全文获取类型
收费全文 | 375篇 |
免费 | 40篇 |
专业分类
林业 | 16篇 |
农学 | 51篇 |
基础科学 | 2篇 |
68篇 | |
综合类 | 33篇 |
农作物 | 18篇 |
水产渔业 | 34篇 |
畜牧兽医 | 166篇 |
园艺 | 5篇 |
植物保护 | 22篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 29篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有415条查询结果,搜索用时 0 毫秒
71.
S Backhaus SV Pereverzev A Loshak JC Davis RE Packard 《Science (New York, N.Y.)》1997,278(5342):1435-1438
Direct measurements of the current-phase relation, I versus Deltaphi, for a weak link coupling two reservoirs of B-phase superfluid helium-3 (3He-B) were made over a wide range of temperatures. The weak link consists of a square array of 100-nanometer-diameter apertures. For temperatures T such that T/Tc >/= 0.6 (where Tc is the superfluid transition temperature), I approximately sin(Deltaphi). At lower temperatures, I(Deltaphi) approaches a straight line. Several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, including direct observation of quantum oscillations and continuous knowledge of Deltaphi, were also observed. 相似文献
72.
Antioxidant and anti‐inflammatory activities of Pinus radiata bark extract in salmonid cell lines 下载免费PDF全文
Allisson Astuya Javiera Ziehe Alejandra Rivera Sebastián Ortiz Viviana Ulloa Marlene Roeckel Estrella Aspé Katherina Fernández 《Aquaculture Research》2017,48(7):3568-3578
A fish meal supply shortage is limiting aquaculture development. Currently, plant‐based proteins, such as soya bean meal, are being used as an alternative protein source, despite that such a diet can adversely affect fish, such as by inducing an inflammatory response. A possible solution is to include dietary additives in farm diets to counteract negative effects. One such solution originates from pine bark extracts, which present bioactive properties. In this study, the antioxidant and anti‐inflammatory properties of Pinus radiata bark extracts were evaluated for the first time in a salmonid cell line. This extract chemically demonstrated antioxidant activity through 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH = 58.4 ± 1.1%) and ferric ion reducing antioxidant power (FRAP = 575 ± 17 mgEqFe(II)·g extract?1) assays. Additionally, the extract showed high flavonoid and phenolic compound contents. Up to 100 mg mL?1, the P. radiata extract showed no cytotoxicity in the CHSE‐214 salmonid embryo cell line. Moreover, the antioxidant activity of the extract (50 μg mL?1) was evaluated by a dichlorofluorescein (DCFH) assay in the SHK‐1 salmon cell line challenged with an oxidant stimulus (H2O2), showing 58.9% activity. The extract also protected DNA from oxidative damage, as observed through a comet assay. When assessing anti‐inflammatory properties in an in vitro inflammation model, the extract significantly reduced the relative expression of the pro‐inflammatory cytokines interleukin‐1β (IL‐1β), tumour necrosis factor‐α (TNF‐α) and interleukin‐8 (IL‐8) and of the inducible cyclooxygenase‐2 (COX‐2) enzyme. These results suggest a potential application of P. radiata bark extract in functional foods in aquaculture. 相似文献
73.
Ocampo Espinoza V Vázquez JE Aguilar MD Ortiz MA Alarcón GJ Rodríguez SD 《Veterinary microbiology》2006,114(1-2):34-40
In Mexico, there are no commercial alternatives for the immunoprophylaxis of bovine Anaplasmosis, a disease responsible for great economic losses. Blood derived Anaplasma marginale used for immunizing susceptible cattle has shown promising results for homologous protection and controversial results against unrelated strains. The present study examined, under controlled conditions, the cross-protective potential of an immunogen composed of blood derived A. marginale of three strains against challenge with strains not included in the immunogens. Groups 1 and 2 were immunized with blood derived Anaplasma from strains Mexico, Morelos and Yucatan, group 4 with strains Morelos, Veracruz and Yucatan, two more groups (2 and 5) of equal conditions were inoculated with an adjuvant alone. Groups 1, 4 and 5 were challenged with Mexico strain; groups 2 and 3 were challenge-inoculated with strain Veracruz; groups 3 and 5 with strains Veracruz and Mexico as controls. Only animals in group 1, immunized and challenged with strain Mexico showed adequate protection. Both groups challenged with strains not included in the immunogens developed poor protection, while all the controls had to be treated to prevent death. 相似文献
74.
María Valeria Romagnoli Juan Pablo A. Ortiz Gerardo D. Cervigni Cintia Heisterborg Rubén H. Vallejos 《Euphytica》1996,90(1):89-93
Summary Somatic embryos of genotype R11 of the alfalfa variety Pampeana were produced from embryogenic calli derived from leaf sections. They were induced by an auxin shock and its development was attempted on six different media. The best condition for somatic embryo production was inducing callus on MS medium plus 10 M 2,4-D and 4,6 M KIN and transferring them, after the auxin shock, to MS with 10–20 mM NH4
+ and 30 mM proline. More than 500 somatic embryos per plate were produced. Embryos were grown to plants on MS or half strength MS media and all regenerated plants resembled the original R11 genotype. This technique could be useful in alfalfa Pampeana improvement using genetic modification. 相似文献
75.
María Iniesta‐Cuerda Irene Snchez‐Ajofrín Olga García‐lvarez Alicia Martín‐Maestro Patricia Peris‐Frau Jos Antonio Ortiz María Rocío Fernndez‐Santos Jos Julin Garde Ana J. Soler 《Reproduction in domestic animals》2019,54(Z4):69-71
Nowadays, the use of foetal calf serum (FCS) during in vitro embryo culture is very controversial. Whilst some authors have encouraged its use, others reject it because of its harmful effects. Although in vitro embryo production in red deer is a promising assisted reproductive technique, it is still in its infancy and a great effort is needed to update the protocols used. The aim of this study was to assess whether FCS supplementation in red deer embryo culture medium is necessary to produce blastocyst and, if so, when is the best time to add it in terms of blastocyst production and quality. In vitro blastocysts were cultured with FCS added at 24, 48 or 96 hours post‐insemination (hpi). In addition, a treatment without FCS was used as control. Six hundred and ninety‐four cumulus–oocyte complexes were collected for in vitro fertilization. Cleavage rate was examined at 48 hpi, and blastocyst yield was recorded on days 6, 7 and 8. FCS had no influence on cleavage and blastocyst rate for any of the treatments studied. However, the number of cells was higher (p = .025) in those blastocysts cultured with FCS from 48 hpi compared with FCS‐free culture media (93.88 ± 7.76 vs. 54.11 ± 8.36). In conclusion, the addition of FCS to the embryo culture medium at 48 hpi improves the quality of red deer blastocyst, although it does not affect the percentage of embryos obtained. 相似文献
76.
Objective To assess the innate resistance of naive Bos taurus, Bos taurus cross Bos indicus and Bos indicus cattle to virulent Babesia bovis, B bigemina and Anaplasma marginale parasites. Design Groups of 10, pure B indicus, fi B indicus cross,/B indicus cross and pure B taurus steers were infected with virulent B bovis, B bigemina and A marginale parasites. Procedure Sequential infections were carried out by intravenous inoculation of infected blood containing 1 times 108 parasites of B bovis, followed by B bigemina and then A marginale. To assess resistance, measurements were made of parasitaemia, rectal temperature, packed cell volume and the number within a group requiring chemotherapy to control infection. There was a recovery period between each infection. Results Infection with B bovis showed that pure B indicus steers were significantly more resistant to B bovis infection than the other groups, with none of this group requiring treatment. There was no significant difference between fi B indicus cross and/B indicus cross with 30% and 20%, respectively, of steers in these groups requiring treatment. The pure B taurus steers were significantly more affected then those in the other three groups with 80% requiring treatment. Infections of B bigemina produced a mild response in comparison to that of B bovis and none of the steers required treatment. However, the pure B taurus group was significantly more affected than the other three groups for all other measurements. After the A marginale infection, B indicus steers were moderately affected with 50% requiring treatment, whereas 70% of the fi B indicus group, 80% of the /B indicus cross group and 100% of the pure B taurus group required treatment. Conclusions All breeds of cattle, ranging from pure B indicus to pure B taurus may be at risk of severe disease if exposed to virulent A marginale. The results confirm that pure B indicus cattle are relatively resistant to B bovis, but there could be a significant risk of severe mortalities if cross-bred herds are exposed to virulent infection. 相似文献
77.
Salimi-Bejestani MR McGarry JW Felstead S Ortiz P Akca A Williams DJ 《Research in veterinary science》2005,78(2):177-181
An ELISA was developed for the detection of Fasciola hepatica antibody in serum of cattle. The assay was applied to sera from 258 naturally infected cattle, 256 non-infected cattle and six calves experimentally infected with F. hepatica. The diagnostic sensitivity and specificity of the ELISA test was 98% (95% confidence intervals, 96-100%) and 96% (95% confidence intervals, 93-98%) respectively at a cut-off value of 15% positivity. The results using sera from the experimentally infected calves showed that antibodies were first detected 2-4 weeks after infection. The ELISA test was also compared to the commercially available Bio-X bovine F. hepatica ELISA kit. A subset of 39 positive sera and 47 negative sera were selected from the samples used to evaluate the in-house test. The results indicated that the agreement between the two tests was almost perfect (k statistic=0.82). 相似文献
78.
Modeling the Exchanges of Energy, Water, and Carbon Between Continents and the Atmosphere 总被引:19,自引:0,他引:19
PJ Sellers RE Dickinson DA Randall AK Betts FG Hall JA Berry GJ Collatz AS Denning HA Mooney CA Nobre N Sato CB Field A Henderson-Sellers 《Science (New York, N.Y.)》1997,275(5299):502-509
Atmospheric general circulation models used for climate simulation and weather forecasting require the fluxes of radiation, heat, water vapor, and momentum across the land-atmosphere interface to be specified. These fluxes are calculated by submodels called land surface parameterizations. Over the last 20 years, these parameterizations have evolved from simple, unrealistic schemes into credible representations of the global soil-vegetation-atmosphere transfer system as advances in plant physiological and hydrological research, advances in satellite data interpretation, and the results of large-scale field experiments have been exploited. Some modern schemes incorporate biogeochemical and ecological knowledge and, when coupled with advanced climate and ocean models, will be capable of modeling the biological and physical responses of the Earth system to global change, for example, increasing atmospheric carbon dioxide. 相似文献
79.
Evaluation of FDR diploid and tetraploid parents in potato under two different day-length environments 总被引:1,自引:0,他引:1
Five tetraploid clones of potato were crossed to each of eight diploid first division restitution (FDR) 2n pollen producers and four tetraploid males using a line × tester mating design. A total of 59 families were obtained and evaluated under long days at Rhinelander (USA). A subset of 49 families were grown under short days at four Peruvian locations. Tuber yield (kg per plant) of 4x-2x families was similar to, or greater than, that of 4x-4x families in short day environments. The diploid clones had breeding values greater than or equal to those of the tetraploid clones. Only families derived from FDR 2n pollinators combined high tuber yield with stability and high dry matter content. Reciprocal recurrent selection would be the best breeding scheme, in which the diploids are testers of the tetraploids and vice-versa. Intra-population improvement could be achieved through phenotypic recurrent selection. The best materials from both breeding pools could then be crossed to produce tetraploid hybrids through unilateral sexual polyploidization (4x-2x crosses). 相似文献
80.
Carlos A. Cairo Juliana Stein Luciana Delgado Santiago Bortolotti Sebastián A. Guelman Juan Pablo A. Ortiz Eligio N. Morandi 《Euphytica》2002,124(3):387-395
Soybean cultivars carrying the `long juvenile trait' show a delayed flowering response under short day conditions. The incorporation
of this character into genotypes of agronomic interest may allow a broader range of sowing dates and latitudes for a single
cultivar adaptation. The objective of this work was to identify molecular markers linked to the juvenile locus in soybean.
Experiments were carried out using two pairs of near isogenic lines(NILs) differing in the presence of the long juvenile trait,
and RAPD markers. Four hundred primers were first screened to find polymorphism associated with the trait. Additional differences
between NILs were sought by digesting the genomic DNA with five restriction enzymes. Polymorphic fragments detected between
NILs were tested for linkage to the juvenile locus in the corresponding F2 segregating populations. Marker bc357-HaeIII was linked (χ2L = 46.316) to the juvenile locus with an estimated recombination frequency of 0.13 ± 0.03in one of the genetic backgrounds
studied. The fragment was cloned, sequenced and converted into a SCAR marker. Moreover,bc357-HaeIII was used as RFLP probe. Both, SCAR and RFLP generated markers linked to the juvenile locus in the two genetic backgrounds
analysed. Results presented in this work can be utilised for both, the localisation of the gene associated with the character
and for tagging the juvenile trait in soybean breeding programs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献