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   949篇
  免费   91篇
林业   49篇
农学   59篇
基础科学   6篇
  185篇
综合类   27篇
农作物   97篇
水产渔业   132篇
畜牧兽医   341篇
园艺   23篇
植物保护   121篇
  2023年   6篇
  2022年   18篇
  2021年   28篇
  2020年   32篇
  2019年   67篇
  2018年   43篇
  2017年   57篇
  2016年   54篇
  2015年   38篇
  2014年   44篇
  2013年   80篇
  2012年   54篇
  2011年   66篇
  2010年   36篇
  2009年   30篇
  2008年   44篇
  2007年   31篇
  2006年   30篇
  2005年   31篇
  2004年   16篇
  2003年   24篇
  2002年   17篇
  2001年   19篇
  2000年   9篇
  1999年   11篇
  1998年   9篇
  1997年   9篇
  1996年   8篇
  1995年   5篇
  1994年   6篇
  1993年   12篇
  1992年   6篇
  1991年   8篇
  1990年   5篇
  1988年   8篇
  1987年   4篇
  1984年   5篇
  1983年   6篇
  1982年   4篇
  1980年   2篇
  1979年   11篇
  1978年   5篇
  1977年   4篇
  1976年   6篇
  1975年   6篇
  1973年   2篇
  1971年   4篇
  1967年   5篇
  1966年   3篇
  1965年   2篇
排序方式: 共有1040条查询结果,搜索用时 10 毫秒
11.
12.
A total of 17 microsatellite deoxyribonucleic acid loci used routinely for horse parentage control were used to evaluate genetic diversity among normal Arabian horses and severe combined immunodeficiency (SCID) carrier Arabian horses (ArS) and normal Arab-Barb horses and SCID carrier Arab-Barb horses (ArbeS). On the basis of the genotype of 186 horses, mean allelic diversity was estimated as 6.82, 5.53, and 6.7059 in normal Arabian horses, ArS, and for both groups of Arab-Barb horses, respectively. Five specific alleles were observed in ArS and ArbeS, with one common with ArS at HMS6, whereas five alleles common between ArS and ArbeS had a high frequency. Expected and observed heterozygosity showed great heterogeneity in the population studied and were similar or higher when compared with other studies on Arabian horses. Coefficient of gene differentiation Gst of Nei associated with Nei’s genetic distance and multivariate correspondence analysis indicated a possible differentiation between the studied populations when analyzed separately according to breed. Probability of assignment of a horse to a specific group was assessed using a full and partial Bayesian approach. In all, 80.6% of Arab horses and 78.2% of Arab-Barb horses were assigned properly with a partial Bayesian test, which provided better results than the full one. These findings will be useful for identification of SCID carrier horses by using the microsatellite deoxyribonucleic acid loci used routinely for horse parentage control in our laboratory.  相似文献   
13.
The distribution of tylosin was studied using a crossover design, in six pigs following i.v. and i.m. administration of 10 mgkg(-1) b.w. Plasma samples were analysed by HPLC and UV absorbance detection. After i.v. administration, t(1/2beta) was 271.3 min, V(d) 14.6 Lkg(-1), V(ss) 9.7 Lkg(-1) and CL 26.8 mLmin(-1)kg(-1). After i.m. administration, a C(max) of 1 microgmL(-1) was reached at 90 min. Mean absorption time was 1988.7 min and bioavailability was 95%.  相似文献   
14.

Two field trials were conducted in 2018 and 2019 to develop practical and economically efficient weed control programs in corn. The experiment included six treatments (cowpea, rice straw, sorghum extract, hoeing, foramsulfuron herbicide and weedy check). The treatments were arranged in randomized complete block design with four replicates. Findings showed that reduction in total weed number was evident with application of hoeing, cowpea and rice straw in 2018 and 2019 seasons, in addition to foramsulfuron herbicide and sorghum extract in 2019. Cowpea, hoeing, foramsulfuron herbicide and rice straw recorded higher reduction in dry biomass of grassy weeds in both seasons. Reductions in N, P and K uptake by weeds because of rice straw and cowpea treatments were similar to hoeing treatment in both seasons. The increases in ear grain weight and grain yield ha?1 due to cowpea and hoeing treatments were similar to rice straw one. In 2019 season, cowpea treatment was the superior practice for improving N, P and K uptake of maize, significantly leveling hoeing for K uptake. The values of gross returns and benefit/cost ratio of cowpea and sorghum extract, respectively, were higher than rice straw application. In conclusion, cowpea as a live mulch achieved acceptable weed control in maize by reducing weeds growth and lowering their ability to deplete the soil nutrients. Also, cowpea treatment improves growth and yield of maize with better utilization of nutrients. Thus, cowpea could be exploited as an eco-friendly method of weed management programs in maize cultivation.

  相似文献   
15.
The resistance to insecticides of three Sudanese strains of A. gossypii (Glov.) collected from cotton fields in the Sudan Gezira Scheme over three seasons (1988, 1989, 1990) and that of two French strains was studied in the laboratory. When compared with a known susceptible strain, the aphids were found to be resistant-to the eight insecticides tested. Evolution of resistance in Sudanese strains during the three crop seasons was observed. Assay of aphid homogcnate for carboxytesterase activity towards the substrates α-naphthyl acetate and β-naphthyl acetate showed that there was no enhancement of this class of enzyme and thus it was not a cause of resistance in this species. A study of interaction between the acetylcholinesterase (AchE) and pirimicarb established the kinetics of the inhibition process. I50 values were found to be much higher for the Sudanese strains than for the susceptible strain. First-order inhibition kinetics revealed that resistance towards pirimicarb in Sudanese-strains was caused by a modified AchE which had a reduced affinity (higher Ka value) and poor carbamylation ability (lower K2 value) for pirimicarb. The resistance mechanisms for the other insecticides remain to be studied.  相似文献   
16.
BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry  相似文献   
17.
Salt stress is more and more becoming a serious problem in the world especially if we consider its damaging effect on the plant growth and yield. The cultivation of medicinal plants, such as Aloe vera, might be an alternative for the saline water use and salt-affected soils occupation. Aloe vera, commonly known as aloe, is one of the primary medicinal plants with multipurpose applications going from pharmaceutical to cosmetic aspects with a promising economic return. Aloe plants were cultivated and irrigated, for 14 months, with drinking water (C0) and with two levels of salt (C1 and C2). Changes in growth, hydrogen peroxide (H2O2), lipid peroxidation and phenolic compounds were examined in leaves at harvest. Depressive effects of salt irrigation on the plant growth parameters and a perturbation in inorganic ion contents were found especially with a high level of salt in the irrigation water. The intracellular oxidative stress was evaluated with the H2O2 production. Our results showed that the H2O2 content increased with the accumulation of the toxic ion (Na) in the leaf tissues. In addition, lipid peroxidation, measured by the malondialdehyde (MDA) level, increased as well with salt augmentation in the irrigation water. In response to salt stress, Aloe leaves showed a significant increase in the levels of phenolic compounds too. These results suggest that Aloe can be planted in soils affected by salinity and irrigated with salt water at least at a moderate concentration used in the present study.  相似文献   
18.
Documentation is a major component of any traceability system where traceability is defined in the ISO Regulation 8402:1994 as the ability to trace the history, application and location of what is under consideration. Traceability systems are record keeping systems designed to track the flow of product or product attributes through the production process or supply chain. All international supply chains are forced to comply with traceability requirements. In this paper, we develop and implement an end-to-end mobile application prototype that traces the poultry production. This application consists of front-end and back-end systems. At the front-end, the worker uses a GPRS enabled handheld device (cell phone, PDA, etc.) to capture information on poultry operations collected at a remote chicken farm and transmit it to a back-end server in the main office. Through customized application the back-end server analyses all information received from the front-end and based on a built-in business process and business rules, intelligently updates various stakeholders of any breach of bio-security measures that requires immediate attention. The proposed system administrators can also access this application via Internet for management decision making. The back-end system consists of web server, defined business application logic and database server.  相似文献   
19.
This study is a continuation of the previous parts and also deals with the colour tests, free sugars and phenolic aglycones of thirty four plants, ranging from the familyMoraceae toRosaceae, with the aim of identifying the type of tannins present.
Zusammenfassung Diese Arbeit ist eine Weiterführung der vorangegangenen Mitteilungen und befaßt sich ebenfalls mit Farbreaktionen, freien Zuckern und phenolischen Aglykonen von weiteren 34 Pflanzen (Morraceae bis Rosaceae) mit dem Ziel, den Typ des jeweils vorliegenden Tannins zu identifizieren.

Resume Suite du travail précédent. Réactions colorées, sucres libres, aglycones phénoliques de 34 autres espèces végétales (Moracées à Rosacées). Essai d'identification des tannins présents dans chaque échantillon.
  相似文献   
20.
Continuing a previous study, the leaves and barks of thirty one plants collected from the botanical gardens in Cairo, were subjected to detailed studies with the aim of identifying the type of tannins present in each plant. The study included colour tests and paper chromatography of both the free sugars and phenolic aglycones. The plants recorded here are those ranging fromAceraceae toFlacourtiaceae.
Zusammenfassung In Fortsetzung dieser Reihe wurden die Blätter- und Rindermaterialien von 31 Pflanzen, gesammelt aus den botanischen Gärten in Kairo, auf ihre Gerbstoffe untersucht. Mit Hilfe der Papierchromatographie wurden sowohl die freien Zucker als auch die phenolischen Komponenten dieser Pflanzen identifiziert.In dieser Mitteilung wurden die Untersuchungsergebnisse der Pflanzen der Familien Aceraceae bis Flacourtiaceae gegeben.

Résumé En poursuivant nos études précédentes, les feuilles et les écorses de 31 plantes cueillies dans les jardins de Caire, ont été soumises à des études détaillées. En vue d'identifier le type des tannins présent dans chaque plante, les études contenaient des expériments par chromatographie sur papier concernant les sucres natifs et les aglycones phénoliques. Les plantes qui ont été rapportées ici sont celles des familles Aceraceae à Flacourtiaceae.
  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