首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   71139篇
  免费   4117篇
  国内免费   7817篇
林业   9109篇
农学   11971篇
基础科学   6819篇
  12381篇
综合类   20279篇
农作物   3637篇
水产渔业   2572篇
畜牧兽医   9549篇
园艺   2158篇
植物保护   4598篇
  2024年   720篇
  2023年   706篇
  2022年   1803篇
  2021年   2668篇
  2020年   2597篇
  2019年   2442篇
  2018年   1677篇
  2017年   2377篇
  2016年   2428篇
  2015年   3124篇
  2014年   2951篇
  2013年   3691篇
  2012年   4278篇
  2011年   4774篇
  2010年   4519篇
  2009年   4284篇
  2008年   4158篇
  2007年   4175篇
  2006年   4043篇
  2005年   3578篇
  2004年   1726篇
  2003年   1535篇
  2002年   1156篇
  2001年   1323篇
  2000年   1573篇
  1999年   1867篇
  1998年   1894篇
  1997年   1579篇
  1996年   1431篇
  1995年   1356篇
  1994年   1180篇
  1993年   1126篇
  1992年   949篇
  1991年   792篇
  1990年   675篇
  1989年   583篇
  1988年   447篇
  1987年   267篇
  1986年   169篇
  1985年   82篇
  1984年   73篇
  1983年   65篇
  1982年   51篇
  1981年   39篇
  1980年   29篇
  1979年   20篇
  1978年   9篇
  1965年   12篇
  1964年   14篇
  1963年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
锦带花新品种抗寒性   总被引:1,自引:0,他引:1  
以两个锦带花新品种贵妃锦带和宝石锦带为试材,以锦带花、红王子锦带和金亮锦带为对照,在观察田间植株自然越冬后的形态特征的基础上,测定其2a扦插苗的1年生枝条在不同低温处理条件下相对电导率、丙二醛和可溶性糖质量分数变化,研究两个新品种的抗寒性.结果表明:在哈尔滨地区,贵妃锦带、宝石锦带和锦带花在室外-36℃自然越冬而不受冻害,红王子锦带和金亮锦带有不同程度的冻害现象.两个新品种的观赏特性比锦带花、红王子锦带和金亮锦带更良好.贵妃锦带、宝石锦带、锦带花、红王子锦带和金亮锦带枝条的半致死温度分别为-40.24、-39.6、-41.59、-32.08和-30.46℃;5种锦带花枝条的相对电导率和丙二醛质量摩尔浓度随处理温度的降低呈升高趋势;两个新品种和锦带花枝条的可溶性糖质量分数随处理温度的降低呈升高趋势,红王子锦带和金亮锦带呈先升高后降低的趋势.  相似文献   
942.
应用截线法、访问法、交尾地调查相结合的方法对我国黑琴鸡东部分布区资源现状进行了调查,并对该分布区巢址的林型、食物丰富度、隐蔽级、干扰级、距水源距离、坡向、坡位、坡度、巢位、海拔高度共10项生境因子进行分析.结果显示:我国东部分布区黑琴鸡种群数量为(24 785±2 737)只.河北围场县塞罕坝林区种群密度最高,达到(7.28±0.875)只/km2,内蒙古红花尔基林区种群密度次之,为(5.347±0.645)只/km2,河北木兰围场林区种群密度第三,为(3.94±0.474)只/km2.在该分布区中,影响巢址选择的生境因子主要有距水源距离、食物丰富度、隐蔽级、林型、坡向和干扰级,其中塞罕坝林区、红花尔基林区和木兰围场林区是黑琴鸡巢址选择的最佳生境.  相似文献   
943.
Saponaria officinalis L. seeds were treated with different concentrations of chemical mutagen to determine the impact of media with various hormone concentrations on the induction of mutated (Saponaria officinalis L.) seeds' adventitious buds and rooting culture by using tissue culture technology. The results indicated that the optimum concentration of the chemical mutagen-EMS was 0.3%; the optimum induction medium was MS+6-BA 1.5 mg · L^-1, NAA 0.1 mg · L^-1 and the optimum rooting medium was MS+0.05 mg · L^-1 NAA.  相似文献   
944.
Reversed-phase high-performance liquid chromatography (RP-HPLC) method with C4 column and C18 column for analyzing β-lactoglobulin and α-lactalbumin in bovine milk was developed and the performance and characteristic of two columns were compared. Shiseido Proteonavi C4 column (250 mm×4.6 mm×5μm) and Shiseido CAPCELL PAK SG 300 C18 column (250 mm× 4.6 mm×5 μm) were used in the experiment. Phase A was composed of 0.1% (V/V) trifluoroacetic acid (TFA) in ultrapure water and Phase B (organic phase) was composed of 0.1% TFA in acetonitrile. Gradient elution was taken. Flow rate was 1 mL min-1. The detection wavelength was 215 nm. The injection volume was 20 μL and the column temperature was 30℃. The results showed that linear relationship was good and recovery of α-lactalbumin and β-lactoglobulin was 86.12%-104.38%, C18 column had stronger ability to resist acid and more stable, and the method with C4 column had excellent sensitivities and good separation.  相似文献   
945.
Value analysis of grain production influencing factors is a complex decision problem. This paper introduced a modified Analytic Hierarchy Process (AHP) accumulation factor, namely Solving Weight by AHP's Accumulation Factor Sequence Evaluating Data. We used the arithmetical average to replace the expert marking, so that the possible decision mistakes by the subjective judgments could be avoided. We computed the case with this method, which obtained attribute value of 17 influencing factors of the potential food production in Heilongjiang Province, and the result of which was reasonable  相似文献   
946.
Six isonitrogenous and isolipidic diets were formulated containing two astaxanthin (AX; 0 and 90 mg/kg) and three vitamin E (VE) levels (0, 25 and 50 mg/kg). There were three replicates (18 crabs per replicate) for each treatment. Juvenile swimming crab (initial weight 31.65 ± 0.06 g/crab) were fed different diets for 8 weeks. After the feeding trial, growth performance was not significantly affected by the different treatments. Crabs fed with AX‐supplemented diets showed more redness. Whole body 22:6n‐3, 22:4n‐6 and 20:5n‐3 levels increased with the dietary addition of AX (= .009, = .002 and = .042, respectively). The malondialdehyde (MDA) concentrations of fresh/frozen hepatopancreas and frozen muscle were significantly decreased by the dietary AX supplementation (p < .001, = .010 and = 0.011, respectively). These findings provide evidence that dietary AX has an ability to improve the redness of the shell and reduce the MDA concentrations of tissues. Furthermore, there is no strong interactive relationship between dietary VE and AX on the coloration and fatty acid concentrations for the swimming crab.  相似文献   
947.
松针是一种可再生的自然资源,而且松针堆肥是一种尚未开发且具有潜在价值的生物有机肥,具有广阔的应用前景。笔者主要综述了松针的主要成分,以及松针堆肥在生物抗衰老、作物抑菌抗病毒、减少田间地表径流和田间土壤改良方面的潜在价值,并指出目前松针堆肥3个主要研究方向,包括松针堆肥在松针降解方面的研究,松针堆肥堆捂条件控制以及松针堆肥作物适宜配方研究。希望为松针在有机肥方面的开发和研究提供理论基础。  相似文献   
948.
Due to the ambient temperature fluctuation during the process of storage, transportation, and sale, frozen fillets may go through frozen-thawed cycles that result in quality changes. In order to detect the frozen-thawed cycles in frozen tilapia fillets, near infrared spectroscopy was applied. The thawing loss, cooking loss, moisture content, total volatile basic nitrogen, and texture profile of fillets in seven frozen-thawed cycles were analyzed to reflect the change of quality. A total of 60 fillets were used to collect the spectra on both dorsal and belly flesh in frozen and thawed state from the first to the seventh cycle. The results showed that there is a better discrimination among the once and the repeated frozen-thawed samples in the frozen state than the thawed state. Frozen samples were still conducive to the differentiation and had higher classification accuracy, ranging from 80% to 93.33%. Dorsal flesh was more beneficial for the differentiation than belly flesh and had the highest accuracy, ranging from 86.67% to 93.33% in the frozen state. These results showed that the nondestructive and fast detection of repeated frozen-thawed cycles in frozen tilapia fillets can be accomplished by near infrared spectroscopy, which has enormous potential for practical application.  相似文献   
949.
The experiment was conducted to investigate the effects of oral administration of probiotics (Bacillus licheniformis and Bacillus subtilis) in combination with prebiotic isomaltooligosaccharide (IMO) on the intestinal microflora and immunological parameters of Penaeus japonicus and its resistence against Vibrio alginolyticus. A basal diet was supplemented with 0% probiotics and prebiotic (control), 108 colony forming unit (CFU) g?1B. licheniformis and 0.2% IMO (T1), 108 CFU g?1B. subtilis and 0.2% IMO (T2), 108 CFU g?1B. licheniformis in combination with 108 CFU g?1B. subtilis and 0.2% IMO (T3). The results showed that the total bacterial counts significantly increased (P<0.05) and Vibrio counts significantly decreased (P<0.05) in the intestine of shrimp with supplementation of dietary synbiotics. Shrimp fed the diet with both Bacillus probiotics and IMO (T3) produced significantly higher immune parameters (phenoloxidase activity, lysozyme activity and nitric oxide synthase activity and superoxide dismutase activity) than the control group (P<0.05). Significant lower cumulative mortality after challenge with V. alginolyticus was also observed in shrimp fed diet with both Bacillus probiotics and IMO (T3) than that in the control group (P<0.05). The results indicated that the oral administration of probiotics (B. licheniformis and B. subtilis) and prebiotic IMO has positive effects on bacterial flora in P. japonicus gut, and can activate non‐specific immunity of shrimp.  相似文献   
950.
The effect of taurine supplementation to a microencapsulated diet at 0 % (T-0 %), 1 % (T-1 %) and 2 % (T-2 %) level on growth performance and taurine content of Nibea albiflora larvae was evaluated. The microencapsulated diet was prepared using wet granulation and fluidized bed coating process. Scanning electron microscopy microphotography of the microencapsulated diet showed the appearance with a dense film around the core. More than 50 % of diet particles were between 250 and 590 μm. A 30-day feeding experiment was conducted with larvae at 15 days after hatching (DAH), in which larvae were weaned at 20 DAH from copepods to the experimental diets or fed copepods throughout the experimental period. The survival and total length of larvae were significantly higher in T-1 % group compared with T-0 % group (P < 0.05). The survival, total length and wet weight of larvae were significantly higher in T-2 % group compared with T-0 % group (P < 0.05). Fish larvae fed copepods had the best growth performance in survival, total length and wet weight, which were significantly higher than those in other treatments (P < 0.05). The taurine content of larvae fed with supplemental taurine (T-2 %, T-1 %) was significantly higher than that of larvae fed without supplemental taurine (T-0 %) (P < 0.05). These results confirmed that taurine is an essential nutrient for N. albiflora larvae.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号