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   252109篇
  免费   14943篇
  国内免费   706篇
林业   23358篇
农学   14017篇
基础科学   2977篇
  42587篇
综合类   25046篇
农作物   17098篇
水产渔业   16547篇
畜牧兽医   96132篇
园艺   6339篇
植物保护   23657篇
  2021年   2470篇
  2020年   2884篇
  2019年   3677篇
  2018年   3965篇
  2017年   4345篇
  2016年   4764篇
  2015年   4290篇
  2014年   5656篇
  2013年   16205篇
  2012年   6116篇
  2011年   8042篇
  2010年   7310篇
  2009年   7862篇
  2008年   7564篇
  2007年   6510篇
  2006年   7211篇
  2005年   6429篇
  2004年   6303篇
  2003年   6129篇
  2002年   5395篇
  2001年   5765篇
  2000年   5470篇
  1999年   5144篇
  1998年   4095篇
  1997年   4169篇
  1996年   3898篇
  1995年   4453篇
  1994年   3862篇
  1993年   3597篇
  1992年   4178篇
  1991年   4420篇
  1990年   4094篇
  1989年   4049篇
  1988年   3560篇
  1987年   3683篇
  1986年   3620篇
  1985年   3884篇
  1984年   3592篇
  1983年   3433篇
  1982年   2843篇
  1981年   2800篇
  1980年   2756篇
  1979年   3205篇
  1978年   2836篇
  1977年   2641篇
  1976年   2453篇
  1975年   2315篇
  1974年   2565篇
  1973年   2528篇
  1972年   2279篇
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
991.
Latissimus dorsi and cutaneous trunci myocutaneous flaps of equal dimension and location were randomly elevated on opposite sides of the thorax in 10 dogs (group 1) and resutured to their respective bed. The procedure was repeated in four additional dogs (group 2); however, the short perforating branches of the thoracodorsal artery and vein were divided at the base of each cutaneous trunci myocutaneous flap, whereas the cutaneous pedicle and underlying cutaneous trunci muscle were divided in the latissimus dorsi myocutaneous flaps to determine subsequent skin survivability and the major source of circulation of each myocutaneous flap. There was little difference in the percentage of skin survival between the latissimus dorsi and cutaneous trunci myocutaneous flaps in group 1 dogs. Circulation to the "skin island" of group 2 latissimus dorsi myocutaneous flaps originated from intramuscular anastomotic connections between the major branch of the thoracodorsal artery entering the latissimus dorsi muscle and the proximal lateral intercostal arteries perforating the muscle. Ligation of the short perforating branches of the thoracodorsal artery resulted in partial skin necrosis in all group 2 cutaneous trunci myocutaneous flaps. Results from this study indicate that it is unnecessary to elevate the latissimus dorsi muscle for major skin flap elevation and survival. The thicker latissimus dorsi myocutaneous flap is more difficult to develop surgically and appears to have no clinical major advantage over the more mobile cutaneous trunci myocutaneous flap or the adjacent thoracodorsal axial pattern flap for closure of large skin defects within the radius of flap rotation.  相似文献   
992.
With electromyography and strain gauges the uterine motility of the sow during the oestrous cycle and early pregnancy was studied. Special attention was paid to characterization of myometrial activity at the time of intrauterine migration of blastocysts.From recordings of 4 animals (3 became pregnant) 3 types of electrical spiking activity (each could be correlated with an elevation of the strain gauge tension) were discerned. Two of them appeared regularly and were suitable for analysis: High Voltage Slow Acticity (with relative high amplitude and low frequency of spikes) and Low Voltage Fast Activity (with relative low aplitude and high frequency of spikes).The sexual status markedly influenced myometrial activity: during prooestrus and oestrus only one type of electrical activity was present whereas the myoelectrical complex (an episode of this activity and the subsequent interval of inactivity) was shorter than 10 min. During dioestrus the myoelectrical complex was longer than 10 min and High Voltage Slow Activity (solely on the cervix and bifurcation) and Low Voltage Fast Activity occurred simultaneously in episodes which mainly appeared to originate on the bifurcation.The characteristics of uterine activity during pregnancy were similar to those of a cyclic sow until day 12. It was only on day 12 that gestation appeared from an increased frequency of myoelectrical complexes.It is concluded that Low Voltage Fast Activity as it was found on the uterine horn at days 8–9 might be involved in the process of intra-uterine migration of blastocysts. In cyclic and in pregnant animals the patterns of Low Voltage Fast Activity were similar. Therefore, the occurrence of Low Voltage Fast Activity is independent of the actual presence of blastocysts. It seems to be exhibited in dependence on the ovarian hormones.  相似文献   
993.
The computer-assisted, kinetics-based enzyme-linked immunosorbent assay for coronavirus antibodies in cats was calibrated to the conventional indirect immunofluorescence assay by linear regression analysis and computerized interpolation (generation of "immunofluorescence assay-equivalent" titers). Procedures were developed for normalization and standardization of kinetics-based enzyme-linked immunosorbent assay results through incorporation of five different control sera of predetermined ("expected") titer in daily runs. When used with such sera and with computer assistance, the kinetics-based enzyme-linked immunosorbent assay minimized both within-run and between-run variability while allowing also for efficient data reduction and statistical analysis and reporting of results.  相似文献   
994.
选用22只“星杂579”成龄母鸡,以电生理方法观察了光照(30lx)及在麻醉状态下光照(30lx)和黑暗对其大脑皮质“Wulst”区电位的影响。结果,黑暗时的电位可因光照而抑制;注射氯胺酮麻醉后,电位明显变小,再给黑暗和光照,电位均没有变化。表明大脑皮质参与了光照对鸡的生理调节过程。  相似文献   
995.
Stress, stressors and the stress response are terms which represent concepts rather than oeing precisely definable. No single theory of stress has been universally accepted. Selye's General Adaptation Syndrome of stress remains the primary theory for the basis of stress research in food-producing animals; however, other concepts and theories have been developed. This paper reviews current theories and suggests that the complexity of research on stress in food-producing animals can be attributed to the lack of concrete theories and concepts regarding identifiable stressors, the endocrine responses stimulated by potential stressors and the complex and integrated biological changes in the neuro-endocrine system resulting from exposure to hypothesized stressors.  相似文献   
996.
997.
998.
999.
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