全文获取类型
收费全文 | 187262篇 |
免费 | 10360篇 |
国内免费 | 126篇 |
专业分类
林业 | 7479篇 |
农学 | 5738篇 |
基础科学 | 1259篇 |
22261篇 | |
综合类 | 32463篇 |
农作物 | 6913篇 |
水产渔业 | 9325篇 |
畜牧兽医 | 97054篇 |
园艺 | 2381篇 |
植物保护 | 12875篇 |
出版年
2018年 | 2424篇 |
2017年 | 2622篇 |
2016年 | 2439篇 |
2015年 | 2147篇 |
2014年 | 2605篇 |
2013年 | 7270篇 |
2012年 | 5005篇 |
2011年 | 6206篇 |
2010年 | 3937篇 |
2009年 | 3890篇 |
2008年 | 6026篇 |
2007年 | 5824篇 |
2006年 | 5633篇 |
2005年 | 5224篇 |
2004年 | 5081篇 |
2003年 | 5084篇 |
2002年 | 4934篇 |
2001年 | 5746篇 |
2000年 | 5527篇 |
1999年 | 4557篇 |
1998年 | 1890篇 |
1997年 | 1902篇 |
1996年 | 1794篇 |
1995年 | 2160篇 |
1994年 | 1967篇 |
1993年 | 1904篇 |
1992年 | 3862篇 |
1991年 | 4127篇 |
1990年 | 4073篇 |
1989年 | 4015篇 |
1988年 | 3793篇 |
1987年 | 3811篇 |
1986年 | 3924篇 |
1985年 | 3827篇 |
1984年 | 3188篇 |
1983年 | 2861篇 |
1982年 | 1974篇 |
1981年 | 1824篇 |
1979年 | 2909篇 |
1978年 | 2390篇 |
1977年 | 2094篇 |
1976年 | 1925篇 |
1975年 | 1993篇 |
1974年 | 2620篇 |
1973年 | 2626篇 |
1972年 | 2527篇 |
1971年 | 2321篇 |
1970年 | 2268篇 |
1969年 | 2091篇 |
1967年 | 1810篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
The cleistogamous species Collomia grandiflora produces dimorphic cross-incompatible flowers on a single plant. The open or chasmogamous flower has smaller, flask-shaped stigmatic papillae, larger pollen grains, longer styles, and faster pollen tube growth rates down the style than the closed or cleistogamous flower. In intermorph crosses, pollen tube growth rates are greatly decreased and fertilization does not occur. 相似文献
952.
953.
954.
Bird SJ 《Science (New York, N.Y.)》1984,224(4649):595-596
955.
956.
957.
Up to 60 percent of the total marine primary production (or about one-fourth of the total global carbon dioxide fixation) passes through the free-living bacterioplankton. Grazing by bacteriovores is probably the predominant fate of the bacteria, although data are scarce. Evidence is presented that previously uncharacterized, small eukaryotes that are able to pass even 0.6-micrometer filters may be responsible for a large fraction (more than 50 percent) of the total grazing in coastal waters. These organisms have not yet been observed microscopically. 相似文献
958.
Borkowska B 《Tree physiology》1986,1(3):303-307
Micropropagation of fruit trees results in the early onset of dormancy in the young plantlets. Prechilling of shoot cultures of sour cherry cvs Schattenmorelle and North Star at 4 degrees C for 6-8 weeks prolonged shoot extension of the plantlets but longer cold treatments adversely affected shoot growth and survival. Chilling of cultures had no affect on rhizogenesis. No significant influence of ABA, GA(3) or ABA + GA(3) was observed on root development. Gibberellic acid A(3) did not stimulate extension of the shoots, but when supplied together with ABA, it significantly decreased both shoot extension and the number of actively growing apices of plantlets of cv Schattenmorelle. The combined hormonal treatment had no effect on plantlets of the North Star cv. 相似文献
959.
B C Flann B A Lodge 《Journal of the Association of Official Analytical Chemists》1986,69(6):1026-1030
The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%. 相似文献
960.