全文获取类型
收费全文 | 931篇 |
免费 | 26篇 |
国内免费 | 1篇 |
专业分类
林业 | 105篇 |
农学 | 39篇 |
基础科学 | 2篇 |
97篇 | |
综合类 | 78篇 |
农作物 | 29篇 |
水产渔业 | 132篇 |
畜牧兽医 | 415篇 |
园艺 | 6篇 |
植物保护 | 55篇 |
出版年
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 22篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 28篇 |
2013年 | 51篇 |
2012年 | 34篇 |
2011年 | 47篇 |
2010年 | 23篇 |
2009年 | 33篇 |
2008年 | 50篇 |
2007年 | 44篇 |
2006年 | 43篇 |
2005年 | 51篇 |
2004年 | 27篇 |
2003年 | 45篇 |
2002年 | 29篇 |
2001年 | 41篇 |
2000年 | 35篇 |
1999年 | 25篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1970年 | 5篇 |
1967年 | 3篇 |
1966年 | 5篇 |
1965年 | 2篇 |
排序方式: 共有958条查询结果,搜索用时 0 毫秒
41.
42.
43.
Ebihara M Sekimoto S Shirai N Hamajima Y Yamamoto M Kumagai K Oura Y Ireland TR Kitajima F Nagao K Nakamura T Naraoka H Noguchi T Okazaki R Tsuchiyama A Uesugi M Yurimoto H Zolensky ME Abe M Fujimura A Mukai T Yada Y 《Science (New York, N.Y.)》2011,333(6046):1119-1121
A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated. 相似文献
44.
45.
A Mycoplasma iowae (MI) species-specific DNA probe (designated pMI-2) of 6.0 kbp (kilobase pairs) was isolated from an MI strain I-695 genomic library prepared in plasmid pUC8 and Escherichia coli strain JM83. When labeled with [32]P by nick translation, the probe hybridized in dot blot assays with 6 reference strains and 8 field isolates of MI but not with 16 other known species of avian mycoplasmas. The pMI-2 probe detected a minimum of 1.5 ng of MI strain I-695 chromosomal DNA. Under identical conditions of hybridization, the probe did not hybridize with a high concentration (200 ng) of M. gallisepticum or M. synoviae chromosomal DNA. 相似文献
46.
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
47.
48.
This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous
fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and
the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension
wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli.
These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably
caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage
of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant
in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction
of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling
might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers. 相似文献
49.
50.
Sujan KC Yamamoto Hiroyuki Matsuo Miyuki Yoshida Masato Naito Kazuhiro Shirai Tatsuya 《Wood Science and Technology》2015,49(6):1157-1169
Wood Science and Technology - Tension wood, when kiln-dried, is likely to deform hugely, which is probably caused by a gelatinous layer of the gelatinous fiber. To elucidate the mechanism behind... 相似文献