全文获取类型
收费全文 | 5088篇 |
免费 | 590篇 |
国内免费 | 176篇 |
专业分类
林业 | 414篇 |
农学 | 549篇 |
基础科学 | 176篇 |
922篇 | |
综合类 | 948篇 |
农作物 | 206篇 |
水产渔业 | 431篇 |
畜牧兽医 | 1576篇 |
园艺 | 110篇 |
植物保护 | 522篇 |
出版年
2024年 | 7篇 |
2023年 | 74篇 |
2022年 | 57篇 |
2021年 | 68篇 |
2020年 | 110篇 |
2019年 | 145篇 |
2018年 | 219篇 |
2017年 | 244篇 |
2016年 | 201篇 |
2015年 | 222篇 |
2014年 | 216篇 |
2013年 | 282篇 |
2012年 | 299篇 |
2011年 | 369篇 |
2010年 | 316篇 |
2009年 | 247篇 |
2008年 | 291篇 |
2007年 | 286篇 |
2006年 | 249篇 |
2005年 | 244篇 |
2004年 | 147篇 |
2003年 | 156篇 |
2002年 | 130篇 |
2001年 | 194篇 |
2000年 | 186篇 |
1999年 | 138篇 |
1998年 | 78篇 |
1997年 | 69篇 |
1996年 | 61篇 |
1995年 | 58篇 |
1994年 | 42篇 |
1993年 | 36篇 |
1992年 | 52篇 |
1991年 | 49篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 36篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1979年 | 9篇 |
1967年 | 4篇 |
1966年 | 6篇 |
1956年 | 4篇 |
1903年 | 4篇 |
1893年 | 4篇 |
1892年 | 7篇 |
排序方式: 共有5854条查询结果,搜索用时 0 毫秒
1.
Impact of grassland contract policy on soil organic carbon losses from alpine grassland on the Qinghai–Tibetan Plateau 下载免费PDF全文
J. Cao Y. Gong E. T. Yeh N. M. Holden J. F. Adamowski R. C. Deo M. Liu J. Zhou J. Zhang W. Zhang S. Zhang D. Sheng S. Yang X. Xu M. Li Q. Feng 《Soil Use and Management》2017,33(4):663-671
Carbon storage in the soils on the Qinghai–Tibetan Plateau plays a very important role in the global carbon budget. In the 1990s, a policy of contracting collective grasslands to smaller units was implemented, resulting in a change from the traditional collective grassland management to two new management patterns: a multi‐household management pattern (MMP: grassland shared by several households without enclosures) and a single‐household management pattern (SMP: grassland enclosed and used by only one household). In 2016, 50 MMP and 54 SMP winter pastures on the Qinghai–Tibetan Plateau were sampled to assess the differences in soil organic carbon (SOC) between the two management patterns. Results showed that average SOC was significantly greater under MMP than under SMP, with an estimated 0.41 Mg C/ha/yr lost due to SMP following the new grassland contract. Based on the government's grassland policy, four grassland utilization scenarios were developed for both summer and winter pastures. We found that if the grassland were managed under SMP, likely C losses ranged between 0.31 × 107 and 6.15 × 107 Mg C/yr across the Qinghai–Tibetan Plateau relative to MMP, which more closely resembles pre‐1990s grassland management. Previous estimates of C losses have only considered land use change (with cover change) and ignored the impacts driven by land management pattern changes (without cover change). The new data suggest that C losses from the Qinghai–Tibetan Plateau are greater than previously estimated, and therefore that the grassland contract policy should be reviewed and SMP households should be encouraged to reunite into the MMP. These findings have potential implications for land management strategies not only on the Qinghai–Tibetan Plateau but also other grazing regions globally where such practices may exist. 相似文献
2.
X M Zhang W Herbst H Lange-Herbst T Schliesser 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(10):765-770
1,268 sera collected from slaughtered pigs in Hassia (FRG) from 1986 to 1988 were tested for antibodies against porcine and human influenza A virus strains using the single radial haemolysis test (SRHT). Antibodies against the porcine strains (subtype H1N1) A/Swine/Arnsberg/1/81, A/Swine/Iowa/15/30 and A/New Jersey/7/76 were detected in 411 (32.4%), 318 (25.1%) and 304 (24.0%) of sera, respectively. Up to 1988 a slight increase (10%) in the seroprevalence to A/Swine/Arnsberg/1/81 was noticed, whereas the results obtained with the other strains showed little variation. Antibodies against the human H1N1 strain A/Singapore/6/86 were only found in sera collected 1987 and 1988 in rates of 1.6% and 3.0%. Serological indication of infections with the human H3N2 strains A/Victoria/1/75, A/Hong Kong/1/68 and A/Philippines/2/82 could be shown in 286 (22.6%), 178 (14.4%) and 135 (10.6%) of the serum samples. Within the three year period the rate of sera positive for antibodies against A/Philippines/2/82 increased from 6.5% to 23.0%, whereas no variation in the rates were found using the other H3N2 strains. Antibodies simultaneously against porcine (H1N1) and human (H3N2) virus strains were detected in 9.9% of all sera tested. 相似文献
3.
利用犬温热,细小病毒性肠炎,犬传染性肝炎,狂犬病等弱毒株,以香菇多糖和动物的核糖,多肽做为免疫增强剂,对异源动物羊,猪,犊牛,家兔进行了免疫应答,筛选出了猪做为异源免疫动物。在免疫增强剂的参与下,完成了多次免疫应答,达到了理想的免疫球蛋白(IgG),通过试验摸清了该制剂的免疫程序,确定了生产工艺,经重复性试验,稳定性试验及含量测定,以及临床应用试验和现志应用试验均达以了预期效果,该制剂经冷冻干燥后 相似文献
4.
5.
6.
7.
8.
Amelinckx S Zhang XB Bernaerts D Zhang XF Ivanov V Nagy JB 《Science (New York, N.Y.)》1994,265(5172):635-639
The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition. 相似文献
9.
10.