全文获取类型
收费全文 | 2125篇 |
免费 | 146篇 |
国内免费 | 46篇 |
专业分类
林业 | 219篇 |
农学 | 119篇 |
基础科学 | 16篇 |
382篇 | |
综合类 | 254篇 |
农作物 | 140篇 |
水产渔业 | 184篇 |
畜牧兽医 | 760篇 |
园艺 | 78篇 |
植物保护 | 165篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 43篇 |
2021年 | 66篇 |
2020年 | 69篇 |
2019年 | 71篇 |
2018年 | 102篇 |
2017年 | 124篇 |
2016年 | 116篇 |
2015年 | 76篇 |
2014年 | 112篇 |
2013年 | 110篇 |
2012年 | 138篇 |
2011年 | 138篇 |
2010年 | 88篇 |
2009年 | 73篇 |
2008年 | 108篇 |
2007年 | 84篇 |
2006年 | 94篇 |
2005年 | 99篇 |
2004年 | 86篇 |
2003年 | 83篇 |
2002年 | 109篇 |
2001年 | 65篇 |
2000年 | 43篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 19篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 13篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1974年 | 3篇 |
1970年 | 7篇 |
1969年 | 3篇 |
1967年 | 7篇 |
1965年 | 6篇 |
1897年 | 2篇 |
1896年 | 2篇 |
排序方式: 共有2317条查询结果,搜索用时 15 毫秒
231.
Pigatto JA Andrade MC Laus JL Santos JM Brooks DE Guedes PM Barros PS 《Veterinary ophthalmology》2004,7(3):205-208
The objective of this study was to examine the endothelial surface morphology and to perform morphometric analysis of the corneal endothelial cells of Yacare caiman (Caiman yacare) using scanning electron microscopy. Morphometric analysis with regard to polygonality, mean cell area, cell density and coefficient of variation of mean cell area was performed. Cell areas were measured using image analysis software. The normal corneal endothelium of Yacare caiman consisted of polygonal cells of uniform size and shape with interdigitations of the cell borders. Microvilli appeared as protrusions on the cellular surface. The average cell area was 270 +/- 24 microm(2) and the endothelial cell density was 3704 +/- 324 cells/mm(2). The coefficient of variation of cell area was 0.22. This study demonstrates that the Yacare caiman corneal endothelium is similar to those described in other vertebrates. 相似文献
232.
Barrera-García VD Gougeon RD Voilley A Chassagne D 《Journal of agricultural and food chemistry》2006,54(11):3982-3989
The sorption in a model system of aroma compounds of enological interest (mixture of the eight derivatives from guaiacol, 4-ethylphenol, and whiskylactone) onto wood was investigated to assess the influence of wood on the concentration of these volatiles during the aging of wine. To evaluate the influence of the solubility of aroma compounds in sorption phenomena, this parameter was determined for each volatile compound in model wine at 10 and 25 degrees C. The solubility is significantly higher in the model wine than in water and remains constant in the range of temperatures studied, except for guaiacol and vanillin. Kinetic and equilibrium sorptions were investigated. Sorption kinetics showed that the sorption equilibrium for all aroma compounds was reached after 6-7 days. From the study of the individual sorption isotherms, two distinct kinds of sorption behavior were observed depending on the presence or not of an ethylenic para substituent conjugated to the phenyl ring. K(ww) partition coefficients between the wood and the model wine were determined, which exhibited an unusual positive variation with temperature. 相似文献
233.
234.
Tabart J Kevers C Pincemail J Defraigne JO Dommes J 《Journal of agricultural and food chemistry》2006,54(17):6271-6276
Small berries such as black currant constitute one of the important sources of potential health-promoting phytochemicals because these fruits are rich sources of compounds with high antioxidant properties. In this work, antioxidant capacities of different parts (buds, leaves, fruits) of various black currant cultivars were compared throughout the growing season with the aim to prepare extracts with high antioxidant capacity. Buds (opened, at the end of March) and leaves (in June) had a higher content in phenolics and antioxidants than fully ripened berries (in July) and the best yield (per branch) was obtained with the leaves collected in June due to their higher biomass. The differences observed among the eight cultivars tested were small. Concerning flavonols, quercetin was dominant in all organs and cultivars, myricetin varied widely among the cultivars, and kampferol was very low. 相似文献
235.
Cardoso LP Celis R Cornejo J Valim JB 《Journal of agricultural and food chemistry》2006,54(16):5968-5975
A Mg/Al layered double hydroxide (LDH) was intercalated with the anionic herbicides 2,4-D, MCPA, and picloram by using three different methodologies: (i) direct synthesis (DS), (ii) regeneration (RE), and (iii) ion exchange (IE). The resulting complexes were characterized and assayed by batch release and column leaching tests, aiming at the controlled release of these herbicides. All the tested LDH-herbicide complexes displayed similar slow herbicide release properties in water, although the IE method seemed to result in complexes with a greater fraction of herbicide in a readily available form. Apparently, the LDH-herbicide complexes released most of the active ingredient present in the complexes at the end of the batch release experiment. This was attributed to the replacement of the intercalated herbicide by carbonate and hydroxyl anions from the aqueous solution. Compared to the free herbicides, the application of the three LDH-herbicide complexes (RE) to soil columns resulted in reduction in the maximum herbicide concentration in leachates and led to the retardation of herbicide leaching through the soil. All LDH-herbicide complexes presented an herbicidal efficacy similar to that of the free (technical) herbicides. Our results indicated the potential applicability of LDHs as supports for the preparation of slow release formulations of acid herbicides such as 2,4-D, MCPA, or picloram. 相似文献
236.
237.
Mayor D Korczak BM Christensen H Bisgaard M Frey J Kuhnert P 《Veterinary microbiology》2006,116(1-3):194-201
Strains of [Actinobacillus] rossii, [Pasteurella] mairii and [Pasteurella] aerogenes can be isolated from abortion in swine. The RTX toxin Pax has previously been found only in those [P.] aerogenes strains isolated from abortion. Nothing is known about RTX toxins in field isolates of the other two species. To gain insight into the distribution of selected RTX toxin genes and their association with abortion, PCR screening for the pax, apxII and apxIII operons on 21 [A.] rossii and seven [P.] mairii isolates was done. Since species can be phenotypically misidentified, the study was backed up by a phylogenetic analysis of all strains based on 16S rRNA, rpoB and infB genes. The pax gene was detected in all [P.] mairii but not in [A.] rossii strains. No apx genes were found in [P.] mairii but different gene combinations for apx were detected in [A.] rossii strains. Most of these strains were positive for apxIII, either alone or in combination with apxII. Whereas pax was found to be associated to strains from abortion no such indication could be found with apx in [A.] rossii strains. Phylogenetically [A.] rossii strains formed a heterogeneous cluster separated from Actinobacillus sensu stricto. [P.] mairii strains clustered with [P.] aerogenes but forming a separate branch. The fact that [P.] aerogenes, [P.] mairii and [A.] rossii can phylogenetically clearly be identified and might contain distinct RTX toxin genes allows their proper diagnosis and will further help to investigate their role as pathogens. 相似文献
238.
239.
The intestinal protozoan parasite Giardia duodenalis (Lambl, 1859) Kofoid & Christiansen, 1915 [syn. Giardia intestinalis and Giardia lamblia] has emerged as a widespread enteric pathogen in humans and domestic animals. In recent years, G. duodenalis has been found in cattle worldwide and longitudinal studies have reported cumulative prevalence of 100% in some herds. In the present study, we determined the prevalence and genetic characterisation of G. duodenalis in 200 dairy cattle from 10 dairy farms in S?o Paulo state, Brazil. All faecal specimens were screened for the presence of G. duodenalis using microscopy examination, enzyme immunoassay (EIA) and polymerase chain reaction (PCR). DNA was extracted from faecal samples and G. duodenalis were identified by amplification of the small subunit ribosomal (SSU-rDNA) and glutamate dehydrogenase (GDH) genes followed by restriction fragment length polymorphism (RFLP) or sequencing analysis. Giardia was identified in eight farm locations (80% prevalence). Overall, 15/200 (7.5%) animals were positive for infection, only one of which was a cow. Giardia duodenalis genotype E was present in 14 of the animals tested. Zoonotic genotype AI was present in one positive sample. Genotype E and genotype A represented 93% and 7% of G. duodenalis infections, respectively. This study demonstrates that G. duodenalis infection was prevalent in dairy calves in S?o Paulo state and that the non-zoonotic genotype E predominates in cattle in this region. Nevertheless, calves naturally infected in Brazil can shed Giardia cysts that can potentially infect humans, and thus, they may represent a public health risk. 相似文献
240.
Kaouane N Porte Y Vallée M Brayda-Bruno L Mons N Calandreau L Marighetto A Piazza PV Desmedt A 《Science (New York, N.Y.)》2012,335(6075):1510-1513
Posttraumatic stress disorder (PTSD) is characterized by a hypermnesia of the trauma and by a memory impairment that decreases the ability to restrict fear to the appropriate context. Infusion of glucocorticoids in the hippocampus after fear conditioning induces PTSD-like memory impairments and an altered pattern of neural activation in the hippocampal-amygdalar circuit. Mice become unable to identify the context as the correct predictor of the threat and show fear responses to a discrete cue not predicting the threat in normal conditions. These data demonstrate PTSD-like memory impairments in rodents and identify a potential pathophysiological mechanism of this condition. 相似文献