全文获取类型
收费全文 | 695篇 |
免费 | 61篇 |
国内免费 | 32篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 21篇 |
2021年 | 45篇 |
2020年 | 74篇 |
2019年 | 55篇 |
2018年 | 38篇 |
2017年 | 34篇 |
2016年 | 25篇 |
2015年 | 32篇 |
2014年 | 43篇 |
2013年 | 50篇 |
2012年 | 37篇 |
2011年 | 31篇 |
2010年 | 23篇 |
2009年 | 37篇 |
2008年 | 26篇 |
2007年 | 37篇 |
2006年 | 35篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有788条查询结果,搜索用时 500 毫秒
731.
732.
The aim of the study was to describe the dependence on ambient temperature of distal joint temperature at the forelimbs of racehorses. The study also investigated the influence of differing ambient temperatures on the temperature difference between joints: this was measured ipsilaterally (i.e. between the carpal and fetlock joints along each forelimb) and contralaterally (i.e. between the same joints of the left and right forelimbs). Sixty-four healthy racehorses were monitored over 10 months. At each session, three thermographic images were taken of the dorsal, lateral and medial aspects of the distal forelimbs. Temperature measurements were made from regions of interest (ROIs) covering the carpal and fetlock joints. There was a strong correlation between ambient temperature and absolute joint temperature at all ROIs. The study also observed a moderate correlation between ambient temperature and the ipsilateral temperature differences between joints when measured from the medial and lateral aspects. No significant correlation was noted when measured dorsally. The mean contralateral temperature differences between joints were all close to 0 °C. The data support previous reports that the temperature distribution between the forelimbs of the healthy equine is generally symmetric, although some horses differ markedly from the average findings. 相似文献
733.
Ziv Attia Ahan Dalal Menachem Moshelion 《The Plant journal : for cell and molecular biology》2020,101(6):1368-1377
Plants can detect pathogen invasion by sensing microbe‐associated molecular patterns (MAMPs). This sensing process leads to the induction of defense responses. Numerous MAMP mechanisms of action have been described in and outside the guard cells. Here, we describe the effects of chitin, a MAMP found in fungal cell walls and insects, on the cellular osmotic water permeability (Pf) of the leaf vascular bundle‐sheath (BS) and mesophyll cells (MCs), and its subsequent effect on leaf hydraulic conductance (Kleaf). BS is a parenchymatic tissue that tightly encases the vascular system. BS cells (BSCs) have been shown to influence Kleaf through changes in their Pf, for example, after sensing the abiotic stress response‐regulating hormone abscisic acid. It was recently reported that, in Arabidopsis, the chitin receptors‐like kinases, chitin elicitor receptor kinase 1 (CERK1) and LYSINE MOTIF RECEPTOR KINASE 5 (LYK5) are highly expressed in the BS as well as the neighboring mesophyll. Therefore, we studied the possible impact of chitin on these cells. Our results revealed that BSCs and MCs exhibit a sharp decrease in Pf in response to chitin treatment. In addition, xylem‐fed chitin decreased Kleaf and led to stomatal closure. However, Atlyk5 mutant showed none of these responses. Complementing AtLYK5 in the BSCs (using the SCARECROW promoter) resulted in the response to chitin that was similar to that observed in the wild‐type. These results suggest that BS play a role in the perception of apoplastic chitin and in initiating chitin‐triggered immunity. 相似文献
734.
Saravana Prakash Thirumuruganandham Herbert M. Urbassek 《Journal of molecular modeling》2009,15(8):959-969
Vibrational excitations of low-frequency collective modes are essential for functionally important conformational transitions
in proteins. We carried out an analysis of the low-frequency modes in the G protein coupled receptors (GPCR) family of cone
opsins based on both normal-mode analysis and molecular dynamics (MD) simulations. Power spectra obtained by MD can be compared
directly with normal modes. In agreement with existing experimental evidence related to transmembrane proteins, cone opsins
have functionally important transitions that correspond to approximately 950 modes and are found below 80 cm−1. This is in contrast to bacteriorhodopsin and rhodopsin, where the important low-frequency transition modes are below 50 cm−1. We find that the density of states (DOS) profile of blue opsin in a solvent (e.g. water) has increased populations in the
very lowest frequency modes (<15 cm−1); this is indicative of the increased thermostability of blue opsin. From our work we found that, although light absorption
behaves differently in blue, green and red opsins, their low-frequency vibrational motions are similar. The similarities and
differences in the domain motions of blue, red and green opsins are discussed for several representative modes. In addition,
the influence of the presence of a solvent is reported and compared with vacuum spectra. We thus demonstrate that terahertz
spectroscopy of low-frequency modes might be relevant for identifying those vibrational degrees of freedom that correlate
to known conformational changes in opsins.
An erratum to this article can be found at 相似文献
735.
Video and acoustic camera techniques for studying fish under ice: a review and comparison 总被引:1,自引:0,他引:1
Robert P. Mueller Richard S. Brown Haakon Hop Larry Moulton 《Reviews in Fish Biology and Fisheries》2006,16(2):213-226
Researchers attempting to study the presence, abundance, size, and behavior of fish species in northern and arctic climates
during winter face many challenges, including the presence of thick ice cover, snow cover, and, sometimes, extremely low temperatures.
This paper describes and compares the use of video and acoustic cameras for determining fish presence and behavior in lakes,
rivers, and streams with ice cover. Methods are provided for determining fish density and size, identifying species, and measuring
swimming speed and successful applications of previous surveys of fish under the ice are described. These include drilling
ice holes, selecting batteries and generators, deploying pan and tilt cameras, and using paired colored lasers to determine
fish size and habitat associations. We also discuss use of infrared and white light to enhance image-capturing capabilities,
deployment of digital recording systems and time-lapse techniques, and the use of imaging software. Data are presented from
initial surveys with video and acoustic cameras in the Sagavanirktok River Delta, Alaska, during late winter 2004. These surveys
represent the first known successful application of a dual-frequency identification sonar (DIDSONTM) acoustic camera under the ice that achieved fish detection and sizing at camera ranges up to 16 m. Feasibility tests of
video and acoustic cameras for determining fish size and density at various turbidity levels are also presented. Comparisons
are made of the different techniques in terms of suitability for achieving various fisheries research objectives. This information
is intended to assist researchers in choosing the equipment that best meets their study needs. 相似文献
736.
STANISLAV LHOTA BRENT LOKEN STEPHANIE SPEHAR ERIC FELL ALEXANDR POSPĚCH NUNUK KASYANTO 《American journal of primatology》2012,74(3):193-198
Miller's Grizzled Langur (Presbytis hosei canicrus) is one of the least known and rarest primates in Borneo. With a limited geographic range along the central coast of East Kalimantan and the highly degraded Kutai National Park, its former stronghold, this subspecies is now extremely rare and has been listed as one of the world's 25 most endangered primates. From June 6 to August 2, 2011, we carried out both direct observation and camera trap surveys at two mineral springs (sepans) in the Wehea Forest, East Kutai district, East Kalimantan. Presbytis hosei canicrus was observed at the large sepan on 3 of 6 observation days and at the small sepan on 2 of 3 observation days with up to 11 individuals observed in a single day at a single site. Camera traps recorded a per day capture rate of 0.72 at the small sepan and 0.25 at the large sepan and a per photo capture rate of 0.50 and 0.005, respectively. These data suggest relatively frequent occurrence of P. h. canicrus at the sepans, but the langurs are rarely encountered elsewhere in the Wehea Forest. The discovery of P. h. canicrus in the Wehea Forest confirms the continued existence of this endangered primate and is the first solid evidence demonstrating that its geographic range extends further inland than previously thought. It is not known whether the population of P. h. canicrus within Wehea Forest is large and stable enough to be considered viable, but it is likely part of a larger population that may possibly occur across surrounding protected forests and logging concessions. Surveying this potentially large population, and securing its protection, should be a priority measure for ensuring the continued existence of P. h. canicrus. 相似文献
737.
Susie Boydston-White Melissa Romeo Tatyana Chernenko Miloš Miljkovi? Max Diem 《生物化学与生物物理学报:生物膜》2006,1758(7):908-914
We have previously reported spectral differences for cells at different stages of the eukaryotic cell division cycle. These differences are due to the drastic biochemical and morphological changes that occur as a consequence of cell proliferation. We correlate these changes in FTIR absorption and Raman spectra of individual cells with their biochemical age (or phase in the cell cycle), determined by immunohistochemical staining to detect the appearance (and subsequent disappearance) of cell-cycle-specific cyclins, and/or the occurrence of DNA synthesis. Once spectra were correlated with their cells' staining patterns, we used methods of multivariate statistics to analyze the changes in cellular spectra as a function of cell cycle phase. 相似文献
738.
739.
Nest material kleptoparasitism likely evolved in birds to reduce the cost of searching for and collecting material themselves. Although nest material kleptoparasitism has been reported commonly in colonially nesting species, reports for solitary breeding species are infrequent, especially for neotropical migratory species. Here, we report potential and actual nest material kleptoparasitism in the Worm‐eating Warbler (Helmitheros vermivorum). We deployed video camera systems at passerine nests (n = 81) in east‐central Arkansas during summers 2011–2012. In one video, we observed a Worm‐eating Warbler stealing nesting material from a Hooded Warbler (Setophaga citrina) nest. One day later, we later observed a Worm‐eating Warbler landing within 0.5 m of the same warbler nest when the female was incubating, which possibly deterred a second theft of nesting material. In a third video recording, we observed another Worm‐eating Warbler landing within 1 m of an Indigo Bunting (Passerina cyanea) nest. As far as we could determine, neither of these latter two nest visits resulted in nest material kleptoparasitism. Potential benefits of nest material kleptoparasitism include reduced competition for limited nest materials, easy access to suitable material, reduced travel distance, and reduction of nest predation risk; however, costs include risk of attack by host or introducing parasites to one''s nest. Importantly, this behavior could ultimately affect the behavioral and life history evolution of a species. We suggest further work should be conducted to determine the prevalence of nest material kleptoparasitism in Worm‐eating Warblers and other solitary breeding passerines, including efforts to quantify the benefits and costs of this behavior. 相似文献
740.
Sung Hee Jo Jiyoung Lee Eunsook Park Dong Wook Kim Dae Hee Lee Choong Min Ryu Doil Choi Jeong Mee Park 《Plant, cell & environment》2019,42(11):2962-2978
Shigella, which infects primates, can be transmitted via fresh vegetables; however, its molecular interactions with plants have not been elucidated. Here, we show that four Shigella strains, Shigella boydii, Shigella sonnei, Shigella flexneri 2a, and S. flexneri 5a, proliferate at different levels in Arabidopsis thaliana. Microscopic studies revealed that these bacteria were present inside leaves and damaged plant cells. Green fluorescent protein (GFP)‐tagged S. boydii and S. flexneri 5a colonized leaves only, whereas S. flexneri 2a colonized both leaves and roots. Using Shigella mutants lacking type III secretion systems (T3SSs), we found that T3SSs that regulate the pathogenesis of shigellosis in humans also play a central role in bacterial proliferation in Arabidopsis. Strikingly, the immunosuppressive activity of two T3S effectors, OspF and OspG, was required for proliferation of Shigella in Arabidopsis. Of note, delivery of OspF or OspG effectors inside plant cells upon Shigella inoculation was confirmed using a split GFP system. These findings demonstrate that the human pathogen Shigella can proliferate in plants by adapting immunosuppressive machinery used in the original host human. 相似文献