全文获取类型
收费全文 | 13902篇 |
免费 | 1426篇 |
国内免费 | 14篇 |
出版年
2022年 | 119篇 |
2021年 | 243篇 |
2020年 | 138篇 |
2019年 | 176篇 |
2018年 | 199篇 |
2017年 | 185篇 |
2016年 | 339篇 |
2015年 | 539篇 |
2014年 | 570篇 |
2013年 | 738篇 |
2012年 | 886篇 |
2011年 | 922篇 |
2010年 | 582篇 |
2009年 | 466篇 |
2008年 | 713篇 |
2007年 | 715篇 |
2006年 | 673篇 |
2005年 | 592篇 |
2004年 | 593篇 |
2003年 | 534篇 |
2002年 | 547篇 |
2001年 | 244篇 |
2000年 | 217篇 |
1999年 | 229篇 |
1998年 | 175篇 |
1997年 | 141篇 |
1996年 | 125篇 |
1995年 | 144篇 |
1994年 | 121篇 |
1993年 | 128篇 |
1992年 | 189篇 |
1991年 | 150篇 |
1990年 | 166篇 |
1989年 | 164篇 |
1988年 | 155篇 |
1987年 | 144篇 |
1986年 | 131篇 |
1985年 | 110篇 |
1984年 | 141篇 |
1983年 | 114篇 |
1982年 | 123篇 |
1981年 | 105篇 |
1980年 | 88篇 |
1979年 | 101篇 |
1978年 | 89篇 |
1977年 | 91篇 |
1976年 | 85篇 |
1975年 | 95篇 |
1974年 | 75篇 |
1973年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined. 相似文献
3.
4.
ABSTRACT The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship. 相似文献
5.
David R. Nelson 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1612)
The world we live in is a biosphere influenced by all organisms who inhabit it. It is also an ecology of genes, with some having rather startling effects. The premise put forth in this issue is cytochrome P450 is a significant player in the world around us. Life and the Earth itself would be visibly different and diminished without cytochrome P450s. The contributions to this issue range from evolution on the billion year scale to the colour of roses, from Darwin to Rachel Carson; all as seen through the lens of cytochrome P450. 相似文献
6.
Victor Horsley 《BMJ (Clinical research ed.)》1910,1(2568):725-726
7.
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
8.
Victor F. Medina Peter M. Jeffers Steven L. Larson Waleska Perez 《International journal of phytoremediation》2000,2(4):287-295
Bleach treatment of plants was studied as a simple alternative to axenic tissue cultures for demonstrating phytodegradation of aqueous and gas-phase environmental contaminants. Parrotfeather (Myriophyllum aquaticum), spinach (Spinacia oleracea), and wheat (Triticum aestivum) were exposed to 0.525% NaC10 solutions for 15 s, then rinsed in deionized water. Plate counts indicated that 97 to 100% of viable bacteria were removed from parrotfeather and spinach. Transformation rates for 2,4,6-trinitrotoluene (TNT) by bleached and untreated parrotfeather were virtually identical. Similarly, treated and untreated spinach, wheat heads, and wheat leaves removed methyl bromide (MeBr) from air at the same rates. However, wheat root with attendant adhering soil was rendered inactive by bleach treatment. Parrotfeather roots examined by dissecting microscope and by electron microscope showed no significant damage caused by bleach treatment. 相似文献
9.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays. 相似文献
10.