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   151275篇
  免费   23351篇
  国内免费   441篇
林业   13113篇
农学   14195篇
基础科学   7580篇
  22226篇
综合类   35719篇
农作物   6753篇
水产渔业   6686篇
畜牧兽医   55802篇
园艺   3050篇
植物保护   9943篇
  2024年   1272篇
  2023年   1332篇
  2022年   2109篇
  2021年   3252篇
  2020年   3360篇
  2019年   3245篇
  2018年   2869篇
  2017年   3662篇
  2016年   3689篇
  2015年   4176篇
  2014年   4213篇
  2013年   6840篇
  2012年   6428篇
  2011年   7503篇
  2010年   6232篇
  2009年   6087篇
  2008年   6781篇
  2007年   6613篇
  2006年   6504篇
  2005年   5780篇
  2004年   3830篇
  2003年   3639篇
  2002年   3146篇
  2001年   4045篇
  2000年   4387篇
  1999年   4009篇
  1998年   2704篇
  1997年   2410篇
  1996年   2239篇
  1995年   2369篇
  1994年   2062篇
  1993年   1961篇
  1992年   2877篇
  1991年   2878篇
  1990年   2595篇
  1989年   2520篇
  1988年   2280篇
  1987年   2227篇
  1986年   2157篇
  1985年   1971篇
  1984年   1574篇
  1983年   1377篇
  1979年   1395篇
  1978年   1139篇
  1975年   991篇
  1974年   1275篇
  1973年   1305篇
  1972年   1242篇
  1971年   1152篇
  1970年   1096篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
浅析内蒙古草地现状、退化成因及发展建议   总被引:4,自引:0,他引:4  
简析了内蒙古草地现状、退化成因,针对其退化的成因提出了几点发展建议,以便为今后发展内蒙古牧畜业提供借鉴参考作用。  相似文献   
992.
谭旭  王秀  童玲 《农机化研究》2013,(1):220-223
针对目前国内农业WebGIS存在的信息单一、功能单调等问题,提出了将标准的地理信息系统开发平台和Google Maps同时应用于农业WebGIS的方法。利用Google Maps提供的开放地图接口自定义GoogleMap类可以为农业WebGIS系统提供详细的地理位置信息的显示、标注以及路线查询等功能。最后通过SuperMap.IS.NET开发平台与Google Maps实现对小汤山农业基地的信息管理,证明该方法实用可行。  相似文献   
993.
994.
995.
  1. The effects of different fibre sources on the growth performance, carcass characteristics and gastrointestinal tract development were studied in growing Greylag geese (Anser anser).

  2. Four experimental diets were formulated with corn (maize) straw silage (CSS), steam-exploded corn (maize) straw, steam-exploded wheat straw, and steam-exploded rice straw as fibre sources. A total of 224 male Greylag geese at 28 d of age were randomly assigned to one of the 4 experimental diets.

  3. The birds fed on the CSS diets had higher average daily feed intakes than those fed on the steam-exploded straws. However, the 4 treatments had similar average daily gain, which contributed to significant differences in feed conversion ratios. The different fibre sources had no significant effects on the carcass characteristics.

  4. The CSS-fed birds had larger gizzards and lower relative length of the caeca than the other three groups. However, the relative weights and lengths of the other gut segments, the relative weights of major organs and the pH values of the gastrointestinal contents were similar between the 4 treatments.

  5. It was concluded that straw fibres with different physico-chemical properties exerted an effect on daily feed intake and gastrointestinal development, especially for the gizzard. The pretreatment of straw had a large effect on utilisation efficiency and animal performance. Steam explosion is a promising straw pretreatment for inclusion in diets for geese.

  相似文献   
996.

Background  

Inkjet micropatterning is a versatile deposition technique with broad applications in numerous fields. However, its application in plant science is largely unexplored. Leaf expansion is one of the most important parameters in the field of plant science and many methods have been developed to examine differential expansion rates of different parts of the leaf lamina. Among them, methods based on the tracking of natural landmarks through digital imaging require a complicated setup in which the leaf must remain fixed and under tension. Furthermore, the resolution is limited to that of the natural landmarks, which are often difficult to find, particularly in young leaves. To study the fine scale expansion dynamics of the leaf lamina using artificial landmarks it is necessary to place small, noninvasive marks on a leaf surface and then recover the location of those marks after a period of time.  相似文献   
997.
针对以往税务稽查选案主要依靠传统的手工操作和计算机随即抽取等两种方法,常出现选案目标与案情实际差异过大而造成纳税检查效果不明显的实际状况,提出国家应构建增值税纳税信息报警系统,实现税务稽查部门按照纳税异常情况的警报提示通过网络平台有针对性地选案的设想,并分析了网络选案系统的基本原理,研究了支撑增值税稽查网络选案系统的指标体系及要求,探讨了嵌入各种涉税业务核算程序和数据时警报系统可以产生的反应。  相似文献   
998.
采用群体遗传学理论与方法研究了陕西省秦川牛场秦川牛保种群30多年来的保种情况,详细地分析了保种群的规模、年龄结构及迁移情况。研究发现,该保种群规模变化剧烈,总的来说规模偏小,尤其是公牛群远小于保种遗传学基本法则规定的最小值;畜群结构不稳定,迁入不规则,该研究结果将为今后采取适当的措施提高保种效果提供科学的参考依据。  相似文献   
999.
1000.
Land use/land cover data for fifteen minor civil divisions (MCDs) in Ulster County, New York (USA) were interpreted from 1968 and 1985 aerial photographs. These data were combined with ancillary physiographic and demographic data as raster layers within a computerized geographic information system (GIS). Class to class changes in land use/land cover were quantified for a study area approximately 30 kilometers by 50 kilometers. The relationships between the land use/land cover variables and the ancillary variables were modeled in a series of weighted least squares regressions employing data spatially aggregated by general soil map unit (N = 44).Between 1968 and 1985, nearly one-third of the study area changed to another land use/land cover class. Land in the urban class increased from 6.7% to 17.8% of the study area, while the forest class declined from 65.0% to 55.2%, and the agriculture class declined from 12.7% to 8.9%. Gains and losses in the remaining five major (Level I) land use/land cover classes were relatively small. Land use changes primarily involved the conversion of land from the forest, agriculture, and vacant classes to the urban class, and from the agriculture class to the forest and vacant classes. Variables accounting for the variance in the land use/land cover class proportions of the soil units were population density, highway proximity, distance to urban centers, mean elevation, mean slope gradient, and soil suitability for farming and for urban development.  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