全文获取类型
收费全文 | 1970篇 |
免费 | 99篇 |
国内免费 | 166篇 |
专业分类
林业 | 277篇 |
农学 | 83篇 |
基础科学 | 491篇 |
328篇 | |
综合类 | 607篇 |
农作物 | 50篇 |
水产渔业 | 101篇 |
畜牧兽医 | 141篇 |
园艺 | 27篇 |
植物保护 | 130篇 |
出版年
2024年 | 5篇 |
2023年 | 30篇 |
2022年 | 39篇 |
2021年 | 38篇 |
2020年 | 36篇 |
2019年 | 74篇 |
2018年 | 44篇 |
2017年 | 48篇 |
2016年 | 68篇 |
2015年 | 57篇 |
2014年 | 53篇 |
2013年 | 87篇 |
2012年 | 143篇 |
2011年 | 92篇 |
2010年 | 93篇 |
2009年 | 77篇 |
2008年 | 109篇 |
2007年 | 232篇 |
2006年 | 171篇 |
2005年 | 122篇 |
2004年 | 125篇 |
2003年 | 54篇 |
2002年 | 38篇 |
2001年 | 50篇 |
2000年 | 36篇 |
1999年 | 36篇 |
1998年 | 39篇 |
1997年 | 29篇 |
1996年 | 32篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 28篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2235条查询结果,搜索用时 31 毫秒
1.
2.
Daisuke Shiode Yasuzumi Fujimori Fuxiang Hu Susumu Shimizu Teisuke Miura 《Fisheries Science》2001,67(1):110-117
SUMMARY: Flume-tank experiments were performed to examine the depth response of a new type of depth-controlled gillnet. Variations of net depth were investigated as the warp was paid out and wound up for different changes of warp length, main sinker weights, and winch speeds. In most experiments, when the warp finished paying out, the net continued to descend and then ascended slightly to an equilibrium depth (overshoot phenomenon). The overshoot distance was nearly constant when the warp was wound up and increased linearly with increasing winch speed when the warp was paid out. An increase in winch speed reduced net settling time, which converged on a constant value for both paying out and winding up. 相似文献
3.
成文法有其局限性 ,这种局限性是其本身固有而又是它自身无法克服的。判例制度正是克服了这一局限性的有效形式。 相似文献
4.
5.
6.
在沙尘暴应急监测方法研究中,通过对总悬浮颗粒物采样仪器及各种采样参数的研究确定和降尘采样器的研制,制定出沙尘暴应急监测方法。 相似文献
7.
马克思主义哲学是创新的科学,它离不开理论创新。实践基础上的理论创新推动了马克思主义哲学的产生和发展,赋予它与时俱进的理论品质,使它永葆科学青春和旺盛的生命力;理论创新离不开马克思主义哲学的指导。马克思主义哲学为理论创新提供正确的世界观,提供科学的方法论,提供正确的方向保证。只有坚持马克思主义哲学的指导,全面贯彻“三个代表”的要求,才能在实践中不断推进理论创新。 相似文献
8.
Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability 总被引:1,自引:0,他引:1
As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution. 相似文献
9.
Heritability and genetic correlations between rumination time and production traits in Holstein dairy cows during different lactation phases
下载免费PDF全文
![点击此处可从《Zeitschrift für Tierzüchtung und Züchtungsbiologie》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Riccardo Moretti Marcos Paulo Gonçalves de Rezende Stefano Biffani Riccardo Bozzi 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2018,135(4):293-299
So far, rumination has been used as a proxy for monitoring dairy cow health at farm level. However, investigating its genetic aspects as well as its correlation with other important productive traits may turn this management tool into a new informative selection criterion. However, scientific evidences on genetic correlation among rumination time (RT) and milk production and milk composition are still scarce. Therefore, the objective of this study was to estimate the heritability of RT across three lactation phases and its genetic correlation with milk production, milk composition and somatic cell count (SCC). Results of our study showed that heritability for RT was 0.34 and was constant across lactation. The mean genetic correlations between RT and milk production and composition traits were 0.07 (milk production), ?0.07 (protein yield), ?0.31 (fat yield), and ?0.32 (fat/protein ratio). The mean genetic correlation between RT and the SCC was 0.05. 相似文献
10.