全文获取类型
收费全文 | 1785篇 |
免费 | 105篇 |
国内免费 | 2篇 |
专业分类
1892篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 23篇 |
2021年 | 40篇 |
2020年 | 35篇 |
2019年 | 35篇 |
2018年 | 84篇 |
2017年 | 58篇 |
2016年 | 89篇 |
2015年 | 131篇 |
2014年 | 125篇 |
2013年 | 141篇 |
2012年 | 155篇 |
2011年 | 146篇 |
2010年 | 97篇 |
2009年 | 61篇 |
2008年 | 117篇 |
2007年 | 81篇 |
2006年 | 78篇 |
2005年 | 64篇 |
2004年 | 50篇 |
2003年 | 56篇 |
2002年 | 54篇 |
2001年 | 31篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1964年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有1892条查询结果,搜索用时 0 毫秒
131.
Kobayashi K Sudiarta IP Kodama T Fukushima T Ara K Ozaki K Sekiguchi J 《The Journal of biological chemistry》2012,287(13):9765-9776
Cell wall metabolism and cell wall modification are very important processes that bacteria use to adjust to various environmental conditions. One of the main modifications is deacetylation of peptidoglycan. The polysaccharide deacetylase homologue, Bacillus subtilis YjeA (renamed PdaC), was characterized and found to be a unique deacetylase. The pdaC deletion mutant was sensitive to lysozyme treatment, indicating that PdaC acts as a deacetylase. The purified recombinant and truncated PdaC from Escherichia coli deacetylated B. subtilis peptidoglycan and its polymer, (-GlcNAc-MurNAc[-L-Ala-D-Glu]-)(n). Surprisingly, RP-HPLC and ESI-MS/MS analyses showed that the enzyme deacetylates N-acetylmuramic acid (MurNAc) not GlcNAc from the polymer. Contrary to Streptococcus pneumoniae PgdA, which shows high amino acid sequence similarity with PdaC and is a zinc-dependent GlcNAc deacetylase toward peptidoglycan, there was less dependence on zinc ion for deacetylation of peptidoglycan by PdaC than other metal ions (Mn(2+), Mg(2+), Ca(2+)). The kinetic values of the activity toward B. subtilis peptidoglycan were K(m) = 4.8 mM and k(cat) = 0.32 s(-1). PdaC also deacetylated N-acetylglucosamine (GlcNAc) oligomers with a K(m) = 12.3 mM and k(cat) = 0.24 s(-1) toward GlcNAc(4). Therefore, PdaC has GlcNAc deacetylase activity toward GlcNAc oligomers and MurNAc deacetylase activity toward B. subtilis peptidoglycan. 相似文献
132.
Length‐weight relationships of 14 fish species from a lowland tropical reservoir in southeastern Brazil 下载免费PDF全文
H. S. Mendonça D. S. Silva‐Camacho S. M. Pinto F. G. Araújo 《Zeitschrift fur angewandte Ichthyologie》2015,31(5):970-972
The present work reports the length‐weight relationships of 14 abundant fish species from a tropical reservoir (Juturnaiba Reservoir), which is the water supply for several municipalities in the northern Rio de Janeiro State, southeastern Brazil. Fishes were collected quarterly in 2006 and 2007 using gillnets of different mesh sizes (15–120 mm stretched mesh) that were set up at sunset and retrieved the following morning, remaining for ca. 15 h. Of the 14 species, eight had no records in the FishBase LWR database; new maximum lengths are given for eight species. 相似文献
133.
M. H. N. Brumano J. L. C. Coelho E. F. Araújo D. O. Silva 《World journal of microbiology & biotechnology》1993,9(2):225-228
Optimum activity of an extracellular pectin lyase produced by Penicillium griseoroseum in submerged culture was after 120 h using 0.1% (w/v) citrus pectin as substrate. Sucrose at 0.1% (w/v) stimulated enzyme production and citrus pectin gave the highest activity of enzyme per unit growth. 相似文献
134.
L‐asparaginase isolated from Streptomyces ansochromogenes promotes Th1 profile and activates CD8+ T cells in human PBMC: an in vitro investigation 下载免费PDF全文
135.
Summary Glucagon increased alanine amino transferase (AAT) activity in perfused rat liver by about 90% over control. Propranolol, the beta receptor antagonist, abolished the effect of glucagon on this enzyme. Well known beta receptor agonists like isoproterenol, norepinephrine and epinephrine also increased the enzyme activity under identical condition and the enhancement was similarly abolished by propranolol. These experiments suggest that the effect of glucagon on AAT was mediated through beta adrenergic receptor. However, the interesting observation was that phenylephrine, alpha receptor agonist and phenoxybenzamine and tolazoline, two alpha receptor antagonists, increased the AAT activity like glucagon in perfusion experiments and the effects of all these three agents were also abolished by propranolol. Glucagon, when perfused with phenoxybenzamine showed some additive effect. From all these results we are proposing that in our system phenoxybenzamine is acting as beta agonist although it is known to be an alpha antagonist. 相似文献
136.
Aristóteles Philippe Nunes Queiroz Maria Lúcia Góes Araújo Nigel E. Hussey Rosângela P. T. Lessa 《Journal of fish biology》2023,102(1):27-43
Understanding the ecological role of species with overlapping distributions is central to inform ecosystem management. Here we describe the diet, trophic level and habitat use of three sympatric stingrays, Hypanus guttatus, H. marianae and H. berthalutzae, through combined stomach content and stable isotope (δ13C and δ15N) analyses. Our integrated approach revealed that H. guttatus is a mesopredator that feeds on a diverse diet of benthic and epibenthic marine and estuarine organisms, principally bivalve molluscs, Alpheus shrimp and teleost fishes. Isotopic data supported movement of this species between marine and estuarine environments. H. berthalutzae is also a marine generalist feeder, but feeds primarily on teleost fishes and cephalopods, and consequently occupies a higher trophic level. In contrast, H. marianae is a mesopredator specialized on shrimps and polychaetas occurring only in the marine environment and occupying a low niche breadth. While niche overlap occurred, the three stingrays utilized the same prey resources at different rates and occupied distinct trophic niches, potentially limiting competition for resources and promoting coexistence. These combined data demonstrate that these three mesopredators perform different ecological roles in the ecosystems they occupy, limiting functional redundancy. 相似文献
137.
Francisco Gerson Araújo Tatiana Pires Teixeira Ana Paula Penha Guedes Márcia Cristina Costa de Azevedo André Luiz Machado Pessanha 《Hydrobiologia》2018,817(1):205-213
Myriophyllum aquaticum is a semi-submerged exotic macrophyte that was introduced to China for many years. This species may be found in an emergent form in aquatic environments or in an amphibious form under drained conditions. Nuisance growth of this species has often been attributed to excessive amounts of nutrients. Therefore, we tested the following hypotheses: (1) high nutrient availability facilitates the establishment of M. aquaticum and (2) fragment type interacts with nutrient availability to determine the colonization and regeneration capacities of M. aquaticum. Two types of fragments were grown in water solutions with two levels of phosphorous. After 3 weeks, the survival rates showed no significant difference between the phosphorous treatments. However, emergent fragments showed higher RGR in the low and high phosphorous treatments than amphibious fragments. In addition, emergent fragments also showed higher regeneration capacities, indicating higher invasiveness in emergent fragments compared to amphibious fragments. Moreover, the high phosphorous concentration caused emergent fragments to produce more branches, indicating that nutrient availability may increase M. aquaticum propagule pressure. Our study highlights that nutrient supply increased emergent fragment establishment and shaped the invasion dynamics of macrophytes, which could help predict the spread and potential impact of exotic macrophytes in natural aquatic ecosystems. 相似文献
138.
Phylogeny and the prediction of tree functional diversity across novel continental settings 下载免费PDF全文
139.
Habitat persistence should influence dispersal ability, selecting for stronger dispersal in habitats of lower temporal stability. As standing (lentic) freshwater habitats are on average less persistent over time than running (lotic) habitats, lentic species should show higher dispersal abilities than lotic species. Assuming that climate is an important determinant of species distributions, we hypothesize that lentic species should have distributions that are closer to equilibrium with current climate, and should more rapidly track climatic changes. We tested these hypotheses using datasets from 1988 and 2006 containing all European dragon- and damselfly species. Bioclimatic envelope models showed that lentic species were closer to climatic equilibrium than lotic species. Furthermore, the models over-predicted lotic species ranges more strongly than lentic species ranges, indicating that lentic species track climatic changes more rapidly than lotic species. These results are consistent with the proposed hypothesis that habitat persistence affects the evolution of dispersal. 相似文献
140.
Passos XS Costa CR Araújo CR Nascimento ES e Souza LK Fernandes Ode F Sales WS Silva Mdo R 《Mycopathologia》2007,163(3):145-151
In this work, we collect data from surveys of bloodstream Candida isolates performed in Brazil from 1996 to 2004. Besides, we analyzed the species distribution of bloodstream Candida isolates together with potential risk factors for candidemia and the susceptibility profile of these isolates in patients
from Hospital das Clínicas in Goiania city, Brazil. Blood samples were collected in the admission day and on every 7 days,
in the intensive care unit (ICU) of a tertiary hospital. Candida isolates were identified by standard protocols that included germ tube formation, chlamydoconidia production on cornmeal
agar and sugar fermentation and assimilation tests. Data of patients were recorded and analyzed according to age at the time
of diagnosis, gender and presence of potential risk factors. Statistical analysis was used to determine if the time of hospital
permanence increased Candida colonization in ICU patients’ blood. The antifungal susceptibility testing was performed by broth microdilution method according
to document NCCLS/CLSI M27–A2. Among the 345 blood samples cultured, candidemia was recovered in 33 patients, which were isolated
51.5% of Candida non-albicans. Fungemia was associated with long-term hospitalization. Fluconazole, itraconzole, voriconazole and amphotericin B exhibited
a potent activity against all isolates of Candida. Voriconazole MICs were much low for all isolates tested. This work confirms data of increase of Candida non-albicans species in bloodstream in ICU and shows that voriconazole in vitro activity was higher than those of itraconazole, fluconazole and amphotericin B. 相似文献