全文获取类型
收费全文 | 18943篇 |
免费 | 1398篇 |
国内免费 | 541篇 |
出版年
2024年 | 16篇 |
2023年 | 133篇 |
2022年 | 308篇 |
2021年 | 578篇 |
2020年 | 405篇 |
2019年 | 513篇 |
2018年 | 583篇 |
2017年 | 487篇 |
2016年 | 712篇 |
2015年 | 1086篇 |
2014年 | 1187篇 |
2013年 | 1386篇 |
2012年 | 1775篇 |
2011年 | 1616篇 |
2010年 | 983篇 |
2009年 | 905篇 |
2008年 | 1154篇 |
2007年 | 986篇 |
2006年 | 892篇 |
2005年 | 747篇 |
2004年 | 743篇 |
2003年 | 657篇 |
2002年 | 593篇 |
2001年 | 248篇 |
2000年 | 227篇 |
1999年 | 224篇 |
1998年 | 159篇 |
1997年 | 152篇 |
1996年 | 148篇 |
1995年 | 115篇 |
1994年 | 106篇 |
1993年 | 118篇 |
1992年 | 115篇 |
1991年 | 108篇 |
1990年 | 80篇 |
1989年 | 77篇 |
1988年 | 61篇 |
1987年 | 65篇 |
1986年 | 53篇 |
1985年 | 52篇 |
1984年 | 39篇 |
1983年 | 48篇 |
1982年 | 27篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 22篇 |
1976年 | 14篇 |
1974年 | 14篇 |
1972年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
G. N. Reiner L. Delgado-Marín N. Olguín S. Sánchez-Redondo M. Sánchez-Borzone E. Rodríguez-Farré C. Suñol D. A. García 《Cell biochemistry and biophysics》2013,67(2):515-525
Phenol compounds, such as propofol and thymol, have been shown to act on the GABAA receptor through interaction with specific sites of this receptor. In addition, considering the high lipophilicity of phenols, it is possible that their pharmacological activity may also be the result of the interaction of phenol molecules with the surrounding lipid molecules, modulating the supramolecular organization of the receptor environment. Thus, in the present study, we study the pharmacological activity of some propofol- and thymol-related phenols on the native GABAA receptor using primary cultures of cortical neurons and investigate the effects of these compounds on the micro viscosity of artificial membranes by means of fluorescence anisotropy. The phenol compounds analyzed in this article are carvacrol, chlorothymol, and eugenol. All compounds were able to enhance the binding of [3H]flunitrazepam with EC50 values in the micromolar range and to increase the GABA-evoked Cl? influx in a concentration-dependent manner, both effects being inhibited by the competitive GABAA antagonist bicuculline. These results strongly suggest that the phenols studied are positive allosteric modulators of this receptor. Chlorothymol showed a bell-type effect, reducing its positive effect at concentrations >100 μM. The concentrations necessary to induce positive allosteric modulation of GABAA receptor were not cytotoxic. Although all compounds were able to decrease the micro viscosity of artificial membranes, chlorothymol displayed a larger effect which could explain its effects on [3H]flunitrazepam binding and on cell viability at high concentrations. Finally, it is suggested that these compounds may exert depressant activity on the central nervous system and potentiate the effects of general anesthetics. 相似文献
22.
Strain LSJC7, with dual resistance to arsenic and tetracycline, was isolated from an antimony tailing in China. Its 16S rRNA gene sequence has the highest similarity to that of Enterobacter cloacae subsp. dissolvens LMG 2683T (97.02%). Here we present the approximately 4.6-Mbp draft genome sequence of strain LSJC7. 相似文献
23.
24.
Angela Gordon 《American anthropologist》2002,104(2):676-677
Fleeting Identities: Perishable Material Culture in Archaeological Research. Penelope Ballard Drooker. ed. Carbondale, 1L: Center for Archaeological Investigations, 2001.410 pp. 相似文献
25.
A rapid extraction method for screening aflatoxin producing potential ofAspergillus flavus group isolates is described. The method is performed using a moist wheat medium with ca. five infected grains extracted with 2 mL of chloroform, and using thin layer chromatography. This method was proved with 95A. flavus isolates from animal feeds. 相似文献
26.
27.
Angela F. Dulhunty Michael R. C. Banyard C. Jill Medveczky 《The Journal of membrane biology》1987,99(2):79-92
Summary Four monoclonal antibodies against the calcium ATPase in sarcoplasmic reticulum (SR) of rabbit fast-twitch skeletal muscle were characterized using SDS-PAGE, Western blots and immunofluorescence. The ultrastructural distribution of the antigens was determined using post-embedding immunolabeling. The antibodies recognized the calcium ATPase in the SR but not in transverse (T-) tubule or plasma membranes. The antibody, D12, had the same binding affinity for the calcium ATPase from fast-twitch (rabbit sternomastoid) and slow-twitch (rabbit soleus) fibers and the affinity fell by 30% after fixation for electron microscopy in both types of muscle fiber. Ultrastructural studies revealed that the density of D12 antibody binding to the terminal cisternae membrane of extensor digitorum longus (edl) and sternomastoid fibers was on average seven times greater than in the slow-twitch soleus and semimembranosus fibers. Since the affinity of the ATPase for the antibody was the same in SR from fast- and slow-twitch muscles, the concentration of calcium ATPase in the terminal cisternae membrane of fast-twitch fibers was seven times greater than in slow-twitch fibers. This conclusion was supported by the fact that the concentration of calcium ATPase in light SR membranes was six times greater in SR from fast-twitch fibers than in SR from slow-twitch fibers. The results provide strong evidence that the different calcium accumulation rates in mammalian fast- and slow-twitch muscles are due to different concentrations of calcium ATPase molecules in the SR membrane. 相似文献
28.
Association of viral and plasmid DNA with the nuclear matrix during productive infection 总被引:1,自引:0,他引:1
The association of simian virus 40 (SV40) DNA or plasmid DNA in subcellular fractions from either infected or transfected cells was examined. In lytically infected cells, approx. 25% of viral specific DNA during the infection cycle was retained in nuclei after washing with low ionic strength buffer and 1% Triton X-100. Viral replicating DNA found in the nuclear matrix was capable of performing limited DNA synthesis by the endogenous DNA polymerase in vitro. Viral DNA synthesized in vitro hybridized preferentially to SV40 Hind-III B and C fragments which are in proximity to the origin of replication. In plasmid-transfected COS-7 cells (SV40-transformed cells), the amount of plasmid DNA found in the nuclear matrix was related to its replication efficiency in cells. More than 80% of the plasmid DNA was tightly associated with subnuclear structures. Little or no plasmid DNA was found in the cytoplasmic fraction. The results suggest that, in extrachromosomal model systems, the association of DNA with nuclear matrix is important for the regulation of DNA replication. 相似文献
29.
The investigation of crop and soil-crop conditions among Andoke and Witoto cultivators in southeast Colombia is used as a basis for assessing Geertz' (1963) model of swidden cultivation. In this respect, the extent to which maniocdominated swiddens in the study area simulate the structure and composition of the forest climax community is questioned. As Geertz (1963) indicates, an initial nutrient boost for crop cultivation results from the preliminary burning of forest debris, but weed competition, rather than progressive loss of soil fertility, is reported to be the primary cause of abandoning manioc cultivation after 2–3 years. While the Andoke and Witoto crop system remains adaptive at the individual field level, particularly in its constituent species, its fundamental adaptation is considered to be its integration into the broader field and fallow system that juxtaposes crop production with extended periods of forest regeneration. 相似文献
30.