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   36715篇
  免费   1127篇
  国内免费   19篇
林业   4675篇
农学   1904篇
基础科学   272篇
  5799篇
综合类   3975篇
农作物   3134篇
水产渔业   3052篇
畜牧兽医   10701篇
园艺   1374篇
植物保护   2975篇
  2021年   246篇
  2020年   280篇
  2019年   331篇
  2018年   3110篇
  2017年   3089篇
  2016年   1546篇
  2015年   348篇
  2014年   468篇
  2013年   864篇
  2012年   1516篇
  2011年   2991篇
  2010年   2631篇
  2009年   1783篇
  2008年   2153篇
  2007年   2347篇
  2006年   754篇
  2005年   748篇
  2004年   698篇
  2003年   769篇
  2002年   565篇
  2001年   520篇
  2000年   535篇
  1999年   409篇
  1998年   206篇
  1997年   218篇
  1996年   171篇
  1995年   205篇
  1994年   170篇
  1993年   187篇
  1992年   305篇
  1991年   330篇
  1990年   325篇
  1989年   329篇
  1988年   312篇
  1987年   252篇
  1986年   307篇
  1985年   262篇
  1984年   224篇
  1983年   213篇
  1979年   254篇
  1978年   171篇
  1975年   173篇
  1974年   240篇
  1973年   215篇
  1972年   255篇
  1971年   236篇
  1970年   206篇
  1969年   194篇
  1968年   164篇
  1966年   165篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Craniofacial malformation in 64 sheep was phenotypically described as mandibular distoclusion. Digital radiographs were examined in order to determine the degree of morphological changes in certain bones of the skull. Therefore, laterolateral standardised digital radiographs were used to determine anatomic reference points. Subsequently, five reference lines were defined and 16 linear and seven angular measurements were determined to describe malformations in the bones of the skull. Statistical analysis revealed a significant shortening of the rostral part of the corpus mandibulae and of the ramus mandibulae. However, the molar part of the mandible remained unchanged. These morphological changes caused premolar and molar malocclusion. No further craniofacial abnormalities, such as an elongation of the maxilla or of the incisive bone, were identified. In conclusion, the phenotypically observed mandibular distoclusion is caused by a shortening of specific parts of the mandible. This form of ovine craniofacial malformation is therefore best described as brachygnathia inferior.  相似文献   
93.
Thoracolumbar disc herniation was diagnosed in a two-year-old ferret using a myelogram followed by a computed tomography scan. The ferret was paraplegic with no control over urination and defecation. Conservative treatment that included cage rest and passive range of motion exercises for three weeks followed by extensive physiotherapy and hydrotherapy resulted in full recovery two months after the onset of treatment. Although intervertebral disc disease has been reported previously in four ferrets, this is the first report in which a postmyelogram computed tomography was used to demonstrate the herniated disc, and physiotherapy was used as principal treatment modality.  相似文献   
94.
95.
96.
97.
98.
Our study was designed to ascertain whether a flexible videoscope could be used to efficiently monitor ulcers of the pars esophagea in a large group of grower-finisher swine. Gastroscopy was performed on 2 separate occasions in 32 pigs following anesthesia with intravenous pentobarbital, and ulcers of the pars esophagea were subjectively graded. The pigs were then necropsied. Grades from the second endoscopic examination were compared for agreement with grades derived from gross inspection of the pars esophagea at necropsy, and with grades derived from histopathologic examination of sections of the same region. The pars esophagea was adequately visualized in all endoscopic examinations. The average duration of each examination, from anesthetic induction, was approximately 8 min. Gastroscopy permitted appreciation of a wide range of focal and diffuse superficial and deep ulcerative lesions of the pars esophagea, but failed to unequivocally identify parakeratosis of the pars esophagea. Agreement between endoscopic and subsequent necroscopic and histopathologic gradings of ulcerations was poor. We concluded that the use of a flexible videoscope permitted rapid inspection of the pars esophagea, and was therefore a practical method of experimentally monitoring the progression of spontaneous gastric ulcers in pigs. We also postulated that the poor agreement between endoscopic and postmortem findings occurred because endoscopy was possibly more sensitive at detecting small and superficial ulcerations. However, further studies are needed to verify the accuracy of endoscopic diagnosis of gastric ulcers in the live pig.  相似文献   
99.
In situ digestion kinetics of neutral detergent insoluble nitrogen (NDIN) from alfalfa (Medicago sativa L.) harvested at one-tenth bloom and eastern gamagrass (Tripsacum dactyloides L.) harvested at the boot (GGB), anthesis (GGA), and physiological maturity (GGM) stages of growth were determined with nonlinear regression techniques. Whole-plant tissue and associated leaf and stem fractions were incubated in the ventral rumen simultaneously. On a wholeplant basis, potential extents of degradation were particularly high (> or =904 g/kg NDIN) for GGB and GGA, relative to those of GGM and alfalfa (772 and 658 g/kg NDIN, respectively). For all plant parts, degradation rates of NDIN were faster (P<.05) for alfalfa than for all gamagrass forages. Degradation rate of NDIN did not differ (P>.05) across maturities for any gamagrass tissue type. These results indicate 1) that phenological development and lignification do not limit the rate of NDIN degradation in gamagrass forages but do markedly limit the potential extent of NDIN availability and 2) that most of the NDIN in these forages is potentially available in the rumen and can contribute to the ruminal N supply. Our secondary objective was to compare estimates of N escaping ruminal degradation that were determined on the basis of NDIN degradation kinetics (NDIN method) with those determined traditionally, on the basis of total residual N. The NDIN method mathematically eliminates all neutral detergent soluble N from consideration as part of the pool of dietary N potentially escaping the rumen intact. Estimates of rumen escape nitrogen determined on the basis of degradation rates of NDIN were consistently less than corresponding estimates that were determined on the basis of total residual N. When ruminal escape N that was determined with the NDIN method was regressed on corresponding estimates with the total residual N method, the slopes of the regression lines were .53 and .66 for assumed passage rates of .02 and .06 h(-1), respectively. For the forages evaluated in this study, these results indicate that neutral detergent soluble N may make important contributions to the pool of N escaping ruminal degradation.  相似文献   
100.
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