全文获取类型
收费全文 | 64889篇 |
免费 | 2182篇 |
国内免费 | 5346篇 |
专业分类
林业 | 9426篇 |
农学 | 9336篇 |
基础科学 | 4749篇 |
10791篇 | |
综合类 | 14785篇 |
农作物 | 4493篇 |
水产渔业 | 3486篇 |
畜牧兽医 | 7571篇 |
园艺 | 2620篇 |
植物保护 | 5160篇 |
出版年
2024年 | 129篇 |
2023年 | 456篇 |
2022年 | 1288篇 |
2021年 | 1991篇 |
2020年 | 1725篇 |
2019年 | 1798篇 |
2018年 | 3824篇 |
2017年 | 4204篇 |
2016年 | 2756篇 |
2015年 | 2335篇 |
2014年 | 2099篇 |
2013年 | 2580篇 |
2012年 | 3787篇 |
2011年 | 5336篇 |
2010年 | 5112篇 |
2009年 | 4128篇 |
2008年 | 3975篇 |
2007年 | 4239篇 |
2006年 | 2667篇 |
2005年 | 2705篇 |
2004年 | 1263篇 |
2003年 | 1115篇 |
2002年 | 853篇 |
2001年 | 837篇 |
2000年 | 1053篇 |
1999年 | 1342篇 |
1998年 | 1210篇 |
1997年 | 1023篇 |
1996年 | 949篇 |
1995年 | 874篇 |
1994年 | 869篇 |
1993年 | 786篇 |
1992年 | 720篇 |
1991年 | 588篇 |
1990年 | 492篇 |
1989年 | 397篇 |
1988年 | 275篇 |
1987年 | 190篇 |
1986年 | 92篇 |
1985年 | 74篇 |
1984年 | 51篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1968年 | 10篇 |
1963年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
An ultrafast optical shutter was used to image ultrasmall objects hidden behind scattering walls by a procedure that selects in time the ballistic component and rejects the scattered diffusive light. Scattering walls used in this experiment included human breast tissue, chicken breast tissue, and a water suspension of polystyrene particles with scattering coefficients up to 21.7. Submillimeter resolution was achieved for two-dimensional ballistic images of a single point, a double-point fluorescence source, and a bar test chart in or behind these different turbid media. 相似文献
72.
In order to optimize design and operation, it is necessary to calculate accurately hydraulic characteristics large central air-conditioning systems. Simplified Model can not be applied to hydraulic calculation of large pipe network topological structure for its large calculation error. Taking into account the regulating characteristics of terminal branch temperature regulating valve, a direct-return chilled water system is studied, an accurate mathematical model of pipe network hydraulic characteristics has been established and a computer logic algorithm with virtual flow has been given. A direct-return pipe network with ten AHU branches is used as simulation calculation object, the pipe network supply-return water pressure difference is calculated, and also the temperature regulating valve opening and actual flow of each branch are calculated in the condition of different supply-return water pressure difference. The calculated results accord with the natural characteristics of high pressure difference unbalanced for direct-return pipe network. The calculation method can ensure calculation convergence. 相似文献
73.
林草措施在西北地区水土保持中的作用及实施探讨 总被引:1,自引:0,他引:1
依据西北地区的自然条件,阐述了开展林草措施的重要性及在水土保持中的作用,提出了林草措施实施当中应当注意的问题及解决方案。 相似文献
74.
75.
76.
Pavarot Noranarttragoon Yuji Ueda Tsutomu Hattori Takashi Matsuishi 《Fisheries Science》2011,77(4):497-502
The yield-per-recruit (YPR) analysis has been used to assess growth overfishing of exploited fish stocks. Since the ex-vessel
price per weight widely depends on the size of the fish, the result of the YPR does not imply the revenue. The value-per-recruit
(VPR) analysis, which is an economic expansion of the YPR analysis, was conducted for bighand thornyhead Sebastolobus macrochir caught off the Pacific coast of northern Honshu, Japan. The results showed that, for the current age at first capture (t
c = 3), the current fishing mortality (F = 0.12) was close to the optimum level. However, for the current F, optimum t
c in the VPR model was 8 years and would lead to a 47% increase compared to the current revenue. The maximum YPR was obtained
at t
c = 6 years, but the revenue at t
c = 6 only gave a 20% increase in the maximum revenue. The difference was caused by the size dependency of the ex-vessel price
per weight. The VPR model would generate fisheries management plans with both economical and biological consideration and
would help in making general consensus of fisheries management strategies. 相似文献
77.
两年的抑菌、刻伤接种和果实贮藏试验表明,双胍盐对柑桔青霉病的防治效果与伊迈唑相接近,可作为苯并咪唑类的替换药剂。 相似文献
78.
79.
80.