全文获取类型
收费全文 | 838篇 |
免费 | 43篇 |
出版年
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 51篇 |
2012年 | 58篇 |
2011年 | 59篇 |
2010年 | 35篇 |
2009年 | 36篇 |
2008年 | 52篇 |
2007年 | 43篇 |
2006年 | 40篇 |
2005年 | 35篇 |
2004年 | 40篇 |
2003年 | 42篇 |
2002年 | 38篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 4篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1971年 | 7篇 |
1940年 | 3篇 |
1939年 | 4篇 |
1935年 | 4篇 |
排序方式: 共有881条查询结果,搜索用时 15 毫秒
801.
Klaus Opwis Thomas Mayer‐Gall Eckhard Schollmeyer Christoph Dammer Tanja Titscher Anna Nickisch‐Hartfiel Oliver Grün Christoph Spurk Christine Schloderer Axel Köppe Christian Dörfler Herbert Bachus 《Engineering in Life Science》2010,10(4):293-296
A new strategy for the biological transformation of sugar‐containing wastewaters from the textile desizing process to biogas was developed. Here, industrial liquors were separated from the following washing step by squeezing the impregnated fabrics after desizing. These waters exhibit a chemical oxygen demand of 40 g/L and allow a direct use in microbial biogas reactors without further treatment or accumulation. After reaching balanced conditions, the microbes continuously produce biogas. Moreover, the chemical oxygen demand can be reduced up to 75%. This new technology seems to be practicable and even attractive for small‐ and medium‐sized enterprises with an annual cotton production down to 2000 t. At this stage, a reliable eco‐balance of the overall process is still pending. Further investigations will be carried out soon. 相似文献
802.
Aereal parts of three Asteraceae from Iran have been analysed for exudate flavonoids. Artemisia oliveriana, Pulicaria gnaphalodes and Tanacetum polycephalum are shown to accumulate mostly 6-methoxylated flavonols and flavones as external aglycones. 相似文献
803.
804.
805.
806.
Food Biophysics - In this contribution, the effect of cooling rates on a wide compositional range of waxes as oleogel structurants was systematically investigated. The different waxes exhibited... 相似文献
807.
808.
Anabela Bensimon‐Brito Maria Leonor Cancela Ann Huysseune Paul Eckhard Witten 《Evolution & development》2012,14(1):116-127
The vertebral column results from a controlled segmentation process associated with two main structures, the notochord and the somites. Pathological fusion of vertebral bodies can result from impaired segmentation during embryonic development or occur postnatally. Here, we explore the process of formation and subsequent fusion of the caudalmost vertebral bodies in zebrafish, where fusion is a normal process, mechanically required to support the caudal fin. To reveal whether the product of fusion is on an evolutionary or a developmental scale, we analyze the mode of formation of vertebral bodies, identify transitory rudiments, and characterize vestiges that indicate previous fusion events. Based on a series of closely spaced ontogenetic stages of cleared and stained zebrafish, parasagittal sections, and detection methods for elastin and mineral, we conclude that the formation of the urostyle involves four fusion events. Although fusion of preural 1 (PU1+) with ural 1 (U1) and fusion within ural 2 (U2+) are no longer traceable during centrum formation (phylogenetic fusion), fusion between the compound centrum [PU1++U1] and U2+ (ontogenetic fusion) occurs after individualization of the centra. This slow process is the last fusion and perhaps the latest fusion during the evolution of the zebrafish caudal fin endoskeleton. Newly described characters, such as a mineralized subdivision within U2+, together with the reinterpretation of known features in an evolutionary–developmental context, strongly suggest that the zebrafish caudal fin endoskeleton is made from more fused vertebral bodies than previously assumed. In addition, these fusion events occur at different developmental levels depending on their evolutionary status, allowing the dissection of fusion processes that have taken place over different evolutionary times. 相似文献
809.
Geobotanical survey of wood-pasture habitats in Europe: diversity,threats and conservation 总被引:1,自引:0,他引:1
Erwin Bergmeier Jörg Petermann Eckhard Schröder 《Biodiversity and Conservation》2010,19(11):2995-3014
Agro-silvopastoral land-use has a long tradition throughout Europe. Depending on the region, wood-pasture occurs as vanishing
relic of historical land-use, or still more or less widespread as multiple-use rangeland. A new development is that former
intensively managed land is being left to evolve towards wood-pasture as an economically and ecologically favourable alternative.
In a review of European wood-pasture habitats we distinguish 24 types based on the geobotanical criteria of region, structure,
land-use and tree species composition. The European wood-pasture types may be classified as hemiboreal and boreal (4 types),
nemoral old-growth (7), nemoral scrub and coppice (5), meridional old-growth (2), meridional scrub and coppice (4), and grazed
orchards (2). Wood-pasture forms part of the cultural heritage of Europe, and may add significantly to the preservation of
regional biodiversity. The role of wood-pasture in ecological restoration planning and the possibilities of maintaining or
enhancing features of wood-pasture deserve more recognition. Many wood-pastures suffer from regeneration failure and are over-mature.
Other threats to wood-pasture include abandonment, intensification, oak disease, overgrazing and clearance. In the European
Union Habitats Directive, wood-pasture habitats are represented but rather inconsistently. We suggest neglected wood-pasture
habitat types to be considered for inclusion. Wood-pasture may form an important element for the economic integrity of rural
areas aiming to improve ecological quality‚ provided they are managed sustainably. 相似文献
810.
Iris Meusel Eckhard Leistner Wilhelm Barthlott 《Plant Systematics and Evolution》1994,193(1-4):115-123
Certain non-liliiflorous taxa within the monocotyledons (e.g.,Strelitzia, Heliconia, Typha) are characterized by compound epicuticular wax rodlets (Strelitzia type). Similar rodlets are also encountered on the surface of the dicotyledonous plantBenincasa hispida (Thunb.)Cogn. Chemical analysis of the surface wax from both sources showed that the rodlets are chemically distinct. The rodlets of the monocotyledons consist exclusively of aliphatic wax lipids, mainly wax esters. In contrast, the rodlets ofBenincasa are cheifly composed of triterpenol acetates and triterpenols. Formation of rodlets is therefore interpreted as ultrastructural convergency. It is concluded that taxonomical studies on wax crystalloids can be misleading when interpreted in terms of micromorphology of crystalloids only. 相似文献