全文获取类型
收费全文 | 99篇 |
免费 | 164篇 |
国内免费 | 76篇 |
专业分类
化学 | 137篇 |
力学 | 2篇 |
数学 | 8篇 |
物理学 | 192篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 7篇 |
2020年 | 18篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 22篇 |
2011年 | 29篇 |
2010年 | 28篇 |
2009年 | 20篇 |
2008年 | 24篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
71.
尿酸微生物传感器的研制及其动力学研究 总被引:2,自引:0,他引:2
以芽孢杆菌为尿酸氧化反应的酶源,采用氧电极为基础电极,制成尿酸微生物传感器。对细菌的诱导培养条件、电极的工作性能、电极再生以及微生物酶反应动力学行为进行了研究。在pH=8.5时,电极的线性范围为1.0×10-5~4.0×10-4 mol/L,检出下限为1.0×10-6 mol/L,测得微生物膜中尿酸酶的表观米氏常数为2.8×10-4 mol/l,酶反应活化能为47000J/mol,温度系数为1.8. 相似文献
72.
During the bombardment of 14.8MeV neutron on natural wolfram samples a γ-ray with energy 291.7keV and halflife 5.17±0.03 sec is observed. From the experimental facts it is assumed that in addition to the two well known transition branches from the decay of 5.2 sec isomer in 138W there exists another 11/2+11/2[615]→5/2-3/2[512] isomeric (E3) transition. The hindrance factor of this new transition is calculated. It is well cosistent with the general empirical rule of k- forbidden isomeric transition. 相似文献
73.
Jia-Qi Wang Chaoxian Chi Han-Shi Hu Xiang Li Mingbiao Luo Jun Li Mingfei Zhou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2364-2368
Heteronuclear Group 3 metal/iron carbonyl anion complexes ScFe(CO)3−, YFe(CO)3−, and LaFe(CO)3− are prepared in the gas phase and studied by mass-selective infrared (IR) photodissociation spectroscopy as well as quantum-chemical calculations. All three anion complexes are characterized to have a metal–metal-bonded C3v equilibrium geometry with all three carbonyl ligands bonded to the iron center and a closed-shell singlet electronic ground state. Bonding analyses reveal that there are multiple bonding interactions between the bare group-3 elements and the Fe(CO)3− fragment. Besides one covalent electron-sharing metal–metal σ bond and two dative π bonds from Fe to the Group 3 metal, there is additional multicenter covalent bonding with the Group 3 atom bonded to Fe and the carbon atoms. 相似文献
74.
Variational iteration method for solving the mechanism of the Equatorial Eastern Pacific El Nino-Southern Oscillation 下载免费PDF全文
A class of coupled system for the E1 Nifio-Southern Oscillation (ENSO) mechanism is studied. Using the method of variational iteration for perturbation theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behaviour of solution for corresponding problem is considered. 相似文献
75.
Fishbone instability excited by barely trapped suprathermal electrons (BTSEs) in tokamaks is investigated theoretically. The frequency of the mode is found to close to procession frequency of BTSEs. The growth rate of the mode is much smaller than that of the ideal magnetohytrodynamic (MHD) internal kink mode that is in contrast to the case of trapped ion driven fishbone instability. The analyses also show that spatial density gradient reversal is necessary for the instability. The correlation of the results with experiments is discussed. 相似文献
76.
77.
采用静电纺丝法制备了(Pr_(0.9)La_(0.1))_2(Ni_(0.74)Cu_(0.21)Ga_(0.05))O_(4+δ)(PLNCG)氧化物纳米纤维。利用热重-差热分析(TG-DTA)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和扫描电子显微镜(SEM)对材料的物相及微观形貌进行分析。研究表明950℃煅烧5 h得到平均直径420 nm、形貌均一的PLNCG氧化物纤维;1 000℃烧结2 h得到紧密附着在Ce_(0.9)Gd_(0.1)O_(2-δ)(CGO)电解质上的网状结构纤维阴极。电化学阻抗谱(EIS)测试结果表明纳米纤维阴极具有比粉体阴极更优越的性能。700℃的极化电阻(RP)为0.134Ω·cm~2,比同组分的粉末阴极减少32%(RP=0.197Ω·cm~2)。以纤维阴极构筑的电解质支撑单电池Ni-CGO/CGO/PLNCG在700℃的最大输出功率密度为231 m W·cm-2。氧分压测试结果表明阴极反应的速率控制步骤为电荷转移过程。 相似文献
78.
微生物酶传感器是将微生物固定于化学电极上,直接利用微生物体内的酶分解底物而测定的一类生物传感器。同酶传感器相比,它有使用寿命长、制作简便、酶源易获得等优点。自1977年首篇报道以来,测定不同氨基酸和其它有机物的微生物传感器相继问世。但由于微生物通常是一个混合酶体系,使得微生物酶传感器选择性较差。文献曾报道用酶抑制剂进行预处理的办法来降低干扰物响应。本文则利用不同酶耐热性的差异进行温度预处理,以及在培养微生物时,使用不同培养基来改善微生物产酶的特性,从而提高微生物酶传感器的选择性。原大肠杆菌膜电极对L-天冬酰胺、L-谷氨酰胺和L-天冬氨酸均有响应,经升温处理后,对L-天冬氨酸的响应消除,即测定L-天冬酰胺或L-谷氨酰胺时,L-天冬氨酸不再产生干扰,再经改变培养基后,L-谷氨酰胺的响应明显减小,而L-天冬酰胺的响应保持不变。 1 实验部分 PXS-215型离子活度计(上海分析仪器厂);501型氨气敏电极(江苏电分析仪器厂);3086-XY函数记录仪;812型控温磁力搅拌器(上海司乐仪器厂);THZ-82型恒温振荡器(上海跃进医疗器械一厂);电热手提高压蒸汽消毒器(上海医用核子仪器厂);LD4-2A离心机(北京医用离心机厂)。 主要试剂为0.100mol/L的L-天冬酰胺、L-谷氨酰胺和L-天冬氨酸,均用生化纯固 相似文献
79.
MI Xue-Ling LUO San-Zhong HE Jia-Qi CHENG Jin-Pei 《有机化学》2003,23(Z1):176-176
Owing to their unique chemical and physical properties, ionic liquids (ILs) have received focus attention for application as solvent alternatives. ILs can be used in place of organic solvents in synthesis, catalysis, electrochem istry and liquid/liquid extractions. The commonly reported ILs have relied on pyridinium or imidazolium cations bearing simple alkyl groups. 相似文献
80.
Jia-Qi Gu Hui Zhao Xiao-Yuan Guo Hao-Yun Sun Jing-Yi Xu Yi-Liang Wei 《Electrophoresis》2022,43(11):1183-1192
Population stratification analyses targeting genetically closely related East Asians have revealed that distinguishable differentiation exists between Han Chinese, Korean, and Japanese individuals, as well as between southern (S-) and northern (N-) Han Chinese. Previous studies offer a number of choices for ancestry informative single nucleotide polymorphisms (AISNPs) to discriminate East-Asian populations. In this study, we collected and examined the efficiency of 1185 AISNPs using frequency and genotype data from various publicly available databases. With the aim to perform fine-scale classification of S-Han, N-Han, Korean, and Japanese subjects, machine-learning methods (Softmax and Random Forest) were used to screen a panel of highly informative AISNPs and to develop a superior classification model. Stepwise classification was implemented to increase and balance the discrimination in the process of AISNP selection, first discriminating Han, Korean, and Japanese individuals, and then characterizing stratification between S-Han and N-Han. The final 272-AISNP panel is an alternative optimization of various previous works, which promises reliable and >90% accuracy in classification of the four East-Asian groups. This AISNP panel and the machine-learning model could be a useful and superior choice in medical genome-wide association studies and in forensic investigations for unknown suspect identity. 相似文献