全文获取类型
收费全文 | 335篇 |
免费 | 26篇 |
专业分类
361篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 22篇 |
2012年 | 13篇 |
2011年 | 23篇 |
2010年 | 12篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 22篇 |
2005年 | 13篇 |
2004年 | 19篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1990年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1978年 | 4篇 |
1942年 | 2篇 |
1939年 | 4篇 |
1938年 | 4篇 |
1936年 | 2篇 |
1933年 | 4篇 |
1930年 | 2篇 |
1928年 | 3篇 |
1925年 | 3篇 |
1922年 | 1篇 |
1917年 | 1篇 |
1915年 | 1篇 |
1914年 | 1篇 |
1912年 | 2篇 |
1911年 | 1篇 |
1910年 | 1篇 |
1908年 | 1篇 |
1906年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 15 毫秒
1.
A lightweight finger printing stand is described which can be adjusted to the proper printing height. Based upon experience printing over 1,100 subjects, 12 advantages of using the stand are suggested. 相似文献
2.
The common hamster (Cricetus cricetus L.), a rodent of the Eurasian steppes and agricultural areas, is threatened by habitat loss. Remnant populations in Western and Central Europe are small, isolated and genetically impoverished. The populations of Belgium, The Netherlands and North Rhine-Westphalia, Germany (BNN), for which Nehring proposed the epiphet canescens, are most affected by this decline. They are distinguished from more eastern populations by large, white areas on throat, chest and forelegs. These traits are sometimes also found in other populations, which casts doubt on their value as diagnostic characteristics. Here, we show that the frequency of occurrence of relatively large chest spots, chin streaks and cuffs on the forelegs is highest in BNN, where a white chest spot occurs in 67–100 % of the sampled individuals, compared to 0–8 % in Central and Eastern European populations. Additionally, hamsters from the Upper Rhine area also display relatively high frequencies of these characters (7–44 %). This suggests a common origin of BNN and Upper Rhine hamsters and an ancient expansion route along the Rhine Valley. A supplementary genetic study of two mitochondrial genes revealed extremely low diversity in both BNN and Upper Rhine hamsters but also clear differentiation and isolation between the two remaining relict populations of North Rhine-Westphalia. 相似文献
3.
Oskar Pineño 《Behavioural processes》2010,84(2):625-628
Rats given presentations of a citric acid solution while recovering from LiCl-induced illness (i.e., a “medicine effect” treatment) subsequently drank more of an aversively conditioned NaCl solution at test, when the NaCl presentation was immediately preceded by citric acid. That is, citric acid passed a summation test of conditioned inhibition. Such an effect was not observed in a group given explicitly unpaired presentations of LiCl and citric acid. It is proposed that enhanced consumption of an aversive taste due to the previous presentation of a “medicine” taste can provide an animal model of human maladaptive behavior in regards to food consumption. 相似文献
4.
Jenni Nordn Philip J. Harrison Louise Mair Juha Siitonen Anders Lundstrm Oskar Kindvall Tord Snll 《Ecology and evolution》2020,10(6):3079-3089
Understanding spatiotemporal population trends and their drivers is a key aim in population ecology. We further need to be able to predict how the dynamics and sizes of populations are affected in the long term by changing landscapes and climate. However, predictions of future population trends are sensitive to a range of modeling assumptions. Deadwood‐dependent fungi are an excellent system for testing the performance of different predictive models of sessile species as these species have different rarity and spatial population dynamics, the populations are structured at different spatial scales, and they utilize distinct substrates. We tested how the projected large‐scale occupancies of species with differing landscape‐scale occupancies are affected over the coming century by different modeling assumptions. We compared projections based on occupancy models against colonization–extinction models, conducting the modeling at alternative spatial scales and using fine‐ or coarse‐resolution deadwood data. We also tested effects of key explanatory variables on species occurrence and colonization–extinction dynamics. The hierarchical Bayesian models applied were fitted to an extensive repeated survey of deadwood and fungi at 174 patches. We projected higher occurrence probabilities and more positive trends using the occupancy models compared to the colonization–extinction models, with greater difference for the species with lower occupancy, colonization rate, and colonization:extinction ratio than for the species with higher estimates of these statistics. The magnitude of future increase in occupancy depended strongly on the spatial modeling scale and resource resolution. We encourage using colonization–extinction models over occupancy models, modeling the process at the finest resource‐unit resolution that is utilizable by the species, and conducting projections for the same spatial scale and resource resolution at which the model fitting is conducted. Further, the models applied should include key variables driving the metapopulation dynamics, such as the availability of suitable resource units, habitat quality, and spatial connectivity. 相似文献
5.
6.
Edward E. Korshin Lyubov G. Zakharova Yakov A. Levin Marina P. Shulaeva Oskar K. Pozdeev 《Bioorganic & medicinal chemistry letters》2013,23(8):2357-2361
A set of racemic N-phenyl-substituted β-amidoamidines hydrochlorides 4, which are structurally related to natural antiviral agent amidinomycin (1), was synthesized in four steps starting from methacryloyl anilide (5). In the final step of the synthetic route, an uncommon monoacylation of β-aminoamidine 8 at the less reactive β-phenylamino-group took place. To rationalize this result, a mechanism which involves initial acylation at the more active amidine-function followed by intramolecular acyl-group transfer to β-phenylamino-group was suggested. All three β-amidoamidines 4d–f bearing long linear aliphatic chain (from n-C8H17 to n-C12H25) revealed significant in vitro activity against influenza A virus (H3N2) and modest cytotoxicity. The in vitro antiviral potency of 4d,e is 6–20 times greater than that of commercial rimantadine with lower EC50 values and higher therapeutic index. The non-toxic in vivo compounds 4d–f showed a beneficial protective effect in influenza A (H3N2) infected mice. 相似文献
7.
Origin of the S‐Shaped JV Curve and the Light‐Soaking Issue in Inverted Organic Solar Cells 下载免费PDF全文
Anton Sundqvist Oskar J. Sandberg Mathias Nyman Jan‐Henrik Smått Ronald Österbacka 《Liver Transplantation》2016,6(6)
Inverted organic solar cells generally exhibit a strong s‐shaped kink in the current–voltage characteristics (JV curve) that may be removed by exposure to UV light (light‐soaking) leading to a drastically improved performance. Using in‐device characterization methods the origin of the light‐soaking issue in inverted solar cells employing titanium dioxide (TiO2) as an electron selective layer is clarified. An injected hole reservoir accumulated at the TiO2/organic interface of the pristine device is observed from extraction current transients; the hole reservoir increases the recombination and results in an s‐shape in the JV curve of pristine devices. The hole reservoir and the s‐shape is a result of the energetics at the selective contact in the pristine device; the effect of UV exposure is to decrease the work function of the indium tin oxide/TiO2‐contact, increasing the built‐in potential. This hinders the build‐up of the hole reservoir and the s‐shape is removed. The proposed model is in excellent agreement with drift‐diffusion simulations. 相似文献
8.
Per Fahlberg Nathalie Buhot Oskar N. Johansson Mats X. Andersson 《Molecular Plant Pathology》2019,20(1):69-77
Non-specific lipid transfer proteins (LTPs) are involved in the transport of lipophilic compounds to the cuticular surface in epidermal cells and in the defence against pathogens. The role of glycophosphatidylinositol (GPI)-anchored LTPs (LTPGs) in resistance against non-host mildews in Arabidopsis thaliana was investigated using reverse genetics. Loss of either LTPG1, LTPG2, LTPG5 or LTPG6 increased the susceptibility to penetration of the epidermal cell wall by Blumeria graminis f. sp. hordei (Bgh). However, no impact on pre-penetration defence against another non-host mildew, Erysiphe pisi (Ep), was observed. LTPG1 was localized to papillae at the sites of Bgh penetration. This study shows that, in addition to the previously known functions, LTPGs contribute to pre-invasive defence against certain non-host powdery mildew pathogens. 相似文献
9.
10.
Ruiqi Xie Jinlian Hu Oskar Hoffmann Yuanchi Zhang Frankie Ng Tingwu Qin Xia Guo 《Biochimica et Biophysica Acta (BBA)/General Subjects》2018,1862(4):936-945
Although tissue engineering has been attracted greatly for healing of critical-sized bone defects, great efforts for improvement are still being made in scaffold design. In particular, bone regeneration would be enhanced if a scaffold precisely matches the contour of bone defects, especially if it could be implanted into the human body conveniently and safely. In this study, polyurethane/hydroxyapatite-based shape memory polymer (SMP) foam was fabricated as a scaffold substrate to facilitate bone regeneration. The minimally invasive delivery and the self-fitting behavior of the SMP foam were systematically evaluated to demonstrate its feasibility in the treatment of bone defects in vivo. Results showed that the SMP foam could be conveniently implanted into bone defects with a compact shape. Subsequently, it self-matched the boundary of bone defects upon shape-recovery activation in vivo. Micro-computed tomography determined that bone ingrowth initiated at the periphery of the SMP foam with a constant decrease towards the inside. Successful vascularization and bone remodeling were also demonstrated by histological analysis. Thus, our results indicate that the SMP foam demonstrated great potential for bone regeneration. 相似文献