全文获取类型
收费全文 | 156868篇 |
免费 | 13640篇 |
国内免费 | 82篇 |
专业分类
170590篇 |
出版年
2022年 | 1146篇 |
2021年 | 2402篇 |
2020年 | 1413篇 |
2019年 | 1778篇 |
2018年 | 2276篇 |
2017年 | 2053篇 |
2016年 | 3467篇 |
2015年 | 5781篇 |
2014年 | 6501篇 |
2013年 | 8201篇 |
2012年 | 10694篇 |
2011年 | 10745篇 |
2010年 | 7004篇 |
2009年 | 6398篇 |
2008年 | 9280篇 |
2007年 | 9335篇 |
2006年 | 8980篇 |
2005年 | 8731篇 |
2004年 | 8683篇 |
2003年 | 8125篇 |
2002年 | 7857篇 |
2001年 | 1673篇 |
2000年 | 1202篇 |
1999年 | 1783篇 |
1998年 | 2334篇 |
1997年 | 1615篇 |
1996年 | 1474篇 |
1995年 | 1366篇 |
1994年 | 1317篇 |
1993年 | 1306篇 |
1992年 | 1137篇 |
1991年 | 1096篇 |
1990年 | 1018篇 |
1989年 | 993篇 |
1988年 | 920篇 |
1987年 | 834篇 |
1986年 | 760篇 |
1985年 | 970篇 |
1984年 | 1236篇 |
1983年 | 1011篇 |
1982年 | 1229篇 |
1981年 | 1252篇 |
1980年 | 1100篇 |
1979年 | 778篇 |
1978年 | 865篇 |
1977年 | 789篇 |
1976年 | 776篇 |
1975年 | 595篇 |
1974年 | 725篇 |
1973年 | 599篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Three acetotrophicMethanosarcina species, which included marine, nonmarine, and thermophilic strains, were grown on acetate in a 10-liter pH auxostat. Specific growth rates and molar growth yields were constant throughout growth. Cell yields were up to 18-fold greater than previously reported. These properties of the pH auxostat indicate that it is a preferred culture method for the biochemical study of methanogenesis from acetate. 相似文献
83.
Linda L. Laack Michael E. Tewes Aaron M. Haines John H. Rappole 《Acta theriologica》2005,50(4):505-514
The ocelotLeopardus pardalis Linnaeus, 1758 is an endangered felid in the United States currently restricted to southern Texas. The objectives of our
study were to obtain data on ocelot parturition dates, fecundity, sex ratios, den characteristics, and first year survival,
all of which are critical in development of population viability models. Sixteen parturition events were recorded ranging
from mid-April to late December for 12 wild ocelots. Cumulatively, litters consisted of 1 or 2 kittens (ˉ = 1.2 ± 0.44 SD).
Cumulative sex ratio was 1∶2.5 (male:female); however, there was no significant difference between the observed sex ratio
and a 1∶1 sex ratio. Ten den sites were in close proximity (≤ 10 m) to dense thornshrub. Adult female ocelots used 2 to 4
den sites for each litter with distance between consecutively occupied dens ranging from 110 to 280 m (ˉ = 158 m ± 93 SD).
An estimated annual survival for ocelots 0 to 1 year of age was 0.68. Evidence suggests that ocelots in the wild may breed
more frequently than had been previously hypothesized. 相似文献
84.
85.
86.
87.
88.
89.
Hydrobiologia - To observe effects on the phosphorus retention mechanisms of a lake after re-colonisation by macrophytes, Potamogeton crispus L. and Elodea canadensis Michx. were planted in lab... 相似文献
90.