全文获取类型
收费全文 | 3155篇 |
免费 | 333篇 |
国内免费 | 3篇 |
出版年
2021年 | 26篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 61篇 |
2015年 | 81篇 |
2014年 | 97篇 |
2013年 | 142篇 |
2012年 | 144篇 |
2011年 | 149篇 |
2010年 | 95篇 |
2009年 | 106篇 |
2008年 | 132篇 |
2007年 | 126篇 |
2006年 | 146篇 |
2005年 | 141篇 |
2004年 | 128篇 |
2003年 | 120篇 |
2002年 | 116篇 |
2001年 | 58篇 |
2000年 | 46篇 |
1999年 | 63篇 |
1998年 | 41篇 |
1997年 | 38篇 |
1996年 | 42篇 |
1995年 | 54篇 |
1994年 | 57篇 |
1993年 | 55篇 |
1992年 | 72篇 |
1991年 | 54篇 |
1990年 | 51篇 |
1989年 | 48篇 |
1988年 | 37篇 |
1987年 | 49篇 |
1986年 | 58篇 |
1985年 | 60篇 |
1984年 | 53篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 36篇 |
1980年 | 25篇 |
1979年 | 44篇 |
1978年 | 30篇 |
1977年 | 23篇 |
1976年 | 30篇 |
1975年 | 23篇 |
1974年 | 28篇 |
1973年 | 31篇 |
1970年 | 33篇 |
1968年 | 19篇 |
排序方式: 共有3491条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
155.
Stephen R. Malone Herman S. Mayeux Hyrum B. Johnson H. Wayne Polley 《American journal of botany》1993,80(12):1413-1418
Stomatal density, stomatal aperture length, area/leaf, and number of stomata/leaf were measured after the annual C3 agronomic grasses oats (Avena sativa) and wheat (Triticum aestivum), the C, woody legume honey mesquite (Prosopis glandulosa), and the perennial C4 grass little bluestem (Schizachyrium scoparium) were grown across a subambient carbon dioxide concentration ([CO2]) gradient from near 200 to 350 μmol/mol in a growth chamber. The purpose was to determine if the size and density of stomata vary in response to atmospheric [CO2] during growth, across a subambient [CO2] range representative of the doubling that has occurred since the last ice age. Changes in stomatal density and aperture length with increasing [CO2] were small when detected. Stomatal density decreased on adaxial flag leaf surfaces of wheat, and aperture length increased slightly with [CO2], Leaf area and number of stomata/flag leaf increased by similar proportions with [CO2] in two wheat cultivars. No consistent relationship between [CO2] and stomatal density or size was detected in mesquite, oats, or little bluestem. We conclude that individual plants of these species lack the plasticity to significantly alter stomatal density and aperture length in response to increasing atmospheric [CO2] in a single generation (annuals) or growing season (perennials). 相似文献
156.
157.
Measurement of cellular DNA mass by flow microfluorometry with use of a biological internal standard 总被引:2,自引:0,他引:2
E Tannenbaum M Cassidy O Alabaster C Herman 《The journal of histochemistry and cytochemistry》1978,26(2):145-148
Use of a biological standard (chicken erythrocytes) mixed with experimental cell populations allows control of all variables in flow microfluorometric determination of DNA content. These variables include both staining and instrument procedures. In addition, the use of a biological standard allows determination of cellular DNA mass in unperturbed cell populations. DNA mass measured by FMF technique correlates closely with values reported in the literature that used biochemical techniques. 相似文献
159.
160.