全文获取类型
收费全文 | 20475篇 |
免费 | 1684篇 |
国内免费 | 5篇 |
出版年
2023年 | 89篇 |
2022年 | 233篇 |
2021年 | 435篇 |
2020年 | 236篇 |
2019年 | 313篇 |
2018年 | 424篇 |
2017年 | 359篇 |
2016年 | 645篇 |
2015年 | 1050篇 |
2014年 | 1180篇 |
2013年 | 1426篇 |
2012年 | 1766篇 |
2011年 | 1671篇 |
2010年 | 1069篇 |
2009年 | 939篇 |
2008年 | 1274篇 |
2007年 | 1309篇 |
2006年 | 1124篇 |
2005年 | 1074篇 |
2004年 | 1045篇 |
2003年 | 954篇 |
2002年 | 908篇 |
2001年 | 216篇 |
2000年 | 158篇 |
1999年 | 168篇 |
1998年 | 241篇 |
1997年 | 157篇 |
1996年 | 145篇 |
1995年 | 127篇 |
1994年 | 114篇 |
1993年 | 110篇 |
1992年 | 89篇 |
1991年 | 80篇 |
1990年 | 84篇 |
1989年 | 70篇 |
1988年 | 56篇 |
1987年 | 63篇 |
1986年 | 46篇 |
1985年 | 53篇 |
1984年 | 46篇 |
1983年 | 67篇 |
1982年 | 41篇 |
1981年 | 35篇 |
1980年 | 39篇 |
1979年 | 36篇 |
1978年 | 51篇 |
1977年 | 37篇 |
1976年 | 36篇 |
1975年 | 34篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Application of Response Surface Methodology to Evaluation of Bioconversion Experimental Conditions 总被引:3,自引:0,他引:3 下载免费PDF全文
Vronique Cheynier Max Feinberg Constantin Chararas Christian Ducauze 《Applied microbiology》1983,45(2):634-639
Using Candida tenuis, a yeast isolated from the digestive tube of the larva of Phoracantha semipunctata (Cerambycidae, Coleoptera), we were able to demonstrate the bioconversion of citronellal to citronellol. Response surface methodology was used to achieve the optimization of the experimental conditions for that bioconversion process. To study the proposed second-order polynomial model, we used a central composite experimental design with multiple linear regression to estimate the model coefficients of the five selected factors believed to influence the bioconversion process. Only four were demonstrated to be predominant: the incubation pH, temperature, time, and the amount of substrate. The best reduction yields (close to 90%) were obtained with alkaline pH conditions (pH 7.5), a low temperature (25°C), a small amount of substrate (15 μl), and short incubation time (16 h). This methodology was very efficient: only 36 experiments were necessary to assess these conditions, and model adequacy was very satisfactory as the coefficient of determination was 0.9411. 相似文献
92.
93.
Nucleotide pools of growing,synchronized and stressed cultures of Saccharomyces cerevisiae 总被引:6,自引:0,他引:6
Günther Ditzelmüller Wilfried Wöhrer Christian P. Kubicek Max Röhr 《Archives of microbiology》1983,135(1):63-67
High pressure liquid chromatography has been used to study the acid soluble nucleotide pool of Saccharomyces cerevisiae under different conditions of growth. ATP, ADP, AMP, NAD, GTP, UTP, UDP, CTP, CDP, and UDP-sugars plus UMP could be separated and were found in concentrations higher than 0.1 mumol per g yeast cell dry weight (= detection limit). During glucose-limited continuous culture the levels of individual nucleotides depended on the growth rate, which was most pronounced with pyrimidine (uridine, cytidine) nucleotides. The energy charge (E.C.) remained high (0.9) at all growth rates (0.07-0.3 h-1). During synchronized growth at a constant growth rate (0.11 h-1) almost all nucleotide levels and the E.C. remained at constant values with the only exception of UDP-sugars and UMP of which increased levels were found during the phase of budding. Under conditions of metabolic stress (addition of antimycin A, deoxyglucose plus iodoacetate) pronounced changes in the levels of purine (adenine and guanine) nucleotides and the E.C. were observed. All other nucleotides were less influenced by these conditions. Only under these conditions IMP accumulation was observed. The results strongly argue against the significance of purine nucleotide or E.C. measurements under viable conditions. In contrast, changes in the levels of pyrimidine nucleotides seem to be indicative of changes in the flux through the metabolic pathways where they act as coenzymes. 相似文献
94.
We have examined the accessibility to diethylpyrocarbonate of spinach chloroplast 4.5S ribosomal RNA when free and when it is part of the ribosomal structure. The modifications in free 4.5S RNA were found mostly in single-stranded regions of the secondary structure model proposed in our previous paper (Kumagai, I. et al. (1982) J.B.C. 257, 12924-28): adenines at positions 17, 19, 33, 36, 54, 55, 60, 64, 68, 72, 77, 86 and 87 were identified as the reactive residues. On the other hand, in 4.5S RNA in 70S ribosomes or 50S subunits, adenine 33 was exclusively modified, and its reactivity was much higher than in free 4.5S RNA. This highly accessible A33 of spinach 4.5S RNA is located within a characteristic seven nucleotide sequence, which is found in the 4.5S rRNAs from spinach, tobacco and a fern but deleted in 4.5S RNAs from maize and wheat. 相似文献
95.
96.
97.
Christian Walther 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1974,90(1):71-73
Summary Using a method of focal drug application it is demonstrated that high potassium concentration, lanthanum, and black widow spider venom accelerate spontaneous transmitter release inTorpedo electric tissue.This investigation was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 138). Thanks are due to Dr. R. Martin and the staff of the Stazione Zoologica, Naples, for supplyingTorpedo, and Dr. N. Frontali, Rome, for a gift of frozen black widow spiders. 相似文献
98.
The effect of energization on the apparent Michaelis–Menten constant for oxyge in nmitochondrial respiration 下载免费PDF全文
Lineweaver-Burk plots of 1/v against 1/[O(2)] for rat liver mitochondrial respiration with succinate or ascorbate+NNN'N'-tetramethyl-p-phenylenediamine as substrates are non-linear. In state 3u (uncoupled by trifluoromethoxycarbonyl cyanide phenylhydrazone) such plots tend to be concave upward, whereas in state 4 (energized) the plots were concave downward. The apparent K(m) for oxygen is larger in state 4 than in state 3u, despite the higher turnover in the latter system. It is postulated that at least one reversible reaction occurs between cytochrome c and cytochrome c oxidase, whose rate is increased on energization (reversed electron transfer); a model including such a reaction is proposed which accounts semiquantitatively for the observations. 相似文献
99.
Christian U. Christensen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1974,93(2):93-104
Summary A method has been developed which allows perfusion of the blood vessels in isolated pelvic skins ofB. bufo. The effect of various doses of vasotocin (AVT) on net water flux (inside medium 220 mOsM, outside medium 11 mOsM) and active sodium transport were compared in perfused and unperfused skins. The unstimulated water flux (Fig. 3) and the active sodium transport (Fig. 6) were unaffected by perfusion. The threshold for stimulation of water flux was between 0.01 and 0.1 nM vasotocin in perfused skins and between 0.1 and 1 nM in unperfused skins. The threshold for stimulation of active sodium transport was between 0.005 and 0.05 nM vasotocin in perfused skins and between 0.05 and 0.5 nM in unperfused skins. The maximal water flux through perfused skins, 4 l/cm2min, was obtained at 1 nM vasotocin. At 10 nM vasotocin the water flux was only 0.7 l/cm2min in unperfused skins. The maximal active sodium transport was approximately of the same magnitude in perfused and unperfused skins, at 0.5 mM and at 50 nM, respectively. 相似文献
100.
A high potential cytochrome c from Chromatium chromatophores 总被引:1,自引:0,他引:1