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   424篇
  免费   18篇
林业   44篇
农学   7篇
基础科学   2篇
  100篇
综合类   19篇
农作物   35篇
水产渔业   13篇
畜牧兽医   182篇
园艺   9篇
植物保护   31篇
  2024年   1篇
  2023年   4篇
  2022年   8篇
  2021年   15篇
  2020年   13篇
  2019年   13篇
  2018年   21篇
  2017年   31篇
  2016年   17篇
  2015年   15篇
  2014年   15篇
  2013年   12篇
  2012年   31篇
  2011年   39篇
  2010年   28篇
  2009年   26篇
  2008年   28篇
  2007年   24篇
  2006年   21篇
  2005年   14篇
  2004年   12篇
  2003年   9篇
  2002年   8篇
  2001年   5篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1992年   1篇
  1990年   2篇
  1989年   2篇
  1987年   3篇
  1985年   1篇
  1983年   1篇
  1981年   1篇
  1977年   1篇
  1976年   1篇
  1972年   1篇
排序方式: 共有442条查询结果,搜索用时 31 毫秒
161.
Many owners are able and willing to perform home monitoring of blood glucose concentrations in diabetic cats. Once owners are familiar with the technique, they appreciate its advantages and show long-term compliance. The success of home monitoring hinges greatly on careful preparation and instruction of the owner. Owners must have ready access to veterinary support if needed. Initially, most owners call for advice, and several of them need repeated explanation or demonstration of the procedure. The frequency of re-evaluations of the diabetic cats by veterinarians is not affected by home monitoring. One of its major advantages is that it enables frequent generation of blood glucose curves. In complicated cases, more than one curve can, therefore, be performed at home before a treatment decision is made. According to preliminary data cats managed with home monitoring may have better glycaemic control than those managed without. However, those results need to be confirmed in a large group of cats.  相似文献   
162.
The objective of the study at hand was to investigate within the framework of a pilot project the preference of weaner pigs for either an ad libitum standard feed with thyme or oregano herb as flavouring additive or an ad libitum standard feed without any herbal additive. Thyme or oregano herbs or a combination of both were offered in two different concentrations each (1% and 0.1%) as additive (experimental diets) in standard diet in comparison to the latter without herbal additive (control diet) free of choice. The dosage of the two herbs in terms of total essential oil(s) in the feeds used in the study was 0.02% or 0.002% (v/w), which was equivalent to 1% or 0.1% herbs in the mixture, respectively. A Latin square according to Williams (1949) was used with 6 groups in order to record possible differences in feed intake. All experimental diets aside from that mixed with 0.1% thyme herb were, in comparison to the control diet, significantly less ingested. Where the weanling was given the choice, it did not choose feed with any flavouring additive. Further studies aimed at assessing the use of herbs as aroma additive in the form of a choice experiment are recommended.  相似文献   
163.
The greenhouse trials were conducted to determine the efficacy of environmentally safe insecticides/fungicides with physical mode of action [Agri-50E (propylene glycol alginate, hydrated) and SB Plant Invigorator] against Trialeurodes vaporariorum (Westwood). The efficacy of Agri-50E on adults and nymphs (first, second, third, and fourth instars) was compared to the commercially available standard Boxer 200 SL (imidacloprid) and an untreated control on greenhouse-grown poinsettia. Insecticides were applied by foliar spraying, Agri-50E (2 or 3 ml/l) two times and Boxer 200 SL (1 ml/l) once. Three and 7 days after first application (DAFA), imidacloprid was more effective than both concentrations of Agri-50E in controlling T. vaporariorum adults, whereas 10 DAFA there were no differences between insecticides. Twelve DAFA, imidacloprid was more effective than Agri-50E in controlling first, second and third instars and after 19 days in controlling second, third, and fourth instars. The results obtained from the poinsettia study, indicated that Agri-50E (2 or 3 ml/l) is successful in controlling T. vaporariorum adults and moderately effective against T. vaporariorum immature stages. In the second experiment, the efficacy of Agri-50E on adults was compared to SB Plant Invigorator (SBPI), the standard treatment Calypso 480 SC (thiacloprid), and an untreated control on greenhouse-grown tomato. Agri-50E (3 ml/l) and SBPI (2 ml/l) were applied four times while Calypso 480 SC (0.4 ml/l) was applied twice. The results obtained from tomato study showed that SBPI was the most effective insecticide against T. vaporariorum adults, followed by Agri-50E and Calypso 480 EC. Beside the ecological benefits, the alternative insecticides Agri-50E and SBPI might have an important role to play in future pest management programs.  相似文献   
164.
Environmental concern due to plant accumulation of natural radionuclides is a major concern in uranium mining areas. To evaluate the risk associated with the transfer of radionuclides to edible plants, the uptake of 238U, 226Ra, and 210Pb by Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) grown in soils contaminated with uranium-mill tailings (UMT) was investigated. Test plants were grown under controlled conditions in substrate composed of soil and UMT in different ratios. Activity concentrations of 238U, 226Ra, and 210Pb in substrate, leaves, and roots were measured and the concentration ratios determined. Soil characteristics were determined, since they directly affect bioavailability of radionuclides. Concentration ratios of 238U, 226Ra, and 210Pb in leaves varied from 0.001 to 0.006, 0.024 to 0.172, and 0.004 to 0.011, respectively, and in roots from 0.020 to 0.126, 0.015 to 0.241, and 0.033 to 1.460, respectively. Concentrations of 238U, 226Ra, and 210Pb in leaves and roots were found to correlate with the amount of 238U, 226Ra, and 210Pb in the substrate. A higher amount of 226Ra accumulated in aboveground parts (57–877 Bq kg?1 d. m. for leaves) compared to 238U (0.6–4.7 Bq kg?1 d. m. for leaves) and 210Pb (8–53 Bq kg?1 d. m. for leaves), which were mainly stored in the roots. The relationships between the amount of radionuclides in plants and soil characteristics and their role in radionuclide uptake are discussed and critically evaluated.  相似文献   
165.
Although Prune dwarf virus (PDV) is one of the most common viruses infecting stone fruits (Prunus spp.), most of the molecular diversity studies have so far focused on the capsid protein (CP) gene. An alternative diagnostic primer pair targeting the movement protein (MP) gene was used in the present work, increasing then polyvalence of PDV detection in cherry samples from Slovakia as compared to the previously published primers amplifying 5′MP-intergenic region-CP-3′UTR fragment. The nearly complete sequence of the RNA3 from 24 Slovak PDV isolates was determined, together with 19 partial sequences of the MP gene for other isolates. Even though the isolates originated from a geographically limited region, analyses showed a high degree of nucleotide sequence diversity between isolates. No clear-cut phylogenetic grouping based on host or geographical origin could be observed. The topology of the MP and CP trees were incongruent for some isolates. Highly supported recombination signals were detected in five PDV isolates, with breakpoints located at different positions in the central part of RNA3, within or close to the intergenic region. Taken together these results extend our understanding of the variability of PDV and for the first time highlight the contribution of recombination to the evolutionary history of this virus.  相似文献   
166.

Purpose

Because the stability of soil aggregates is affected by many factors, we studied aggregates formed in forest and agricultural soils in different soil types (Cambisols, Luvisols, Chernozems). We evaluated: (1) the differences in water-stable aggregates (WSA) as related to soil type and land management and (2) the relationships between quantitative and qualitative parameters of soil organic matter (SOM), particle-size distribution and individual size classes of WSA.

Materials and methods

Soil samples were taken from three localities (Sobě?ice, Báb, Vieska nad ?itavou). Each study locality included both a forest and an agricultural soil-sampling area.

Results and discussion

We found that in forest soils, the proportion of water-stable macroaggregates (WSAma) relative to water-stable microaggregates (WSAmi) was greater than in agricultural soils. When all soils were assessed together, positive statistically significant correlations were observed between the size classes WSAma > 1 mm and organic carbon (Corg) content; however, the WSAmi content was negatively correlated with Corg content. Favorable humus quality positively influenced the stabilization of WSAma > 5 mm; however, we found it had a negative statistically significant effect on stabilization of WSAma 1–0.25 mm. In agricultural soils, the stabilization of WSAma was associated with humified, i.e., stable SOM. The WSAma content was highly positively influenced mainly by fulvic acids bound with clay and sesquioxides; therefore, we consider this humus fraction to be a key to macroaggregate stability in the studied agricultural soils. On the other side, all fractions of humic and fulvic acids participated on the formation of WSAma in forest soil, which is a major difference in organic stabilization agents of macroaggregates between studied forest and agricultural soils. Another considerable difference is that WSAmi in agricultural soils were stabilized primarily with humic acids and in forest soils by fulvic acids. Moreover, in forest soils, a higher content of labile carbon in WSA had a positive effect on formation of WSAmi.

Conclusions

The observed changes in individual size classes of WSA and interactions between SOM, particle-size distribution, and WSA have a negative impact on soil fertility and thereby endanger agricultural sustainability.
  相似文献   
167.
This study discusses a novel approach for fabrication of floating photocatalyst which can be efficiently exploited for photodegradation of dyes in aqueous solutions. A fabrication of the floating photocatalyst consisted of two steps: transformation of the poly(ε-caprolactone) beads (PCLb) into poly(ε-caprolactone) foam (PCLf) with porous structure in supercritical carbon-dioxide and subsequent loading of PCLf with TiO2 nanoparticles (NPs). Morphological characterization of the PCLf before and after TiO2 NPs loading was carried out by FESEM. The presence of titanium on the surface and inside the PCLf was detected by EDX. Photocatalytical activity of the floating photocatalyst was investigated in aqueous solution of textile dyes C.I. Acid Orange 7 (AO7) and C.I. Basic Yellow 28 (BY28) which were exposed to lamp that simulates the sun light. In addition to sustainable floatability for a long period of time, developed floating photocatalyst exhibited high rate of photodegradation since the complete discoloration of AO7 and BY28 solutions and photocatalysts alone occurred after 300 and 180 min of illumination, respectively. Its photocatalytic activity was preserved after three repeated photodegradation cycles with unchanged chemical structure that was confirmed by FTIR analysis.  相似文献   
168.
169.
170.

Objective

To evaluate three routinely used tidal volumes (VT; 10, 12 and 15 mL kg?1) for controlled mechanical ventilation (CMV) in lung-healthy anaesthetized dogs by assessing alveolar ventilation (VTalv) and dead space (DS).

Study design

Prospective, randomized clinical trial.

Animals

A total of 36 client-owned dogs.

Methods

Dogs were randomly allocated to a VT of 10 (G10), 12 (G12) or 15 (G15) mL kg?1. After induction CMV was started. End-tidal carbon dioxide tension was maintained at 4.7–5.3 kPa by changing the respiratory frequency (fR; 6 < fR < 30 breaths minute?1). After 29 minutes, cardiovascular and respiratory variables were recorded for 3 minutes using a multiparameter monitor, volumetric capnography (VCap) and a blood gas analyser. The ratios of VTalv to body weight (VTalv kg?1) and airway DS to VT (VDaw/VT), Bohr's DS (VDBohr), Enghoff's DS (VDBE) and the volume of expired carbon dioxide per breath (VTCO2,br) were calculated. Mean airway pressure (MawP), fR and peak inspiratory pressure (PIP) were recorded. Data were analysed using one-way anova and Student–Newman–Keuls tests with a statistical significance set at p < 0.05.

Results

No differences were observed for demographic data and cardiovascular variables between groups. A total of three dogs were excluded because of technical difficulties and one because of fR > 30. VTalv kg?1 (p = 0.001) increased and VDBohr (p = 0.002) decreased with greater VT. VTCO2,br (p = 0.017) increased and VDaw/VT (p = 0.006), VDBE (p = 0.008) and fR (p = 0.002) decreased between G10 and G15. PIP (p = 0.013) was significantly higher in G15 compared with that in G10 and G12. No changes were observed in MawP.

Conclusions and clinical relevance

A VT of 15 mL kg?1 is most appropriate for CMV in lung-healthy dogs (as evaluated by respiratory mechanics and VCap) and does not impair cardiovascular variables.  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