全文获取类型
收费全文 | 204篇 |
免费 | 27篇 |
国内免费 | 2篇 |
出版年
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 9篇 |
2010年 | 12篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 2篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有233条查询结果,搜索用时 743 毫秒
41.
The energy produced from the investment in biofuel crops needs to account for the environmental impacts on soil, water, climate change and ecosystem services. A regionalized approach is needed to evaluate the environmental costs of large-scale biofuel production. We present a regional pan-European simulation of rapeseed ( Brassica napus ) cultivation. Rapeseed is the European Union's dominant biofuel crop with a share of about 80% of the feedstock. To improve the assessment of the environmental impact of this biodiesel production, we performed a pan-European simulation of rapeseed cultivation at a 10 × 10 km scale with Environmental Policy Integrated Climate (EPIC). The model runs with a daily time step and model input consists of spatialized meteorological measurements, and topographic, soil, land use, and farm management practices data and information. Default EPIC model parameters were calibrated based on literature. Modelled rapeseed yields were satisfactory compared with yields at regional level reported for 151 regions obtained for the period from 1995 to 2003 for 27 European Union member countries, along with consistent modelled and reported yield responses to precipitation, radiation and vapour pressure deficit at regional level. The model is currently set up so that plant nutrient stress is not occurring. Total fertilizer consumption at country level was compared with IFA/FAO data. This approach allows us to evaluate environmental pressures and efficiencies arising from and associated with rapeseed cultivation to further complete the environmental balance of biofuel production and consumption. 相似文献
42.
ZHENZHEN YI WEIBO SONG THORSTEN STOECK KHALED A. S. AL‐RASHEID ABDULAZIZ A. AL‐KHEDHAIRY JUN GONG HONGWEI MA ZIGUI CHEN 《Zoological Journal of the Linnean Society》2009,157(2):227-236
The morphologically unique ciliate Psammomitra has long been considered as a systematically uncertain stichotrich. This is mainly because of its highly specialized morphology and a lack of either detailed information concerning its ontogenesis, or molecular data. Based on the small subunit rRNA (SSrRNA) gene and alpha‐tubulin gene sequences, we re‐evaluated the phylogenetic position of Psammomitra retractilis using multiple algorithms. Phylogenetic trees inferred from the SSrRNA gene sequences representing a total of 53 spirotrichs demonstrated the closest relationship of Psammomitra was with Holosticha‐like taxa, with strong support, which clearly suggested that Psammomitra should be placed into the order Urostylida although it branched at a rather deep level, and is likely to be closely related to Holostichidae. With consideration to molecular evidence and morphological characters, Psammomitra should be a clearly outlined taxon at about the rank of family, i.e. Psammomitridae stat. nov. , within the order Urostylida. The improved diagnosis for this family is as follows: Urostylida possessing extremely contractile, elongated body which consists of three parts: head, trunk, and slender tail; midventral complex composed of midventral pairs only and restricted to about anterior 1/3 of ventral surface; frontal, frontoterminal, and transverse cirri present; one left and one right marginal rows which commence near proximal end of adoral zone and extend to near rear body end. 相似文献
43.
Carlos García-Estrada Inmaculada Vaca Ricardo V Ullán Marco A van den Berg Roel AL Bovenberg Juan Francisco Martín 《BMC microbiology》2009,9(1):104-15
Background
Penicillium chrysogenum converts isopenicillin N (IPN) into hydrophobic penicillins by means of the peroxisomal IPN acyltransferase (IAT), which is encoded by the penDE gene. In silico analysis of the P. chrysogenum genome revealed the presence of a gene, Pc13g09140, initially described as paralogue of the IAT-encoding penDE gene. We have termed this gene ial because it encodes a protein with high similarity to IAT (IAL for IAT-Like). We have conducted an investigation to characterize the ial gene and to determine the role of the IAL protein in the penicillin biosynthetic pathway. 相似文献44.
In this study, the relationship between the concentration of extra-heavy crude petroleum in a clayey material and the toxicity, field capacity, temperature, and growth of a tropical forage grass (Brachiara humidicola) was determined empirically. For this type of petroleum the acute toxicity (Microtox®) was slight (CE50 = 63200 - 76400 mg/kg) even at high hydrocarbon concentrations (29279 mg/kg). Nonetheless, serious impacts were encountered in terms of an increase in soil temperature (+ 1.3 °C), reduction in field capacity (-10.7%) and reduction in aerial biomass (-97%). The relationship between hydrocarbon concentration and biomass resulted in a typical dose-response curve (r = 0.99), where a concentration of 2626 mg/kg of hydrocarbons corresponds to a maintenance of 90% biomass. Furthermore, during the duration of this study (one year) the biodegradation was proportional to the pasture biomass production (r = 0.997) indicating a synergistic relationship between the petroleum biodegrading microorganisms in the rhizosphere and the pasture. 相似文献
45.
Angela Karp Steve J.Hanley Sviatlana O.Trybush William Macalpine Ian Shield 《Acta Botanica Sinica》2011,(2)
Willows (Salix spp.) are a very diverse group of catkin-bearing trees and shrubs that are widely distributed across temperate regions of the globe.Some species respond well to being grown in short rotation coppice (SRC) cycles,which are much shorter than conventional forestry.Coppicing reinvigorates growth and the biomass rapidly accumulated can be used as a source of renewable carbon for bioenergy and biofuels.As SRC willows re-distribute nutrients during the perennial cycle they require only minimal nitro... 相似文献
46.
47.
Terry Flum Gary L. Huxel Cheri S. LaRue Bart Hardison Jeffrey R. Duncan James A. Drake 《Hydrobiologia》1993,271(2):75-85
Experimental testing of ecological theory in the field is often difficult because of the number of factors influencing the
test system. Adequate control of relevant variables may require the use of laboratory microcosms for the performance of proper
experimental tests. Our efforts to study the effects of species invasion sequence on community structure and ecosystem properties
of the developing system, requires that the experimental systems be closed. To meet our demanding experimental requirements,
we have designed a closed artificial stream that permits careful control over algal species introductions while minimizing
the risks of contamination by unwanted species. In assessing the performance of these streams, we examined the variability
among experimental replicates in water chemistry parameters and biomass accumulation. Those water chemistry parameters that
were not greatly influenced by biological processes in the streams (Ca, Mg, bicarbonate, and sulfate) had average coefficients
of variation less than 10%. Those parameters that were clearly influenced by biological processes (P, N, Fe, and Si) had average
coefficients of variation ranging from 13.5%–40.4%. Ash free dry mass had an average coefficient of variation of 23.3%, but
chlorophyll a was much more variable at 183%. This pattern of variation indicates that the artificial streams performed well in terms of
replicability, but some experimental goals may require carefully conceived designs that adequately partition sources of variation
in biologically mediated variables to obtain satisfactory results. 相似文献
48.
Mycotoxin Research - Six laboratories analyzed portions of the same aqueous acetonitrile extracts of three peanut butters for aflatoxin concentrations by an HPLC procedure (using immunoaffinity... 相似文献
49.
Phospholipid, cholesterol, polypeptide and glycoprotein composition of hepatic endosome subfractions. 总被引:6,自引:3,他引:3
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The composition of hepatic endosome subfractions was compared directly with that of plasma membranes and Golgi-apparatus fractions. The neutral lipid and phospholipid composition of two endosome subfractions separated on Nycodenz gradients from a parent endosome fraction was similar to that of plasma membranes. The phospholipid/cholesterol ratios and the sphingomyelin contents were high, as in plasma membranes. However, the phosphatidylserine content was low. Endosomal subfractions contained a simpler polypeptide profile than did plasma membranes. However, a large number of glycoproteins were common to both fractions. Two endosome-specific glycoproteins, of Mr 59 000 and 38 000, were identified. Sialic acid was present at concentrations higher than in plasma membranes. The results indicate that endosomal membranes have a similar composition to plasma membranes that probably reflects their functional interaction during endocytosis and receptor recycling. 相似文献
50.
Oocysts of Eimeria saudiensis n. sp. (Apicomplexa: Eimeriidae) are described from the feces of the Arabian oryx, Oryx leucoryx , from the Riyadh Zoo, Saudi Arabia. The oocysts were ellipsoidal or slightly ovoid, 31.2 times 24.5 (24.3–36.5 times 20.0–27.6) μm with a bilayered wall about 1.7 μm thick. The micropyle was covered by a dome-shaped cap. The oocyst residuum was absent, but tiny polar granules were present. The sporocysts were elongate ovoid, 14.3 times 7.2 (11.5–18.5 times 6.0–9.0) μm, had a Stieda body, but lacked a substiedal body. The sporocyst residuum was present, composed of numerous small granules. The sporozoites were elongate club-shaped, and contained two prominent refractile bodies. 相似文献