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   333篇
  免费   14篇
林业   37篇
农学   12篇
基础科学   3篇
  133篇
综合类   21篇
农作物   16篇
水产渔业   12篇
畜牧兽医   76篇
园艺   6篇
植物保护   31篇
  2024年   1篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   10篇
  2019年   10篇
  2018年   4篇
  2017年   9篇
  2016年   9篇
  2015年   9篇
  2014年   13篇
  2013年   21篇
  2012年   30篇
  2011年   16篇
  2010年   11篇
  2009年   21篇
  2008年   20篇
  2007年   30篇
  2006年   18篇
  2005年   11篇
  2004年   17篇
  2003年   15篇
  2002年   15篇
  2001年   8篇
  2000年   7篇
  1999年   3篇
  1998年   4篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1994年   2篇
  1993年   4篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   5篇
  1988年   2篇
  1977年   1篇
  1970年   1篇
  1939年   2篇
排序方式: 共有347条查询结果,搜索用时 78 毫秒
331.
Objective: To review the rationale behind and experiences with traditional and newly evolving concepts of fluid therapy in the traumatized patient, and to review conventional and novel fluid preparations for use in trauma resuscitation. Data sources: Human and veterinary clinical and research studies. Human data synthesis: Current treatment guidelines recommend aggressive fluid resuscitation with lactated ringers solution (LRS) or saline as optimum management of hemorrhagic shock in trauma, regardless of whether bleeding is controlled or not. The rationale behind this strategy is to restore intravascular volume as rapidly as possible to ensure adequate vital organ perfusion. Recently, this strategy has been challenged, especially in patients with uncontrolled hemorrhage, as neither laboratory evidence nor clinical trials support this practice. Current research indicates that vigorous fluid infusion may exacerbate bleeding and cause severe hemodilution, both impairing resuscitation outcome. As a result, a new line of thinking is emerging that balances the risks and benefits of intravenous volume infusion by offering the clinician alternative treatment strategies and emphasizes continuous endpoint‐oriented monitoring. ‘Hypotensive’ or ‘hypovolemic’ resuscitation techniques as well as initial volume replacement with fluids other than LRS or saline (e.g., hypertonic saline [HTS], HTS with dextran 70 [HTS‐D]) have been introduced in human medical practice as additional options for treatment of victims of trauma under certain circumstances. Clinical studies evaluating the use of hemoglobin‐based oxygen carriers (HBOCs) in the trauma setting are underway and may soon lead to an expansion of the fluid arsenal available to the clinician for treatment of trauma patients. Veterinary data synthesis: Based on available animal data, neither strict guidelines nor a clear fluid preference for resuscitation of traumatic shock have been defined. Although systematic clinical trials are missing, combinations of crystalloid and colloid (natural or artificial) appear to be as effective for resuscitation as crystalloid alone. Judicious use of an HBOC (e.g., Oxyglobin®) as a substitute for blood/red blood cells may be recommended in situations where whole blood or pRBCs are not or not yet available. Conclusions: The search for optimal methods of fluid resuscitation in trauma is ongoing. At this point the best solution is a differentiated approach to fluid therapy, one that tailors type and volume of resuscitation solution(s) used to the type and severity of injury in an individual patient and uses monitoring of perfusion and oxygenation parameters to guide resuscitation. Crystalloid fluids are effective for resuscitation but may need to be combined with or replaced by colloidal fluids in certain clinical situations.  相似文献   
332.
Abstract: This study was designed to validate in vitro oxygen saturation (SO2) measurements with the NOVA CO-Oximeter (Nova Biomedical Corp, Waltham, Mass, USA) in canine blood containing hemoglobin (Hb) glutamer-200 bovine (Hb-200; Oxyglobin, Biopure, Cambridge, Mass, USA) as a Hb-based oxygen carrier recently introduced into clinical practice. In the first set of experiments, stored blood from 6 mixed-breed canine blood donors was used. Target PO2 levels were reached in aliquots of blood samples by tonometry. Oxygen saturation was then measured with the test device and calculated based on known PO2 values. In the second set of experiments, total oxygen content was directly measured by means of an oxygen-specific electrode in aliquots of fresh whole arterial, venous, and mixed (arterial-venous) blood withdrawn from the same canine blood donors. Hb-200 was added to those blood samples to yield plasma Hb concentrations of 1.62, 3.25, 6.50, and 9.75 g/dL. Based on Hb content and SO2 measured by the NOVA CO-Oximeter in these samples, total oxygen content was also calculated for each sample and compared with measured values. A strong correlation was found between SO2 values measured with the co-oximeter in samples after tonometry, and calculated SO2 based on known PO2. Directly measured total blood O2 content varied by ≤ 5% from values computed based on co-oximeter measurements of Hb content and SO2. These results did not change with different levels of oxygenation of the samples or different plasma Hb-200 concentrations. In conclusion, the NOVA CO-Oximeter is an accurate analyzer for measurement of SO2 after Hb-200 administration to canine blood.  相似文献   
333.
The efficiency of our anther culture protocol was tested with high‐ and low‐responding genotypes, ‘Svilena’ and ‘Berengar’, and 93 F1 winter wheat crosses in 2010 and 2011. Based on data for these genotypes, the effect of genotype influenced the number of embryo‐like structures, regenerated plantlets and green plantlets, while the number of albino plantlets was affected by genotype, year and environmental factors. Although genotype also influenced the production of green plantlets from breeding crosses, with green plantlets per 100 anthers ranging from 0.04 to 28.67, the average regeneration rate over all crosses was 5.3 green plantlets/100 anthers, which resulted in a total of 11 416 well‐rooted green plantlets. The survival rate of green plantlets following acclimatization was 97.21% in 2010 and 96.34% in 2011. In this study, the phenomenon of albinism and genotype dependency did not hinder the production of more than five thousand green plantlets each year. In our experiments, anther culture proved to be an efficient method in winter wheat breeding programmes with lower costs than alternative technologies.  相似文献   
334.
335.
A multicentre, randomized, blinded study compared the efficacy of pradofloxacin with that of a combination of amoxycillin/clavulanic acid in the treatment of deep pyoderma in dogs. Dogs with clinical lesions of deep pyoderma and a positive bacterial culture were included in the study. At each visit, they were evaluated with lesion, pruritus and general condition scores. Dogs were treated either with pradofloxacin at 3 mg kg-1 once daily or with amoxycillin at 10 mg kg-1 and clavulanic acid at 2.5 mg kg-1 twice daily and evaluated weekly for 3 weeks and every 2 weeks thereafter until 2 weeks past clinical remission. Maximal treatment duration was 9 weeks, and maximal evaluation period was 11 weeks. Of the 56 dogs treated with pradofloxacin (group 1), 48 dogs (86%) achieved clinical remission, four dogs improved, four dogs did not respond and a recurrence of clinical signs was not seen in any patient after 11 weeks. Of the 51 dogs treated with amoxycillin/clavulanic acid (group 2), 37 dogs achieved clinical remission (73%), three dogs showed improvement, five dogs showed no response and in six dogs, clinical signs recurred within 2 weeks of cessation of therapy. These results indicate that pradofloxacin is an efficacious therapy comparable to amoxycillin/clavulanic acid for deep bacterial pyoderma in dogs.  相似文献   
336.
The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na+, Ca2+, or Al3+ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na+ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca2+ and Al3+ decreased it. The 1H‐NMR relaxometry analyses showed that Al3+ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca2+ or Na+. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.  相似文献   
337.
In a previous experiment, plants were able to immobilize or solubilize Cadmium (Cd) in a sandy acid soil enriched with 40 μmol Cd kg–1, because Cd solution concentration was decreased by maize (Zea mays) and sunflower (Helianthus annuus), and increased by flax (Linum usitatissimum L. ssp. usitatissimum) and spinach (Spinacia oleracea). It is assumed that the equilibrium with Cd fractions in the soil solid phase and the chemical form of Cd in the soil solution were affected. In the present study, the effect of the four plant species mentioned above on Cd binding in soil was investigated by means of a fractionation of soil Cd with a sequential extraction of seven steps. The seven fractions of Cd are operationally defined by the extraction sequence that follows the order of increasing acidity with extractants of different complexing and redox properties. In the unplanted soil, Cd was predominantly present in the exchangeable Fraction I (F. I) and easily mobilizable Fraction II (F. II) (64%). Significant concentrations of Cd were found in F. III (occluded in Mn oxides; 22%) and F. IV (organically bound; 10%). Fractions V (occluded in poorly crystalline Fe oxides), F. VI (occluded in well crystallized Fe oxides), and F. VII (residual fraction) amounted to less than 5% of the total soil Cd concentration. The plants changed the binding of Cd in soil in a different manner. All plants decreased F. I, but F. II was increased by maize and spinach, decreased by flax or remained unaffected by sunflower. Fraction III was not affected by maize and flax, but decreased by sunflower and spinach, and F. IV was not affected by sunflower and spinach, but was increased by maize and flax. These changes of Cd fractions were not related to the changes the plants had caused in total Cd or Cd2+ concentration of the soil solution. These results show that plant species differ in how they affect Cd binding to the soil solid phase, but this effect is not related to how they affect Cd in soil solution. The mechanisms by which plants affect the relationship between the soil solid and liquid phase are still unclear.  相似文献   
338.
The development and use of the conceptual framework of ecosystem services (ES) has been very successful in supporting the broad diffusion and application of ES within science and policy communities. However, most of the currently proposed interpretations of the framework neither correlate to environmental planning nor to decision-making contexts at the local and regional scale, which is a potential reason for the slow adoption and practice of the ES conceptual framework. This paper proposes a practice-oriented ES evaluation (PRESET) model specifically adapted to the requirements of local and regional planning and decision-making contexts, and discusses its potential benefits and implications for practice. Through the usage of PRESET we suggest making a distinction between ‘offered ES’, ‘utilized ES’, ‘human input’, and ‘ES benefits’ as relevant information for decision-making. Furthermore, we consider it important to link these decision-support categories to different value dimensions relevant in planning and management practice. PRESET provides guidance to inject the ES concept into planning, but needs to be implemented together with concrete assessment methods, indicators and data. The planning strategic benefits of using PRESET include its reference to existing legislative objectives, avoiding the risk that monetized ES values might dominate decision-making, clarification of human contributions, and easier identification of land use conflicts and synergies. Examples are given for offered and utilized ES, as well as for respective evaluation approaches and instruments of implementation.  相似文献   
339.
Summary C-banding andin situ hybridization were used to determine the chromosomal constitution of the greenbug-resistant germplasm GRS 1204. The results showed that this line had the radiation-induced non-homoeologous wheat-rye translocation chromosomes T2AS-1RS·1RL and T2AL·2AS-1RS. C-banding analysis further revealed the presence of a wheat-Agropyron elongatum translocation chromosome T1BL·1BS-3Ae#1L in line GRS 1204, that was derived from Teewon. The greenbug resistance of line GRS 1204 is similar to that of line GRS 1201 that was earlier shown to have the greenbug resistance geneGb6 located on the 1RS arm of the wheat-rye translocation chromosome T1AL·1RS. BecauseGb6 in line GRS 1204 is present on one of the non-homoeologous translocation chromosomes, agronomically line GRS 1201 should be the better adapted source ofGb6 resistance and be used in cultivar improvement.  相似文献   
340.
Recent advances in alien gene transfer in wheat   总被引:3,自引:0,他引:3  
Summary The recent advances in alien gene transfer from distantly-related species into wheat are reviewed in the present paper. The main achievements during the last ten years include the great expansion of the range of wide hybridization and development of new techniques for production and characterization of wheat-alien chromosome translocations. Updated results of wide hybridization since 1983 and comprehensive characterization of wheat-alien translocation lines in our laboratory are compiled. The future outlook for alien gene transfer in wheat is also discussed.  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