全文获取类型
收费全文 | 74531篇 |
免费 | 3455篇 |
国内免费 | 8409篇 |
专业分类
林业 | 9451篇 |
农学 | 12348篇 |
基础科学 | 7108篇 |
12753篇 | |
综合类 | 21193篇 |
农作物 | 3835篇 |
水产渔业 | 2752篇 |
畜牧兽医 | 9874篇 |
园艺 | 2230篇 |
植物保护 | 4851篇 |
出版年
2024年 | 169篇 |
2023年 | 723篇 |
2022年 | 1910篇 |
2021年 | 2778篇 |
2020年 | 2645篇 |
2019年 | 2537篇 |
2018年 | 1741篇 |
2017年 | 2477篇 |
2016年 | 2519篇 |
2015年 | 3253篇 |
2014年 | 3103篇 |
2013年 | 3865篇 |
2012年 | 4500篇 |
2011年 | 5009篇 |
2010年 | 4725篇 |
2009年 | 4470篇 |
2008年 | 4354篇 |
2007年 | 4357篇 |
2006年 | 4205篇 |
2005年 | 3726篇 |
2004年 | 1797篇 |
2003年 | 1667篇 |
2002年 | 1293篇 |
2001年 | 1463篇 |
2000年 | 1676篇 |
1999年 | 1981篇 |
1998年 | 1961篇 |
1997年 | 1636篇 |
1996年 | 1497篇 |
1995年 | 1421篇 |
1994年 | 1236篇 |
1993年 | 1177篇 |
1992年 | 985篇 |
1991年 | 823篇 |
1990年 | 704篇 |
1989年 | 603篇 |
1988年 | 466篇 |
1987年 | 284篇 |
1986年 | 179篇 |
1985年 | 85篇 |
1984年 | 77篇 |
1983年 | 70篇 |
1982年 | 57篇 |
1981年 | 46篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1965年 | 12篇 |
1964年 | 14篇 |
1963年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
The high-precision displacement measuring technology of optic-measuring mechanics is, for the first time,successfully applied on the similar model of the model land-layer with a new-type variable modulus of elasticity. The angle of movement and the distributed displacement of upper and lower rock-layers are measured. The technology is a combination of laser's technology and the modern chemical sticker-it is called the sticking moire interferometry. Compared with the measured values, the result is very satisfactory. 相似文献
973.
为对菲牛蛭抗凝血活性物质的提取进行优化,通过采取不同方法对菲牛蛭活体(6种)、干体(6种)及唾液腺分泌物(3种)进行提取得出最适提取方法。结果表明对于菲牛蛭活体和干体均是采取80%预冷丙酮提取得到的抗凝血物质含量高,最高分别达至(61.20±1.13)AT-U/g和(89.19±1.13)AT-U/g;对于菲牛蛭唾液腺分泌物则是采取10%的三氯乙酸提取得到的抗凝血物质含量高,最高达(24.41±0.98)AT-U/g。研究结果得出了适合菲牛蛭活体、干体和唾液腺分泌物中提取抗凝血活性物质的最适方法,有利于推动水蛭素的大规模生产和广泛的临床应用。 相似文献
974.
Wang Yuanliang Li Shiqi 《保鲜与加工》1992,(2):116-121
Several aspects of the conditional equation derived from the accumulative equation are discussed in detail. The results indicate that the conditional equation not only is well consistent with the principles of electronegativity and absolute hardness equalization, but also satisfies the bonding of a full -prerequisite condition, e. g. two like electronic charge species repel and unlike attract each other'. In addition these principles are in the accumulative state. Mathematically, some other aspects of the conditional equation are worth studying based on the generalization of this equation. 相似文献
975.
Cao Changxiu Wang WanLiang 《保鲜与加工》1989,(5):68-75
The predictive intelligent control scheme is proposed, which is based on approximation theory and numerical method of Chcbyshev orthogonal polynomial. It has the practical value to the cold storge using widely electromagnetic valve and can be also applied similar systems in orther area. 相似文献
976.
This paper uses the method of mixed-type series to derive the analyticsolution of cylindrical shell roof,being simply supported transversely,arbitra-rily restrained longitudinally and subjected to gereral transverse local loads.This paper also presents the analytic expressions of the solutions for somekinds of local load.Some examples of this kind of shell roof subjected to ainlined single force near the middle of it with free lorgitudinal edges aregiven.The computation shows that the convergence of the solution is woll 相似文献
977.
Wang Dongyun 《保鲜与加工》1988,(1)
On the basis of outlining our present situation of city water supply and itsgeological map compilation,this paper suggests a new principle which should befollowed in the compiling work of city water supply hydrogeological maps and themain contents of compilation and the ways of expression as one of the map com-piliing plans to be discussed in this field. 相似文献
978.
Wang Bingle Song Liquan 《保鲜与加工》1988,(2)
This paper presents a new method by using mass and acceleration parameters for balancing inertial force of mechanism. Compared with other balance methods, this one is simple, clear and superior in regularity when the balancing equation of complex mechanism is established, and its solving procedure is also easy. The new methcd is convenient to learn and use as well as convenient to program. 相似文献
979.
Wang Xeqin 《保鲜与加工》1988,(2)
This paper presents the equal theory of the sine wave voltage and PWM waveform in the integration of time. Using the graphic method as well as the comparison method of sequential integration the PWM control pattern is calculated. Depending on an example for PWM circuit inverter the microcomputer is investi-gated. The method is simple and effective. It is specially adeguate to the engineering control. 相似文献
980.
Wang XiaoruMi Linshu 《保鲜与加工》1990,(3)
Based on the experiment, magnetizing characteristic and its mathematical model of iron for the reactance transformer DKB has been studied in this paper. Its simulating calculation model has been achieved and implemented by program. The result of the simulation is satisfactory compared with that of the experiment. 相似文献