全文获取类型
收费全文 | 2459篇 |
免费 | 84篇 |
国内免费 | 59篇 |
出版年
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 33篇 |
2020年 | 24篇 |
2019年 | 40篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 29篇 |
2015年 | 60篇 |
2014年 | 123篇 |
2013年 | 114篇 |
2012年 | 107篇 |
2011年 | 113篇 |
2010年 | 85篇 |
2009年 | 84篇 |
2008年 | 73篇 |
2007年 | 107篇 |
2006年 | 88篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 79篇 |
2002年 | 76篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 60篇 |
1998年 | 51篇 |
1997年 | 45篇 |
1996年 | 50篇 |
1995年 | 68篇 |
1994年 | 54篇 |
1993年 | 26篇 |
1992年 | 60篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 44篇 |
1988年 | 47篇 |
1987年 | 38篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 54篇 |
1983年 | 49篇 |
1982年 | 57篇 |
1981年 | 49篇 |
1980年 | 31篇 |
1979年 | 33篇 |
1978年 | 14篇 |
1977年 | 21篇 |
1976年 | 4篇 |
1974年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有2602条查询结果,搜索用时 15 毫秒
71.
A. Beyer 《Protein science : a publication of the Protein Society》1997,6(10):2043-2058
The AAA protein family, a recently recognized group of Walker-type ATPases, has been subjected to an extensive sequence analysis. Multiple sequence alignments revealed the existence of a region of sequence similarity, the so-called AAA cassette. The borders of this cassette were localized and within it, three boxes of a high degree of conservation were identified. Two of these boxes could be assigned to substantial parts of the ATP binding site (namely, to Walker motifs A and B); the third may be a portion of the catalytic center. Phylogenetic trees were calculated to obtain insights into the evolutionary history of the family. Subfamilies with varying degrees of intra-relatedness could be discriminated; these relationships are also supported by analysis of sequences outside the canonical AAA boxes: within the cassette are regions that are strongly conserved within each subfamily, whereas little or even no similarity between different subfamilies can be observed. These regions are well suited to define fingerprints for subfamilies. A secondary structure prediction utilizing all available sequence information was performed and the result was fitted to the general 3D structure of a Walker A/GTPase. The agreement was unexpectedly high and strongly supports the conclusion that the AAA family belongs to the Walker superfamily of A/GTPases. 相似文献
72.
Ischemia-Induced Inhibition of Calcium Uptake into Rat Brain Microsomes Mediated by Mg2+ /Ca2+ ATPase
Abstract: It is well established that ischemia is associated with prolonged increases in neuronal intracellular free calcium levels. Recent data suggest that regulation of calcium uptake and release from the endoplasmic reticulum is important in maintaining calcium homeostasis. The endoplasmic reticulum Mg2+ /Ca2+ ATPase is the major mechanism for sequestering calcium in this organelle. Inhibition of this enzyme may play a causal role in the loss of calcium homeostasis. In order to investigate the effect of ischemia on calcium sequestration into the endoplasmic reticulum, microsomes were isolated from control and ischemic whole brain homogenates by differential centrifugation. Calcium uptake was measured by radioactive calcium (45 Ca2+ ) accumulation in the microsomes mediated by Mg2+ /Ca2+ ATPase. Ischemia caused a statistically significant inhibition of presteady-state and steady-state calcium uptake. Duration of ischemia was directly proportional to the degree of inhibition. Decreased calcium uptake was shown not to be the result of increased calcium release from ischemic compared with control microsomes nor the result of selective isolation of ischemic microsomes from the homogenate with a decreased capacity for calcium uptake. The data demonstrate that ischemia inhibits the ability of brain microsomes to sequester calcium and suggest that loss of calcium homeostasis is due, in part, to ischemia-induced inhibition of endoplasmic reticulum Mg2+ /Ca2+ ATPase. 相似文献
73.
脱落酸对线粒体Na^+—K^+ATPase活性的影响 总被引:3,自引:0,他引:3
在提取大豆(Glycine m ax)黄化子叶的线粒体时,于清洗和悬浮介质中加入ABA,发现40 μm ol/L(±) ABA 对线粒体膜结合Na+ -K+ ATPase 活性及线粒体吸氧速率有明显的促进作用。ABA 可使16℃与27℃培养的大豆子叶线粒体膜结合Na+ -K+ ATPase Arrhenius图的折点温度分别下降6.3℃和5.9℃,并将该酶的底物动力学曲线由正协同曲线转变为非协同曲线。表明ABA 可降低线粒体的膜相变温度 相似文献
74.
Krzysztof J. Rakowski Janusz J. Zwiazek Michael J. Sumner 《Trees - Structure and Function》1995,9(4):190-194
Eastern white pine (Pinus strobus L.) seedlings were grown in controlled environment growth cabinets and fumigated with 0.4 and 1.6 g m–3 hydrogen fluoride for 2–28 days. Plasma membranes were isolated from needles of treated and control seedlings and their chemical composition and ATPase activity examined to determine early effects of hydrogen fluoride action. In plants treated for 2 days with both fluoride levels, ratios of plasma membrane free sterols:phospholipids and sterols:proteins were drastically higher than ratios in control plants. Seedlings treated with hydrogen fluoride for 8 days contained plasma membranes with elevated phospholipid:protein and sterol:protein ratios and their plasma membrane ATPase activity was higher than that of control plants. Prolonged, 28-day hydrogen fluoride treatment with 1.6 g m–3 level was the only treatment which produced a drastic inhibition of plasma membrane ATPase activity. During the initial stages of hydrogen fluoride treatment, treated cells did not show alterations of ultrastructure which were previously shown in cells of plants treated with soil applied sodium fluoride. The results of the present study indicate that the plasma membranes may be among the initial sites of hydrogen fluoride injury to plants as well as initial sites of defense reaction. 相似文献
75.
观察为期4周模拟失重对大鼠心肌收缩性能与收缩蛋白性质的影响,发现模拟失重大鼠左心室乳头肌等长收缩的力学特征发生下列变化:发展张力峰值降低29%(P〈0.01);达到张力峰值的时间延长10%(P〈0.05);舒张一半的时间缩短11%,但未达到显著水平(P〉0.05)。心肌力学参数的这些变化表明模拟失重使大鼠心肌收缩性能降低。进一步研究显示,模拟失重大鼠左室心肌肌原纤维Ca^2+,Mg^2+-ATP酶 相似文献
76.
Three proton pumps,morphology and movements 总被引:3,自引:0,他引:3
J. N. Telford T. A. Langworthy E. Racker 《Journal of bioenergetics and biomembranes》1984,16(5-6):335-351
The diameter of F1 coupling factor and the distance it protrudes from the membrane of bovine heart submitochondrial particles were measured quantitatively using horse spleen ferritin as a standard. Employing the freeze-etch technique, particles of similar size were found on membranes of submitochondrial particles and on membranes of particles first depleted by F1, then reconstituted by addition of F1. The extramembranous size of F1 is 9.7 nm and F1 protrudes from the membrane surface by about 13.6 nm. Bacteriorhodopsin and cytochrome oxidase were incorporated into lipids derived from membranes of extremely thermoacidophilic microorganisms by the octylglucoside dilution method. The bacteriorhodopsin pump was fully functional provided high concentrations of valinomycin were added. With decanoyl-N-methylglucamide as detergent the pump was very active in the absence of valinomycin. Concentrations of gramicidin that collapsed the pH in bacteriorhodopsin liposomes prepared with soybean phospholipid had little or no effect on these rigid proteoliposomes. Very high concentrations (30 µg per ml) were partially effective, suggesting a mechanism other than formation of a gramicidin dimer channel. Cytochrome oxidase lost virtually all activity when incorporated into these rigid liposomes but was fully reactivated on addition of suitable detergents.Abbreviations SMP
submitochondrial vesicles prepared from bovine heart mitochondria exposed to sonic oscillation in the presence of pyrophosphate
- F1
the water-soluble coupling factor of the mitochondrial ATPase complex
- CF1
the water-soluble coupling factor of the chloroplast ATPase complex
- ASU vesicles
submitochondrial vesicles prepared from bovine heart mitochondria disrupted by sonic oscillation in ammonia, then passed through Sephadex and treated with urea
- OSCP
oligomycin sensitivity-conferring protein
- Mega 8, 9, and 10
for octoylnanoyl, and decanoyl-N-methylglucamide
- 1799
bis-(hexafluoroacetonyl)acetone
- PMS
N-methylphenazonium methosulfate 相似文献
77.
Prakash C. Misra Theodore A. Craig Frederick L. Crane 《Journal of bioenergetics and biomembranes》1984,16(2):143-152
Carrot (Daucus carota L.) cells grown in suspension culture oxidized exogeneous NADH. The NADH oxidation was able to stimulate K+ (86Rb+) transport into cells, but it did not affect sucrose transport.N,N'-Dicyclohexyl-carbodiimide, diethylstilbestrol, and oligomycin, which only partially inhibited NADH oxidation, almost completely collapsed the K+ (86Rb+) transport. Vanadate, which is less effective as an ion transport inhibitor, was less effective in inhibiting the NADH-driven transport of K+ (86Rb+).p-Fluormethoxycarbonylcyanide phenylhydrazone inhibits the K+ transport over 90% including that induced by NADH. The results are interpreted as evidence that a plasma membrane redox system in root cells is closely associated with the ATPase which can drive K+ transport. Because of the inhibitor effects, it appears that membrane components common to the redox system and ATPase function in the transport of K+. 相似文献
78.
Calcium fluxes at plasmalemma and tonoplast 总被引:4,自引:2,他引:2
A. E. S. MACKLON 《Plant, cell & environment》1984,7(6):407-413
Abstract. An account is given of the characterization of calcium fluxes across plasmalemma and tonoplast membranes of root cortical cells, using compartmental analysis. Some of the assumptions associated with the method are discussed. Recent evidence regarding the concentration of free Ca2+ in plant cells, and the mechanisms driving active calcium transport across cell membranes, is reviewed. It is proposed that the evidence from whole cell studies and work at the molecular level is mutually supportive, and some speculation is ventured about the general pattern of calcium transport in higher plant cells. 相似文献
79.
Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review 总被引:36,自引:0,他引:36
A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed. 相似文献
80.