全文获取类型
收费全文 | 2522篇 |
免费 | 212篇 |
国内免费 | 1篇 |
出版年
2022年 | 23篇 |
2021年 | 56篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 54篇 |
2017年 | 37篇 |
2016年 | 77篇 |
2015年 | 113篇 |
2014年 | 132篇 |
2013年 | 129篇 |
2012年 | 191篇 |
2011年 | 166篇 |
2010年 | 104篇 |
2009年 | 97篇 |
2008年 | 126篇 |
2007年 | 101篇 |
2006年 | 104篇 |
2005年 | 98篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 72篇 |
2001年 | 39篇 |
2000年 | 45篇 |
1999年 | 43篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1994年 | 20篇 |
1992年 | 33篇 |
1991年 | 41篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 23篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 26篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 20篇 |
1973年 | 18篇 |
1972年 | 19篇 |
1971年 | 19篇 |
1969年 | 15篇 |
排序方式: 共有2735条查询结果,搜索用时 15 毫秒
91.
Hutchinson–Gilford progeria syndrome (HGPS) is caused by an LMNA mutation that results in the production of the abnormal progerin protein. Children with HGPS display phenotypes of premature aging and have an average lifespan of 13 years. We found earlier that the targeting of the transmembrane protein PLA2R1 overcomes senescence and improves phenotypes in a mouse model of progeria. PLA2R1 is regulating the JAK/STAT signaling, but we do not yet know whether targeting this pathway directly would influence cellular and in vivo progeria phenotypes. Here, we show that JAK1/2 inhibition with ruxolitinib rescues progerin‐induced cell cycle arrest, cellular senescence, and misshapen nuclei in human normal fibroblasts expressing progerin. Moreover, ruxolitinib administration reduces several premature aging phenotypes: bone fractures, bone mineral content, grip strength, and a trend to increase survival in a mouse model of progeria. Thus, we propose that ruxolitinib, an FDA‐approved drug, should be further evaluated as a drug candidate in HGPS therapy. 相似文献
92.
Verena Gswein Carla Rodrigues Jos D. Silvestre Fausto Freire Guillaume Habert Jakob Knig 《Journal of Industrial Ecology》2020,24(1):178-192
The built environment is the largest single emitter of CO2 and an important consumer of energy. Much research has gone into the improved efficiency of building operation and construction products. Life Cycle Assessment (LCA) is commonly used to assess existing buildings or building products. Classic LCA, however, is not suited for evaluating the environmental performance of developing technologies. A new approach, anticipatory LCA (a‐LCA), promises various advantages and can be used as a design constraint during the product development stage. It helps overcome four challenges: (i) data availability, (ii) stakeholder inclusion, (iii) risk assessment, and (iv) multi‐criteria problems. This article's contribution to the line of research is twofold: first, it adapts the a‐LCA approach for construction‐specific purposes in theoretical terms for the four challenges. Second, it applies the method to an innovative prefabricated modular envelope system, the CleanTechBlock (CTB), focusing on challenge (i). Thirty‐six CTB designs are tested and compared to conventional walls. Inclusion of technology foresight is achieved through structured scenario analysis. Moreover, challenge (iv) is tackled through the analysis of different environmental impact categories, transport‐related impacts, and thickness of the wall assemblies of the CTB. The case study results show that optimized material choice and product design is needed to reach the lowest environmental impact. Methodological findings highlight the importance of context‐specific solutions and the need for benchmarking new products. 相似文献
93.
94.
95.
X. Yin E. Griesshaber A. Checa F. Nindiyasari-Behal I. Sánchez-Almazo A. Ziegler W.W. Schmahl 《Journal of structural biology》2021,213(2):107707
Shells of calcifying foraminifera play a major role in marine biogeochemical cycles; fossil shells form important archives for paleoenvironment reconstruction. Despite their importance in many Earth science disciplines, there is still little consensus on foraminiferal shell mineralization. Geochemical, biochemical, and physiological studies showed that foraminiferal shell formation might take place through various and diverse mineralization mechanisms.In this study, we contribute to benthic foraminiferal shell calcification through deciphering crystallite organization within the shells. We base our conclusions on results gained from electron backscattered diffraction (EBSD) measurements and describe microstructure/texture characteristics within the laminated shell walls of the benthic, symbiontic foraminifera: Ammonia tepida, Amphistegina lobifera, Amphistegina lessonii. We highlight crystallite assembly patterns obtained on differently oriented cuts and discuss crystallite sizes, morphologies, interlinkages, orientations, and co-orientation strengths.We show that: (i) crystals within benthic foraminiferal shells are mesocrystals, (ii) have dendritic-fractal morphologies and (iii) interdigitate strongly. Based on crystal size, we (iv) differentiate between the two layers that comprise the shells and demonstrate that (v) crystals in the septa have different assemblies relative to those in the shell walls. We highlight that (vi) at junctions of different shell elements the axis of crystal orientation jumps abruptly such that their assembly in EBSD maps has a bimodal distribution. We prove (vii) extensive twin-formation within foraminiferal calcite; we demonstrate (viii) the presence of two twin modes: 60°/[0 0 1] and 77°/~[6 –6 1] and visualize their distributions within the shells.In a broader perspective, we draw conclusions on processes that lead to the observed microstructure/texture patterns. 相似文献
96.
Shannon B. Johnson Anders Warén Verena Tunnicliffe Cindy Van Dover C. Geoffrey Wheat Thomas F. Schultz 《分类学与生物多样性》2013,11(3):278-295
Large symbiont-hosting snails of the genus Alviniconcha (Gastropoda: Abyssochrysidae) are among the dominant inhabitants of hydrothermal vents in the Western Pacific and Indian oceans. The genus was originally described as monotypic, but unique DNA sequences for mitochondrial genes revealed six distinct evolutionary lineages that we could not distinguish based on external morphology. Subsumed under the name Alviniconcha hessleri Okutani & Ohta, the distinct allopatric and sympatric lineages have been assigned placeholder epithets that complicate scientific communications. Based on the present multi-gene sequence data, we hereby describe five Alviniconcha species (in the order of their discovery) – A. kojimai sp. nov., A. boucheti sp. nov., A. marisindica sp. nov., A. strummeri sp. nov. and A. adamantis sp. nov. Thus, we restrict application of the name A. hessleri to specimens that are genetically similar (≥95% for COI) to those found at localities in the Mariana Trough. Single distinct Alviniconcha species inhabit vent fields along the Central Indian Ridge, the Mariana volcanic arc, and the Mariana back-arc basin, whereas vents in the Manus, Fiji and Lau back-arc basins may host two or three additional species. Formal recognition of these species facilitates future attempts to assess their physiological differences and symbiont associations. Furthermore, their reported distributions have significant biogeographic implications, affecting estimates of the diversity within and overlap among Indo-Pacific vent localities.http://zoobank.org/urn:lsid:zoobank.org:pub:1E4B2E71-9F1D-479E-9A9A-22A9E303AAE5 相似文献
97.
The aquatic duckweed Spirodela polyrhiza propagates itself vegetatively by forming turions – bud‐like perennation organs – in the autumn, which spend the winter on the bottom of ponds and then germinate in the following spring and proliferate on the water surface. Newly formed turions usually require a period of cold after‐ripening and light to germinate effectively, but an ample supply of exogenous sugar can lead to germination even in the dark and independent of after‐ripening. The results of the present study indicate that the availability of readily metabolised carbohydrates is a determining factor for turion germination. Freshly harvested turions do not contain soluble, low‐molecular weight carbohydrates at a level sufficient to allow germination to take place, but after‐ripened turions do. Augmentation of the soluble carbohydrate content during after‐ripening derives from gradual breakdown of reserve starch of the turions. The long time required for any germination to be observed in turions incubated in darkness and the limited frequency of germination in the dark (about 50% of turion population), even with an ample external sugar, supply emphasise that both after‐ripening and light are essential for ensuring rapid germination and subsequent frond proliferation at an ecologically appropriate time. The carbohydrate supply required for rapid proliferation of the fronds produced at germination is provided by the rapid light‐induced breakdown of turion reserve starch. 相似文献
98.
Sarah K. Oettl Jana Gerstmeier Shafaat Y. Khan Katja Wiechmann Julia Bauer Atanas G. Atanasov Clemens Malainer Ezzat M. Awad Pavel Uhrin Elke H. Heiss Birgit Waltenberger Daniel Remias Johannes M. Breuss Joel Boustie Verena M. Dirsch Hermann Stuppner Oliver Werz Judith M. Rollinger 《PloS one》2013,8(10)
In vitro screening of 17 Alpine lichen species for their inhibitory activity against 5-lipoxygenase, microsomal prostaglandin E2 synthase-1 and nuclear factor kappa B revealed Cetrelia monachorum (Zahlbr.) W.L. Culb. & C.F. Culb. As conceivable source for novel anti-inflammatory compounds. Phytochemical investigation of the ethanolic crude extract resulted in the isolation and identification of 11 constituents, belonging to depsides and derivatives of orsellinic acid, olivetolic acid and olivetol. The two depsides imbricaric acid (4) and perlatolic acid (5) approved dual inhibitory activities on microsomal prostaglandin E2 synthase-1 (IC50 = 1.9 and 0.4 µM, resp.) and on 5-lipoxygenase tested in a cell-based assay (IC50 = 5.3 and 1.8 µM, resp.) and on purified enzyme (IC50 = 3.5 and 0.4 µM, resp.). Additionally, these two main constituents quantified in the extract with 15.22% (4) and 9.10% (5) showed significant inhibition of tumor necrosis factor alpha-induced nuclear factor kappa B activation in luciferase reporter cells with IC50 values of 2.0 and 7.0 µM, respectively. In a murine in vivo model of inflammation, 5 impaired the inflammatory, thioglycollate-induced recruitment of leukocytes to the peritoneum. The potent inhibitory effects on the three identified targets attest 4 and 5 a pronounced multi-target anti-inflammatory profile which warrants further investigation on their pharmacokinetics and in vivo efficacy. 相似文献
99.
100.
The perception of emotions is often suggested to be multimodal in nature, and bimodal as compared to unimodal (auditory or visual) presentation of emotional stimuli can lead to superior emotion recognition. In previous studies, contrastive aftereffects in emotion perception caused by perceptual adaptation have been shown for faces and for auditory affective vocalization, when adaptors were of the same modality. By contrast, crossmodal aftereffects in the perception of emotional vocalizations have not been demonstrated yet. In three experiments we investigated the influence of emotional voice as well as dynamic facial video adaptors on the perception of emotion-ambiguous voices morphed on an angry-to-happy continuum. Contrastive aftereffects were found for unimodal (voice) adaptation conditions, in that test voices were perceived as happier after adaptation to angry voices, and vice versa. Bimodal (voice + dynamic face) adaptors tended to elicit larger contrastive aftereffects. Importantly, crossmodal (dynamic face) adaptors also elicited substantial aftereffects in male, but not in female participants. Our results (1) support the idea of contrastive processing of emotions (2), show for the first time crossmodal adaptation effects under certain conditions, consistent with the idea that emotion processing is multimodal in nature, and (3) suggest gender differences in the sensory integration of facial and vocal emotional stimuli. 相似文献