全文获取类型
收费全文 | 452篇 |
免费 | 24篇 |
出版年
2022年 | 4篇 |
2018年 | 4篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 30篇 |
2010年 | 14篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 12篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1979年 | 7篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1865年 | 3篇 |
1859年 | 3篇 |
1858年 | 7篇 |
1857年 | 48篇 |
1855年 | 8篇 |
1854年 | 24篇 |
1853年 | 8篇 |
1852年 | 4篇 |
排序方式: 共有476条查询结果,搜索用时 15 毫秒
1.
Schott 《Plant Systematics and Evolution》1858,8(6):177-182
Ohne Zusammenfassung 相似文献
2.
3.
H. Schott 《Plant Systematics and Evolution》1857,7(53):421-422
Ohne Zusammenfassung 相似文献
4.
H. Schott 《Plant Systematics and Evolution》1857,7(30):237-238
Ohne Zusammenfassung 相似文献
5.
6.
A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset,Ontario 总被引:10,自引:10,他引:0
Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt. 相似文献
7.
This study was performed to determine the biological activity in mice of eight species of Solidago (goldenrod) and to determine some of the chemical groups present in these species. Biologically active substances were present in all of the species tested. Tests of six species were positive for alkaloids. All but one of the species contained demonstrable saponins. All of the species contained tannins, whereas six or seven species were positive for flavonoids. Quaternary bases were not found in any of the species tested. A comparison of the biological activity in mice of these species of Solidago, extracts of which were injected intraperitoneally, showed their descending order of activity to be: (1)S. flexicaulis L., (2)S. hispida Muhl., (3)S. juncea Ait., (4)S. serotina Ait., (5)S. canadensis L., (6)S. rugosa Ait., (7)S. uliginosa Nutt., and (8)S. squarrosa Muhl. 相似文献
8.
9.
Josef Maier Karin Schott Thomas Werner Adelbert Bacher Irmgard Ziegler 《Experimental cell research》1993,204(2)
Fragments of cDNA coding for rat, murine, and human sepiapterin reductase (SR) were amplified by PCR via primer positioning close to the reported 3′-end of the coding region in the rat enzyme. They were sequenced and used as probes for mRNA detection. Northern blot analysis detected two mRNA species for SR. Their sizes were 1.3 and 2.1 kb for rat, 1.3 and 2.3 kb for mouse, and 1.6 and 2.1 kb for human cell lines. Comparison of rat cell lines and rat tissues indicated that in tissues only the 1.3-kb species is present. Washing of the Northern blots under different stringency conditions indicated a more stable interaction of the 1.3-kb mRNA species with the cDNA probe as compared to the 2.3-kb species. The 1.3-kb species corresponds to the reported 28.2-kDa molecular mass of rat SR monomer. SR mRNA expression is absent in the human NK-like cell line YT and in the murine erythroleukemia subclone B8/3, which both lack SR activity. Moreover, the relative mRNA expression correlates with the enzymatic activities of different cell lines within the same species. This indicates that SR activity is regulated by its steady state mRNA levels. 相似文献
10.
Malcolm Cämmerer Thomas Mayer Carolin Schott Juliane Steingroewer Ralf Petrich Helko Borsdorf 《Engineering in Life Science》2023,23(4):e2200039
The cultivation of algae either in open raceway ponds or in closed bioreactors could allow the renewable production of biomass for food, pharmaceutical, cosmetic, or chemical industries. Optimal cultivation conditions are however required to ensure that the production of these compounds is both efficient and economical. Therefore, high-frequency analytical measurements are required to allow timely process control and to detect possible disturbances during algae growth. Such analytical methods are only available to a limited extent. Therefore, we introduced a method for monitoring algae release volatile organic compounds (VOCs) in the headspace above a bioreactor in real time. This method is based on ion mobility spectrometry (IMS) in combination with a membrane inlet (MI). The unique feature of IMS is that complete spectra are detected in real time instead of sum signals. These spectral patterns produced in the ion mobility spectrum were evaluated automatically via principal component analysis (PCA). The detected peak patterns are characteristic for the respective algae culture; allow the assignment of the individual growth phases and reflect the influence of experimental parameters. These results allow for the first time a continuous monitoring of the algae cultivation and thus an early detection of possible disturbances in the biotechnological process. 相似文献