全文获取类型
收费全文 | 17974篇 |
免费 | 987篇 |
国内免费 | 1748篇 |
专业分类
林业 | 1476篇 |
农学 | 1662篇 |
基础科学 | 1098篇 |
2235篇 | |
综合类 | 7612篇 |
农作物 | 1118篇 |
水产渔业 | 809篇 |
畜牧兽医 | 2656篇 |
园艺 | 1112篇 |
植物保护 | 931篇 |
出版年
2024年 | 124篇 |
2023年 | 365篇 |
2022年 | 800篇 |
2021年 | 826篇 |
2020年 | 798篇 |
2019年 | 764篇 |
2018年 | 542篇 |
2017年 | 830篇 |
2016年 | 596篇 |
2015年 | 963篇 |
2014年 | 942篇 |
2013年 | 1071篇 |
2012年 | 1363篇 |
2011年 | 1445篇 |
2010年 | 1276篇 |
2009年 | 1114篇 |
2008年 | 1096篇 |
2007年 | 997篇 |
2006年 | 923篇 |
2005年 | 774篇 |
2004年 | 470篇 |
2003年 | 384篇 |
2002年 | 479篇 |
2001年 | 389篇 |
2000年 | 327篇 |
1999年 | 195篇 |
1998年 | 112篇 |
1997年 | 98篇 |
1996年 | 90篇 |
1995年 | 89篇 |
1994年 | 80篇 |
1993年 | 56篇 |
1992年 | 69篇 |
1991年 | 72篇 |
1990年 | 35篇 |
1989年 | 44篇 |
1988年 | 33篇 |
1987年 | 26篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1965年 | 1篇 |
1964年 | 3篇 |
1962年 | 1篇 |
1956年 | 6篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
以陕西长武旱塬为例,分别对研究区农地和5个不同林龄(9、12、16、19 a和23 a)苹果园的土壤剖面氢氧稳定同位素进行测定,利用Craig-Gordon模型定量估算其土壤平均蒸发量,并基于“空间换时间”方法分析果园种植及生长对土壤蒸发的影响。结果表明:农地及9、12、16、19、23 a林龄苹果园的土壤蒸发量均随苹果树的种植及生长呈现先减少再增大的趋势,年均蒸发量分别为129、104、89、119、128、136 mm;苹果园的土壤蒸发量变化与叶面积指数呈显著负相关(R=-0.713);苹果园种植的前中期(9~12 a)土壤蒸发量随叶面积指数增加逐渐减小,而在中后期(12~23 a)深层土壤水被大量消耗造成的干旱胁迫使得果树叶面积减少,从而导致林下土壤蒸发量又逐渐增大。 相似文献
95.
96.
Yi Shuping Gai Xuchang Xu Xiangsui 《保鲜与加工》1992,(2):65-70
Based on Group Technology, part families of the norm of working hour are formed according to the similarity among components. With the progressive regerssion, the models of the norm of working hour are built for every part family. A computer aided norm model building program and a computer aided norm of working hour planning system are developed. The system is successfully integrated with CAD/CAPP system. Some examples of the model building and calculation results are illustrated as well. 相似文献
97.
A developing method is given which based on object-oriented modeling techniques for management information systems.The modeling techniques,especially,from CDM to PDM conversion,make it possible that the method can be used for developing such management information systems which based on relational database.The result shows that it can raise the efficency of the system developing,improve the system tability,enhance the system maintenability. 相似文献
98.
Based on analyzing about blasting mode of slope in the construction of road, the paper shows that pre splitting blasting is mostly suitable in the section of severely weathering soft rock with developed joints and fractures, introduced the laying out about the hole of pre splitting blasting that can apply in the high slope of the expressway in the section, and designed the parameter. The practice shows that it gained favourable effect by this method. 相似文献
99.
According to Electrodynamics in curved spacetime, the interaction between gravitational waves (GW) and electromagnetic (EM) fields will produce perturbative electromagnetic fields. In a special EM system, namely, a Gaussian beam (Gb) propagating through a static magnetic field, the photon flux along the direction of the electric field of the Gb will be only a pure perturbative photon flux,when a GW propagates along the symmetric axis of a Gaussian beam. Detailed alanysis and calculation of the photon flux along several typical surfaces are performed, and a possible optimum plane which can receive perturbative photons up to 10~4s~(-1) is proposed. It is possible to provide an important method to detection of GW. 相似文献
100.
In the general directing-operation expert systems.the information of directingoperation is often shown after the subprocess has finished,The aim of the thesis is to enhance thefunction of directing-operation,and suggest that we add the self-tuning predictor in the expertsystems and use it to direct the present operation.We have shown the case oftemperature-predicting experiment made in the small wine distillatorv so that we can illustrate thatit is feasible to use the predictor to direct the operation. 相似文献