全文获取类型
收费全文 | 6196篇 |
免费 | 448篇 |
国内免费 | 299篇 |
专业分类
林业 | 1378篇 |
农学 | 381篇 |
基础科学 | 300篇 |
664篇 | |
综合类 | 2416篇 |
农作物 | 471篇 |
水产渔业 | 215篇 |
畜牧兽医 | 453篇 |
园艺 | 88篇 |
植物保护 | 577篇 |
出版年
2024年 | 10篇 |
2023年 | 113篇 |
2022年 | 128篇 |
2021年 | 221篇 |
2020年 | 169篇 |
2019年 | 193篇 |
2018年 | 128篇 |
2017年 | 186篇 |
2016年 | 225篇 |
2015年 | 240篇 |
2014年 | 284篇 |
2013年 | 361篇 |
2012年 | 441篇 |
2011年 | 456篇 |
2010年 | 384篇 |
2009年 | 343篇 |
2008年 | 356篇 |
2007年 | 360篇 |
2006年 | 319篇 |
2005年 | 293篇 |
2004年 | 189篇 |
2003年 | 219篇 |
2002年 | 192篇 |
2001年 | 155篇 |
2000年 | 161篇 |
1999年 | 143篇 |
1998年 | 86篇 |
1997年 | 91篇 |
1996年 | 78篇 |
1995年 | 60篇 |
1994年 | 60篇 |
1993年 | 49篇 |
1992年 | 54篇 |
1991年 | 52篇 |
1990年 | 39篇 |
1989年 | 39篇 |
1988年 | 32篇 |
1987年 | 14篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有6943条查询结果,搜索用时 15 毫秒
81.
82.
83.
GIS在林业专题制图中的应用 总被引:10,自引:0,他引:10
论述了运用于理信息系统软件完成应用遥感技术进行思茅地区样地清查及进行“二项调查”的制衅工作,重点阐明了整个制作过程、成果分析、该注意的几点事项。成果得到相关部门的认可,该方法可应用于林业专题图的制作。 相似文献
84.
85.
86.
Guo Jianfen Xie Jinsheng Lu Haoliang Liu Dongxia Yang Yusheng Chen Guangshui 《中国林学(英文版)》2004,6(1):33-36
The amount of carbon returned through litterfall and its seasonal pattern were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata) (CF) in Sanming, Fujian Province, China. Mean annual carbon return through total litterfall over 3 years (from 1999 to 2001)
was 5.097 t·hm−2 in the NF, 4.337 t·hm−2 in the CK and 2.502 t·hm−2 in the CF respectively. Of the total carbon return in the three forests, leaf contribution accounted for 58.96%, 68.53% and
56.12% and twig 24.41%, 22.34% and 26.18%, respectively. The seasonal patterns of carbon return from total litterfall and
leaf-litter were quite similar among the three forests. A peak of carbon input from litterfall in the NF and the CK occurred
in spring except for the highest annual C return through branch litter of the NF in summer, while the CF showed the maximum
C return in summer. The results of this study demonstrate that the natural forest has a greater C return through litterfall
than monoculture plantations, which is beneficial to the increase of soil organic matter storage and the maintenance of soil
fertility.
[Supported by the Teaching and Research Award Program of MOE P.R.C. (TRAPOYT) and the Key Basic Research Project of Fujian
Province (2000F004)] 相似文献
87.
88.
Stand structure and the regeneration ofChamaecyparis pisifera on sites with and without well-developed soil in an old-growth coniferous forest, Akasawa Forest Reserve, central Japan,
were investigated, along with their relationships to other important coniferous species. Of stems ofC. pisifera≥5 cm diameter at breast height, stems with intermediate size were absent in stands on the developed-soil site, while those
with smaller size increased in stands on the undeveloped-soil site, which supported a higher density ofC. pisifera. In the stands without recent tree-fall of canopy stems on the developed-soil site, canopy stems ofC. pisifera were distributed uniformly and the understory stems, patchily. On the other hand, both canopy and understory stems ofC. pisifera in stands on the undeveloped-soil site were distributed patchily. In the understory,C. pisifera occurred as clonal patches formed by vegetative reproduction on various types of microsites including bare rocks. However,
the clonal patches did not occur in a stand on the developed-soil site with dense saplings of an evergreen conifer,Thujopsis dolabrata, which can expand vegetatively with a well developed soil layer. Gap formation may induceC. pisifera to develop tree-form stems from shrubby clonal patches. On developed-soil sites,C. pisifera stands that survive a long disturbance-free period on this site need catastrophic disturbance for their regeneration, which
will eliminateT. dolabrata in the understory and create bare soil for colonization ofC. pisifera from seeds. On undeveloped-soil sites,C. pisifera replaces itself continuously by effective vegetative reproduction. Ground instability and the wet condition of this site
may promote the replacement. 相似文献
89.
90.
The dynamic mating systems of conifers 总被引:4,自引:0,他引:4
J. B. Mitton 《New Forests》1992,6(1-4):197-216
Conifer mating systems vary among species and within species; both ecological variables and genetic variation cause mating systems to be dynamic. Within species, estimates of rates of outcrossing vary among populations, among loci, and among individuals within stands. The level of outcrossing varies with stand density, age, and the abundance of local and foreign pollen. Variation in the mating success of both males and females violates the assumption that populations are randomly mating and at equilibrium, and justifies more quantitative analyses of mating systems. Allelic frequencies in the pollen pool and in the pool of receptive female surfaces may vary through a season and among seasons, producing positively assortative mating in time. Seed and seedling viability selects against homozygotes for lethal alleles and favors heterozygous genotypes, biasing estimates of outcrossing. Particularly fruitful topics of research include the genetic consequences of polyembryony, differential male and female mating success, and associations between specific genotypes and floral phenology. 相似文献