全文获取类型
收费全文 | 18358篇 |
免费 | 1626篇 |
国内免费 | 7篇 |
出版年
2022年 | 105篇 |
2021年 | 267篇 |
2020年 | 172篇 |
2019年 | 243篇 |
2018年 | 244篇 |
2017年 | 259篇 |
2016年 | 430篇 |
2015年 | 621篇 |
2014年 | 788篇 |
2013年 | 941篇 |
2012年 | 1165篇 |
2011年 | 1183篇 |
2010年 | 733篇 |
2009年 | 713篇 |
2008年 | 946篇 |
2007年 | 948篇 |
2006年 | 910篇 |
2005年 | 860篇 |
2004年 | 804篇 |
2003年 | 793篇 |
2002年 | 791篇 |
2001年 | 362篇 |
2000年 | 281篇 |
1999年 | 313篇 |
1998年 | 230篇 |
1997年 | 190篇 |
1996年 | 168篇 |
1995年 | 188篇 |
1994年 | 138篇 |
1993年 | 182篇 |
1992年 | 222篇 |
1991年 | 173篇 |
1990年 | 175篇 |
1989年 | 177篇 |
1988年 | 158篇 |
1987年 | 155篇 |
1986年 | 150篇 |
1985年 | 157篇 |
1984年 | 151篇 |
1983年 | 139篇 |
1982年 | 159篇 |
1981年 | 132篇 |
1980年 | 130篇 |
1979年 | 110篇 |
1978年 | 100篇 |
1977年 | 92篇 |
1975年 | 100篇 |
1974年 | 130篇 |
1973年 | 99篇 |
1972年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
1.
2.
3.
4.
5.
6.
7.
Internode length in Pisum. I. The effect of the Le/le gene difference on endogenous gibberellin-like substances 总被引:2,自引:0,他引:2
The allelopathic potential of the dry fruits of Washingtonia filifera (L. Linden) H. Wendl. was investigated. Leachates from fruits inhibited the germination of lettuce, wheat, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg 1−1 ) and gibberellic acid (50 mg 1−1 ). The effect of kinetin was more pronounced at 25°C than at 20°C. Substances inhibiting germination were localized in the pericarp of the fruit and were resistant to high temperature. 相似文献
8.
Myoglobin (Mb) is the classic vertebrate oxygen-binding protein present in aerobic striated muscles. It functions principally in oxygen delivery and provides muscle with its characteristic red colour. Members of the Antarctic icefish family (Channichthyidae) are widely thought to be extraordinary for lacking cardiac Mb expression, a fact that has been attributed to their low metabolic rate and unusual evolutionary history. Here, we report that cardiac Mb deficit, associated with pale heart colour, has evolved repeatedly during teleost evolution. This trait affects both gill- and air-breathing species from temperate to tropical habitats across a full range of salinities. Cardiac Mb deficit results from total pseudogenization in three-spined stickleback and is associated with a massive reduction in mRNA level in two species that evidently retain functional Mb. The results suggest that near or complete absence of Mb-assisted oxygen delivery to heart muscle is a common facet of teleost biodiversity, even affecting lineages with notable oxygen demands. We suggest that Mb deficit may affect how different teleost species deal with increased tissue oxygen demands arising under climate change. 相似文献
9.
Stewart A. Hill Stephen E. Scheckler James F. Basinger 《American journal of botany》1997,84(1):85-103
A new fern-like fossil plant is described from the lower Upper Devonian of southern Ellesmere Island, Canadian Arctic Archipelago. The plant occurs in an Archaeopteris-dominated flora preserved in the Nordstrand Point Formation (Mid-Late Frasnian) near Bird Fiord. The plant has a pinnate vegetative system with three branch orders and laminate sphenopteroid pinnules. Primary pinnae usually diverge from the main axis in distichous pairs (quadriseriate), but can depart singly (biseriate). Each primary pinna bears a basal catadromic aphlebia. Anatomically, the plant exhibits a mesarch, bipolar protostele that is ribbon- to clepsydropsoid-shaped in the main axis. Primary pinna traces are also initially bipolar and crescent-shaped, but may become four-ribbed before dividing into a pair of bipolar traces. The morphology and anatomy of this plant are nongymnospermous and are most similar to Zygopteridales (particularly Rhacophytaceae and Zygopteridaceae). The Frasnian age of Ellesmeris shows that laminated foliage had evolved in some zygopterid ferns much earlier than previously recognized. The Sphenopteris-like pinnules of Ellesmeris indicate the need for caution when attributing such a convergent foliar design to other plant groups, such as the Devonian gymnosperms. 相似文献
10.