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   503篇
  免费   13篇
林业   4篇
农学   3篇
基础科学   2篇
  47篇
综合类   137篇
农作物   5篇
水产渔业   28篇
畜牧兽医   184篇
植物保护   106篇
  2021年   5篇
  2020年   5篇
  2018年   5篇
  2016年   7篇
  2014年   4篇
  2013年   15篇
  2012年   5篇
  2011年   6篇
  2010年   14篇
  2009年   15篇
  2008年   10篇
  2007年   7篇
  2006年   17篇
  2005年   4篇
  2003年   4篇
  1998年   14篇
  1997年   17篇
  1996年   16篇
  1995年   16篇
  1994年   17篇
  1993年   14篇
  1992年   15篇
  1991年   13篇
  1990年   6篇
  1989年   11篇
  1988年   10篇
  1987年   19篇
  1986年   17篇
  1985年   7篇
  1984年   6篇
  1983年   6篇
  1982年   8篇
  1981年   13篇
  1980年   10篇
  1979年   13篇
  1978年   6篇
  1977年   7篇
  1976年   6篇
  1961年   4篇
  1959年   6篇
  1958年   9篇
  1957年   8篇
  1956年   7篇
  1954年   4篇
  1948年   6篇
  1947年   4篇
  1945年   4篇
  1943年   4篇
  1941年   4篇
  1940年   6篇
排序方式: 共有516条查询结果,搜索用时 656 毫秒
511.
Interference between two freely expanding Bose-Einstein condensates has been observed. Two condensates separated by approximately 40 micrometers were created by evaporatively cooling sodium atoms in a double-well potential formed by magnetic and optical forces. High-contrast matter-wave interference fringes with a period of approximately 15 micrometers were observed after switching off the potential and letting the condensates expand for 40 milliseconds and overlap. This demonstrates that Bose condensed atoms are "laser-like"; that is, they are coherent and show long-range correlations. These results have direct implications for the atom laser and the Josephson effect for atoms.  相似文献   
512.
513.
Ocean images were obtained at three widely separated locations on the earth as part of NASA's ocean color experiment. Digital computer enhancement and band-ratioing techniques were applied to radiometrically corrected spectral data to emphasize patterns of chlorophyll distribution and, in one case, of bottom topography. The chlorophyll pattern in the Yellow Sea between China and Korea was evident in a scene produced from shuttle orbit 24. The effects of the discharge from the Yangtze and other rivers were also observed. Two scenes from orbits 30 and 32 revealed the movement of patches of plankton in the Gulf of Cádiz. Geometric corrections of these images permitted ocean current velocities in the vicinity to be deduced. The variability in water depth over the Grand Bahama Bank was estimated by using the blue-green channel of the instrument. The very clear water conditions in the area caused bottom-reflected sunlight to produce a sensor signal that was inversely related to the depth of the water.  相似文献   
514.
515.
Although non-steroidal anti-inflammatory drugs (NSAIDs) are effective in reducing pain and inflammation, these agents have adverse effects. Selective inhibitors of COX-2 are an alternative to traditional NSAIDs. Deramaxx® [Novartis Animal Health US, Inc. (NAH), Greensboro, NC, USA] contains the selective COX-2 inhibitor, deracoxib, and is approved for the relief of pain and inflammation associated with orthopedic surgery and osteoarthritis in dogs. The safety of Deramaxx was evaluated in two target animal safety studies: 40 dogs (four dogs/sex/group) received 0, 4, 6, 8, or 10 mg/kg/day deracoxib once daily for 21 days; and 60 dogs (five dogs/sex/group) received 0, 2, 4, 6, 8, or 10 mg/kg/day deracoxib once daily for 6 months. There was a dose-dependent trend towards increased blood urea nitrogen (BUN) in treated dogs, however mean BUN values remained within the reference range at the labeled doses. In both trials, histopathology revealed focal renal tubular degeneration/regeneration in some dogs receiving ≥6 mg/kg/day deracoxib. Focal renal papillary necrosis was seen in one dog treated with 8 mg/kg/day and in three dogs receiving 10 mg/kg/day deracoxib on the 6-month study. No other parameters of renal function were adversely affected for either study. Results show that Deramaxx is safe and well-tolerated in dogs when administered as directed.  相似文献   
516.
This study was conducted to determine the effect of pre‐exposure of oocytes to Ricinus communis (RCA‐1) lectin and osteopontin (OPN) in uterine tube fluid (UTF) on in vitro sperm–egg binding and fertilization. In vitro‐matured bovine oocytes were incubated (39°C, 5% CO2 in air) for 2 h in the following treatments: (i) 500 μl of fertilization medium (FM); (ii) 250 μl of FM with 0.25 ml of non‐luteal ampullary uterine tube fluid (NLAUTF); (iii) 250 μl of FM with 250 μl of NLAUTF and 4 μl of RCA‐1 lectin; (iv) 250 μl of FM with 250 μl of NLAUTF, a rabbit polyclonal antibody (1:200) against purified bovine milk OPN, and RCA‐1 lectin; (v) 500 μl of FM and RCA‐1 lectin. Following incubation, oocytes were washed, placed in FM with 2 μg heparin, and incubated with 1 × 105 frozen–thawed spermatozoa per 10 oocytes. Oocytes used to assess sperm binding were stained with Hoescht 33342, and the number of sperm bound per zona pellucida counted. The remaining oocytes were fixed in acid alcohol, stained with 1% acetate‐orcein and observed to determine the presence of pronuclei. More sperm bound to the zona pellucida (mean ± SEM) when oocytes were incubated in treatment 3 (59.0 ± 5.5) than in treatments 2 (46.4 ± 5.6), 4 (18.1 ± 5.4), 5 (33.4 ± 5.6) or 1 (32.5 ± 5.6). More oocytes were fertilized when incubated in treatment 3 (91% ± 3.0) than in 2 (84% ± 3.0), 4 (40% ± 3.0), 5 (77% ± 3.0) or 1 (76% ± 3.0). As in previous studies, this study suggests that RCA‐1 lectin enhances binding of UTF‐derived OPN to bovine oocytes, resulting in increased sperm–egg binding and fertilization in vitro and a possible role in fertilization.  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