全文获取类型
收费全文 | 9973篇 |
免费 | 676篇 |
国内免费 | 3篇 |
专业分类
10652篇 |
出版年
2023年 | 53篇 |
2022年 | 99篇 |
2021年 | 196篇 |
2020年 | 131篇 |
2019年 | 187篇 |
2018年 | 196篇 |
2017年 | 160篇 |
2016年 | 290篇 |
2015年 | 428篇 |
2014年 | 452篇 |
2013年 | 557篇 |
2012年 | 640篇 |
2011年 | 659篇 |
2010年 | 501篇 |
2009年 | 414篇 |
2008年 | 528篇 |
2007年 | 527篇 |
2006年 | 527篇 |
2005年 | 465篇 |
2004年 | 474篇 |
2003年 | 442篇 |
2002年 | 421篇 |
2001年 | 122篇 |
2000年 | 96篇 |
1999年 | 118篇 |
1998年 | 148篇 |
1997年 | 88篇 |
1996年 | 89篇 |
1995年 | 106篇 |
1994年 | 87篇 |
1993年 | 93篇 |
1992年 | 77篇 |
1991年 | 69篇 |
1990年 | 76篇 |
1989年 | 60篇 |
1988年 | 60篇 |
1987年 | 45篇 |
1986年 | 54篇 |
1985年 | 39篇 |
1984年 | 64篇 |
1983年 | 55篇 |
1982年 | 67篇 |
1981年 | 77篇 |
1980年 | 62篇 |
1979年 | 56篇 |
1978年 | 47篇 |
1977年 | 41篇 |
1976年 | 37篇 |
1975年 | 37篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Leonardi J Fernandez-Valdivia R Li YD Simcox AA Jafar-Nejad H 《Development (Cambridge, England)》2011,138(16):3569-3578
Mutations in Drosophila rumi result in a temperature-sensitive loss of Notch signaling. Rumi is a protein O-glucosyltransferase that adds glucose to EGF repeats with a C-X-S-X-P-C consensus sequence. Eighteen of the 36 EGF repeats in the Drosophila Notch receptor contain the consensus O-glucosylation motif. However, the contribution of individual O-glucose residues on Notch to the regulation of Notch signaling is not known. To address this issue, we carried out a mutational analysis of these glucosylation sites and determined their effects on Notch activity in vivo. Our results indicate that even though no single O-glucose mutation causes a significant decrease in Notch activity, all of the glucose residues on Notch contribute in additive and/or redundant fashions to maintain robust signaling, especially at higher temperatures. O-glucose motifs in and around the ligand-binding EGF repeats play a more important role than those in other EGF repeats of Notch. However, a single O-glucose mutation in EGF12 can be compensated by other O-glucose residues in neighboring EGF repeats. Moreover, timecourse cell aggregation experiments using a rumi null cell line indicate that a complete lack of Rumi does not affect Notch-Delta binding at high temperature. In addition, rumi fully suppresses the gain-of-function phenotype of a ligand-independent mutant form of Notch. Our data suggest that, at physiological levels of Notch, the combined effects of multiple O-glucose residues on this receptor allow productive S2 cleavage at high temperatures and thereby serve as a buffer against temperature-dependent loss of Notch signaling. 相似文献
992.
Doubtful allegations of adverse effects of creatine supplementation have been released through the press media and through
scientific publications. In the present review we have tried to separate the wheat from the chaff by looking for the experimental
evidence of any such claims. Anecdotal reports from athletes have appeared on muscle cramp and gastrointestinal complaints
during creatine supplementation, but the incidence of these is limited and not necessarily linked to creatine itself. Despite
several unproved allegations, liver (enzymes, urea) and kidneys (glomerular filtration urea and albumin excretion rates) show
no change in functionality in healthy subjects supplemented with creatine, even during several months, in both young and older
populations. The potential effects (production of heterocyclic amines) of mutagenicity and carcinogenicity induced by creatine
supplementation have been claimed by a French Sanitary Agency (AFSSA), which might put consumers at risk. Even if there is
a slight increase (within the normal range) of urinary methylamine and formaldehyde excretion after a heavy load of creatine
(20 g/day) this is without effect on kidney function. The search for the excretion of heterocyclic amines remains a future
task to definitively exclude the unproved allegation made by some national agencies. We advise that high-dose (>3–5 g/day)
creatine supplementation should not be used by individuals with pre-existing renal disease or those with a potential risk
for renal dysfunction (diabetes, hypertension, reduced glomerular filtration rate). A pre-supplementation investigation of
kidney function might be considered for reasons of safety, but in normal healthy subjects appears unnecessary. 相似文献
993.
Gustavo Ciudad Isaac Reyes Milko A. Jorquera Laura Azócar Lukas Y. Wick Rodrigo Navia 《World journal of microbiology & biotechnology》2011,27(11):2505-2512
A novel three-phase solid–gas–liquid bioreactor (SGLB) concept using gaseous alcohol and liquid rapeseed oil with immersed
microorganisms overlying a nutrient agar phase (solid) is proposed for biodiesel (fatty acid alkyl esters, FAAE) production
based on the high hydrophobicity and negative surface charge showed by the fungi Rhizopus oryzae. This novel bioreactor was thought to increase oil bioavailability and decrease alcohol toxicity for effective microbial
growth, reaching high yields of FAAE production without any pretreatment. High growth rates were reached for R. oryzae using a SGLB simultaneously reaching a high FAAE production yield, up to 50% using methanol and up to 70% using ethanol at
144 h of incubation at 20°C. To compare the effect of gaseous alcohol, the same experiments were carried out in a three-phase
solid–liquid–liquid bioreactor (SLLB), where the alcohol was added in liquid phase, showing significant R. oryzae growth but no FAAE formation. This suggests that the inhibitory effect of alcohol is more significant in lipase activity
than in R. oryzae growth, and the use of alcohol in gaseous phase may decrease both of them. The experimental procedure using SGLB showed that
when R. oryzae is maintained alive, it can catalyze at the same time the hydrolysis, esterification and transesterification of triglycerides
from rapeseed oil, but its activity strongly depends on the used growth media. Therefore, the application of gaseous alcohol
coupled with R. oryzae as immobilized whole cell catalysts may be a potential alternative to the use of commercial lipases for biodiesel production. 相似文献
994.
Rodrigo Mendonça de Lucena Sávia Gavazza Lourdinha Florencio Mario T. Kato Marcos Antonio de MoraisJr 《World journal of microbiology & biotechnology》2011,27(12):2893-2902
The microorganisms diversity in a full-scale UASB reactor treating domestic sewage was studied by molecular techniques, with
the objective of identifying the population differences associated with the specific methanogenic activity (SMA) of the sludges.
Samples were collected at levels A (0.8 m; bottom), B (1.3 m), C (1.8 m), D (2.3 m) and E (2.8 m). Actinobacteria was dominant at the three lower points and should have been primarily responsible for the degradation of organic matter.
DNA sequences belonging to Methanomicrobiales order of Archaea domain was detected in all five levels with the majority producing methane from hydrogen and carbon dioxide. Points A and
E showed similar bacteria variety. The SMA of point A was the highest (0.374 g COD-CH4/g SSV.d); however, the point E showed much lower value, probably due to the predominance of Proteobacteria phylum, including sulfate-reducing bacteria. In the overall, the results obtained can be considered important because data
from full-scale UASB reactors treating domestic sewage remain scarce. 相似文献
995.
Zahra Zamani Masoud Bahar Marie Agnès Jacques Mohammad Reza Lak Alireza Akhavan 《World journal of microbiology & biotechnology》2011,27(10):2371-2378
Xanthomonad-like bacteria that are associated with common bacterial blight of bean in Iran were identified on the basis of
their colonial morphology, biochemical and serological properties, presence of a specific DNA fragment using PCR primers and
pathogenicity on bean. Xanthomonas axonopodis pv. phaseoli (Xap) strains were further characterized using rep-PCR and restriction fragment length polymorphism (RFLP). RFLP profiles
generated by the restriction endonucleases RsaI, TaqI, HaeIII and Sau96I and rep-PCR analysis revealed that Iranian strains were relatively genetically homogenous. The similarity coefficients
among the strains ranged from 0.87 to 1. The genetic diversity coefficients among strains from three infected provinces, Isfahan,
Markazi and Lorestan, were 0.019, 0.072 and 0.033, respectively. The low overall level of polymorphism within Xap isolates
collected from the three Iranian infected regions could suggest that few initial inoculum introductions might have distributed
among these different bean-growing areas in Iran. 相似文献
996.
997.
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
998.
999.
1000.
Tobe SW Stone JA Brouwers M Bhattacharyya O Walker KM Dawes M Genest J Grover S Gubitz G Lau D Pipe A Selby P Tremblay MS Warburton DE Ward R Woo V Leiter LA Liu PP 《CMAJ》2011,183(15):E1135-E1150