全文获取类型
收费全文 | 1079篇 |
免费 | 76篇 |
国内免费 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 17篇 |
2022年 | 19篇 |
2021年 | 57篇 |
2020年 | 30篇 |
2019年 | 63篇 |
2018年 | 44篇 |
2017年 | 39篇 |
2016年 | 50篇 |
2015年 | 66篇 |
2014年 | 72篇 |
2013年 | 56篇 |
2012年 | 86篇 |
2011年 | 84篇 |
2010年 | 43篇 |
2009年 | 44篇 |
2008年 | 66篇 |
2007年 | 57篇 |
2006年 | 47篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 32篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1202条查询结果,搜索用时 15 毫秒
11.
Two-dimensional crystals of avidin were obtained on mixed lipid monolayers containing biotinylated lipids (N-biotinyl-dipalmitoyl-L-alpha-phosphatidyl ethanolamine and dioleoyl phosphatidyl choline) by specific interaction. Image analysis of electron micrographs of these crystals revealed p2 symmetry with the unit cell parameters a = 66 +/- 2 A, b = 68 +/- 1 A, and gamma = 121 +/- 4 degrees. The projection map showed, at a resolution of about 27 A, that the four subunits within one avidin molecule are separated into two parts. Comparison between avidin and streptavidin reveals that avidin molecule binds to the lipid monolayer in an orientation similar to that of streptavidin. 相似文献
12.
In the first part of the present work the interaction of glycophorin with dimyristoylphosphatidylcholine (DMPC) is studied by freeze fracture electron microscopy, densitometry, calorimetry, and 90 degree static light scattering. An exothermic lipid/protein interaction energy of WP = 190 kJ.mol-1 was found by application of the well known Van Laar relation for the displacement of the freezing point and the Gibbs-Duhem relationship. Secondly, the effects of Ca2+ on the lipid/protein interaction were studied. Following Ca2+ addition a remarkable decoupling of the interaction of the glycophorin head group with the bilayer surface was revealed by densitometry and gold-labeling electron microscopy. It is estimated that about 80% of lipid once disturbed by the adsorption of glycophorin head groups is decoupled after addition of Ca2+. Thirdly, the selective interaction of glycophorin with binary lipid mixtures was studied, including the mixtures of DMPC with dimyristoylphosphatidylserine (DMPS) and dilauroylphosphatidylcholine (DLPC), and the mixture of dipalmitoylphosphatidylcholine (DPPC) with DLPC. 相似文献
13.
Phyto- and protozooplankton biomass during austral summer in surface waters of the Weddell Sea and vicinity 总被引:3,自引:3,他引:0
Summary Phyto- and protozooplankton were sampled in the upper 10 m of the water column in austral summer during a cruise of RV Polarstern from January 6 to February 20 1985 in the eastern Bransfield Strait vicinity and in the northern, southeastern (off Vestkapp, twice: I and II) and southern Weddell Sea (Vahsel Bay across the Filchner Depression to Gould Bay). The plankton assemblages are discussed in relation to physical, chemical and biological factors in the different geographical areas in summer. Phytoplankton biomass (Phytoplankton carbon, PPC) ranged from 4–194 g carbon/l and consisted on average of 65% diatoms and 35% autotrophic flagellates. Whereas in the northwest phytoplankton assemblages were dominated by small nanoflagellates (78% of PPC), higher biomass of diatoms (54–94% of PPC) occurred at the other sampling sites. In general autotrophic flagellates and small pennate diatoms dominated at oceanic stations; in neritic areas large centric diatoms prevailed. Chlorophyll a concentrations ranged from 0.25–3.14/g chl a/l with a mean of 1.13/gmg chlorophyll a/l and an average phytoplankton carbon/chlorophyll a ratio of 39. Protozooplankton biomass (Protozooplankton carbon, PZC) ranged from 0–67 g carbon/l and consisted of 49% ciliates, 49% heterotrophic dinoflagellates and 2% tintinnids. Heterotrophic dinoflagellates were more important in the northern investigation areas (58%–84% of PZC). Ciliates dominated the protozooplankton in the southeast and south (56%–65% of PZC); higher abundances of tintinnids were observed only in the south (11% of PZC). The most remarkable feature of the surface waters was the high protozooplankton biomass: protozooplankton amounted to 25% on an average of the combined biomass of PPC plus PZC for the entire investigation period. Protozoan biomass in the southeastern and southern Weddell Sea occasionally exceeded phytoplankton biomass. Temperature, salinity, and inorganic nutrients were generally lower in the southern regions; at most of these stations a meltwater layer occurred in the upper meters of the water column. We suggest that this physical regime allows a well developed summer system with a high proportion of heterotrophic microplankton. In the eastern Bransfield Strait, in the northern Weddell Sea and close to the coast off Vestkapp (I), however, early summer conditions occurred with less protozooplankton contribution.Contribution no. 427 from the Alfred-Wegener-Institute for Polar and Marine Research 相似文献
14.
Long noncoding RNAs(IncRNAs)act as essential regulators of various diseases.However,the func-tions of IncRNAs in sepsis-induced acute lung injury(SALI)remain un... 相似文献
15.
Jia-Chen Hu Chen-Xi Zheng Bing-Dong Sui Wen-Jia Liu Yan Jin 《World journal of stem cells》2022,14(5):318-329
Poor healing of cutaneous wounds is a common medical problem in the field of traumatology. Due to the intricate pathophysiological processes of wound healing, the use of conventional treatment methods, such as chemical molecule drugs and traditional dressings, have been unable to achieve satisfactory outcomes. Within recent years, explicit evidence suggests that mesenchymal stem cells (MSCs) have great therapeutic potentials on skin wound healing and regeneration. However, the direct application of MSCs still faces many challenges and difficulties. Intriguingly, exosomes as cell-secreted granular vesicles with a lipid bilayer membrane structure and containing specific components from the source cells may emerge to be excellent substitutes for MSCs. Exosomes derived from MSCs (MSC-exosomes) have been demonstrated to be beneficial for cutaneous wound healing and accelerate the process through a variety of mechanisms. These mechanisms include alleviating inflammation, promoting vascularization, and promoting proliferation and migration of epithelial cells and fibroblasts. Therefore, the application of MSC-exosomes may be a promising alternative to cell therapy in the treatment of cutaneous wounds and could promote wound healing through multiple mechanisms simultaneously. This review will provide an overview of the role and the mechanisms of MSC-derived exosomes in cutaneous wound healing, and elaborate the potentials and future perspectives of MSC-exosomes application in clinical practice. 相似文献
16.
L M Sui J Lennon C Ma I McCann I Woo P H Pétra 《The Journal of steroid biochemistry and molecular biology》1999,68(3-4):119-127
Wild type, partially and fully-deglycosylated human sex steroid-binding protein (SBP or SHBG) cDNAs lacking the native cucaryotic signal sequence were cloned into a yeast expression vector containing the Saccharomyces cerevisiae alpha-factor for extracellular secretion. Following transformation into Pichia pastoris, the wild type and all constructed mutants were successfully expressed. The levels were lower for the deglycosylated mutants indicating that oligosaccharide side chains may play a role in SBP secretion. Under fermentation conditions, the wild type protein was expressed at a level of 4 mg/l while the fully-deglycosylated mutant T7A/N351Q/N367Q was expressed at about 1.5 mg/l. The latter was purified from several fermentation runs and was found to be completely deglycosylated, electrophoretically homogeneous and fully active. The aminoterminus was found to have the sequence NH2QSAHDPPAV- indicating that cleavage of the alpha-factor occurred at the A(+7)-Q(+8) peptide bond. The molecular mass of the subunit was determined to be 39,717.8 Da, which is in complete agreement with the amino acid sequence of the T7A/N351Q/N367/Q mutant. The equilibrium constants for the dissociation of 5alpha-dihydrotestosterone and steroid binding specificity were found to be identical to that of the human plasma protein indicating that the missing N-terminal segment NH2-LRPVLPT and the removal of oligosaccharide side chains do not affect the stability and active conformation of the protein. In conclusion, the data presented reveal that the SBP mutant T7A/N351Q/N367/Q is the protein of choice for solving the three-dimensional structure. 相似文献
17.
关于提高血气分析仪测量精度的探讨 总被引:1,自引:0,他引:1
姜穗 《上海生物医学工程》2007,28(4):248-250
血气分析已广泛用于昏迷、休克、严重外伤的危急病人的血液酸碱度、氧分压、二氧化碳分压的测量。测量数据的准确性至关重要。本文对与测量精度有关的几个环节如计量检定、质控与定标、样本采集与测量、日常维护与故障处理进行探讨,提出提高血气分析精度的解决方案。 相似文献
18.
19.
红穗醋栗色素理化性质的研究 总被引:1,自引:0,他引:1
本试验研究了红穗醋栗色素的理化性质,结果表明:红穗醋栗色素热稳定性很好,而光照对其有一定的降解作用。pH值对该色素影响明显,宜在酸性食品中应用。几种金属离子Na~ 、Ca~(2 )、Al~(3 )、Zn~(2 )。Cu~(2 )对该色素的色泽没有影响;而Fe~(3 )、Sn~(2 )则有不良影响。食品中常含的几种添加物葡萄糖、蔗糖、淀粉和抗坏血酸对该色素无不良影响。红穗醋栗色素对Na_2SO_3的还原性耐性较强,对H_2O_2的耐氧化性很差。防腐剂苯甲酸钠对该色素也有一定的不良影响。 相似文献
20.