全文获取类型
收费全文 | 1312篇 |
免费 | 98篇 |
国内免费 | 161篇 |
专业分类
林业 | 78篇 |
农学 | 136篇 |
基础科学 | 65篇 |
548篇 | |
综合类 | 459篇 |
农作物 | 151篇 |
水产渔业 | 20篇 |
畜牧兽医 | 57篇 |
园艺 | 15篇 |
植物保护 | 42篇 |
出版年
2024年 | 6篇 |
2023年 | 38篇 |
2022年 | 57篇 |
2021年 | 54篇 |
2020年 | 57篇 |
2019年 | 65篇 |
2018年 | 65篇 |
2017年 | 76篇 |
2016年 | 85篇 |
2015年 | 59篇 |
2014年 | 57篇 |
2013年 | 83篇 |
2012年 | 117篇 |
2011年 | 70篇 |
2010年 | 63篇 |
2009年 | 71篇 |
2008年 | 53篇 |
2007年 | 66篇 |
2006年 | 50篇 |
2005年 | 36篇 |
2004年 | 38篇 |
2003年 | 31篇 |
2002年 | 27篇 |
2001年 | 31篇 |
2000年 | 26篇 |
1999年 | 22篇 |
1998年 | 19篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1962年 | 2篇 |
排序方式: 共有1571条查询结果,搜索用时 31 毫秒
991.
Rahul Behl 《Fish physiology and biochemistry》2006,32(3):203-207
The changes in catalase activity in carp (Cyprinus carpio) ovarian follicles at different developmental stages were investigated. The effect of follicle-stimulating hormone (FSH) on catalase activity and estradiol secretion by carp ovarian follicles was studied to establish a developmental role of catalase in folliculogenesis in fish ovary. The follicular homogenates from large follicles showed higher (9.45 ± 0.64 units/mg protein) catalase-specific activity than the small follicles (2.94 ± 0.22 units/mg protein). The FSH significantly (P < 0.05) stimulated the catalase activity in both size categories of the follicles in vitro. At the dose level of 100 ng FSH/ml culture medium, about 38 and 25% increase in catalase-specific activity was observed compared with the respective controls in small and large follicles respectively. The increase in catalase after FSH treatment was also accompanied by a similar increase in estradiol secretion. This study indicates that catalase might play a functional role in carp ovarian follicles. 相似文献
992.
试验以长期施肥为研究对象,采用Bremner提出的土壤有机氮分级方法对菜田土壤有机氮组分进行研究。结果表明,与不施肥(BN0)相比,单施化肥对菜田土壤有机氮含量和组分的影响较小。与单施化肥相比,有机肥与化肥配施能够显著提高菜田土壤全氮、酸解有机氮的含量,分别提高了19.7%和26.7%;在酸解氮中,其对氨基酸态氮和酸解未知态氮提高幅度分别为36.6%、32.1%,而对氨基糖态氮和氨态氮增幅较小。在不同肥料处理中,菜田土壤各种有机氮含量依次为:氨基酸态氮非酸解性氮酸解未知态氮氨态氮氨基糖态氮。长期有机无机肥配施使菜田土壤的供氮能力显著提高,也是维持菜田土壤肥力最适的施肥方式。 相似文献
993.
Chenopodium album L. (bathu) leaves and roots were selected to evaluate their antifungal potential against the Ascochyta rabiei responsible for chickpea blight that causes destructive yield losses. Methanolic extract of C. album leaves and roots was prepared and their various applied concentrations, viz., 1%, 2%, 3%, 4% and 5% were tested against A. rabiei. Leaf extracts were found more effective and showed significant antifungal activity over the root extracts. C. album leaf was found effective in screening bioassays, so this was subjected for fractional guided bioassays. Different various organic fractions of leaf extract were isolated, viz., n-hexane, chloroform, ethyl acetate and n-butanol. These isolated fractions were serially diluted to check their minimum inhibitory concentration (MIC) along with a synthetic fungicide (72% WP, Puslan). The MIC of various concentrations from 500 mg/mL to 1.95 mg/mL was recorded after 24 h and 48 h intervals. Ethyl acetate and synthetic fungicides were found most effectual in retarding conidial germination with MIC of 1.95 mg/mL after 48 h incubation periods. Chloroform fraction also inhibited the fungal growth whereas n-hexane and n-butanol fraction were found to be ineffective. 相似文献
994.
Wing-Keong Ng Hong-Aik Lim Siew-Ling Lim & Che-Omar Ibrahim 《Aquaculture Research》2002,33(15):1199-1207
The aim of this study was to evaluate whether pretreatment of palm kernel meal (PKM) with a commercial feed enzyme (Allzyme Vegpro?) or solid‐state fermentation of PKM with the cellulolytic fungus Trichoderma koningii (Oudemans) could improve the nutritive value of raw PKM in the diets of red hybrid tilapia, Oreochromis sp. Seven isonitrogenous (30% crude protein) and isoenergetic (15.1 kJ g?1) practical diets were formulated and fed close to apparent satiation to triplicate groups of 14 fish (mean initial weight 5.1 ± 0.1 g) for 10 weeks. The diets consisted of a control diet which did not contain any PKM, raw PKM diets, enzyme‐treated PKM (EPKM) or fermented PKM (FPKM) diets at 20% and 40% (dry weight basis) inclusion rates. The growth performance and feed utilization efficiency of tilapia fed 20% PKM or 20% EPKM were not significantly different (P > 0.05) from those of fish fed the control diet. Fish fed diets containing 40% EPKM showed significantly higher growth and feed utilization efficiency than fish fed 40% raw PKM owing to the improved dry matter, protein, lipid and energy digestibility of the enzyme‐treated PKM diets. The apparent protein and lipid digestibility of the 20% EPKM and 40% EPKM diets were not significantly different, and nor was the growth and feed utilization efficiency of fish fed these two diets. Hybrid tilapia fed FPKM‐based diets at all dietary inclusions tested showed the poorest growth, and this might indicate the presence of antinutrients in the resultant fungal biomass. In conclusion, it is anticipated that, with further optimization of enzyme pretreatment of PKM, higher levels of PKM could be included in the diets of hybrid tilapia, thereby reducing the impact of rising costs to feed tilapia. 相似文献
995.
不同Zn浓度对黑麦草根分泌物、根际Zn形态及植物Zn蓄集的影响 总被引:6,自引:0,他引:6
A glasshouse experiment was conducted using a root-bag technique to study the root exudates, rhizosphere Zn fractions, and Zn concentrations and accumulations of two ryegrass cultivars (Lolium perenne L. cvs. Airs and Tede) at different soil Zn levels (0, 2, 4, 8, and 16 mmol kg-1 soil). Results indicated that plant growth of the two cultivars was not adversely affected at soil Zn level≤8 mmol kg-1. Plants accumulated more Zn as soil Zn levels increased, and Zn concentrations of shoots were about 540 /μg g-1 in Aris and 583.9μg g-1 in Tede in response to 16 mmol Zn kg-1 soil. Zn ratios of shoots to roots across the soil Zn levels were higher in Tede than in Airs, corresponding with higher rhizosphere available Zn fractions (exchangeable, bound to manganese oxides, and bound to organic matter) in Airs than in Tede. Low-molecular-weight (LMW) organic acids (oxalic, tartaric, malic, and succinic acids) and amino acids (proline, threonine, glutamic acid, and aspartic acid, etc.) were detected in root exudates, and the concentrations of LMW organic acids and amino acids increased with addition of 4 mmol Zn kg-1 soil compared with zero Zn addition. Higher rhizosphere concentrations of oxalic acid, glutamic acid, alanine, phenylalanine, leucine, and proline in Tede than in Airs likely resulted in increased Zn uptake from the soil by Tede than by Airs. The results suggested that genotypic differences in Zn accumulations were mainly because of different root exudates and rhizosphere Zn fractions. 相似文献
996.
基于稀疏表示的大米品种识别 总被引:4,自引:3,他引:1
为了实现机器视觉准确判别大米品种,提出了一种基于稀疏表示的大米品种识别方法。以长江米、圆江米、粳米、泰国香米、红香米和黑米等6种大米籽粒图像作为研究对象,采用颜色和形态结构参数表示单个籽粒。每种大米随机选取50粒作为训练样本,200粒作为测试样本。所有训练样本组成稀疏表示方法的数据词典,对每一个测试样本,计算其在数据词典上的投影,将具有最小投影误差的类作为测试样本所属的品种。最后将提出的方法与BP网络和SVM的识别结果做了对比和分析。试验结果表明,提出的方法对于6个大米品种的综合识别准确率为99.6%,获得了最好的分类效果。为大米品种的识别提供了一种新的有效方案。 相似文献
997.
Kachare D. P. Chavan J. K. Kadam S. S. 《Plant foods for human nutrition (Dordrecht, Netherlands)》1988,38(2):155-162
The seeds of 13 improved cowpea cultivars were analysed for proximate composition, methionine, tryptophan and polyphenols. Considerable genetic variations were observed for the contents of protein, nonprotein nitrogen, limiting amino acids and polyphenols. The globulins contributed about 50% of the total seed proteins. A significant proportion of proteins of high protein cultivars was found to be insoluble. The proteins of most of the cultivars were found deficient in methionine and tryptophan. Methionine and tryptophan levels were negatively correlated with protein and positively correlated with carbohydrate contents. The cultivars with colored seed coats contained higher amounts of polyphenols. The difference in polyphenol content between various cultivars were due to seed coat polyphenols. 相似文献
998.
为研究小黑麦外观品质性状的遗传规律,利用SD 04-1等6个小黑麦品种进行完全双列杂交,采用胚乳性状的遗传模型及其分析方法对亲本和F1所结种子的粒长、粒宽、粒厚等性状进行遗传分析.结果表明,种子外观性状的表现同时受制于胚乳核基因、母体植株基因和细胞质基因三套遗传体系.控制种子粒长的遗传效应主要是种子直接加性效应(VA=0.138**),种子的粒宽、粒厚、长宽比和长厚比的遗传效应主要受母体显性效应控制(母体遗传方差占总遗传方差的35.59%~51.52%),粒长和粒厚存在细胞质效应.研究还发现,小黑麦粒长、长宽比、长厚比以胚乳直接遗传率为主,粒厚的细胞质遗传率也达到了极显著水平.就外观性状总体情况而言,参试亲本以P1 (SD 04-1)、P3(04草鉴3)为好,其三种遗传效应能显著改善多数外观性状. 相似文献
999.
Whole rice grain comprising endosperm, embryo (or germ), and bran has potential beneficial health effects in addition to provision of nutrients. The distribution of phenolic acids and anthocyanins in endosperm, embryo, and bran of white, red, and black rice grains was investigated in this study. The total phenolic content (TPC) was highest in the bran, averaging 7.35 mg GAE/g and contributing 60%, 86% and 84% of phenolics in white, red and black rice. The average TPC of the embryo and endosperm were 2.79 and 0.11 mg GAE/g accounting for 17% and 23%, 4% and 10% and 7% and 9% in white, red and black rice, respectively. The antioxidant capacity determined using DPPH and ORAC displayed a trend similar to TPC. Free/conjugated phenolic acids in white, red and black rice bran accounted for 41%, 65% and 85% of total acids. Bound phenolic acids in rice bran accounted for 90% of total acids in whole grain. Cis-p-coumaric was detected in bound form in bran while cis-sinapic acid was detected in the free/conjugated form in embryo and bran. Cyanidin-3-O-glucoside and peonidin-3-O-glucoside were identified mainly in black rice bran as the total anthocyanins. Cyanindin-3-O-rutinoside was also detected in black rice bran. 相似文献
1000.
Ivana SedejMarijana Saka? Anamarija Mandi?Aleksandra Mišan Vesna TumbasMiroslav Hadna?ev 《Journal of Cereal Science》2011,54(3):347-353
This study examined the antioxidant properties of the ethanolic extracts of wheat milling fractions (wheat flour type 500 and type 850, and bran) and their polyphenol and tocopherol content, and rheological characteristics of wheat dough supplemented with buckwheat flours (light and wholegrain). The results obtained in this study were correlated with our previously published data on wheat flour type 400, wholegrain wheat flour and buckwheat flours.Buckwheat flours exhibited significantly higher (P < 0.05) antiradical activity on hydroxyl (OH), superoxide anion (O2−) and (1,1-diphenyl-2-picrylhydrazyl) DPPH radicals, antioxidant activity and reducing power than all investigated wheat milling fractions when their corresponding IC50 values were compared.The rheological parameters of wheat dough supplemented with light and wholegrain buckwheat flour (0-50%) were obtained by using Mixolab. Results indicated changes in protein and starch properties of dough.The obtained results indicate the benefit of using buckwheat flours in wheat-based food products, i.e. their contribution in functional and tailor-made-food production. 相似文献