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   42006篇
  免费   2474篇
  国内免费   676篇
林业   1862篇
农学   1719篇
基础科学   566篇
  6088篇
综合类   6856篇
农作物   1700篇
水产渔业   2010篇
畜牧兽医   20792篇
园艺   652篇
植物保护   2911篇
  2022年   394篇
  2021年   589篇
  2020年   639篇
  2019年   639篇
  2018年   943篇
  2017年   1051篇
  2016年   894篇
  2015年   832篇
  2014年   1014篇
  2013年   2117篇
  2012年   1630篇
  2011年   1844篇
  2010年   1328篇
  2009年   1328篇
  2008年   1697篇
  2007年   1511篇
  2006年   1395篇
  2005年   1213篇
  2004年   1121篇
  2003年   1102篇
  2002年   957篇
  2001年   1283篇
  2000年   1271篇
  1999年   957篇
  1998年   402篇
  1997年   434篇
  1996年   355篇
  1995年   400篇
  1992年   667篇
  1991年   793篇
  1990年   696篇
  1989年   729篇
  1988年   669篇
  1987年   630篇
  1986年   670篇
  1985年   591篇
  1984年   463篇
  1983年   413篇
  1979年   554篇
  1978年   433篇
  1977年   358篇
  1976年   365篇
  1975年   396篇
  1974年   462篇
  1973年   475篇
  1972年   450篇
  1970年   366篇
  1969年   401篇
  1968年   357篇
  1967年   359篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
Three mature Quarter Horse geldings were used in 2 Latin square experiments to measure the effect of cutting and vacuum cleaning of oats on digestibility. The horses were fed at the maintenance level of digestible energy (DE) as recommended by the NRC.12The data were analyzed by Latin square analysis of variance, and Tukey's t test was used to determine any differences between specific means.No significant differences among treatments were observed during either experiment, indicating that the digestibility of nutrients from oats was not affected by cutting and vacuum cleaning. Differences in the digestibility of the ether extract (EE) fraction between periods of experiment 1 were noted.  相似文献   
46.
47.
48.
A 14-week-old male unilaterally cryptorchid Clumber spaniel was presented for acute lethargy. Physical examination revealed abdominal pain, and a single testis was palpated in the scrotum. Abdominal ultrasound and computed tomography (CT) revealed a poorly vascularized, ovoid structure immediately caudal to the left kidney with scant regional peritoneal effusion. Left intra-abdominal testicular torsion was confirmed at surgery, and routine cryptorchidectomy was performed. The patient recovered uneventfully from anesthesia and surgery.Key clinical message:The most common CT characteristics of testicular torsion were present in this case and correlated well with sonographic findings to allow for rapid, accurate diagnosis and surgical planning of unilateral, non-neoplastic, intra-abdominal cryptorchid testicular torsion in a juvenile dog. Contrast enhanced CT facilitated accurate localization of the undescended testis and evaluation of testicular perfusion and may be a useful alternative to ultrasound for diagnosing testicular torsion, especially in indeterminate cases.  相似文献   
49.
The survival period of 22 S. gallinarum strains in chicken feces was examined. The suspension of the bacterium was homogenized with a certain feces quantity. The initial ratio was 10(7) to 10(9) colony forming units per gram of feces. The results show that the growth of 5 strains was completely inhibited within 24 hours post homogenization, 7 strains were still positive to S. gallinarum for 24 hours, 5 strains were positive for 48 hours and the last 5 strains were positive for 4 days. Additionally, the effect of tryptose soy (TSB) and Rappaport-Vassiliadis (RV) nutrient broths on the isolation rate of S. gallinarum from feces was examined at 37 degrees C and 43 degrees C. It was shown that the TSB medium was the best at 37 degrees C, in this experiment. The S. gallinarum concentration in RV medium was decreased at 37 degrees C from 9.1 x 10(8) to 1.6 x 10(6) and at 43 degrees C from 9.1 x 10(8) to 4.1 x 10(2).  相似文献   
50.
A Generalized Marker Regression Mapping (GMR) approach was developed for mapping Quantitative Trait Loci (QTL) affecting binary polygenic traits in a single-family half-sib design. The GMR is based on threshold-liability model theory and regression of offspring phenotype on expected marker genotypes at flanking marker loci. Using simulation, statistical power and bias of QTL mapping for binary traits by GMR was compared with full QTL interval mapping based on a threshold model (GIM) and with a linear marker regression mapping method (LMR). Empirical significance threshold values, power and estimates of QTL location and effect were identical for GIM and GMR when QTL mapping was restricted to within the marker interval. These results show that the theory of the marker regression method for QTL mapping is also applicable to binary traits and possibly for traits with other non-normal distributions. The linear and threshold models based on marker regression (LMR and GMR) also resulted in similar estimates and power for large progeny group sizes, indicating that LMR can be used for binary data for balanced designs with large families, as this method is computationally simpler than GMR. GMR may have a greater potential than LMR for QTL mapping for binary traits in complex situations such as QTL mapping with complex pedigrees, random models and models with interactions.  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