全文获取类型
收费全文 | 3567篇 |
免费 | 536篇 |
国内免费 | 12篇 |
专业分类
林业 | 203篇 |
农学 | 330篇 |
基础科学 | 40篇 |
680篇 | |
综合类 | 409篇 |
农作物 | 154篇 |
水产渔业 | 427篇 |
畜牧兽医 | 1403篇 |
园艺 | 76篇 |
植物保护 | 393篇 |
出版年
2023年 | 58篇 |
2022年 | 25篇 |
2021年 | 17篇 |
2020年 | 52篇 |
2019年 | 100篇 |
2018年 | 202篇 |
2017年 | 187篇 |
2016年 | 164篇 |
2015年 | 155篇 |
2014年 | 166篇 |
2013年 | 199篇 |
2012年 | 200篇 |
2011年 | 244篇 |
2010年 | 210篇 |
2009年 | 171篇 |
2008年 | 213篇 |
2007年 | 194篇 |
2006年 | 175篇 |
2005年 | 162篇 |
2004年 | 116篇 |
2003年 | 109篇 |
2002年 | 66篇 |
2001年 | 142篇 |
2000年 | 149篇 |
1999年 | 95篇 |
1998年 | 46篇 |
1997年 | 44篇 |
1996年 | 36篇 |
1995年 | 31篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 37篇 |
1991年 | 38篇 |
1990年 | 40篇 |
1989年 | 23篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1971年 | 4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4115条查询结果,搜索用时 15 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
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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.
Seasonal Changes in the Milt Quality of Waigieu Seaperch,Psammoperca waigiensis: Implications for Artificial Propagation
下载免费PDF全文
![点击此处可从《Journal of the World Aquaculture Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Milt quality of Waigieu seaperch was sampled at the beginning, the middle, and the end of the spawning season to assess if the sampling season has an effect on milt quality parameters. The milt volume and total sperm production were higher at the middle of the spawning season while the sperm concentration in milt was significantly higher at the beginning and the end of the spawning season. Sperm morphology and the major parameters of seminal plasma (pH, total protein, Mg2+, or Ca2+ concentrations) did not differ throughout the spawning season. The concentrations of Na+ and the osmolality increased throughout the spawning season. The percentage of motile cells did not differ during the spawning season while the duration of sperm motility (swimming duration) and velocity (swimming speed) were significantly different during the spawning season. The fertilization rate (75.7 ± 6.8%) and hatching rate (56.5 ± 3.1%) at the middle of the spawning season were higher than at the beginning and end periods. Results indicated that milt quality parameters and fertility success in the middle of the spawning season were higher compared to earlier and later sampling dates. Thus, we recommend collecting milt during this time for maximal fertilization and hatching success. 相似文献
3.
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
4.
5.
6.
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
7.
8.
James F X Wellehan Maud Lafortune Darryl J Heard 《Journal of zoo and wildlife medicine》2004,35(2):197-202
Traumatic elbow luxation was diagnosed in a common squirrel monkey (Saimiri sciureus) and a bonnet macaque (Macaca radiata). In the common squirrel monkey, the luxation was complicated by an ulnar fracture and would not stay reduced when attempts at closed reduction were made. The luxation was surgically reduced and a transarticular type I external skeletal fixator was placed. In the bonnet macaque, closed reduction was performed and the elbow was stabilized using a cast. Both monkeys regained good function of the injured elbows. 相似文献
9.
10.
P.A. Benjama M. El Gadda E. El Boustani C. El Modafar X. Nesme J. Cubero 《EPPO Bulletin》2004,34(3):403-406
Le meilleur moyen de contrôle du crown gall ( Agrobacterium tumefaciens ) est la prévention et donc la détection de la bactérie pathogène dans les sols prévus pour les pépinières. Pour cela nous avons essayé une approche moléculaire utilisant la PCR pour caractériser le plasmide pTi par le couple des amorces spécifiques F14/F44 dans les sols de diverses régions marocaines. Cette technique de détection représente un indicateur potentiel d'avertissement sur l'état d'infection des sols et plants par A. tumefaciens qui permet ainsi de déclencher la lutte biologique par le NoGall, produit commercial australien, hébergeant l'antagoniste K1026 . 相似文献