全文获取类型
收费全文 | 989篇 |
免费 | 68篇 |
国内免费 | 5篇 |
出版年
2021年 | 37篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 33篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 40篇 |
2014年 | 42篇 |
2013年 | 66篇 |
2012年 | 58篇 |
2011年 | 82篇 |
2010年 | 50篇 |
2009年 | 31篇 |
2008年 | 46篇 |
2007年 | 48篇 |
2006年 | 32篇 |
2005年 | 41篇 |
2004年 | 36篇 |
2003年 | 33篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 7篇 |
1969年 | 9篇 |
1968年 | 4篇 |
排序方式: 共有1062条查询结果,搜索用时 78 毫秒
81.
Effects of Selenium Supplementation on Antioxidant Defense and Glucose Homeostasis in Experimental Diabetes Mellitus 总被引:1,自引:0,他引:1
Erbayraktar Z Yilmaz O Artmann AT Cehreli R Coker C 《Biological trace element research》2007,118(3):217-226
The objective of this study was to investigate the effects of different forms of Se supplementation on the antioxidant defense
and glucose homeostasis in experimental diabetes. Sodium selenate (SS) or selenomethionine (SM) were administered (2 μmol
Se kg−1 day−1) via orogastric route to streptozotocine (STZ)-induced diabetic rats in addition to basal diet for 12 weeks. Glucose levels
in whole blood, glutathione peroxidase (GSH-Px) activity in erythrocytes, Se and fructosamine levels in plasma were evaluated
monthly. Plasma Se levels increased significantly in all diabetic groups compared to basal measurements, being more prominent
in SM group [p(SM3/SM0) = 0.018]. The increase in GSH-Px activities was significant at the end of the second month in SS [p(SS2/SS0) = 0.028], whereas at the end of the third month in SM the value was lower [p(SM3/SM0) = 0.018] and the unsupplemented diabetic control (DC) groups, p(DC3/DC0) = 0.012. Glucose increased significantly only in DC group. Fructosamine increased gradually in all diabetic groups, being
significant in DC and SS groups. At the end of the third month, highest fructosamine levels were observed in SS group, which
were significantly higher than the SM group [p(SM/SS) = 0.010]. In conclusion, Se augmented the antioxidant defense by increasing
GSH-Px activity and this effect was more prominent when Se was supplemented as SM, which exerted positive effects also on
glucose homeostasis. 相似文献
82.
Richard W. Osman Robert B. Whitlatch 《Journal of experimental marine biology and ecology》2007,342(1):40-53
Over the past 30 years southern New England, USA has been invaded by several species of ascidians, including Botrylloides violaceus, Diplosoma listerianum, Styela clava, and Ascidiella aspersa. These species have become dominate in coastal embayments and marinas but are usually absent from more open water coastal areas. A colonial ascidian, Didemnum sp. has invaded southern New England during the past 10 years and we first observed this species in eastern Long Island Sound in 2000. It has become the dominant at several field sites while remaining in low abundance at others. We conducted an experiment at two places, a protected marina and an open coast site, to examine its ability to compete with the established fouling community. Small colonies of Didemnum were transplanted onto panels with communities that varied in age from one to four weeks old and these treatments along with controls with only Didemnum were exposed at both sites. In most treatments Didemnum became a dominant species in the communities at both sites but it reached higher abundances at the open coast site. Potential causes of the observed differences are predation on other species of ascidians at the open coast site reducing recruitment of these species and competition, lower tolerance for elevated temperatures at the marina site, or other environmental parameters that might affect growth rates. 相似文献
83.
84.
85.
Composting rapidly reduces levels of extractable oxytetracycline in manure from therapeutically treated beef calves 总被引:9,自引:0,他引:9
Oxytetracycline (OTC) is a broad-spectrum antibiotic used in livestock production. The widespread use and relative persistence of OTC may encourage development of antibiotic-resistant bacteria. The objective of this study was to determine whether composting would substantially reduce the concentration of OTC found in manure from medicated animals. The effect of OTC on composting was also investigated. Five beef calves were medicated for 5 days with 22 mg/kg/day of OTC. Approximately 23% of the OTC fed to the calves was recovered in the manure. Manure samples collected from calves prior to and after medication were mixed with straw and woodchips, and aliquots of the subsequent mixtures were treated in laboratory composters for 35 days. In addition, aliquots of the OTC-containing mixture were incubated at 25 degrees C or sterilized followed by incubation at 25 degrees C. The presence of OTC did not appear to affect composting processes. Within the first six days of composting, levels of extractable OTC in the compost mixture decreased from 115+/-8 microg/g dry weight to less than 6+/-1 microg/g dry weight (a 95% reduction). In contrast, levels of extractable OTC in room temperature incubated and sterilized mixtures decreased only 12-25% after 37 and 35 days, respectively. Levels of total heterotrophic bacteria and OTC-resistant bacteria in the finished compost mixture were roughly 30-fold higher and 10-fold lower, respectively, than levels in the mixture prior to composting. Although the basis of the OTC disappearance during composting is not known, the preponderence of OTC-sensitive bacteria and the decrease of OTC-resistant bacteria in the finished compost suggests that OTC residues have been rendered biologically inactive or unavailable. 相似文献
86.
Canakci S Inan K Kacagan M Belduz AO 《Journal of microbiology and biotechnology》2007,17(8):1262-1270
Some hot springs located in the west of Turkey were investigated with respect to the presence of thermophilic microorganisms. Based on phenotyping characteristics and 16S rRNA gene sequence analysis, 16 of the isolates belonged to the genus Geobacillus and grew optimally at about 60 degrees C on nutrient agar. 16S rRNA gene sequence analysis showed that these isolates resembled Geobacillus species by > or = 97%, but SDS-PAGE profiles of these 16 isolates differ from some of the other species of the genus Geobacillus. However, it is also known that analysis of 16S rRNA gene sequences may be insufficient to distinguish between some species. It is proposed that recN sequence comparisons could accurately measure genome similarities for the Geobacillus genus. Based on recN sequence analysis, isolates 11, IT3, and 12 are strains of G stearothermophilus; isolate 14.3 is a strain of G thermodenitrificans; isolates 9.1, IT4.1, and 4.5 are uncertain and it is required to make further analysis. The presence of xylanase and arabinofuranosidase activities, and their optimum temperature and pH were also investigated. These results showed that 7 of the strains have both xylanase and arabinofuranosidase activities, 4 of them has only xylanase, and the remaning 5 strains have neither of these activities. The isolates 9.1, 7.1, and 3.3 have the highest temperature optima (80 degrees C), and 7.2, 9.1, AO4, 9.2, and AO17 have the highest pH optima (pH 8) of xylanase. Isolates 7.2, AO4, AC15, and 12 have optimum arabinofuranosidase activities at 75 degrees C, and only isolate AC 15 has the lowest pH of 5.5. 相似文献
87.
88.
Cengiz?KayaEmail author Muhammed?Ashraf Osman?Sonmez Atilla?L.?Tuna Tahir?Polat Salih?Aydemir 《Acta Physiologiae Plantarum》2015,37(1):1741
The effects of thiamin (Thi) applied as seed soaking or foliar spray on some key physiological parameters were investigated in two differentially salt-responsive maize (Zea mays L.) cultivars, DK 5783 and Apex 836 F1, exposed to saline stress in two different experiments. An initial experiment (germination experiment) was designed to identify appropriate doses of Thi which could lessen the deleterious effects of salt on plants and screen all available maize cultivars for their differential tolerance to salt stress (100 mM NaCl). The seeds of nine maize cultivars were soaked for 24 h in solutions containing six levels of Thi (25, 50, 75, 100, 125 and 150 mg l?1). Based on the results obtained from the germination experiment, maize cultivar DK 5783 was found to be the most salt tolerant and Apex 836 as the most sensitive cultivar. Also, of six Thi levels used, two levels (100 and 125 mg l?1) were chosen for subsequent studies. In the second experiment (glasshouse experiment), two maize cultivars, DK 5783 (salt tolerant) and Apex 836 (salt sensitive) were subjected to saline regime (100 mM NaCl) and two levels of Thi (100 and 125 mg l?1) applied as foliar spray. Salt stress markedly suppressed shoot and root dry mass, total chlorophylls (“a” + “b”), leaf water potential and maximum fluorescence yield (Fv/Fm) in the plants of both maize cultivars, but it increased proline accumulation, leaf osmotic pressure, malondialdehyde (MDA) and hydrogen peroxide (H2O2) concentrations, electrolyte leakage (EL) as well as activities of some key antioxidant enzymes, superoxide dismutase (SOD; EC. 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and catalase (CAT; EC. 1.11.1.6). Salt-induced reduction in plant growth parameters was higher in the salt-sensitive cultivar, Apex 836, which was found to be associated with relatively increased EL, and MDA and H2O2 levels, and decreased activities of the key antioxidant enzymes. Application of Thi as seed soaking or foliar spray partly mitigated the deleterious effects of salinity on plants of both maize cultivars. The most promising effect of Thi on alleviation of adverse effects of salt stress on maize plants was found when it was applied as foliar spray at 100 mg l?1. Thiamin application considerably reduced tissue Na+ concentration, but improved those of N, P, Ca2+ and K+ in the salt-stressed maize plants. Exogenously applied thiamin-induced growth improvement in maize plants was found to be associated with reduced membrane permeability, MDA and H2O2 levels, and altered activities of some key antioxidant enzymes such as CAT, SOD and POD as well as increased photosynthetic pigment concentration under saline regime. 相似文献
89.