首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   129篇
  免费   13篇
  142篇
  2024年   1篇
  2023年   2篇
  2022年   2篇
  2021年   9篇
  2020年   1篇
  2019年   2篇
  2018年   5篇
  2017年   9篇
  2016年   4篇
  2015年   8篇
  2014年   10篇
  2013年   5篇
  2012年   7篇
  2011年   16篇
  2010年   3篇
  2009年   5篇
  2008年   2篇
  2007年   3篇
  2006年   2篇
  2005年   2篇
  2004年   7篇
  2003年   1篇
  2002年   1篇
  2001年   3篇
  2000年   3篇
  1999年   1篇
  1998年   3篇
  1996年   1篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1987年   2篇
  1986年   3篇
  1985年   4篇
  1982年   4篇
  1981年   1篇
  1978年   1篇
  1977年   2篇
  1975年   1篇
  1969年   1篇
  1960年   1篇
排序方式: 共有142条查询结果,搜索用时 15 毫秒
81.
Reuter, M., Piller, W.E., Harzhauser, M., Kroh, A., Rögl, F. & ?ori?, S. 2010: The Quilon Limestone, Kerala Basin, India: an archive for Miocene Indo‐Pacific seagrass beds. Lethaia, Vol. 44, pp. 76–86. The facies of the fossiliferous Quilon Limestone in SW India is described for the first time in detail at the Padappakkara‐type locality. Facies (fossiliferous, micrite‐rich, bioturbated sediment with intercalated sand pockets) and faunal composition (epiphytic foraminifers, seagrass feeding Smaragdia gastropods, bioimmuration of celleporiform bryozoan colonies) indicate a seagrass environment. The large discoidal archaiasin foraminifer Pseudotaberina malabarica, in particular, is considered as a proxy for seagrass communities. Recent seagrasses have their centre of generic richness in the Indo‐Pacific where they cover wide areas in the tidal and shallow sub‐tidal zones. However, their geological record is only fragmentary and their palaeobiogeographic distribution has a big stratigraphical gap in the Miocene Western Indo‐Pacific region. The described nannoplankton flora and planktonic foraminifers from the Quilon Formation demonstrate that the deposition of the studied seagrass bed occurred in nannoplankton biozone NN3. This timing suggests formation during the closure of the Tethyan Seaway. The Quilon Limestone is thus an early Western Indo‐Pacific seagrass bed and an important step in reconstructing the history of seagrass communities. □Quilon Formation, Pseudotaberina malabarica, seagrass facies, Burdigalian, Indo‐Pacific.  相似文献   
82.
Deuterium NMR spectra are reported for lysozyme crystals, powders, and frozen solutions. At high water contents the spectrum is a superposition of a narrow central component and a quadrupole doublet. The quadrupole splitting and the relaxation rates of both components, monitored as a function of water content and temperature, are discussed in terms of models for the water-protein interaction. The anisotropy of the water molecule motion is clearly demonstrated by the deuterium quadrupole splitting observed in the protein single crystal, but such splittings were not found in protein powders and frozen protein solutions. We therefore suggest that the most useful view of such data is to consider the water-protein interactions at the surface to be mixed rapidly and that a distribution of interactions be invoked rather than an oversimplified view often taken of a two or n-site mixing where n is small.  相似文献   
83.
Bombyx mori is most common silkmoth used for the commercial production of the silk. The different environmental conditions may affect development of silkmoth and hence the output of silkworm. Present study investigated effects of different photoperiodic conditions on the development of silkmoth. Three experiments were performed on newly hatched larvae. In experiment1, larvae were divided into three groups; group 1, 8L:16D (8 h light and 16 h dark), group 2, 12L:12D (12 h light and 12 h dark) and group 3, 16L:8D (16 h light and 8 h dark). In experiment 2, larvae were exposed to either continuous light or continuous dark. In experiment 3, larvae were divided into three groups. Each group received light of similar duration (16L:8D) and intensity (1.1 ± 0.1 PAR) but of different wavelengths; i.e. long wavelength red light (640 nm), short wavelength blue light (450 nm) and white light. Larvae were fed on young mulberry (Morus alba) leaves. Temperature and humidity were maintained at 26 (±2) °C and 75 (±5)%, respectively, throughout the study. Observations on change in body length of larvae were made on every alternate day. We also calculated the shell ratio, time taken in cocoon formation and emergence. Results from experiment show that the larvae underwent significant change in body length but with faster growth rate under 12L:12D photoperiod in comparison to 8L:16D and 16L:8D. Time taken in cocoon formation and hatching was significantly less, while shell ratio was significantly higher in 12L:12D in comparison to other groups. We did not observe much effect of monochromatic light on the development of silkmoth.  相似文献   
84.
85.
A theoretical investigation on the effect of electrostatic interaction on dust acoustic wave (DAW) has been carried out in weakly nonlinear limit in strongly coupled regime with fluctuating dust charge. The generalized hydrodynamic set of equations is employed in the hydrodynamic limit. The dust?dust electrostatic interaction couples with dust charge fluctuation, as well as the viscosity of the medium, and provides the dissipative effect, which leads to the formation of shock wave in such a system. The novel feature of the present work is that, in the presence of charge fluctuation, the effective electrostatic temperature starts affecting the behavior and also enhancing the formation of monotonic shock wave. In this investigation, the dissipative effect arising due to charge fluctuation is dominant in comparison to the viscosity of the medium in the presence of electrostatic temperature.  相似文献   
86.
In this study, we sought to investigate the biology (diet and reproduction) and ethnobiology (fishers knowledge and fishing spots used to catch snappers) of five species of snappers (Lutjanidae), including Lutjanus analis, Lutjanus synagris, Lutjanus vivanus, Ocyurus chrysurus, and Romboplites saliens at five sites along the northeast (Riacho Doce, Maceió in Alagoas State, and Porto do Sauípe, Entre Rios at Bahia State) and the southeast (SE) Brazilian coast (Paraty and Rio de Janeiro cities at Rio de Janeiro State, and Bertioga, at São Paulo State.). We collected 288 snappers and interviewed 86 fishermen. The stomach contents of each fish were examined and macroscopic gonad analysis was performed. Snappers are very important for the fisheries of NE Brazil, and our results indicated that some populations, such as mutton snapper (L. analis) and lane snapper (L. synagris), are being caught when they are too young, at early juvenile stages. Local knowledge has been shown to be a powerful tool for determining appropriate policies regarding management of target species, and artisanal fishermen can be included in management processes. Other suggestions for managing the fisheries are discussed, including proposals that could provide motivation for artisanal fishermen to participate in programs to conserve resources, such as co-management approaches that utilize local knowledge, the establishment of fishing seasons, and compensation of fishermen, through 'payment for environmental services'. These suggestions may enhance the participation of local artisanal fishermen in moving to a more realistic and less top-down management approach of the fish population.  相似文献   
87.
Poly(d2NH2A-dT): two-dimensional NMR shows a B to A conversion in high salt   总被引:6,自引:0,他引:6  
B Borah  J S Cohen  F B Howard  H T Miles 《Biochemistry》1985,24(25):7456-7462
Poly(d2NH2A-dT) forms a structure in high salt that is clearly distinct from the B form present in low salt. Two-dimensional nuclear Overhauser effect (2D NOE) NMR spectra establish that the conformation of the high-salt form is not Z. Correlations of observed cross peaks in the 2D NOE spectra and estimated interproton distances of the common DNA conformations are consistent only with an A form or closely related structure. This interpretation is also consistent with the negative circular dichroic band observed in the high-salt form of poly(d2NH2A-dT) and in A-form ribohomopolymer helices containing 2NH2A.  相似文献   
88.
Chowdhury P  Borah JM  Goswami P  Das AM 《Steroids》2011,76(5):497-501
A facile synthesis of the side chain of loteprednol etabonate, namely, chloromethyl-17α-[(ethoxycarbonyl))oxy]-11β-hydro of loteprednol etabonate, viz., chloromethyl-17α-[(ethoxycarbonyl))oxy]-11xy-3-oxoandrosta-1,4-diene-17β-carboxylate - an ocular soft corticosteroid, has been described starting from a 20-oxopregnane, namely, 3β-acetoxy-pregn-5(6),16(17)-diene-20-one (16-dehydropregnenolone acetate, i.e., 16-DPA) using our recently developed metal-mediated halogenation as a key reaction.  相似文献   
89.
[Rh(CO)2Cl]2 reacts with two mole equivalent of 2-acetylpyridine (a), 3-acetylpyridine (b) and 4-acetylpyridine (c) to afford chelate [Rh(CO)Cl(η2-N∩O)] (1a) and non-chelate [Rh(CO)2Cl(η1-N∼O)] (1b, 1c) complexes, where, N∩O = a, N∼O = b, c. Oxidative addition (OA) of 1a-1c with CH3I and C2H5I yields penta coordinate rhodium(III) complexes, [Rh(COR)ClI(η2-N∩O)] {R = -CH3 (2a); -C2H5 (3a)} and [Rh(COR)(CO)ClI(η1-N∼O)] {R = -CH3 (2b, 2c); -C2H5 (3b, 3c)}. Kinetic study for the reaction of 1a-1c with CH3I indicates a pseudo-first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester was evaluated at different initial CO pressures 5, 10 and 20 bar at ∼25 °C and higher turn over numbers (TON = 1581-1654) were obtained compared to commercial Monsanto’s species [Rh(CO)2I2] (TON = 1000) under the reaction conditions: temperature = 130 ± 1 °C, pressure = 15-32 bar, rpm = 450, time = 1 h and catalyst: substrate = 1: 1900.  相似文献   
90.
Thirty-four senior dogs (pointers 8 - 11 years, beagles 9 - 11 years) were used to evaluate the effects of oligosaccharides on nutritional and immunological characteristics. Dogs were randomly allotted to treatments [1% chicory (CH), 1% mannan-oligosaccharide (MOS), 1% chicory + 1% MOS (CM), or no supplementation (control, CON)] in a parallel design with a 4 week baseline period followed by a 4 week treatment period. Dietary supplementation with MOS or CM tended (P = 0.07) to increase food intake due, in part, to an increase in fermentable fibre and a decrease in energy content of the diet. Although wet faecal output increased (P < 0.05) for dogs supplemented with MOS or CM, when corrected for food intake, no differences were noted. The CM treatment increased (P < 0.05) faecal score (1 = hard and dry, 5 = watery liquid), although these scores remained in a desirable range (3 to 3.5). Chicory supplementation increased (P = 0.07) fat digestibility. Chicory or MOS increased (P  0.05) faecal bifidobacteria concentrations 0.4 and 0.5 log10 cfu/g DM, respectively, compared to the CON, while MOS decreased (P < 0.05) faecal E. coli concentrations. Oligosaccharides did not affect white blood cell (WBC) concentrations, but CH and CM tended to increase (P = 0.10) neutrophil concentrations compared to control dogs. Peripheral lymphocyte concentrations were decreased in dogs supplemented with MOS (P = 0.06) and CM (P < 0.05). Chicory and MOS alter faecal microbial populations and certain indices of the immune system of senior dogs.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号