全文获取类型
收费全文 | 10239篇 |
免费 | 732篇 |
国内免费 | 1041篇 |
专业分类
林业 | 685篇 |
农学 | 1525篇 |
基础科学 | 466篇 |
1501篇 | |
综合类 | 3842篇 |
农作物 | 560篇 |
水产渔业 | 531篇 |
畜牧兽医 | 1271篇 |
园艺 | 298篇 |
植物保护 | 1333篇 |
出版年
2024年 | 79篇 |
2023年 | 251篇 |
2022年 | 474篇 |
2021年 | 517篇 |
2020年 | 576篇 |
2019年 | 597篇 |
2018年 | 425篇 |
2017年 | 634篇 |
2016年 | 677篇 |
2015年 | 569篇 |
2014年 | 583篇 |
2013年 | 695篇 |
2012年 | 810篇 |
2011年 | 780篇 |
2010年 | 568篇 |
2009年 | 519篇 |
2008年 | 449篇 |
2007年 | 453篇 |
2006年 | 360篇 |
2005年 | 286篇 |
2004年 | 238篇 |
2003年 | 172篇 |
2002年 | 155篇 |
2001年 | 128篇 |
2000年 | 111篇 |
1999年 | 119篇 |
1998年 | 97篇 |
1997年 | 76篇 |
1996年 | 81篇 |
1995年 | 66篇 |
1994年 | 72篇 |
1993年 | 86篇 |
1992年 | 64篇 |
1991年 | 51篇 |
1990年 | 42篇 |
1989年 | 42篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1962年 | 3篇 |
1956年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
101.
A Coptis Chinesis is the dry rhizoma of ranunculaceous Coptis Chinesis Franch or Coptis deltoidea C. 7. Cheng et Hisao, or Coptis teeta Wall. It is the traditional Chinese herb, which is used in the contagious diseases. In recent years, its new pharmacological actions have been reported, which are antitumour, hypoglycemic response, immunoloregulation, improving the functions of cardiovascular. The important pharmacological functions of Coptis Chinesis are hypoglycemic response, improving the functions of cardiovascular, antitumour. With the deeply researching of Coptis Chinesis pharmacology, and the continuous founding of pharmacological mechanism, new preparation will be widely applied in the clinic. 相似文献
102.
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
103.
Based on the data of dynamic tests of small single-storey steel frames,the suitability of simplified hi-linear restoring force model in earthquake response analysis is discussed, and the Maximum displacement response MD, the sum of squares of the displacements in the whole vibrating history SSD, and the total dissipated energy EI are considered respectively as equivalent object. 相似文献
104.
Huang Zongming 《保鲜与加工》1996,(3):42-48
Parameters dominating elasto- plastic earthquake response of SDOF systems,relation between ground motion amplitude and elasto- plastic response of SDOF systems are presented in this paper. 相似文献
105.
Yang Changqi 《保鲜与加工》1995,(1):81-86
This paper presents the basic equations and algorithm of vehicle crashworthinessbriefly.Take a light-truck for example,some applied problems in ustng Engineering WorkStationto analysis truck crashworthiness are discussed.A installation method of contact surface is intro-duced,Finally,a nurnerical simulation result is presented. 相似文献
106.
Pushover analysis is a tool to study the inelastic behavior of structures under strong seismic action. The 3D-pushover analysis was performed to analyze the inelastic lateral-torsional coupled response of multistory asymmetric structures. The symmetric frame and frame-wall systems were studied in this paper, and the capability curve of the top displacement and base shear,the story drift and the position of rotation center were compared with reference to corresponding symmetric structures. The characters of inelastic response of multistory asymmetric structures were found. The conclusion provides reference for performance-based seismic design of asymmetric structures. 相似文献
107.
108.
A reservoir operational rule for irrigation in Japan 总被引:1,自引:0,他引:1
Yutaro Senga 《Irrigation and Drainage Systems》1991,5(2):129-140
Operation of a reservoir for irrigation is more complicated and difficult than that for domestic water supply in Japan, owing to the fact that a requirement for irrigation takes various value depending upon effective rainfall on farmland, soil condition, and so on. Therefore, the reservoirs should be operated to correspond with demand, inflow, and unknown droughts occurring in the future. However, the reservoirs have been operated under operators' experiences without formal operational rules, because any effective theories or methods have been neither developed nor used in Japan at present.On operation of the reservoirs, there are two targets — promotion of effective release and restriction of release in preparation for droughts — conflicting with each other. It is useful to set up the operation with Required Storage for Drought Curve (RSDC) Method to achieve reasonable operation harmonizing those two targets. RSDC is composed with Target Line (TL) and Restrictive Release Lines (RRLs). TL is a target storage level to guarantee that storage will never empty until the end of the irrigation period under a certain probability. If actual storage remains above TL, effective release will be promoted. RRLs are storage levels pointing out the basis of restricting release. If actual storage falls below TL, release will be restrained in accordance with RRLs in order to get over uncertain droughts occurring in the future.In this paper, the theory of RSDC is described and the effectiveness of Rule Curve (RC) based on RSDC Method is illustrated by simulation on a single reservoir for irrigation. 相似文献
109.
利用大量的统计资料,研究了防旱减灾经济效益的计算方法,其中重点提出了临时抗旱措施的经济效益计算方法,可供今后计算抗旱效益时应用和参考。 相似文献
110.
In spite of several attempts at integrated operation planning, multiple reservoirs in Japan have been operated by trial and error without any formal rules. Subjects of integrated operation are not only showing optimal usage of daily storage levels as an operational policy but also providing a countermeasure for droughts.Objectives of this study are to make a formal operation rule of multiple reservoirs for irrigation using the theory of Required Storage for Drought Curve (RSDC) Method and to propose operational policy for multiple reservoirs as large water supply systems. The Iwaki river basin, on which there are four reservoirs for irrigation parallel with each other, is considered to be a model river basin with a large water system for this case study.From results of simulations using historical data, comparing an individual operation rule with an integrated operation rule on several indices, effectiveness of the latter rule is recognized. Under integrated operation, water losses are minimized and excessive water conservation can be avoided over the whole area to benefit while target river discharge is maintained at key control points because water usage from all reservoirs is well balanced in relation to water availability. 相似文献