全文获取类型
收费全文 | 8958篇 |
免费 | 457篇 |
国内免费 | 1448篇 |
专业分类
化学 | 8727篇 |
晶体学 | 116篇 |
力学 | 346篇 |
综合类 | 48篇 |
数学 | 105篇 |
物理学 | 1521篇 |
出版年
2024年 | 27篇 |
2023年 | 113篇 |
2022年 | 217篇 |
2021年 | 232篇 |
2020年 | 276篇 |
2019年 | 223篇 |
2018年 | 190篇 |
2017年 | 248篇 |
2016年 | 391篇 |
2015年 | 313篇 |
2014年 | 332篇 |
2013年 | 504篇 |
2012年 | 604篇 |
2011年 | 533篇 |
2010年 | 473篇 |
2009年 | 659篇 |
2008年 | 655篇 |
2007年 | 559篇 |
2006年 | 546篇 |
2005年 | 458篇 |
2004年 | 388篇 |
2003年 | 311篇 |
2002年 | 226篇 |
2001年 | 228篇 |
2000年 | 222篇 |
1999年 | 190篇 |
1998年 | 186篇 |
1997年 | 161篇 |
1996年 | 152篇 |
1995年 | 149篇 |
1994年 | 146篇 |
1993年 | 136篇 |
1992年 | 93篇 |
1991年 | 83篇 |
1990年 | 65篇 |
1989年 | 46篇 |
1988年 | 67篇 |
1987年 | 54篇 |
1986年 | 53篇 |
1985年 | 49篇 |
1984年 | 61篇 |
1983年 | 34篇 |
1982年 | 69篇 |
1981年 | 40篇 |
1980年 | 31篇 |
1979年 | 37篇 |
1978年 | 13篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1966年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
Moon Hwan Cho Seung Chang Yang Nam Keun Yang Yongjin Kang Jaejung Ko 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(4):279-287
The thermodynamic parameters for the interaction of Cu2+, Ni2+, Co2+, Cd2+, andAg+ with the new title ligand have been determined by titration calorimetry in 50% THF–methanol (V/V) at 25 °C.Ag+ exhibited remarkably higher complexation selectivity.Ag+ and several transition metal ions have been transportedusing this ligand as carrier in a bulk liquid membrane. CompetitiveAg+–M2+ transport studies have also beencarried out for the same system. In this membrane transport study, high transport of Ag+ was observed in both single and competitiveAg+–M2+ transport studies. The complexformation of N,N-bis[o-(diphenylphosphino)benzylidene]ethylenediamine (P2N2) with silver,[Ag(P2N2)] (NO3), (1) is reported. Complex 1 has been characterized by X-ray crystallography. 1 ismonoclinic, space group P21/n (No. 14), with cell dimensionsa = 13.398(4) , b=12.577(5) , c = 21.521(4) , =100.14(2) , V = 3570(2) 3 and Z = 4. 相似文献
92.
Sodium-dicyclohexyl- 18-crown-6 complex cation was used as carrier for the uphill transport of zinc as Zn(SCN)42? complex anion. By using L-cysteine as a metal ion acceptor in the receiving phase at the optimized pH of 7.6, the amount of zinc transport through the liquid membrane after 90 min was 97.2 ± 1.0%. The selectivity and efficiency of zinc transport from aqueous solutions containing equimolar mixtures of Ag+, Cd2+ Co2+, Cu2+, Fe2+, Ni2+, Pb2+, Pd2+, Sr2+, Bi3+, Cr3+ and Fe3+ ions was investigated. In the presence of NH2OH.HCl as a suitable masking agent in the source phase, the interfering effect of Cu2+ and Pb2+ ions was diminished drastically. 相似文献
93.
As12Se44—: a New Selenoarsenate Anion with a Polyarsenic Cage in the Compound [Co(NH3)6]2As12Se4 · 12 NH3 Orange coloured crystals of [Co(NH3)6]2As12Se4 · 12 NH3 were prepared by the reduction of As4Se4 with a solution of sodium in liquid ammonia and subsequent precipitation with CoBr2. The X‐ray structure determination shows them to contain the selenoarsenate anion As12Se44—, which consists of a central As12‐cage with four exo‐bonded, formally negatively charged Se atoms. The structure of the As12‐cage is equivalent to the main polyphosphorus building unit of a known organopolyphosphane and of tubular P12 in the compound (CuI)3P12. 相似文献
94.
A comparison is made between the distribution of residue preferences, three dimensional nearest neighbour contacts, preferred rotamers, helix-helix crossover angles and peptide bond angles in three sets of proteins: a non-redundant set of accurately determined globular protein structures, a set of four-helix bundle structures and a set of membrane protein structures. Residue preferences for the latter two sets may reflect overall helix stabilising propensities but may also highlight differences arising out of the contrasting nature of the solvent environments in these two cases. The results bear out the expectation that there may be differences between residue type preferences in membrane proteins and in water soluble globular proteins. For example, the -branched residue types valine and isoleucine are considerably more frequently encountered in membrane helices. Likewise, glycine and proline, residue types normally associated with `helix-breaking' propensity are found to be relatively more common in membrane helices. Three dimensional nearest neighbour contacts along the helix, preferred rotamers, and peptide bond angles are very similar in the three sets of proteins as far as can be ascertained within the limits of the relatively low resolution of the membrane proteins dataset. Crossing angles for helices in the membrane protein set resemble the four helix bundle set more than the general non-redundant set, but in contrast to both sets they have smaller crossing angles consistent with the dual requirements for the helices to form a compact structure while having to span the membrane. In addition to the pairwise packing of helices we investigate their global packing and consider the question of helix supercoiling in helix bundle proteins. 相似文献
95.
用电纺法制备了TiO2/P(VdF-HFP)(聚偏氟乙烯-六氟丙烯共聚物)杂化纤维微孔膜, 用SEM观察了杂化纤维微孔膜的形貌, 并测算了这类由超细纤维相互搭接而形成的微孔膜的孔隙率. 这种微孔膜吸附LiPF6/EC-DMC-EMC(碳酸乙烯酯-二甲基碳酸酯-碳酸甲乙酯)电解质溶液后得到凝胶聚合物电解质膜. 用电化学方法测试了聚合物电解质膜的离子电导率、锂离子迁移数等参数, 并研究了TiO2纳米晶的掺入对聚合物电解质电化学性能的影响. 结果表明, TiO2的掺入降低了P(VdF-HFP)聚合物基体的结晶度, 改善了凝胶聚合物电解质的低温电化学性能. 相似文献
96.
基于芘的荧光熄灭的单质碘荧光敏感膜的研究 总被引:8,自引:0,他引:8
单质碘熄灭固定于增塑的PVC膜中的芘的荧光,且这种熄灭作用可逆。本据此研制了用于测定单质碘浓度的荧光敏感膜,最佳膜组成为2~4mg芘、50mgPVC粉、100mg邻苯二甲酸二异辛酯,测定碘的浓度范围为2.26×10^-5~1.04×10^-3mol/L。此膜测定单质碘的重现性好,响应时间小于40s。除Fe^3+、Bi^3+外,其它常见离子均无干扰。将此膜用于食盐中碘的测定,结果令人满意。 相似文献
97.
热致液晶共聚酯酰胺/PET共混物的流变性能和原位增强特性 总被引:3,自引:1,他引:3
采用Instron3211型毛细管流变仪研究了PEA/PET共混物的流变性能,据此探讨共混物熔体的可纺性,讨论了共混物配比与复合纤维力学性能的关系,并且偏光显微镜,扫描电镜研究纤维的结构。结果表明,共混物的表观粘度低于PET的粘度,当PEA为10%,共混物的表观粘度达到最小值;且PEA含量低于10%时,共混物的可纺性即,表现出良好的原位增强效果。 相似文献
98.
Jingye Li Fumihiro Muto Akihiro Oshima Masakazu Washio Shigetoshi Ikeda Yoneho Tabata Chihiro Matsuura 《European Polymer Journal》2006,42(6):1222-1228
New proton exchange membranes (PEMs) were prepared by pre-irradiation induced grafting of α-methylstyrene (AMS)/styrene (STY)/divinylbenzene (DVB) into the crosslinked polytetrafluoroethylene (RX-PTFE) films and successively sulfonated. The new PEMs showed the improved glass transition temperature and chemical stability as compared with the PEMs prepared by pre-irradiation induced grafting of STY/DVB. The balance of the cost, grafting kinetic, thermal properties and the properties of the resulted proton exchange membrane is the key point of this work. 相似文献
99.
A high sensitivity, multichannel fluorescence detector with small volume has been developed for capillary column liquid chromatography. Using an intensified linear photodiode array to monitor fluorescence emission, several important mixtures exhibiting native fluorescence have been examined following high efficiency separation on a capillary column. By correlating mass spectral, fluorescence spectral, and retention time data, information of potential utility in the structural elucidation of aromatic molecules contained in complex mixtures can be obtained. Examples include the separation and spectral examination of the polyaromatic compounds in samples of both biological and environmental interest. 相似文献
100.
一类新的毛细管气相色谱固定液—侧链液晶冠醚聚硅氧烷的研究 总被引:7,自引:0,他引:7
合成了一种新的毛细管气相色谱用固定液——侧链含冠醚液晶的聚硅氧烷,这种固定液易于涂渍在弹性石英毛细管柱上,柱效高,热稳定性好,极性中等,它具有高分子液晶和高分子冠醚固定液的双重保留性能,适于分离多种异构体。 相似文献