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   135647篇
  免费   7788篇
  国内免费   70篇
林业   5577篇
农学   4644篇
基础科学   862篇
  17483篇
综合类   18964篇
农作物   5087篇
水产渔业   7089篇
畜牧兽医   72975篇
园艺   1798篇
植物保护   9026篇
  2020年   1171篇
  2019年   1410篇
  2018年   2229篇
  2017年   2489篇
  2016年   2295篇
  2015年   2000篇
  2014年   2451篇
  2013年   5731篇
  2012年   4350篇
  2011年   5163篇
  2010年   3502篇
  2009年   3547篇
  2008年   5153篇
  2007年   4970篇
  2006年   4642篇
  2005年   4262篇
  2004年   4109篇
  2003年   4174篇
  2002年   3809篇
  2001年   4773篇
  2000年   4641篇
  1999年   3747篇
  1998年   1471篇
  1997年   1452篇
  1996年   1341篇
  1995年   1599篇
  1994年   1327篇
  1993年   1359篇
  1992年   2762篇
  1991年   2902篇
  1990年   2866篇
  1989年   2897篇
  1988年   2610篇
  1987年   2593篇
  1986年   2539篇
  1985年   2400篇
  1984年   1956篇
  1983年   1716篇
  1982年   1154篇
  1979年   1650篇
  1978年   1284篇
  1977年   1135篇
  1976年   1100篇
  1975年   1165篇
  1974年   1357篇
  1973年   1448篇
  1972年   1378篇
  1971年   1195篇
  1970年   1247篇
  1969年   1146篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Skeletal muscle genes are potential candidates for production and meat quality. Screening a subtracted cDNA library constructed with mRNA obtained from longissimus dorsi muscles of F1 hybrids Landrace × Yorkshire and their female parents Yorkshire, we isolated two partial sequences coding for the H3-K4-specific methyltransferase (KIAA1717) and skeletal muscle myosin regulatory light chain (HUMMLC2B) genes. Database search revealed KIAA1717 and HUMMLC2B encoded proteins with SET domain and EF-hand calcium binding motif, respectively. In the present work we identified their partial polymorphisms and two SNPs, one (C1354T) at the 3′ untranslated region (UTR) of KIAA1717 and one (A345G) at the SINE (PRE-1) element of HUMMLC2B, both created/disrupted a restriction site for endonuclease Msp I. The selected pigs were genotyped at the KIAA1717 C1354T and HUMMLC2B A345G sites by means of a PCR-RFLP protocol. Significant associations were observed for the KIAA1717 C1354T polymorphic site with meat marbling (longissimus doris (p < 0.05), biceps femoris (p < 0.01)) and intramuscular fat (p < 0.01). HUMMLC2B A345G were significantly associated with meat pH (longissimus doris (p < 0.05), biceps femoris (p < 0.01)), drip loss (p < 0.01), water holding capacity (p < 0.01) and meat color value (longissimus doris (p < 0.01), biceps femoris (p < 0.05)). Further studies are needed to confirm these preliminary results.  相似文献   
992.
993.
994.
995.
Horses serve as an intermediate host for several species of Sarcocystis, all of which utilize canids as the definitive host. Sarcocystis spp. infection and formation of latent sarcocysts in horses often appears to be subclinical, but morbidity can occur, especially when the parasite burden is large. A serological survey was conducted to determine the presence of antibodies against Sarcocystis spp. in seemingly healthy horses from the Galicia region of Spain. Western blot analyses using Sarcocystis neurona merozoites as heterologous antigen suggested greater than 80% seroprevalance of Sarcocystis spp. in a sample set of 138 horses. The serum samples were further tested with enzyme-linked immunosorbent assays (ELISAs) based on recombinant S. neurona-specific surface antigens (rSnSAGs). As expected for horses from the Eastern Hemisphere, less than 4% of the serum samples were positive when analyzed with either the rSnSAG2 or the rSnSAG4/3 ELISAs. An additional 246 horses were tested using the rSnSAG2 ELISA, which revealed that less than 3% of the 384 samples were seropositive. Collectively, the results of this serologic study suggested that a large proportion of horses from this region of Spain are exposed to Sarcocystis spp. Furthermore, the anti-Sarcocystis seroreactivity in these European horses could be clearly distinguished from anti-S. neurona antibodies using the rSnSAG2 and rSnSAG4/3 ELISAs.  相似文献   
996.
The response to oral glucose was examined in 10 obese and 9 lean age-matched, neutered cats. In all cats, oral administration of 2 g/kg glucose was followed by a prompt increase in glucose, insulin, and glucagon-like peptide (GLP)-1. There were significant differences between lean and obese cats in the areas under the curve for glucose, insulin, and GLP-1. However, the responses were variable, and a clear distinction between individual lean and obese cats was not possible. Therefore, this test cannot be recommended as a routine test to examine insulin resistance in individual cats as it is used in people. A further disadvantage for routine use is also the fact that this test requires gastric tubing for the correct administration of the glucose and associated tranquilization to minimize stress and that it was associated with development of diarrhea in 25% of the cats. GLP-1 concentrations were much lower in obese than lean cats. The low GLP-1 concentrations in obese cats might indicate a contribution of GLP-1 to the lower insulin sensitivity of obese cats, but this hypothesis needs to be further investigated.  相似文献   
997.
Forty piglets (average body weight = 5.32 kg) were used to investigate the effect of dietary crude protein (CP) content on immunological responses following a challenge with enterotoxigenic Escherichia coli (ETEC) K88. Pigs, housed 4 per pen, were randomly allotted to 2 diets: 1) a high, 225 g/kg CP diet (HCP) or 2) a low, 176 g/kg CP diet (LCP) supplemented with crystalline amino acids. Pigs were orally challenged with 6 mL of an ETEC K88 suspension containing 1010 cfu/mL on d 8 after weaning. Blood samples were collected from 10 pigs (1 pig/pen) on d 7 (at weaning), −24 h, 8 h, 72 h and 7 d after the challenge for determination of plasma urea N (PUN) and serum concentrations of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) and haptoglobin (Hp). Tumor necrosis factor alpha, IL-1β and Hp were measured as indicators of inflammatory responses. The concentrations of serum TNF-α at 8 h, 72 h and 7 d after challenge were similar to the level observed at 24 h before challenge but higher (P < 0.05) than the weaning level. Pigs fed the LCP diet had lower (P = 0.032) concentrations of IL-1β (72 vs. 116 pg/mL) at 8 h post-challenge compared with those fed the HCP diet. Likewise, pigs fed the LCP diet tended to have lower (P = 0.088) concentration of Hp (9 vs. 25 mg/dL) compared with those fed the HCP diet at 8 h post-challenge. Compared with the weaning concentration, PUN concentration at 72 h after ETEC challenge was higher (P < 0.05) in pigs fed the HCP diet. The results indicate that the LCP diet supplemented with crystalline amino acids reduced inflammatory responses, as indicated by serum IL-1β, in piglets infected with ETEC K88.  相似文献   
998.
999.
The purpose of this study was to determine the clinical course and outcome associated with keratomycosis in horses in the mid‐Atlantic USA. Records of horses diagnosed with keratomycosis at New Bolton Center from November 2006 to November 2007 with positive fungal culture were retrospectively studied. Neither horses with ulcerative keratitis and a negative fungal culture nor those with stromal abscesses were included. Subject details, history, clinical findings, therapy and outcome were recorded. Thirty horses fitted both inclusion criteria (diagnosis of keratomycosis and positive corneal fungal culture). Fourteen of 30 cases occurred during summer. Aspergillus was the most commonly cultured fungal genus (17/30, or 57%) followed by Alternaria (4/30). Seventeen horses had positive bacterial and fungal cultures. Fifteen of 30 horses were treated surgically by a keratectomy and amnion (8) or conjunctival (7) graft. Itraconazole was the most common topical anti‐fungal therapy and was utilised in 25/30 horses. Globe survival was 97% (29/30). All surviving globes had a positive menace response and were visual at the last examination. It was concluded that in the mid‐Atlantic USA, fungal keratitis is common, has the highest incidence in summer, and is usually associated with a positive outcome. Aspergillus may be a relatively more common corneal pathogen in this region than elsewhere in the USA. Surgical cases were more likely to have fungal hyphae identified on cytology and tended to be hospitalised longer than medical cases. There was no apparent association between surgical disease and all other patient, organism and treatment variables.  相似文献   
1000.
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