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   2643篇
  免费   141篇
林业   223篇
农学   295篇
基础科学   35篇
  619篇
综合类   119篇
农作物   211篇
水产渔业   330篇
畜牧兽医   669篇
园艺   72篇
植物保护   211篇
  2023年   37篇
  2022年   78篇
  2021年   83篇
  2020年   102篇
  2019年   127篇
  2018年   165篇
  2017年   160篇
  2016年   130篇
  2015年   85篇
  2014年   126篇
  2013年   228篇
  2012年   187篇
  2011年   164篇
  2010年   141篇
  2009年   100篇
  2008年   109篇
  2007年   104篇
  2006年   87篇
  2005年   67篇
  2004年   52篇
  2003年   45篇
  2002年   33篇
  2001年   41篇
  2000年   34篇
  1999年   27篇
  1998年   18篇
  1997年   16篇
  1996年   9篇
  1995年   7篇
  1994年   8篇
  1993年   8篇
  1992年   11篇
  1991年   16篇
  1990年   15篇
  1989年   11篇
  1988年   13篇
  1987年   14篇
  1986年   7篇
  1985年   6篇
  1984年   8篇
  1983年   8篇
  1982年   5篇
  1981年   11篇
  1980年   5篇
  1979年   15篇
  1974年   8篇
  1973年   8篇
  1971年   8篇
  1969年   6篇
  1967年   4篇
排序方式: 共有2784条查询结果,搜索用时 15 毫秒
171.
Leaching of pesticides in tea brew.   总被引:2,自引:0,他引:2  
A cup of tea that cheers can also be an important route of human exposure to pesticide residues. It is important to evaluate the percent transfer of pesticide residue from dried (made) tea to tea infusion, as tea is subjected to an infusion process prior to human consumption. To investigate the pesticide translocation, 13 pesticides commonly used on tea were studied by subjection of fortified teas to infusion. Analytes of interest were quantified by gas-liquid chromatography with nitrogen-phosphorus and electron capture detectors. Interestingly, water solubility of pesticides did not necessarily indicate a shift of residues toward their preferential accumulation in infusion. The pesticides with larger partition coefficient (K(ow)) values remained nonextractable in infusing water. Further, boiling for longer periods (extended brewing time) resulted in higher transfer of pesticides to tea brew.  相似文献   
172.
1. The primary antibody response to sheep erythrocytes was determined by haemagglutination test in guinea fowl. The effects of various genetic and non‐genetic factors on immune response to sheep RBCs in guinea fowl were also estimated.

2. The immune response to sheep RBCs was normally distributed in guinea fowl with mean titre at 1.534 ± 0.014.

3. In guinea fowl, effects on titre values of sire and variety (feather colour) were significant whereas sex and sex × variety interaction effects were non‐significant.

4. The estimate of heritability for immune response to sheep RBCs in guinea fowl was 0.35 ±0.17.  相似文献   

173.
Field experiments were conducted at the Crop Research and Seed Multiplication Farm of Burdwan University, Burdwan, West Bengal, India, to evaluate the influence of integrated nutrient management on soil physicochemical properties in a mustard (Brassica campestris cv. ‘B9’) cropping system. The experiment was conducted during the winter seasons of 2011–2012 and 2012–2013 in old alluvial soil (pH 6–7). Seven different doses of biofertilizers (Azotobacter and phosphate solubilizing bacteria (PSB)), vermicomposts, organic (cow dung), and chemical fertilizers were applied on mustard in both the experimental seasons. The results indicated an improvement in soil quality by increasing soil porosity and water holding capacity significantly, as well as gradual build-up of the soil micronutrient status after harvesting of the crop. Dual applications of biofertilizers and vermicomposts have contributed significantly to higher soil organic matter, available nitrogen (N), phosphorus (P), and potassium (K) contents as well as micronutrient availability of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) and subsequently increased the soil health.  相似文献   
174.
A novel heme peroxidase MGP from the latex of Ipomoea carnea subsp. fistulosa (morning glory) belonging to the Convolvulaceae family was purified to homogeneity using ammonium sulfate precipitation, anion exchange, hydrophobic interaction, and gel filtration chromatography. The enzyme is glycosylated and has a molecular mass of 42.06 kDa (MALDI-TOF) and an isoelectric point of pH 4.3. The enzyme has high yield, broad substrate specificity, and a high stability toward pH, temperature, chaotrophs, and organic solvents. The extinction coefficient (epsilon 280 (1%)) of the enzyme was estimated as 20.56 and it consists of 13 tryptophan, 9 tyrosine, and 8 cysteine residues forming 4 disulfide bridges. There is significant effect of inhibitors targeting S-S bridges (mercaptoethanol, l-cysteine, glutathione), as well as of inhibitors targeting heme (sodium azide and hydroxylamine) on peroxidase activity, whereas inhibition was not observed with ethylmaleinimide due to the absence of reduced cysteine in the enzyme. Polyclonal antibodies against the enzyme have been raised in rabbit, and immunodiffusion suggests that the antigenic determinants of MGP are unique. The N-terminal sequence of MGP (D-E-A-C-I-F-S-A-V-K-E-V-V-D-A) exhibited considerable similarity to the sequence of other known plant peroxidases. Spectroscopic studies (absorbance, fluorescence, and circular dichroism) reveal that MGP has secondary structural features with alpha/beta type with approximately 20% alpha-helicity.  相似文献   
175.
As one of the most important and essential macronutrients next to nitrogen,phosphorus(P)is important for plant development,but it is the least mobile nutrient element in plant and soil.Globally,P is mined from geological sediments and added to agricultural soils so as to meet the critical requirements of crop plants for agronomic productivity.Phosphorus exists in soil in both organic and inorganic forms.The various inorganic forms of the element in soil are salts with calcium,iron,and aluminum,whereas the organic forms come from decaying vegetation and microbial residue.There is a huge diversity of plant microbiomes(epiphytic,endophytic,and rhizospheric)and soil microbiomes that have the capability to solubilize the insoluble P and make it available to plant.The main mechanism for the solubilization of inorganic P is by the production of organic acids,which lowers soil pH,or by the production of acid and alkaline phosphatases,which causes the mineralization of organic P.The P-solubilizing and-mobilizing microorganisms belong to all three domains,comprising archaea,bacteria,and eukarya.The strains belonging to the genera Arthrobacter,Bacillus,Burkholderia,Natrinema,Pseudomonas,Rhizobium,and Serratia have been reported as efficient and potential P solubilizers.The use of P solubilizers,alone or in combination with other plant growth-promoting microbes as an eco-friendly microbial consortium,could increase the P uptake of crops,increasing their yields for agricultural and environmental sustainability.  相似文献   
176.
Genetic Resources and Crop Evolution - Zea mays ssp. parviglumis is the progenitor of maize and assume to have tolerance against various biotic and abiotic stresses. It...  相似文献   
177.
Genetic variation and phylogenetic relationships among 50 wild and cultivated accessions of 19 Indian Citrus genotypes were examined through comparison of Directed Amplification of Minisatellite DNA (DAMD) markers and morphological characters. DAMD-PCR analysis with four primers resulted in amplification of a total of 45 bands, of which 35 (78 %) were polymorphic. Morphometric evaluation using 76 morphological characters showed high level of variability ranging from 0.18 to 1.00 (avg 0.39), whereas the Jaccard’s coefficient values of genetic similarity calculated from DAMD data ranged from 0.41 to 1.00 (avg 0.68), indicating moderate genetic divergence among the accessions studied. UPGMA dendrograms generated separately from morphometric and DAMD data segregated all the accessions of Citrus into four main clusters, each containing a true basic species and their probable hybrids. The grouping of individual accessions/genotypes under respective species or cultivars in DAMD dendrogram was based purely on their genetic relationships rather than geographical origin. There was no absolute congruence between the data and dendrograms generated from morphometric and DAMD analyses. The study demonstrates the resolving power of DAMD markers for discrimination of individual genotypes of Citrus under its respective species, hybrid or cultivar groups and inferring their genetic and phylogenetic relationships as well. This is the first report on application of DAMD markers in Citrus.  相似文献   
178.
It is globally accepted that soil carbon (C) dynamics are at the core of interlinked environmental problems,deteriorating soil quality and changing climate.Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen (N) availability and moisture-temperature interactions.This article reviews the management aspects of soil C dynamics in light of recent advances,particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate.Globally,drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability,resulting in a higher decomposition rate and a considerable decline in soil organic C (SOC) levels due to increased soil CO2 emissions,degraded soil quality,and increased atmospheric CO2 concentrations,leading to climate warming.Predicted climate warming is proposed to enhance SOC decomposition,which may further increase soil N availability,leading to higher soil CO2 efflux.However,a literature survey revealed that soil may also act as a potential C sink,if we could manage soil inorganic N pools and link microbial processes properly.Studies also indicated that the relative,rather than the absolute,availability of inorganic N pools might be of key importance under changing climate,as these N pools are variably affected by moisture-temperature interactions,and they have variable impacts on SOC turnover.Therefore,multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.  相似文献   
179.
Analysis of differential pore-volume distribution (DPVD) patterns of a commercial Clinoptilolite has been conducted experimentally using an analyzer by measuring the N2 adsorption isotherm. The commercial material was fractionated by sieving through sequential sieves: <125 µ (Z8; fine), 125–250 µ (Z9; medium), and >250 µ (Z10; coarse). The DPVD of the fractions were calculated from the hysteresis loop according to the adsorption and desorption curves of Dollimore-Heal (DH) model. The adsorption cycle had produced dissimilar differential pore volume distribution patterns. For the 10-nm pore width, fine and medium fractions had a maximum pore volume up to 0.0016 cm3/g nm, while the coarse fraction had a little greater value up to 0.002 cm3/g nm. Moreover, the medium fraction had too many hills and valleys in the DPVD. However, the desorption cycle–based DH analysis did not show any marked variation in the DPVD pattern.  相似文献   
180.
We investigated the effects of Arbuscular Mycorrhiza (AM) fungi and various phosphorus (P) levels on the distribution and availability of P in dominant soils of Bihar, India. Potassium chloride (KCl)-P (labile P), sodium hydroxide (NaOH)-P (Fe-Al-bound P), hydrochloric acid (HCl)-P (Ca-bound P), and residual P (Res-P) fractions were analyzed in the soils under maize plant. Ca-bound P was the most abundant P fraction in the alkaline soils (65% of the total P) followed by neutral soil (35% of the total P), whereas it was less abundant (<4%) in the acidic soil type. Fe-Al-bound P was found to be highest for acidic soil (65% of the total P). Soils under the inoculation with Glomus mossae and control gave the highest and lowest values (15.63 mg kg?1 and 10.74 mg kg?1 respectively) for the labile fraction which was similar to the organically bound residual fractions of P (200.17 mg kg?1 and 193.66 mg kg?1 respectively. Inoculation of the soils with AM fungi leads to the redistribution of P fractions in different soils which consequently helps in improvement of available P in soil conducive for plant uptake.  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