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   5494篇
  免费   326篇
  国内免费   4篇
林业   274篇
农学   257篇
基础科学   10篇
  1039篇
综合类   621篇
农作物   639篇
水产渔业   437篇
畜牧兽医   2133篇
园艺   77篇
植物保护   337篇
  2023年   28篇
  2022年   89篇
  2021年   126篇
  2020年   101篇
  2019年   113篇
  2018年   150篇
  2017年   164篇
  2016年   188篇
  2015年   170篇
  2014年   212篇
  2013年   294篇
  2012年   364篇
  2011年   431篇
  2010年   231篇
  2009年   227篇
  2008年   331篇
  2007年   319篇
  2006年   275篇
  2005年   256篇
  2004年   241篇
  2003年   198篇
  2002年   213篇
  2001年   151篇
  2000年   128篇
  1999年   79篇
  1998年   32篇
  1997年   18篇
  1996年   20篇
  1995年   21篇
  1993年   21篇
  1992年   28篇
  1991年   27篇
  1990年   33篇
  1989年   37篇
  1988年   31篇
  1987年   40篇
  1986年   18篇
  1985年   33篇
  1984年   23篇
  1983年   27篇
  1981年   19篇
  1980年   15篇
  1978年   21篇
  1977年   19篇
  1976年   28篇
  1975年   14篇
  1974年   20篇
  1973年   22篇
  1972年   22篇
  1971年   15篇
排序方式: 共有5824条查询结果,搜索用时 15 毫秒
31.
32.
Disease resistance mediated by the resistance gene Xa21 is developmentally controlled in rice. We examined the relationship between Pathogenesis Related (PR) defense gene expression and Xa21-mediated developmental disease resistance induced by Xanthomonas oryzae pv. oryzae (Xoo). OsPR1a, OsPR1b, and OsPR1c genes were cloned and their induction was analyzed, in addition to the OsPR10a gene, at the juvenile and adult stages in response to a wildtype Xoo strain that induces a resistance response (incompatible interaction) and an isogenic mutant Xoo strain that does not (compatible interaction). We found that the adult stage leaves are more competent to express these OsPR1 genes and that the Xa21 locus is required for the highest levels of induction.  相似文献   
33.
34.
Background: Gut is a crucial organ for the host’s defense system due to its filtering action of the intestinal membrane from hazardous foreign substances. One strategy to strengthen the gut epithelial barrier function is to upregulate beneficial microflora populations and their metabolites. Sophorolipid(SPL), which is a glycolipid biosurfactant, could increase beneficial microflora and decrease pathogenic bacteria in the gastrointestinal tract.Therefore, herein, we conducted an experiment with b...  相似文献   
35.
The occurrence of Bovine Spongiform Encephalopathy (BSE, so called mad cow diseases) that was first identified in England in 1986 was considered as being limited to only European countries, including England. However, the outbreak in Asia as well as North America since 2001 has amplified the fear that there isn't any nation in the world that is a safe area. In order to assess the risk of BSE outbreak in each country, the Office International des Epizooties (OIE) and EU have respectively established criteria, where OIE has set 5 levels and EU has set 4 levels. The Scientific Steering Committee (SSC) of the European Commission conducted a Geographical BSE Risk(GBR) assessment for 64 nations, such as the United States, etc., as of April 29, 2003. However, as of July 1, 2005, the duty of GBR assessment is expected to be transferred to a newly established body called EFSA (European Food Safety Authority, located in Parma, Italy). As Korea has not undergone a GBR assessment up to now, this study analyzed the risk of BSE outbreak in Korea by reviewing BSE prevention measures, etc., that have been put in place. This study shall be a barometer for estimating the GBR assessment level of Korea.  相似文献   
36.
Canine adenovirus type 1 infection of a Eurasian river otter (Lutra lutra)   总被引:1,自引:0,他引:1  
A 10-year-old female Eurasian river otter (Lutra lutra) died after prolonged anorexia and weight loss in the Seoul Grand Park Zoo, Seoul, Republic of Korea. On necropsy, the liver was found to be swollen and friable with 1 lobe enlarged and necrotic. The other organs showed no significant alterations except for mild atrophy of the right kidney. Microscopically, there was multifocal hepatic necrosis. The hepatocytes around the necrotic areas were swollen and contained large basophilic intranuclear inclusions. Periportal infiltration by plasma cells and lymphocytes was also evident. Transmission electron microscopy revealed characteristic hexagonal virus particles sized approximately 70 nm in diameter in the nuclei of the hepatocytes, which were consistent with an adenovirus. Polymerase chain reaction of the formalin-fixed, paraffin-embedded liver sections was used to determine whether the virus was either the canine adenovirus type 1 (CAV-1), canine adenovirus type 2 (CAV-2), or some other viral agent. The results of these tests showed that the virus was CAV-1. To our knowledge, this is the first report on a CAV-1 infection in an otter.  相似文献   
37.
Large scale surveillance of FMD non-structural protein (NSP) antibody in pigs was conducted to monitor for FMD virus circulation in Taiwan using Ceditest and UBI NSP ELISA kits after recurrence of FMD in 2009. A total of 53,759 serum samples were collected from pigs in the auction markets in 2009. There were 43 farms with positive FMD NSP reactors to both NSP ELISA tests in the nationwide surveillance. After tracing back, clinical examination and the NSP ELISA testing using both Ceditest and UBI on 14 follow-up serum samples from all the herds with confirmed NSP reactors in 2009, there were 4 farms classified as positive on follow-up testing criteria. In this surveillance, we have demonstrated that the NSP ELISA tests of outbreak farms followed by clinical and serological investigation could be used to detect FMD circulation in the pig population in Taiwan even while the national compulsory vaccination program is ongoing.  相似文献   
38.
Somatotropin and adipose tissue metabolism: substrate and temporal effects   总被引:2,自引:0,他引:2  
The purpose of these studies was to determine the time course for changes in feed intake, blood metabolites, and lipogenic activity in adipose tissue in response to the initiation of porcine somatotropin (pST) treatment and following withdrawal from treatment in barrows. An initial study was conducted to determine the impact of chronic pST treatment (4 wk of daily injection; 0 vs 4 mg/d) on adipose tissue lipid metabolism in barrows (initial weight 67 kg). Feed efficiency was improved 27%, backfat thickness was decreased 43%, and glucose and lactate oxidation and incorporation into lipid in adipose tissue was reduced 70 to 86% in pST-treated pigs. Palmitate esterification was decreased 44%, whereas palmitate oxidation was unaffected. In vitro metabolism of lactate, glucose, and palmitate in liver slices was not affected by pST treatment. The time-course for changes in intake and adipose tissue metabolism in response to 7 d of pST (0 vs 4 mg/d) treatment and 7 d of withdrawal was examined in subsequent studies in barrows (initial weight 75 kg). Feed intake during pST treatment was significantly (P < .05) less than in control pigs within 24 h of the initiation of treatment and remained low through 3 d after withdrawal. Adipose tissue biopsies were obtained on d 0, 1, 2, 4, and 7 of the treatment phase and on d 2, 4, and 7 after withdrawal from 7 d of treatment. Maximal inhibition of lipogenesis by pST treatment in adipose tissue in vitro was observed on d 4 (-68%) and d 7 (-69%). Similarly, fatty acid synthase activity declined during the treatment period, with the greatest change noted on d 7 (-26%). After withdrawal from treatment, lipogenesis gradually increased, returning to control values 7 d after withdrawal. Levels of IGF-I began to increase from d 1 to d 7 of treatment, continually decreased during withdrawal, and were normalized by the end of the withdrawal period. Plasma urea nitrogen concentrations decreased during treatment, increased during the withdrawal phase, and were normalized 4 d after the last pST treatment. Overall results indicate that most of the metabolic changes in response to pST occur within 1 wk of treatment and return to pretreatment values after 7 d of withdrawal from treatment.  相似文献   
39.
This study examined the effects of road transportation on metabolic and immunological responses in dairy heifers. Twenty Holstein heifers in early pregnancy were divided into non‐transported (NT; n = 7) and transported (T; n = 13) groups. Blood was collected before transportation (BT), immediately after transportation for 100 km (T1) and 200 km (T2), and 24 h after transportation (AT). The T heifers had higher (P < 0.05) blood cortisol and non‐esterified fatty acid concentrations after T1 and T2 than did NT heifers. By contrast, the T heifers had lower (P < 0.05) serum triglyceride concentrations after T1 and T2 than had the NT heifers. The serum cortisol and triglyceride concentrations returned (P > 0.05) to the BT concentrations at 24 h AT in the T heifers. The granulocyte‐to‐lymphocyte ratio and the percentage of monocytes were higher (P < 0.05) after T2 in the T heifers than in the NT heifers, suggesting that transportation stress increased the numbers of innate immune cells. T heifers had higher (P < 0.01) plasma haptoglobin concentrations than NT heifers 24 h AT. In conclusion, transportation increased cortisol secretion and was correlated with increased metabolic responses and up‐regulation of peripheral innate immune cells in dairy heifers.  相似文献   
40.
Ventricular bands are strand‐like intraventricular structures extending between adjacent papillary muscles; a papillary muscle and the ventricular wall or the interventricular septum and ventricular wall. Examination of the domestic dog right ventricle documented six ventricular band types. Eighty‐five of the 89 examined hearts had at least one right ventricular band. In the current study, the right ventricle of the 85 dog hearts was re‐examined for more than one ventricular band type. Seven patterns of multiple different bands were identified in the 24 dog hearts. The patterns (i.e., combinations) of different ventricular bands were grouped into three categories. Category 1 had five different patterns of bands. Each pattern had two different band types. Category 2 had one combination of three different bands. Category 3 had one combination of four different bands. The presence of right ventricular bands around the trabecula septomarginalis dextra was also documented. All 24 dog hearts with multiple ventricular bands had a trabecula septomarginalis dextra. The main goal of this study was documentation of multiple right ventricular band patterns. A secondary goal was documentation of the combined presence of these bands and a trabecula septomarginalis dextra. In the dog, the ventricular bands and trabecula are both thin, strand‐like intraventricular structures with variable branching patterns before blending into the ventricular wall. The gross similarity of these structures and lack of information on their combined presence could precipitate their misidentification.  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