全文获取类型
收费全文 | 4190篇 |
免费 | 290篇 |
国内免费 | 333篇 |
专业分类
4813篇 |
出版年
2023年 | 81篇 |
2022年 | 72篇 |
2021年 | 126篇 |
2020年 | 141篇 |
2019年 | 171篇 |
2018年 | 139篇 |
2017年 | 206篇 |
2016年 | 188篇 |
2015年 | 142篇 |
2014年 | 184篇 |
2013年 | 346篇 |
2012年 | 159篇 |
2011年 | 233篇 |
2010年 | 139篇 |
2009年 | 206篇 |
2008年 | 207篇 |
2007年 | 254篇 |
2006年 | 198篇 |
2005年 | 198篇 |
2004年 | 125篇 |
2003年 | 135篇 |
2002年 | 125篇 |
2001年 | 105篇 |
2000年 | 93篇 |
1999年 | 81篇 |
1998年 | 66篇 |
1997年 | 63篇 |
1996年 | 58篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 43篇 |
1992年 | 53篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 7篇 |
排序方式: 共有4813条查询结果,搜索用时 15 毫秒
21.
22.
目的:筛选适合油田的生物表面活性剂生产菌。方法:通过发酵培养,研究生物表面活性剂生产菌生长代谢规律;采用正交试验法,优选出其最佳培养条件;通过室内驱油实验评价生物表面活性剂驱油效果。结果:2#菌株最佳培养时间为96小时,最优发酵培养条件为:葡萄糖4.0 g、玉米浆1.6 g、Na2HPO40.1 g、KH2PO40.05 g、MgSO40.05 g、CaCl20.005 g、水100 mL、pH 7.2,培养温度35℃,摇床转速120 r/min,生物表面活性剂驱油提高采收率6.16%。结论:筛选出最优生物表面活性剂产生菌2#,菌株具备产表面活性剂的能力且产物量较高,其生物表面活性剂驱油效果良好。 相似文献
23.
Plant-derived extracts and phytochemicals have long been a subject of research in an effort to develop alternatives to conventional
insecticides but with reduced health and environmental impacts. In this review we compare the bioactivities of some plant
extracts with those of commercially available botanical insecticides against two important agricultural pests, the cabbage
looper, Trichoplusia ni and the armyworm, Pseudaletia unipuncta. Test materials included extracts of Azadirachta indica (neem), A. excelsa (sentang), Melia volkensii, M. azedarach (Chinaberry) and Trichilia americana, (all belonging to the family Meliaceae) along with commercial botanical insecticides ryania, pyrethrum, rotenone and essential
oils of rosemary and clove leaf. Most of the extracts and botanicals tested proved to be strong growth inhibitors, contact
toxins and significant feeding deterrents to both lepidopteran species. However, there were interspecific differences with
T. ni generally more susceptible to the botanicals than the armyworm, P. unipuncta. All botanicals were more inhibitory to growth and toxic (through feeding) to T. ni than to P. unipuncta, except for M. azedarach which was more toxic to P. unipuncta than to T. ni. Athough, pyrethrum was the most toxic botanical to both noctuids, A. indica, A. excelsa, and M. volkensii were more toxic than ryania, rotenone, clove oil and rosemary oil for T. ni. As feeding deterrents, pyrethrum was the most potent against T. ni, whereas A. indica was the most potent against the armyworm. Based upon growth inhibition, chronic toxicity, and antifeedant activity, some
of these plant extracts have levels of activity that compare favorably to botanical products currently in commercial use and
have potential for development as commercial insecticides. 相似文献
24.
Muhammed Akif Akgz 《化学与生物多样性》2019,16(12)
Phytochemicals, which are commonly found at different levels in many medicinal plants, are natural strong antioxidants used in traditional medicine. In this research, determination of differences of phytochemical compositions and biological properties were aimed as periodically (pre‐, full and post flowering) and daily (6 am, 1 pm and 8 pm) in Achillea gypsicola Hub.‐Mor . The volatile oils belonging to A. gypsicola were obtained by hydrodistillation and analyzed by gas chromatography‐flame ionization detection (GC‐FID) and gas chromatography‐mass spectrometry (GC/MS). The antimicrobial activities of the volatile oils were determined with disc diffusion method. The microdilution method was used to determine minimum inhibitory concentration (MIC). Total phenolic and flavonoid contents were determined by spectrophotometric methods and antioxidant capacities were evaluated by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical, reducing power (RP) and metal chelating activity (MCA) assay. In addition, the phenolic acid and flavonoid compositions were evaluated by reversed phase‐high‐performance liquid chromatography (RP‐HPLC). This study presented a comprehensive report for the first time on evaluation of the phytochemical composition and the biological properties of A. gypsicola at different phenological stages. Thirty‐two compounds, containing the major component as camphor, 1,8‐cineole and borneol, were detected. Designated harvest time for the highest yield of volatile oils was found to be at full flowering stage‐1 pm. It has been observed that the volatile oil composition changes periodically and even daily. Also, in this research, menthol and menthone were found as the composition of volatile oil in Achillea species for the first time. Full flowering stage was found as the richest period in terms of phenolic acid and flavonoid compositions of A. gypsicola for the first time. The species examined in this research showed a high antioxidant and antimicrobial activity in comparison to other studies with Achillea species. The volatile oils exhibited high performances with range of inhibition zones (8.3–42.3 mm) and minimum inhibitory concentration values (2.25—144 μg/ml). Besides, a high correlation between antioxidant activity and phenolic content of A. gypsicola was found. These results suggest that A. gypsicola can be used as a safe source in the cosmetic, food and pharmaceutical industries. 相似文献
25.
Pedro M. Martin-Sanchez Anna A. Gorbushina Hans-Jörg Kunte Jörg Toepel 《Biofouling》2016,32(6):635-644
A wide variety of fungi and bacteria are known to contaminate fuels and fuel systems. These microbial contaminants have been linked to fuel system fouling and corrosion. The fungus Hormoconis resinae, a common jet fuel contaminant, is used in this study as a model for developing innovative risk assessment methods. A novel qPCR protocol to detect and quantify H. resinae in, and together with, total fungal contamination of fuel systems is reported. Two primer sets, targeting the markers RPB2 and ITS, were selected for their remarkable specificity and sensitivity. These primers were successfully applied on fungal cultures and diesel samples demonstrating the validity and reliability of the established qPCR protocol. This novel tool allows clarification of the current role of H. resinae in fuel contamination cases, as well as providing a technique to detect fungal outbreaks in fuel systems. This tool can be expanded to other well-known fuel-deteriorating microorganisms. 相似文献
26.
早熟金柚果皮挥发油的提取及GC-MS分析 总被引:1,自引:0,他引:1
采用水蒸气蒸馏法提取早熟金柚果皮挥发油,通过正交实验优选获得早熟金柚果皮挥发油提取的工艺参数,结果表明:早熟金柚果皮挥发油的最佳提取工艺是将柚皮粉碎60 s,加水5倍,提取6 h。采用GC-MS联用技术对早熟金柚果皮挥发油的化学成分进行分离鉴定,共分离出44个峰,鉴定出了其中的25种化合物,占峰面积的98.43%。用面积归一化法测定了各个组分的相对百分含量,其主要成分有柠檬烯(65.82%)、β-月桂烯(25.52%)、4-侧柏烯(1.78%)、紫苏烯(0.44%)、氧化芳樟醇(0.42%)。 相似文献
27.
目的:将新疆南疆地区栽种的主要经济作物之一小白杏应用于化妆品领域,发挥其保持皮肤弹性、柔软和透明的功效。方法:以小白杏杏仁油为原料,运用正交实验设计,加入一定量的乳化剂,通过改变乳化温度、时间、转速,使油相与水相搅拌均匀。结果:最佳配方为:杏仁油13%,羊毛脂4%,蜂蜡3%,尿素3%,乳化剂1.5%,温度85℃,时间7 min,转速140 r/min。结论:以新疆小白杏杏仁油为主要原料,可研制适合于干性皮肤的防皲裂护手霜。 相似文献
28.
Bioremediation of oil polluted aquatic systems and soils with novel preparation `Rhoder' 总被引:4,自引:0,他引:4
This paper summarises the experience accumulated duringthe field application of biopreparation `Rhoder' (solely or in a combinationwith preliminary mechanical collection of free oil) for remediation of oil polluted aquatic systems and soils in the Moscow region and Western Siberia during 1994–1999.It was demonstrated that `Rhoder' had a very high efficiency (>99%) for bioremediation of the open aquatic surfaces (100 m2 bay of the River Chernaya, two 5,000 m2 lakes in Vyngayakha) at initial level of oil pollution of 0.4–19.1 g/l. During remediation of the wetland (2,000 m2) in Urai (initial level of oil pollution of 10.5 g/l), a preliminary mechanical collection of oil was applied (75% removal) followed by a triple treatment with `Rhoder'. It resulted in an overall treatment efficiency of 94%. Relatively inferior results of bioremediation of the 10,000 m2 wetland in Vyngayakha (65% removal) and the 1,000 m2 marshy peat soil in Nizhnevartovsk (19% removal) can be attributed to the very high initial level of oil pollution (24.3 g/l and >750 g/g dry matter, respectively) aggravated by the fact that it was impossible to apply a preliminary mechanical collection of oil on these sites. A possible strategy for remediation of such heavily polluted sitesis discussed. 相似文献
29.
《Bioscience, biotechnology, and biochemistry》2013,77(6):1166-1170
The present study explored the possibility that aroma components generated by the oxidation of olive oil may enhance the palatability of olive oil. Using a mouse behavioral model, we found that olive oil oxidized at room temperature for 3 weeks after opening the package, and heated olive oil were both significantly preferred over non-oxidized olive oil. Furthermore, this preference was enhanced with an additive of oxidized refined olive oil flavoring preparation at a certain concentration. These results suggest that the aroma of oxidized fat might be present in most fats, and might act as a signal that makes possible the detection of fats or fatty acid sources. 相似文献
30.
Mukhopadhyay I Nazir A Mahmood K Saxena DK Das M Khanna SK Chowdhuri DK 《Cell biology and toxicology》2002,18(1):1-11
The effect of argemone oil on hsp70expression and tissue damage was investigated by studying β-galactosidase activity, Western blotting and hybridization, and
trypan blue staining in the larval tissues of transgenic Drosophila melanogaster(hsp70-lacZ)Bg
9. Different concentrations of argemone oil were mixed with food and third-instar larvae were allowed to feed on them for different
time intervals (2, 4, 24, and 48 h). Argemone oil was found to induce hsp70even in the lowest concentration of the adulterant while maximum tissue damage was observed in the higher two treatment groups.
Malpighian tubules and midgut tissue reflected maximum damage as evidenced by both high β-galactosidase activity and trypan
blue staining in these tissues. A prior temperature shock treatment to the larvae was enough to protect the larvae from argemone
oil-induced tissue damage as evidenced by little or no trypan blue staining. The present study suggests the cytotoxic potential
of argemone oil and further strengthens the evidence for the use of hsp70as a biomarker in risk assessment.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献