全文获取类型
收费全文 | 1649篇 |
免费 | 95篇 |
出版年
2023年 | 8篇 |
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 19篇 |
2017年 | 23篇 |
2016年 | 30篇 |
2015年 | 52篇 |
2014年 | 62篇 |
2013年 | 88篇 |
2012年 | 103篇 |
2011年 | 107篇 |
2010年 | 60篇 |
2009年 | 64篇 |
2008年 | 96篇 |
2007年 | 88篇 |
2006年 | 80篇 |
2005年 | 93篇 |
2004年 | 98篇 |
2003年 | 99篇 |
2002年 | 79篇 |
2001年 | 33篇 |
2000年 | 20篇 |
1999年 | 34篇 |
1998年 | 32篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 36篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 14篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 6篇 |
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
1.
Pernilla Christensen Frauke Ecke Per Sandström Mats Nilsson Birger Hörnfeldt 《Population Ecology》2008,50(2):169-179
There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested
that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings
in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation
(LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF).
We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the
rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference
was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest
yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other
recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive
importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly,
at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially
of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline
of C. rufocanus in boreal Sweden. 相似文献
2.
3.
Mats Thulin 《Nordic Journal of Botany》1993,13(1):51-52
The new species Kalanchoe subrosulata from deciduous bushlands in southwestern Somalia and northeastern Kenya is described and illustrated. 相似文献
4.
5.
6.
7.
8.
T B Svets-Ténéta-Guri? V N Mats O B Kovchegova 《Biulleten' eksperimental'no? biologii i meditsiny》1989,108(9):259-261
A method of recording slow ROSP's changes of the brain in chronic animals was used. It has been shown that wakefulness was accompanied by quasisinusoidal oscillations of ROSP (periods--several seconds). During slow sleep, oscillations of ROSP became more complicated and their periods were longer. It is suggested that transitions from sleep to wakefulness and vice versa are connected with removal of maximums of oxidative metabolism tension between biochemical systems characterized by different rhythms of self-regulation. Rhythmic oscillations of ROSP reveal the possibility of separate functional system of the ROSP of the brain cortex to synchronize their oscillations in the brain tissue (biochemical synergism). 相似文献
9.
The authors studied the influence of gallic salt of cynoglossophin-heliosupin alkaloid (cyngal), extracted from Cynoglossum officinale L. on the gastric secretion of rats. Cyngal proved to stimulate the secretory function of the rat stomach, beginning from the dose of 0.25 mg/kg. This action is explained by the capacity of the preparation to release histamine from the labile depot. 相似文献
10.
A N Mats E V Cheprasova S I Elkina E V Koriakin 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1987,(5):67-71
Nonspecific adhesiveness of lymphocytes to polyacrylonitrile fiber and the antigen-specific adhesiveness of T-lymphocytes to Shigella flexneri pellicular immunosorbent have been studied in dysentery patients. Short courses of treatment with indomethacin, but not with thymalin (the preparation of thymic hormones), used for immunomodulation, have accelerated the normalization of nonspecific lymphocyte adhesiveness during regression of the disease, while indomethacin, in contrast to thymalin, inhibits antigen-specific T-lymphocyte adhesiveness which increases with the development of immune response. 相似文献