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   840篇
  免费   55篇
  国内免费   1篇
林业   33篇
农学   22篇
基础科学   1篇
  99篇
综合类   96篇
农作物   13篇
水产渔业   57篇
畜牧兽医   501篇
园艺   32篇
植物保护   42篇
  2024年   3篇
  2023年   21篇
  2022年   13篇
  2021年   29篇
  2020年   31篇
  2019年   37篇
  2018年   27篇
  2017年   28篇
  2016年   20篇
  2015年   33篇
  2014年   32篇
  2013年   26篇
  2012年   86篇
  2011年   79篇
  2010年   43篇
  2009年   32篇
  2008年   73篇
  2007年   51篇
  2006年   43篇
  2005年   42篇
  2004年   41篇
  2003年   40篇
  2002年   27篇
  2001年   5篇
  2000年   4篇
  1999年   7篇
  1998年   3篇
  1997年   6篇
  1996年   4篇
  1995年   3篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1984年   1篇
排序方式: 共有896条查询结果,搜索用时 12 毫秒
81.
Germin-like protein (GLP) markers were associated with quantitative trait loci (QTL) for resistance to the rice blast pathogen, Magnaporthe oryzae in multiple rice (Oryza sativa) mapping populations. Twelve paralogous OsGLP gene family members are located within the physical QTL region on chromosome 8, and gene silencing studies suggest that they contribute collectively to the resistance phenotype. We compared sequence and expression profiles of OsGLP alleles in two resistant and two susceptible parental rice lines to find functional polymorphisms that correlated with the resistant phenotype. Based on coding and promoter sequences, the genes belong to two germin subfamily groups (GER3 and GER4). OsGLP members from both subfamilies were constitutively expressed and developmentally regulated in all cultivars. Transient induction above constitutive levels was observed for some OsGLPs, especially GER4 subfamily members, at early time points after M. oryzae infection and mechanical wounding. Varying 5′ regulatory regions and differential expression of some family members between resistant and susceptible cultivars corresponded with differential hydrogen peroxide (H2O2) accumulation after the same stimuli. OsGLP of both GER subfamilies localized to the plant cell wall. The protein location and early gene induction suggest that OsGLPs protect rice leaves at early stages of infection before fungal penetration and subsequent ingress. Our data suggest that regulation of OsGLP genes defines resistant versus susceptible phenotypes.  相似文献   
82.
This paper investigates the ethical values, moral principles, methods and reform proposals in aquaculture ethics scholarship to develop a comprehensive and balanced list of aquaculture ethical principles. A Systematic Quantitative Literature Review methodology is employed to parse 150 journal articles on aquaculture ethics. Methodologies, specific ethical values, broad principles, recommended reforms and trends over time are quantified and assessed. Through analysis of invoked values and recommended reforms, six core marine economy ethics principles are identified: Environmental Protection, Fairness, Stakeholder Participation, Harm Prevention, Beneficence and Trustworthiness. A comprehensive multidimensional legitimacy model is employed to uncover ethical gaps and identify promising areas for future aquaculture ethics research.  相似文献   
83.
Understanding the strengths and weaknesses of alternative assessment methods, harvest strategies and management approaches are an important part of operationalizing single‐species and ecosystem‐based fisheries management. Simulations run using two variants of a whole‐of‐ecosystem model for the Southern and Eastern Scalefish and Shark Fishery (SESSF) area shows that (a) data‐rich assessments outperform data‐poor assessments for target species and that this performance is reflected in the values of many system‐level ecosystem indicators; (b) ecosystem and multispecies management outperforms single‐species management applied over the same domain; (c) investment in robust science‐based fisheries management pays dividends even when there are multiple jurisdictions, some of which are not implementing effective management; and (d) that multispecies yield‐oriented strategies can deliver higher total catches without a notable decline in overall system performance, although the resulting system structure is different to that obtained with other forms of ecosystem‐based management.  相似文献   
84.
Baitfish such as golden shiners are subjected to stress during harvesting, grading, and transport. Their small size makes it difficult to measure the stress response with the biological indicator cortisol using conventional assay methods for plasma. This paper examines the development and validation of methods for whole-body cortisol extraction from individual baitfish. Three types of extracts were tested: (1) an ethyl ether unaltered extract (UA); (2) an extract reconstituted in phosphate buffered saline (PBS); (3) an extract that had been increased in volume by the addition of food-grade vegetable oil (VO). These extracts were evaluated using validation tests with radioimmunoassays (RIA) and enzyme-linked immunosorbent assays (ELISA). The UA extract produced inadequate volumes of extract for multiple assays and could not be used for the determination of cortisol in a single fish. The PBS reconstitution method failed the precision recovery of serial dilutions (62.3%), linearity (R 2: 0.7864), and parallelism validation tests. The VO volume-boosting method passed all validation tests [intra-assay coefficent of variation (%CV): 16.3 for ELISA and 5.9 for RIA; inter-assay %CV: 10.3; spiked recovery: 102.0%; dilution recovery: 93.0%; linearity R 2: 0.9435; log of serial dilutions was parallel] and provided enough extract for multiple assays from an individual baitfish. Based on these results, we conclude that the VO volume-boosting method presents a means for determining cortisol from individual baitfish using either RIA or ELISA assays.  相似文献   
85.
Discovery and directed evolution of a glyphosate tolerance gene   总被引:2,自引:0,他引:2  
The herbicide glyphosate is effectively detoxified by N-acetylation. We screened a collection of microbial isolates and discovered enzymes exhibiting glyphosate N-acetyltransferase (GAT) activity. Kinetic properties of the discovered enzymes were insufficient to confer glyphosate tolerance to transgenic organisms. Eleven iterations of DNA shuffling improved enzyme efficiency by nearly four orders of magnitude from 0.87 mM-1 min-1 to 8320 mM-1 min-1. From the fifth iteration and beyond, GAT enzymes conferred increasing glyphosate tolerance to Escherichia coli, Arabidopsis, tobacco, and maize. Glyphosate acetylation provides an alternative strategy for supporting glyphosate use on crops.  相似文献   
86.
Several states and countries have adopted targets for deep reductions in greenhouse gas emissions by 2050, but there has been little physically realistic modeling of the energy and economic transformations required. We analyzed the infrastructure and technology path required to meet California's goal of an 80% reduction below 1990 levels, using detailed modeling of infrastructure stocks, resource constraints, and electricity system operability. We found that technically feasible levels of energy efficiency and decarbonized energy supply alone are not sufficient; widespread electrification of transportation and other sectors is required. Decarbonized electricity would become the dominant form of energy supply, posing challenges and opportunities for economic growth and climate policy. This transformation demands technologies that are not yet commercialized, as well as coordination of investment, technology development, and infrastructure deployment.  相似文献   
87.
The objective of this study was to investigate the potential impacts of imperfect Mycobacterium avium subsp. paratuberculosis (MAP) vaccines on the dynamics of MAP infection in US dairy herds using a mathematical modeling approach. Vaccine-based control programs have been implemented to reduce the prevalence of MAP infection in some dairy herds; however, MAP vaccines are imperfect. Vaccines can provide partial protection for susceptible calves, reduce the infectiousness of animals shedding MAP, lengthen the latent period of infected animals, slow the progression from low shedding to high shedding in infectious animals, and reduce clinical disease. To quantitatively study the impacts of imperfect MAP vaccines, we developed a deterministic multi-group vaccination model and performed global sensitivity analyses. Our results explain why MAP vaccination might have a beneficial, negligible, or detrimental effect in the reduction of prevalence and show that vaccines that are beneficial to individual animals may not be useful for a herd-level control plan. The study suggests that high efficacy vaccines that are aimed at reducing the susceptibility of the host are the most effective in controlling MAP transmission. This work indicates that MAP vaccination should be integrated into a comprehensive control program that includes test-and-cull intervention and improved calf rearing management.  相似文献   
88.
Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.  相似文献   
89.
We retrospectively evaluated the medical records and obtained follow-up information for nine horses which had been treated for cecocolic intussusception (CCI) between January 1982 and April 1998. During the 16-year study period, CCI was diagnosed in nine of 748 horses in which exploratory celiotomy was undertaken for abdominal pain, representing an incidence of 1.2%. Most affected horses (78%) were less than four years of age (median age was 12 months, age range was five months to 15 years). Cecocolic intussusception affected male horses (78%) more commonly than female horses. The most common clinical presentation was abdominal pain of a severe, acute nature or milder but recurrent signs of abdominal pain persisting in spite of conservative treatment for several days. Correction of CCI by either simple reduction or reduction followed by partial typhlectomy was successful if compromise of the intestine by devitalization and adhesion formation was not found at surgery. Definitive diagnosis of CCI necessitates exploratory celiotomy, although an ultrasonographic examination of the abdomen may confirm the diagnosis in some cases. When recognized early during the course of disease, surgical correction of CCI is associated with a favorable outcome; of the eight horses which underwent surgery in our series, five horses (63%) survived surgical correction of CCI. Handling of compromised gut during reduction of CCI necessitates extreme caution because the risk of intestinal tearing is quite high.  相似文献   
90.
Accurate identification of the bovine pathogen Tritrichomonas foetus is sometimes complicated by the presence of other trichomonadid protozoa in clinical samples. A highly specific and reproducible approach for differentiating 3 common types of bovine trichomonadid protozoa found in the bovine preputial cavity, T. foetus, Pentatrichomonas hominis, and a Tetratrichomonas species, was developed using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. Universal trichomonadid protozoa primers, TFR1 and TFR2, were used to amplify the 5.85 rRNA gene and internal transcribed spacer regions (ITSRs), and the products were digested with the restriction enzyme HpyCH4IV. Restriction fragment length polymorphism analysis was performed on 55 trichomonad isolates from bovine preputial washing and scraping samples. The RFLP results correlated 100% with 5.85 rRNA gene and ITSR sequence resultsand PCR results with primers specific for T. foetus. The results of this study demonstrate that PCR and RFLP analysis can be used in lieu of DNA sequencing to identify the specific trichomonadid protozoa isolated from the bovine preputial cavity.  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