全文获取类型
收费全文 | 5431篇 |
免费 | 611篇 |
国内免费 | 2篇 |
出版年
2021年 | 55篇 |
2020年 | 44篇 |
2019年 | 56篇 |
2018年 | 74篇 |
2017年 | 50篇 |
2016年 | 79篇 |
2015年 | 150篇 |
2014年 | 171篇 |
2013年 | 223篇 |
2012年 | 280篇 |
2011年 | 276篇 |
2010年 | 181篇 |
2009年 | 161篇 |
2008年 | 225篇 |
2007年 | 214篇 |
2006年 | 196篇 |
2005年 | 213篇 |
2004年 | 192篇 |
2003年 | 192篇 |
2002年 | 212篇 |
2001年 | 193篇 |
2000年 | 176篇 |
1999年 | 151篇 |
1998年 | 78篇 |
1997年 | 62篇 |
1996年 | 59篇 |
1995年 | 46篇 |
1994年 | 56篇 |
1993年 | 50篇 |
1992年 | 111篇 |
1991年 | 107篇 |
1990年 | 84篇 |
1989年 | 110篇 |
1988年 | 91篇 |
1987年 | 95篇 |
1986年 | 74篇 |
1985年 | 91篇 |
1984年 | 59篇 |
1983年 | 66篇 |
1982年 | 53篇 |
1981年 | 48篇 |
1980年 | 54篇 |
1979年 | 68篇 |
1978年 | 49篇 |
1977年 | 70篇 |
1976年 | 50篇 |
1975年 | 49篇 |
1974年 | 42篇 |
1973年 | 42篇 |
1971年 | 39篇 |
排序方式: 共有6044条查询结果,搜索用时 62 毫秒
941.
942.
943.
Aud H. Halbritter Simone Fior Irene Keller Regula Billeter Peter J. Edwards Rolf Holderegger Sophie Karrenberg Andrea R. Pluess Alex Widmer Jake M. Alexander 《Journal of evolutionary biology》2018,31(6):784-800
Studies of genetic adaptation in plant populations along elevation gradients in mountains have a long history, but there has until now been neither a synthesis of how frequently plant populations exhibit adaptation to elevation nor an evaluation of how consistent underlying trait differences across species are. We reviewed studies of adaptation along elevation gradients (i) from a meta‐analysis of phenotypic differentiation of three traits (height, biomass and phenology) from plants growing in 70 common garden experiments; (ii) by testing elevation adaptation using three fitness proxies (survival, reproductive output and biomass) from 14 reciprocal transplant experiments; (iii) by qualitatively assessing information at the molecular level, from 10 genomewide surveys and candidate gene approaches. We found that plants originating from high elevations were generally shorter and produced less biomass, but phenology did not vary consistently. We found significant evidence for elevation adaptation in terms of survival and biomass, but not for reproductive output. Variation in phenotypic and fitness responses to elevation across species was not related to life history traits or to environmental conditions. Molecular studies, which have focussed mainly on loci related to plant physiology and phenology, also provide evidence for adaptation along elevation gradients. Together, these studies indicate that genetically based trait differentiation and adaptation to elevation are widespread in plants. We conclude that a better understanding of the mechanisms underlying adaptation, not only to elevation but also to environmental change, will require more studies combining the ecological and molecular approaches. 相似文献
944.
Jeanette Edwards 《Ethnos》2018,83(4):724-743
Family history research is popular in England. As a social practice it straddles social class and is confined to neither the middle nor the working classes, but shows an enthusiastic and flourishing interest in the workings of social class and in micro-histories of the region. This article focuses on experts in family history research in a region of the north west of England where it is referred to colloquially as ‘family treeing’. Here family treeing is inflected by a post-industrial landscape and recent social and economic transformations with attendant threats to working-class life and dignity. Family treeing is about caring for the dead, but it is also, significantly, about caring for the living, and not only kin. It is an active practice of belonging both to people and places, and entails constant acts of reciprocity. 相似文献
945.
946.
Carolina I. Calviño Priscila Edwards Martina Fernández María Andrea Relva Cecilia Ezcurra 《Biological invasions》2018,20(10):2715-2722
Species of Alnus (alders) have become invaders in several parts of the world. Here we report the presence of three naturalized alien species: A. glutinosa, A. incana and A. rubra from several populations in nature reserves of northwestern Patagonia, an area of remarkably high biodiversity. Alnus glutinosa had been cited previously for Chile and southern Argentina, but A. incana and A. rubra are here reported for the first time. As we found morphological variation within and among the populations of these introduced species that makes their discrimination difficult, we used chloroplast (trnH-psbA) and nuclear ribosomal (ITS) DNA sequences to confirm their identifications from morphological characteristics. Results from nuclear and chloroplast sequence data confirm the morphological tentative identification of the three species and remark the utility of molecular information together with morphology for the detection of introduced species of taxonomically difficult groups. The invasive characteristics of these alien tree species are discussed in relation to the conservation of the nature reserves where they are found. 相似文献
947.
Ben J. Bowles Karolina Dziemidowicz Felipe L. Lopez Mine Orlu Catherine Tuleu Andrew J. Edwards Terry B. Ernest 《AAPS PharmSciTech》2018,19(6):2598-2609
Co-processed excipients may enhance functionality and reduce drawbacks of traditional excipients for the manufacture of tablets on a commercial scale. The following study aimed to characterise a range of co-processed excipients that may prove suitable for dispersible tablet formulations prepared by direct compression. Co-processed excipients were lubricated and compressed into 10.5-mm convex tablets using a Phoenix compaction simulator. Compression profiles were generated by varying the compression force applied to the formulation and the prepared tablets were characterised for hardness, friability, disintegration and fineness of dispersion. Our data indicates that CombiLac, F-Melt type C and SmartEx QD100 were the top 3 most suitable out of 16 co-processed excipients under the conditions evaluated. They exhibited good flow properties (Carr’s index ? 20), excellent tabletability (tensile strength >?3.0 MPa at 0.85 solid fraction), very low friability (<?1% after 15 min), rapid disintegration times (27–49 s) and produced dispersions of ideal fineness (<?250 μm). Other co-processed excipients (including F-Melt type M, Ludiflash, MicroceLac, Pharmaburst 500 and Avicel HFE-102) may be appropriate for dispersible tablets produced by direct compression providing the identified disintegration and dispersion risks were mitigated prior to commercialisation. This indicates that robust dispersible tablets which disintegrate rapidly could be manufactured from a range of co-processed excipients. 相似文献
948.
949.
Leslie Edwards Danielle Turner Cody Champion Megha Khandelwal Kailee Zingler Cassidy Stone Ruwini D. Rajapaksha Jing Yang Mahinda I. Ranasinghe Alexander Kornienko Liliya V. Frolova Snezna Rogelj 《Bioorganic & medicinal chemistry letters》2018,28(10):1879-1886
Compounds based on the 2,3-distyrylindole scaffold were found to exhibit bactericidal properties upon irradiation with white light. At the concentration of 1?μM, the lead compound 1 completely (ca. 109?CFU/mL) eradicated such Gram-positive organisms as S. aureus (MRSA, MSSA), E. faecalis (VRE), S. pyogenes and S. mutans when irradiated with white light for 2?min. At the concentration of 5?μM and in the presence of polymyxin E at non-bactericidal 1.25?μg/mL concentration, 1 also showed a 7-log to 9-log reductions in bacterial counts of such Gram-negative organisms as multi-drug resistant (MDR) A. baumannii, MDR P. aeruginosa, E. coli and Klebsiella pneumoniae (CRE: KPC and NDM-1), also when irradiated with white light for 2?min. The structure-activity relationship studies revealed that unsubstituted at benzene rings 2,3-distyrylindole 2 was most potent and gave a 5-order of magnitude eradication of a MRSA strain at the concentration of 30?nM upon irradiation with white light. Initial mechanistic experiments revealed the disruption of bacterial cell membrane, but indicated that singlet oxygen production, which is commonly associated with photodynamic therapy, may not play a role in the bactericidal effects of the 2,3-distyrylindoles. 相似文献
950.
Travis R. Helgren Elif S. Seven Congling Chen Thomas E. Edwards Bart L. Staker Jan Abendroth Peter J. Myler James R. Horn Timothy J. Hagen 《Bioorganic & medicinal chemistry letters》2018,28(8):1376-1380
Methionine aminopeptidase (MetAP) is a dinuclear metalloprotease responsible for the cleavage of methionine initiator residues from nascent proteins. MetAP activity is necessary for bacterial proliferation and is therefore a projected novel antibacterial target. A compound library consisting of 294 members containing metal-binding functional groups was screened against Rickettsia prowazekii MetAP to determine potential inhibitory motifs. The compounds were first screened against the target at a concentration of 10?µM and potential hits were determined to be those exhibiting greater than 50% inhibition of enzymatic activity. These hit compounds were then rescreened against the target in 8-point dose–response curves and 11 compounds were found to inhibit enzymatic activity with IC50 values of less than 10?µM. Finally, compounds (1–5) were docked against RpMetAP with AutoDock to determine potential binding mechanisms and the results were compared with crystal structures deposited within the PDB. 相似文献