首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   72821篇
  免费   4600篇
  国内免费   5027篇
林业   8233篇
农学   5016篇
基础科学   4605篇
  12272篇
综合类   33802篇
农作物   3446篇
水产渔业   2291篇
畜牧兽医   7869篇
园艺   2105篇
植物保护   2809篇
  2024年   307篇
  2023年   1462篇
  2022年   2308篇
  2021年   2673篇
  2020年   2586篇
  2019年   2765篇
  2018年   1584篇
  2017年   2723篇
  2016年   3361篇
  2015年   2808篇
  2014年   4068篇
  2013年   4078篇
  2012年   5788篇
  2011年   5722篇
  2010年   4490篇
  2009年   4479篇
  2008年   3973篇
  2007年   4605篇
  2006年   3882篇
  2005年   3094篇
  2004年   2505篇
  2003年   2166篇
  2002年   1583篇
  2001年   1473篇
  2000年   1322篇
  1999年   1014篇
  1998年   838篇
  1997年   734篇
  1996年   657篇
  1995年   683篇
  1994年   599篇
  1993年   450篇
  1992年   372篇
  1991年   322篇
  1990年   245篇
  1989年   223篇
  1988年   165篇
  1987年   114篇
  1986年   55篇
  1985年   35篇
  1984年   28篇
  1983年   9篇
  1982年   24篇
  1981年   18篇
  1980年   10篇
  1979年   11篇
  1978年   9篇
  1962年   6篇
  1956年   8篇
  1955年   4篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
The design of multi-controller and multi-mode control law is presented for the three-link Acrobot on horizontal bar by employing Human simulated intelligent control method based on sensory-motor Schema.Imitated the characteristics of gymnast's swing-up and handstand movement,the control process of robot is divided by six sequence phase.Then the sensory cell and motor cell and the group of sensory-motor schema is designed based on the analysis of quality-quantity combination.The simulation results show that the controller ensures the gesture and the energy to the desired goal,farther more the motion control of giant swing backword is realized in the simulation.  相似文献   
962.
Based on the result of NiMH battery performance experiments, changing trend of maximal temperature and difference in temperature of HEV NiMH battery in different SOC and different charging current is analyzed. Considering the working situation of HEV NiMH battery and the theory of battery quick charging, a control strategy for NiMH battery quick charging is described which adapts to HEV regenerative braking system based on Mascc law. By Modeling and simulating the process of NiMH battery quick charging with this strategy, constant voltage charge method and constant current charge method, validates this control strategy.  相似文献   
963.
In this paper,four models are selected as the representatives and applied to nonlinear dynamic analysis program for space frames which is based on the beam-column elements using the finite element flexibility method and the fiber model.Park's test on combined axial and bending columns under cyclic loading are taken as the calibrations,comparisons to material and structural member level are drawn and the analytical results of various models are discussed.  相似文献   
964.
Reference efficiency of a pair of gear drive without planetary motion is the base to calculate efficiency of the whole planetary gear train. The authors find reference efficiency for speed increase is higher than that of the same drive used for speed reduction. This is different from the earlier viewpoint. New equations are derived for correctly calculating the reference efficiency of spur gear and helical gear with internal conjugate and external conjugate either in the state of speed increase or speed reduction respectively. The equations are also used to calculate efficiency of 2K-H planetary gear train.  相似文献   
965.
966.
967.
In this paper, the historical reasons of formation of the village inside the city are analyzed. It is indicated that such situation for the villages inside the city are the result of joint action of both the villagers and the government. The foundation of villages inside the city laid on the simple compensation for farmers in confiscating the rural land and lack of intelligence aids. In this paper, the ideas and measures for their reconstruction are put forward based on consideration of the reasons of their formation and difficulties in the reconstruction.  相似文献   
968.
Critical information system in Interact is in face of increasingly security problems. More attention has been focused on the survivability of information system, which is the capability of system to continue its mission even in the presence of damage to the system. The authors first introduce the definition of survivability. According to four function properties of survivability, which are Resistance, Recognition, Recovery, and Adaption, the authors design a model of survivable system structure and then explain survivability requirement, survivability strategy in this model. Additionally, they provide possible technical solutions for the survivability of systems, categorized by different aspects of our survivability strategy.  相似文献   
969.
In this paper, the selection of type, function and technological requirements of EMCS for Shenzhen Underground has been introduced.Based on the investigation for EMCS's worldwide applications and the analysis of practice in Shenzhen Underground, the comparison and selection of PLC and DDC have been done completely.At the same time,the introduction of EMCS is organized by the center level, station level and the spot level.  相似文献   
970.
Hydrodynamic models have been widely applied to river and coastal engineering projects. Understanding the hydrodynamic process is a prerequisite to modeling the pollution and sediment transport process. Hydrodynamic models of varying degrees of complexity should be selected appropriately according to the object of study, physical properties of the flow domain and hydrodynamic features. The essential procedure of hydrodynamic simulation is described in this paper. The main problems such as selection of model dimension in physical space, choice of variables, boundary conditions, initialization, design of computational grid, model resolution, parameterization of smaller scale fluctuations and sub-grid scale processes, model calibration and verification are investigated.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号