全文获取类型
收费全文 | 4704篇 |
免费 | 376篇 |
国内免费 | 2篇 |
专业分类
5082篇 |
出版年
2023年 | 33篇 |
2022年 | 31篇 |
2021年 | 76篇 |
2020年 | 42篇 |
2019年 | 42篇 |
2018年 | 97篇 |
2017年 | 100篇 |
2016年 | 121篇 |
2015年 | 175篇 |
2014年 | 219篇 |
2013年 | 281篇 |
2012年 | 353篇 |
2011年 | 328篇 |
2010年 | 219篇 |
2009年 | 196篇 |
2008年 | 271篇 |
2007年 | 286篇 |
2006年 | 236篇 |
2005年 | 239篇 |
2004年 | 243篇 |
2003年 | 227篇 |
2002年 | 220篇 |
2001年 | 100篇 |
2000年 | 112篇 |
1999年 | 89篇 |
1998年 | 65篇 |
1997年 | 36篇 |
1996年 | 53篇 |
1995年 | 29篇 |
1994年 | 40篇 |
1993年 | 22篇 |
1992年 | 45篇 |
1991年 | 49篇 |
1990年 | 33篇 |
1989年 | 34篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 27篇 |
1973年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有5082条查询结果,搜索用时 15 毫秒
971.
M Jiménez F García-Cánovas F García-Carmona J L Iborra J A Lozano 《Biochemistry international》1985,11(1):51-59
The present work deals with isoproterenol oxidation by mushroom tyrosinase and sodium metaperiodate. Intermediates produced at short reaction time were characterized by scanning repetitive spectrophotometry and the stoichiometry of the respective aminochrome appearance was established. The oxidation pathway from isoproterenol to aminochrome is parallel to the previously proposed for L-dopa oxidation by mushroom tyrosinase, whose steps are as follow: Isoproterenol----o-quinone-H+----o-quinone----leukoaminochrome---- aminochrome. The stoichiometry for the conversion of o-quinone-H+ into the aminochrome of isoproterenol followed the equation: 2 o-quinone-H+----isoproterenol + aminochrome. The kinetics of chemical reactions that take place from the o-quinone-H+ to aminochrome has been studied as a system of various chemical reactions coupled to an enzymatic reaction (EzCC: Enzymatic-Chemical-Chemical mechanism). 相似文献
972.
973.
Peter L. Falkingham Karl T. Bates Marco Avanzini Matthew Bennett Emese M. Bordy Brent H. Breithaupt Diego Castanera Paolo Citton Ignacio Díaz‐Martínez Jim O. Farlow Anthony R. Fiorillo Stephen M. Gatesy Patrick Getty Kevin G. Hatala Jahn J. Hornung James A. Hyatt Hendrik Klein Jens N. Lallensack Anthony J. Martin Daniel Marty Neffra A. Matthews Christian A. Meyer Jesper Milàn Nicholas J. Minter Novella L. Razzolini Anthony Romilio Steven W. Salisbury Lara Sciscio Ikuko Tanaka Ashleigh L. A. Wiseman L. D. Xing Matteo Belvedere 《Palaeontology》2018,61(4):469-480
The collection and dissemination of vertebrate ichnological data is struggling to keep up with techniques that are becoming commonplace in the wider palaeontological field. A standard protocol is required to ensure that data is recorded, presented and archived in a manner that will be useful both to contemporary researchers, and to future generations. Primarily, our aim is to make the 3D capture of ichnological data standard practice, and to provide guidance on how such 3D data can be communicated effectively (both via the literature and other means) and archived openly and in perpetuity. We recommend capture of 3D data, and the presentation of said data in the form of photographs, false‐colour images, and interpretive drawings. Raw data (3D models of traces) should always be provided in a form usable by other researchers (i.e. in an open format). If adopted by the field as a whole, the result will be a more robust and uniform literature, supplemented by unparalleled availability of datasets for future workers. 相似文献
974.
975.
Angela D. Carraway Sue L. Povlock Melinda L. Houston David S. Johnston Jim Peterson 《Journal of inorganic biochemistry》1995,60(4):267-276
Electron paramagnetic resonance spectra of a number of ferric heme peptide derivatives, in aqueous-detergent and various aqueous-alcohol solvent mixtures, have been obtained using samples in the concentration range 0.1–1.0 mM. Some of these were clearly monomeric, homogeneous, mixed-ligand adducts, entirely suitable for use as model systems for hemoprotein specroscopic studies. As anticipated, the measured EPR parameters were largely independent of solvent environment. Surprisingly, micellar preparations of ferric heme undecapeptide in mildly alkaline solution showed no evidence for the formation of a hydroxide adduct, contrary to a previous report [S. Mazumdar, O. K. Medhi and S. Mitra, Inorg. Chem.30 700 (1991)]. 相似文献
976.
In vitro fertilizing capacity of frozen-thawed boar semen 总被引:2,自引:0,他引:2
We describe a porcine semen cryopreservation technique and assess the in vitro fertilizing capacity of the frozen-thawed spermatozoa. The thawed spermatozoa did not lose the physiological properties of motility, viability, and acrosome reaction or capacity to fertilize in vitro. Immediately after thawing, the spermatozoa showed 51% mean motility, 60% viability, and 5% induced acrosome reaction. After 2.5 h of incubation in TALP medium, the spermatozoa exhibited 61% motility, 63% viability and 40% induced acrosome reaction. The average in vitro fertilization capacity of thawed spermatozoa was 68% compared with that of spermatozoa from fresh semen (85%). The percentage of polyspermy was highly variable, with frozen-thawed samples ranging from 0 to 28% and fresh samples from 0 to 30%. The results obtained with frozen semen from 5 boars of different breeds did not show considerable variation. This suggests that the freezing-thawing technique is reproducible and adequate for in vitro fertilization. 相似文献
977.
María Belén Jiménez-Díaz Joaquín Rullas Teresa Mulet Laura Fernández Carmen Bravo Domingo Gargallo-Viola I?igo Angulo-Barturen 《Cytometry. Part A》2005,67(1):27-36
BACKGROUND: Microscopic analysis of blood smears is currently the most frequently used method to measure parasitemias in experiments of drug efficacy in murine models of malaria. However, it is subjective and labour intensive, which preclude its utilization in large-scale evaluation programs. Flow cytometry is an alternative method, but due to the limited specificity achieved with the currently available techniques, it has not been widely used in murine models of malaria during preclinical evaluation. We describe a new flow cytometric method based on the differences of autofluorescence and DNA content measured after staining with YOYO-1 that are observed in infected erythrocytes compared with noninfected erythrocytes. METHODS: Samples of blood from Plasmodium yoelii-infected animals were fixed with glutaraldehyde, incubated with RNAase, and stained with YOYO-1 in 96-well plate format. After acquisition, erythrocytes gated in logarithmic side/scatter plots were analyzed in bidimensional FL-2/YOYO-1 plots in comparison with unidimensional YOYO-1 analysis. RESULTS: The infected erythrocytes showed a characteristic pattern of staining different from that of noninfected erythrocytes. In routine evaluation, the limit of sensitivity was 0.01% and the measurements of parasitemia were linear at parasitemias above 0.1%. Interestingly, using this approach, infected reticulocytes could be differentiated from infected normocytes. CONCLUSIONS: The method described is robust, increases the specificity and sensitivity of detection in routine testing, and is especially well suited for detection of low parasitemias in murine models of malaria. 相似文献
978.
The textural discontinuity hypothesis: an exploration at a regional level. Shortened version: exploring Holling's TDH 下载免费PDF全文
Dave Raffaelli Alice Hardiman Jim Smart Tsuyuko Yamanaka Piran C. L. White 《Oikos》2016,125(6):797-803
Dominant physical and biological processes in ecosystems occur at specific scales of space and time. The life‐spans and the life‐spaces (areas used by species over their lifetime) become entrained to operate at similar scales. Because life‐spans and life‐spaces are related to body size, ecosystems display polymodality in body size distributions: Holling's textural discontinuity hypothesis, TDH. Falsification of the TDH requires either changing the frequencies of the dominant processes or changing the species. Both are difficult to achieve for regional‐scale faunas, but the transformation of the terrestrial fauna of New Zealand by humans over the past 800 years provides an opportunity to explore the effect of changing the species. Our analyses of the pre and post first‐contact with humans assemblages show that species body size spectra are polymodal and similar (the spectrum is conservative in shape), both pre‐ and post‐spectra exhibiting three distinct modes, despite significant changes in the taxonomic make‐up of the fauna. Our findings are consistent with the TDH, but not consistent with other known competing explanations. There is also a compelling case that invasions and introductions have been more successful in the body size range that falls between modes. This is also consistent with the TDH, but not necessarily at odds with explanations based on propagule pressure. 相似文献
979.
980.