全文获取类型
收费全文 | 846篇 |
免费 | 65篇 |
国内免费 | 130篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 21篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 26篇 |
2016年 | 26篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 50篇 |
2012年 | 38篇 |
2011年 | 50篇 |
2010年 | 31篇 |
2009年 | 45篇 |
2008年 | 37篇 |
2007年 | 48篇 |
2006年 | 37篇 |
2005年 | 48篇 |
2004年 | 30篇 |
2003年 | 16篇 |
2002年 | 31篇 |
2001年 | 27篇 |
2000年 | 16篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有1041条查询结果,搜索用时 93 毫秒
91.
Production of succinic acid from sugarcane molasses supplemented with a mixture of corn steep liquor powder and peanut meal as nitrogen sources by Actinobacillus succinogenes 下载免费PDF全文
92.
以7个糯玉米品种为材料,测定其籽粒发育过程中淀粉粒粒度分布及淀粉合成相关酶活性的变化,分析两者之间的关系。结果表明,随着籽粒发育,糯玉米淀粉粒平均粒径逐渐增大,可溶性淀粉合成酶(SSS)和淀粉分支酶(SBE)活性呈单峰曲线变化。籽粒发育前期,小淀粉粒(≤7.4μm)所占体积较大;随着籽粒发育,小淀粉粒所占体积减少,大淀粉粒(>7.4μm)所占体积增多;籽粒发育后期,大淀粉粒所占体积较大。相关分析表明, SSS和SBE活性与大淀粉粒体积增大速率和平均粒径增大速率均呈显著或极显著正相关。因此, SSS和SBE是影响糯玉米胚乳淀粉粒粒度分布形成的主要酶, SSS和SBE活性越高,淀粉粒平均粒径越大,大淀粉粒所占体积越多。 相似文献
93.
Optimising the capacity of field trials to detect the effect of genetically modified maize on non‐target organisms through longitudinal sampling 下载免费PDF全文
J. Comas B. Lumbierres C. Comas X. Pons R. Albajes 《The Annals of applied biology》2015,166(2):183-195
To assess risks of cultivation of genetically modified crops (GMCs) on non‐target arthropods (NTAs), field tests are necessary to verify laboratory results and in situations where exposure pathways are very complex and cannot be reproduced in the laboratory. A central concern in the design of field trials for this purpose is whether the tests are capable of detecting differences in the abundance or activity of NTAs in a treated crop in comparison with a non‐treated comparator plot. The detection capacity of a trial depends on the abundance and variability of the taxon, the values assumed for type I (α) and II (β) errors, and the characteristics of the trial and statistical design. To determine the optimal trial layout and statistical analysis, 20 field trials carried out in Spain from 2000 to 2009 to assess risks of GMCs on NTAs were examined with α and β set at 0.05 and 0.20, respectively. In this article we aim to determine the optimal number of sampling dates during a season, or longitudinal samples, in the design of field trials for assessing effects of GM maize on NTAs, and the ones that contribute most to achieving detectable treatment effects (dc) less than 50% of the mean of the control. Detection capacities are a function of the number of individual samples taken during the season but a high number of samples is rarely justified because gains of repeated sampling can be relatively low. These gains depend primarily on field tests relative experimental variability in individual samplings (i.e. experimental variability relative to the mean of the control in each sampling date) which in turn depends on the sampling method (visual counts, pitfall traps or yellow sticky traps) and the density (or abundance) of the taxon in question. Taxa showing more density (or abundance) have less relative experimental variability. The smaller the experimental variability, the lower the profit of increasing the number of sampling dates. Sticky traps have a good effect detection capacity and need very few sampling dates, whereas visual counts and pitfall traps have a poorer effect detection capacity and need more individual samples to achieve dc values lower than 50%. In maize field trials, it is recommended to concentrate sampling efforts in certain growth stages; the optimal ones for achieving an acceptable detection capacity are variable but, in general, samples in the first half of the season render better detection capacity than samples in the second half. 相似文献
94.
95.
96.
97.
玉米秸秆分批补料获得高还原糖浓度酶解液的条件优化 总被引:3,自引:1,他引:2
木质纤维素高浓度还原糖水解液的获得是纤维乙醇产业化发展的方向。在发酵工业领域,分批补料法是实现这一目标的重要研究途径。本研究采用分批补料法对获得高浓度玉米秸秆酶解还原糖的条件进行了优化。以稀硫酸预处理的玉米秸秆为原料,考察了液固比、补加量与补加时间对分批补料糖化的影响。结果表明,秸秆高浓度酶解液条件的初始物料为20% (重量/体积),木聚糖酶220 U/g (底物),纤维素酶6 FPU/g (底物),果胶酶50 U/g (底物),在24 h、48 h后分批补加8%预处理后的物料,同时添加与补料量相应的木聚糖酶20 U/g (底物),纤维素酶2 FPU/g (底物),72 h后,最终糖化结果与非补料法相比,还原糖浓度从48.5 g/L提高到138.5 g/L,原料的酶解率最终达到理论值的62.5%。试验结果表明补料法可以显著提高秸秆水解液还原糖浓度。 相似文献
98.
99.
玉米黄粉中含有约质量分数60%的蛋白质,但很难直接应用,必须进行预处理.本文以玉米黄粉为原料,利用蛋白酶产生菌LN01进行液体发酵,分别研究了液体接种量、初始pH、培养温度和培养时间等因素对LN01菌株水解玉米黄粉蛋白的影响.实验结果表明,LN01菌株水解玉米黄粉蛋白的最佳发酵条件为:初始pH值为6.0,液体种子接种量... 相似文献
100.
Dorn B Forrer HR Jenny E Wettstein FE Bucheli TD Vogelgsang S 《Journal of applied microbiology》2011,111(3):693-706
Aims: To quantify and to compare the occurrence of Fusarium species in maize kernels and stalk pieces, to analyse mycotoxins in kernels and maize crop residues, to evaluate two approaches to obtain kernel samples and to compare two methods for mycotoxin analyses. Methods and Results: The occurrence of Fusarium species in maize kernels and stalk pieces from a three‐year maize hybrid trial and 12 kernel samples from grower’s fields was assessed. Nine to 16 different Fusarium species were detected in maize kernels and stalks. In kernels, F. graminearum, F. verticillioides and F. proliferatum were the most prevalent species whereas in stalks, they were F. equiseti, F. proliferatum and F. verticillioides. In 2006, 68% of the kernel samples exceeded the recommended limit for pig feed for deoxynivalenol (DON) and 42% for zearalenone (ZON), respectively. Similarly, 75% of the samples from grower’s fields exceeded the limits for DON and 50% for ZON. In maize crop residues, toxin concentrations ranged from 2·6 to 15·3 mg kg?1 for DON and from 0·7 to 7·4 mg kg?1 for ZON. Both approaches to obtain maize kernel samples were valid, and a strong correlation between mycotoxin analysis using ELISA and LC‐MS/MS was found. Conclusions: The contamination of maize kernels, stalk pieces and remaining crop residues with various mycotoxins could pose a risk not only to animal health but also to the environment. With the hand‐picked sample, the entire Fusarium complex can be estimated, whereas combine harvested samples are more representative for the mycotoxin contents in harvested goods. Significance and Impact of the Study: This is the first multi‐year study investigating mycotoxin contamination in maize kernels as well as in crop residues. The results indicate a high need to identify cropping factors influencing the infection of maize by Fusarium species to establish recommendations for growers. 相似文献