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   3275篇
  免费   141篇
  国内免费   3篇
林业   235篇
农学   463篇
基础科学   87篇
  850篇
综合类   83篇
农作物   271篇
水产渔业   70篇
畜牧兽医   978篇
园艺   98篇
植物保护   284篇
  2023年   22篇
  2022年   36篇
  2021年   49篇
  2020年   86篇
  2019年   87篇
  2018年   119篇
  2017年   136篇
  2016年   108篇
  2015年   83篇
  2014年   94篇
  2013年   296篇
  2012年   140篇
  2011年   157篇
  2010年   125篇
  2009年   113篇
  2008年   111篇
  2007年   138篇
  2006年   143篇
  2005年   110篇
  2004年   71篇
  2003年   77篇
  2002年   72篇
  2001年   57篇
  2000年   51篇
  1999年   53篇
  1998年   41篇
  1997年   43篇
  1996年   34篇
  1995年   34篇
  1994年   29篇
  1993年   28篇
  1992年   30篇
  1991年   36篇
  1990年   31篇
  1989年   38篇
  1988年   45篇
  1987年   34篇
  1986年   29篇
  1985年   24篇
  1984年   25篇
  1983年   26篇
  1982年   22篇
  1980年   34篇
  1979年   37篇
  1978年   20篇
  1976年   20篇
  1971年   20篇
  1970年   37篇
  1969年   24篇
  1968年   23篇
排序方式: 共有3419条查询结果,搜索用时 31 毫秒
61.
Upflow anaerobic sludge blanket (UASB)reactors were used to treat municipal wastewater attemperatures of 6, 11, 15, 20 and 32 °C and athydraulic retention times (HRTs) ranging from 48 to 3 h overan operational period of approximately 860 days. The Monodmodel was used to evaluate substrate utilization. TheArrhenius model was used to calculate the activationenergies from which temperature coefficients weredetermined. It was found that the maximum specific substrateutilization rate constant (k) decreased from 0.387 d-1(at 32 °C) to 0.041 d-1 (at 6 °C). Thedecay rate constant (kd), yield coefficient (Yg),half velocity constant (Ks) and maximum specific growthrate (μm ) were also impacted by temperature in theUASB treatment of municipal wastewater.  相似文献   
62.
Grain legumes, the important constituents of sustainability‐based cropping systems and energy‐limited vegetarian diets have long been the subject of scientific research. Tremendous technological strides were made in the so‐called orphan crops, in terms of both varietal improvement and generation of basic information. Despite recalcitrancy and high genotype dependency, in vitro culture techniques such as organogenesis, in vitro mutagenesis, embryo rescue and in vitro gene transfer have been deployed for improvement of several grain legumes and these played an important role in introgression of desirable genes from related and distant species and creation of additional genetic variability. Stable and reproducible regeneration protocols resulted in the development of genetically modified chickpea, pigeon pea, cowpea, mungbean, etc., while embryo rescue was deployed successfully for recovery of interspecific recombinants, a few of them exploited for the development of commercial cultivars. Nevertheless, doubled haploidy witnessed limited success and protoplast regeneration and in vitro mutagenesis remained of academic interest. The present review focuses on the progress, achievements, constraints and perspectives of using in vitro technology in grain legume improvement.  相似文献   
63.
Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km− 2 yr− 1) and Tirthan (80 t km− 2 yr− 1) watersheds were higher than that of the Indian average (69 t km− 2 yr− 1) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km− 2 yr− 1). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro-power projects in the Lesser Himalayan region.  相似文献   
64.
G. Singh 《林业研究》2009,20(2):144-150
Tree-crop interactions were monitored by measuring tree growth characters of Prosopis cineraria L. and Tecomella undulata L. and yields of Vigna radiata (L) in agroforestry systems in degraded lands of Indian Desert. Potential competition for resource between the trees and associated crop was analyzed by measuring soil water contents, soil organic matters and NH4-N at different depths of soil layers i.e., 0–25 cm, 25–50 cm and 50–75 cm in the experimental plots. The plots size were 16 m × 18 m (D1), 20 m × 18 m (D2) and 32 m × 18 m (D3) with tree densities of 208, 138 and 104 trees·ha−1 after June 2002, respectively. Results showed that tree height increased by 3% to 7% during June 2002 to June 2004. Collar diameter increased by 30% and 11% in D1, 23% and 19% in D2 and 18% and 36% in D3 plots, respectively, in P. cineraria and T. undulata in two years period. The increase in crown diameter was 9% to 18% in P. cineraria and 11% to 16% in T. undulata. Tree growth was relatively greater in 2002 than in 2003. Yield of V. radiata increased linearly from D1 to D3 plots. Lowest soil water content at 1 m distance from tree base indicated greater utilization of soil water within the tree rooting zone. Concentrations of soil organic matters and NH4-N were the highest (p<0.05) in 0–25 cm soil layer. P. cineraria was more beneficial than T. undulata in improving soil conditions and increasing crop yield by 11.1% and thus more suitable for its integration in agricultural land. The yield of agricultural crop increased when density of tree species was appropriate (i.e., optimum tree density), though it varied with tree size and depended upon resource availability. The result indicated bio-economic benefits of optimum density of P. cineraria and T. undulata over traditional practices of maintaining random trees in farming system in arid zones. Biography: G. Singh (1961– ), male, Scientist E and Head, Division of Forest Ecology, Arid Forest Research Institute, New Pali Road, Jodhpur-342005, India.  相似文献   
65.
Jamun (Syzygium cumini) is a tropical, underutilized fruit which is highly perishable in nature. It is a good source of vitamin C, tannins, gallic acid and anthocyanins and its beneficial effects are mostly due to the presence of bioactive compounds (pigments and phenolic compounds) in it. Due to astringent and fibrous nature, preparation of jam from jamun pulp is quite difficult, but other fruits (apple and kiwifruit) can be incorporated in it to improve its quality. This study aims to develop jam from blends of jamun with other fruits and analyse various physico-chemical, nutritional, textural and sensory properties. It was found that physico-chemical properties of jams were not found to vary greatly, but the jamun–kiwifruit jam was found to have fairly high amount of antioxidants(46.75 ± 0.67%), tartaric acid (26.24 ± 0.02 mg/100g sample), ascorbic acid (0.08 ± 0.01 mg/100 g sample) and lactic acid (23.95 ± 0.01 mg/100g sample) and lowest amount of 5-hydroxymethyl-2-furaldehyde (0.38 ± 0.04 mg/100 g sample). Jamun jam and jamun–kiwifruit jam possessed the texture required for jam while jamun–apple jam was found to be a relatively harder gel. Jam made with jamun and kiwifruit pulp was found to have highest acceptability on the basis of sensory evaluation.  相似文献   
66.
In the past five decades, constant research has been directed towards yield improvement in pigeonpea resulting in the deployment of several commercially acceptable cultivars in India. Though, the genesis of hybrid technology, the biggest breakthrough, enigma of stagnant productivity still remains unsolved. To sort this productivity disparity, genomic research along with conventional breeding was successfully initiated at ICRISAT. It endowed ample genomic resource providing insight in the pigeonpea genome combating production constraints in a precise and speedy manner. The availability of the draft genome sequence with a large‐scale marker resource, oriented the research towards trait mapping for flowering time, determinacy, fertility restoration, yield attributing traits and photo‐insensitivity. Defined core and mini‐core collection, still eased the pigeonpea breeding being accessible for existing genetic diversity and developing stress resistance. Modern genomic tools like next‐generation sequencing, genome‐wide selection helping in the appraisal of selection efficiency is leading towards next‐generation breeding, an awaited milestone in pigeonpea genetic enhancement. This paper emphasizes the ongoing genetic improvement in pigeonpea with an amalgam of conventional breeding as well as genomic research.  相似文献   
67.
Inheritance of fertility restorer gene in pigeonpea was studied using F2 and BC1F1 populations derived from cross AL103A × IC245273. It was found to be controlled by single dominant gene. Out of 228 SSR primer pairs, 33 primer pairs showed parental polymorphism, while four primers were found polymorphic in bulk segregant analysis (BSA). These four primers viz., CcM 1615, CcM 0710, CcM 0765 and CcM 1522 were used for genotyping of F2 population and were found to be placed at 3.1, 5.1, 28.1 and 45.8 cM, respectively. Two of them, CcM 1615 and CcM 0710, evinced clear and unambiguous bands for fertility restoration in F2 population. The Rf gene was mapped on linkage group 6 between the SSR markers CcM 1615 and CcM 0710 with the distances of 3.1 and 5.1 cM, respectively. The accuracy of the CcM 1615 was validated in 18 restorers and six maintainer lines. The marker CcM 1615 amplified in majority of male restorer lines with a selection accuracy of 91.66%.  相似文献   
68.
In the 2014 and 2015 crop seasons, the efficacies of different types, rates and combinations of mineral oil and insecticide foliar sprays for reducing Potato virus Y (PVY) spread were tested in controlled field trials in New Brunswick (NB), Canada. Experimental plots were planted with certified PVY-free Goldrush, supplemented with known virus-infected seed to raise PVY inoculum to 2.3% and 3% at the beginning of the 2014 and 2015 seasons, respectively. Treatments consisted of mineral oil-only sprays at different application rates, insecticide-only sprays of differing numbers, and several combined mineral oil and insecticide spray regimes, all compared to a no-spray control treatment. PVY spread to 18% (2014) and 22% (2015) of initially virus-free plants in no-spray control plots, with significant reductions observed in PVY spread in several treatments. Greatest PVY reductions, as low as 4% (2014) and 12% (2015), were in combined mineral oil and insecticide spray treatments, followed by oil-only sprays; while insecticide-only sprays did not significantly reduce PVY spread. As well as measuring PVY spread to marked test plants and randomly collected post-harvest tuber sample from the plots, exhibited similar treatment pattern for PVY incidence. Multiple logistic regression modeling confirmed the relative efficacy of combined oil and insecticide sprays for reducing PVY spread, while accounting for variable inoculum and aphid factors. Modeling also highlighted the importance of planting low-PVY seed initially, and of early application of foliar sprays. Local best management practice recommendations for reduction of in-field PVY spread were discussed.  相似文献   
69.
The analysis of residuals computes general adaptabilities (GAs) and specific adaptabilities (SAs) of genotypes similar to combining ability analysis. The residual analysis is simple and robust being based on the first-degree statistics, and is assumption-free. A unique statistic of ratio of variances (VR) of residuals for individual genotypes allows comparing their stability. The residuals analysis of genotype × environment (GE) interactions was performed for grain yield (t ha?1) of 25 rice (Oryza sativa L.) genotypes, including two developed by marker-assisted selection for root traits quantitative trait loci (QTL), tested across 16 sites. Results were compared with the linear regression analysis for (i) full set of 16 sites showing adequacy of linear model and (ii) subset of nine-poor sites showing inadequacy of linear model. There was agreement between the two analyses for situation (i) but not for situation (ii) when the regression analysis fails because of nonlinearity but the residual analysis retains its validity.  相似文献   
70.
With continuous outbreaks of stripe rust (Puccinia striiformis f. sp. tritici) epidemics and rapid breakdown of deployed resistance in bread wheat (Triticum aestivum L.) cultivars in North West Plains Zone (NWPZ) in India warrant knowledge and deployment of new and durable sources of resistance to stripe rust. Bread wheat cultivar PBW 343, until recently the most widely cultivated wheat variety in India, is now highly susceptible to stripe rust (score 9 on a 1–9 scale), whereas PBW 621 (score 5.05–5.65) and HD 2967 (score 5.40–6.20) show low levels of resistance. We conducted an experiment, spanning three crop seasons (2013–2014 to 2015–2016), in which parental lines, F1 and F2 populations, F3 and F4 families from two bread wheat crosses, PBW 621/PBW 343 and HD 2967/PBW 343 were generated and evaluated for stripe rust resistance against a virulent pathotype. While the F1 revealed partial dominance, the segregation pattern for stripe rust resistance in F2 and F3 showed transgressive segregation for resistance in both crosses. Chi-square analysis indicated that resistant segregants possessed two genes, one contributed by PBW 621 or HD 2967 (depending on the cross) and the other, unexpectedly but obviously, came from the most susceptible cultivar, PBW 343. Possible genetic mechanisms for this residual resistance and implications for breeding programs are discussed.  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