全文获取类型
收费全文 | 2035篇 |
免费 | 307篇 |
国内免费 | 165篇 |
出版年
2024年 | 20篇 |
2023年 | 37篇 |
2022年 | 41篇 |
2021年 | 47篇 |
2020年 | 120篇 |
2019年 | 129篇 |
2018年 | 116篇 |
2017年 | 104篇 |
2016年 | 105篇 |
2015年 | 111篇 |
2014年 | 97篇 |
2013年 | 135篇 |
2012年 | 79篇 |
2011年 | 154篇 |
2010年 | 78篇 |
2009年 | 117篇 |
2008年 | 81篇 |
2007年 | 112篇 |
2006年 | 87篇 |
2005年 | 94篇 |
2004年 | 78篇 |
2003年 | 75篇 |
2002年 | 82篇 |
2001年 | 78篇 |
2000年 | 54篇 |
1999年 | 48篇 |
1998年 | 37篇 |
1997年 | 25篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 28篇 |
1993年 | 15篇 |
1992年 | 23篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
排序方式: 共有2507条查询结果,搜索用时 15 毫秒
101.
102.
Aims: To produce single cell protein (SCP) by using waste capsicum powder produced during capsanthin extraction as a substrate. Methods and results: The extraction [CPM (capsicum powder medium)] from waste capsicum powder was used as culture medium to cultivate four yeast strains. The main composition of CPM was determined. The average concentration of total sugar, total nitrogen and phosphorous of CPM were 16·3, 3·7 g l?1 and 785·4 mg l?1, respectively. Four yeast strains were cultured in two CPMs, and the cell mass, protein content of cells and specific growth rate of cells were determined. Addition of corn steep liquor significantly increased the cell mass production. Presence of capsaicin in CPM did not show inhibition of cell growth of yeast tested. Conclusions: CPM contained sufficient nutrients and could be used as a good medium to produce SCP. Candida utilis 1769 was chosen as the biomass producer because of its highest SCP formation (6·8 g l?1) and higher specific growth rate (0·12 h?1). The amino acid composition of its protein was well balanced. Significance and Impact of the Study: Utilization of waste capsicum powder can reduce environmental pollution and increase protein supply for animal feed. 相似文献
103.
Ivan?Mu?ozEmail author Joan?Rieradevall Xavier?Doménech Lloren??Milà 《The International Journal of Life Cycle Assessment》2004,9(4):272-280
Goal, Scope and Background Gipuzkoa is a department of the Vasque Country (Spain) with a population of about 700,000 people. By the year 2000 approximately
85% of municipal solid waste in this area was managed by landfilling, and only 15% was recycled. Due to environmental law
restrictions and landfill capacity being on its limit, a planning process was initiated by the authorities. LCA was used,
from an environmental point of view, to assess 7 possible scenarios arising from the draft Plan for the 2016 time horizon.
Main Features In each scenario, 9 waste flows are analysed: rest waste, paper and cardboard, glass containers, light packaging, organic-green
waste, as well as industrial/commercial wood, metals and plastics, and wastewater sludge. Waste treatments range from recycling
to energy recovery and landfilling.
Results Recycling of the waste flows separated at the source (paper and cardboard, glass, light packaging, organic-green waste, wood
packaging, metals and plastics) results in net environmental benefits caused by the substitution of primary materials, except
in water consumption. These benefits are common to the 7 different scenarios analysed. However, some inefficiencies are detected,
mainly the energy consumption in collection and transport of low density materials, and water consumption in plastic recycling.
The remaining flows, mixed waste and wastewater sludge, are the ones causing the major environmental impacts, by means of
incineration, landfilling of partially stabilised organic material, as well as thermal drying of sludge. With the characterisation
results, none of the seven scenarios can be clearly identified as the most preferable, although, due to the high recycling
rates expected by the Plan, net environmental benefits are achieved in 9 out of 10 impact categories in all scenarios when
integrated waste management is assessed (the sum of the 9 flows of waste). Finally, there are no relevant differences between
scenarios concerning the number of treatment plants considered. Nevertheless, only the effects on transportation impacts were
assessed in the LCA, since the plant construction stage was excluded from the system boundaries.
Conclusions The results of the study show the environmental importance of material recycling in waste management, although the recycling
schemes assessed can be improved in some aspects. It is also important to highlight the environmental impact of incineration
and landfilling of waste, as well as thermal drying of sludge using fossil fuels. One of the main findings of applying LCA
to integrated waste management in Gipuzkoa is the fact that the benefits of high recycling rates can compensate for the impacts
of mixed waste and wastewater sludge.
Recommendations and Outlook Although none of the scenarios can be clearly identified as the one having the best environmental performance, the authorities
in Gipuzkoa now have objective information about the future scenarios, and a multidisciplinary panel could be formed in order
to weight the impacts if necessary. In our opinion, LCA was successfully applied in Gipuzkoa as an environmental tool for
decision making. 相似文献
104.
The present study deals with the production of citric acid from a ram horn peptone (RHP) by Aspergillus niger NRRL 330. A medium from RHP and a control medium (CM) were compared for citric acid production using A. niger in a batch culture. For this purpose, first, RHP was produced. Ram horns were hydrolyzed by treatment with acids (6 N H2SO4, 6 N HCl) and neutralizing solutions. The amounts of protein, nitrogen, ash, some minerals, total sugars, total lipids and amino acids of the RHP were determined. RHP was compared with peptones with a bacto-tryptone from casein and other peptones. The results from RHP were similar to those of standard peptones. The optimal concentration of RHP for the production of citric acid was found to be 4% (w/w). A medium prepared from 4% RHP was termed ram horn peptone medium (RHPM). In comparison with CM, the content of citric acid in RHPM broth (84 g/l) over 6 days was 35% higher than that in CM broth (62 g/l). These results show that citric acid can be produced efficiently by A. niger from ram horn. 相似文献
105.
Sanna V Kirschvink N Gustin P Gavini E Roland I Delattre L Evrard B 《AAPS PharmSciTech》2004,5(2):17-23
The purpose of this research was to investigate the effects of processing conditions on the characteristics of solid lipid
microparticles (SLM) with a potential application as carriers for pulmonary administration. Compritol (5.0% wt/wt) SLM dispersions
were prepared by rotor-stator homogenization, at different surfactant concentrations and emulsification times. The SLM were
characterized, in terms of morphology and size, after lyophilization and sterilization by autoclaving process. In vivo assessment
was carried out in rats by intratracheal instillation of either placebo or SLM dispersion, and by bronchoalveolar lavage for
cytological analysis. Mean particle size of 4 to 5 μm was achieved using 0.3% and 0.4% (wt/wt) of emulsifier (Poloxamer 188)
and emulsification times of 2 and 5 minutes. The particles showed spherical shape and smooth surface. The morphology of microparticles,
the size, and the size distribution were not substantially modified after lyophilization and sterilization. Total cell counts
showed no significant differences between placebo and SLM 0.5% or 2.5% groups. Regarding cytology, percentage of polymorphonuclear
neutrophils and macrophages did not significantly differ between groups. These results suggest that a single intratracheal
administration of the SLMs does not induce a significant inflammatory airway response in rats and that the SLMs might be a
potential carrier for encapsulated drug via the pulmonary route. 相似文献
106.
Charge displacements during ATP-hydrolysis and synthesis of the Na+-transporting FoF1-ATPase of Ilyobacter tartaricus 下载免费PDF全文
Transient electrical currents generated by the Na(+)-transporting F(o)F(1)-ATPase of Ilyobacter tartaricus were observed in the hydrolytic and synthetic mode of the enzyme. Two techniques were applied: a photochemical ATP concentration jump on a planar lipid membrane and a rapid solution exchange on a solid supported membrane. We have identified an electrogenic reaction in the reaction cycle of the F(o)F(1)-ATPase that is related to the translocation of the cation through the membrane bound F(o) subcomplex of the ATPase. In addition, we have determined rate constants for the process: For ATP hydrolysis this reaction has a rate constant of 15-30 s(-1) if H(+) is transported and 30-60 s(-1) if Na(+) is transported. For ATP synthesis the rate constant is 50-70 s(-1). 相似文献
107.
The conformation of an elastin-mimetic recombinant protein, [(VPGVG)4(VPGKG)]39, is investigated using solid-state NMR spectroscopy. The protein is extensively labeled with 13C and 15N, and two-dimensional 13C-13C and 15N-13C correlation experiments were carried out to resolve and assign the isotropic chemical shifts of the various sites. The Pro 15N, 13Calpha, and 13Cbeta isotropic shifts, and the Gly-3 Calpha isotropic and anisotropic chemical shifts support the predominance of type-II beta-turn structure at the Pro-Gly pair but reject a type-I beta-turn. The Val-1 preceding Pro adopts mostly beta-sheet torsion angles, while the Val-4 chemical shifts are intermediate between those of helix and sheet. The protein exhibits a significant conformational distribution, shown by the broad line widths of the 15N and 13C spectra. The average chemical shifts of the solid protein are similar to the values in solution, suggesting that the low-hydration polypeptide maintains the same conformation as in solution. The ability to measure these conformational restraints by solid-state NMR opens the possibility of determining the detailed structure of this class of fibrous proteins through torsion angles and distances. 相似文献
108.
The bioremediation of aged polychlorinated biphenyl (PCB)-contaminated soils is adversely affected by the low bioavailability of the pollutants. Randomly methylated-beta-cyclodextrins (RAMEB) were tested as a potential PCB-bioavailability-enhancing agent in the aerobic treatment of two aged-contaminated soils. The soils, contaminated by about 890 and 8500 mg/kg of Aroclor 1260 PCBs, were amended with biphenyl (4 g/kg), inorganic nutrients (to adjust their C:N ratio to 20:1), and variable amounts of RAMEB (0%, 0.5%, or 1.0% [w/w]) and treated in both aerobic 3-L solid-phase reactors and 1.5-L packed-bed loop reactors for 6 months. Notably, significant enhancement of the PCB biodegradation and dechlorination, along with a detectable depletion of the initial soil ecotoxicity, were generally observed in the RAMEB-treated reactors of both soils. RAMEB effects were different in the two soils, depending upon the treatment conditions employed, and generally increased proportionally with the concentration at which RAMEB was applied. RAMEB, which was slowly metabolized by the soil's aerobic microorganisms, was found to markedly enhance the occurrence of the indigenous aerobic, cultivable biphenyl-growing bacteria harboring genes homologous to those of two highly specialized PCB degraders (i.e., bphABC genes of Pseudomonas pseudoalcaligenes KF707 and bphA1A2A3A4BC1 genes of Rhodococcus globerulus P6) and chlorobenzoic acid-degrading bacteria as well as the occurrence of PCBs in the water phase of the soil reactors. These findings indicate that RAMEB enhanced the aerobic bioremediation of the two soils by increasing the bioavailability of PCBs and the occurrence of specialized bacteria in the soil reactors. 相似文献
109.
Schutyser MA Weber FJ Briels WJ Rinzema A Boom RM 《Biotechnology and bioengineering》2003,82(5):552-563
In previous work we reported on the simulation of mixing behavior of a slowly rotating drum for solid-state fermentation (SSF) using a discrete particle model. In this investigation the discrete particle model is extended with heat and moisture transfer. Heat transfer is implemented in the model via interparticle contacts and the interparticle heat transfer coefficient is determined experimentally. The model is shown to accurately predict heat transfer and resulting temperature gradients in a mixed wheat grain bed. In addition to heat transfer, the addition and subsequent distribution of water in the substrate bed is also studied. The water is added to the bed via spray nozzles to overcome desiccation of the bed during evaporative cooling. The development of moisture profiles in the bed during spraying and mixing are studied experimentally with a water-soluble fluorescent tracer. Two processes that affect the water distribution are considered in the model: the intraparticle absorption process, and the interparticle transfer of free water. It is found that optimum distribution can be achieved when the free water present at the surface of the grains is quickly distributed in the bed, for example, by fast mixing. Alternatively, a short spraying period, followed by a period of mixing without water addition, can be applied. The discrete particle model developed is used successfully to examine the influence of process operation on the moisture distribution (e.g., fill level and rotation rate). It is concluded that the extended discrete particle model can be used as a powerful predictive tool to derive operating strategies and criteria for design and scale-up for mixed SSF and other processes with granular media. 相似文献
110.
Pichler M Knicker H Kögel-Knabner I 《Journal of industrial microbiology & biotechnology》2001,26(1-2):83-89
In Central Europe, composting and anaerobic digestion of municipal solid waste (MSW) is used as pretreatment before landfilling
to reduce landfill emissions. MSW samples were analyzed before, during, and after pretreatment to assess the stability of
the organic matter. Chemolytic, nuclear magnetic resonance (NMR) spectroscopic, and respiration parameters were correlated
to evaluate a substitution of the time-consuming respiration analysis by chemical parameters. 13C cross polarization magic angle spinning (CPMAS) NMR spectroscopy showed a preferential biodegradation of O-alkyl carbon
(carbohydrates) and a selective accumulation of plastics during all pretreatments, confirming findings from chemolytic analyses.
Principal component analysis exhibited a strong association between the respiration rate, the carbohydrate content, and the
O-alkyl C content, corroborating that carbohydrates are the most important compounds of MSW with regard to the emission potential.
Rank correlation (Spearman) also showed strong relationships between the respiration rate and the content of carbohydrates
(r=0.75) and of O-alkyl C (r=0.72). Journal of Industrial Microbiology & Biotechnology (2001) 26, 83–89.
Received 20 April 2000/ Accepted in revised form 21 July 2000 相似文献