全文获取类型
收费全文 | 849篇 |
免费 | 63篇 |
国内免费 | 131篇 |
专业分类
1043篇 |
出版年
2023年 | 10篇 |
2022年 | 14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1043条查询结果,搜索用时 15 毫秒
31.
《Archives of animal nutrition》2013,67(3):183-195
During the last few years, animal nutrition has been confronted with genetically modified organisms (GMO), and their significance will increase in the future. The study presents investigations on the substantial equivalence of the transgenic Bt (Bacillus thuringiensis) corn and the corresponding nontransgenic hybrid Cesar and parameters of nutrition physiology such as digestibility and energy content for poultry, pigs and ruminants. The results of the analysed corn samples as well as of the silage samples illustrated substantial equivalence in all investigated ingredients, such as crude nutrients, amino acids, fatty acids, minerals and non‐starch polysaccharides. The results of the experiments using poultry, pigs, wethers and fattening bulls were not influenced by the genetic modification of corn. The determined values for the digestibilities and the energy contents for poultry, pigs and wethers were not affected by the used corn variety. Neither the examined parameters of the fattening experiments with bulls nor the slaughter results showed any significant differences between the bulls fed on silages made from the nontransgenic or transgenic corn. 相似文献
32.
Nitrous oxide emissions during establishment of eight alternative cellulosic bioenergy cropping systems in the North Central United States 下载免费PDF全文
Lawrence G. Oates David S. Duncan Ilya Gelfand Neville Millar G. Philip Robertson Randall D. Jackson 《Global Change Biology Bioenergy》2016,8(3):539-549
Greenhouse gas (GHG) emissions from soils are a key sustainability metric of cropping systems. During crop establishment, disruptive land‐use change is known to be a critical, but under reported period, for determining GHG emissions. We measured soil N2O emissions and potential environmental drivers of these fluxes from a three‐year establishment‐phase bioenergy cropping systems experiment replicated in southcentral Wisconsin (ARL) and southwestern Michigan (KBS). Cropping systems treatments were annual monocultures (continuous corn, corn–soybean–canola rotation), perennial monocultures (switchgrass, miscanthus, and poplar), and perennial polycultures (native grass mixture, early successional community, and restored prairie) all grown using best management practices specific to the system. Cumulative three‐year N2O emissions from annuals were 142% higher than from perennials, with fertilized perennials 190% higher than unfertilized perennials. Emissions ranged from 3.1 to 19.1 kg N2O‐N ha?1 yr?1 for the annuals with continuous corn > corn–soybean–canola rotation and 1.1 to 6.3 kg N2O‐N ha?1 yr?1 for perennials. Nitrous oxide peak fluxes typically were associated with precipitation events that closely followed fertilization. Bayesian modeling of N2O fluxes based on measured environmental factors explained 33% of variability across all systems. Models trained on single systems performed well in most monocultures (e.g., R2 = 0.52 for poplar) but notably worse in polycultures (e.g., R2 = 0.17 for early successional, R2 = 0.06 for restored prairie), indicating that simulation models that include N2O emissions should be parameterized specific to particular plant communities. Our results indicate that perennial bioenergy crops in their establishment phase emit less N2O than annual crops, especially when not fertilized. These findings should be considered further alongside yield and other metrics contributing to important ecosystem services. 相似文献
33.
Duc Khanh Le Quang Khai Le Thi Thuy Hang Tran Duc Viet Nguyen Thi Hang Dao Thi Thuy Nguyen Xuan Lam Truong Quang Cuong Nguyen Huy Phong Pham Thi Thu Thuy Phan Gajendra Babu Baktavachalam 《Journal of Asia》2019,22(2):493-498
Susceptibility of Asian corn borer (ACB), Ostrinia furnacalis (Guenée) to Bacillus thuringiensis (Bt) Cry1Ab protein was studied between 2015 and 2016 with 11 ACB populations, collected from various geographical regions in Vietnam. A concentration range of Cry1Ab from 0.20 to 26.10 ng/cm2 of diet was evaluated against F1 ACB neonates using diet surface-overlay bioassays. Mortality data was recorded daily until seven days after infestation. Growth inhibition was recorded at the end of seven days. The median lethal concentration (LC50) varied ≈3-fold among the different populations, ranging from 0.58 to 1.83 ng/cm2 of diet with an overall mean of 0.86 ng/cm2 of diet. Even the lowest concentration of 0.20 ng/cm2 caused 73.53% growth inhibition. >90% growth inhibition was achieved at 0.82 ng/cm2 or higher concentrations. The results reflect natural variation in Bt susceptibility among ACB populations rather than variation caused by prior exposure to selection pressures. LC99 value (17.26 ng/cm2) was generated by pooling mortality data across different populations. The upper fiducial limit of LC99 (24.38 ng/cm2) could be a potential diagnostic dose for future resistance monitoring programs. The findings from this study suggest that ACB populations in Vietnam are highly susceptible to Cry1Ab protein. This is the first report of Cry1Ab susceptibility of different ACB populations in Vietnam and will serve as a baseline for future resistance monitoring work. 相似文献
34.
为了解玉米秸秆还田对土壤微生物群落功能多样性的影响,采用ECO-Biolog微平板法,分析了以无玉米秸秆还田为对照(CK),6000 kg·hm-2(S1)、9000 kg·hm-2(S2)、12000 kg·hm-2(S3)和15000 kg·hm-2(S4)四个秸秆还田量的土壤微生物碳源代谢特征。结果表明:随着玉米秸秆还田量的增加,土壤微生物平均颜色变化率(AWCD)也随之增加,24~96 h的AWCD值变化迅速,96 h后进入平稳期,S4处理AWCD值始终大于其他处理;秸秆还田对Shannon指数与Simpson指数没有显著影响(P>0.05),但与CK相比,S4处理McIntosh指数显著增加了57.5%(P<0.05);主成分分析结果显示,秸秆还田影响着土壤微生物群落碳代谢能力,S1、CK、S2和S3处理在PC1和PC2上出现显著的分异,糖类、多聚物类、羧酸类碳源是研究区域内土壤微生物利用的主要碳源。因此,在东北黑土区增加玉米秸秆还田量能够提高土壤微生物对碳源的利用能力,提升黑土肥力。 相似文献
35.
Corn silk (Stigma Maydis) has been utilized as an important herb against obesity by Chinese, Korean, and Native Americans, but its phytochemicals and mechanisms(s) against obesity have not been deciphered completely. This study aimed to identify promising bioactive constituents and mechanism of action(s) of corn silk (CS) against obesity via network pharmacology. The compounds from CS were identified using Gas Chromatography Mass Spectrometry (GC-MS) and were confirmed ultimately by Lipinski’s rule via SwissADME. The relationships of the compound-targets or obesity-related targets were confirmed by public bioinformatics. The signaling pathways related to obesity, protein-protein interaction (PPI), and signaling pathways-targets-bioactives (STB) were constructed, visualized, and analyzed by RPackage. Lastly, Molecular Docking Test (MDT) was performed to validate affinity between ligand(s) and protein(s) on key signaling pathway(s). We identified a total of 36 compounds from CS via GC-MS, all accepted by Lipinski’s rule. The number of 36 compounds linked to 154 targets, 85 among 154 targets related directly to obesity-targets (3028 targets). Of the final 85 targets, we showed that the PPI network (79 edges, 357 edges), 12 signaling pathways on a bubble chart, and STB network (67 edges, 239 edges) are considered as therapeutic components. The MDT confirmed that two key activators (β-Amyrone, β-Stigmasterol) bound most stably to PPARA, PPARD, PPARG, FABP3, FABP4, and NR1H3 on the PPAR signaling pathway, also, three key inhibitors (Neotocopherol, Xanthosine, and β-Amyrone) bound most tightly to AKT1, IL6, FGF2, and PHLPP1 on the PI3K-Akt signaling pathway. Overall, we provided promising key signaling pathways, targets, and bioactives of CS against obesity, suggesting crucial pharmacological evidence for further clinical testing. 相似文献
36.
37.
Cysteine proteinases predominate in the midgut fluid (MF) and oral secretion (OS) of adult western corn rootworm (WCR) based on their mild acidic pH optima (pH 6.0), enhanced activities after treatment with thiol reducing agents, and inhibition by selective cysteine proteinase inhibitors (PIs). Four cysteine PIs including E-64, calpeptin, calpain inhibitor II, and leupeptin (also a serine PI) strongly inhibited azocaseinolytic activity in a dose-dependent manner in both the MF and OS. The most significant effect on adult female WCR of cysteine PI consumption with corn pollen was the reduction in fecundity, but female survival was not apparently affected. Mean fresh weights for all PI-fed females were also lower than control groups. All PI-fed groups [E-64, calpain inhibitor I (Cal I) and leupeptin] had a significantly lower daily egg production than respective corn pollen-fed controls. E-64 was more potent than leupeptin and Cal I on inhibiting fecundity, which correlates with their relative anti-proteinase potency in vitro. E-64, Cal I, and leupeptin at 1.5-2 nmol/beetle/day reduced fecundity down to 25-45% of control values. Reduced egg production by PI-fed beetles results from a combination of the direct inhibition of protein digestion and a post-ingestive negative feedback mechanism, which reduces food intake. The supplement of ten essential amino acids into the E-64-treated pollen enhanced up to 3.7-fold the number of eggs laid compared to the E-64-fed group without these amino acids, suggesting that egg production is dependent on the supply of essential amino acids from corn pollen proteolysis. 相似文献
38.
Ethanol production from corn cob hydrolysates by <Emphasis Type="Italic">Escherichia coli</Emphasis> KO11 总被引:2,自引:0,他引:2
de Carvalho Lima KG Takahashi CM Alterthum F 《Journal of industrial microbiology & biotechnology》2002,29(3):124-128
Corn cob hydrolysates, with xylose as the dominant sugar, were fermented to ethanol by recombinant Escherichia coli KO11. When inoculum was grown on LB medium containing glucose, fermentation of the hydrolysate was completed in 163 h and
ethanol yield was 0.50 g ethanol/g sugar. When inoculum was grown on xylose, ethanol yield dropped, but fermentation was faster
(113 h). Hydrolysate containing 72.0 g/l xylose and supplemented with 20.0 g/l rice bran was readily fermented, producing
36.0 g/l ethanol within 70 h. Maximum ethanol concentrations were not higher for fermentations using higher cellular concentration
inocula. A simulation of an industrial process integrating pentose fermentation by E. coli and hexose fermentation by yeast was carried out. At the first step, E. coli fermented the hydrolysate containing 85.0 g/l xylose, producing 40.0 g/l ethanol in 94 h. Baker's yeast and sucrose (150.0
g/l) were then added to the spent fermentation broth. After 8 h of yeast fermentation, the ethanol concentration reached 104.0
g/l. This two-stage fermentation can render the bioconversion of lignocellulose to ethanol more attractive due to increased
final alcohol concentration. Journal of Industrial Microbiology & Biotechnology (2002) 29, 124–128 doi:10.1038/sj.jim.7000287
Received 20 February 2002/ Accepted in revised form 04 June 2002 相似文献
39.
Nutritional requirements for germination and growth of the entomopathogenic fungus Beauveria bassiana are not complex. For germination to occur, a utilizable source of carbon must be present; however, a nitrogen source is needed for continued hyphal growth, otherwise lysis ensues. Compounds that can serve as utilizable carbon-energy sources for germination include glucose, N-acetylglucosamine, glucosamine, chitin, starch, lanolin, hydrocarbons in crude oil, and some longer-chain fatty acids. Both organic and inorganic sources of nitrogen are readily utilized for growth. Conidia undergo active metabolism soon after being placed in a suitable growth medium, indicating that conidia are released from their state of dormancy several hours before emergence of the germ tube can be observed. Because of the nutritional versatility of B. bassiana, this fungus should be able to survive and be infective in several types of natural environments. 相似文献
40.
用热分析法研究了农田生态条件下玉米秸杆腐解过程腐解物的热解变化特征 ,并探讨了腐解物中不同组分对腐解物热解特征的影响。结果表明 ,腐解物 DTA曲线的 2 80℃、3 3 0℃、4 50℃放热峰 ,DTG曲线的第二失重峰和 h330℃ /h4 50℃ 值可作为表征腐解进程的特征峰和特征值。由腐解物 DTA、DTG所得能量各参数 ( ΔH,E)与文献 [3 ]所述腐解物能态 ( Qv)呈现波动起伏 ,趋于稳定 2个阶段相符 ,二者相互印证 ,显示热分析方法用于植物残体腐解进程研究的可行性。 DTA的2 80℃放热峰主要由苯 -醇溶性物、水溶性物引起。苯 -醇溶性物、水溶性物和纤维素、半纤维素是影响腐解物热解及其能态变化特征的主要物质组分。木质素组分对腐解后期腐解物的热解及其能态特征趋于稳定具有重要作用 相似文献