全文获取类型
收费全文 | 44577篇 |
免费 | 10325篇 |
国内免费 | 2027篇 |
专业分类
化学 | 46617篇 |
晶体学 | 415篇 |
力学 | 894篇 |
综合类 | 52篇 |
数学 | 3273篇 |
物理学 | 5678篇 |
出版年
2023年 | 153篇 |
2022年 | 238篇 |
2021年 | 396篇 |
2020年 | 1474篇 |
2019年 | 2793篇 |
2018年 | 1205篇 |
2017年 | 870篇 |
2016年 | 3641篇 |
2015年 | 3786篇 |
2014年 | 3746篇 |
2013年 | 4578篇 |
2012年 | 3626篇 |
2011年 | 2953篇 |
2010年 | 3301篇 |
2009年 | 3295篇 |
2008年 | 2903篇 |
2007年 | 2285篇 |
2006年 | 1924篇 |
2005年 | 2017篇 |
2004年 | 1804篇 |
2003年 | 1645篇 |
2002年 | 2282篇 |
2001年 | 1620篇 |
2000年 | 1471篇 |
1999年 | 530篇 |
1998年 | 191篇 |
1997年 | 164篇 |
1996年 | 178篇 |
1995年 | 134篇 |
1994年 | 155篇 |
1993年 | 127篇 |
1992年 | 120篇 |
1991年 | 100篇 |
1990年 | 110篇 |
1989年 | 84篇 |
1988年 | 93篇 |
1987年 | 65篇 |
1986年 | 73篇 |
1985年 | 97篇 |
1984年 | 73篇 |
1983年 | 71篇 |
1982年 | 51篇 |
1981年 | 49篇 |
1980年 | 47篇 |
1979年 | 39篇 |
1977年 | 40篇 |
1976年 | 38篇 |
1975年 | 35篇 |
1974年 | 51篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Two copper complexes [Cu(TTA)2(4,4′‐azpy)] (1) and [Cu‐(TTA)2(3,3′‐azpy)] (2) (HTTA = 1,1,1‐trifluoro‐3‐(2‐thenoyl)‐acetone, 4,4′‐azpy = 4,4′‐azobispyridine, 3,3′‐azpy = 3,3′‐azobispyridine) were synthesized and characterized. The crystal structures were determined by X‐ray diffraction analysis. The crystal 1 belongs to triclinic with space group P1 , a = 0.8515(2) nm, b = 0.9259(2) nm, c = 0.9468(2) nm, a = 66.126(9)°, β = 79.667(9)°, γ = 90.13(1)°, Z = 1, V = 0.6692(2) nm3, Dc = 3.425 g/cm3, γ = 2.113 mm?1, F(000) = 694, R1 = 0.0594, wR2 = 0.1499. The crystal 2 belongs to monoclinic with space group P21/c, a = 1.0661(2) nm, b = 1.4296(3) ran, c = 1.0041(3) nm, β = 114.50(3)°, V = 1.3926(5) nm3, Z = 2, Dc = 1.646 g/ cm3, μ = 1.015 mm?1, F(000) = 694, R1, = 0.0535, wR2 = 0.1113. In the crystals of complexes 1 and 2, the copper atoms have distorted octahedral symmetry. The two compounds possess very similar one‐dimensional linear chains linked through the rodlike 4,4′‐azpy ligands or 3,3′‐azpy ligands. 相似文献
992.
The electronic structures of complexes and one‐dimensional metallomacrocycles with cyanide as bridged ligand, such as [MacM(CN)2]? and [MacM(CN)]n [Mac=phthalocyanine, tetrabenzoporphyrine; M=Co(III), Rh(III)] have been investigated using density functional theory. The results of this study show that the intrinsic semiconductivity properties depend on the frontier bands. The valence band is composed by the π‐macrocycle orbital. The conduction band for the cobalt polymers is a mixture of orbitals between this metal and the cyanide ligand along of the stacking direction. However, in the rhodium polymers such a band is exclusively composed of the π* system of the macrocycles. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002 相似文献
993.
Alexander J. Blake Binod B. De Wan‐Sheung Li Neil R. Thomas 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):m570-m574
In the title compounds, [N‐(phenyl{2‐[N‐(S)‐(2‐picolyl)prolylamino]phenyl}methylene)‐(S)‐phenylalaninato]nickel(II), [Ni(C33H30N4O3)], (I), [N‐(phenyl{2‐[N‐(S)‐(3‐picolyl)prolylamino]phenyl}methylene)‐(S)‐phenylalaninato]nickel(II) hemihydrate, [Ni(C33H30N4O3)]·0.5H2O, (II), and [N‐({2‐[N‐(S)‐ethylprolylamino]phenyl}phenylmethylene)‐(S)‐phenylalaninato]nickel(II), [Ni(C29H29N3O3)], (III), the NiII centres have approximate square‐planar coordination geometries from N3O donor sets. The picolyl N atoms in (I) and (II) are too remote from the metal centres to interact significantly, but the metal coordination geometries experience tetrahedral distortion and/or displacement of the metal centre from the N3O plane. These are linked to conformational differences between the ligands of the symmetry‐independent complexes (Z′ = 2), which in turn are related to molecular packing. In (III), where a less sterically demanding ethyl group replaces the picolyl substituents, there are none of the distortions or displacements seen in (I) and (II). 相似文献
994.
Chun‐Bo Liu Guang‐Bo Che Chuan‐Bi Li Yun‐Cheng Cui 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(4):m153-m155
An in situ reaction under hydrothermal conditions leads to the formation of the title compound, diaqua(pyridine‐2‐carboxylato)(pyridine‐2,6‐dicarboxylato)indium(II) trihydrate, [In(C6H4NO2)(C7H3NO4)(H2O)2]·3H2O, in which the central InIII atom is seven‐coordinated by one pyridine‐2,6‐dicarboxylate ligand, one pyridine‐2‐carboxylate ligand and two water molecules in a pentagonal–bipyramidal coordination environment. An indium(III)–water chain based on an unusual water pentamer is observed. 相似文献
995.
Detection of a biomarker for Alzheimer's disease from synthetic and clinical samples using a nanoscale optical biosensor 总被引:9,自引:0,他引:9
Haes AJ Chang L Klein WL Van Duyne RP 《Journal of the American Chemical Society》2005,127(7):2264-2271
A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease. 相似文献
996.
Young Hyun Cho Wanno Lee Kun Ho Chung Geun Sik Choi Chang Woo Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):531-538
The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level
of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a
higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased
with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the
high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and
the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological
and meteorological conditions. 相似文献
997.
Yi‐Zhen Tang Hao Sun Ya‐Ru Pan Xiu‐Mei Pan Rong‐Shun Wang 《International journal of quantum chemistry》2007,107(6):1495-1501
The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
998.
Wei Sun Yan‐Tuan Li Zhi‐Yong Wu Ning‐Yu Xiao 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(3):m111-m113
In the crystal structure of the title complex, [Ni2(C10H20N4O2)(C12H12N2)2](ClO4)2 or [Ni(dmaeoxd)Ni(dmbp)2](ClO4)2 {H2dmaeoxd is N,N′‐bis[2‐(dimethylamino)ethyl]oxamide and dmbp is 4,4′‐dimethyl‐2,2′‐bipyridine}, the deprotonated dmaeoxd2− ligand is in a cis conformation and bridges two NiII atoms, one of which is located in a slightly distorted square‐planar environment, while the other is in an irregular octahedral environment. The cation is located on a twofold symmetry axis running through both Ni atoms. The dmaeoxd2− ligands interact with each other via C—H⋯O hydrogen bonds and π–π interactions, which results in an extended chain along the c axis. 相似文献
999.
3-Mercaptopropionic acid monolayer protected gold nanoclusters (MPA-MPCs) were synthesized and characterized by transmission electorn microscopy,UV-Vis spectroscopy,X-ray photoelectron spectroscopy and Fourler transform infrared spectroscopy.The exact value of quantized double-layer capacitance of MPCs in aqueous media was obtained by differential pulse voltammograms. 相似文献
1000.
Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied by AMI MO calculations, and the results are compared with those of the MNDO method. It was found that the two semi- empirical methods predict essentially the same proton transfer mechanism, but MNDO tends to overestimate the activation barriers. Participation of one solvate vater in the proton transfer led to a considerable lovering of the activation barrier, by nearly the same amount, in both methods. One notable conflict between the two methods was that the methoxy-O-protonated form of methyl carbamate, in the gas phase, can be a local energy minimum with MNDO, whereas it leads to dissociation into two species Instead of an optimized structure with AM1. It was concluded that the MNDO method can be useful for this type of process, especially when one is interested in the relative activation barriers only. 相似文献