全文获取类型
收费全文 | 665篇 |
免费 | 24篇 |
专业分类
林业 | 11篇 |
农学 | 16篇 |
基础科学 | 2篇 |
85篇 | |
综合类 | 115篇 |
农作物 | 10篇 |
水产渔业 | 15篇 |
畜牧兽医 | 400篇 |
园艺 | 7篇 |
植物保护 | 28篇 |
出版年
2020年 | 4篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 33篇 |
2012年 | 27篇 |
2011年 | 47篇 |
2010年 | 14篇 |
2009年 | 4篇 |
2008年 | 31篇 |
2007年 | 37篇 |
2006年 | 21篇 |
2005年 | 21篇 |
2004年 | 29篇 |
2003年 | 16篇 |
2002年 | 22篇 |
2001年 | 20篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 10篇 |
1972年 | 3篇 |
1971年 | 9篇 |
1970年 | 10篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1967年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有689条查询结果,搜索用时 15 毫秒
681.
Governments frequently formulate policies designed to stimulate regional economic development. Rarely, however, are efforts made to measure local preferences for economic development outcomes. While the political process should eventually sort out how well local governments are meeting the needs of their constituents, the irreversible nature of many development outcomes makes it preferable to incorporate local preferences directly into the decision making process. This paper presents a straightforward means of measuring preference trade‐offs. The analytical hierarchy procedure is applied to local economic development outcomes in three Virginia counties and is shown to improve the targeting of industries by incorporating local preferences in the targeting process. The method has wide applicability for different development decisions. 相似文献
682.
Comparative studies on the antibacterial and free radical scavenging activities of the n-hexane, dichloromethane and methanol extracts of the seeds of Prunus padus and P. spinosa have been carried out. General toxicity of these extracts has also been determined. 相似文献
683.
Modelling soil water and salt dynamics under pulsed and continuous surface drip irrigation of almond and implications of system design 总被引:1,自引:1,他引:1
The HYDRUS-2D model was experimentally verified for water and salinity distribution during the profile establishment stage (33?days) of almond under pulsed and continuous drip irrigation. The model simulated values of water content obtained at different lateral distances (0, 20, 40, 60, 100?cm) from a dripper at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140 and 160?cm soil depths at different times (5, 12, 19, 26 and 33?days of profile establishment) were compared with neutron probe measured values under both irrigation scenarios. The model closely predicted water content distribution at all distances, times and soil depths as RMSE values ranged between 0.017 and 0.049. The measured mean soil water salinity (ECsw) at 25?cm from the dripper at 30, 60, 90 and 150?cm soil depth also matched well with the predicted values. A correlation of 0.97 in pulsed and 0.98 in continuous drip systems with measured values indicated the model closely predicted total salts in the root zone. Thus, HYDRUS-2D successfully simulated the change in soil water content and soil water salinity in both the wetting pattern and in the flow domain. The initial mean ECsw below the dripper in pulsed (5.25?dSm?1) and continuous (6.07?dSm?1) irrigations decreased to 1.31 and 1.36?dSm?1, respectively, showing a respective 75.1 and 77.6% decrease in the initial salinity. The power function [y?=?ax ?b ] best described the mathematical relationship between salt removal from the soil profile as a function of irrigation time under both irrigation scenarios. Contrary to other studies, higher leaching fraction (6.4–43.1%) was recorded in pulsed than continuous (1.1–35.1%) irrigation with the same amount of applied water which was brought about by the variation in initial soil water content and time of irrigation application. It was pertinent to note that a small (0.012) increase in mean antecedent water content (θ i ) brought about 8.25–9.06% increase in the leaching fraction during the profile establishment irrespective of the emitter geometry, discharge rate, and irrigation scenario. Under similar θ i , water applied at a higher discharge rate (3.876?Lh?1) has resulted in slightly higher leaching fraction than at a low discharge rate (1.91?Lh?1) under pulsing only owing to the variation in time of irrigation application. The influence of pulsing on soil water content, salinity distribution, and drainage flux vanished completely when irrigation was applied daily on the basis of crop evapotranspiration (ETc) with a suitable leaching fraction. Therefore, antecedent soil water content and scheduling or duration of water application play a significant role in the design of drip irrigation systems for light textured soils. These factors are the major driving force to move water and solutes within the soil profile and may influence the off-site impacts such as drainage flux and pollution of the groundwater. 相似文献
684.
Cañero AI Cox L Redondo-Gómez S Mateos-Naranjo E Hermosín MC Cornejo J 《Journal of agricultural and food chemistry》2011,59(10):5528-5534
The purpose of this study was to understand the effect produced by the addition of the herbicides terbuthylazine (N(2)-tert-butyl-6-chloro-N(4)-ethyl-1,3,5-triazine-2,4-diamine) and glyphosate (N-(phosphonomethyl)glycine) on photosystem II photochemistry of young plants of Olea europaea L. under greenhouse conditions. The effect of soil amendment with an organic residue from olive oil production was also assessed. Terbuthylazine reduced the efficiency of photosystem II photochemistry of plants due to chronic photoinhibition, and this effect was counterbalanced by soil amendment with the organic waste, whereas the photosystem II photochemistry of olive plants was not affected by glyphosate or by glyphosate and organic waste addition. In this study, we have shown that the soil application of terbuthylazine is a source of indirect phytotoxicity for olive plants. We have also observed that the olive plants were not affected by higher amounts of glyphosate in the soil. 相似文献
685.
Arthrotomy versus arthroscopy and partial synovectomy for treatment of experimentally induced infectious arthritis in horses. 总被引:2,自引:0,他引:2
A L Bertone D M Davis H U Cox S S Kamerling E D Roberts K A Caprile K A Gossett 《American journal of veterinary research》1992,53(4):585-591
To evaluate the clinical, laboratory, and histologic effects of 2 methods of treatment for infectious arthritis in horses, Staphylococcus aureus (3.4 to 3.9 x 10(3) colony-forming units) was inoculated into the tarsocrural joints of 8 horses on day 0. Each horse was treated with phenylbutazone (2 g, PO, q 24 h) and gentamicin sulfate (2.2 mg/kg of body weight, IV, q 8 h) for 14 days. On day 2, general anesthesia was induced, and each horse had 1 tarsocrural joint treated by arthrotomy, with removal of accessible fibrin and lavage with 3 L of sterile balanced electrolyte solution. An indwelling plastic drain was placed in the standing horse to provide a means for lavage with 3 L of balanced electrolyte solution twice daily for 72 hours. The contralateral tarsocrural joint was treated via arthroscopic debridement, synovectomy, and lavage with 3 L of balanced electrolyte solution. Arthrotomy and arthroscopic portals were allowed to heal by second intention. Lameness and thermographic examinations, analysis and bacteriologic culture of synovia, CBC, and WBC differential count were performed prior to inoculation and on days 1, 3, 6, 8, and 13. On day 14, each horse was euthanatized, and the joints were measured, opened, and photographed. Synovium and articular cartilage were obtained for semiquantitative histologic (H&E stain) and histochemical (safranin O fast green stain) evaluation. Lameness and joint circumference were significantly (P less than 0.05) greater in limbs treated by arthroscopy, synovectomy, and lavage. Arthrotomy with lavage eliminated the S aureus infection significantly (P less than 0.05) earlier than arthroscopy, synovectomy, and lavage, however, both treatments eliminated the infection in all but a single joint.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
686.
For yield based site-specific management to be successful in fields with crop rotations, changes in management zones between
crops must be determined. The study objectives were to determine if yield classes change between crops within a rotation and
whether soil properties can predict the yield classes or the year-to-year changes. A percentile classification method was
used to categorize yearly soybean (Glycine max) and rice (Oryza sativa) yield in two fields with soybean-rice-soybean rotations into low, medium and high yield classes. There was little agreement
in yield classifications between years. Yield class based on soil properties was predicted accurately by linear discriminant
analysis in Field 1 20–67% of the time and in Field 2 13–83% of the time. Predictions in Field 1 were based on soil available
Mg and P, elevation and the deep soil apparent electrical conductivity (ECa). Predictions in Field 2 were based on soil texture, soil available P, K and Mg, and pH. The linear discriminant analysis
was also able to predict year-to-year changes in yield class. Changes in class in Field 1 could be predicted by total soil
C and N, silt, and soil available Mg and P depending on the year. Soil texture, soil available P, K and Mg, total soil C and
pH, elevation and deep soil ECa predicted yield changes in Field 2 depending on the year. The results of this study indicate only limited success at management
zone definition in a soybean-rice rotation. Further investigation is needed with other crop rotation sequences to verify the
findings of this study. 相似文献
687.
Yvonne Underhill‐Sem Elizabeth Cox Anita Lacey Margot Szamier 《Asia Pacific viewpoint》2014,55(3):306-318
Addressing the multiple dimensions of gender inequality requires commitments by policy‐makers, practitioners and scholars to transformative practices. One challenge is to assemble a coherent conceptual framework from diverse knowledges and experiences. In this paper, we present a framework that emerged from our involvement in changing market culture in the Pacific, which we name a radical empowerment of women approach. We draw on detailed narratives from women market vendors and women‐led new initiatives in marketplaces to explain this approach. We argue that the primary focus of recently developed projects for marketplaces in the Pacific is technical and infrastructural, which is insufficient for addressing gendered political and economic causes of poor market management and oppressive conditions for women vendors. By exploring the complex array of motives and effects of the desire to transform or improve marketplaces in the Pacific, we caution against simplistic technical or infrastructural solutions. This paper also introduces the practice of working as a cooperative, hybrid research collaboration. The knowledges and analyses that we bring to this issue demonstrate that substantive analysis generated from diverse and shifting ‘locations’ and roles, but underpinned by a shared vision of, and commitment to, gender justice, can provide distinctive policy and research insights. 相似文献
688.
S.S.J. Buah J.W. Maranville A. Traore P. J. BrameI‐Cox 《Journal of plant nutrition》2013,36(11):2303-2318
Little information is available on the response of grain sorghum [Sorghum bicolor (L.) Moench] genotypes differing in nitrogen (N) use efficiency (NUE) (g DM g N‐1) to added N fertilizer. Such knowledge is important for reducing the reliance upon fertilizer N. A dryland field experiment was conducted in 1993 and 1994 at Mead, NE evaluating the agronomic responsiveness of 13 sorghum genotypes differing in NUE to three N rates (0, 50 and 100 kg N ha‐1) and also to determine physiological factors that contribute to improved NUE. The experiment was conducted on a fine montmorillonitic, mesic, Typic Argiudoll soil. Total N at maturity, dry matter, and grain yield were used to calculate NUE terms. Genotype differences were found for all measured variables both years, but no N rate by genotype effects were significant. Nitrogen fertilizer enhanced plant N contents and grain yield, but decreased NUE for total biomass and grain production. An early freeze in 1993 markedly reduced the later maturing genotype grain yields which, in turn, influenced NUE group comparisons. All genotypes in the study attained their full yield potential in 1994. The linear response to N rate of the N non‐responsive group was significantly less than the moderately responsive or N responsive group. High NUE sorghums had greater yields than low NUE types averaged over N levels only in 1994 since Naga White, a high NUE type, did not reach maturity in 1993. There was no difference in the linear response to N between these two groups. A linear increase in grain yield with increasing N rate was significantly greater for hybrids than lines. The results suggest that specific selection for high NUE sorghums will not diminish responsiveness to applied N. 相似文献
689.
The F4 fimbrial antigen of Escherichia coli and its receptors 总被引:11,自引:0,他引:11
F4 or K88 fimbriae are long filamentous polymeric surface proteins of enterotoxigenic Escherichia coli (ETEC), consisting of so-called major (FaeG) and minor (FaeF, FaeH, FaeC, and probably FaeI) subunits. Several serotypes of F4 have been described, namely F4ab, F4ac, and F4ad. The F4 fimbriae allow the microorganisms to adhere to F4-specific receptors present on brush borders of villous enterocytes and consequently to colonize the small intestine. Such ETEC infections are responsible for diarrhea and mortality in neonatal and recently weaned pigs. In this review emphasis is put on the morphology, genetic configuration, and biosynthesis of F4 fimbriae. Furthermore, the localization of the different a, b, c, and d epitopes, and the localization of the receptor binding site on the FaeG major subunit of F4 get ample attention. Subsequently, the F4-specific receptors are discussed. When the three variants of F4 (F4ab, F4ac, and F4ad) are considered, six porcine phenotypes can be distinguished with regard to the brush border adhesiveness: phenotype A binds all three variants, phenotype B binds F4ab and F4ac, phenotype C binds F4ab and F4ad, phenotype D binds F4ad, phenotype E binds none of the variants, and phenotype F binds F4ab. The following receptor model is described: receptor bcd is found in phenotype A pigs, receptor bc is found in phenotype A and B pigs, receptor d is found in phenotype C and D pigs, and receptor b is found in phenotype F pigs. Furthermore, the characterization of the different receptors is described in which the bcd receptor is proposed as collection of glycoproteins with molecular masses ranging from 45 to 70 kDa, the bc receptor as two glycoproteins with molecular masses of 210 an 240 kDa, respectively, the b receptor as a glycoprotein of 74 kDa, and the d receptor as a glycosphingolipid with unknown molecular mass. Finally, the importance of F4 fimbriae and their receptors in the study of mucosal immunity in pigs is discussed. 相似文献