全文获取类型
收费全文 | 9762篇 |
免费 | 827篇 |
国内免费 | 2篇 |
专业分类
10591篇 |
出版年
2023年 | 52篇 |
2022年 | 113篇 |
2021年 | 220篇 |
2020年 | 134篇 |
2019年 | 160篇 |
2018年 | 208篇 |
2017年 | 168篇 |
2016年 | 317篇 |
2015年 | 476篇 |
2014年 | 506篇 |
2013年 | 702篇 |
2012年 | 845篇 |
2011年 | 842篇 |
2010年 | 534篇 |
2009年 | 495篇 |
2008年 | 601篇 |
2007年 | 657篇 |
2006年 | 588篇 |
2005年 | 548篇 |
2004年 | 530篇 |
2003年 | 495篇 |
2002年 | 472篇 |
2001年 | 87篇 |
2000年 | 58篇 |
1999年 | 88篇 |
1998年 | 125篇 |
1997年 | 79篇 |
1996年 | 72篇 |
1995年 | 67篇 |
1994年 | 46篇 |
1993年 | 43篇 |
1992年 | 37篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 11篇 |
1969年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Emilia L Lim Diane L Trinh David W Scott Andy Chu Martin Krzywinski Yongjun Zhao A Gordon Robertson Andrew J Mungall Jacqueline Schein Merrill Boyle Anja Mottok Daisuke Ennishi Nathalie A Johnson Christian Steidl Joseph M Connors Ryan D Morin Randy D Gascoyne Marco A Marra 《Genome biology》2015,16(1)
BackgroundDiffuse large B-cell lymphoma (DLBCL) is an aggressive disease, with 30% to 40% of patients failing to be cured with available primary therapy. microRNAs (miRNAs) are RNA molecules that attenuate expression of their mRNA targets. To characterize the DLBCL miRNome, we sequenced miRNAs from 92 DLBCL and 15 benign centroblast fresh frozen samples and from 140 DLBCL formalin-fixed, paraffin-embedded tissue samples for validation.ResultsWe identify known and candidate novel miRNAs, 25 of which are associated with survival independently of cell-of-origin and International Prognostic Index scores, which are established indicators of outcome. Of these 25 miRNAs, six miRNAs are significantly associated with survival in our validation cohort. Abundant expression of miR-28-5p, miR-214-5p, miR-339-3p, and miR-5586-5p is associated with superior outcome, while abundant expression of miR-324-5p and NOVELM00203M is associated with inferior outcome. Comparison of DLBCL miRNA-seq expression profiles with those from other cancer types identifies miRNAs that were more abundant in B-cell contexts. Unsupervised clustering of miRNAs identifies two clusters of patients that have distinct differences in their outcomes. Our integrative miRNA and mRNA expression analyses reveal that miRNAs increased in abundance in DLBCL appear to regulate the expression of genes involved in metabolism, cell cycle, and protein modification. Additionally, these miRNAs, including one candidate novel miRNA, miR-10393-3p, appear to target chromatin modification genes that are frequent targets of somatic mutation in non-Hodgkin lymphomas.ConclusionsOur comprehensive sequence analysis of the DLBCL miRNome identifies candidate novel miRNAs and miRNAs associated with survival, reinforces results from previous mutational analyses, and reveals regulatory networks of significance for lymphomagenesis.
Electronic supplementary material
The online version of this article (doi:10.1186/s13059-014-0568-y) contains supplementary material, which is available to authorized users. 相似文献992.
993.
994.
Cristiano S. Mota Maria G. Rivas Carlos D. Brondino Isabel Moura José J. G. Moura Pablo J. González Nuno M. F. S. A. Cerqueira 《Journal of biological inorganic chemistry》2011,16(8):1255-1268
Metal-dependent formate dehydrogenases (Fdh) from prokaryotic organisms are members of the dimethyl sulfoxide reductase family
of mononuclear molybdenum-containing and tungsten-containing enzymes. Fdhs catalyze the oxidation of the formate anion to
carbon dioxide in a redox reaction that involves the transfer of two electrons from the substrate to the active site. The
active site in the oxidized state comprises a hexacoordinated molybdenum or tungsten ion in a distorted trigonal prismatic
geometry. Using this structural model, we calculated the catalytic mechanism of Fdh through density functional theory tools.
The simulated mechanism was correlated with the experimental kinetic properties of three different Fdhs isolated from three
different Desulfovibrio species. Our studies indicate that the C–H bond break is an event involved in the rate-limiting step of the catalytic cycle.
The role in catalysis of conserved amino acid residues involved in metal coordination and near the metal active site is discussed
on the basis of experimental and theoretical results. 相似文献
995.
André T. Fernandes Manuela M. Pereira Catarina S. Silva Peter F. Lindley Isabel Bento Eduardo Pinho Melo Lígia O. Martins 《Journal of biological inorganic chemistry》2011,16(4):641-651
The contribution of the disulfide bridge in CotA-laccase from Bacillus subtilis is assessed with respect to the enzyme’s functional and structural properties. The removal of the disulfide bond by site-directed
mutagenesis, creating the C322A mutant, does not affect the spectroscopic or catalytic properties and, surprisingly, neither
the long-term nor the thermodynamic stability parameters of the enzyme. Furthermore, the crystal structure of the C322A mutant
indicates that the overall structure is essentially the same as that of the wild type, with only slight alterations evident
in the immediate proximity of the mutation. In the mutant enzyme, the loop containing the C322 residue becomes less ordered,
suggesting perturbations to the substrate binding pocket. Despite the wild type and the C322A mutant showing similar thermodynamic
stability in equilibrium, the holo or apo forms of the mutant unfold at faster rates than the wild-type enzyme. The picosecond
to nanosecond time range dynamics of the mutant enzyme was not affected as shown by acrylamide collisional fluorescence quenching
analysis. Interestingly, copper uptake or copper release as measured by the stopped-flow technique also occurs more rapidly
in the C322A mutant than in the wild-type enzyme. Overall the structural and kinetic data presented here suggest that the
disulfide bridge in CotA-laccase contributes to the conformational dynamics of the protein on the microsecond to millisecond
timescale, with implications for the rates of copper incorporation into and release from the catalytic centres. 相似文献
996.
997.
998.
Quraishi UM Abrouk M Murat F Pont C Foucrier S Desmaizieres G Confolent C Rivière N Charmet G Paux E Murigneux A Guerreiro L Lafarge S Le Gouis J Feuillet C Salse J 《The Plant journal : for cell and molecular biology》2011,65(5):745-756
Monitoring nitrogen use efficiency (NUE) in plants is becoming essential to maintain yield while reducing fertilizer usage. Optimized NUE application in major crops is essential for long-term sustainability of agriculture production. Here, we report the precise identification of 11 major chromosomal regions controlling NUE in wheat that co-localise with key developmental genes such as Ppd (photoperiod sensitivity), Vrn (vernalization requirement), Rht (reduced height) and can be considered as robust markers from a molecular breeding perspective. Physical mapping, sequencing, annotation and candidate gene validation of an NUE metaQTL on wheat chromosome 3B allowed us to propose that a glutamate synthase (GoGAT) gene that is conserved structurally and functionally at orthologous positions in rice, sorghum and maize genomes may contribute to NUE in wheat and other cereals. We propose an evolutionary model for the NUE locus in cereals from a common ancestral region, involving species specific shuffling events such as gene deletion, inversion, transposition and the invasion of repetitive elements. 相似文献
999.
José Bonomi Barufi Nathalie Korbee Mariana C. Oliveira Félix L. Figueroa 《Journal of applied phycology》2011,23(3):457-466
We have studied the effects of nitrate supply under photosynthetic active radiation (PAR) plus ultraviolet radiation (UVR)
exposure on photosynthetic pigments (chlorophyll a and carotenoids), photoprotective UV screen mycosporine-like amino acids (MAAs), and photosynthetic parameters, including
the maximum quantum yield (F
v/F
m) and electron transport rate (ETR) on the red agarophyte Gracilaria tenuistipitata. Apical tips of G. tenuistipitata were cultivated under ten different concentrations of NO3− for 7 days. It has been shown that G. tenuistipitata cultured under laboratory conditions has the ability to accumulate high amounts of MAAs following a nitrate concentration-dependent
manner under PAR + UVR. Two MAAs were identified, shinorine and porphyra-334. The relative concentration of the first increased
under high concentrations of nitrate, while the second one decreased. The presence of antheraxanthin is reported for the first
time in this macroalgae, which also contains zeaxanthin, lutein, and β-carotene. The accumulation of pigments, photoprotective
compounds, and photosynthetic parameters of G. tenuistipitata is directly related to N availability. All variables decreased under low N supplies and reached constant maximum values with
supplements higher than 0.5 mM NO3−. Our results suggest a high potential to acclimation and photoprotection against stress factors (including high PAR and UVR)
directly related to N availability for G. tenuistipitata. 相似文献
1000.
Toshiyuki Fukao Jörn Oliver SassPetri Kursula Eva ThimmUdo Wendel Can FiciciogluKamel Monastiri Nathalie GuffonIvo Bari? Marie-therese ZabotNaomi Kondo 《生物化学与生物物理学报:疾病的分子基础》2011,1812(5):619-624
Succinyl-CoA:3-ketoacid CoA transferase (SCOT) deficiency is an inborn error of ketone body metabolism and causes episodic ketoacidosis. We report clinical and molecular analyses of 5 patients with SCOT deficiency. Patients GS07, GS13, and GS14 are homozygotes of S405P, L327P, and R468C, respectively. GS17 and GS18 are compound heterozygotes for S226N and A215V, and V404F and E273X, respectively. These mutations have not been reported previously. Missense mutations were further characterized by transient expression analysis of mutant cDNAs. Among 6 missense mutations, mutants L327P, R468C, and A215V retained some residual activities and their mutant proteins were detected in immunoblot analysis following expression at 37 °C. They were more stable at 30 °C than 37 °C, indicating their temperature sensitive character. The R468C mutant is a distinct temperature sensitive mutant which retained 12% and 51% of wild-type residual activities at 37 and 30 °C, respectively. The S226N mutant protein was detected but retained no residual activity. Effects of missense mutations were predicted from the tertiary structure of the SCOT molecule. Main effects of these mutations were destabilization of SCOT molecules, and some of them also affected catalytic activity. Among 5 patients, GS07 and GS18 had null mutations in both alleles and the other three patients retained some residual SCOT activities. All 5 developed a first severe ketoacidotic crisis with blood gas pH < 7.1, and experienced multiple ketoacidotic decompensations (two of them had seven such episodes). In general, the outcome was good even following multiple ketoacidotic events. Permanent ketosis or ketonuria is considered a pathognomonic feature of SCOT deficiency. However, this condition depends not only on residual activity but also on environmental factors. 相似文献