全文获取类型
收费全文 | 937篇 |
免费 | 66篇 |
专业分类
1003篇 |
出版年
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 17篇 |
2017年 | 7篇 |
2016年 | 24篇 |
2015年 | 39篇 |
2014年 | 51篇 |
2013年 | 52篇 |
2012年 | 69篇 |
2011年 | 71篇 |
2010年 | 41篇 |
2009年 | 27篇 |
2008年 | 57篇 |
2007年 | 51篇 |
2006年 | 43篇 |
2005年 | 57篇 |
2004年 | 37篇 |
2003年 | 44篇 |
2002年 | 55篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有1003条查询结果,搜索用时 15 毫秒
991.
992.
993.
In two experiments of 3 × 3 Latin square with growing pigs, the effect was investigated of supplementation of 5 % or 10 % (2.5 % vs. 5 % DM) polyol mixture and 2.5 % or 5 % of xylitol on digestibility of diet, N-balance, blood clinical-chemical parameters and insulin level in serum. Apparent digestibility of crude protein was lower for the diet with 10 % polyol mixture compared to the control. Sugar alcohols were not found in faeces. Arabinitol, mannitol and rhamnitol were excreted in the urine 25–67 %. Little sorbitol and xylitol were found in urine on diets with polyol mixture 5–10 %. On xylitol diets the pigs did not excrete xylitol in urine. Plasma glucose rose in pigs fed xylitol. Blood total protein and albumin decreased in pigs fed polyol mixture. ALAT-activities were higher for xylitol diets than for the controls. Serum insulin tended to increase in pigs fed polyol mixture 10 % one hour after feeding, and in xylitol feeding two hours after feeding; these values were higher with increasing xylitol inclusion in diet. 相似文献
994.
Carina Lundmark Simon Matti Annica Sandström 《European Journal of Wildlife Research》2014,60(4):637-644
Adaptive co-management (ACM) is a key concept in science and an increasingly adopted policy response in conservation, associated with a number of positive outcomes. However, the effects and mechanisms of co-management arrangements, including the conditions under which ACM gives rise to higher levels of internal and external legitimacy, are yet to be explored. This endeavor, in turn, requires theoretically driven models providing assumptions and outlining testable hypotheses. Considering the social challenges of ACM and using an institutional change within the Swedish carnivore management system aimed at achieving legitimacy through co-management as an illustrative example, this article develops a conceptual model that encompasses conditions and possible explanations to ACM outcomes. More specifically, drawing on lessons from social theory, we model the impact of three key factors—social networks, deliberation and learning—on the external and internal legitimacy resulting from ACM arrangements. Based on the model proposed, the popular assumptions of ACM outcomes can thus be empirically scrutinized and the conditions for increased legitimacy through ACM arrangements better comprehended. 相似文献
995.
Diatoms have been studied in an annually laminated sulphide mud which was deposited after the impoundment of the sea-bay of Gennarbyviken. It was possible to follow how the measured decrease in salinity in the basin was reflected by the diatom flora of the sediment which had been deposited concurrently 相似文献
996.
Penelope Gray Hanna Kann Ville N. Pimenoff Tiina Eriksson Tapio Luostarinen Simopekka Vnsk Helj-Marja Surcel Helena Faust Joakim Dillner Matti Lehtinen 《PLoS medicine》2021,18(6)
BackgroundCervical cancer elimination through human papillomavirus (HPV) vaccination programs requires the attainment of herd effect. Due to its uniquely high basic reproduction number, the vaccination coverage required to achieve herd effect against HPV type 16 exceeds what is attainable in most populations. We have compared how gender-neutral and girls-only vaccination strategies create herd effect against HPV16 under moderate vaccination coverage achieved in a population-based, community-randomized trial.Methods and findingsIn 2007–2010, the 1992–1995 birth cohorts of 33 Finnish communities were randomized to receive gender-neutral HPV vaccination (Arm A), girls-only HPV vaccination (Arm B), or no HPV vaccination (Arm C) (11 communities per trial arm). HPV16/18/31/33/35/45 seroprevalence differences between the pre-vaccination era (2005–2010) and post-vaccination era (2011–2016) were compared between all 8,022 unvaccinated women <23 years old and resident in the 33 communities during 2005–2016 (2,657, 2,691, and 2,674 in Arms A, B, and C, respectively). Post- versus pre-vaccination-era HPV seroprevalence ratios (PRs) were compared by arm. Possible outcome misclassification was quantified via probabilistic bias analysis. An HPV16 and HPV18 seroprevalence reduction was observed post-vaccination in the gender-neutral vaccination arm in the entire study population (PR16 = 0.64, 95% CI 0.10–0.85; PR18 = 0.72, 95% CI 0.22–0.96) and for HPV16 also in the herpes simplex virus type 2 seropositive core group (PR16 = 0.64, 95% CI 0.50–0.81). Observed reductions in HPV31/33/35/45 seroprevalence (PR31/33/35/45 = 0.88, 95% CI 0.81–0.97) were replicated in Arm C (PR31/33/35/45 = 0.79, 95% CI 0.69–0.90).ConclusionsIn this study we only observed herd effect against HPV16/18 after gender-neutral vaccination with moderate vaccination coverage. With only moderate vaccination coverage, a gender-neutral vaccination strategy can facilitate the control of even HPV16. Our findings may have limited transportability to other vaccination coverage levels.Trial registrationClinicalTrials.gov number , https://clinicaltrials.gov/ct2/show/ NCT00534638. NCT00534638相似文献
997.
An automatic method using dyed cellulose as a substrate was developed to determine the solubilizing activity of a cellulase complex. The automatic analyzer was connected to a fermentor and enzyme activity was successfully assayed during fermentation. A useful sampling arrangement was developed and the analysis was sensitive enough to make a short reaction time possible. Cellulase production with Trichoderma viride was used as a model process. 相似文献
998.
999.
Maarit Hallikainen Essi Sarkkinen Ingmar Wester Matti Uusitupa 《BMC cardiovascular disorders》2002,2(1):14-7
Background
The short-term cholesterol-lowering efficacy of plant stanol esters has been open to debate, and the data from different clinical studies with hypercholesterolemic subjects are variable, partly due to lack of systematic studies. Therefore, we investigated the time in days needed to obtain the full cholesterol-lowering effect of stanol esters in hypercholesterolemic subjects. 相似文献1000.
Leif Schulman Kalle Ruokolainen Leo Junikka Ilari E. Sääksjärvi Matti Salo Sanna-Kaisa Juvonen Jukka Salo Mark Higgins 《Biodiversity and Conservation》2007,16(11):3011-3051
Protected areas are crucial for Amazonian nature conservation. Many Amazonian reserves have been selected systematically to
achieve biodiversity representativeness. We review the role natural-scientific understanding has played in reserve selection,
and evaluate the theoretical potential of the existing reserves to cover a complete sample of the species diversity of the
Amazonian rainforest biome. In total, 108 reserves (604,832 km2) are treated as strictly protected and Amazonian; 87 of these can be seen as systematically selected to sample species diversity
(75.3% of total area). Because direct knowledge on all species distributions is unavailable, surrogates have been used to
select reserves: direct information on some species distributions (15 reserves, 14.8% of total area); species distribution
patterns predicted on the basis of conceptual models, mainly the Pleistocene refuge hypothesis, (5/10.3%); environmental units
(46/27.3%); or a combination of distribution patterns and environmental units (21/22.9%). None of these surrogates are reliable:
direct information on species distributions is inadequate; the Pleistocene refuge hypothesis is highly controversial; and
environmental classifications do not capture all relevant ecological variation, and their relevance for species distribution
patterns is undocumented. Hence, Amazonian reserves cannot be safely assumed to capture all Amazonian species. To improve
the situation, transparency and an active dialogue with the scientific community should be integral to conservation planning.
We suggest that the best currently available approach for sampling Amazonian species diversity in reserve selection is to
simultaneously inventory indicator plant species and climatic and geological conditions, and to combine field studies with
remote sensing. 相似文献