全文获取类型
收费全文 | 7686篇 |
免费 | 826篇 |
国内免费 | 3篇 |
出版年
2021年 | 125篇 |
2020年 | 71篇 |
2019年 | 75篇 |
2018年 | 92篇 |
2017年 | 68篇 |
2016年 | 150篇 |
2015年 | 296篇 |
2014年 | 300篇 |
2013年 | 436篇 |
2012年 | 571篇 |
2011年 | 496篇 |
2010年 | 300篇 |
2009年 | 255篇 |
2008年 | 438篇 |
2007年 | 454篇 |
2006年 | 376篇 |
2005年 | 327篇 |
2004年 | 341篇 |
2003年 | 330篇 |
2002年 | 322篇 |
2001年 | 128篇 |
2000年 | 104篇 |
1999年 | 103篇 |
1998年 | 102篇 |
1997年 | 67篇 |
1996年 | 65篇 |
1995年 | 73篇 |
1994年 | 76篇 |
1993年 | 78篇 |
1992年 | 84篇 |
1991年 | 75篇 |
1990年 | 80篇 |
1989年 | 75篇 |
1988年 | 75篇 |
1987年 | 51篇 |
1986年 | 59篇 |
1985年 | 80篇 |
1984年 | 69篇 |
1983年 | 66篇 |
1982年 | 62篇 |
1981年 | 72篇 |
1980年 | 60篇 |
1979年 | 60篇 |
1978年 | 54篇 |
1976年 | 64篇 |
1975年 | 45篇 |
1974年 | 46篇 |
1973年 | 46篇 |
1972年 | 43篇 |
1971年 | 44篇 |
排序方式: 共有8515条查询结果,搜索用时 14 毫秒
1.
2.
Ludy Keino Frederick Baijukya Wilson Ng’etich Abigael N. Otinga John R. Okalebo Ruth Njoroge John Mukalama 《PloS one》2015,10(12)
Low soybean yields in western Kenya have been attributed to low soil fertility despite much work done on nitrogen (N) and phosphorus (P) nutrition leading to suspicion of other nutrient limitations. To investigate this, a nutrient omission trial was set up in the greenhouse at the University of Eldoret-Kenya to diagnose the nutrients limiting soybean production in Acrisols from Masaba central and Butere sub-Counties, and Ferralsols from Kakamega (Shikhulu and Khwisero sub-locations) and Butula sub-Counties and to assess the effect of liming on soil pH and soybean growth. The experiment was laid out in a completely randomized design with ten treatments viz; positive control (complete), negative control (distilled water), complete with lime, complete with N, minus macronutrients P, potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and with, micro-nutrients boron (B), molybdenum (Mo), manganese (Mn), copper (Cu) and zinc (Zn) omitted. Visual deficiency symptoms observed included interveinal leaf yellowing in Mg omission and N addition and dark green leaves in P omission. Nutrients omission resulted in their significantly low concentration in plant tissues than the complete treatment. Significantly (P≤ 0.05) lower shoot dry weights (SDWs) than the complete treatment were obtained in different treatments; omission of K and Mg in Masaba and Shikhulu, Mg in Khwisero, K in Butere and, P, Mg and K in Butula. Nitrogen significantly improved SDWs in soils from Kakamega and Butula. Liming significantly raised soil pH by 9, 13 and 11% from 4.65, 4.91 and 4.99 in soils from Masaba, Butere and Butula respectively and soybean SDWs in soils from Butere. The results show that, poor soybean growth was due to K, Mg and P limitation and low pH in some soils. The results also signify necessity of application of small quantities of N for initial soybean use. 相似文献
3.
Steven D. Johnson Marco G. Balducci Alison Bijl Miguel Castañeda-Zárate Ruth J. Cozien Carmen R. Ortmann Timotheüs van der Niet 《Ecological Entomology》2020,45(3):751-755
1. Diel rhythms of foraging activity by animal flower visitors can reflect niche partitioning and are considered an important component of selection on floral traits. However, it has been notoriously difficult to obtain objective information on the patterns of flower visitation by crepuscular and nocturnal insects. 2. Motion-activated cameras were used for field-based studies of hawkmoth foraging behaviour on six African plant species. 3. The results showed that short-tongued hawkmoth species forage mainly around dusk and then sporadically throughout the night, whereas long-tongued hawkmoth species feed consistently throughout the night, with a peak shortly before midnight. 4. These results provide the first quantitative estimates of diel patterns of interactions between multiple hawkmoth and plant species and, when combined with qualitative reports from other studies, suggest that differences in diel activity between the two main hawkmoth functional groups (short- and long-tongued) are consistent across the Old and New Worlds. 相似文献
4.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
5.
6.
7.
8.
Steven W. Kortum Rhonda M. Lachance Barbara A. Schweitzer Gopichand Yalamanchili Hayat Rahman Michael D. Ennis Rita M. Huff Ruth E. TenBrink 《Bioorganic & medicinal chemistry letters》2009,19(20):5919-5923
Herein we describe the design and synthesis of a novel series of potent thienopyrimidine P2Y12 inhibitors and the negative impact protein binding has on the inhibition of platelet aggregation. 相似文献
9.
10.