全文获取类型
收费全文 | 823篇 |
免费 | 63篇 |
出版年
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 41篇 |
2013年 | 44篇 |
2012年 | 50篇 |
2011年 | 52篇 |
2010年 | 30篇 |
2009年 | 32篇 |
2008年 | 37篇 |
2007年 | 28篇 |
2006年 | 26篇 |
2005年 | 30篇 |
2004年 | 21篇 |
2003年 | 16篇 |
2002年 | 30篇 |
2001年 | 22篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 9篇 |
1971年 | 5篇 |
1970年 | 8篇 |
1968年 | 5篇 |
1967年 | 5篇 |
1965年 | 5篇 |
排序方式: 共有886条查询结果,搜索用时 15 毫秒
1.
Lipid extract isolated from biomasses of Lodderomyces elongisporus IMET H 128 grown on gas oil 7(B.p. 240–380°C) and fractions of the lipid extract (acetone soluble and fatty acid fractions) reduced the concentration of potato virus X in inoculated as well as in secondarily infected leaves markedly. The antiphytoviral inactive phosphatide fraction was converted into a fraction with high activity by partial hydrolysis with SO2 as acting agent. 相似文献
2.
Effects of exogenous applied lipids being of microbial origin on the water use efficiency (WUE) and the biomass production have been studied in pot and field experiments using crop plants. Lipid mixtures extracted from the cells of Candida maltosa EH 15 increased the WUE (9…16%) and the grain yield (÷x = 10%) of the wheat and barley plants under dry conditions. The fatty acid fraction separated from the lipid mixtures also improved the WUE especially under stress (20…100%) and the biomass production. The phosphatide fraction emulsified with sulfonate containing solvents was not physiologically active. 相似文献
3.
Roger Scholz Falk Hoffmann Sandra von Sachsen Welf-Guntram Drossel Carsten Klöhn Christian Voigt 《Journal of biomechanics》2013
In total hip arthroplasty and particularly in revision surgery, computer assisted pre-operative prediction of the best possible anchorage strategy for implant fixation would be a great help to the surgeon. Computer simulation relies on validated numerical models. In the current study, three density–elasticity relationships (No. 1–3) from the literature for inhomogeneous material parameter assignment from CT data in automated finite element (FE) modeling of long bones were evaluated for their suitability for FE modeling of human pelvic bone. Numerical modal analysis was conducted on 10 FE models of hemipelvic bone specimens and compared to the gold standard provided by experimental modal analysis results from a previous in-vitro study on the same specimens. Overall, calculated resonance frequencies came out lower than measured values. Magnitude of mean relative deviation of numerical resonance frequencies with regard to measured values is lowest for the density–elasticity relationship No. 3 (−15.9%) and considerably higher for both density–elasticity relationships No. 1 (−41.1%) and No. 2 (−45.0%). Mean MAC values over all specimens amount to 77.8% (No. 1), 78.5% (No. 2), and 83.0% (No. 3). MAC results show, that mode shapes are only slightly influenced by material distribution. Calculated resonance frequencies are generally lower than measured values, which indicates, that numerical models lack stiffness. Even when using the best suited (No. 3) out of three investigated density–elasticity relationships, in FE modeling of pelvic bone a considerable underestimation of model stiffness has to be taken into account. 相似文献
4.
Hui Zhou Brenda Vonk Johannes A. Roubos Roel A.L. Bovenberg Christopher A. Voigt 《Nucleic acids research》2015,43(21):10560-10570
Optimizing bio-production involves strain and process improvements performed as discrete steps. However, environment impacts genotype and a strain that is optimal under one set of conditions may not be under different conditions. We present a methodology to simultaneously vary genetic and process factors, so that both can be guided by design of experiments (DOE). Advances in DNA assembly and gene insulation facilitate this approach by accelerating multi-gene pathway construction and the statistical interpretation of screening data. This is applied to a 6-aminocaproic acid (6-ACA) pathway in Escherichia coli consisting of six heterologous enzymes. A 32-member fraction factorial library is designed that simultaneously perturbs expression and media composition. This is compared to a 64-member full factorial library just varying expression (0.64 Mb of DNA assembly). Statistical analysis of the screening data from these libraries leads to different predictions as to whether the expression of enzymes needs to increase or decrease. Therefore, if genotype and media were varied separately this would lead to a suboptimal combination. This is applied to the design of a strain and media composition that increases 6-ACA from 9 to 48 mg/l in a single optimization step. This work introduces a generalizable platform to co-optimize genetic and non-genetic factors. 相似文献
5.
The new genusTervidmonea (type-species:T. daniensis n.gen. n.sp., ? Fam. Terviidae) is described from the Baltic Danian, from Danian ‘Geschiebe’ (glacial erratic drift material) of Northern Germany, from the Upper Maastrichtian of the Maastricht region, and from the Palaeogene ‘Nummuliten-Mergel’ of Bavaria. The zoarium is erect (‘ldmoneiform’), with alternating uniserial fascicles on the frontal side, as inExidmonea David et al. The dorsal face lacks kenozooids and bears a prominent globular ovicell (gynozooid), by which it differs from the genusTervia Jullien 1882. Certain taxa from the Eocene of the U.S.A. referred toTervia by Canu & Bassler (1920) are considered as congeneric withTervidmonea: T. tumida Smitt,T. globulifera Canu & Bassler, andT. pyrifera Canu & Bassler. However, the identity with the RecentTervia tumida from the Arctic realm remains doubtful and so does the present-day occurrence ofTervidmonea. 相似文献
6.
7.
8.
Robin M. Voigt Christopher B. Forsyth Stefan J. Green Ece Mutlu Phillip Engen Martha H. Vitaterna Fred W. Turek Ali Keshavarzian 《PloS one》2014,9(5)
Intestinal dysbiosis and circadian rhythm disruption are associated with similar diseases including obesity, metabolic syndrome, and inflammatory bowel disease. Despite the overlap, the potential relationship between circadian disorganization and dysbiosis is unknown; thus, in the present study, a model of chronic circadian disruption was used to determine the impact on the intestinal microbiome. Male C57BL/6J mice underwent once weekly phase reversals of the light:dark cycle (i.e., circadian rhythm disrupted mice) to determine the impact of circadian rhythm disruption on the intestinal microbiome and were fed either standard chow or a high-fat, high-sugar diet to determine how diet influences circadian disruption-induced effects on the microbiome. Weekly phase reversals of the light:dark (LD) cycle did not alter the microbiome in mice fed standard chow; however, mice fed a high-fat, high-sugar diet in conjunction with phase shifts in the light:dark cycle had significantly altered microbiota. While it is yet to be established if some of the adverse effects associated with circadian disorganization in humans (e.g., shift workers, travelers moving across time zones, and in individuals with social jet lag) are mediated by dysbiosis, the current study demonstrates that circadian disorganization can impact the intestinal microbiota which may have implications for inflammatory diseases. 相似文献
9.
Linn S. Lehnert Stephanie Kramer-Schadt Sophia Sch?nborn Oliver Lindecke Ivo Niermann Christian C. Voigt 《PloS one》2014,9(8)
Over recent years, it became widely accepted that alternative, renewable energy may come at some risk for wildlife, for example, when wind turbines cause large numbers of bat fatalities. To better assess likely populations effects of wind turbine related wildlife fatalities, we studied the geographical origin of the most common bat species found dead below German wind turbines, the noctule bat (Nyctalus noctula). We measured stable isotope ratios of non-exchangeable hydrogen in fur keratin to separate migrants from local individuals, used a linear mixed-effects model to identify temporal, spatial and biological factors explaining the variance in measured stable isotope ratios and determined the geographical breeding provenance of killed migrants using isoscape origin models. We found that 72% of noctule bat casualties (n = 136) were of local origin, while 28% were long-distance migrants. These findings highlight that bat fatalities at German wind turbines may affect both local and distant populations. Our results indicated a sex and age-specific vulnerability of bats towards lethal accidents at turbines, i.e. a relatively high proportion of killed females were recorded among migratory individuals, whereas more juveniles than adults were recorded among killed bats of local origin. Migratory noctule bats were found to originate from distant populations in the Northeastern parts of Europe. The large catchment areas of German wind turbines and high vulnerability of female and juvenile noctule bats call for immediate action to reduce the negative cross-boundary effects of bat fatalities at wind turbines on local and distant populations. Further, our study highlights the importance of implementing effective mitigation measures and developing species and scale-specific conservation approaches on both national and international levels to protect source populations of bats. The efficacy of local compensatory measures appears doubtful, at least for migrant noctule bats, considering the large geographical catchment areas of German wind turbines for this species. 相似文献
10.