全文获取类型
收费全文 | 8692篇 |
免费 | 512篇 |
国内免费 | 869篇 |
专业分类
林业 | 796篇 |
农学 | 689篇 |
基础科学 | 708篇 |
2272篇 | |
综合类 | 3861篇 |
农作物 | 493篇 |
水产渔业 | 219篇 |
畜牧兽医 | 488篇 |
园艺 | 209篇 |
植物保护 | 338篇 |
出版年
2024年 | 44篇 |
2023年 | 148篇 |
2022年 | 263篇 |
2021年 | 331篇 |
2020年 | 345篇 |
2019年 | 348篇 |
2018年 | 290篇 |
2017年 | 392篇 |
2016年 | 517篇 |
2015年 | 405篇 |
2014年 | 533篇 |
2013年 | 611篇 |
2012年 | 776篇 |
2011年 | 712篇 |
2010年 | 517篇 |
2009年 | 535篇 |
2008年 | 429篇 |
2007年 | 448篇 |
2006年 | 383篇 |
2005年 | 320篇 |
2004年 | 267篇 |
2003年 | 215篇 |
2002年 | 147篇 |
2001年 | 138篇 |
2000年 | 142篇 |
1999年 | 97篇 |
1998年 | 76篇 |
1997年 | 92篇 |
1996年 | 73篇 |
1995年 | 75篇 |
1994年 | 78篇 |
1993年 | 57篇 |
1992年 | 61篇 |
1991年 | 57篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Zhaolong CHENG Yongtao LI Matthew Keith PINE Tao ZUO Mingxiang NIU Jun WANG 《Integrative zoology》2023,18(1):169-182
The associations between feeding activities and environmental variables inform animal feeding tactics that maximize energetic gains by minimizing energy costs while maximizing feeding success. Relevant studies in aquatic animals, particularly marine mammals, are scarce due to difficulties in the observation of feeding behaviors in aquatic environments. This data scarcity concurrently hinders ecosystem-based fishery management in the context of small toothed-cetacean conservation. In the present study, a passive acoustic monitoring station was deployed in an East Asian finless porpoise habitat in Laizhou Bay to investigate potential relationships between East Asian finless porpoises and their prey. The data revealed that porpoises were acoustically present nearly every day during the survey period. Porpoise detection rates differed between spring and autumn in concert with activities of fish choruses. During spring, fish choruses were present throughout the afternoon, and this was the time when porpoise vocalizations were the most frequently detected. During autumn, when fish choruses were absent, porpoise detection rates decreased, and diurnal patterns were not detected. The close association between fish choruses and finless porpoise activities implies an “eavesdropping” feeding strategy to maximize energetic gains, similar to other toothed cetaceans that are known to engage similar feeding strategies. Underwater noise pollution, particularly those masking fish choruses, could interrupt finless porpoises’ feeding success. Fisheries competing soniferous fishes with finless porpoise could impact finless porpoise viability through ecosystem disruption, in addition to fishing gear entanglement. 相似文献
92.
海河二道闸和防潮闸优化调度研究 总被引:1,自引:0,他引:1
汛期为腾空海河河道并保证二道闸下咸水不致上溯,二道闸闸下水位应控制在1.0m左右。利用一维非恒定流模型对海河自西河闸至入海口河段进行数值模拟,研究了西河闸分流量为80、100、120m3/s3种情况下,海河防潮闸和二道闸优化调度结果。 相似文献
93.
巢湖流域沿岸分布着很多圩区,人们在圩内进行各种农业活动,圩区营养盐的输出是造成巢湖流域非点源污染的重要因素。为了解圩区农业非点源营养盐的输出特征,笔者通过在巢湖流域河网地区选择比较典型的圩区,于2014年水稻生长期进行了较系统的野外调查观测、取样和室内水质分析,探讨在自然降雨-径流的条件下圩区各类营养盐的浓度变化及输出特征。2014年稻季共进行了9次排水,排水量总计73.09 mm,径流系数为0.37,9次排水事件总氮(TN)和总磷(TP)的平均浓度分别是3.42、0.22 mg/L,圩区水体处于富营养化水平。降雨-径流强度是影响营养盐浓度变化的重要因素,稻季生长期内TN和TP的输出量是0.28、0.017 kg/hm2,占稻季施肥总量的1.7%和0.16%。径流量是影响营养盐输出总量的关键因素,同时施肥量和施肥至排水事件的间隔天数也是是影响营养盐输出的重要因素。 相似文献
94.
95.
Yang Chunwei 《保鲜与加工》1988,(4)
This paper studies the tactics choice and its improvement in the development of economy by means of Markovian Decision Programming. An optimal decision and the maximum expected revenue can be obtained. The . paper also presents the procedures and formulas of numerical evaluation. 相似文献
96.
Li Maoqin Duan Yurong 《保鲜与加工》1989,(4):22-29
In this paper, a kind of grey linear programming with grey interval coefficients is discussed,the definitions of the first and second whitenized linear programmlngs and the grey dual linear programmings are presented, the relationships between the solutions of the above three kinds of programming and the solution of the primal programming are explored, and some new conclusions are obtained. 相似文献
97.
Liu Chongde Wang Xiaoming Gu Lan 《保鲜与加工》1992,(6):10-17
A optimal design with whole structure parameters and its program are carried out. A reasonable model is established. Using the method a optimal design with whole structure parameters by original parameters of American P&H2300xp excavator was calculated. The size,carried out by the method,approximates to the size of P&H2300xp excavator very well. 相似文献
98.
Li Jianping Zhang Wanping Chen Tinghuai Shu Wenzhi 《保鲜与加工》1997,(2):63-68
Based on the optimal control theory and Lagrange interpolation an optimal design model of plane cascades of 3D blade in an arbitrary surface of revolution is established. Using wavelet theory to solve the model, and lots of numerical results are obtained. The results show that the wavelet method is more effective than the conventional methods. 相似文献
99.
The edge-edge connectivity of a graph is defined,and a class of quasi-regulargraphs is proposed with a maximum edge-edge connectivity. 相似文献
100.