全文获取类型
收费全文 | 331篇 |
免费 | 19篇 |
国内免费 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 17篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 14篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有373条查询结果,搜索用时 15 毫秒
91.
Yakandawala N Gawande PV Lovetri K Madhyastha S 《Journal of applied microbiology》2007,102(3):722-727
AIMS: To determine the effect of a composition comprising ovotransferrin (OT), protamine sulfate (PS) and ethylenediaminetetraacetic acid (EDTA) on biofilm formation by catheter-associated bacteria. METHODS AND RESULTS: The in vitro activity of OT, PS and EDTA alone and in combinations against biofilm formation by Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis and Staphylococcus epidermidis was investigated. All the three compounds either alone or in combinations failed to inhibit the growth completely at the concentrations tested. However, the subinhibitory concentrations of three compounds in a composition showed synergistic inhibitory effect on biofilm formation by K. pneumoniae, Ps. aeruginosa and S. epidermidis. Furthermore, 79-95% reduction in Ps. aeruginosa and S. epidermidis biofilm formation was observed in a clear vinyl urinary catheter treated with the composition. CONCLUSION: The subinhibitory concentrations of OT, PS and EDTA in a composition were effective in reducing biofilm formation by catheter-associated bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that a synergistic composition-comprising non-antibiotic generally regarded as safe (GRAS) compounds such as OT, PS and EDTA may be used in the prevention of catheter-related infections. 相似文献
92.
Critical nutrient loads to prevent duckweed dominance loads in polder ditches were assessed using the eutrophication model
PCDitch. In this article the ecological target was set at 50% duckweed coverage. This may be very high for ditches with a
nature function, but is not unreasonable for ditches in agricultural areas, with upwelling nutrient rich groundwater, run-off
and drainage. Since the change from a ditch with submersed vegetation to duckweed coverage is often a sudden shift, the choice
of the amount of duckweed coverage does not influence the calculated loading very much. The main topic of this paper is to
present a method to calculate critical loads of nutrients when ecological targets have been set. Sediment type, residence
time and water depth influenced the critical loading rates. The calculated critical phosphorus load ranged from 1.8 to 10.2 g P m−2 year−1, while the calculated critical nitrogen load stretched from 12.1 to 43.8 g N m−2 year−1. The concentration ranges that were derived from the loading rate were 0.19–0.42 mg P l−1 and 1.3–3.3 mg N l−1. Since PCDitch does not distinguish between Lemna spp. and Azolla spp., no definite conclusions were drawn concerning the effects of nitrogen reduction. In a model situation a pristine ditch
was loaded with phosphorus, which resulted into complete duckweed coverage during summer within a few years. When reducing
the phosphorus load, it took 10 years before the original situation was reached again. Dredging would accelerate the process
of recovery significantly, because the water depth would increase and the phosphorus release from the sediments in summer
would decrease.
Received September 2003; accepted in revised form February 2005 相似文献
93.
Rona Cabo Sigrunn Hernes Audun Slettan Margaretha Haugen Shu Ye Rune Blomhoff M. Azam Mansoor 《Genes & nutrition》2015,10(3)
Data on the effect of combined genetic polymorphisms, involved in folate metabolism, on the concentration of serum folate after folic acid supplementation are scarce. Therefore, we investigated the impact of seven gene polymorphisms on the concentration of serum folate and p-tHcy in healthy subjects after short-term folic acid supplementation. In a randomized, double blind, crossover study, apparently healthy subjects were given either 0.8 mg folic acid per day (n = 46) or placebo (n = 45) for 14 days. The washout period was 14 days. Fasting blood samples were collected on day 1, 15, 30 and 45. Data on subjects on folic acid supplementation (n = 91) and on placebo (n = 45) were used for the statistical analysis. The concentration of serum folate increased higher in subjects with higher age (53.5 ± 7.0 years) than in subjects with lower age (24.3 ± 3.2 years) after folic acid supplementation (p = 0.006). The baseline concentration of serum folate in subjects with polymorphism combination, reduced folate carrier protein, RFC1-80 GA and methylenetetrahydrofolate reductase, MTHFR677 CT+TT, was lower than RFC1-80 AA and MTHFR677 CT+TT (p = 0.002). After folic acid supplementation, a higher increase in the concentration of serum folate was detected in subjects with polymorphism combination RFC1-80 GA and MTHFR677 CC than RFC1-80 GG and MTHFR CT+TT combination (p < 0.0001). The baseline concentration of plasma total homocysteine (p-tHcy) was altered by combined polymorphisms in genes associated with folate metabolism. After folic acid supplementation, in subjects with combined polymorphisms in methylenetetrahydrofolate dehydrogenase, MTHFD1-1958 and MTHFR-677 genes, the concentration of p-tHcy was changed (p = 0.002). The combination of RFC1-80 and MTHFR-677 polymorphisms had a profound affect on the concentration of serum folate in healthy subjects before and after folic acid supplementation. 相似文献
94.
Higashida H Salmina A Hashii M Yokoyama S Zhang JS Noda M Zhong ZG Jin D 《FEBS letters》2006,580(20):4857-4860
ADP-ribosyl cyclase activity in the crude membrane fraction of neuroblastomaxglioma NGPM1-27 hybrid cells was measured by monitoring [(3)H] cyclic ADP-ribose (cADPR) formation from [(3)H] NAD(+). Bradykinin (BK) at 100nM increased ADP-ribosyl cyclase activity by about 2.5-fold. Application of 300nM BK to living NGPM1-27 cells decreased NAD(+) to 78% of the prestimulation level at 30s. In contrast, intracellular cADPR concentrations were increased by 2-3-fold during the period from 30 to 120s after the same treatment. Our results suggest that cADPR is one of the second messengers downstream of B(2) BK receptors. 相似文献
95.
Epistasis plays an important role in the genetic basis of rice yield traits. Taking interactions into account in breeding programs will help the development of high-yielding rice varieties. In this study, three sets of near isogenic lines (NILs) targeting three QTLs for spikelets per panicle (SPP), namely qSPP1, qSPP2 and qSPP7, which share the same Zhenshan 97 genetic background, were used to produce an F 2 population in which the three QTLs segregated simultaneously. The genotypes of the individual F 2 plants at the three QTLs were replaced with three markers that are closely linked to the corresponding QTLs. These QTLs were validated in the F 2 and F 3 popula- tions at the single marker level. qSPP7 exhibited major pleiotropic effects on SPP, plant height and heading date. Multifactor analysis of variance was performed for the F 2 population and its progeny. Additive × additive interaction between qSPP2 and qSPP7 had significant effects on SPP in both the F 2 population and its progeny. Both additive and additive × additive interactions could explain about 73% of the total SPP phenotypic variance. The SPP performance of 27 three-locus combinations was ranked and favorable combinations were rec- ommended for rice breeding in different ecosystems. 相似文献
96.
Leaf mineral concentrations of co‐occurring Erica arborea, Juniperus communis and Myrtus communis were measured at bimonthly intervals throughout a year in a natural CO2 spring and in a nearby control site with similar soil chemistry in a Mediterranean environment. There were different responses to the elevated [CO2] (c. 700 μL L?1) of the spring site plants depending on the element and the species. In the CO2 spring site K, Ca, Mg, Mn, Al, Fe, and Ti leaf concentrations and the ratio C/N showed significant greater values in at least one or two of the three species. Leaf S concentration were greater in all three species. Leaf concentrations of N, Sr, Co, and B were lower in at least one or two species, and those of C and Ba were lower in all the three studied species near the CO2 spring. P, Na, Zn, Si, Cu, Ni, Cr, Pb, Mo, V and Cd leaf concentrations and the specific leaf area (SLA, measured in Myrtus communis) did not show any consistent or significant pattern in response to the elevated [CO2] of the spring site. There was a slight trend towards maximum concentrations of most of these elements during autumn–winter and minimum values during the spring season, especially in Myrtus communis. Multivariate principal component analyses based on the leaf elemental concentrations clearly differentiated the two sites and the three species. Lower concentrations at the spring site were not the result of a dilution effect by increased structural or nonstructural carbon. In contrast to most experimental studies of CO2 enrichment, mainly conducted for short periods, several of these elements had greater concentrations in the CO2 spring site. Nutrient acclimation and possible causes including decreased nutrient export, increased nutrient uptake capacity, photosynthetic down‐regulation, Mediterranean water stress, and higher H2S concentration in the spring site are discussed. 相似文献
97.
H C Lange M Eman G van Zuijlen D Visser J C van Dam J Frank M J de Mattos J J Heijnen 《Biotechnology and bioengineering》2001,75(4):406-415
An integrated approach is used to develop a rapid sampling strategy for the quantitative analysis of in vivo kinetic behavior based on measured concentrations of intracellular metabolites in Saccharomyces cerevisiae. Emphasis is laid on small sample sizes during sampling and analysis. Subsecond residence times are accomplished by minimizing the dead volume of the sterile sampling system and by maximizing flow rates through application of vacuum to the sampling tubes in addition to the overpressure in the fermenter. A specially designed sample tube adapter facilitates sampling intervals of 4 to 5 s for various test tube types. Statistical analysis of the results obtained from enzymatic and liquid chromatography mass spectrometry (LC-MSMS) analysis of the metabolite concentrations was used to optimize the sampling protocol. The most notable improvement is reached through the introduction of vacuum drying of the cell extract. The presented system is capable of reliably dealing with fermenter samples as small as 1-g with a variation of less than 3%, and is thus ideally suited for intracellular measurements on small, lab-scale fermenters. 相似文献
98.
B. Rossa A. V. Tüffers G. Naidoo D. J. VON Willert 《Plant biology (Stuttgart, Germany)》1998,111(3):216-221
Gas exchange characteristics, chlorophyll a fluorescence and leaf water potential were investigated in the giant reed, Arundo donax, under natural conditions in an estuarine mangrove swamp in Durban, South Africa. Maximum photosynthetic CO2 uptake ranged between 19.8 and 36.7 μmol m?2 s?1, depending on irradiance, and appeared to be regulated by leaf conductance. There was no saturation of CO2 uptake or electron transport through PSII (ETR) with increasing irradiance up to 2500 μmol photons m?2 s?1. A linear relationship between CO2 uptake, corrected for respiration (A), and ETR has only been reported for C4 species and C3 species when photorespiration is eliminated. From this relationship, it was calculated that 8.5 electrons were transported through PSII for the fixation of one mole of CO2. Predawn leaf water potential was about ?0.5 MPa and decreased to ?1.5 MPa on a cloudy day and to ?2.1 MPa on a clear day. Diurnal change in leaf water potential had little influence on leaf conductance and hence CO2 uptake. The molar water use efficiency (WUE) ranged between 4.1 and 9.3 μmol mmol?1. Percentage photorespiration was between 36 and 39%. 相似文献
99.
Desensitization of CholecystokininB Receptors in GH3 Cells 总被引:1,自引:0,他引:1
Abstract: Desensitization of the cholecystokinin (CCK) octapeptide (CCK-8)-induced rise in intracellular free calcium concentration ([Ca2+ ],) was characterized in GH3 cells, a pituitary tumor cell line, which are known to possess CCKB receptor subtype. The CCK-8-induced [Ca2+ ], transient was reduced following the initial application of CCK-8. A similar desensitization of the CCK-8-induced response was observed following the first application of thyrotropin-releasing hormone (TRH). By contrast, the TRH- induced response was not desensitized by the preceding application of CCK-8. Desensitization of the CCK-8-induced [Ca2+ ], transient was associated with diminished inositol 1,4,5-trisphosphate formation. The recovery of desensitization of the CCK-8-induced response was delayed by a phosphoserine/phosphothreonine phosphatase inhibitor, calyculin A (100 n M ). The responsiveness to CCK-8 was also reduced by phorbol 12, 13-dibutyrate (PDBu), and this effect of PDBu was completely abolished by preincubation with staurosporine. Staurosporine significantly attenuated the desensitization caused by preincubation with CCK-8, but this effect was too small to attribute the desensitization to the protein kinase C transduction pathway alone. It is likely that desensitization of CCK receptors involves multiple transduction pathways. 相似文献
100.
U. Münster 《Antonie van Leeuwenhoek》1993,63(3-4):243-274
Data concerning concentrations and fluxes of dissolved organic compounds (DOC) from marine and lacustrine environments are reviewed and discussed. Dissolved free amino acids and carbohydrates comprised the main fraction in the labile organic carbon pool. Dissolved free amino acids in marine waters varied between 3–1400 nM and those of freshwaters between 2.6–4124 nM. Dissolved free carbohydrates varied between 0.4–5000 nM in marine systems and between 14–1111 nM in freshwaters. The turnover times of both substrate pools varied in marine waters between 1.4 hours and 948 days and in freshwaters between 2 hours and 51 days. Measurements of stable12/13C-ratio and14C-isotope dating in ocean deep water samples revealed DOC turnover times between 2000–6000 years. Studies on carbon flows within the aquatic food webs revealed that about 50% of photosynthetically fixed carbon was channelled via DOC to the bacterioplankton. Excreted organic carbon varied between 1–70% of photosynthetically fixed carbon in marine waters and between 1–99% in freshwaters. The labile organic carbon pool represented only 10–30% of the DOC. The majority (70–90%) of the DOC was recalcitrant to microbial assimilation. Only 10–20% of the DOC could be easily chemically identified. Most of the large bulk material represented dissolved humic matter and neither the chemical structure nor the ecological function of the DOC is as yet clearly understood.Abbreviations ATP
Adenosine Tri-Phosphate
- AMS
Accelerated Mass Spectrometry
- BSA
Bovine Serum Albumin
- GlAse
GlucosidAse activity
- DAA
Dissolved Amino Acids
- DCAA
Dissolved Combined Amino Acids
- DFAA
Dissolved Free Amino Acids
- DTAA
Dissolved Total Amino Acids
- DCHO
Dissolved Carbohydrates
- DCCHO
Dissolved Combined Carbohydrates
- DFCHO
Dissolved Free Carbohydrates
- DTCHO
Dissolved Total Carbohydrates
- DLCFaAc
Dissolved Long Chain Fatty Acids
- DSCFaAc
Dissolved Short Chain Fatty Acids
- DOC
Dissolved Organic Carbon
- DOM
Dissolved Organic Matter
- DHM
Dissolved Humic Matter
- DTPhOH
Dissolved Total Phenolic compounds
- DCPhOH
Dissolved Combined Phenolic compounds
- DFPhOH
Dissolved Free Phenolic conpounds
- EOC
Excreted Organic Carbon
- HS
Humic Substances
- HPLC
High Performance Liquid Chromatography
- HTCO
High-Temperature Catalytic Oxidation
- (Kt+Sn)
Transport Constant + Natural Substrate from Michaelis Menten Kinetics
- LOCP
Labile Organic Carbon Pool
- OM
Organic Matter
- MEE
Microbial Extracellular Enzymes
- PER
Percent of Extracellular Release
- PhDOC
Photosynthetically derived Dissolved Organic Carbon
- POC
Particulate Organic Carbon
- ROCP
Recalcitrant Organic Carbon Pool
- Tt
Turnover time
- UDOC
Utilizable Dissolved Organic Carbon
- Vmax
Maximum Uptake Velocity
- WCO
Wet Chemical Oxidation
Dedicated to Prof. Drs. J. Overbeck on the occasion of his 70th birthday 相似文献