全文获取类型
收费全文 | 4344篇 |
免费 | 146篇 |
国内免费 | 169篇 |
出版年
2023年 | 44篇 |
2022年 | 49篇 |
2021年 | 75篇 |
2020年 | 75篇 |
2019年 | 120篇 |
2018年 | 127篇 |
2017年 | 63篇 |
2016年 | 66篇 |
2015年 | 86篇 |
2014年 | 249篇 |
2013年 | 303篇 |
2012年 | 186篇 |
2011年 | 261篇 |
2010年 | 160篇 |
2009年 | 169篇 |
2008年 | 160篇 |
2007年 | 221篇 |
2006年 | 187篇 |
2005年 | 228篇 |
2004年 | 133篇 |
2003年 | 160篇 |
2002年 | 128篇 |
2001年 | 96篇 |
2000年 | 94篇 |
1999年 | 86篇 |
1998年 | 99篇 |
1997年 | 78篇 |
1996年 | 71篇 |
1995年 | 86篇 |
1994年 | 71篇 |
1993年 | 65篇 |
1992年 | 49篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 37篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 32篇 |
1985年 | 44篇 |
1984年 | 60篇 |
1983年 | 49篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 41篇 |
1978年 | 26篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 11篇 |
1973年 | 15篇 |
排序方式: 共有4659条查询结果,搜索用时 343 毫秒
1.
Low-angle laser-light scattering (LALLS) was employed to measure the absolute molecular weight of chicken liver NAD+ kinase (NADK). The weight-average molecular weight (Mw) was found to be 275 000 +/- 15 000. The corresponding value for the second virial coefficient was -1.65 X 10(-3) ml X mol X g2. The value for Mw is in close accord with estimates reported for pigeon liver (270 000) and C. utilis (260 000) NADK. If the active enzyme is a dimer, the weight difference between pigeon/chicken liver and rabbit liver (136 000) NADK would indicate that the latter enzyme is an active monomer unit. 相似文献
2.
《Developmental cell》2021,56(16):2329-2347.e6
3.
4.
The non-receptor tyrosine phosphatase PTPN22 has a vital function in inhibiting antigen-receptor signaling in T cells, while polymorphisms in the PTPN22 gene are important risk alleles in human autoimmune diseases. We recently reported that a key physiological function of PTPN22 was to prevent naïve T cell activation and effector cell responses in response to low affinity antigens. PTPN22 also has a more general role in limiting T cell receptor-induced proliferation. Here we present new data emphasizing this dual function for PTPN22 in T cells. Furthermore, we show that T cell activation modulates the expression of PTPN22 and additional inhibitory phosphatases. We discuss the implication of these findings for our understanding of the roles of PTPN22 in regulating T cell responses and in autoimmunity. 相似文献
5.
David Dávila Silvia Fernández Ignacio Torres-Alemán 《The Journal of biological chemistry》2016,291(5):2510-2523
Disruption of insulin-like growth factor I (IGF-I) signaling is a key step in the development of cancer or neurodegeneration. For example, interference of the prosurvival IGF-I/AKT/FOXO3 pathway by redox activation of the stress kinases p38 and JNK is instrumental in neuronal death by oxidative stress. However, in astrocytes, IGF-I retains its protective action against oxidative stress. The molecular mechanisms underlying this cell-specific protection remain obscure but may be relevant to unveil new ways to combat IGF-I/insulin resistance. Here, we describe that, in astrocytes exposed to oxidative stress by hydrogen peroxide (H2O2), p38 activation did not inhibit AKT (protein kinase B) activation by IGF-I, which is in contrast to our previous observations in neurons. Rather, stimulation of AKT by IGF-I was significantly higher and more sustained in astrocytes than in neurons either under normal or oxidative conditions. This may be explained by phosphorylation of the phosphatase PTEN at the plasma membrane in response to IGF-I, inducing its cytosolic translocation and preserving in this way AKT activity. Stimulation of AKT by IGF-I, mimicked also by a constitutively active AKT mutant, reduced oxidative stress levels and cell death in H2O2-exposed astrocytes, boosting their neuroprotective action in co-cultured neurons. These results indicate that armoring of AKT activation by IGF-I is crucial to preserve its cytoprotective effect in astrocytes and may form part of the brain defense mechanism against oxidative stress injury. 相似文献
6.
Miranda Kleijn Harry O. Voorma Adri A. M. Thomas 《Journal of cellular biochemistry》1995,59(4):443-452
Mitogenic stimulation of protein synthesis is accompanied by an increase in elF-4E phosphorylation. The effect on protein synthesis by induction of differentiation is less well known. We treated P19 embryonal carcinoma cells with the differentiating agent retinoic acid and found that protein synthesis increased during the first hour of addition. However, the phosphorylation state, as well as the turnover of phosphate on elF-4E, remained unchanged. Apparently, the change in protein synthesis after RA addition is regulated by another mechanism than elF-4E phosphorylation. By using P19 cells overexpressing the EGF receptor, we show that the signal transduction pathway that leads to phosphorylation of elF-4E is present in P19 cells; the EGF-induced change in phosphorylation of elF-4E in these cells is likely to be regulated by a change in elF-4E phosphatase activity. These results suggest that the onset of retinoic acid-induced differentiation is triggered by a signal transduction pathway which involves changes in protein synthesis, but not elF-4E phosphorylation. © 1995 Wiley-Liss, Inc. 相似文献
7.
Fioretta Rambelli Maurizio Brigotti Simonetta Sperti Lucio Montanaro 《Bioscience reports》1987,7(9):737-743
Diphtheria toxin fragment A interacts with Cibacron blue in solution, although it is not retained by blue Sepharose columns. Difference spectral titration of fragment A with the dye gives a dissociation constant of the order of 10–5 M and a 11 stoichiometry for the complex. In equilibrium dialysis experiments Cibacron blue behaves as a competitive inhibitor of the binding of NAD to diphtheria toxin fragment A. The dye inhibits in a non-competitive way the fragment A-catalysed transfer of ADP-ribose from NAD to elongation factor 2 (EF2). By affinity chromatography on blue Sepharose a binding of EF2 and of ADP-ribosyl-EF2 with the dye is also demonstrated. GDP, GTP and GDP(CH2)P are able to displace EF2 from blue Sepharose. 相似文献
8.
9.
The activity of the enzymes 5'-nucleotidase (EC 3.1.3.5), adenosine nucleosidase (EC 3.2.2.7), adenine phosphoribosyl transferase (EC 2.4.2.7) and acid phosphatase (EC 3.1.3.2) was determined in sections of tomato plant ( Lycopersicon esculentum Mill. cv. Bellina). The distribution of the enzymes changed markedly during development and a role for these enzymes in cytokinin metabolism is suggested. 相似文献
10.
Summary ThePhysarum plasmodium shows rhythmic contractile activities with a period of a few min. Phases of the oscillation in the plasmodium migrating unindirectionally agreed sideways throughout at the frontal part. So, time course of an intracellular chemical component was determined by analyzing small pieces cut off successively from the frontal part of the large plasmodium. Intracellular NAD(P)H concentration oscillated with the same period as the rhythmic contraction but with a different phase advancing about 1/3 of the period. UV irradiation suppressed the rhythmic contraction without affecting the rhythmic variation of NAD(P)H. Thus, the NAD(P)H oscillator works independently of the rhythmic contractile system, but seems entraining with each other.Abbreviations UV
ultraviolet
- NADH
nicotinamide adenine dinucleotide, reduced form
- NADPH
nicotinamide adenine dinucleotide phosphate, reduced form
- ATP
adenosine 5-triphosphate
- cAMP
cyclic adenosine 3, 5-monophosphate
- FMNH2
flavin mononucleotide, reduced form
- TCA
tricarboxylic acid
- BSA
bovine serum albumin
- DTT
dithiothreitol 相似文献