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   523篇
  免费   31篇
林业   49篇
农学   12篇
基础科学   7篇
  150篇
综合类   36篇
农作物   23篇
水产渔业   61篇
畜牧兽医   156篇
园艺   21篇
植物保护   39篇
  2024年   1篇
  2023年   8篇
  2022年   13篇
  2021年   17篇
  2020年   16篇
  2019年   17篇
  2018年   26篇
  2017年   20篇
  2016年   19篇
  2015年   22篇
  2014年   21篇
  2013年   34篇
  2012年   34篇
  2011年   41篇
  2010年   30篇
  2009年   26篇
  2008年   37篇
  2007年   35篇
  2006年   26篇
  2005年   23篇
  2004年   24篇
  2003年   18篇
  2002年   15篇
  2001年   3篇
  2000年   6篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1994年   3篇
  1993年   1篇
  1992年   2篇
  1989年   3篇
  1985年   1篇
  1980年   2篇
  1977年   1篇
  1964年   1篇
  1956年   1篇
排序方式: 共有554条查询结果,搜索用时 31 毫秒
481.
ObjectivesAn ultrasound (US)-guided ventral suprainguinal approach to block the femoral nerve (FN) within the iliopsoas muscle (IPM) has recently been described in dogs. The goal of the present study was to provide the operator with additional information to locate the FN within the IPM in dogs and cats using US.Study designThe study was carried out in three phases: a dissection of the FN (phase 1); an in vivoUS-assisted nerve study (phase 2), and an anatomical cross-sectional study (phase 3).AnimalsNine healthy adult beagle dogs and nine healthy adult cats.MethodsDissections were performed to investigate the anatomical characteristics of the FN and its related structures in one dog and one cat. Ultrasound scans of the left and right FN were performed in eight dogs and eight cats. The FN diameter and the distance between the FN and the external iliac artery (EIA) in US images and in anatomical cryosections were measured.ResultsThe median FN diameter did not differ significantly between cats and dogs (1.1 mm versus 1.0 mm) or between the two techniques (US versus anatomical cross-sectional study) (1.1 mm versus 1.1 mm in dogs; 1.0 mm versus 1.1 mm in cats). The US and anatomical measurements of the median distances between the FN and EIA differed significantly between dogs and cats (8.2 mm versus 5.8 mm by US; 5.7 mm versus 4.8 mm in the anatomical study).Conclusions and clinical relevanceThe distance between the EIA and FN is reproducible in beagle dogs and cats and can be used in locating the FN within the IPM.  相似文献   
482.
ObjectivesTo establish an effective alfaxalone concentration to be used for bath immersion of fire-bellied toads (Bombina orientalis) and to describe its effects.Study designProspective experimental study.AnimalsThirteen oriental fire-bellied toads.MethodsThe study was carried out in two phases. The pilot phase involved five animals and aimed to identify an alfaxalone concentration capable of producing induction of anesthesia, defined as immobility with a head down position and loss of responsiveness to stimulation with a stick. The following trial in an additional eight toads used the effective alfaxalone concentration established during the pilot phase. Data from 11 animals (three toads in the pilot study and the eight additional toads) were analyzed. Twenty minutes after immersion in the anesthetic solution, the toads were removed from the bath, and heart rate, respiratory rate, the righting, myotactic and the nociceptive withdrawal reflexes were evaluated every 5 minutes. The loss of both righting and nociceptive withdrawal reflexes was considered indicative of a surgical depth of anesthesia. The time elapsed from anesthetic induction to return of righting reflex, the quality of recovery and the occurrence of undesired effects were observed and recorded.ResultsImmersion was found to be a suitable anesthetic technique for oriental fire-bellied toads and 200 mg L−1 alfaxalone concentration produced anesthetic induction in 10 out of 11 toads. Side effects, such as skin irritation, erythema and changes in cutaneous pigmentation, were not observed in any animal. The duration of anesthesia ranged from 10 to 30 minutes after removal of the toads from the alfaxalone bath, and surgical depth of anesthesia was never achieved.Conclusions and clinical relevanceIt was concluded that alfaxalone anesthesia induced by immersion in a concentration of 200 mg L−1 is only suitable for toads undergoing non-invasive short procedures.  相似文献   
483.
The formulation of quality indices for a given land area can be considered of great practical interest, both for highlighting the specific characteristics of that area, and for establishing the best management methods to adopt in order to exploit the soil’s maximum potential. Among other things, the specific formulation of the parameters considered here enables us to simulate specific measures designed to modify poor chemical, physical or biological characteristics (AQI, MQI), or to achieve a more rational form of soil management (AQI). We believe that one of the most interesting aspects of the proposed method is its tree-structured approach, which enables us to formulate an overall synthetic index by going through successive levels of aggregation. In this way, we are able to meet the contrasting needs of those, on the one hand, who are concerned about the inevitable loss of information inherent in every process of synthesis, and those, on the other hand, whose decision-making tasks require them to have concise quantitative information. The choice concerning which level of aggregation to operate will strictly depend on the objectives one is pursuing through the use of such indices.  相似文献   
484.
Mass spectrometry has been used to map chymosin from a fermentative source. The copresence of the two known genetic variants A (Asp(244)) and B (Gly(244)) was ascertained in bovine chymosin. By contrast, either the A or the B genetic variant occurred in the three commercial samples of recombinant calf chymosin (RCC). Specific biomarker proteins were searched to identify the enzyme source, in both bovine chymosin and RCC samples. Analyzing the derived tryptic peptides, evidence was provided that RCC and bovine chymosin are mainly formed by (1-323), (3-323), and (40p-323) (suffix "p" denotes residues in the pro-segment region of chymosin), whereas the minor components, (4-323), (5-323), and (6-323), were only detected in bovine chymosin. Additionally, the three commercial RCC samples contained the protein species (1-323), (38p-323), (39p-323), and (40p-323) and the shorter form (3-323). Differentiation of the natural and bioengineered enzyme is based upon the detection of these unique minor components by mass spectrometry.  相似文献   
485.
The parameters affecting the determination of some heavy metals in rainwater of Florence and its suburbs are investigated The maximum sensitivity for zinc determination by DPASV is obtained for a pulse amplitude of +50 mV. Samples of rainwater, collected in the center of Florence, show a metal concentration which is higher than samples collected in the suburb for the same meteorological event. Other sampling along the Tyrrenean seashore revealed a higher metal concentration in relation to the section of the coast that receives the polluted waters of the Arno river. In samples acidified to pH = 2, Cu and Zn are partially released in a very slow process.  相似文献   
486.
Today, emmer wheat, T. turgidum subsp. dicoccon, widely grown in the past is a candidate crop for sustainable agriculture in Italy. As part of a research project aimed at the enhanced use of the hulled wheat germplasm, molecular characterization was carried out to understand the genetic structure of the crop and to identify accessions of interest. A collection of 194 accessions was analyzed with 15 microsatellite loci (SSRs), while only a sample of 38 accessions was tested with 19 RFLP probes. The marker loci were selected on the basis of their independent genomic distribution. Genetic distances and allelic frequencies were calculated for each marker class. The genetic relationships were visualized with dendrograms. RFLP loci were, on average, less polymorphic than SSRs. An average Dice's genetic distance of 0.22 for RFLPs vs 0.38 for SSRs was detected, while an expected average heterozygosity per locus of 0.23 for RFLPs vs 0.26 for SSRs was also estimated. With a least number of 10 loci per marker class it was possible to identify each genotype. The most diverse accessions had different geographic origins. Germplasms from Italy and Ethiopia appear to belong to a more primitive genepool, given that a group of accessions from these countries were genetically differentiated from a Russian-Iranian group.  相似文献   
487.
Silybum marianum (L.) Gaertn. (milk thistle), grown as a medicinal plant in several countries, is considered as a weed in pastures and cereal crops but also as an interesting plant for biomass production. As an additional contribution to the full exploitation of a such promising species, two Sardinian populations of S. marianum were investigated for chemical composition, bioactive compounds and antioxidant properties at vegetative and reproductive stages. Dry matter yield was affected by the phenogical stage and differed between populations, ranging from 148 to 246 g plant?1. Chemical composition did not differ between populations. Antioxidant capacity detected by means of ABTS [(2,2′-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt)] and by DPPH (1,1-diphenyl-2-picrylhydrazyl) methods ranged from 3.45 to 5.42 and 3.83 to 6.32 mmol/100 g dry weight of Trolox equivalent antioxidant capacity, respectively. Differences in antioxidant capacity and bioactive compound contents in the different plant organs were found and also a significant linear correlation between antioxidant capacity and total phenolics and flavonoids, at flowering compared to vegetative stage. Research highlights antioxidant capacity in different organs of milk thistle and encourages the exploitation of biomass also as functional food, source of natural antioxidants and as a complementary fodder.  相似文献   
488.
A 3-year field experiment on a calcareous Fluventic Xerochrept planted with corn (Zea mays L.) was carried out to evaluate the effects of amending the soil with high and low rates of composted municipal waste on soil enzyme activities (alkaline phosphomonoesterase, phosphodiesterase, arylsulphatase, dehydrogenase, and l-asparaginase). These enzyme activities all increased when compost was added at rates of up to 90 t ha-1, and the phosphatases continued to show a linear increase with compost rates of up to 270 t ha-1. The addition of mineral fertilizer increased enzyme activities in unamended soil, and masked the stimulating effect of compost on the amended soils. Heavy metals did not affect soil enzyme activities up to a compost addition of at least three times the amount specified by Italian law.  相似文献   
489.
Studies on badland areas in the Vallcebre basin (Pyrenees) suggest that erosion rates are controlled by the weathering rate of mudrocks. To obtain the temporal pattern of physical weathering and its control on the erosive processes, monitoring of regolith temperatures at different aspect, depth and lithology, and periodical determination of regolith moisture and bulk density were carried out. Changes in surface regolith have also been monitored by means of photographic techniques, using an especially designed tripod. Finally, the hydrological and erosive response of the regolith trough the seasons were studied using rainfall simulations. The results obtained support and confirm previous knowledge on the role of frost action in mudrock weathering and the role of subsequent regolith development and wetness status on infiltration and runoff generation. These seasonal changes of behaviour are so important that they raise serious questions about the validity of observations or experiments carried out in only one season.This work confirms that erosion processes are controlled by regolith formation during winter and regolith depletion by storm rainfall erosion during summer, spring and early autumn. It also raises important points about annual trends of infiltration and erodibility, that should be used as guidelines for modelling runoff and sediment production.  相似文献   
490.
  • 1 The view that whales are malicious monsters has been pervasive throughout history. Conversely, the idea that these animals experience suffering has emerged only recently. One way of investigating perceptual, as well as behavioural, shifts is assessing general public reactions to mortality events involving wild, rare and charismatic animals.
  • 2 Here, the responses of 118 individuals to questions regarding the mass stranding of seven sperm whales (Physeter macrocephalus) along the Adriatic Sea coast of Italy in December 2009 are reported through interviews taken at the stranding site and in the direct proximity of the dead animals.
  • 3 When asked why the whales were stranded, 44.1% of the respondents suggested anthropogenic causes and 21.2% non‐anthropogenic. The remaining 34.7% mentioned a generic ‘disorientation’ or stated they did not know. When asked how they felt about the whales, 68.6% expressed feelings of compassion or care towards the animals. Clearly non‐compassionate attitudes accounted for only 4.1% of the sample. Finally, 21.2% expressed feelings that were ambiguous in terms of being suggestive of compassionate or non‐compassionate attitudes, including 11.9% amazement, 4.2% deprecation and 5.1% powerlessness.
  • 4 These results are in stark contrast with information obtained from accounts of similar events that have occurred in historical times, up until the first half of the 20th century. For centuries, responses to cetacean live strandings—typically including killing and harming of the animals—were either utilitarian or characterized by feelings including fear and a desire to ‘subjugate the beast’, with no apparent concern for their suffering and death.
  • 5 It is concluded that attitudes towards whales—today strikingly revolving around sadness, compassion and a sense of loss—have changed dramatically over time, with a steep turnaround in the 1970/1980s. Full appreciation of the ongoing evolution in public perception can channel marine conservation efforts and assist in the design of response strategies to marine mammal strandings. Copyright © 2010 John Wiley & Sons, Ltd.
  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