全文获取类型
收费全文 | 314篇 |
免费 | 37篇 |
国内免费 | 15篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 19篇 |
2019年 | 19篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 19篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有366条查询结果,搜索用时 437 毫秒
281.
In the present study, Xyrichtys novacula (Labridae) were sampled at five locations around the islands of Ibiza and Formentera (western Mediterranean Sea). Isotopic signatures of δ13C, δ15N and the C:N ratio were analysed in relation to locality, sex and size differences. δ13C and δ15N partitioning was also studied in the reproductive spawning period. There were significant differences in the δ13C signature between localities for both sexes, but not for δ15N. Sex differences were also found with a mean ±s.e . value of ?17·38 ± 0·06‰δ13C and 8·36 ± 0·05‰δ15N for females and ?17·17 ± 0·07‰δ13C and 8·80 ± 0·06‰δ15N for males. Increasing total length in both sexes was positively correlated with δ15N enrichment and a significant positive linear regression was established for both variables. During the reproductive spawning period, there were changes in δ13C fractioning with enrichment in postspawning females and males (with respect to prespawning and spawning periods) and δ15N impoverishment in postspawning females (with respect to prespawning and spawning periods). Xyrichtys novacula uses local food sources, as confirmed by δ13C and δ15N, and females and males use different food sources, thus avoiding intraspecific competition. This was confirmed by δ15N enrichment as size increased. Spawning leads to special requirements for gonad maturation, which is reflected in the isotopic signatures for both sexes. 相似文献
282.
Thibault Sterckeman Lise Duquène Jérôme Perriguey Jean-Louis Morel 《Plant and Soil》2005,276(1-2):335-345
Our purpose was to quantify the effect of rhizosphere processes on the availability of soil cadmium and zinc to various plant
species. E values for Cd and Zn were measured on two contaminated soils differing mainly in their pH (6.2 and 8.1). L values were measured for six plant species with contrasting metal uptakes. The difference between E and L values quantifies the mobilization of the element which was non-phyto-available prior to cultivation. For Zn, L values were 1.2 to 5.6 times greater than the E values, depending on the plant species. The increase in Zn availability was greater in the basic soil. For Cd, L values in the basic soil were 1.1 to 2 times greater than the E value. In the slightly acid soil, plants did not enhance the cadmium availability. The mobilization of non-labile metal could
be due to exudates from roots or microflora, phytosiderophores being responsible for the highest mobilization. The lower availability
of Fe or Zn could explain the greater mobilization in the basic soil. 相似文献
283.
The binding and uptake of insulin in perfused rat liver has been investigated with specifically labelled 125I-A14-tyrosyl insulin as a tracer and compared with a commercially available iodo-insulin preparation. The commercial preparation did not show saturation uptake kinetics and the clearance from the perfusate remained low and constant throughout a wide concentration range. A14 labelled insulin showed saturation kinetics and high clearance at low carrier concentration, falling rapidly with increasing carrier concentration and reaching a steady state value of 1 ml/min. These results emphasize the importance of using specifically labelled insulin in physiological and biochemical studies of hepatic insulin metabolism. Perfusion with A14 tyrosine-labelled insulin at 4 degrees C showed apparent saturation with binding to the plasma membrane fraction. Perfusion at 37 degrees C also showed apparent saturation with uptake predominantly to the ligandosome fraction. These results implicate the plasma membrane-ligandosome pathway in the hepatic uptake of insulin at both physiological and pharmacological concentrations of the hormone. 相似文献
284.
Fanelli F Belluomo I Di Lallo VD Cuomo G De Iasio R Baccini M Casadio E Casetta B Vicennati V Gambineri A Grossi G Pasquali R Pagotto U 《Steroids》2011,76(3):244-253
Background
The simultaneous, rapid and reliable measurement of a wide steroid panel is a powerful tool to unravel physiological and pathological hormone status. Clinical laboratories are currently dominated by high-throughput immunoassays, but these methods lack specificity due to cross-reactivity and matrix interferences. We developed and validated an isotopic dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method for the simultaneous measurement of cortisol, corticosterone, 11deoxycortisol, androstenedione, deoxycorticosterone (DOC), testosterone, 17OHprogesterone, dehydroepiandrosterone (DHEA) and progesterone in serum, and compared it to routine immunoassays employed in our laboratory. We also established adult reference intervals in 416 healthy subjects.Methods
0.9 ml of serum were spiked with labelled internal standards (IS) and extracted on C18 cartridges. Eluate was injected into a two-dimensional LC-system, purified in a perfusion column and separated on a C8 column during a 21 min gradient run. Analytes were revealed by atmospheric pressure chemical ionization (APCI) followed by multiple reaction monitoring (MRM) analysis.Results
Of the four immunoassays compared with the ID-LC-MS/MS method, only the results of ElecsysE170 for cortisol, testosterone in males and progesterone > 1 ng/ml were in agreement with ID-LC-MS/MS. ElecsysE170 for testosterone in females and progesterone < 1 ng/ml, Immulite2000 for androstenedione, DSL-9000 for DHEA and 17OHP Bridge for 17OHprogesterone, respectively, showed poor agreement. Reference intervals and steroid age and fertility related fluctuations were established.Conclusion
Our ID-LC-MS/MS method proved to be reliable and sensitive in revealing steroid circulating concentrations in adults and in highlighting the limits of routine immunoassays at low concentrations. 相似文献285.
Gilbert A Silvestre V Segebarth N Tcherkez G Guillou C Robins RJ Akoka S Remaud GS 《Plant, cell & environment》2011,34(7):1104-1112
Efforts to understand the cause of 12C versus 13C isotope fractionation in plants during photosynthesis and post‐photosynthetic metabolism are frustrated by the lack of data on the intramolecular 13C‐distribution in metabolites and its variation with environmental conditions. We have exploited isotopic carbon‐13 nuclear magnetic resonance (13C NMR) spectrometry to measure the positional isotope composition (δ13Ci, ‰) in ethanol samples from different origins: European wines, liquors and sugars from C3, C4 and crassulacean acid metabolism (CAM) plants. In C3‐ethanol samples, the methylene group was always 13C‐enriched (~2‰) relative to the methyl group. In wines, this pattern was correlated with both air temperature and δ18O of wine water, indicating that water vapour deficit may be a critical defining factor. Furthermore, in C4‐ethanol, the reverse relationship was observed (methylene‐C relatively 13C‐depleted), supporting the concept that photorespiration is the key metabolic process leading to the 13C distribution in C3‐ethanol. By contrast, in CAM‐ethanol, the isotopic pattern was similar to but stronger than C3‐ethanol, with a relative 13C‐enrichment in the methylene‐C of up to 13‰. Plausible causes of this 13C‐pattern are briefly discussed. As the intramolecular δ13Ci‐values in ethanol reflect that in source glucose, our data point out the crucial impact on the ratio of metabolic pathways sustaining glucose synthesis. 相似文献
286.
《Bioscience, biotechnology, and biochemistry》2013,77(6):1528-1532
The emission of light in the marine ostracod Cypridina hilgendorfii (presently Vargula hilgendorfii) is produced by the Cypridina luciferin-luciferase reaction in the presence of molecular oxygen. Cypridina luciferin has an asymmetric carbon derived from isoleucine, and the absolute configuration is identical to the C-3 position in L-isoleucine or D-alloisoleucine. To determine the stereoselective incorporation of the isoleucine isomers (L-isoleucine, D-isoleucine, L-alloisoleucine, and D-alloisoleucine), we synthesized four 2H-labeled isoleucine isomers and examined their incorporation into Cypridina luciferin by feeding experiments. Judging by these results, L-isoleucine is predominantly incorporated into Cypridina luciferin. This suggests that the isoleucine unit of Cypridina luciferin is derived from L-isoleucine, but not from D-alloisoleucine. 相似文献
287.
John W. Finley Phyllis E. Johnson Philip G. Reeves Richard A. Vanderpool Mary Briske-Anderson 《Biological trace element research》1994,42(2):81-96
Biliary/pancreatic (B/P) secretions are a major component of endogenous secretions, and endogenously secreted Zn is a primary
means of Zn homeostasis. This study examined whether B/P fluid alters the absorption/reabsorption of Zn and, in doing so,
whether this contributes to homeostatic control of Zn. Animal experiments utilized rats fed 10 or 300 μg Zn/kg diet. An open-ended
gut perfusion study in which65Zn-labeled B/P fluid or67Zn-labeled and digested diet found significantly decreased Zn absorption from B/P fluid. Although Zn absorption from both
sources was less in animals fed diets higher in Zn, there was no interaction of treatment and diet. Further studies utilizing
cultured human colon carcinoma cells (CACO-2) as in vitro models of gut enterocytes found that the presence of B/P fluid significantly
decreased Zn retention and/or transport and resulted in a redistribution of cellular Zn after 1200 min of incubation. These
studies show that a substance in B/P fluid can decrease the absorption of Zn and also suggest that dietary Zn and Zn associated
with B/P secretions are absorbed from distinct pools. However, the lack of an interactive effect with diet, and the amount
of time required to see differences in CACO-2 cells, suggest that differences in absorption are not a major contributor to
Zn homeostasis.
US Department of Agriculture, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action
employer and all agency services are available without discrimination. 相似文献
288.
Bacchi Márcio Arruda De Nadai Fernandes Elisabete A. 《Biological trace element research》1994,(1):663-668
The effectiveness of industrial washing operation in minimizing soil in sugar cane delivered to mills is evaluated. Instrumental
neutron activation analysis was the nuclear analytical technique chosen for this work, with Fe, Hf, Sc, and Th selected as
soil tracers. On the basis of differences between elemental concentration of integral and prepared cane, that is before and
after washing, the feasibility of the method for evaluation of the washing efficiency is demonstrated. 相似文献
289.
D Costalago NAF Miranda NA Strydom R Perissinotto 《African Journal of Aquatic Science》2016,41(4):389-398
South African estuarine systems are becoming increasingly altered by anthropogenic and environmental factors, but the consequences of such changes for these systems are still not fully understood. The most common approach for evaluating the ecological status of aquatic systems is studying their associated foodwebs. Due to their high abundance and important ecological role, the larvae of estuarine round herring Gilchristella aestuaria (Gilchrist, 1913) are key candidates for examining the foodweb structure and function of southern African estuaries. The foodwebs and trophic interactions of G. aestuaria larvae in six estuaries in South Africa were compared using larvae sampled in November 2013 and analysed using δ13C and δ15N and Bayesian isotopic mixing models. The main prey type for G. aestuaria larvae in all estuaries was zooplankton. We found a high similarity among the Kariega, Gamtoos, Great Fish and Sundays estuaries in terms of consumers and potential sources for both δ13C and δ15N signatures. Significant differences were found in δ13C values among marine-dominated estuaries, such as the Kromme Estuary, and the more freshwater-dominated systems. In addition, in the Kromme Estuary particulate organic matter was very important in the diet of G. aestuaria larvae. Our results suggest that both food availability and physical environmental parameters strongly affect the diet and condition of G. aestuaria and, consequently, the entire foodweb in the system. 相似文献
290.
Paradoxical effects of temperature and solar irradiance on the photodegradation state of killed phytoplankton
下载免费PDF全文
![点击此处可从《Journal of phycology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rémi Amiraux Christian Jeanthon Frédéric Vaultier Jean‐François Rontani 《Journal of phycology》2016,52(3):475-485
The aim of this paper was to study the effects of temperature and irradiance on the photodegradation state of killed phytoplankton cells. For this purpose, killed cells of the diatom Chaetoceros neogracilis RCC2022 were irradiated (photosynthetically active radiation) at 36 and 446 J · s?1 · m?2 (for the same cumulative dose of irradiation energy) and at two temperatures (7°C and 17°C). Analyses of specific lipid tracers (fatty acids and sterols) revealed that low temperatures and irradiances increased photooxidative damages of monounsaturated lipids (i.e., palmitoleic acid, cholesterol and campesterol). The high efficiency of type II photosensitized degradation processes was attributed to: (i) the relative preservation of the sensitizer (chlorophyll) at low irradiances allowing a longer production of singlet oxygen and (ii) the slow diffusion rate of singlet oxygen through membranes at low temperatures inducing more damages. Conversely, high temperatures and irradiances induced (i) a rapid degradation of the photosensitizer and a loss of singlet oxygen by diffusion outside the membranes (limiting type II photosensitized oxidation), and (ii) intense autoxidation processes degrading unsaturated cell lipids and oxidation products used as photodegradation tracers. Our results may explain the paradoxical relationship observed in situ between latitude and photodegradation state of phytoplankton cells. 相似文献