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   1662篇
  免费   57篇
  国内免费   4篇
林业   152篇
农学   47篇
基础科学   4篇
  256篇
综合类   69篇
农作物   88篇
水产渔业   194篇
畜牧兽医   784篇
园艺   17篇
植物保护   112篇
  2023年   1篇
  2022年   28篇
  2021年   46篇
  2020年   17篇
  2019年   26篇
  2018年   27篇
  2017年   40篇
  2016年   55篇
  2015年   66篇
  2014年   84篇
  2013年   129篇
  2012年   95篇
  2011年   127篇
  2010年   49篇
  2009年   65篇
  2008年   115篇
  2007年   110篇
  2006年   110篇
  2005年   108篇
  2004年   117篇
  2003年   96篇
  2002年   68篇
  2001年   51篇
  2000年   28篇
  1999年   13篇
  1998年   9篇
  1997年   7篇
  1996年   2篇
  1995年   6篇
  1994年   4篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1977年   1篇
  1974年   3篇
  1973年   1篇
排序方式: 共有1723条查询结果,搜索用时 15 毫秒
991.
992.
In ultrasonographic diagnosis of ovarian disorders and the estrous cycle in sows, transverse observation of the uterus yielded more characteristic findings than observation of sagittal sections. Transverse ultrasonography revealed that the low progesterone (P) type uterus showed a round structure, while the high P type uterus showed a flattened structure. These results corresponded well with rectal palpation findings: the low P type uterus had a hard, pipe-like structure and the high P type a soft, balloon-like structure. For gilts, we employed a minimum convex type transrectal prostate probe that had an approximately 18 cm insertion handle. The images of the uterus obtained thereby were a similar to those obtained from sows. The above results suggest that it should be possible to diagnose and treat many ovarian disorders in sows and gilts based only on the ultrasonograhic findings. In short, ultrasonograhic findings of a round structure of the uterine wall might be an indication for PMSG (pregnant mare serum gonadotropin) treatment, while findings of a flattened structure might be an indication for PGF(2) (alpha) administration.  相似文献   
993.
To elucidate perithecial wall development in Magnaporthe grisea, monoconidial isolates were collected from the surfaces of six perithecia in five crosses. Genotypes of these isolates were characterized based on colony color, mating type and repetitive DNA elements. Each set of isolates from four perithecia possessed the genetic markers from only one parent in each cross. However, each set of isolates from the other two perithecia had markers from both parents. Tissues containing both parental genomic components may thus take part in construction of perithecial wall. Received 13 October 2000/ Accepted in revised form 12 March 2001  相似文献   
994.
The effect of long-storage and silica gel desiccation of hyacinth bulbs (Hyacinthus orientalis L.) on in vitro bulblet formation was investigated.Bulbs of 3 cultivars were stored at 25°C and 50–60% relative humidity for 17 months. This long-term storage of bulbs markedly enhanced bulblet initiation from scales and growth of regenerated bulblets.Bulbs of 5 cultivars were desiccated with silica gel for 5 and 20 h before in vitro propagation. The total number of bulblets increased as a result of 5 h desiccation with silica gel. Bulb desiccation for 20 h caused a large increase in the growth rate of bulblets. This desiccation treatment with silica gel is a practical method to obtain many and more regenerative explants in the in vitro propagation of hyacinth.  相似文献   
995.
Effects of darkness during the growing-period on the internode elongation of tulips were investigated. The last internode was the longest one when grown under natural light conditions, while continuous darkness caused the first internode to elongate the most. Application of a 5-day dark treatment to growing tulips during the phase of rapid stem extension resulted in significant increase in the length of the first internode. It was effective in obtaining taller tulips owing to increased elongation of the first internode, and may be effectively applied to tulip cut-flower production.  相似文献   
996.
997.
We report the case of a 4-year-old, castrated 4.2-kg Scottish fold cat with recurrent epistaxis that was unresponsive to medical therapy. Diathermocoagulation of the nasal mucosa with a diode laser controlled the epistaxis and there was no significant recurrence of epistaxis during 1 year of follow-up.  相似文献   
998.
999.
The aim of the present study was to investigate whether changes in body temperature are related to the ovarian cycle in elephants. Rectal, tongue or fecal temperature was measured for 2 Asian and 5 African elephants using an electric thermometer. Evaluation of ovarian cycles was based on the changes in serum or fecal progestin. The mean +/- SD values of the rectal, tongue, and fecal temperatures were 36.3 +/- 0.3 (2 Asian), 36.2 +/- 0.5 (1 African) and 36.5 +/- 0.3 C (4 African), respectively; the fecal temperature was the highest of the 3 temperatures (P<0.01). The longitudinal changes in body temperatures correlated with the ovarian cycle, with higher temperatures occurring during the luteal phase. The fecal temperatures of one acyclic African elephant did not change cyclically. These results suggest that measurement of body temperature can be used to easily evaluate the ovarian cyclicity of an individual animal, although it might not be able to determine the ovarian cycle length.  相似文献   
1000.
Seven avian polyomaviruses (APVs) were isolated from seven psittacine birds of four species. Their whole genome sequences were genetically analyzed. Comparing with the sequence of BFDV1 strain, nucleotide substitutions in the sequences of seven APV isolates were found at 63 loci and a high level of conservation of amino acid sequence in each viral protein (VP1, VP2, VP3, VP4, and t/T antigen) was predicted. An A-to-T nucleotide substitution was observed in non-control region of all seven APV sequences in comparison with BFDV1 strain. Two C-to-T nucleotide substitutions were also detected in non-coding regions of one isolate. A phylogenetic analysis of the whole genome sequences indicated that the sequences from the same species of bird were closely related. APV has been reported to have distinct tropism for cell cultures of various avian species. The present study indicated that a single amino acid substitution at position 221 in VP2 was essential for propagating in chicken embryonic fibroblast culture and this substitution was promoted by propagation on budgerigar embryonic fibroblast culture. For two isolates, three serial amino acids appeared to be deleted in VP4. However, this deletion had little effect on virus propagation.  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