全文获取类型
收费全文 | 132460篇 |
免费 | 7269篇 |
国内免费 | 93篇 |
专业分类
林业 | 5381篇 |
农学 | 4269篇 |
基础科学 | 831篇 |
17035篇 | |
综合类 | 21482篇 |
农作物 | 5393篇 |
水产渔业 | 6688篇 |
畜牧兽医 | 67961篇 |
园艺 | 1800篇 |
植物保护 | 8982篇 |
出版年
2020年 | 1177篇 |
2019年 | 1375篇 |
2018年 | 2031篇 |
2017年 | 2330篇 |
2016年 | 2095篇 |
2015年 | 1742篇 |
2014年 | 2224篇 |
2013年 | 5290篇 |
2012年 | 4114篇 |
2011年 | 5093篇 |
2010年 | 3245篇 |
2009年 | 3389篇 |
2008年 | 4971篇 |
2007年 | 4666篇 |
2006年 | 4353篇 |
2005年 | 4088篇 |
2004年 | 3850篇 |
2003年 | 3973篇 |
2002年 | 3542篇 |
2001年 | 4150篇 |
2000年 | 4252篇 |
1999年 | 3372篇 |
1998年 | 1474篇 |
1997年 | 1387篇 |
1996年 | 1288篇 |
1995年 | 1529篇 |
1994年 | 1358篇 |
1993年 | 1231篇 |
1992年 | 2584篇 |
1991年 | 2700篇 |
1990年 | 2591篇 |
1989年 | 2611篇 |
1988年 | 2368篇 |
1987年 | 2348篇 |
1986年 | 2427篇 |
1985年 | 2340篇 |
1984年 | 1881篇 |
1983年 | 1677篇 |
1982年 | 1149篇 |
1979年 | 1748篇 |
1978年 | 1397篇 |
1977年 | 1151篇 |
1976年 | 1212篇 |
1975年 | 1292篇 |
1974年 | 1500篇 |
1973年 | 1514篇 |
1972年 | 1405篇 |
1971年 | 1304篇 |
1970年 | 1251篇 |
1969年 | 1283篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Ziaei N Guy JH Edwards SA Blanchard PJ Ward J Feuerstein D 《British poultry science》2008,49(2):195-201
1. The objective of this study was to investigate whether it is possible to reduce phosphorus (P) excretion by feeding a lower level of dietary P than that currently recommended, without compromising welfare, and whether this is sensitive to the level of dietary calcium (Ca). 2. A randomised complete block design was used with a total of 224 1-d-old male chicks of a commercial genotype in two batches. Chicks had a 10-d adaptation period. After this, they were moved to cages and allocated to one of 4 dietary treatments (4 and 3 birds per cage in batch 1 and 2, respectively). A standard level of Ca and P (8.3 and 6.6 g/kg, respectively) was compared with three lower levels of Ca (7.3, 6.3 and 5.3 g/kg) all at the same reduced level of P (5.5 g/kg). Records were made of live weight of birds on an individual basis and feed and water consumption on a cage basis. Every 7 d, the dry matter (DM) content of a sample of mixed excreta from each cage was measured. Birds were slaughtered and samples taken for analysis of plasma mineral content, retention of N, Ca and P and tibia bone strength. 3. The initial reduction in dietary mineral level did not adversely affect performance or bone strength. However, decreasing dietary Ca level below 7.3 g/kg, at constant P, led to reduced feed consumption and bone strength. Dietary treatment had no significant overall effect on water intake, water : feed ratio, excreta DM content, Ca and P retention or metabolisability of DM. There was no significant correlation between mean plasma Ca or P level and DM content of rectal digesta. 4. In conclusion, reducing dietary P from 6.6 to 5.5 g/kg to reduce potential environmental impact of broiler production had an adverse effect on bird welfare when the level of Ca was reduced below 7.3 g/kg, as a result of decreased feed intake in the early growth period and reduced skeletal strength. 相似文献
912.
The objective of this study was to evaluate the acute phase response (APR) in cloned pigs derived from two different cell lines [C1 (n = 2) and C2 (n = 7)] as compared to genetically similar non-cloned pigs (CONT; n = 11) following a lipopolysaccharide (LPS; 25 microg/kg BW) challenge. Pigs were weaned at 21 days of age and maintained in individual pens in the same room until sample collection approximately 1 week later. Blood samples were collected every 30 min for 2 h prior to and 4h after the LPS challenge. Serum samples were analyzed for cortisol, tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6). Average gestational length for cloned pigs, 118.8 +/- 0.97 days, was longer (P < 0.005) than that of CONT pigs, 114+/-0.41 days. For serum cortisol, there was a time by group interaction (P < 0.0001) such that the cortisol response was greater in CONT pigs as compared to C2 pigs (P < 0.0001), but not different from C1 pigs (P > 0.74). A time by group interaction (P < 0.0001) was observed for serum TNF-alpha such that the TNF-alpha response was greater in CONT pigs as compared to C2 pigs (P = 0.0002) and tended to be greater (P < 0.06) than C1 pigs. A time by group interaction (P < 0.0001) was also observed for serum IL-6 such that the serum IL-6 response was greater (P < 0.003) in CONT pigs as compared to C2 pigs and there was a trend (P = 0.10) for serum IL-6 to be greater in CONT pigs compared to the C1 pigs. These are the first results to demonstrate that cortisol and proinflammatory cytokine profiles associated with the APR of cloned pigs are altered compared to genetically similar non-cloned pigs. Our results also indicate that the cell line from which clones are derived may dictate the APR. The hormone and cytokine profiles reported herein are a significant contribution towards our understanding, and perhaps our ability to prevent or reduce the incidence of premature deaths in cloned animals and warrants further investigation of the immune system of cloned animals. 相似文献
913.
Immune mediated hemolytic anemia (IMHA) in dogs is a severe disease with a high mortality rate. As human immunoglobulin (HIG) was reported to be beneficial for the treatment of IMHA in dogs we examined the influence of HIG on the course of the disease in our dogs with IMHA. Of 22 dogs with primary IMHA 9 dogs received in addition to routine immunosuppressive therapy HIG at a dose of 0.19 to 0.68 g/kg (median 0.35 g/kg), 13 dogs did not receive HIG (-HIG group). Both groups were similar in terms of age, weight, the presence of autoagglutination, spherocytosis, positive Coombs' test, icterus and pigmenturia. The lowest hematocrit measured during the disease was significantly lower in the +HIG group compared to the -HIG group and dogs in the +HIG group received significantly more transfusions than those of the -HIG group. This is an indication for more severe disease signs of the +HIG group dogs. Although mortality during hospitalization and the time from hospital admission to release or death was not significantly different between the two groups, we interpret this similar course of the IMHA despite more severe signs of the +HIG group dogs as a potential positive effect of the HIG therapy. 相似文献
914.
McKenna SL Barkema HW McClure JT Rogers LA 《The Canadian veterinary journal. La revue veterinaire canadienne》2003,44(4):312-313
A 2-year-old, purebred Holstein heifer with exercise intolerance and cardiovascular compromise was diagnosed at postmortem with tetralogy of Fallot, which typically results in death within a few months of life. Survival past the age of 2 was unexpected. The concurrent endocarditis of the pulmonic valve is discussed. 相似文献
915.
Genetic analysis of human and swine influenza A viruses isolated in Northern Italy during 2010–2015 下载免费PDF全文
C. Chiapponi E. Ebranati E. Pariani S. Faccini A. Luppi L. Baioni R. Manfredi V. Carta M. Merenda P. Affanni M. E. Colucci L. Veronesi G. Zehender E. Foni 《Zoonoses and public health》2018,65(1):114-123
Influenza A virus (IAV) infection in swine plays an important role in the ecology of influenza viruses. The emergence of new IAVs comes through different mechanisms, with the genetic reassortment of genes between influenza viruses, also originating from different species, being common. We performed a genetic analysis on 179 IAV isolates from humans (n. 75) and pigs (n. 104) collected in Northern Italy between 2010 and 2015, to monitor the genetic exchange between human and swine IAVs. No cases of human infection with swine strains were noticed, but direct infections of swine with H1N1pdm09 strains were detected. Moreover, we pointed out a continuous circulation of H1N1pdm09 strains in swine populations evidenced by the introduction of internal genes of this subtype. These events contribute to generating new viral variants—possibly endowed with pandemic potential—and emphasize the importance of continuous surveillance at both animal and human level. 相似文献
916.
Serum samples of five goats inoculated with Toxoplasma gondii were analyzed using the enzyme linked immunosorbent assay (ELISA), indirect hemagglutination (IHA) and western blotting (WB). Antibodies detected by ELISA peaked between 19 and 62 days after inoculation and persisted throughout the experiment with no association to parasitaemia. Using WB, the main antigens detected had molecular weights of approximately 68, 62, 50, 48, 42, 34, 28, 26, 22 and 19 kDa. Antibody titers of between 1:256 and 1:32000 were observed using IHA, with a significant drop in activity after treatment with 2-mercapto-ethanol between days 12 and 48. This coincided with the parasitaemic period that occurs between 5 and 64 days after inoculation. 相似文献
917.
918.
919.
920.
Influence of Disease Process and Duration on Acute Phase Proteins in Serum and Peritoneal Fluid of Horses with Colic 下载免费PDF全文
T.H. Pihl E. Scheepers M. Sanz A. Goddard P. Page N. Toft P.H. Andersen S. Jacobsen 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2015,29(2):651-658