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   228篇
  免费   3篇
  国内免费   2篇
林业   10篇
农学   5篇
基础科学   7篇
  9篇
综合类   80篇
农作物   2篇
水产渔业   1篇
畜牧兽医   112篇
园艺   3篇
植物保护   4篇
  2022年   3篇
  2018年   2篇
  2016年   3篇
  2015年   2篇
  2014年   4篇
  2012年   11篇
  2011年   13篇
  2010年   6篇
  2009年   8篇
  2008年   17篇
  2007年   4篇
  2006年   17篇
  2005年   10篇
  2004年   12篇
  2003年   11篇
  2002年   6篇
  2001年   8篇
  2000年   9篇
  1999年   8篇
  1998年   5篇
  1997年   2篇
  1995年   4篇
  1994年   5篇
  1993年   3篇
  1990年   5篇
  1989年   4篇
  1986年   2篇
  1979年   3篇
  1974年   3篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1966年   1篇
  1960年   1篇
  1958年   2篇
  1957年   3篇
  1956年   3篇
  1955年   1篇
  1954年   2篇
  1948年   1篇
  1947年   1篇
  1942年   1篇
  1941年   2篇
  1939年   2篇
  1937年   1篇
  1936年   1篇
  1935年   2篇
  1932年   1篇
  1931年   1篇
  1893年   1篇
排序方式: 共有233条查询结果,搜索用时 15 毫秒
141.
Magnetic fields measured by Voyager 1 show that the spacecraft crossed or was crossed by the termination shock on about 16 December 2004 at 94.0 astronomical units. An estimate of the compression ratio of the magnetic field strength B (+/- standard error of the mean) across the shock is B2/B1 = 3.05 +/- 0.04, but ratios in the range from 2 to 4 are admissible. The average B in the heliosheath from day 1 through day 110 of 2005 was 0.136 +/- 0.035 nanoteslas, approximately 4.2 times that predicted by Parker's model for B. The magnetic field in the heliosheath from day 361 of 2004 through day 110 of 2005 was pointing away from the Sun along the Parker spiral. The probability distribution of hourly averages of B in the heliosheath is a Gaussian distribution. The cosmic ray intensity increased when B was relatively large in the heliosheath.  相似文献   
142.
介绍了利用各种栽培架和新型栽培基质,进行菜秧、小株型青菜无土栽培技术要点,以为苏南地区小白菜的多样栽培提供参考。  相似文献   
143.
144.
The Texas A&M University Medical Sciences Library (MSL) supports lifelong learning for Texas veterinarians and College of Veterinary Medicine and Biomedical Sciences (CVMBS) alumni through several ongoing outreach efforts. The MSL provides free document delivery and literature search services to practicing veterinarians in support of patient care. The MSL also responded to unique opportunities to expand services and increase its visibility through collaborations with the American Association of Equine Practitioners and CABI, provider of VetMed Resource. The MSL continues to explore ways to expand its mission-critical veterinary outreach work and market library services to veterinarians through participation in continuing education, regional meetings, and veterinary student instruction.  相似文献   
145.
The aim was to determine the persistent efficacy of copper oxide wire particles (COWP) against Haemonchus contortus in sheep, using the harmonization guidelines protocol. Thirty-six male lambs (2 months old) reared free of gastrointestinal nematodes were used (average body weight of 10.8±3.8kg). Before and for the duration of the study, lambs were kept in raised cages with slatted floors and were offered ad libitum a complete mixed diet. Animals were divided into six groups (n=6): one non-treated control group (G0) and five groups treated with one COWP capsule (1.7g of copper oxide; Copinox(?)). Animals in each group were treated on pre-defined dates before the artificial infection was applied: days -35 (G1), -28 (G2), -21 (G3), -14 (G4) and -7 (G5). On day 0 animals were infected with 3700 H. contortus infective larvae per animal. Animals were humanely slaughtered between days 22 and 23 post-infection. The abomasums were individually washed to obtain the contents. These organs were subjected to separate artificial digestions. Adult parasites were counted from the abomasum contents and the larvae from the digested material. Worm burden geometric means were calculated for each group. A significant worm burden reduction in either of the treated groups (G1, G2, G3, G4, and G5) compared to the control (G0) was considered as persistence of the anthelmintic effect. Copper levels were determined from individual liver samples of each animal. The geometric mean worm burden of the control group (G0) was 1959. Compared to the control, worm burdens geometric means were significantly reduced in groups G1 (1108), G4 (528) and G5 (1063) (P<0.03). Efficacies in G1, G4 and G5 were 43.4%, 73.0% and 45.7% respectively. No significant reduction was found for G2 (1342) and G3 (1430). A larger quantity of Cu was found in the livers of treated animals compared to the control group (P<0.05) except for G3 (P=0.06). A negative association between Cu liver content and worm burdens was found (r=-0.42, P<0.05). Live weight gain was similar in all groups and no clinical or post-mortem manifestations of Cu toxicity were recorded in treated animals.  相似文献   
146.
Results obtained by the Goddard Space Flight Center magnetometers on Voyager 1 are described. These results concern the large-scale configuration of the Jovian bow shock and magnetopause, and the magnetic field in both the inner and outer magnetosphere. There is evidence that a magnetic tail extending away from the planet on the nightside is formed by the solar wind-Jovian field interaction. This is much like Earth's magnetosphere but is a new configuration for Jupiter's magnetosphere not previously considered from earlier Pioneer data. We report on the analysis and interpretation of magnetic field perturbations associated with intense electrical currents (approximately 5 x 10(6) amperes) flowing near or in the magnetic flux tube linking Jupiter with the satellite Jo and induced by the relative motion between Io and the corotating Jovian magnetosphere. These currents may be an important source of heating the ionosphere and interior of Io through Joule dissipation.  相似文献   
147.
Magnetic field studies by Voyager 1 have confirmed and refined certain general features of the Saturnian magnetosphere and planetary magnetic field established by Pioneer 11 in 1979. The main field of Saturn is well represented by a dipole of moment 0.21 +/- 0.005 gauss-R(s)(3) (where 1 Saturn radius, R(s), is 60,330 kilometers), tilted 0.7 degrees +/- 0.35 degrees from the rotation axis and located within 0.02 R(s) of the center of the planet. The radius of the magnetopause at the subsolar point was observed to be 23 R(s) on the average, rather than 17 R(s). Voyager 1 discovered a magnetic tail of Saturn with a diameter of approximately 80 R(s). This tail extends away from the Sun and is similar to type II comet tails and the terrestrial and Jovian magnetic tails. Data from the very close flyby at Titan (located within the Saturnian magnetosphere) at a local time of 1330, showed an absence of any substantial intrinsic satellite magnetic field. However, the results did indicate a very well developed, induced magnetosphere with a bipolar magnetic tail. The upper limit to any possible internal satellite magnetic moment is 5 x 10(21) gauss-cubic centimeter, equivalent to a 30-nanotesla equatorial surface field.  相似文献   
148.
149.
150.
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