全文获取类型
收费全文 | 1194篇 |
免费 | 23篇 |
出版年
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 14篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 23篇 |
2015年 | 11篇 |
2014年 | 16篇 |
2013年 | 31篇 |
2012年 | 43篇 |
2011年 | 44篇 |
2010年 | 41篇 |
2009年 | 25篇 |
2008年 | 50篇 |
2007年 | 44篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 40篇 |
2003年 | 57篇 |
2002年 | 38篇 |
2001年 | 55篇 |
2000年 | 40篇 |
1999年 | 31篇 |
1998年 | 12篇 |
1992年 | 24篇 |
1991年 | 30篇 |
1990年 | 26篇 |
1989年 | 24篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 34篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 17篇 |
1972年 | 13篇 |
1971年 | 12篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1968年 | 8篇 |
1967年 | 11篇 |
1966年 | 10篇 |
排序方式: 共有1217条查询结果,搜索用时 109 毫秒
861.
862.
A striking potential of the amphiphilic dipeptides, Arg-Phe or Asp-Phe, to induce aggregation of a model protein, alcohol dehydrogenase in its native-like state, has been demonstrated under physiologically relevant conditions, using dynamic light scattering, fluorescence spectroscopy, circular dichroism, transmission electron- and atomic force microscopy. The peptide action resulted in accumulation of a variety of morphologically distinct supramolecular structures profoundly differing from those generated by the heat-induced aggregation at the early stages of the process, when amyloid fibril assemblies were not detectable. The biogenic amphiphilic agents are suggested to act as regulators of structural transformations of native-like proteins. 相似文献
863.
864.
Cytoplasmic inorganic pyrophosphatase of rat liver can be phosphorylated by cAMP-dependent protein kinase on a serine residue with a concomitant increase in enzymic activity. Phosphorylation is also observed in the absence of protein kinase, but in this case much higher concentrations of ATP are required and the stability characteristics of the phosphoenzyme resemble those of an acyl phosphate. Kinase-free phosphorylation of the animal inorganic pyrophosphatase, unlike that of microbial pyrophosphatases, does not activate the enzyme. Pyrophosphatase may thus provide a new example of an enzyme whose evolution involves convergence of regulatory phosphorylation mechanisms. 相似文献
865.
Mouna Kehili Lisa Marie Schmidt Wienke Reynolds Ayachi Zammel Carsten Zetzl Irina Smirnova Noureddine Allouche Sami Sayadi 《Biotechnology for biofuels》2016,9(1):261
Background
In today’s consumer perception of industrial processes and food production, aspects like food quality, human health, environmental safety, and energy security have become the keywords. Therefore, much effort has been extended toward adding value to biowastes of agri-food industries through biorefinery processing approaches. This study focused, for the first time, on the valorization of tomato by-products of a Tunisian industry for the recovery of value-added compounds using biorefinery cascade processing.Results
The process integrated supercritical CO2 extraction of carotenoids within the oil fractions from tomato seeds (TS) and tomato peels (TP), followed by a batch isolation of protein from the residues. The remaining lignocellulosic matter from both fractions was then submitted to a liquid hot water (LHW) hydrolysis. Supercritical CO2 experiments extracted 5.79% oleoresin, 410.53 mg lycopene/kg, and 31.38 mg β-carotene/kg from TP and 26.29% oil, 27.84 mg lycopene/kg, and 5.25 mg β-carotene/kg from TS, on dry weights. Protein extraction yields, nearing 30% of the initial protein contents equal to 13.28% in TP and 39.26% in TS, revealed that TP and TS are a rich source of essential amino acids. LHW treatment run at 120–200 °C, 50 bar for 30 min showed that a temperature of 160 °C was the most convenient for cellulose and hemicellulose hydrolysis from TP and TS, while keeping the degradation products low.Conclusions
Results indicated that tomato by-products are not only a green source of lycopene-rich oleoresin and tomato seed oil (TSO) and of protein with good nutritional quality but also a source of lignocellulosic matter with potential for bioethanol production. This study would provide an important reference for the concept and the feasibility of the cascade fractionation of valuable compounds from tomato industrial by-products.
866.
Polycationic ligands of different chemical classes stimulate DNA strand displacement between short oligonucleotides in a protein‐free system 下载免费PDF全文
The ability of polycationic ligands to stimulate DNA strand displacement between short oligonucleotides in a protein‐free system is demonstrated. We show that two ligands, tetracationic aliphatic amine (spermine) and a dicationic intercalating drug (chloroquine), promote strand displacement in a concentration‐dependent manner. At low concentrations both ligands decelerate spontaneous strand displacement because of their impact on the stability of the DNA duplex. At elevated concentrations they accelerate strand displacement via formation of intermediate structures containing three DNA strands. The rate of the last process does not correlate with the thermal dissociation rate of the entire DNA duplex. It indicates that, possibly, the action of these agents cannot be explained by their influence on the stability of the DNA duplex. In general, our results suggest that the ability to stimulate DNA strand displacement appears to be a common feature of polycations of different chemical and structural classes. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 633–641, 2016. 相似文献
867.
V. V. Aleksandrov V. A. Bryzgunov E. V. Grabovski A. N. Gritsuk I. V. Volobuev E. D. Kazakov Yu. G. Kalinin V. D. Korolev Ya. I. Laukhin S. F. Medovshchikov K. N. Mitrofanov G. M. Oleinik V. G. Pimenov E. A. Smirnova G. I. Ustroev I. N. Frolov 《Plasma Physics Reports》2016,42(4):355-361
Results are presented from measurements of the parameters of high-temperature plasma in the Z-pinch neck formed when a current of up to 3.5 MA flows through a low-density polymer load. To enhance the effect of energy concentration, a deuterated microporous polyethylene neck with a mass density of 100 mg/cm3 and diameter of 1–1.3 mm was placed in the central part of the load. During the discharge current pulse, short-lived local hot plasma spots with typical dimensions of about 200–300 μm formed in the neck region. Their formation was accompanied by the generation of soft X-ray pulses with photon energies of E > 0.8 keV and durations of 3–4 ns. The plasma electron temperature in the vicinity of the hot spot was measured from the vacuum UV emission spectra of the iron diagnostic admixture and was found to be about 200–400 eV. The appearance of hot plasma spots was also accompanied by neutron emission with the maximum yield of 3 × 1010 neutrons/shot. The neutron energy spectra were studied by means of the time-of-flight method and were found to be anisotropic with respect to the direction of the discharge current. 相似文献
868.
N P Lopina T I Smirnova M A Pastushenkova I V Paramonova A V Kargapolov L S Iaguzhinski? 《Biokhimii?a (Moscow, Russia)》1990,55(8):1362-1366
The effects of some parameters of the incubation medium (tonicity, H+ and Pi concentration) on the phospholipid content in rat mitochondrial extracts prepared by normal extraction and by extraction with strongly acidified solvent mixtures, were studied. It was found that after normal extraction with a chloroform-methanol mixture, 8% to 25% of mitochondrial phospholipids can be additionally extracted by acidified solvent mixtures. The concentration of weakly extractable lipids depends on the tonicity and ionic composition of the incubation medium. It was suggested that there exist in mitochondria two lipid pools, a loosely and a tightly-bound ones; the equilibrium between these pools is effectively regulated by medium tonicity and other external factors. 相似文献
869.
S G Donich V I Smirnova V V Likhvantsev N P Buglak Iu P Svirgunenko 《Biulleten' eksperimental'no? biologii i meditsiny》1991,111(6):622-623
I/v dalargin injection (20-25 g/kg) to narcotized rats in case of total myoplegia effectively protect hemodynamic changes under nociceptive stimulation. Bilateral truncal vagotomy partially decrease the protective effect of dalargin. Protective effect of the medicine results in activation of central and peripheral opioid receptors. 相似文献
870.
N. R. Meychik A. V. Smirnova N. P. Matveeva Yu. I. Nikolaeva I. P. Ermakov 《Russian Journal of Plant Physiology》2009,56(2):211-218
Changes in the composition of ionogenic groups of the polymeric matrix of the cell walls of lily (Lilium longiflorum Thunb.) pollen grains were studied during its activation at the early stages of pollen germination. In the cell walls isolated from nonactivated and activated pollen grains, four types of ionogenic groups were identified: amino groups, carboxylic groups of uronic acids, phenolic OH-groups. and groups with pKa 7–8. During the early stages of germination, ionization constants of each type groups remained unchanged, but the quantitative composition of ionogenic groups in the intine changed. In this matrix, a decrease in the content of phenolic groups and demethylated carboxylic groups of uronic acids was detected. It is supposed that, at early stages of germination, the intine loses some part of acid pectins and some phenolic compounds. 相似文献