全文获取类型
收费全文 | 719篇 |
免费 | 32篇 |
专业分类
751篇 |
出版年
2022年 | 6篇 |
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 20篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 42篇 |
2012年 | 47篇 |
2011年 | 45篇 |
2010年 | 32篇 |
2009年 | 28篇 |
2008年 | 54篇 |
2007年 | 36篇 |
2006年 | 40篇 |
2005年 | 31篇 |
2004年 | 22篇 |
2003年 | 30篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 4篇 |
排序方式: 共有751条查询结果,搜索用时 15 毫秒
11.
Pla M La Paz JL Peñas G García N Palaudelmàs M Esteve T Messeguer J Melé E 《Transgenic research》2006,15(2):219-228
Maize is one of the main crops worldwide and an increasing number of genetically modified (GM) maize varieties are cultivated
and commercialized in many countries in parallel to conventional crops. Given the labeling rules established e.g. in the European
Union and the necessary coexistence between GM and non-GM crops, it is important to determine the extent of pollen dissemination
from transgenic maize to other cultivars under field conditions. The most widely used methods for quantitative detection of
GMO are based on real-time PCR, which implies the results are expressed in genome percentages (in contrast to seed or grain
percentages). Our objective was to assess the accuracy of real-time PCR based assays to accurately quantify the contents of
transgenic grains in non-GM fields in comparison with the real cross-fertilization rate as determined by phenotypical analysis.
We performed this study in a region where both GM and conventional maize are normally cultivated and used the predominant
transgenic maize Mon810 in combination with a conventional maize variety which displays the characteristic of white grains
(therefore allowing cross-pollination quantification as percentage of yellow grains). Our results indicated an excellent correlation
between real-time PCR results and number of cross-fertilized grains at Mon810 levels of 0.1–10%. In contrast, Mon810 percentage
estimated by weight of grains produced less accurate results. Finally, we present and discuss the pattern of pollen-mediated
gene flow from GM to conventional maize in an example case under field conditions. 相似文献
12.
B. G. Cuevas J. Meléndez-Estrada R. Contreras M. A. Amezcua-Allieri 《Soil & Sediment Contamination》2012,21(1):31-41
The aim of this study was to evaluate anthracene removal using activated soil reactors, previously inoculated, under both aerobic and anaerobic conditions. In the reactors, the soil was maintained at 60% moisture (weight basis), room temperature, in the dark, and under constant agitation at 100 rpm. Two experiments were run during and after acclimatization to evaluate anthracene removal under both aerobic and anaerobic conditions. The first one took place during inoculum acclimatization using three different concentrations of anthracene (50, 100, and 500 mg anthracene/L per day) during 90 days. The second experiment took place after acclimatization (during 132 days). The results of anthracene removal were compared with controls in which no additional inoculum was added. During the two experiments, the behavior of pH, chemical oxygen demand (COD), and biogas production was evaluated. Results indicate that the bacterial community adapted for removal of anthracene became enriched through the acclimatization process. Anthracene biodegradation occurred in the soil model with both types of reactors (aerobic and anaerobic), but the rates and extent of biodegradation in the aerobic reactor were higher (95%) than those in anaerobic conditions (74%). Microbial activity also contributed to enhancing bioremediation in the soil by reducing anthracene sorption. 相似文献
13.
14.
15.
Jean-Marie Normand Maria V. Sanchez-Vives Christian Waechter Elias Giannopoulos Bernhard Grosswindhager Bernhard Spanlang Christoph Guger Gudrun Klinker Mandayam A. Srinivasan Mel Slater 《PloS one》2012,7(10)
Immersive virtual reality (IVR) typically generates the illusion in participants that they are in the displayed virtual scene where they can experience and interact in events as if they were really happening. Teleoperator (TO) systems place people at a remote physical destination embodied as a robotic device, and where typically participants have the sensation of being at the destination, with the ability to interact with entities there. In this paper, we show how to combine IVR and TO to allow a new class of application. The participant in the IVR is represented in the destination by a physical robot (TO) and simultaneously the remote place and entities within it are represented to the participant in the IVR. Hence, the IVR participant has a normal virtual reality experience, but where his or her actions and behaviour control the remote robot and can therefore have physical consequences. Here, we show how such a system can be deployed to allow a human and a rat to operate together, but the human interacting with the rat on a human scale, and the rat interacting with the human on the rat scale. The human is represented in a rat arena by a small robot that is slaved to the human’s movements, whereas the tracked rat is represented to the human in the virtual reality by a humanoid avatar. We describe the system and also a study that was designed to test whether humans can successfully play a game with the rat. The results show that the system functioned well and that the humans were able to interact with the rat to fulfil the tasks of the game. This system opens up the possibility of new applications in the life sciences involving participant observation of and interaction with animals but at human scale. 相似文献
16.
Koval' OA Boguslavskiĭ EG Oleĭnikova SB Chernolovskaia EL Litvak VV Nadolinnyĭ VA Blasov VV 《Bioorganicheskaia khimiia》2003,29(6):632-639
DNA was found to be cleaved in neutral solutions containing arenes and copper (II) salts. The reaction is comparable in efficiency with the DNA cleavage by such systems as Cu(II)-phenanthroline and Cu(II)-ascorbic acid, but, in contrast to the latter, the system Cu(2+)-arene does not require the presence of an exogenous reducing agent or hydrogen peroxide. The system Cu(2+)-arene does not cleave DNA under anaerobic conditions. Catalase, sodium azide, and bathocuproine, which is a specific chelator of Cu(I), completely inhibit the reaction. The data obtained allow one to suppose that Cu(I) ions, superoxide radical, and singlet oxygen participate in the reaction. It has been shown by the EPR method using spin traps that the reaction proceeds with formation of alkoxyl radicals, which can insert breaks in the DNA molecule. For effective cleavage of DNA in the Cu(II)-o-bromobenzoic acid system, the radicals have to be generated by a specific copper-DNA-o-bromobenzoic acid complex, in which copper ions are most probably coordinated with oxygen atoms of the DNA phosphate groups. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2003, vol. 29, no. 6; see also http://www.maik.ru. 相似文献
17.
Melø TM Håberg AK Risa Ø Kondziella D Henry PG Sonnewald U 《Neurochemical research》2011,36(10):1801-1808
Evaluating early changes in cerebral metabolism in hydrocephalus can help in the decision making and the timing of surgical
intervention. This study was aimed at examining the tricarboxylic acid (TCA) cycle rate and 13C label incorporation into neurotransmitter amino acids and other compounds 2 weeks after rats were subjected to kaolin-induced
progressive hydrocephalus. In vivo and ex vivo magnetic resonance spectroscopy (MRS), combined with the infusion of [1,6-13C]glucose, was used to monitor the time courses of 13C label incorporation into the different carbon positions of glutamate in the forebrains of rats with hydrocephalus as well
as in those of controls. Metabolic rates were determined by fitting the measured data into a one-compartment metabolic model.
The TCA cycle rate was 1.3 ± 0.2 μmoles/gram/minute in the controls and 0.8 ± 0.4 μmoles/gram/minute in the acute hydrocephalus
group, the exchange rate between α-ketoglutarate and glutamate was 4.1 ± 2.5 μmoles/gram/minute in the controls and 2.7 ± 2.6 μmoles/gram/minute
in the hydrocephalus group calculated from in vivo MRS. There were no statistically significant differences between these
rates. Hydrocephalus caused a decrease in the amounts of glutamate, alanine and taurine. In addition, the concentration of
the neuronal marker N-acetyl aspartate was decreased. 13C Labelling of most amino acids derived from [1,6-13C]glucose was unchanged 2 weeks after hydrocephalus induction. The only indication of astrocyte impairment was the decreased
13C enrichment in glutamine C-2. This study shows that hydrocephalus causes subtle but significant alterations in neuronal metabolism
already early in the course of the disease. These sub-lethal changes, however, if maintained and if ongoing might explain
the delayed and programmed neuronal damage as seen in chronic hydrocephalus. 相似文献
18.
Naess SN Sliwka HR Partali V Melø TB Razi Naqvi K Jackson HL Lockwood SF 《Chemistry and physics of lipids》2007,148(2):63-69
The surface and aggregation properties of a synthetic, highly water-soluble carotenoid, the tetracationic astaxanthin-lysine conjugate (Asly), have been examined through measurements of surface tension, optical absorption and dynamic light scattering. The following parameters were determined: critical aggregation concentration c(M), surface concentration Gamma, molecular area a(m), free energy of adsorption and aggregation (DeltaG(ad) degrees and DeltaG(M) degrees , respectively), and the aggregate size r(H). The compound forms true monomolecular solutions in water below c(M); aggregates emerge only at rather high concentrations (> or =2.18 mM). 相似文献
19.
Stability of tissue culture medium pH as a function of autoclaving,time, and cultured plant material
Robert M. Skirvin Mel C. Chu Mary L. Mann Heather Young Joseph Sullivan Thomas Fermanian 《Plant cell reports》1986,5(4):292-294
Autoclaving is a standard procedure for sterilizing nutrient media for plant tissue cultures. Most tissue cultures are grown at pH 5.2 to 5.8 with pH adjustments being made prior to autoclaving. This paper reports that there are significant differences between initial pH levels and pH levels following autoclaving, particularly in the pH range of 5.7 to 8.5. This effect is noted with and without agar. In addition, we report that with time the pH of the medium drifts into the acid range. When Cucumis callus was added to the medium, the pH was changed significantly within 48 hours. The amount and direction (increase or decrease of pH) was significantly correlated with the original pH. This suggests that researchers should be wary of the true pH situation in their medium. In addition, in publications authors should specify whether their medium pH value was determined before or after autoclaving. 相似文献
20.
Effect of Cetylpyridinium Chloride on Microbial Adhesion to Hexadecane and Polystyrene 总被引:1,自引:1,他引:1 下载免费PDF全文
Microbial adhesion at the oil-water interface is a subject of both basic interest (e.g., as a technique for the measurement of hydrophobicity) and applied interest (e.g., for use in two-phase oil-water mouthwashes for the desorption of oral microorganisms). In general, surfactants inhibit microbial adhesion to oils and other hydrophobic surfaces. In the present study, we demonstrated that the cationic surfactant cetylpyridinium chloride (CPC) significantly enhanced microbial adhesion to hexadecane and various oils, as well as to the solid hydrophobic surface polystyrene. CPC increased adhesion to hexadecane of Escherichia coli, Candida albicans and Acinetobacter calcoaceticus MR-481 and of expectorated oral bacteria from near 0% to over 90%. The CPC concentration required for optimal enhancement of adhesion was a function of the initial cell density. This phenomenon was inhibited by high salt concentrations and, in the case of E. coli, by a low pH. CPC-pretreated cells were able to bind to hexadecane, but CPC-pretreated hexadecane was unable to bind untreated cells. Another cationic, surface-active antimicrobial agent, chlorhexidine gluconate, was similarly able to promote microbial adhesion to hexadecane. The results suggest that (i) CPC enhances microbial adhesion to hexadecane by binding via electrostatic interactions at the cell surface, thus diminishing surface charge and increasing cell surface hydrophobicity, and (ii) this phenomenon may have applications in oral formulations and in the use of hydrocarbon droplets as a support for cell immobilization. 相似文献