全文获取类型
收费全文 | 6822篇 |
免费 | 340篇 |
国内免费 | 806篇 |
专业分类
林业 | 909篇 |
农学 | 1136篇 |
基础科学 | 529篇 |
1214篇 | |
综合类 | 1896篇 |
农作物 | 407篇 |
水产渔业 | 314篇 |
畜牧兽医 | 833篇 |
园艺 | 218篇 |
植物保护 | 512篇 |
出版年
2024年 | 15篇 |
2023年 | 39篇 |
2022年 | 170篇 |
2021年 | 265篇 |
2020年 | 245篇 |
2019年 | 247篇 |
2018年 | 167篇 |
2017年 | 224篇 |
2016年 | 209篇 |
2015年 | 290篇 |
2014年 | 268篇 |
2013年 | 345篇 |
2012年 | 420篇 |
2011年 | 436篇 |
2010年 | 416篇 |
2009年 | 421篇 |
2008年 | 364篇 |
2007年 | 362篇 |
2006年 | 420篇 |
2005年 | 410篇 |
2004年 | 201篇 |
2003年 | 146篇 |
2002年 | 116篇 |
2001年 | 134篇 |
2000年 | 151篇 |
1999年 | 212篇 |
1998年 | 167篇 |
1997年 | 153篇 |
1996年 | 128篇 |
1995年 | 115篇 |
1994年 | 106篇 |
1993年 | 107篇 |
1992年 | 105篇 |
1991年 | 70篇 |
1990年 | 79篇 |
1989年 | 74篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 2篇 |
排序方式: 共有7968条查询结果,搜索用时 15 毫秒
861.
野生大豆病毒病的初步鉴定 总被引:2,自引:0,他引:2
我国野生大豆资源丰富,病毒病是主要病害,发病早,危害重,又是栽培大豆病毒病的感染来源。野生大豆病毒病的发病症状类型较多,其毒原种类尚不清楚。 相似文献
862.
Duck enteritis virus (DEV) is a herpesvirus that causes an acute, contagious, and fatal disease. In the present article, we introduce a quantitative real-time polymerase chain reaction (PCR) assay for DEV DNA using TaqMan technology and a two-step protocol. It was confirmed to be rapid, sensitive, and specific for DEV detection. The primers and probe were designed and directed to the DNA polymerase gene of DEV. The method will provide a valuable tool for rapid laboratory diagnosis of DEV infection. By virtue of its high-throughput format and its ability to accurately quantify the viral DNA, the method may be useful for large epidemiological surveys and clarification of pathogenesis, such as latency and reactivation of the virus. 相似文献
863.
864.
Survey of intestinal parasites in pigs from intensive farms in Guangdong Province, People's Republic of China 总被引:2,自引:0,他引:2
Weng YB Hu YJ Li Y Li BS Lin RQ Xie DH Gasser RB Zhu XQ 《Veterinary parasitology》2005,127(3-4):333-336
The prevalence of intestinal parasites was investigated in intensive pig farms in Guangdong Province, China between July 2000 and July 2002. Faecal samples from 3636 pigs (both sexes and five age groups) from 38 representative intensive pig farms employing different parasite control strategies were examined for the presence of helminth ova and protozoan oocysts, cysts and/or trophozoites using standard techniques. Of the 3636 pigs sampled, 209 (5.7%) were infected with Trichuris suis, 189 (5.2%) with Ascaris, 91 (2.5%) with Oesophagostomum spp., 905 (24.9%) with coccidia (Eimeria spp. and/or Isospora suis) and 1716 (47.2%) with Balantidium coli. These infected pigs were mainly from farms without a strategic anti-parasite treatment regime. Concurrent infection of multiple parasites was common, and T. suis was the most common nematode infecting breeding, young and mature pigs. The results of the present investigation provide relevant 'base-line' data for assessing the effectiveness of control strategies against intestinal parasitism in intensively raised pigs in Guangdong Province, China. 相似文献
865.
866.
K P Nephew S Xie D M Broermann-Ridder K E McClure W F Pope 《Journal of animal science》1992,70(6):1911-1915
Mechanisms of intrauterine migration were examined in 55 ewes. In the first experiment, corpora lutea were removed from unilaterally ovariectomized ewes on d 4 (d 0 = estrus) and pregnancy was maintained by giving exogenous progesterone. In Exp. 2, the reproductive tract was altered surgically such that embryos initially entered the uterine horn contralateral to the site of ovulation. In Exp. 3, ewes received beads of silastic polydimethylsiloxane that released either cholesterol or estradiol-17 beta in an attempt to mimic embryonic synthesis of estradiol. In the fourth experiment, unilaterally ovariectomized ewes were superovulated and spacing of embryos within the uterus was then examined. In all experiments, ewes were slaughtered on d 15 and recovery of embryos or beads from each uterine horn indicated that migration had occurred. All ewes in Exp. 1 and 2 that had two conceptuses experienced embryonic migration. Beads impregnated with estradiol migrated farther (P less than .01) than cholesterol-containing beads (27.6 +/- 4.3 vs 12.5 +/- 1.6 cm, respectively). In Exp. 4, only one conceptus had migrated into the contralateral horn in all ewes. These results demonstrated that 1) embryonic migration was not affected by local vs systemic exposure to progesterone, 2) embryos migrated into the unoccupied horn, regardless of the initial horn of entry, 3) estradiol may stimulate embryonic migration, and 4) conceptuses were not equally distributed between horns. 相似文献
867.
ABSTRACT One of the major concerns with Fusarium head blight (FHB) of barley is the potential health risks to livestock and humans through the accumulation of the mycotoxin deoxynivalenol (DON) in infected grain. To define the role of the host in DON accumulation during the early stages of disease development, we conducted a series of greenhouse experiments. We inoculated single spikelets of greenhouse-grown plants with Fusarium graminearum, moved the plants to a dew chamber, and harvested the inoculated spikelets after 72 h for DON analysis. We conducted a quantitative trait locus (QTL) analysis using a genetic mapping population, constructed with the parents Stander and Frederickson, that segregated for DON accumulation after single-spikelet inoculation in two experiments. A single QTL on chromosome 3 explained 18 and 35% of the phenotypic variation in the two experiments. To validate this QTL for DON accumulation, we used a DNA marker to select near-isogenic lines from a family from the mapping population that was segregating at this QTL. Disease symptom development was similar between the nearisogenic lines; however, the mean DON concentration of the lines homozygous for the allele from the high DON parent was 2.5-fold more than the lines homozygous for the alternate allele. A time course experiment showed that this effect on toxin accumulation was observed at 10 days post inoculation. The near-isogenic lines developed in this study should prove useful for further exploration of the role of DON in FHB. 相似文献
868.
Poultry coccidiosis is the major parasitic disease of poultry and, until now, no recombinant vaccine has been developed. Short oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs (CpG ODNs) have been shown to be effective immunoprotective agents and vaccine adjuvants in mammalian systems. Their use in poultry to protect against intracellular parasites has not been reported to date. The present work investigated the effects of CpG ODN treatment on host susceptibility to Eimeria infection in two chicken strains with different genetic background, SC and TK. The data show that CpG ODN enhanced the birds' resistance to coccidiosis in a normally susceptible chicken strain (TK), as shown by reduced oocyst shedding and improved weight gain. CpG treatment had a differential effect on body weight gains and serum antibody responses, depending on the chicken strain and ODN dose, delivery route, and backbone. This study shows for the first time that CpG ODNs could be used as immunoprotective agents in Eimeria-infected chickens to enhance resistance to the pathogen and improve performance. Future research is needed to optimize their use alone and as vaccine adjuvants that may lead to better and more efficient vaccine applications. 相似文献
869.
Babu U Dalloul RA Okamura M Lillehoj HS Xie H Raybourne RB Gaines D Heckert RA 《Veterinary immunology and immunopathology》2004,101(3-4):251-257
Our previous work showed that the cell-mediated immunity (CMI) was enhanced by live Salmonella vaccine (LV). The objective of this study was to evaluate the impact of live and killed Salmonella vaccines on Salmonella enteritidis (SE) clearance and to determine if the clearance was mediated by cell-mediated and/or humoral immunity. Chickens were first immunized at 2 weeks of age followed by a booster dose at 4 weeks, challenged with live SE 2 weeks later (6-week-old) and tested for CMI, antibody response and SE clearance 1-week post SE-challenge (7-week-old). Spleen cell proliferation induced by SE-flagella and Concanavalin A (Con A) were significantly higher and SE shedding was significantly lower in the LV group. The splenic CD3 population was significantly lower and B cells were higher in the control group compared to all the SE-challenged groups (with and without vaccination). Serum antibody to SE-flagella and envelope were significantly higher in the KV group compared to all the other groups. These results suggest that LV protects against SE infection, probably by enhancing the CMI. 相似文献
870.
Ebron VH Yang Z Seyer DJ Kozlov ME Oh J Xie H Razal J Hall LJ Ferraris JP Macdiarmid AG Baughman RH 《Science (New York, N.Y.)》2006,311(5767):1580-1583
Artificial muscles and electric motors found in autonomous robots and prosthetic limbs are typically battery-powered, which severely restricts the duration of their performance and can necessitate long inactivity during battery recharge. To help solve these problems, we demonstrated two types of artificial muscles that convert the chemical energy of high-energy-density fuels to mechanical energy. The first type stores electrical charge and uses changes in stored charge for mechanical actuation. In contrast with electrically powered electrochemical muscles, only half of the actuator cycle is electrochemical. The second type of fuel-powered muscle provides a demonstrated actuator stroke and power density comparable to those of natural skeletal muscle and generated stresses that are over a hundred times higher. 相似文献