全文获取类型
收费全文 | 9568篇 |
免费 | 1031篇 |
国内免费 | 384篇 |
出版年
2023年 | 40篇 |
2022年 | 54篇 |
2021年 | 226篇 |
2020年 | 206篇 |
2019年 | 268篇 |
2018年 | 298篇 |
2017年 | 271篇 |
2016年 | 375篇 |
2015年 | 511篇 |
2014年 | 583篇 |
2013年 | 613篇 |
2012年 | 835篇 |
2011年 | 692篇 |
2010年 | 509篇 |
2009年 | 442篇 |
2008年 | 583篇 |
2007年 | 494篇 |
2006年 | 463篇 |
2005年 | 429篇 |
2004年 | 439篇 |
2003年 | 417篇 |
2002年 | 379篇 |
2001年 | 250篇 |
2000年 | 201篇 |
1999年 | 181篇 |
1998年 | 100篇 |
1997年 | 92篇 |
1996年 | 67篇 |
1995年 | 54篇 |
1994年 | 65篇 |
1993年 | 39篇 |
1992年 | 93篇 |
1991年 | 69篇 |
1990年 | 61篇 |
1989年 | 46篇 |
1988年 | 45篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 44篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 26篇 |
1976年 | 21篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
1.
M.M. van Katwijk D. C. R. Hermus D.J. de Jong R. M. Asmus V.N. de Jonge 《Helgoland Marine Research》2000,54(2-3):117-128
A conceptual model is proposed, describing potential Zostera marina habitats in the Wadden Sea, based on reported data from laboratory, mesocosm and field studies. Controlling factors in the
model are dynamics, degree of desiccation, turbidity, nutrients and salinity. A distinction has been made between a higher
and a lower zone of potential habitats, each suitable for different morphotypes of Z. marina. The model relates the decline of Z. marina in the Wadden Sea to increased sediment and water dynamics, turbidity, drainage of sediments (resulting in increased degree
of desiccation) and total nutrient loads during the twentieth century. The upper and lower delineation of both the higher
and the lower zone of potential Z. marina habitats appear to be determined by one or a combination of several of these factors. Environmental changes in one of these
factors will therefore influence the borderlines of the zones. The lower zone of Z. marina will be mainly affected by increased turbidity, sediment dynamics, degree of desiccation during low tide and nutrient load.
The higher zone will be affected by increases in water and sediment dynamics, desiccation rates and nutrient loads. Potential
Z. marina habitats are located above approx. –0.80 m mean sea level (when turbidity remains at the same level as in the early 1990s)
in sheltered, undisturbed locations, and preferably where some freshwater influence is present. At locations with a high,
near-marine, salinity, the nutrient load has to be low to allow the growth of Z. marina. The sediment should retain enough water during low tide to keep the plants moist. Our results suggest that the return of
Z. marina beds within a reasonable time-scale will require not only suitable habitat conditions, but also revegetation measures, as
the changes in the environment resulting from the disappearance of Z. marina may impede its recovery, and the natural import of propagules will be unlikely. Furthermore, the lower zone of Z. marina may require a genotype that is no longer found in the Wadden Sea.
Received: 26 April 1999 / Received in revised form: 15 October 1999 / Accepted: 16 October 1999 相似文献
2.
In a study of the effect of glycerin in transport media on Vibrio parahaemolyticus and Salmonella, it was found that a concentration of 30% glycerin was highly inhibitory for V. parahaemolyticus and to a lesser degree for Salmonella. The incorporation of peptone or human feces in media did not reduce the inhibitory effect of glycerin. In media with 15% glycerin, viable counts of V. parahaemolyticus and Salmonella increased after 24 hr of incubation both in the presence and absence of feces. Due to the concurrent increase in the total bacterial count in the media containing feces, no enrichment effect was noted. 相似文献
3.
4.
Human erythrocyte and brain acetylcholinesterase are preferentially inhibited by the P(-)-isomers of C(+/-)P(+/-)-soman. The enzymes inhibited by the P(-)-isomers behave similarly with respect to oxime-induced reactivation and aging. HI-6 is the best reactivator for C(+)P(-)-soman-inhibited acetylcholinesterases. Oxime-induced reactivation of the C(-)P(-)-soman-inhibited acetylcholinesterases is much more difficult to achieve. 相似文献
5.
6.
7.
Jun‐juan Wang Qi‐min Zhang Wei‐wei Ni Xin Zhang Ying Li Ai‐li Li Peng Du Chun Li Su‐su Yu 《Microbiology and immunology》2019,63(8):303-315
We investigated the correlation between the beneficial effect of Lactobacillus acidophilus on gut microbiota composition, metabolic activities, and reducing cow's milk protein allergy. Mice sensitized with β‐lactoglobulin (β‐Lg) were treated with different doses of L. acidophilus KLDS 1.0738 for 4 weeks, starting 1 week before allergen induction. The results showed that intake of L. acidophilus significantly suppressed the hypersensitivity responses, together with increased fecal microbiota diversity and short‐chain fatty acids (SCFAs) concentration (including propionate, butyrate, isobutyrate, and isovalerate) when compared with the allergic group. Moreover, treatment with L. acidophilus induced the expression of SCFAs receptors, G‐protein–coupled receptors 41 (GPR41) and 43 (GPR43), in the spleen and colon of the allergic mice. Further analysis revealed that the GPR41 and GPR43 messenger RNA expression both positively correlated with the serum concentrations of transforming growth factor‐β and IFN‐γ (p < .05), but negatively with the serum concentrations of IL‐17, IL‐4, and IL‐6 in the L. acidophilus–treated group compared with the allergic group (p < .05). These results suggested that L. acidophilus protected against the development of allergic inflammation by improving the intestinal flora, as well as upregulating SCFAs and their receptors GPR41/43. 相似文献
8.
野大豆叶绿体在低温(77K)时出现三条荧光发射谱带,它们来源于不同的色素蛋白复合体。 在纳秒脉冲激光激发下,捕光天线色素的相对荧光量子产额,随激光强度的增加有明显下降现象。用激子理论和动力学方程讨论和计算了激子扩散参量。指出激子转移是随机的,非相干的。 相似文献
9.
10.
Compression wood (CW) contains higher quantities of β-1-4-galactan than does normal wood (NW). However, the physiological
roles and ultrastructural distribution of β-1-4-galactan during CW formation are still not well understood. The present work
investigated deposition of β-1-4-galactan in differentiating tracheids of Cryptomeria japonica during CW formation using an immunological probe (LM5) combined with immunomicroscopy. Our immunolabeling studies clearly
showed that differences in the distribution of β-1-4-galactan between NW (and opposite wood, OW) and CW are initiated during
the formation of the S1 layer. At this stage, CW was strongly labeled in the S1 layer, whereas no label was observed in the S1 layer of NW and OW. Immunogold labeling showed that β-1-4-galactan in the S1 layer of CW tracheids significantly decreased during the formation of the S2 layer. Most β-1-4-galactan labeling was present in the outer S2 region in mature CW tracheids, and was absent in the inner S2 layer that contained helical cavities in the cell wall. In addition, delignified CW tracheids showed significantly more labeling
of β-1-4-galactan in the secondary cell wall, suggesting that lignin is likely to mask β-1-4-galactan epitopes. The study
clearly showed that β-1-4-galactan in CW was mainly deposited in the outer portion of the secondary cell wall, indicating
that its distribution may be spatially consistent with lignin distribution in CW tracheids of Cryptomeria japonica. 相似文献