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   135474篇
  免费   7944篇
  国内免费   69篇
林业   5580篇
农学   4645篇
基础科学   862篇
  17480篇
综合类   18957篇
农作物   5071篇
水产渔业   7088篇
畜牧兽医   72978篇
园艺   1798篇
植物保护   9028篇
  2020年   1171篇
  2019年   1411篇
  2018年   2228篇
  2017年   2489篇
  2016年   2295篇
  2015年   2000篇
  2014年   2452篇
  2013年   5732篇
  2012年   4351篇
  2011年   5168篇
  2010年   3503篇
  2009年   3548篇
  2008年   5152篇
  2007年   4970篇
  2006年   4641篇
  2005年   4262篇
  2004年   4109篇
  2003年   4176篇
  2002年   3810篇
  2001年   4775篇
  2000年   4642篇
  1999年   3750篇
  1998年   1471篇
  1997年   1452篇
  1996年   1341篇
  1995年   1600篇
  1994年   1328篇
  1993年   1359篇
  1992年   2763篇
  1991年   2901篇
  1990年   2866篇
  1989年   2898篇
  1988年   2611篇
  1987年   2593篇
  1986年   2542篇
  1985年   2400篇
  1984年   1956篇
  1983年   1716篇
  1982年   1154篇
  1979年   1649篇
  1978年   1284篇
  1977年   1135篇
  1976年   1101篇
  1975年   1164篇
  1974年   1357篇
  1973年   1448篇
  1972年   1378篇
  1971年   1199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 109 毫秒
871.
872.
873.
874.
875.
876.
Although most of the magnetic flux observed on the sun originates in the low-latitude sunspot belts, this flux is gradually dispersed over a much wider range of latitudes by supergranular convective motions and meridional circulation. Numerical simulations show how these transport processes interact over the 11-year sunspot cycle to produce a strong "topknot" polar field, whose existence near sunspot minimum is suggested by the observed strength of the interplanetary magnetic field and by the observed areal extent of polar coronal holes. The required rates of diffusion and flow are consistent with the decay rates of active regions and with the rotational properties of the large-scale solar magnetic field.  相似文献   
877.
Alleviation of postanesthetic hypoxemia in the horse   总被引:1,自引:0,他引:1       下载免费PDF全文
This study was designed to investigate the effect of the nasotracheal insufflation of oxygen at a flow rate of 15 L/min on the arterial partial pressure of oxygen during the recovery period following inhalation anesthesia in the horse. It has been stated that this is a suitable flow rate to prevent postoperative hypoxemia but without any experimental evidence to support those statements. Horses being used for the study of healing of cartilage were anesthetized on two separate occasions. Following one period of anesthesia they were allowed to recover breathing room air, and following the other period of anesthesia oxygen was insufflated into the trachea at 15 L/min throughout the recovery period. This permitted each horse to act as its own control and allowed statistical analysis using Student's t-test for paired samples.

The insufflated horses had a higher arterial partial pressure of oxygen during the recovery period than did the noninsufflated horses (p < 0.05).

  相似文献   
878.
1. One hundred and twenty (60 male and 60 female) 21‐d‐old Ross 1 broiler chicks were reared in cages in rooms kept at 21°C or 31°C and were killed at body weights of 1.0, 1.5, 2.0, 2.5 or 3.0 kg.

2. Birds reared at either of the two temperatures ate similar quantities of food to reach their slaughter weight although at 31°C they took longer to reach it.

3. The meat yields of the birds at each slaughter weight were similar at both rearing temperatures, but at body weights greater than 2.0 kg, the broilers reared at 21 °C had more breast meat than those reared at 31°C.

4. Females ate more food than males to reach each of the slaughter weights. The females deposited more fat and had a greater skin weight than the males and, although they had a similar amount of total meat, they had more breast meat.  相似文献   

879.
880.
Adult populations ofMaladera matrida Argaman (Coleoptera: Scarabaeidae), a beetle highly injurious to agricultural crops, were studied in the coastal plain of Israel from 1985 to 1988. There were two generations annually. Adults emerged in March, April or May and disappeared in October or November. The beetles are on the wing, mate, and feed at twilight and in the dark. Feeding and mating behavior, sex ratio, and preferred food plants were studied.  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