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排序方式: 共有811条查询结果,搜索用时 15 毫秒
51.
XU Ming REN Haiqing LI Xiazhen Research Institute of Wood Industry Chinese Academy of Forestry Beijing P.R.China 《中国林业科技(英文版)》2007,(3)
The variation of tensile strength parallel to grain in Chinese fir and I-214 poplar wood from plantations was studied in this paper. Aaccording to the national standards The Testing Methods for Physical and Mechanical Properties of Wood (GB 1927 to 1943 ? 1991), the small clear wood samples were cut and tested, which represent the south and north of trees with heights of 1.3, 3.3, 5.3 and 7.3 m. The results showed: the tensile strength parallel to grain of the north wood was higher than that of south wood. ANOVA shows that the tensile strength parallel to the grain with height is of significant difference (at 0.05 level). 相似文献
52.
Atsushi IKEDA 《中国林业科技(英文版)》2002,(4)
Chinese fir (Cunninghamia lanceolata) and poplar (Populus spp.) wood meal were phenolated in the presence of sulfuric acid used as a catalyst. The effects of reaction time and reaction temperature on the wood liquefaction were investigated. The results showed that the reaction temperature had the greater influence on the residue content than reaction time. Additionally, the liquefaction curve for the Chinese fir and Poplar were similar in general. 相似文献
53.
TIAN Xiaorui SHU Lifu WANG MingyuThe Research Institute of Forest Ecology. Environment Protection. Chinese Academy of Forestry. Beijing . China 《中国林业科技(英文版)》2002,(4)
The fuelbreaks were established in south China from 1950s. With the active work of local communities and state government, the fuelbreaks have been built for 398,000 kilometers. In some areas, fuelbreaks and firebreaks have constructed a network primarily, such as in the provinces of Fujian, Guangdong, Guangxi. The fuelbreaks can prevent forest fire effectively. That has been approved by actual examples and burning tests. The fuelbreaks also benefit the forest ecosystem and environment. This paper makes a review on fuelbreaks research and application in China, discussed present research achievements about fuelbreaks mechanism and its development. In the future, the Chinese government and local communities will increase investment in the construction of firebreaks network with fuelbreaks as focal points. 相似文献
54.
樟子松是沙地主要针叶造林树种,沙地樟子松林天然分布于内蒙古自治区呼伦贝尔市红花尔基;红花尔基地区的气候特点为高纬度、低海拔、寒冷半湿润、短无霜期。沙地樟子松于20 世纪50 年代在科尔沁沙地引种成功,但一直不能天然更新,并于 20 世纪 90 年代初出现了生长衰退、枯梢直至死亡的现象,而天然沙地樟子松林无论在更新还是生长上却一直处于健康状态。为了认识天然沙地樟子松林天然林的更新特征,于 2004 年 7-8 月对红花尔基天然沙地樟子松林的20 块样地、3 种林窗(2 圆形、5 窄长方形、3 宽长方形)樟子松天然更新指数进行了调查。结果表明,林龄大的林分(大于 50 年)总平均更新指数高于林龄小的林分(小于 50 年),最大更新指数达29株m-2。更新的苗龄绝大多数小于10年生。回归分析表明,林龄是决定天然更新的主要因子;虽然樟子松是阳性树种,但林冠的郁闭度似乎对天然更新没有直接影响。林窗更新调查结果表明,林窗内更新指数都较高;对于圆形林窗更新高峰出现在林窗南缘和东缘,而对于窄长方形林窗,更新高峰则出现于东缘;而且更新苗龄相对较大(最大达 38 年)。上述结果表明樟子松更新苗具有一定的耐阴性,但如果没有较大林窗或较大的其它干扰,如火、风雪害或皆伐等,更新苗木将很难进行入主林冠层。 相似文献
55.
The annual ring width, density and shrinkage variation from pith to bark in Chinese fir (Cunninghamia lanceolata) and Boka sugi (Cryptomeria japonicd) were studied and compared. The results show that the ring width decreased sharply from pith to bark for Chinese fir. However, the ring width variation pattern for Boka sugi followed a different way, i.e., the ring width decreased to the fifth ring, increased to the tenth ring, decreased again to the fifteenth, and then increased to the twentieth, where it became constant. The large variations of Boka sugi appeared to show the maintenance of fast growth for many years. The annual ring mean density of Chinese fir increased gradually from pith to bark. However, the density changes for Boka sugi indicated the opposite trend, i.e., the mean density decreased gradually from pith to bark. The former showed a pattern as the same as a pine and a larch, and the latter was often found in a cedar and a cypress. The longitudinal shrinkage in juvenile wood was much hig 相似文献
56.
一中国鸡蛋的市场占有量和发展方向
亚洲是全球最大的蛋品市场,全球养殖蛋鸡70亿只,中国蛋鸡数量13亿只,占全球蛋鸡养殖总量的18.5%,中国的鸡蛋产量占全球37.2%。可见中国是全球最重要的蛋品市场。中国大部分蛋鸡采用笼养的模式,美国93%的蛋鸡都采用笼养。从蛋品的消费量来看,中国位列世界第四,2011年人均消费鸡蛋295个(见表1)。 相似文献
57.
鸡蛋生产和蛋品加工是全球化的技术,其相关知识具有通用性。当养殖场所有生产要素都达到平衡时,家禽生产必然收获成功,包括品种、营养(饲料和水)、保健、禽舍、设备和饲养员等。饲料成本占据禽类肉蛋生产成本的60%-80%。虽然设备投资仅占2%-3%,但对饲料成本的节约却起到决定性的作用。控制成本要跟踪记录盈利水平,主要参数有饲料、用水量、温度、能耗等相关费用。 相似文献
58.
Benjamin Ruiz 《中国禽业导刊》2014,(19):32-33
一家禽业概况
拉丁美洲有25个国家,其中巴西和阿根廷是全球玉米、大豆的主产国和出口国,巴西和墨西哥分别是全球第三大和第五大鸡肉生产国,墨西哥是全球第三大鸡蛋生产国,人均鸡蛋消费量位居全球第一(人均365个),鸡肉和鸡蛋是大多数拉丁美洲国家人们每天的主食。 相似文献
59.
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