全文获取类型
收费全文 | 129篇 |
免费 | 8篇 |
专业分类
林业 | 1篇 |
11篇 | |
综合类 | 23篇 |
农作物 | 28篇 |
水产渔业 | 8篇 |
畜牧兽医 | 64篇 |
植物保护 | 2篇 |
出版年
2020年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
1941年 | 2篇 |
1939年 | 1篇 |
1937年 | 2篇 |
1936年 | 1篇 |
1935年 | 5篇 |
1934年 | 5篇 |
1933年 | 5篇 |
1927年 | 1篇 |
1926年 | 1篇 |
1925年 | 2篇 |
排序方式: 共有137条查询结果,搜索用时 15 毫秒
51.
Lunar anorthosites 总被引:2,自引:0,他引:2
Sixty-one of 1676 lunar rock fragments examined were found to be anorthosites, markedly different in composition, color, and specific gravity from mare basalts and soil breccias. Compositional similiarity to Tycho ejecta analyzed by Surveyor 7 suggests that the anorthosites are samples of highlands material, thrown to Tranquillity Base by cratering events. A lunar structural model is proposed in which a 25-kilometer anorthosite crust, produced by magmatic fractionation, floats on denser gabbro. Where early major impacts punched through the crust, basaltic lava welled up to equilibrium surface levels and solidified (maria). Mascons are discussed in this context. 相似文献
52.
Abstract AIM: To provide baseline data on the levels and patterns of antibacterial drug resistance expressed by Gram-negative bacteria isolated from poultry carcasses in New Zealand. METHODS: Between July and December 2006, isolates of Escherichia coli (n=407) and Salmonella spp. (n=3) originating from carcass-rinse samples were submitted by testing laboratories affiliated to five major poultry processing plants. Isolates of Campylobacter jejuni (n=193) originating from retail poultry carcasses in 2005–2006 were retrieved from the Massey University archives. All isolates underwent disc diffusion susceptibility testing against panels of 12 (Enterobacteriaceae) and six (Campylobacter spp.) antibacterial drugs. Cephalothin-resistance in isolates of E. coli was confirmed using ETest strips, and confirmation of the resistance phenotypes for a subset of C. jejuni isolates used microbroth dilution assays. Patterns within the resistance phenotypes of the isolates were investigated using hierarchical clustering, and logistic regression modelling. RESULTS: The majority of isolates (71.5% E. coli, 99% C. jejuni, and all three Salmonella spp. isolates) were fully susceptible to the drugs that were tested. Four (1%) E. coli isolates showed resistance to three or more drugs. The proportions of susceptible E. coli differed between the five processing plants. Resistances were detected in E. coli isolates, using disc diffusion to cephalothin (18.2%), ampicillin (4.4%), tetracycline (4.4%) and gentamicin (1.5%). There was an association between cephalothin-resistant isolates of E. coli and decreased susceptibility to gentamicin. Using ETests to ascertain the minimum inhibitory concentrations (MIC) of E. coli for cephalothin gave inconsistent results. One of 193 C. jejuni isolates was resistant to erythromycin, and microbroth dilution assays confirmed that this panel of C. jejuni was generally susceptible to antibacterial drugs. CONCLUSIONS: The levels of resistance shown by Gram-negative bacteria isolated from chicken carcasses in New Zealand are among the lowest reported around the world. No resistance to extended-spectrum cephalosporin drugs was detected in E. coli, suggesting that CTX-M and AmpC beta-lactamases are rare or absent. Salmonella spp. are rarely isolated from poultry carcasses during routine testing in New Zealand, and the isolates identified during this study were fully susceptible to the drugs tested. A panel of C. jejuni isolates originating from retail poultry carcasses were susceptible to first-line and second-line antibacterial drugs. The use of cephalothin as a marker of resistance to first-generation cephalosporins may not be appropriate for non-type-specific E. coli of animal origin. 相似文献
53.
Daniel F Kripke Caroline M Nievergelt EJ Joo Tatyana Shekhtman John R Kelsoe 《Journal of circadian rhythms》2009,7(1):2-10
Background
Clinical symptoms of affective disorders, their response to light treatment, and sensitivity to other circadian interventions indicate that the circadian system has a role in mood disorders. Possibly the mechanisms involve circadian seasonal and photoperiodic mechanisms. Since genetic susceptibilities contribute a strong component to affective disorders, we explored whether circadian gene polymorphisms were associated with affective disorders in four complementary studies. 相似文献54.
PO Wennberg TF Hanisco L Jaegle DJ Jacob EJ Hintsa EJ Lanzendorf JG Anderson R Gao ER Keim SG Donnelly LAD Negro DW Fahey SA McKeen RJ Salawitch CR Webster RD May RL Herman MH Proffitt JJ Margitan EL Atlas SM Schauffler F Flocke CT McElroy TP Bui 《Science (New York, N.Y.)》1998,279(5347):49-53
The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected. 相似文献
55.
Sean C Anderson Andrew B Cooper Olaf P Jensen Cóilín Minto James T Thorson Jessica C Walsh Jamie Afflerbach Mark Dickey‐Collas Kristin M Kleisner Catherine Longo Giacomo Chato Osio Daniel Ovando Iago Mosqueira Andrew A Rosenberg Elizabeth R Selig 《Fish and Fisheries》2017,18(4):732-741
Fishery managers must often reconcile conflicting estimates of population status and trend. Superensemble models, commonly used in climate and weather forecasting, may provide an effective solution. This approach uses predictions from multiple models as covariates in an additional “superensemble” model fitted to known data. We evaluated the potential for ensemble averages and superensemble models (ensemble methods) to improve estimates of population status and trend for fisheries. We fit four widely applicable data‐limited models that estimate stock biomass relative to equilibrium biomass at maximum sustainable yield (B/BMSY). We combined these estimates of recent fishery status and trends in B/BMSY with four ensemble methods: an ensemble average and three superensembles (a linear model, a random forest and a boosted regression tree). We trained our superensembles on 5,760 simulated stocks and tested them with cross‐validation and against a global database of 249 stock assessments. Ensemble methods substantially improved estimates of population status and trend. Random forest and boosted regression trees performed the best at estimating population status: inaccuracy (median absolute proportional error) decreased from 0.42 – 0.56 to 0.32 – 0.33, rank‐order correlation between predicted and true status improved from 0.02 – 0.32 to 0.44 – 0.48 and bias (median proportional error) declined from ?0.22 – 0.31 to ?0.12 – 0.03. We found similar improvements when predicting trend and when applying the simulation‐trained superensembles to catch data for global fish stocks. Superensembles can optimally leverage multiple model predictions; however, they must be tested, formed from a diverse set of accurate models and built on a data set representative of the populations to which they are applied. 相似文献
56.
L. C. Dickey M. F. Dallmer E. R. Radewonuk N. Parris M. Kurantz J. C. Craig 《Cereal Chemistry》1997,74(5):676-680
Corn milled to <1 mm using a screen mill was sieved and the particles >590 μm were soaked for 1 hr in solutions with a range of glucose concentration providing liquid specific gravities above and below that of the lighter fraction (corn germ). A suspension of these particles was pumped through a hydrocyclone to separate the germ particles and to rinse watersoluble compounds from the corn. The specific gravity of the hydrocyclone streams (suspensions), as well as liquid phase (after solids settling) was measured, and product compositions and particle sizes were determined. This work shows that a germ-enriched fraction of corn ground to <1 mm, can be separated with a hydrocyclone. To enable computer simulation of the corn-treatment process, the experimental data was used to construct a two-component model of the hydrocyclone separation of the milled corn. In the model, the milled and sieved corn is virtually separated into germ and endosperm streams that are fed to paired hydrocyclone models. Hydrocyclone bypassing streams that simulate particles entrained to the contrary outlet (underflow for germ and overflow for endosperm particles) were included in the simulation to bring the model into agreement with the experimental product compositions. 相似文献
57.
58.
59.
60.
Investigation of the effect of Equivac® HeV Hendra virus vaccination on Thoroughbred racing performance 下载免费PDF全文
K Schemann EJ Annand PA Reid MF Lenz PC Thomson NK Dhand 《Australian veterinary journal》2018,96(4):132-141