全文获取类型
收费全文 | 1953篇 |
免费 | 203篇 |
国内免费 | 407篇 |
出版年
2024年 | 11篇 |
2023年 | 45篇 |
2022年 | 45篇 |
2021年 | 55篇 |
2020年 | 108篇 |
2019年 | 110篇 |
2018年 | 86篇 |
2017年 | 100篇 |
2016年 | 85篇 |
2015年 | 89篇 |
2014年 | 113篇 |
2013年 | 155篇 |
2012年 | 78篇 |
2011年 | 98篇 |
2010年 | 75篇 |
2009年 | 115篇 |
2008年 | 111篇 |
2007年 | 107篇 |
2006年 | 91篇 |
2005年 | 102篇 |
2004年 | 72篇 |
2003年 | 63篇 |
2002年 | 73篇 |
2001年 | 44篇 |
2000年 | 39篇 |
1999年 | 40篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 29篇 |
1995年 | 30篇 |
1994年 | 31篇 |
1993年 | 37篇 |
1992年 | 23篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 3篇 |
排序方式: 共有2563条查询结果,搜索用时 15 毫秒
991.
Malcolm Anastasius Celine Luquain-Costaz Maaike Kockx Wendy Jessup Leonard Kritharides 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2018,1863(10):1257-1273
The ‘cholesterol efflux capacity (CEC)’ assay is a simple in vitro measure of the capacities of individual sera to promote the first step of the reverse cholesterol transport pathway, the delivery of cellular cholesterol to plasma HDL.This review describes the cell biology of this model and critically assesses its application as a marker of cardiovascular risk. We describe the pathways for cell cholesterol export, current cell models used in the CEC assay with their limitations and consider the contribution that measurement of serum CEC provides to our understanding of HDL function in vivo. 相似文献
992.
M. Srinivasa Rao O. Shaila P. Sreelakshmi S. Vennila M. Vanaja A.V.M. Subba Rao M. Maheswari K. Sammi Reddy 《Journal of Asia》2018,21(2):531-537
Experiments were conducted to understand the direct and indirect effects of temperature and elevated CO2 (eCO2), on tritrophic interactions of cowpea (Vigna unguiculata subsp. unguiculata L.), legume aphid Aphis craccivora Koch and coccinellid predator Menochilus sexmaculatus Fab. Reduction of the leaf nitrogen (6%), amino acid (6%) and protein (7%) of cowpea foliage with increased carbon (13%) and C:N ratio (21%) at eCO2 over aCO2 indicated the dilution of biochemical constituents at first trophic level. Shortened development time, DT and increment of reproductive rate, RR at eCO2 over ambient CO2(aCO2)was significant with increase in temperature from 20 to 35?°C. Reduction of the mean degree day, DD requirement of both nymphal (75.79?±?15.163) and adult stages (157.15?±?67.04) at eCO2 over aCO2 and same was reflected in the summation DD for both the stages at eCO2 (232.96?±?80.32)and aCO2 (247.07?±?64.77) across six temperatures. The ‘rm’ and ‘Ro’ increased gradually with increase in temperature followed the non-linear trend and reached maximum values at 27?°C with shortened ‘T’ across 20 to 35?°C temperatures at eCO2 indicating the significant variation of growth and development at the second trophic level. Decreased grub duration (23%) with increased predation capacity (19%) of M. sexmaculatus on A. craccivora at eCO2 over ambient was noted, indicating the incidence of A. craccivora is likely to be higher with increased predation in the future climate change scenario. 相似文献
993.
Anna Kocira Michał Świeca Sławomir Kocira Urszula Złotek Anna Jakubczyk 《Saudi Journal of Biological Sciences》2018,25(3):563-571
In the present study, application of Ecklonia maxima extract (Kelpak SL – a water soluble concentrate) was optimized and its impact on yield, nutraceutical and nutritional potential of Phaseolus vulgaris L. (var. Aura and Toska) was measured. The study was carried out in 2012 and 2013 in Poland. During the growing season, 0.2% and 0.4% solution of Kelpak SL was applied by single and double spraying of plants. These four treatments with Kelpak SL were compared with the control, where no biostimulator was applied. Kelpak SL treatments stimulated the yield of both cultivars studied. The application of E. maxima extract had no effect on the content of starch, free sugars or proteins in seeds of either of the tested cultivars. The highest level of phenolics was found for double sprayed Toska plants. All the tested variants of Kelpak SL application significantly increased the content of anthocyanins in the seeds. Also, both the reducing power and antiradical ability of Aura seeds were elevated in all the studied treatments. E. maxima extract is a natural, environmentally friendly and safe preparation increasing the yield and nutraceutical quality of beans without any negative effect on their nutritional quality. 相似文献
994.
This study investigated the feasibility of using an invasive snail, Pomacea canaliculata, as a food source and water purifier for the commercial breeding of the loach Misgurnus anguillicaudatus. The predatory potential of M. anguillicaudatus (3.5–5.5?g) against hatchling snails was evaluated in aquaria and simulated paddy fields. Some hatchling snails left the water to avoid being preyed upon by the loaches, and approximately 10 hatchlings died per day in the presence of five loaches in aquaria, whereas a weaker snail control effect was observed in the simulated paddy fields. The growth of rice seedlings (Oryza sativa) was not reduced by the presence of hatchling snails alone, but the shoot biomass of seedlings coexisting with snails was promoted after introducing the loaches. Additionally, the presence of P. canaliculata adults improved the aquatic environment in the short term for loach breeding by decreasing the turbidity of the water. Importantly, M. anguillicaudatus (12–18?g) mortality decreased and its weight increased in the presence of adult snails. 相似文献
995.
Mariana G. Tarragó Claudia C.S. Chini Karina S. Kanamori Gina M. Warner Ariel Caride Guilherme C. de Oliveira Micaela Rud Adrienne Samani Kyaw Z. Hein Runqing Huang Diana Jurk Dong Seong Cho James J. Boslett Jordan D. Miller Jay L. Zweier João F. Passos Jason D. Doles David J. Becherer Eduardo N. Chini 《Cell metabolism》2018,27(5):1081-1095.e10
996.
Vinícius Rodrigues de Araujo Patrícia Lisboa Gabriel Boaventura Fabiele Caramez Luciane Pires Elaine Oliveira 《Free radical research》2018,52(8):850-855
Saliva has been reported as a potential biological fluid for biochemical monitoring. This study investigated salivary markers of exercise intensity, oral mucosal immunity, and redox homeostasis in soccer athletes subjected to an acute high-intensity interval exercise (HIIE) protocol characterised by a repeated sprint ability test. Thirty-two professional soccer athletes were recruited and saliva aliquots were collected at rest and immediately after HIIE protocol. When compared with pre-test values we observed that HIIE protocol induced moderate changes for total protein (p?=?.015; effect size (ES)?=?0.51; smallest worthwhile change (SWC)factor?=?5.7) and for cortisol levels (p?.0001; ES?=?0.49; SWCfactor?=?3.9). Lactate levels showed very large changes (p?.000; ES?=?1.35; SWCfactor?=?10.8), while Ig-A alterations were considered unclear. Besides, transferrin changes were trivial and maintained its levels at rest and after HIIE below the proposed threshold of 0.5?mg/dL. Regarding redox homeostasis we observed unclear effects for TBARs, MDA, GSH, GSSG, CAT, and SOD while uric acid showed large decreases (p?=?.005; ES?=?0.80; SWCfactor?=??5.4). HIIE protocol as a physical test conducted in soccer athletes increased salivary concentration of exercise intensity markers, such as lactate, total protein, and cortisol, but did not affect Ig-A levels. Redox homeostasis in saliva seems to be more related with uric acid levels as a possible key factor TBARs homeostasis. 相似文献
997.
Effect of growth temperature on photosynthetic capacity and respiration in three ecotypes of Eriophorum vaginatum
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jessica L. Schedlbauer Ned Fetcher Katherine Hood Michael L. Moody Jianwu Tang 《Ecology and evolution》2018,8(7):3711-3725
Ecotypic differentiation in the tussock‐forming sedge Eriophorum vaginatum has led to the development of populations that are locally adapted to climate in Alaska's moist tussock tundra. As a foundation species, E. vaginatum plays a central role in providing topographic and microclimatic variation essential to these ecosystems, but a changing climate could diminish the importance of this species. As Arctic temperatures have increased, there is evidence of adaptational lag in E. vaginatum, as locally adapted ecotypes now exhibit reduced population growth rates. Whether there is a physiological underpinning to adaptational lag is unknown. Accordingly, this possibility was investigated in reciprocal transplant gardens. Tussocks of E. vaginatum from sites separated by ~1° latitude (Coldfoot: 67°15′N, Toolik Lake: 68°37′, Sagwon: 69°25′) were transplanted into the Toolik Lake and Sagwon sites and exposed to either an ambient or an experimental warming treatment. Five tussocks pertreatment combination were measured at each garden to determine photosynthetic capacity (i.e., Vcmax and Jmax) and dark respiration rate (Rd) at measurement temperatures of 15, 20, and 25°C. Photosynthetic enhancements or homeostasis were observed for all ecotypes at both gardens under increased growth temperature, indicating no negative effect of elevated temperature on photosynthetic capacity. Further, no evidence of thermal acclimation in Rd was observed for any ecotype, and there was little evidence of ecotypic variation in Rd. As such, no physiological contribution to adaptational lag was observed given the increase in growth temperature (up to ~2°C) provided by this study. Despite neutral to positive effects of increased growth temperature on photosynthesis in E. vaginatum, it appears to confer no lasting advantage to the species. 相似文献
998.
Michael Strljbe Guido R. M. M. Haenen Henk Van Den Berg Aalt Bast 《Free radical research》1997,26(6):515-521
A relatively simple and widely applied method for quantitating the total antioxidant capacity of body fluids and drug solutions based on the absorbance of the ABTS radical cation was evaluated. In this assay, the end-point is an antioxidant-induced decrease in absorbance at a fixed time. This decrease is used as an index of total antioxidant capacity. It is shown that Trolox, potassium cyanide and quercetin all decrease the absorbance of ABTS radical cations at a fixed time, but by different mechanisms. Trolox scavenges the ABTS radical, potassium cyanide inhibits radical formation, while quercetin acts by both mechanisms. Using this method antioxidant capacity may be overestimated, due to both a scavenger effect and an effect on the rate of ABTS oxidation. To distinguish between these effects, a post-addition assay was used in which the sample is added when the formation of radicals is stable. Using post- addition assay conditions enables discrimination between effects on radical scavenging and on the radical formation, two major mechanisms for antioxidant action. In extrapolating the results to an ill vivo situation it should be questioned: (i) whether the peroxidase process does indeed mimic the process of radical formation in vivo, and (ii) whether the ABTS radicals do resemble the radical species involved in an in vivo situation. Results obtained in the ABTS radical-based methods should therefore be reviewed critically before the antioxidant capacity can be assessed. 相似文献
999.
Effects of long-term soil acidification due to nitrogen fertilizer inputs in Wisconsin 总被引:18,自引:0,他引:18
Barak Phillip Jobe Babou O. Krueger Armand R. Peterson Lloyd A. Laird David A. 《Plant and Soil》1997,197(1):61-69
Agroecosystems are domesticated ecosystems intermediate between natural ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of human activity are particularly likely in agroecosystems because of the intensity of that activity, which include nutrient inputs intended to supplement native nutrient pools and to support greater biomass production and removal. At a long-term fertility trial in South-Central Wisconsin, USA, significant increases in exchangeable acidity were accompanied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ with application of ammoniacal N fertilizer. Plant analysis shows that a considerable portion of the alkalinity generated by assimilation of N (and to a lesser extent by S) is sequestered in the above-ground plant parts as organic anions and is not returned to the soil if harvested. Elemental analysis of Ca-saturated soil clays indicates an loss of 16% of the CEC of the soil clay and minor increases in Fe and Al. The reversibility of these changes due to prolonged acidification is doubtful if the changes are due to soil weathering. 相似文献
1000.
Thermal denaturation of iso-1-cytochrome c variants: comparison with solvent denaturation.
下载免费PDF全文
![点击此处可从《Protein science : a publication of the Protein Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
L. M. Herrmann B. E. Bowler 《Protein science : a publication of the Protein Society》1997,6(3):657-665
Thermal denaturation studies as a function of pH were carried out on wild-type iso-1-cytochrome c and three variants of this protein at the solvent-exposed position 73 of the sequence. By examining the enthalpy and Tm at various pH values, the heat capacity increment (delta Cp), which is dominated by the degree of change in nonpolar hydration upon protein unfolding, was found for the wild type where lysine 73 is normally present and for three variants. For the Trp 73 variant, the delta Cp value (1.15 +/- 0.17 kcal/mol K) decreased slightly relative to wild-type iso-1-cytochrome c (1.40 +/- 0.06 kcal/mol K), while for the Ile 73 (1.65 +/- 0.07 kcal/mol K) and the Val 73 (1.50 +/- 0.06 kcal/mol K) variants, delta Cp increased slightly. In previous studies, the Trp 73, Ile 73, and Val 73 variants have been shown to have decreased m-values in guanidine hydrochloride denaturations relative to the wild-type protein (Hermann L, Bowler BE, Dong A, Caughey WS. 1995. The effects of hydrophilic to hydrophobic surface mutations on the denatured state of iso-1-cytochrome c: Investigation of aliphatic residues. Biochemistry 34:3040-3047). Both the m-value and delta Cp are related to the change in solvent exposure upon unfolding and other investigators have shown a correlation exists between these two parameters. However, for this subset of variants of iso-1-cytochrome c, a lack of correlation exists which implies that there may be basic differences between the guanidine hydrochloride and thermal denaturations of this protein. Spectroscopic data are consistent with different denatured states for thermal and guanidine hydrochloride unfolding. The different response of m-values and delta Cp for these variants will be discussed in this context. 相似文献