全文获取类型
收费全文 | 18065篇 |
免费 | 980篇 |
国内免费 | 1718篇 |
专业分类
林业 | 1656篇 |
农学 | 1506篇 |
基础科学 | 997篇 |
2028篇 | |
综合类 | 7854篇 |
农作物 | 1125篇 |
水产渔业 | 859篇 |
畜牧兽医 | 2676篇 |
园艺 | 1166篇 |
植物保护 | 896篇 |
出版年
2024年 | 96篇 |
2023年 | 340篇 |
2022年 | 769篇 |
2021年 | 876篇 |
2020年 | 817篇 |
2019年 | 771篇 |
2018年 | 524篇 |
2017年 | 829篇 |
2016年 | 637篇 |
2015年 | 943篇 |
2014年 | 932篇 |
2013年 | 1162篇 |
2012年 | 1496篇 |
2011年 | 1508篇 |
2010年 | 1380篇 |
2009年 | 1299篇 |
2008年 | 1190篇 |
2007年 | 1191篇 |
2006年 | 896篇 |
2005年 | 678篇 |
2004年 | 459篇 |
2003年 | 314篇 |
2002年 | 350篇 |
2001年 | 343篇 |
2000年 | 278篇 |
1999年 | 156篇 |
1998年 | 91篇 |
1997年 | 76篇 |
1996年 | 60篇 |
1995年 | 53篇 |
1994年 | 47篇 |
1993年 | 46篇 |
1992年 | 38篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 25篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1956年 | 5篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用一段从PEG胁迫的鹰嘴豆幼苗叶片所构建的cDNA文库中得到的EST序列,通过3¢RACE方法克隆到一个鹰嘴豆C2H2型锌指蛋白基因ZF1,该基因不含内含子,编码一条244个氨基酸残基的多肽,含有两个典型的Cys2/His2锌指结构。其氨基酸序列含有一个可能的核定位型号,农杆菌介导的洋葱表皮细胞GFP瞬时表达实验表明,ZF1蛋白位于细胞核内。半定量RT-PCR分析表明,ZF1在鹰嘴豆的根、茎、叶、花、幼荚和幼胚中均有表达,在茎和叶中表达较弱,为组成型转录因子。半定量RT-PCR和实时荧光定量PCR检测结果显示,ZF1不但受高温及干旱诱导,而且还受6-苄基腺嘌呤(6-BA)、脱落酸(ABA)、乙烯利(Et)、赤霉素(GA3)、吲哚-3-乙酸(IAA)、茉莉酸甲酯(MeJA)、水杨酸(SA)和氧胁迫诱导。这些结果表明,ZF1基因可能作为一个核调控因子参与植物的生长代谢以及多种生物与非生物胁迫的应答。 相似文献
992.
The removal of oxytetracycline (OTC) in water by UV, UV/TiO2, UV/Zeolite, and UV/Composite photocatalyst with different ratio was investigated respectively with a 32W low voltage mercury lamp. The effects of composite photocatalyst concentration, initial OTC concentration and pH value on degradation were also investigated. It was shown that the UV/Composite photocatalyst with 10% TiO2 and 90% Zeolite was an effective one to remove OTC in water. And in a solution with 50 mg/L OTC in ultrapure water the OTC was removed by 99% within 120 min with the help of 300 mg/L composite photocatalyst. The degradation of OTC by UV/Composite photocatalyst was little influenced by its initial concentration, but influenced by its initial pH. In the environment with pH+2~10, the OTC was removed by more than 95% within 120 min with the help of UV/Composite photocatalyst, when the pH is above 10, the removal rate is rapidly decreased. 相似文献
993.
The distribution of turbulence intensity under different rotation speed was analyzed to seek micro indexes reflecting hydraulic conditions of active sludge system by PIV (Particle Image Velocimetry) in a stirring SBR (Sequencing Batch Reactor). Based on the SBR degradation capacity, flocs structure under different rotating speed of stirring paddle, the influences of turbulence intensity on the degradation capacity were studied, and the indexes of turbulence intensity in the main part of stirring zone and other parts were given. The results show that the specified degradation constant of the pollutants in the active sludge reactor increases firstly and then decreases with the increasing of turbulence intensity. The optimum indexes of turbulence intensity in the experiment are 1.4% of main part and 0.34% of other parts. The turbulence intensity indexes in the active sludge system reflect part differences of hydraulic conditions. The turbulence intensity has remarkable influence on the breaking up of active sludge in the main part of stirring zone, while it has good correlation with the collision and gathering of sludge flocs in other parts of the reactor. 相似文献
994.
To use fly ash, it is necessary to understand its activity variation under different wet conditions. Four low-calcium wet fly ash preparations are simulated in the laboratory. Fly ash activity is indicated by measuring specific compressive stre 相似文献
995.
996.
福建省太阳总辐射计算方法及时空分布 总被引:1,自引:1,他引:1
根据福州1971—2008年、建瓯1992—2008年、广州1991—2008年、汕头1991—2008年、南昌1991—2008年、赣州1991—2008年共6站历年各月太阳总辐射和日照百分率,采用最小二乘法拟合出各地太阳总辐射的计算公式:Q=Q0(a+bs),通过精度对比,确定了福州模式为适用于福建的计算公式,推算出福建各地逐月、季、年太阳总辐射,利用GIS绘制得各季及年太阳总辐射空间分布图,分析福建太阳总辐射时空分布特征,结果表明:福建省太阳总辐射季节及年分布总体趋势是从福建的东南部沿海向西北部减少;季节平均每月太阳总辐射从大到小顺序排列为夏季、春季(秋季)、冬季。 相似文献
997.
气候变化对福州植物气候生产力的影响分析 总被引:1,自引:2,他引:1
利用Thornthwaite Memoriae模型估算了福州市近30多年来的植物气候生产力的状况,在分析了年均气温、降水量、风速和相对湿度年际变化的基础上,探讨了植物气候生产力的变化原因。植物气候生产力与年均气温、风速成正比,故20世纪70年代后期和90年代后,受其影响,植物气候生产力在增大;植物气候生产力与年降水量和相对湿度成反比,所以20世纪70年代前期以及80年代,植物气候生产力在逐渐降低。 相似文献
998.
To be effectively heated in incinerator for MSW is very important for stabilization and completeness combustion, the smaller produce of the PCDD/Fs. At the same time, the transient heat transfer characteristics of the MSW lump decides the stay time of the MSW in incinerator and effects on the operation feature of the combustion equipments. All of these would lead to design the reasonable and clean combustion project, the optimum incinerator and recover energy system. The component, shape, dimension, property, the hardly and inner structure feature of the MSW lump are taken in account, and the effective conduct heat coefficient has been adopted. And then, the physical model is setup with different shape(ball, cylinder, squareness), and the 3-D mathematical model and conduct heat efficient with porous feature for transient heat transfer of MSW lump are presented, at the same time, the simulation tests are gotten in various boundary and the interesting conclusions are gotten: The center stable temperature of the MSW lump is mostly decided by the inner gas temperature of the incinerator and the heated area of the lump. The transient heat transfer characteristics is variously effected by the shape of the MSW lump in incinerator. The transient process becomes longer and the center stable temperature decreases, the volatile can't be easily separated out and the combustion efficiency decreases because of the increasing of the lump feature dimension. 相似文献
999.
In 1995, Padmanabhan and Vrat presented inventory models for deteriorating items with a constant selling price and stock dependent selling rate . Based on the result, in 2000, Kun-Jen Chung, Peter Chu and Shaw-Ping Lan devoloped the necessary and sufficient conditions of the existence and uniqueness of the optimal solutions of the profit per unit time functions without backlogging and with complete backlogging. Actually, the selling price need not be constant, it may be variable . This paper puts forward an EOQ model when the selling price is variable without backlogging, discusses the existence and uniqueness of optimum solution. The example is provided to illustrate the model. The theoretical evidence is provided for the inventory system to make management decision. 相似文献
1000.
With the rapid increase of the Internet user and widely application of Web,the current network technology is facing great challenge. More and more multimedia operations occupy plenty of bandwidth,and result in the network congestion. Therefore,people begin to use QoS to utilize the bandwidth effectively,and ensure the transport of the emergent operation data. The paper introduces the protocols and basic components of QoS,then expatiates the conception and the basic principles of policy control QoS, moreover,emphasizes the structure model of policy control QoS and how it runs. At last,it introduces the transport process of data packets under the control of policies in a policy control QoS system,and how to make the policies in the real world. 相似文献