全文获取类型
收费全文 | 1590篇 |
免费 | 81篇 |
国内免费 | 2篇 |
专业分类
林业 | 109篇 |
农学 | 27篇 |
基础科学 | 4篇 |
253篇 | |
综合类 | 174篇 |
农作物 | 76篇 |
水产渔业 | 86篇 |
畜牧兽医 | 800篇 |
园艺 | 33篇 |
植物保护 | 111篇 |
出版年
2023年 | 17篇 |
2022年 | 9篇 |
2021年 | 26篇 |
2020年 | 39篇 |
2019年 | 46篇 |
2018年 | 37篇 |
2017年 | 39篇 |
2016年 | 43篇 |
2015年 | 41篇 |
2014年 | 41篇 |
2013年 | 81篇 |
2012年 | 103篇 |
2011年 | 138篇 |
2010年 | 38篇 |
2009年 | 69篇 |
2008年 | 104篇 |
2007年 | 108篇 |
2006年 | 88篇 |
2005年 | 95篇 |
2004年 | 82篇 |
2003年 | 84篇 |
2002年 | 62篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 18篇 |
1974年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有1673条查询结果,搜索用时 0 毫秒
1.
Sergei Gorshkov Galina Gorshkova Barbara Colorni Hillel Gordin 《Journal of the World Aquaculture Society》2004,35(2):167-177
To produce a monosex female population of European sea bass Dicentrarchus labrax, fry were fed dry diets containing dosages of 12.5, 25, and 50 mg/kg food of either the natural estrogen estradiol-170β(E2) or the synthetic estrogen 17α-ethynylestradiol (EE2) for 60 d starting at 88 d post-hatch (dph). A complete feminization (100%) was achieved in all E2-treated groups at the age of 11 mo (330 dph). All affected fish had ovaries similar in size and histological structure to those of control females. In the E2-treated groups, feminized fish were heavier and longer than untreated controls (males and females combined). In control groups females exhibited significantly higher body weight and total length than males. Untreated females from control groups and females from the group treated with E2 at 12.5 mg/kg food had similar body weight, suggesting that in sea bass growth is related to phenotypic sex. In the Entreated groups, survival rates were similar to those of the control fish. A relatively high percentage of females was obtained in the EE2-treated groups (from 38.6 to 96.5%). However, the gonadal development in these fish was significantly suppressed and a dose-dependent reduction of gonadal sizes was evident. Treatments with the EE2 (12-5, 25, and 50 mg/kg food) resulted in many fish having abnormal (2.9-5.4-39.8%, respectively) and sterile (0.6-6.0-21.6%, respectively) gonads. Effects also included significantly lower weight and shorter length when compared with controls. Furthermore, fish fed with EE2 at the dosage of 50 mg/kg food had high mortality rate. A simple protocol was developed for the complete feminization in sea bass in which the fry (80-100 dph) were fed to satiation two times daily with a diet containing 12.5 me of E2/ks food for a period of 60 d. 相似文献
2.
3.
Hamish M Aiken Nathan J Bott Ivona Mladineo Francisco E Montero Barbara F Nowak & Craig J Hayward 《Fish and Fisheries》2007,8(3):167-180
Global distribution of platyhelminth parasites and their host specificities are not well known. Our hypothesis was that platyhelminth parasites of large pelagic fishes are common around the world. We analysed molecular variation in three different taxa of platyhelminth parasites infecting four species of tunas: yellowfin tuna (Thunnus albacares, Scombridae) from Western Australia, southern bluefin tuna (Thunnus maccoyii, Scombridae) from South Australia, Pacific bluefin tuna (Thunnus orientalis, Scombridae) from Pacific Mexico and northern bluefin tuna (T. thynnus, Scombridae) from two localities in the Mediterranean (Spain and Croatia). Comparisons of ITS2 and partial 28S rDNA demonstrated two congeneric species of blood flukes (Digenea: Sanguinicolidae) from multiple hosts and localities: Cardicola forsteri from southern bluefin and northern bluefin tunas, and Cardicola sp. from Pacific bluefin and northern bluefin tunas; and a gill fluke, Hexostoma thynni (Polyopisthocotylea: Hexostomatidae), from yellowfin, southern bluefin and northern bluefin tunas. Partial 28S rDNA indicates that a second type of fluke on the gills, Capsala sp. (Monopisthocotylea: Capsalidae), occurs on both southern bluefin and Pacific bluefin tunas. This appears to be the first report of conspecific platyhelminth parasites of teleosts with a wide‐ranging geographical distribution that has been confirmed through molecular approaches. Given the brevity of the free‐living larval stage of both taxa of flukes on the gills (H. thynni and Capsala sp.), we conclude that the only feasible hypothesis for the cosmopolitan distribution of these flatworms is migrations of host tunas. Host migration also seems likely to be responsible for the widespread occurrence of the two species of blood flukes (Cardicola spp.), although it is also possible that these were translocated recently by the spread of infected intermediate hosts. 相似文献
4.
Neuraminidase production by Erysipelothrix rhusiopathiae 总被引:1,自引:0,他引:1
In order to characterise neuraminidase activity by Erysipelothrix, 85 isolates of Erysipelothrix spp. from a variety of sources including human clinical, marine and terrestrial animals, and the environment were investigated for neuraminidase production. Neuraminidase activity was detected by a peanut lectin haemagglutination method. The effects of media, incubation conditions and pH on the production and activity of neuraminidase were also investigated. Enzyme activity was detected only in the supernatants of the isolates of Erysipelothrix rhusiopathiae which had been incubated in cooked meat broth and Todd Hewitt broth supplemented with horse serum after 16 and 36 h incubation at 37 degrees C. The maximum titres were reached at 40 h in cooked meat broth and 56 h in Todd Hewitt broth supplemented with horse serum. All 58 isolates and the type strain (ATCC 19414) of E. rhusiopathiae produced detectable neuraminidase activity with titres between 10 and 320. The optimal pH for the enzyme activity varied among the isolates with a pH between 6.0 and 7.0 covering the highest enzyme activity of the most. There was no statistically significant difference in the level of neuraminidase activity between isolates from different sources (p > 0.05). Neuraminidase activity was not detected in the non-pathogenic Erysipelothrix spp. such as E. tonsillarum. Neuraminidase was detected only in E. rhusiopathiae suggesting its possible role as a virulence factor. Enzyme production and activity were medium and pH dependent. The peanut lectin haemagglutination assay is a simple, rapid and sensitive method and is particularly useful for the analysis of multiple samples. 相似文献
5.
OBJECTIVE: To describe the clinical signs, diagnostic evaluation and surgical management of an alpaca with splenic torsion. ANIMALS: Six-year-old female alpaca. RESULTS: Splenic torsion and uterine torsion were the inciting cause for persistent abdominal discomfort in this alpaca. Rectal examination, abdominocentesis, and transabdominal ultrasonographic findings were suggestive of a splenic lesion. Surgical management involved splenectomy of a necrotized spleen. CONCLUSIONS: Although rare in occurrence, splenic torsion should be considered as a potential cause of abdominal discomfort in alpacas. Splenectomy is a reasonable and successful method of treatment for a devitalized spleen secondary to splenic torsion in alpacas. CLINICAL RELEVANCE: Splenic torsion causes persistent abdominal discomfort in camelids and may be associated with uterine torsion. Rectal examination, transabdominal ultrasound and abdominocentesis are useful diagnostic tools to differentiate splenic torsion from other causes of abdominal discomfort. Splenectomy is an uncomplicated procedure in camelids and has a favorable prognosis. 相似文献
6.
Diniz PP Maggi RG Schwartz DS Cadenas MB Bradley JM Hegarty B Breitschwerdt EB 《Veterinary research》2007,38(5):697-710
The purpose of this study was to determine the serological and molecular prevalence of Bartonella spp. infection in a sick dog population from Brazil. At the S?o Paulo State University Veterinary Teaching Hospital in Botucatu, 198 consecutive dogs with clinicopathological abnormalities consistent with tick-borne infections were sampled. Antibodies to Bartonella henselae and Bartonella vinsonii subsp. berkhoffii were detected in 2.0% (4/197) and 1.5% (3/197) of the dogs, respectively. Using 16S-23S rRNA intergenic transcribed spacer (ITS) primers, Bartonella DNA was amplified from only 1/198 blood samples. Bartonella seroreactive and/or PCR positive blood samples (n=8) were inoculated into a liquid pre-enrichment growth medium (BAPGM) and subsequently sub-inoculated onto BAPGM/blood-agar plates. PCR targeting the ITS region, pap31 and rpoB genes amplified B. henselae from the blood and/or isolates of the PCR positive dog (ITS: DQ346666; pap31 gene: DQ351240; rpoB: EF196806). B. henselae and B. vinsonii subsp. berkhoffii (pap31: DQ906160; rpoB: EF196805) co-infection was found in one of the B. vinsonii subsp. berkhoffii seroreactive dogs. We conclude that dogs in this study population were infrequently exposed to or infected with a Bartonella species. The B. henselae and B. vinsonii subsp. berkhoffii strains identified in this study are genetically similar to strains isolated from septicemic cats, dogs, coyotes and human beings from other parts of the world. To our knowledge, these isolates provide the first Brazilian DNA sequences from these Bartonella species and the first evidence of Bartonella co-infection in dogs. 相似文献
7.
8.
Microbially derived off-flavor is a major problem in apple juice production as it diminishes the sensory quality of the juice significantly. Fifteen relevant off-flavor compounds that are formed in apple juice, for example, by the strains Alicyclobacillus acidoterrestris and Actinomycetes (Streptomyces ssp.) were investigated with respect to their sensory relevance. The odor threshold values (i.e., detection and recognition values) were determined for all compounds in the matrix apple juice. Odor threshold values for fenchyl alcohol are reported here for the first time. The obtained values were set in relation to the limits of detection and quantification of a previously published GC-MS method. Eight tainted apple juice samples were analyzed for the presence of the 2 strains and the 15 off-flavor compounds. Both strains could be found in the samples; the presence of Streptomyces ssp. as spoilage bacteria of apple juice is reported for the first time. In samples with distinct off-flavor, 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 1-octen-3-ol, fenchyl alcohol, geosmin, and guaiacol as well as 2,6-dibromophenol were determined in concentrations higher than the detection threshold. 相似文献
9.
Sabine Augustin Jan Evers Hans-Peter Dietrich Johannes Eichhorn Thomas Haussmann Regina Icke Ansgar Isenberg Wolfgang Lux Monica Musio Hans Pretzsch Winfried Riek Thomas Rötzer Bernd Schultze Andreas Schulze Jörg Schröder Walter Seidling Nicole Wellbrock Klaus von Wilpert Barbara Wolff 《European Journal of Forest Research》2005,124(4):251-260
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and
other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system
in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse
effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary
air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring
was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and
feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal
Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives
of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification
and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading
to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected
level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis
(crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative,
as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the
extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.
相似文献
Sabine AugustinEmail: |
10.
Effects of N, NP, and NPKS fertilizers applied to four-year old hybrid poplar plantations 总被引:1,自引:0,他引:1
Mineral fertilizers were applied to adjacent plantations of 2, 4-year old, hybrid poplars: clone 27 (Northwest, P. deltoides × P. balsamifera) and 794 (Brooks, P. deltoides × P. × petrowskyana), in north eastern Alberta. Fertilization was done in May 2003 to see whether growth rates could be increased and rotations
shortened. Three fertilizers (N, NP and NPKS + Cu + Zn) were applied at each of three rates (supplying N at 0, 100 and 200 kg ha−1) in a factorial randomized block design to the two separate plantations. Fertilization with 200 kg ha−1 N and 100 kg ha−1 P increased volume growth of clone 27 by 1 m3 ha−1 year−1 over 2 years. Clone 794 showed no volume response to fertilization, but produced 8.7 m3 ha−1 more than clone 27. Leaf area, dry mass and nutrient concentrations of both clones increased in the first year after fertilization,
showing that fertilizer uptake occurred. Decrease in leaf size between 2003 and 2004 was affected by fertilizer level in clone
794. There were differences between some nutrient concentrations in the soils occupied by the two clones, and clone 794 had
higher leaf concentrations of N, K, Ca, S, Mn, Zn, B and Mo than clone 27. Fertilization of 4-year old plantations of either
clone was unwarranted, and planting clone 794 would be likely to provide greater yield than planting and fertilizing clone
27. 相似文献