全文获取类型
收费全文 | 433篇 |
免费 | 27篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 27篇 |
2013年 | 22篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 22篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1965年 | 4篇 |
1964年 | 2篇 |
1961年 | 2篇 |
1949年 | 1篇 |
1921年 | 1篇 |
排序方式: 共有460条查询结果,搜索用时 15 毫秒
91.
A summary account is given of the development of a small Late-Glacial lake at Snellegem-St. Andries, Belgium. Sedimentation, hydrology, water quality and biotic succession clearly depended on climatic conditions and catchment processes (soil stability and leaching, vegetation). Special attention is drawn to a period of low water level near the end of the Allerød and the abundance of Fragilaria in certain periods. 相似文献
92.
Insect communities on experimental mugwort (Artemisia vulgaris L.) plots along an urban gradient 总被引:5,自引:0,他引:5
We studied the ability of insect herbivores and their natural enemies to colonize exposed, potted mugwort plants (Artemisia vulgaris L.) along a rural-urban gradient in 1994 in Hamburg (northern Germany). Ectophagous insects, leafmines and galls were monitored
weekly from mid-May to mid-September. Endophagous insects were counted by harvesting and dissecting the stems at the end of
the growing season. The rural-urban gradient was characterized by a gradient of vegetation-free areas and increasing proportion
of ground covered in concrete, tarmac, paving and other impermeable surfaces surrounding the Artemisia plots, i.e. six different zones of increasing isolation. Numbers of insect species (herbivores, parasitoids and predators)
decreased along the gradient from 43 to 12. Monophagous herbivores were not more affected than polyphagous herbivores, but
parasitoids, especially rare species, were more strongly affected by isolation than predators. Some dominant herbivorous species
were very successful colonizers and occurred in inner city sites devoid of all natural vegetation. Sometimes their abundance
increased in the inner city to significantly higher densities than in the urban fringe. Isolation appeared to be the main
reason for the observed patterns, since area and soil conditions were held constant in the experiment. Microclimate and pollution
were considered to play a minor role.
Received: 16 January 1997 / Accepted: 26 August 1997 相似文献
93.
94.
Alexander Krah Denys Pogoryelov Julian D. Langer Peter J. Bond Thomas Meier José D. Faraldo-Gómez 《BBA》2010,1797(6-7):763-772
The functional mechanism of the F1Fo ATP synthase, like many membrane transporters and pumps, entails a conformational cycle that is coupled to the movement of H+ or Na+ ions across its transmembrane domain, down an electrochemical gradient. This coupling is an efficient means of energy transduction and regulation, provided that ion binding to the membrane domain, known as Fo, is appropriately selective. In this study we set out to establish the structural and energetic basis for the ion-binding selectivity of the membrane-embedded Fo rotors of two representative ATP synthases. First, we use a biochemical approach to demonstrate the inherent binding selectivity of these rotors, that is, independently from the rest of the enzyme. We then use atomically detailed computer simulations of wild-type and mutagenized rotors to calculate and rationalize their selectivity, on the basis of the structure, dynamics and coordination chemistry of the binding sites. We conclude that H+ selectivity is most likely a robust property of all Fo rotors, arising from the prominent presence of a conserved carboxylic acid and its intrinsic chemical propensity for protonation, as well as from the structural plasticity of the binding sites. In H+-coupled rotors, the incorporation of hydrophobic side chains to the binding sites enhances this inherent H+ selectivity. Size restriction may also favor H+ over Na+, but increasing size alone does not confer Na+ selectivity. Rather, the degree to which Fo rotors may exhibit Na+ coupling relies on the presence of a sufficient number of suitable coordinating side chains and/or structural water molecules. These ligands accomplish a shift in the relative binding energetics, which under some physiological conditions may be sufficient to provide Na+ dependence. 相似文献
95.
96.
97.
Joel Jimenez Villarreal Blanca Murillo Ortiz Sandra Martinez Garza Diana Isabel Rivas Armendriz Víctor Daniel Boone Villa Pilar Carranza Rosales Nadia Denys Betancourt Martínez Hctor Delgado Aguirre Javier Morn Martínez 《Journal of biochemical and molecular toxicology》2019,33(1)
Differentiated cells telomere length is an indicator of senescence or lifespan; however, in peripheral blood leukocytes the relative shortening of the telomere has been considered as a biological marker of aging, and lengthening telomere as an associated risk to cancer. Individual’s age, type of tissue, lifestyle, and environmental factors make telomere length variable. The presence of environmental carcinogens such as arsenic (As) influence as causal agents of these alterations, the main modes of action for As described are oxidative stress, reduction in DNA repair capacity, overexpression of genes, alteration of telomerase activity, and damage to telomeres. The telomeres of leukocytes resulting a finite capacity of replication due to the low or no activity of the telomerase enzyme, therefore, elongation telomere in this kind of cells is a potential biological marker associated with the development of chronic diseases and carcinogenesis. 相似文献
98.
99.
Recreational travel is a recognized vector for the spread of invasive species in North America. However, there has been little quantitative analysis of the risks posed by such travel and the associated transport of firewood. In this study, we analyzed the risk of forest insect spread with firewood and estimated related dispersal parameters for application in geographically explicit invasion models. Our primary data source was the U.S. National Recreation Reservation Service database, which records camper reservations at > 2,500 locations nationwide. For > 7 million individual reservations made between 2004 and 2009 (including visits from Canada), we calculated the distance between visitor home address and campground location. We constructed an empirical dispersal kernel (i.e., the probability distribution of the travel distances) from these "origin-destination" data, and then fitted the data with various theoretical distributions. We found the data to be strongly leptokurtic (fat-tailed) and fairly well fit by the unbounded Johnson and lognormal distributions. Most campers ( approximately 53%) traveled <100 km, but approximately 10% traveled > 500 km (and as far as 5,500 km). Additionally, we examined the impact of geographic region, specific destinations (major national parks), and specific origin locations (major cities) on the shape of the dispersal kernel, and found that mixture distributions (i.e., theoretical distribution functions composed of multiple univariate distributions) may fit better in some circumstances. Although only a limited amount of all transported firewood is likely to be infested by forest insects, this still represents a considerable increase in dispersal potential beyond the insects' natural spread capabilities. 相似文献
100.
Seal J Lamotte Y Donche F Bouillot A Mirguet O Gellibert F Nicodeme E Krysa G Kirilovsky J Beinke S McCleary S Rioja I Bamborough P Chung CW Gordon L Lewis T Walker AL Cutler L Lugo D Wilson DM Witherington J Lee K Prinjha RK 《Bioorganic & medicinal chemistry letters》2012,22(8):2968-2972
A novel series of quinoline isoxazole BET family bromodomain inhibitors are discussed. Crystallography is used to illustrate binding modes and rationalize their SAR. One member, I-BET151 (GSK1210151A), shows good oral bioavailability in both the rat and minipig as well as demonstrating efficient suppression of bacterial induced inflammation and sepsis in a murine in vivo endotoxaemia model. 相似文献