全文获取类型
收费全文 | 2055篇 |
免费 | 54篇 |
国内免费 | 174篇 |
专业分类
化学 | 807篇 |
晶体学 | 9篇 |
力学 | 342篇 |
综合类 | 9篇 |
数学 | 554篇 |
物理学 | 562篇 |
出版年
2024年 | 5篇 |
2023年 | 31篇 |
2022年 | 22篇 |
2021年 | 24篇 |
2020年 | 26篇 |
2019年 | 43篇 |
2018年 | 30篇 |
2017年 | 43篇 |
2016年 | 55篇 |
2015年 | 52篇 |
2014年 | 83篇 |
2013年 | 158篇 |
2012年 | 163篇 |
2011年 | 168篇 |
2010年 | 125篇 |
2009年 | 141篇 |
2008年 | 95篇 |
2007年 | 99篇 |
2006年 | 95篇 |
2005年 | 94篇 |
2004年 | 77篇 |
2003年 | 66篇 |
2002年 | 48篇 |
2001年 | 44篇 |
2000年 | 32篇 |
1999年 | 41篇 |
1998年 | 34篇 |
1997年 | 41篇 |
1996年 | 41篇 |
1995年 | 21篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 17篇 |
1987年 | 24篇 |
1986年 | 9篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 1篇 |
排序方式: 共有2283条查询结果,搜索用时 15 毫秒
211.
金属和试剂分别过量时测定不同配合物组成的新方法何锡文,唐志新,张贵珠,杨万龙,于贵英,史慧明(南开大学化学系,天津,300071)关键词配合物组成,穷举法,光度分析本文用穷举法推导了一种新的数学模型,该法不需要假定配合比,就能测定当试剂和金属分别过量... 相似文献
212.
对近期发展的固体圆二色(CD)光谱测试方法进行了概述、评价和比较, 着重探讨了“浓度效应”的存在使固体CD光谱失真的原因. 通过对本课题组和其他作者已报道的四种化合物的固体CD谱再测试的反思, 强调了依手性化合物的手性光谱学性质不同, 根据浓度梯度实验选择其合适测试浓度的必要性. 对固有手性的阻转异构化合物(S)-1,1'-联二萘酚(S-BINOL)进行了成膜法固体CD谱浓度梯度测试, 发现所得固体薄膜CD谱中也存在着“浓度效应” 相似文献
213.
Five new Cu(II) complexes [Cu(psa)(phen)] · 3H2O (1), [Cu(psa)(2bpy)] · 0.5H2O (2), [Cu(psa)(2bpy)(H2O)] · 3H2O (3), [Cu(psa)(4bpy)] · H2O (4), and [Cu(psa)0.5(N3)(2bpy)] (5) (H2psa = phenylsuccinic acid, phen = 1,10-phenanthroline, 2bpy = 2,2′-bipyridine, and 4bpy = 4,4′-bipyridine) were obtained under solvothermal conditions and characterized by single-crystal X-ray diffraction. Complexes 2 and 3 were formed by one-pot reaction. In complex 2, Cu(II) ion is four-coordinated and locates at a slightly distorted square center. In complex 3, the coordinated water molecule occupies the axial site of Cu(II) ion forming a tetragonal pyramid geometry. Complexes 1 and 3 are of 1D chain structures, and extended into 2D supramolecular network by hydrogen bonds. Complex 2 is of zipper structure, and further assembled into 2D supramolecular network by hydrogen bonds and π–π stacking interactions. Complex 4 is a 3D CdSO4-like structure with twofold interpenetration, while complex 5 is a dinuclear compound. The different structures of complexes 1–5 can be attributed to using the auxiliary ligands, indicating an important role of the auxiliary ligands in assembly and structure of the title complexes. 相似文献
214.
Two novel 3D coordination polymers {[Mn(aip)(DMF)]}n, CPO-9, and {[Mn3(Hatp)2(atp)2](H2O)2(DEF)4}n CPO-10 (aip = 5-aminoisophthalate, atp = 2-aminoterephthalate, DMF = dimethylformamide, DEF = diethylformamide) have been synthesized by solvothermal methods. Their properties have been studied by single-crystal X-ray diffraction, thermogravimetric analysis, high-temperature powder X-ray diffraction and magnetic susceptibility measurements. The crystal structure of CPO-9 is based on infinite chains of carboxylato-bridged five-coordinated Mn(II) ions that are crosslinked via the aip ligands to form a 3D structure. CPO-10 is based on linear trinuclear building units of carboxylato-bridged octahedral Mn(II) ions that are crosslinked by the atp ligands into a 3D structure. Both compounds have 1D channels that contain solvent molecules. The solvent accessible void volume for CPO-10 is 51.9% of the unit cell volume. For both compounds, however, the solvent molecules cannot be removed without the collapse of the structures into amorphous phases at 250 °C. The magnetic susceptibility measurements indicate antiferromagnetic couplings between the Mn(II) ions in both compounds. The magnetic data have been fitted using theoretical approaches. 相似文献
215.
对近期发展的固体圆二色(CD)光谱测试方法进行了概述、评价和比较, 着重探讨了“浓度效应”的存在使固体CD光谱失真的原因. 通过对本课题组和其他作者已报道的四种化合物的固体CD谱再测试的反思, 强调了依手性化合物的手性光谱学性质不同, 根据浓度梯度实验选择其合适测试浓度的必要性. 对固有手性的阻转异构化合物(S)-1,1'-联二萘酚(S-BINOL)进行了成膜法固体CD谱浓度梯度测试, 发现所得固体薄膜CD谱中也存在着“浓度效应” 相似文献
216.
Magnetic diphase nanostructures of ZnFe2O4/γ-Fe2O3 were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe2O4/γ-Fe2O3 was formed, in which the presence of ZnFe2O4 enhanced the thermal stability of γ-Fe2O3. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe2O3. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe2O3 content. 相似文献
217.
Amor Ben Ali Minh Trang Dang Annie Hémon-Ribaud Vincent Maisonneuve 《Journal of solid state chemistry》2007,180(6):1911-1917
Single crystals of [H3dien]·(FeF6)·H2O (I) and [H3dien]·(CrF6)·H2O (II) are obtained by solvothermal synthesis under microwave heating. I is orthorhombic (Pna21) with a=11.530(2) Å, b=6.6446(8) Å, c=13.787(3) Å, V=1056.3(2) Å3 and Z=4. II is monoclinic (P21/c) with a=13.706(1) Å, b=6.7606(6) Å, c=11.3181(9) Å, β=99.38(1)°, V=1034.7(1) Å3 and Z=4. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R1/wR2 reliability factors 0.028/0.066 for I and 0.035/0.102 for II. The structures of I and II are built up from isolated FeF6 or CrF6 octahedra, water molecules and triprotonated amines. In both structures, each octahedron is connected by hydrogen bonds to six organic cations and two water molecules. The iron-based compound is also characterized by 57Fe Mössbauer spectrometry: the hyperfine structure confirms the presence of Fe3+ in octahedral coordination and reveals the existence of paramagnetic spin fluctuations. 相似文献
218.
Igor Djerdj Georg Garnweitner Markus Niederberger 《Journal of solid state chemistry》2007,180(7):2154-2165
The preparation of lanthanum hydroxide and manganese oxide nanoparticles is presented, based on a nonaqueous sol-gel process involving the reaction of La(OiPr)3 and KMnO4 with organic solvents such as benzyl alcohol, 2-butanone and a 1:1 vol. mixture thereof. The lanthanum manganese oxide system is highly complex and surprising results with respect to product composition and morphology were obtained. In dependence of the reaction parameters, the La(OH)3 nanoparticles undergo a shape transformation from short nanorods with an average aspect ratio of 2.1 to micron-sized nanofibers (average aspect ratio is more than 59.5). Although not directly involved, KMnO4 plays a crucial role in determining the particle morphology of La(OH)3. The reason lies in the fact that KMnO4 is able to oxidize the benzyl alcohol to benzoic acid, which presumably induces the anisotropic particle growth in [0 0 1] direction upon preferential coordination to the ±(1 0 0), ±(0 1 0) and ±(−110) crystal facets. By adjusting the molar La(OiPr)3-to-KMnO4 ratio as well as by using the appropriate solvent mixture it is possible to tailor the morphology, phase purity and microstructure of the La(OH)3 nanoparticles. Postsynthetic thermal treatment of the sample containing La(OH)3 nanofibers and β-MnOOH nanoparticles at the temperature of 800 °C for 8 h yielded polyhedral LaMnO3 and worm-like La2O3 nanoparticles as final products. 相似文献
219.
Qing-Long Bai Chun-Hua Zhang Juan-Juan Song Jing-Hai Liu Yan-Chun Feng Li-Mei Duan Chuan-Hui Cheng 《中国化学快报》2016,27(5):764-768
A metal-free purple H2Pc single crystal was synthesized by a facile solvothermal method, and its solubility and near-infrared (NIR) optical properties were also investigated due to its potential applications as a light-emitting layer for OLEDs. The H2Pc single crystal is insoluble in 1-chlorine naphthalene and other organic solvents. It gives a wide absorption in the range from 620 nm to 679 nm and a wide emission in near 922 nm. As an active light-emitting layer, H2Pc was employed to fabricate electroluminescent (EL) devices with a structure of ITO/NPB (30 nm)/Alq3:H2Pc (30 nm)/BCP (20 nm)/Alq3 (20 nm)/Al. The emission center is at 936 nm when the H2Pc doping concentration is 20 wt%. The doping concentration strongly governs the emission intensity. When doping concentration decreases from 10 wt% to 1 wt%, the emission intensity remarkably fades, and simultaneously the emission center undergoes a blue shift. 相似文献
220.
As a pivotal domain within envelope protein, fusion peptide (FP) plays a crucial role in pathogenicity and therapeutic intervention. Taken into account the limited FP annotations in NCBI database and absence of FP prediction software, it is urgent and desirable to develop a bioinformatics tool to predict new putative FPs (np-FPs) in retroviruses. In this work, a sequence-based FP model was proposed by combining Hidden Markov Method with similarity comparison. The classification accuracies are 91.97% and 92.31% corresponding to 10-fold and leave-one-out cross-validation. After scanning sequences without FP annotations, this model discovered 53,946 np-FPs. The statistical results on FPs or np-FPs reveal that FP is a conserved and hydrophobic domain. The FP software programmed for windows environment is available at https://sourceforge.net/projects/fptool/files/?source=navbar. 相似文献