suggests low adaptability of current UK wheat germplasm across future UK climates. More generally, approaches demonstrated here will be critical to enable adaptation of global crops to near-term climate change. 相似文献
105.
106.
Neuza Domingues André R. A. Marques Rita Diogo Almeida Calado Inês S. Ferreira Cristiano Ramos José Ramalho Maria I. L. Soares Telmo Pereira Luís Oliveira José R. Vicente Louise H. Wong Inês C. M. Simões Teresa M. V. D. Pinho e Melo Andrew Peden Cláudia Guimas Almeida Clare E. Futter Rosa Puertollano Winchil L. C. Vaz Otília V. Vieira 《Traffic (Copenhagen, Denmark)》2023,24(7):284-307
107.
Glycosylation sites identified by solid-phase Edman degradation: O-linked glycosylation motifs on human glycophorin A 总被引:10,自引:2,他引:8
Pisano Anthony; Redmond John W.; Williams Keith L.; Gooley Andrew A. 《Glycobiology》1993,3(5):429-435
The human red blood cell sialoglycoprotein, glycophorin A (GpA),contains a mucin-like extensively O-glycosylatedextracellular domain which carries the MN blood group antigens.We have revised the sites of O-glyccsylation in the extracellulardomain of GpA by automated solid-phase Edman degradation, whichallowed positive identification and quantitation of O-glycosylatedSer and Thr residues, as well as the single N-glycosylationsite. One N-linked and 16 O-linked sites were identified. Carbohydratewas absent on Ser 1, Ser14, Ser15, Ser23, Thr28 and Thr58 inGpA. We propose that the glycosyltransferases present in erythrocytesrecognize specific flanking sequences around potential O-glycosylationsites. All 16 O-glycosylation sites are explained on the basisof four motifs. Three motifs are associated with Thr-glycosylation:XaaProXaaXaa where at least one Xaa = Thr;ThrXaaXaaXaa where at least one Xaa = Thr;XaaXaaThrXaa where at least one X = Argor Lys. The fourth motif is associated with Ser-glycosylation:SerXaaXaaXaa where at least one Xaa = Ser.These simple rules explain the glycosylation (or lack of it)on 21 of 22 Ser/Thr in the extracellular domain of GpA. glycophorin A O-glycosylation motif solid-phase Edman degradation 相似文献
108.
Andrew J. Veselka Andrés Aponte-Gutiérrez Osmary A. Medina-Báez James I. Watling 《Biotropica》2023,55(2):540-550
Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CTmax) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CTmax occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CTmax are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material. 相似文献
109.
R. Ashton Lavoie Jeffrey T. Zugates Andrew T. Cheeseman Matt A. Teten Srivatsan Ramesh Julia M. Freeman Summer Swango Jeremy Fitzpatrick Amod Joshi Bradley Hollers Zufan Debebe Tyler K. Lindgren Amber N. Kozak Vinay K. Kondeti Mary K. Bright Eric J. Yearley Alexander Tracy Jacob A. Irwin Michael Guerrero 《Biotechnology and bioengineering》2023,120(10):2953-2968
Adeno-associated virus-based gene therapies have demonstrated substantial therapeutic benefit for the treatment of genetic disorders. In manufacturing processes, viral capsids are produced with and without the encapsidated gene of interest. Capsids devoid of the gene of interest, or “empty” capsids, represent a product-related impurity. As a result, a robust and scalable method to enrich full capsids is crucial to provide patients with as much potentially active product as possible. Anion exchange chromatography has emerged as a highly utilized method for full capsid enrichment across many serotypes due to its ease of use, robustness, and scalability. However, achieving sufficient resolution between the full and empty capsids is not trivial. In this work, anion exchange chromatography was used to achieve empty and full capsid resolution for adeno-associated virus serotype 5. A salt gradient screen of multiple salts with varied valency and Hofmeister series properties was performed to determine optimal peak resolution and aggregate reduction. Dual salt effects were evaluated on the same product and process attributes to identify any synergies with the use of mixed ion gradients. The modified process provided as high as ≥75% AAV5 full capsids (≥3-fold enrichment based on the percent full in the feed stream) with near baseline separation of empty capsids and achieved an overall vector genome step yield of >65%. 相似文献
110.
Cody Raul Cardenas Andrew J. Mularo Andreas S. Chavez Rachelle M. M. Adams 《Biotropica》2023,55(1):145-159
The coevolutionary relationship between fungus-growing ants (Formicidae: Attini: Attina) and their symbionts has been well studied in the Panamanian rain forests. To further understand the ecological context of these evolutionary relationships, we have examined the population-genetic structure of the fungus-growing ant species Mycetomoellerius mikromelanos Cardenas, Schultz, Adams 2021 in the Panama Canal Zone. We specifically investigated the presence of population structure, the significance of geographic features (i.e., creeks) limiting gene flow, and relatedness between ant colonies. To accomplish this, we genotyped 85 ant colonies from nine creeks across an approximately 30 km transect in Parque National Soberanía, Panama, using double-digest restriction-site-associated DNA sequencing. We did not find distinct population structure using two genetic clustering methods; however, we did detect an effect of isolation by distance. Furthermore, related colonies were frequently detected on the same creek or neighboring creeks, and some at further geographic distances. Collectively, these findings demonstrate that new colonies tend to establish on natal creeks and occasionally on distant creeks following long-distance dispersal events. We discuss how population-genetic patterns reveal the natural history of M. mikromelanos in Parque National Soberanía and how these results fit into the context of fungus-growing ant mutualisms. Abstract in Spanish is available with online material. 相似文献