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   4546篇
  免费   265篇
  国内免费   3篇
林业   316篇
农学   176篇
基础科学   20篇
  1200篇
综合类   214篇
农作物   324篇
水产渔业   491篇
畜牧兽医   1608篇
园艺   92篇
植物保护   373篇
  2023年   41篇
  2022年   48篇
  2021年   169篇
  2020年   181篇
  2019年   227篇
  2018年   180篇
  2017年   200篇
  2016年   181篇
  2015年   138篇
  2014年   199篇
  2013年   320篇
  2012年   367篇
  2011年   360篇
  2010年   212篇
  2009年   192篇
  2008年   311篇
  2007年   329篇
  2006年   224篇
  2005年   187篇
  2004年   158篇
  2003年   149篇
  2002年   153篇
  2001年   27篇
  2000年   22篇
  1999年   27篇
  1998年   14篇
  1997年   14篇
  1996年   12篇
  1995年   13篇
  1994年   13篇
  1993年   13篇
  1992年   8篇
  1991年   8篇
  1990年   10篇
  1989年   15篇
  1988年   10篇
  1987年   11篇
  1986年   9篇
  1985年   7篇
  1984年   10篇
  1983年   6篇
  1982年   7篇
  1980年   4篇
  1977年   4篇
  1974年   2篇
  1973年   3篇
  1972年   2篇
  1969年   3篇
  1966年   4篇
  1955年   2篇
排序方式: 共有4814条查询结果,搜索用时 15 毫秒
1.
Increasingly, economies that have traditionally benefited from offshoring are losing some of their strategical advantages, with a consequent increase in backshoring by developed economies. This paper describes the phenomenon and tries to shed light on the current challenges, trends, and debates in the area, and on the main determinants of backshoring. A new phenomenon known as nearshoring is also analysed—this consists of relocating some previously offshored manufacturing activities so that they are now close to previous core locations, but not so close as to suffer from disagglomeration effects. This combines the advantages of offshoring and backshoring.  相似文献   
2.
St. Augustinegrass is well suited for lawns and commercial landscapes. While many genotypes are cross‐fertile, all cultivars are propagated vegetatively in sod production. To ensure varietal purity, development of sterile triploid hybrids by crossing tetraploid and diploid genotypes has been successfully used in other warm‐season turfgrasses. Applying this model in St. Augustinegrass would be beneficial to sod producers and turf managers who require purity for certification and uniformity for performance, respectively. This study was conducted to develop colchicine‐induced tetraploid lines of St. Augustinegrass. Seeds of cultivar ‘Raleigh’ were treated with four colchicine concentrations at four exposure times. A non‐treated control was included among the treatments. Seedlings that germinated were screened for genome size changes using flow cytometry. Line DSA 13005 and two progeny lines derived through selfing, DSA 16001 and DSA 16016, were corroborated as tetraploids (2n = 4x = 36) through chromosome counts. These lines will be used in future breeding efforts to attempt development of sterile triploid cultivars of St. Augustinegrass.  相似文献   
3.
Water, Air, & Soil Pollution - The treatment efficiency of Chlorella sorokiniana and Scenedesmus species, immobilized in sodium alginate, was evaluated for removing nitrate from groundwater....  相似文献   
4.
Stem canker on germinating potato sprouts is often caused by seed-borne inoculum of the fungus Rhizoctonia solani. However, high amounts of free-living plant-parasitic nematodes have been found in field patches of potato plants with stem canker. Fungicide treatment of the seed tubers can be used to avoid stem canker caused by seed-borne inoculum but it is unknown if nematodes can affect this. To investigate whether free-living plant-parasitic nematodes, the root-lesion nematode Pratylenchus penetrans or a combination of several plant-parasitic nematode genera in a full nematode community, may have a negative effect on the fungicide seed treatment, a pot experiment with seed tubers inoculated with R. solani, half of which were treated with fungicides, was performed. The seed-borne inoculum caused severe damage to the plants, while no fungal damages were observed on the fungicide treated plants. This shows that the nematodes did not affect the fungicide treatment. The probability of black scurf decreased in treatments with a full nematode community, which may be due to the action of fungal-feeding nematodes.  相似文献   
5.
In a preliminary in vitro study, a Panax ginseng extract exhibited an evident antibacterial activity against Yersinia ruckeri and Lactococcus garvieae and affected the respiratory burst and proliferation of rainbow trout Oncorhynchus mykiss leukocytes. Subsequently, the effects of a dietary ginseng extract supplementation on growth, blood biochemical profile, innate immune response and resistance against Y. ruckeri infection were investigated in vivo in rainbow trout juveniles. Four experimental diets were obtained by adding 0.0%, 0.01%, 0.02%, 0.03% of ginseng ethanolic extract to a commercial feed. Each diet was fed to triplicate groups of fish (mean body weight 30.5 ± 0.15 g) at 1% of body weight day?1 for 10 weeks. The dietary supplementation with ginseng extract did not affect growth performance, feed utilization, biometric traits and fish whole body composition (P > 0.05). No major changes due to graded levels of ginseng extract in the diet were observed in blood biochemical parameters except for increasing plasma triglycerides and non‐esterified fatty acids in fish fed diets including 0.01% and 0.02% of extract (P < 0.05). The innate immune response was barely modulated by the dietary addition of ginseng extract. Serum lysozyme and leukocytes respiratory burst activities were just slightly increased in fish fed all the ginseng extract‐supplemented diets compared with controls, whereas serum antiproteases and leukocyte MPO were not affected (P > 0.05). The dietary administration of ginseng extract induced a reduction in mortality of rainbow trout infected with Y. ruckeri, although no significant differences between treated and control groups were observed (P > 0.05).  相似文献   
6.
7.
The aim of this study was to determine the effects of ultraviolet radiation (UVR) on bioaccumulation of UV‐absorbing compounds acquired through the diet, in larvae and postlarvae of Pleoticus muelleri, and to assess tissue antioxidant activity, survival, and development. Mysis stage I were exposed to two artificial radiation treatments: M‐PAR (photosynthetically active radiation, range = 400–700 nm) and M‐PAR + UVR (280–700 nm). The experimental larvae received a mixed dietary treatment of Artemia persimilis and the microalga Pavlova lutheri, reared under two radiation regimes: PAR (D‐PAR) and PAR + UVR (D‐PAR + UVR). Shrimp from all treatments reached 8 d postlarval stage (PL8), except those under M‐PAR + UVR treatment fed the D‐PAR‐cultured algae, which had 0% survival. Larvae in M‐PAR + UVR and M‐PAR treatments fed with D‐PAR + UVR diet presented the highest survival rates (70 and 75%, respectively), with 37 and 41% increase in PL size. UV‐absorbing compounds were detected in microalgae and PL subject to PAR + UVR treatments. Antioxidant activity, quantified by measuring the free‐radical 1,1‐diphenyl‐2‐picrylhydrazyl in homogenates of PL8, decayed drastically under radiation treatment M‐PAR + UVR fed with algae of the D‐PAR + UVR treatment. It is concluded that the bioaccumulation of UV‐absorbing compounds and the highest antioxidant activity in PL could improve the biochemical and photophysiological responses of shrimp under UVR stress.  相似文献   
8.

Background

Fixed arrays of single nucleotide polymorphism (SNP) markers have advantages over reduced representation sequencing in their ease of data analysis, consistently higher call rates, and rapid turnaround times. A 6 K SNP array represents a cost-benefit “sweet spot” for routine genetics and breeding applications in rice. Selection of informative SNPs across species and subpopulations during chip design is essential to obtain useful polymorphism rates for target germplasm groups. This paper summarizes results from large-scale deployment of an Illumina 6 K SNP array for rice.

Results

Design of the Illumina Infinium 6 K SNP chip for rice, referred to as the Cornell_6K_Array_Infinium_Rice (C6AIR), includes 4429 SNPs from re-sequencing data and 1571 SNP markers from previous BeadXpress 384-SNP sets, selected based on polymorphism rate and allele frequency within and between target germplasm groups. Of the 6000 attempted bead types, 5274 passed Illumina’s production quality control. The C6AIR was widely deployed at the International Rice Research Institute (IRRI) for genetic diversity analysis, QTL mapping, and tracking introgressions and was intensively used at Cornell University for QTL analysis and developing libraries of interspecific chromosome segment substitution lines (CSSLs) between O. sativa and diverse accessions of O. rufipogon or O. meridionalis. Collectively, the array was used to genotype over 40,000 rice samples. A set of 4606 SNP markers was used to provide high quality data for O. sativa germplasm, while a slightly expanded set of 4940 SNPs was used for O. sativa X O. rufipogon populations. Biparental polymorphism rates were generally between 1900 and 2500 well-distributed SNP markers for indica x japonica or interspecific populations and between 1300 and 1500 markers for crosses within indica, while polymorphism rates were lower for pairwise crosses within U.S. tropical japonica germplasm. Recently, a second-generation array containing ~7000 SNP markers, referred to as the C7AIR, was designed by removing poor-performing SNPs from the C6AIR and adding markers selected to increase the utility of the array for elite tropical japonica material.

Conclusions

The C6AIR has been successfully used to generate rapid and high-quality genotype data for diverse genetics and breeding applications in rice, and provides the basis for an optimized design in the C7AIR.
  相似文献   
9.
Environmental conditions influence phenology and physiological processes of plants. It is common for maize and sorghum to be sown at two different periods: the first cropping (spring/summer) and the second cropping (autumn/winter). The phenological cycle of these crops varies greatly according to the planting season, and it is necessary to characterize the growth and development to facilitate the selection of the species best adapted to the environment. The aim of this study was to characterize phenological phases and physiological parameters in sorghum and maize plants as a function of environmental conditions from the first cropping and second cropping periods. Two parallel experiments were conducted with both crops. The phenological characterization was based on growth analyses (plant height, leaf area and photoassimilate partitioning) and gas exchange evaluations (net assimilation rate, stomatal conductance, transpiration and water-use efficiency). It was found that the vegetative stage (VS) for sorghum and maize plants was 7 and 21 days, respectively, longer when cultivated during the second cropping. In the first cropping, the plants were taller than in the second cropping, regardless of the crop. The stomatal conductance of sorghum plants fluctuated in the second cropping during the development period, while maize plants showed decreasing linear behaviour. Water-use efficiency in sorghum plants was higher during the second cropping compared with the first cropping. In maize plants, in the second cropping, the water-use efficiency showed a slight variation in relation to the first cropping. It was concluded that the environmental conditions as degree-days, temperature, photoperiod and pluvial precipitation influence the phenology and physiology of both crops during the first and the second cropping periods, specifically cycle duration, plant height, leaf area, net assimilation rate, stomatal conductance and water-use efficiency, indicating that both crops respond differentially to environmental changes during the growing season.  相似文献   
10.
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