全文获取类型
收费全文 | 276篇 |
免费 | 16篇 |
专业分类
林业 | 7篇 |
农学 | 4篇 |
50篇 | |
综合类 | 32篇 |
农作物 | 9篇 |
水产渔业 | 6篇 |
畜牧兽医 | 172篇 |
园艺 | 5篇 |
植物保护 | 7篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 16篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 15篇 |
2007年 | 30篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有292条查询结果,搜索用时 15 毫秒
1.
2.
Microbial activity is affected by changes in the availability of soil moisture. We examined the relationship between microbial activity and water potential in a silt loam soil during four successive drying and rewetting cycles. Microbial activity was inferred from the rate of CO2 accumulating in a sealed flask containing the soil sample and the CO2 respired was measured using gas chromatography. Thermocouple hygrometry was used to monitor the water potential by burying a thermocouple in the soil sample in the flask. Initial treatment by drying on pressure plates brought samples of the test soil to six different water potentials in the range -0.005 to -1.5MPa. Water potential and soil respiration were simultaneously measured while these six soil samples slowly dried by evaporation and were remoistened four times. The results were consistent with a log-linear relationship between water potential and microbial activity as long as activity was not limited by substrate availability. This relationship appeared to hold for the range of water potentials from ?0.01 to ?8.5 MPa. Even at ?0.01 MPa (wet soil) a decrease in water potential from ?0.01 to ?0.02 MPa caused a 10% decrease in microbial activity. Rewetting the soil caused a large and rapid increase in the respiration rate. There was up to a 40-fold increase in microbial activity for a short period when the change in water potential following rewetting was greater than 5 MPa. Differences in microbial activity between the wetter and drier soil treatments following rewetting to the original water potentials are discussed in terms of the availability of energy substrate. 相似文献
3.
More adults of the citrus psylla,Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), dispersed when the number of eggs, nymphs or adults on the citrus increased (positive correlations) and also when new leaves that were present decreased (negative correlation). More psylla were trapped close to high obstacles than in an open area, even though the obstacles were at a distance from the psylla-infested orchard. 相似文献
4.
Staton VW Crowell-Davis SL 《Journal of the American Veterinary Medical Association》2003,222(12):1709-1712
OBJECTIVE: To identify factors (eg, familiarity, sex, neutering status, and time of year) associated with aggression between domestic ferrets and test a method for reducing aggression when introducing ferrets. DESIGN: Prospective trial. ANIMALS: 56 healthy domestic ferrets. PROCEDURE: To identify variables associated with aggression, pairs were placed in an enclosed area and observed. To test whether increasing familiarity would decrease aggression when introducing ferrets, pairs of ferrets were housed in separate cages next to each other or in separate rooms for 2 weeks prior to introduction. RESULTS: 49 of 82 pairs of strangers fought, but 31 cage mate pairs did not. Time of year had no apparent effect. Pairs consisting of 2 neutered females or 2 sexually intact males were significantly more likely to fight than were pairs consisting of a neutered female and a sexually intact male. Pairs caged next to each other for 2 weeks prior to introduction were no less likely to fight than were control pairs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that familiarity, sex, and neutering status are important determinants of aggression between ferrets. If unfamiliar neutered ferrets are introduced, then pairing 2 males or a male and female would likely result in the lowest levels of aggression. However, neutered females and sexually intact males are not indiscriminately aggressive, as a neutered female can be paired with a sexually intact male without resulting in aggression. Caging ferrets next to each other for 2 weeks does not decrease aggression when the ferrets are introduced. 相似文献
5.
Samii VF Les Clifford M Schulz KS Keyak JH Stover SM 《American journal of veterinary research》2002,63(8):1159-1166
OBJECTIVE: To evaluate subchondral bone density patterns in elbow joints of clinically normal dogs by use of computed tomographic (CT) osteoabsorptiometry. SAMPLE POPULATION: 20 cadaver forelimbs from 10 clinically normal dogs. PROCEDURE: Each elbow joint was imaged in parasagittal and transverse planes of 1.5-mm thickness. Slice data were converted to dipotassium phosphate equivalent density (PPED) values. Sagittal, parasagittal, and transverse medial coronoid process topographic maps were constructed. Defined zones were created for each of the 3 CT planes, and confluence and peak PPED values were determined. RESULTS: The lowest PPED value was 340 mg/ml (articular and subchondral confluence), and the highest was 1780 mg/ml (peak subchondral density). Detectable effects of joint laterality were not found in the confluence or peak PPED measurements or in the peak-to-confluence PPED ratio for all 3 CT planes. Significant differences were found among zones in all 3 planes for confluence and peak PPED measurements and between sagittal and transverse planes for peak-to-confluence PPED ratios. Subjectively, the pattern of density distribution among dogs was fairly consistent for the sagittal and parasagittal slices. Three specific patterns of density distribution were apparent on the transverse topographic maps of the medial coronoid process that corresponded to conformational differences. CONCLUSIONS AND CLINICAL RELEVANCE: The use of CT osteoabsorptiometry provides a repeatable technique that can be used to noninvasively examine bone density and the effects of stress acting on joints in vivo. Variability in density values for any of the CT planes was not identified among clinically normal dogs. 相似文献
6.
Wengelnik K Vidal V Ancelin ML Cathiard AM Morgat JL Kocken CH Calas M Herrera S Thomas AW Vial HJ 《Science (New York, N.Y.)》2002,295(5558):1311-1314
During asexual development within erythrocytes, malaria parasites synthesize considerable amounts of membrane. This activity provides an attractive target for chemotherapy because it is absent from mature erythrocytes. We found that compounds that inhibit phosphatidylcholine biosynthesis de novo from choline were potent antimalarial drugs. The lead compound, G25, potently inhibited in vitro growth of the human malaria parasites Plasmodium falciparum and P. vivax and was 1000-fold less toxic to mammalian cell lines. A radioactive derivative specifically accumulated in infected erythrocytes to levels several hundredfold higher than in the surrounding medium, and very low dose G25 therapy completely cured monkeys infected with P. falciparum and P. cynomolgi. 相似文献
7.
The Effects of Mepivacaine Hydrochloride on Antimicrobial Activity and Mechanical Nociceptive Threshold During Amikacin Sulfate Regional Limb Perfusion in the Horse 下载免费PDF全文
8.
Susan J. Holcombe VMD MS Alicia L. Bertone DVM PhD David S. Biller DVM Valerie Haider DVM 《Veterinary radiology & ultrasound》1995,36(2):119-125
The purpose of this study was to define normal gross anatomic structures in the equine stifle with magnetic resonance images. Magnetic resonance (MR) images were made in sagittal, 15° supinated, transverse, and dorsal planes of two equine stifles. The MR images were scrutinized by comparing MR images to dissection specimens and frozen cross sections of stifle joints. Sagittal and 15° supinated images were the most valuable in assessing articular cartilage, subchondral bone, and soft tissue structures within the joint. Cranial and caudal cruciate ligaments, medial and lateral menisci, meniscotibial and meniscofemoral ligaments, long digital extensor tendon, and patellar ligaments were easily evaluated. MR images provided substantially more gross anatomical information than the currently available imaging modalities. 相似文献
9.
Abstract: Transnationalism needs to be understood as a set of practices fashioned through the life course as well as in relation to contextual factors that include state policy and experiences of discrimination that affect entry to the labour force. The paradox of transnationalism is that families make strategic decisions to separate in order to maintain family unity and to advance the welfare of children. Emigrants from Hong Kong to Canada in the latter decades of the twentieth century were motivated by concern for family welfare and the quality of education in Canada. Yet economic livelihood prospects remained greater in Hong Kong than in Canada, prompting many families to become transnational ‘astronaut’ families with one or more members working in Hong Kong. Migration decisions tend to occur around key points of life‐course transition involving entry to and graduation from education, and entry to and exit from the labour force. Transnational practices are complex and multigenerational, involving different patterns for young adults, those in their middle years and the elderly. 相似文献
10.