全文获取类型
收费全文 | 3250篇 |
免费 | 360篇 |
国内免费 | 476篇 |
出版年
2023年 | 94篇 |
2022年 | 57篇 |
2021年 | 95篇 |
2020年 | 133篇 |
2019年 | 176篇 |
2018年 | 122篇 |
2017年 | 138篇 |
2016年 | 150篇 |
2015年 | 122篇 |
2014年 | 132篇 |
2013年 | 206篇 |
2012年 | 128篇 |
2011年 | 177篇 |
2010年 | 142篇 |
2009年 | 172篇 |
2008年 | 158篇 |
2007年 | 187篇 |
2006年 | 171篇 |
2005年 | 155篇 |
2004年 | 118篇 |
2003年 | 134篇 |
2002年 | 108篇 |
2001年 | 99篇 |
2000年 | 80篇 |
1999年 | 54篇 |
1998年 | 70篇 |
1997年 | 50篇 |
1996年 | 51篇 |
1995年 | 52篇 |
1994年 | 43篇 |
1993年 | 60篇 |
1992年 | 41篇 |
1991年 | 40篇 |
1990年 | 29篇 |
1989年 | 40篇 |
1988年 | 21篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 27篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 11篇 |
排序方式: 共有4086条查询结果,搜索用时 437 毫秒
21.
The relationship between nitrification potential and nitrogen accumulation was studied in an early successional sere on Mt.
Fuji. Soil organic nitrogen accumulated with the invasion ofPolygonum cuspidatum and successively withMiscanthus oligostachyus and other species. Laboratory incubation experiments showed a higher nitrification potential at theM. oligostachyus state. The numbers of nitrifying bacteria increased with the progress of succession. No significant difference in nitrate
reductase activity was found between pioneer and succeeding species. The soil solution at theM. oligostachyus stage contained a lower level of nitrate than rainwater, while that of the bare ground and theP. cuspidatum stage contained a higher nitrate level than rainwater. It was concluded that the high nitrate levels in the soil solution
of the bare ground and theP. cuspidatum stage were due to lower nitrate-absorbing activity, leading to loss of nitrogen with precipitation, while the lower nitrate
levels at theM. oligostachyus stage when higher nitrification activity occurred were due to higher nitrate-absorbing activity, preventing net loss of nitrogen
from the ecosystem. 相似文献
22.
23.
24.
25.
Artur Scheib 《Journal of mathematical biology》1989,27(3):369-372
A random competition model is reformulated as an urn model and its behavior is analysed. 相似文献
26.
27.
Kiyoshi Akeo Yasuhiko Tanaka Tatsuji Fujiwara 《In vitro cellular & developmental biology. Plant》1988,24(7):705-710
Summary The endocytotic process in cultured human RPE cells was observed after 1 min, 20 min, and 2 h incubation with cationized ferritin.
Within 1 min the ferritin particles were seen to attach to the cell membrane, especially between microvilli. Uncoated and
coated pits could be recognized on the cell membranes, and uncoated and coated endocytotic vesicles were found in the cytoplasm
after 20 min of incubation. These vesicles were surrounded by abundant microfilaments and had no visible membranes. Loss of
membrane may be an initial step in the process of developing into the irregular clumps of ferritin particles found inside
the plasma membrane. With time, more irregular clumps of ferritin, smaller than the particles introduced during incubation,
appeared just beneath the cell membrane. Lysosomes were adjacent to the clumps of ferritin particles associated with microtobules
and finally degraded these particles. The phagolysosomes containing many particles were surrounded by many microtubules. Small
ferritin particles surrounded but had not entered the rough endoplasmic reticulums, and no particles were seen either around
or in the Golgi apparatus.
Presented at the 7th International Congress of Eye Research, Nagoya, Japan, 27 September 1986. 相似文献
28.
Mycelium ofBeauveria bassiana can be grown in liquid culture, filtered, and the mycelium dried. After rehydration the mycelium sporulates.
Two carbohydrate sources (sucrose and maltose), and one nitrogen/vitamin source (yeast extract) were tested for mycelium growth
and subsequent conidial production. Maximum mycelium growth (12.31 mg/ml), in liquid culture, was in the sucrose (3.5%)/yeast
extract (3.5%) medium, but mycelium from a maltose (2%)/yeast extract (0.75%) medium produced the maximum of 4.62×106 conidia/mg dry mycelium after incubation in moist Petri dishes.
Using the data on mycelium yield (in liquid culture) and conidial production (by dry mycelium) it is calculated that the sucrose
(3.5%)/yeast extract (3.5%) and the maltose (2%)/yeast extract (0.75%) media produce most conidia per media volume (an equivalent
of 3.52–3.72×107 conidia/ml).
相似文献
29.
J. H. B. Diederen M. P. Peppelenbosch H. G. B. Vullings 《Cell and tissue research》1992,268(1):117-121
Summary A morphometric study was made of the ultrastructure of adipokinetic cells in resting adults of Locusta migratoria at 3, 23, and 43 days after imaginal ecdysis. The nucleus, rough endoplasmic reticulum, and Golgi apparatus enlarge with age, which indicates that the synthesis and packaging of secretory substances increases during ageing. The size of the storage compartment, consisting of secretory and ergastoplasmic granules, does not increase earlier than 23–43 days after imaginal ecdysis. The lysosomal compartment markedly enlarges between 3 and 23 days; later on, the growth of this compartment, especially of autophagosomes, is less prominent. This suggests that lysosomal destruction initially compensates for the production of new secretory granules, assuming that exocytosis of secretory granules by adipokinetic cells is insignificant in resting locusts. Afterwards, lysosomal destruction may no longer be sufficient to prevent over-production of secretory granules, as is suggested by the increase in the number of these granules between 23 and 43 days. This coincides with the appearance of a considerable number of large ergastoplasmic granules, which represent a spatially more efficient form of storage of secretory material than the much smaller secretory granules. The increase with age in the amount of secretory products indicates that the biosynthetic activity of the adipokinetic cells is not (finely) tuned to their releasing activity. 相似文献
30.
树干径流过程的动态响应模型 总被引:1,自引:0,他引:1
本文用实验测试法测量了干流过程。结果表明,干流过程曲线与R-L-C电路瞬态响应过程(包括输入、输出曲线)极为相似。据此,可用R-L-C电路瞬态响应过程曲线拟合干流过程,求出解析解。在计算机上调试参数,讨论其水文学意义,定性分析参数与影响干流因子的关系,取得了满意的结果。 相似文献