全文获取类型
收费全文 | 2418篇 |
免费 | 254篇 |
国内免费 | 2篇 |
出版年
2022年 | 14篇 |
2021年 | 28篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 21篇 |
2016年 | 63篇 |
2015年 | 113篇 |
2014年 | 113篇 |
2013年 | 144篇 |
2012年 | 172篇 |
2011年 | 183篇 |
2010年 | 98篇 |
2009年 | 106篇 |
2008年 | 147篇 |
2007年 | 172篇 |
2006年 | 155篇 |
2005年 | 146篇 |
2004年 | 147篇 |
2003年 | 146篇 |
2002年 | 124篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 35篇 |
1998年 | 39篇 |
1997年 | 30篇 |
1996年 | 29篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1976年 | 7篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1972年 | 10篇 |
1971年 | 11篇 |
1969年 | 5篇 |
排序方式: 共有2674条查询结果,搜索用时 250 毫秒
891.
James Belcher Kirsty J. McLean Sarah Matthews Laura S. Woodward Karl Fisher Stephen E. J. Rigby David R. Nelson Donna Potts Michael T. Baynham David A. Parker David Leys Andrew W. Munro 《The Journal of biological chemistry》2014,289(10):6535-6550
The production of hydrocarbons in nature has been documented for only a limited set of organisms, with many of the molecular components underpinning these processes only recently identified. There is an obvious scope for application of these catalysts and engineered variants thereof in the future production of biofuels. Here we present biochemical characterization and crystal structures of a cytochrome P450 fatty acid peroxygenase: the terminal alkene forming OleTJE (CYP152L1) from Jeotgalicoccus sp. 8456. OleTJE is stabilized at high ionic strength, but aggregation and precipitation of OleTJE in low salt buffer can be turned to advantage for purification, because resolubilized OleTJE is fully active and extensively dissociated from lipids. OleTJE binds avidly to a range of long chain fatty acids, and structures of both ligand-free and arachidic acid-bound OleTJE reveal that the P450 active site is preformed for fatty acid binding. OleTJE heme iron has an unusually positive redox potential (−103 mV versus normal hydrogen electrode), which is not significantly affected by substrate binding, despite extensive conversion of the heme iron to a high spin ferric state. Terminal alkenes are produced from a range of saturated fatty acids (C12–C20), and stopped-flow spectroscopy indicates a rapid reaction between peroxide and fatty acid-bound OleTJE (167 s−1 at 200 μm H2O2). Surprisingly, the active site is highly similar in structure to the related P450BSβ, which catalyzes hydroxylation of fatty acids as opposed to decarboxylation. Our data provide new insights into structural and mechanistic properties of a robust P450 with potential industrial applications. 相似文献
892.
Donna L. Runft Kristie C. Mitchell Basel H. Abuaita Jonathan P. Allen Sarah Bajer Kevin Ginsburg Melody N. Neely Jeffrey H. Withey 《Applied and environmental microbiology》2014,80(5):1710-1717
The human diarrheal disease cholera is caused by the aquatic bacterium Vibrio cholerae. V. cholerae in the environment is associated with several varieties of aquatic life, including insect egg masses, shellfish, and vertebrate fish. Here we describe a novel animal model for V. cholerae, the zebrafish. Pandemic V. cholerae strains specifically colonize the zebrafish intestinal tract after exposure in water with no manipulation of the animal required. Colonization occurs in close contact with the intestinal epithelium and mimics colonization observed in mammals. Zebrafish that are colonized by V. cholerae transmit the bacteria to naive fish, which then become colonized. Striking differences in colonization between V. cholerae classical and El Tor biotypes were apparent. The zebrafish natural habitat in Asia heavily overlaps areas where cholera is endemic, suggesting that zebrafish and V. cholerae evolved in close contact with each other. Thus, the zebrafish provides a natural host model for the study of V. cholerae colonization, transmission, and environmental survival. 相似文献
893.
894.
Donna Koslowsky Yanni Sun Jordan Hindenach Terence Theisen Jasmin Lucas 《Nucleic acids research》2014,42(3):1873-1886
One of the most striking examples of small RNA regulation of gene expression is the process of RNA editing in the mitochondria of trypanosomes. In these parasites, RNA editing involves extensive uridylate insertions and deletions within most of the mitochondrial messenger RNAs (mRNAs). Over 1200 small guide RNAs (gRNAs) are predicted to be responsible for directing the sequence changes that create start and stop codons, correct frameshifts and for many of the mRNAs generate most of the open reading frame. In addition, alternative editing creates the opportunity for unprecedented protein diversity. In Trypanosoma brucei, the vast majority of gRNAs are transcribed from minicircles, which are approximately one kilobase in size, and encode between three and four gRNAs. The large number (5000–10 000) and their concatenated structure make them difficult to sequence. To identify the complete set of gRNAs necessary for mRNA editing in T. brucei, we used Illumina deep sequencing of purified gRNAs from the procyclic stage. We report a near complete set of gRNAs needed to direct the editing of the mRNAs. 相似文献
895.
A H+-ATPase That Energizes Nutrient Uptake during Mycorrhizal Symbioses in Rice and Medicago truncatula 总被引:1,自引:0,他引:1
Ertao Wang Nan Yu S. Asma Bano Chengwu Liu Anthony J. Miller Donna Cousins Xiaowei Zhang Pascal Ratet Million Tadege Kirankumar S. Mysore J. Allan Downie Jeremy D. Murray Giles E.D. Oldroyd Michael Schultze 《The Plant cell》2014,26(4):1818-1830
Most plant species form symbioses with arbuscular mycorrhizal (AM) fungi, which facilitate the uptake of mineral nutrients such as phosphate from the soil. Several transporters, particularly proton-coupled phosphate transporters, have been identified on both the plant and fungal membranes and contribute to delivering phosphate from fungi to plants. The mechanism of nutrient exchange has been studied in plants during mycorrhizal colonization, but the source of the electrochemical proton gradient that drives nutrient exchange is not known. Here, we show that plasma membrane H+-ATPases that are specifically induced in arbuscule-containing cells are required for enhanced proton pumping activity in membrane vesicles from AM-colonized roots of rice (Oryza sativa) and Medicago truncatula. Mutation of the H+-ATPases reduced arbuscule size and impaired nutrient uptake by the host plant through the mycorrhizal symbiosis. Overexpression of the H+-ATPase Os-HA1 increased both phosphate uptake and the plasma membrane potential, suggesting that this H+-ATPase plays a key role in energizing the periarbuscular membrane, thereby facilitating nutrient exchange in arbusculated plant cells. 相似文献
896.
Adam J Ericsen Gabriel J Starrett Justin M Greene Michael Lauck Muthuswamy Raveendran David Rio Deiros Mariel S Mohns Nicolas Vince Brian T Cain Ngoc H Pham Jason T Weinfurter Adam L Bailey Melisa L Budde Roger W Wiseman Richard Gibbs Donna Muzny Thomas C Friedrich Jeffrey Rogers David H O’Connor 《Genome biology》2014,15(11):478
Background
A small percentage of human immunodeficiency virus (HIV)-infected people and simian immunodeficiency virus (SIV)-infected macaques control virus replication without antiretroviral treatment. The major determinant of this control is host expression of certain major histocompatibility complex alleles. However, this association is incompletely penetrant, suggesting that additional loci modify the major histocompatibility complex's protective effect. Here, to identify candidate control-modifying loci, we sequence the genomes of 12 SIV-infected Mauritian cynomolgus macaques that experienced divergent viral load set points despite sharing the protective M1 major histocompatibility complex haplotype.Results
Our genome-wide analysis of haplotype-level variation identifies seven candidate control-modifying loci on chromosomes 2, 3, 7, 8, 9, 10, and 14. The highest variant density marks the candidate on chromosome 7, which is the only control-modifying locus to comprise genes with known immunological function. Upon closer inspection, we found an allele for one of these genes, granzyme B, to be enriched in M1(+) controllers. Given its established role as a cytotoxic effector molecule that participates in CD8-mediated killing of virus-infected cells, we test the role of variation within gzmb in modifying SIV control by prospectively challenging M1(+) granzyme B-defined macaques.Conclusions
Our study establishes a framework for using whole genome sequencing to identify haplotypes that may contribute to complex clinical phenotypes. Further investigation into the immunogenetics underlying spontaneous HIV control may contribute to the rational design of a vaccine that prevents acquired immune deficiency syndrome.897.
Takahiro Ishikawa Saeka Tomatsu Yoshiaki Tsunoda Jongho Lee Donna S. Hoffman Shinji Kakei 《PloS one》2014,9(10)
The cerebellum generates its vast amount of output to the cerebral cortex through the dentate nucleus (DN) that is essential for precise limb movements in primates. Nuclear cells in DN generate burst activity prior to limb movement, and inactivation of DN results in cerebellar ataxia. The question is how DN cells become active under intensive inhibitory drive from Purkinje cells (PCs). There are two excitatory inputs to DN, mossy fiber and climbing fiber collaterals, but neither of them appears to have sufficient strength for generation of burst activity in DN. Therefore, we can assume two possible mechanisms: post-inhibitory rebound excitation and disinhibition. If rebound excitation works, phasic excitation of PCs and a concomitant inhibition of DN cells should precede the excitation of DN cells. On the other hand, if disinhibition plays a primary role, phasic suppression of PCs and activation of DN cells should be observed at the same timing. To examine these two hypotheses, we compared the activity patterns of PCs in the cerebrocerebellum and DN cells during step-tracking wrist movements in three Japanese monkeys. As a result, we found that the majority of wrist-movement-related PCs were suppressed prior to movement onset and the majority of wrist-movement-related DN cells showed concurrent burst activity without prior suppression. In a minority of PCs and DN cells, movement-related increases and decreases in activity, respectively, developed later. These activity patterns suggest that the initial burst activity in DN cells is generated by reduced inhibition from PCs, i.e., by disinhibition. Our results indicate that suppression of PCs, which has been considered secondary to facilitation, plays the primary role in generating outputs from DN. Our findings provide a new perspective on the mechanisms used by PCs to influence limb motor control and on the plastic changes that underlie motor learning in the cerebrocerebellum. 相似文献
898.
899.
Manishkumar Patel Alexa Gleason Stacey O'Malley Brett Connolly Donna Suresch John Virostko Neil Phillips Shu-An Lin Tsing-Bau Chen Michael Klimas Richard J. Hargreaves Cyrille Sur David L. Williams Jr Alvin C. Powers Bohumil Bednar 《PloS one》2014,9(9)
Background
Type 2 diabetes results from failure of the β-cells to compensate for increased insulin demand due to abnormal levels of metabolic factors. The ob/ob(lep-/-) mouse has been extensively studied as an animal model of type 2 diabetes. Previous studies have shown a correlation between β-cell function and bioluminescent imaging in lean genetically engineered mice. The ability to noninvasively monitor β-cell function in ob/ob mice could provide new information on β-cell regulation in type 2 diabetes.Methods
To create the B6 Albino ob/ob MIP-luc mice (ob/ob-luc), the ob/ob mouse was crossed with the CD1 MIP-luc mouse. All mice were backcrossed over multiple generations to ensure the genetic background of the transgenic mice was over 96% similar to the background of the original ob/ob mouse. Animal weight, blood glucose levels, insulin in plasma, and in vivo bioluminescence (BLI) were monitored weekly or biweekly for up to 70 weeks of age. BL imaging was performed using IVIS Spectrum (Perkin Elmer) and calculated by integrating the bioluminescence signal between 5 and 10 min after i.v. injection of D-luciferin. Insulin immunohistochemistry determined islet beta cell count and insulin secretion assay determined islet insulin function.Results
There were significant increases in BLI and insulin levels as the ob/ob-luc mice aged while glucose levels gradually decreased. Ob/ob-luc were sacrificed at different time points to determine ex vivo BLI, islet function and total β-cell numbers using a cell counting training algorithm developed for the Vectra image analysis system (Perkin Elmer). The number of β-cells increased as the mice aged and all three ex vivo measurements correlated with BLI.Conclusions
The ob/ob-luc mice can serve as a model of metabolic stress, similar to human type 2 diabetes using BLI as a surrogate marker for β-cell function. 相似文献900.