首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18656篇
  免费   139篇
林业   3791篇
农学   1549篇
基础科学   167篇
  3269篇
综合类   818篇
农作物   2262篇
水产渔业   2063篇
畜牧兽医   1659篇
园艺   1180篇
植物保护   2037篇
  2023年   36篇
  2022年   77篇
  2021年   83篇
  2020年   103篇
  2019年   123篇
  2018年   2850篇
  2017年   2807篇
  2016年   1278篇
  2015年   146篇
  2014年   132篇
  2013年   231篇
  2012年   949篇
  2011年   2248篇
  2010年   2194篇
  2009年   1328篇
  2008年   1401篇
  2007年   1657篇
  2006年   112篇
  2005年   155篇
  2004年   151篇
  2003年   192篇
  2002年   90篇
  2001年   45篇
  2000年   74篇
  1999年   26篇
  1998年   20篇
  1997年   15篇
  1996年   11篇
  1995年   8篇
  1994年   7篇
  1993年   18篇
  1992年   18篇
  1991年   14篇
  1990年   14篇
  1989年   15篇
  1988年   22篇
  1987年   13篇
  1986年   7篇
  1985年   6篇
  1984年   7篇
  1983年   8篇
  1981年   9篇
  1979年   14篇
  1977年   6篇
  1974年   8篇
  1973年   8篇
  1971年   7篇
  1969年   7篇
  1968年   8篇
  1967年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Tropical Animal Health and Production - The rise of antibiotic resistance and its global outreach has recently become a subject of increasing importance in veterinary research with an objective to...  相似文献   
102.
Dynamics of salmonella infection in fryer roaster turkeys   总被引:2,自引:0,他引:2  
  相似文献   
103.
In northern Pakistan, many farming communities rely on domestic yak (Bos grunniens) as a principle source of income. A 2006 participatory disease surveillance report from this region indicated that foot-and-mouth disease (FMD) is the most prevalent annual disease of yak. Our objectives of this study were to determine exposure levels of yak to FMD virus; implement a vaccination program based on current, regional FMD virus serotypes and subtypes; and quantify immune responses following vaccination. Blood samples were used to determine pre-vaccination exposure of animals to FMD virus by antibody presence to non-structural proteins of FMD virus using a 3-ABC trapping indirect ELISA. Vaccine used consisted of FMD serotypes ‘O’ (PanAsia-2), ‘A’ (Iran-05), and ‘Asia-1’ (Shamir), but changed later during the study to match newly circulating viruses in the country (‘O’-PanAsia-2; ‘A’-Turk-06 and Asia-1-Sindh-08). Three hundred sixty-three blood samples were tested from selected villages to determine pre-vaccination FMD virus exposure in yak with an average of 37.7%. Immune responses from initial vaccination and booster dose 30 days later showed clear protective levels (as mean percent inhibition) of antibodies against structural proteins of serotypes ‘O,’ ‘A,’ and ‘Asia-1.’ These responses remained above threshold positive level even at day 210 following initial vaccination. Results of sero-surveillance and anecdotal information of repeated FMD outbreaks demonstrate the persistence of FMD virus of yak in northern Pakistan. Laboratory results and field observations clearly indicated that yak can be protected against FMD with a good quality vaccine with FMD serotype(s) matching current, regionally circulating FMD virus.  相似文献   
104.
Melanocortin 3 and 4 receptors (MC3R and MC4R) are known as the main receptors for melanocortin-induced hypophagia in mammalian and poultry. Also, central glutamatergic system has mediatory role on function of the melanocortin system in some brain areas. So, the aim of the current study was to determine the role of MC3/MC4 receptors agonist on food intake and its interaction with glutamatergic in 3-h food-deprived (FD3) neonatal broilers. In experiment 1, chickens were intracerebroventricular (ICV) injected with control solution, MTII (MC3/MC4 receptors agonist; 2.45, 4.8 and 9.8 pmol). In experiment 2, control solution, SHU9119 (MC3/MC4 receptors antagonist; 0.5, 1 and 2 nmol) were ICV injected. In experiment 3, birds ICV injected with control solution, SHU9119 (0.5 nmol), MTII (9.8 pmol) and co-injection of the SHU9119 + MTII. Experiments 4–8 were similar to experiment 3, except birds injected with MK-801 (NMDA glutamate receptors antagonist, 15 nmol), CNQX (AMPA glutamate receptors antagonist; 390 nmol), AIDA (mGLUR1 glutamate receptors antagonist; 2 nmol), LY341495 (mGLUR2 glutamate receptors antagonist; 150 nmol) and UBP1112 (mGLUR3 glutamate receptors antagonist; 2 nmol) instead of SHU9119. Then, cumulative food intake was recorded until 120 min after injection. According to the results, dose dependent hypophagia observed after ICV injection of the MTII (p < 0.05). ICV injection of SHU9119 significantly increased food intake in birds (p < 0.05). Co-injection of SHU9119 + MTII significantly inhibited MTII- induced hypophagia in neonatal chicks (p < 0.05). In addition, hypophagia- induced by MTII was significantly attenuated with co-injection of MTII + MK-801(p < 0.05). These results suggested MC3 and MC4 receptors have inhibitory role on food intake and this effect is probably mediated by NMDA glutamate receptors in neonatal chickens.  相似文献   
105.
A polymerase chain reaction (PCR) assay targeting the hyaC-hyaD gene was developed and used to identify strains of Pasteurella multocida belonging to serogroup-A. A set of serogroup-specific-PCR primers amplified a 564 bp product from genomic DNA prepared from bacterial cells or directly from bacterial colonies. This method detected as low as 10 ng of bacterial DNA and had a specificity of 100% for P. multocida serogroup-A. A nested PCR method yielded a single 374 bp product. All fifty isolates were also shown to be identical by restriction fragment length polymorphism (RFLP) analysis of the PCR products after digestion with BglII.  相似文献   
106.
Identification and estimation of the prevalence of Pasteurella multocida organisms in different animal and avian species in India during November 2000 to July 2003 was carried out. Out of 418 samples collected from different outbreaks suspected to be caused by P. multocida, a total of 206 bacterial cultures were identified as P. multocida on the basis of cultural, morphological and biochemical characteristics. All the 206 cultures were isolated from different domestic animal species (cattle, buffalo, sheep, goat, pig and rabbit), avian species (chicken, duck, quail, turkey, goose) and wild animals such as leopard and deer. Serotyping of P. multocida cultures revealed the presence of various serotypes (A:1, A:3, A:1,3, A:4, B:2, D:1 and -:1) among the livestock population. P. multocida polymerase chain reaction (PCR) assay applied on different forms of bacterial cultures (bacterial culture lysate, direct bacterial colony and mixed bacterial culture lysate) yielded an amplified product of approximately 460 bp specific for P. multocida. The results of PCR assay correlated well with conventional methods of identification. The present investigation revealed the presence of varied serotypes among livestock and PCR assay was found to be useful for rapid, sensitive and specific diagnosis of pasteurellosis in animals and avian species.  相似文献   
107.
Two experiments were undertaken to select the efficient method applied for goat estrous synchronization. In experiment 1, a total of 120 does (Capra hircus) were divided into five groups with a randomized block design, and the does of treatment 1 were synchronized by intravaginal sponges impregnated with 30 mg Levonorgestrel inserted for 10 days. Does of treatments 2, 3, and 4 were treated with further injection of 25 IU follicle-stimulating hormone (FSH), 0.05 mg prostaglandin F2 alpha (PGF), and 25 IU FSH + 0.05 mg PGF at sponge withdrawal, respectively. The does in the control group (n = 40) without estrous synchronization treatment and natural estrous does were observed. In experiment 2, a total of 140 does in five goat farms in breeding and non-breeding seasons were treated with the selective efficient procedure. The results presented that all the employed treatments were capable of inducing and synchronizing estrous goats. According to estrous response and economy, the use of intravaginal sponges impregnated with 30 mg Levonorgestrel and 0.05 mg PGF (treatment 3) is the first choice for estrous synchronization, and 95.0% of synchronized does demonstrated estrus, which was significantly higher than that of treatment 1 (P < 0.05) and control group (P < 0.01). The percentages of ovulating of treatments 3 and 4 were the same (95.0%), which were significantly higher than that of treatment 1 (P < 0.01). The ovulation rates among different groups were not significant (P > 0.05). When the selective procedure was applied to five goat farms, 85.7% (120/140) of does demonstrated estrus, and the kidding percentage, litter size, and prolificacy rate were 53.6%, 0.95, and 177%, respectively.  相似文献   
108.
This work discusses some of the important considerations of wild ostrich evolution, behaviour and ecology, as items included in ostrich production. In the process considerable research was conducted by collating information from peer-reviewed papers; textbooks; manuals; and PubMed and Agricola searches. Selected areas reviewed included activity of ostriches; feeding and water needs; sexual maturity; egg laying and natural incubation; selected physiological parameters; and predation. There is an immediate and urgent need to conserve and protect the rapidly declining populations of wild ostriches with the committed involvement of governments and funding bodies.  相似文献   
109.
A study was conducted to evaluate the macro and trace mineral contents of ten enset varieties collected from Sidama zone of southern Ethiopia. Samples of leaf lamina, leaf midrib, pseudostem and corm were taken from ten enset varieties at the age of 5 to 6 years during the main rainy season. The dry weight of each variety and fraction were also determined. Mineral contents in fractions of different enset varieties were analysed and compared with nutrient requirements of ruminants. The contribution of different enset fractions to the total dry weight was variable (P < 0.05), the highest being from pseudostem and the lowest from leaf lamina. There were varietal differences (P < 0.05) in macro and trace mineral content in different fractions except phosphorus (P) content of leaf lamina. Most enset fractions were rich sources of major minerals such as P, potassium (K), calcium (Ca) (except corm) and magnesium (Mg). Sodium (Na) content was very low. Most fractions were rich in iron (Fe) and manganese (Mn), but deficient in copper (Cu), except leaf lamina. Zinc (Zn) content was high in corm, but low in other fractions. This account of the macro and trace mineral content of different enset varieties and fractions could help in strategic supplementation intended to alleviate mineral deficiencies.  相似文献   
110.
An ultrastructural study was performed on chloride cells of euryhaline R.r.Caspicus of south of Caspian Sea. The chloride cells are distributed in the interlamellar region of filaments. They are oval to elongated form with an apical positioned nucleus, expanded tubular system and heteromorphic mitochondria. These cells are surrounded by pavement cell and accessory cell. A small and depressed surface formed by pavement cells is in contact with the aquatic milieu. There is also channel system in accessory cells. One of the typical features was the important changes in microtubules and mitochondria of chloride cells in some fishes. Swelling and rupture of cristae and degeneration of microtubules were from these changes.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号