全文获取类型
收费全文 | 495篇 |
免费 | 31篇 |
专业分类
526篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 35篇 |
2013年 | 30篇 |
2012年 | 42篇 |
2011年 | 26篇 |
2010年 | 27篇 |
2009年 | 25篇 |
2008年 | 30篇 |
2007年 | 21篇 |
2006年 | 22篇 |
2005年 | 24篇 |
2004年 | 19篇 |
2003年 | 11篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有526条查询结果,搜索用时 0 毫秒
451.
Paolo Ganis Giovanni Valle Luciano Pandolfo Roberta Bertani Fabiano Visentin 《Biopolymers》1999,49(7):541-549
In this study are reported the syntheses of three bis(diarylhydrazonecarbonyl)methylene derivatives [{ArPhCNNH C(O)}2CH2] [Ar = 2 C5H4N (5), C6H5 (6), and 2‐C4H3S (7)], obtained by condensation of corresponding hydrazones with carbon suboxide, C3O2. The solid‐state self‐assembly of these carbonyl derivatives, giving rise to polymeric and dimeric networks, is described. In the formation of these structural features, in addition to N—H· · ·OC intermolecular hydrogen bonds, stabilizing intramolecular NH· · · π (systems) and intermolecular CO· · ·π (systems) interactions also seem to play an important role. Solution 1H‐nmr data of compounds 5–7 indicate that the polymeric and dimeric structures are not maintained in solution and show the occurrence of keto‐enolic equilibria. © 1999 John Wiley & Sons, Inc. Biopoly 49: 541–549, 1999 相似文献
452.
Fabiano de Aquino Ximenes Marcelo Valle de Sousa Jürgen Puls Francides Gomes da Silva Jr. Edivaldo Ximenes Ferreira Filho 《Current microbiology》1999,38(1):18-21
A low-molecular-weight xylanase activity (XynI) was isolated from the fungus Acrophialophora nainiana after growth in a solid medium containing wheat bran. XynI was purified to apparent homogeneity by ultrafiltration and gel
filtration chromatography. The purified enzyme had a molecular weight value of approx. 17 kDa, as determined by SDS-PAGE.
This enzyme was most active at 50°C and pH 6.0. At 50°C the half-life was 150 min. The apparent K
m
value for birchwood xylan was much lower than the K
m
value for oat spelt xylan. XynI was activated by L-cysteine, DTE, β-mercaptoethanol, and L-tryptophan. XynI did not show
significant sequence homology with other xylanases. The analysis of hydrolysis products of xylans and wood pulps showed that
XynI was able to release xylooligomers ranging from X2 to X3 and X2 to X6, respectively. The enzyme was not active against
acetylated xylan. A small amount of xylose was released from deacetylated, birchwood, and oat spelt xylans. The results obtained
with enzymatic treatment of Kraft pulp indicated a reduction in the amount of chlorine compounds required for the process
and enhanced brightness gain.
Received: 6 May 1998 / Accepted: 29 July 1998 相似文献
453.
The seagrass Posidonia oceanica is the most productive system of theMediterranean Sea. In order to gather information on the
temporal andspatial variability of the suspended particulate matter in relation tobacterial dynamics, water samples were collected
at 10 cm above thesediments over a period of 13 months in the Prelo Bay (Ligurian Sea, NWMediterranean). Measurements of seston
concentration, as well as theelemental (POC and PON) and biochemical composition (lipids, proteins,carbohydrates and nucleic
acids) of particulate matter were carried out toassess the origin, composition and bacterial contribution to the foodpotentially
available in the seagrass system to consumers. Lipids andproteins were the main biochemical classes of organic compounds,
followed bycarbohydrates. Despite the highly refractory composition of the seagrassleaves, particulate organic matter was
mostly composed of labile compounds(69.9% of POC). POM temporal patterns were controlled by currentspeed at the sediment–water
interface that resuspended only smallparticles largely colonised by bacteria after an intensive process offractionation and
aging. In the seagrass system, the POM appears to bedominated by bacteria (density ranging from 0.7 to 2.5×109 cells l™1, representing more than48.3% of POC and 68.7% of the biopolymeric carbon, as the sumof lipid, protein and carbohydrate carbon).
This feature was characteristicof the seagrass system since much lower bacterial densities were foundoutside the Posidonia
meadow. Bacteria were negatively correlated with theconcentration of nitrite and nitrate suggesting a selective utilisation
ofinorganic nutrients to support their growth.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
454.
455.
Summary Through the use of ultrathin layer polyacrylamide gel isoelectric focusing it is possible to obtain a resolution of the bands of 1AT so as to be able to easily recognize all six PiM subtypes. The optimal resolution of the PiM subtypes is obtained without deforming the pattern of the Pi phenotypes. In addition to high resolution, ultrathin layer polyacrylamide gel isoelectric focusing permits a notable reduction of fees to 1/5 of the usual. 相似文献
456.
Organic matter consumption and decomposition were studied in four experimental systems, having collected different organic
substrates in the Ross Sea in December 1994. For the experimental approach selected, processes normally acting on a mixed
pool of substances could be separated and the main features of each phenomenon could be focused on. Through the strict relationship
between each experimental system and natural conditions shown by organic matter assessment, ectoenzymatic activity trends
and their relation with Antarctic water substrates could be described. Through ice melting the water column becomes rich in
large pools of substrates, as well as enzyme-producing micro-organisms, capable of quick development. The quantitative predominance
of leucine-aminopeptidase throughout the year is well known, but its relative importance seems to decrease when, owing to
production events, the environment is enriched with autotrophic- and heterotrophic-derived substances, leading to glycolytic
enzymes expression. Thus, ectoenzymatic activity is supposed to be one of the factors responsible for organic matter variations,
showing quantitative and qualitative changes depending on substrate availability.
Received: 26 September 1997 / Accepted: 17 May 1998 相似文献
457.
Raquel dos Anjos Fazioli Lúcia Mary Singer-Vermes Suely Sanae Kashino Eva Burger Marcello Fabiano De Franco Maura Moscardi-Bacchi Vera Lúcia Garcia Calich 《Mycopathologia》1994,126(3):137-146
The specific delayed-type hypersensitivity (DTH) response was evaluated in resistant (A/SN) and susceptible (B10.A) mice intraperitoneally infected with yeasts from a virulent (Pb18) or from a non-virulent (Pb265)Paracoccidioides brasiliensis isolates. Both strains of mice were footpad challenged with homologous antigens. Pb18 infected A/SN mice developed an evident and persistent DTH response late in the course of the disease (90th day on) whereas B10.A animals mounted a discrete and ephemeral DTH response at the 14th day post-infection. A/SN mice infected with Pb265 developed cellular immune responses whereas B10.A mice were almost always anergic. Histological analysis of the footpads of infected mice at 48 hours after challenge showed a mixed infiltrate consisting of predominantly mononuclear cells. Previous infection of resistant and susceptible mice with Pb18 did not alter their DTH responses against heterologous unrelated antigens (sheep red blood cells and dinitrofluorobenzene) indicating that the observed cellular anergy was antigen-specific. When fungal related antigens (candidin and histoplasmin) were tested in resistant mice, absence of cross-reactivity was noted. Thus, specific DTH responses againstP. brasiliensis depend on both the host's genetically determined resistance and the virulence of the fungal isolate.Abbreviations DTH
delayed-type hypersensitivity
- DNFB
dinitrofluorobenzene
- FN18
Fava Netto's antigen obtained from isolate Pb18
- FN265
Fava Netto's antigen obtained from isolate Pb265
- SRBC
sheep red blood cells 相似文献
458.
459.
Borges AA Campos GM Moreli ML Moro Souza RL Saggioro FP Figueiredo GG Livonesi MC Moraes Figueiredo LT 《Microbes and infection / Institut Pasteur》2008,10(10-11):1150-1157
The hantavirus pulmonary syndrome (HPS) is an emerging syndrome in the Americas. The disease results from intense immune activation and changes in vascular permeability. The aim of this study was to determine the profile of serum cytokines in HPS patients looking for correlation with the clinical parameters, severity and outcome of illness. Studying 21 HPS patients, we found that IL-6 may have an important role in the pathogenesis of HPS, being associated with fatal outcome. Our results also support a mixed Th1/Th2 immune response during the course of HPS and that the magnitude of Th1 response effector cytokines is correlated to HPS severity. The decreased levels of TGF-beta observed in HPS patients suggest that immunoregulatory activity could be damaged in these patients. 相似文献
460.
Alexis E. Lysionek Marcela B. Zubillaga María J. Salgueiro Ricardo A. Caro Natalia M. Leonardi Eduardo Ettlin José R. Boccio 《Biological trace element research》2003,94(1):73-77
The iron bioavailability and acute oral toxicity in rats of a ferrous gluconate compound stabilized with glycine (SFG), designed for food fortification, was studied in this work by means of the prophylactic method and the Wilcoxon method, respectively. For the former studies, SFG was homogenously added to a basal diet of low iron content, reaching a final iron concentration of 20.1±2.4 mg Fe/kg diet. A reference standard diet using ferrous sulfate as an iron-fortifying source (19.0±2.1 mg Fe/kg diet) and a control diet without iron additions (9.3±1.4 mg Fe/kg diet) were prepared in the laboratory in a similar way. These diets were administered to three different groups of weaning rats during 23 d as the only type of solid nourishment. The iron bioavailability of SFG was calculated as the relationship between the mass of iron incorporated into hemoglobin during the treatment and the total iron intake per animal. This parameter resulted in 36.6±6.2% SFG, whereas a value of 35.4±8.0% was obtained for ferrous sulfate. The acute toxicological studies were performed in two groups of 70 female and 70 male Sprague-Dawley rats that were administered increasing doses of iron from SFG. The LD50 values of 1775 and 1831 mg SFG/kg body wt were obtained for female and male rats, respectively, evidencing that SFG can be considered as a safe compound from a toxicological point of view. 相似文献