全文获取类型
收费全文 | 11182篇 |
免费 | 894篇 |
国内免费 | 711篇 |
专业分类
化学 | 7385篇 |
晶体学 | 293篇 |
力学 | 335篇 |
综合类 | 43篇 |
数学 | 1535篇 |
物理学 | 3196篇 |
出版年
2023年 | 103篇 |
2022年 | 228篇 |
2021年 | 207篇 |
2020年 | 240篇 |
2019年 | 308篇 |
2018年 | 251篇 |
2017年 | 232篇 |
2016年 | 307篇 |
2015年 | 297篇 |
2014年 | 409篇 |
2013年 | 841篇 |
2012年 | 643篇 |
2011年 | 727篇 |
2010年 | 515篇 |
2009年 | 518篇 |
2008年 | 551篇 |
2007年 | 527篇 |
2006年 | 462篇 |
2005年 | 364篇 |
2004年 | 322篇 |
2003年 | 328篇 |
2002年 | 303篇 |
2001年 | 204篇 |
2000年 | 206篇 |
1999年 | 147篇 |
1998年 | 103篇 |
1997年 | 112篇 |
1996年 | 130篇 |
1995年 | 126篇 |
1994年 | 134篇 |
1993年 | 122篇 |
1992年 | 137篇 |
1991年 | 110篇 |
1990年 | 95篇 |
1989年 | 119篇 |
1988年 | 82篇 |
1986年 | 87篇 |
1985年 | 130篇 |
1984年 | 123篇 |
1983年 | 98篇 |
1982年 | 100篇 |
1981年 | 103篇 |
1980年 | 85篇 |
1979年 | 99篇 |
1978年 | 76篇 |
1977年 | 103篇 |
1976年 | 81篇 |
1975年 | 87篇 |
1974年 | 92篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants
of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of
SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric,
molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study
the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable
protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species
in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the
ligand at room temperature and stabilization of a single conformer upon complex formation have been established from1H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate
highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed
for an orthorhombic crystal system. 相似文献
32.
Suoyuan Lian Lei Gao Zhenhui Kang Di Wu Yang Lan Lin Xu 《Solid State Communications》2004,132(6):375-378
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed. 相似文献
34.
高分子阳离子絮凝剂用于炼油废水处理研究 总被引:15,自引:0,他引:15
用聚二甲基二烯丙基氯化铵型高分子阳离子絮凝剂处理炼油废水考察了险油和化学耗氧量的动态变化规律。对产生的浮渣性质及滤饼的成份进行了研究。并且与聚合铝的处理效果进行对照。研究结果表明,HCA除油和化学耗管氧量的性能优于PAC,HCA产生的浮渣是PAC的三分之一,而浮渣中的含油量则是PAC的三倍。 相似文献
35.
S. Balasubrahmanyam B. Viswanathan V. R. S. Rao J. C. Kuriacose 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(3):301-309
The effect of60Co -radiation on La2CuO4 solid catalyst prepared by the ceramic method has been studied. Gamma irradiation of La2CuO4 samples has been found to increase the Cu+ content, electrical conductivities and decrease the magnetic susceptibilities of the catalyst. The results have been interpreted on the basis of the crystal field model of the structure of La2CuO4. 相似文献
36.
37.
38.
本文采用电导、pH滴定法研究了乙醇-水溶液中希土与1′-苯基-3′-甲基-5′-氧代吡唑-4′-基乙醛酸(简称H2A)的配位反应.合成了15种新的希土固态配合物.通过元素分析、化学分析、水份分析确定了配合物的化学组成为RE(HA)3·nH2O(RE=Ce、Pr、Sm、Tm、Lu、n=1;RE=La、Nd、Eu、Gd、Tb、Dy、Ho、Er、Yb、Y,n=1-2).并对配合物的红外光谱、核磁共振谱、热稳定性、紫外光谱、溶解性及摩尔电导进行了测定. 相似文献
39.
Svein G. Dahl Peter A. Kollman Shashidhar N. Rao U. Chandra Singh 《Journal of computer-aided molecular design》1992,6(3):207-222
Summary The side-chain conformations of psychoactive phenothiazine drugs in crystals are different from those of biologically inactive ring sulfoxide metabolites. This study examines the potential energies, molecular conformations and electrostatic potentials in chlorpromazine, levomepromazine (methotrimeprazine), their sulfoxide metabolites and methoxypromazine. The purpose of the study was to examine the significance of the different crystal conformations of active and inactive phenothiazine derivatives, and to determine why phenothiazine drugs lose most of their biological activity by sulfoxidation. Quantum mechanics and molecular mechanics calculations demonstrated that conformations with the side chain folded over the ring structure had lowest potential energy in vacuo, both in the drugs and in the sulfoxide metabolites. In the sulfoxides, side chain conformations corresponding to the crystal structure of chlorpromazine sulfoxide were characterized by stronger negative electrostatic potentials around the ring system than in the parent drugs. This may weaken the electrostatic interaction of sulfoxide metabolites with negatively charged domains in dopamine receptors, and cause the sulfoxides to be virtually inactive in dopamine receptor binding and related pharmacological tests. 相似文献
40.
Two layered amine-templated cobalt squarates, [C6N2H14]2[Co2(C4O4)3(H2O)4], I, and [C3N2H5]2[Co2(C4O4)3(H2O)4], II, have been prepared under hydrothermal conditions. Both I and II contain chains formed by dimers comprising two cobalt atoms bound to the squarate units, the chains being connected through hydrogen bond interactions. An amine-templated cobalt squarate of the formula [C4N2H12][Co(C4O4)2(H2O)4][H2O]2, III, as well as its Ni, Zn and Cd analogues have been prepared by room temperature reactions. III has a layered architecture wherein the cobalt-squarate monomers are linked by the amine molecules. Co and Zn analogues of [Ni(C4O4)(H2O)2(C3N2H4)] with ligating imidazole units have also been prepared and characterized. 相似文献