全文获取类型
收费全文 | 89092篇 |
免费 | 4427篇 |
国内免费 | 9579篇 |
专业分类
林业 | 9707篇 |
农学 | 12620篇 |
基础科学 | 7279篇 |
13648篇 | |
综合类 | 29869篇 |
农作物 | 4885篇 |
水产渔业 | 3079篇 |
畜牧兽医 | 12507篇 |
园艺 | 3845篇 |
植物保护 | 5659篇 |
出版年
2024年 | 260篇 |
2023年 | 988篇 |
2022年 | 2526篇 |
2021年 | 3494篇 |
2020年 | 3028篇 |
2019年 | 3080篇 |
2018年 | 2153篇 |
2017年 | 3174篇 |
2016年 | 2900篇 |
2015年 | 4107篇 |
2014年 | 3992篇 |
2013年 | 4775篇 |
2012年 | 5943篇 |
2011年 | 6356篇 |
2010年 | 6271篇 |
2009年 | 5741篇 |
2008年 | 5303篇 |
2007年 | 5418篇 |
2006年 | 5049篇 |
2005年 | 4426篇 |
2004年 | 2191篇 |
2003年 | 2063篇 |
2002年 | 1853篇 |
2001年 | 1835篇 |
2000年 | 1878篇 |
1999年 | 2037篇 |
1998年 | 1759篇 |
1997年 | 1582篇 |
1996年 | 1436篇 |
1995年 | 1297篇 |
1994年 | 1099篇 |
1993年 | 1137篇 |
1992年 | 895篇 |
1991年 | 748篇 |
1990年 | 636篇 |
1989年 | 514篇 |
1988年 | 390篇 |
1987年 | 238篇 |
1986年 | 127篇 |
1985年 | 66篇 |
1984年 | 47篇 |
1983年 | 42篇 |
1982年 | 49篇 |
1981年 | 51篇 |
1980年 | 32篇 |
1979年 | 16篇 |
1965年 | 15篇 |
1964年 | 11篇 |
1963年 | 12篇 |
1956年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
992.
<中华人民共和国种子法>(以下简称<种子法>)实施后,随着种子企业改革的不断深入和种子市场的进一步放开,种子的推广和销售格局发生了根本变化.彻底打破了过去计划经济体制下的种子公司一家独有局面.在不违反<种子法>规定的前提下,谁都可以推广和销售玉米新品种. 相似文献
993.
994.
In this study the influence of the low-intensity ultrasound treatment on excess sludge has been observed.The oxygen uptake rate(OUR),soluble chemical oxygen demand(SCOD),soluble total nitrogen(TN) and soluble total phosphorus(TP) were examined for three power levels of 0.03 W/mL, 0.05 W/mL and 0.1 W/mL as well as two time series of 0~5 min and 0~30 min.It showed that there were two stages of ultrasonic treatment: the first stage took place within the flocs in four minutes,in which SCOD,TN,TP were dissolved from flocs.In the second stage,the microbial activities have been strengthened,as well as OUR,TN,TP have increased greatly. 相似文献
995.
The solubility and processability of polyaniline can be increased through aniline copoly with o-anisidine. Poly(aniline-co-o-anisidine) have good electrochromism .On condition that mole ratio between aniline and anisidine is 3:1,better reaction conditions of synthesizing poly(aniline-co-o-anisidine) with good solubility ,electrochromism and high yield was gotten through researches for effects of monomer ratio,monomer concentration,the amount of oxidant ,reaction times,reaction temperature,acid concentration on properties of poly(aniline-co-o-anisidine).The structure of polymers were characterized by IR spectrum. 相似文献
996.
随着我国种子市场管理体制改革的不断深入,种子市场主体呈现多元化发展趋势。2006年5月19日,国务院办公厅下发了《国务院办公厅关于种子管理体制改革和加强种子市场监管的意见》,该意见的出台,无疑加快了国有种子企业体制改革的步伐。《种子法》经过近5年的市场洗礼,虽然中国原先的2700多家国有地市县中小型种业公司逐渐退出,真正能靠自身经营维持生存的为数不多,替代他们的是民营新建的中小型种业公司。 相似文献
997.
Low frequency oscillation of electric power system is a problem which electric workers always care about. The influences of prime mover characteristics were ignored in the past research. The paper introduces the models of steam turbine system and each part of electric power system, and calculates the corresponding eigenvalues, then analyzes the influences of steam turbine system on low frequency oscillation. 相似文献
998.
Complexity of mutual act and different sensation of different tourists are important factors influencing regional tourism resources evaluation. Fuzzy mathematic method can be used to up quantitative evaluation method on tourism resources evaluation. Taking Wushan Small Three Gorges as an example, the author carries out the evaluation of the tourism resources in the Three Gorges Reservoir. At the same time, the authors consider that five factors, such as improvement of the comunication of tourism resources, quickening the Steps of urbanization in reservior area, must be done well. 相似文献
999.
1000.
The important character of non-magnetic high manganese ZG25 Mn18Cr4 alloy is rapid work-hardening under external stress. With X-ray diffraction and TEM analysis, it is proved that the microstructures of both undeformed and deformed matrixes are austenite and carbide with some striation structure in the matrixes, the amount of stripes in the deformed matrix is obviously more than that in the undeformed matrix. Electronic diffraction analysis confirmed that the stripes in coarse austenite grains are high density lamination fault sheets. A great deal of lamination fault sheets produced by plastic deformation divides up austenite matrix, shortens the free distance of dislocation movement and results in the rapid work-hardening of ZG25Mn18Cr4 alloy. 相似文献