全文获取类型
收费全文 | 3427篇 |
免费 | 99篇 |
国内免费 | 397篇 |
专业分类
化学 | 3067篇 |
晶体学 | 27篇 |
力学 | 51篇 |
数学 | 9篇 |
物理学 | 769篇 |
出版年
2024年 | 12篇 |
2023年 | 298篇 |
2022年 | 81篇 |
2021年 | 87篇 |
2020年 | 109篇 |
2019年 | 109篇 |
2018年 | 83篇 |
2017年 | 93篇 |
2016年 | 104篇 |
2015年 | 85篇 |
2014年 | 110篇 |
2013年 | 183篇 |
2012年 | 304篇 |
2011年 | 203篇 |
2010年 | 168篇 |
2009年 | 224篇 |
2008年 | 199篇 |
2007年 | 220篇 |
2006年 | 180篇 |
2005年 | 141篇 |
2004年 | 147篇 |
2003年 | 89篇 |
2002年 | 62篇 |
2001年 | 72篇 |
2000年 | 57篇 |
1999年 | 62篇 |
1998年 | 68篇 |
1997年 | 60篇 |
1996年 | 49篇 |
1995年 | 39篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 24篇 |
1991年 | 27篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1975年 | 15篇 |
1968年 | 1篇 |
排序方式: 共有3923条查询结果,搜索用时 828 毫秒
91.
Pasynskii A. A. Grigoriev V. N. Torubaev Yu. V. Blokhin A. I. Shapovalov S. S. Dobrokhotova Zh. V. Novotortsev V. M. 《Russian Chemical Bulletin》2003,52(12):2689-2700
Transmetallation of the dichalcogenide complexes [CpMn(CO)2]2(-X2) (X = S or Se) with M(CO)5(thf) (M = Cr or W) afforded new heterometallic complexes CpMn(CO)2(-Se2)Cr(CO)5, CpMn(CO)2(-Se2)[Cr(CO)5]2, CpMn(CO)2(-X2)[W(CO)5]2 (X = S or Se), and CpMn(CO)2(-Se2)[Cr(CO)5][W(CO)5]. According to the X-ray diffraction data, their molecular structures contain the cyclic MnX2 fragments coordinated by one or two M(CO)5 groups via the X atoms. Study of thermal decomposition of the manganese complexes with different Mn : M : X ratios (M = Cr, W; X = S, Se, Te) by differential scanning calorimetry (DSC) and thermogravimetry demonstrated that this process took place at rather low temperatures (100—400 °C) and was accompanied by complete elimination of the CO groups followed by elimination of the Cp groups. At any metal to chalcogen ratio, the resulting inorganic chalcogenides contained no impurities of metal oxides and carbides. 相似文献
92.
简要总结了我们在C=C及C=O双键低温加氢双金属催化剂方面的最新研究成果. 首先, 我们以环己烯加氢为探针反应, 证明了平行使用多种研究手段的重要性, 包括单晶表面的基础研究与DFT计算, 多晶表面的合成与表征, 负载型催化剂的制备与性能测试等. 其次, 总结了双金属催化剂在其他加氢反应, 如丙烯醛C=O双键的选择性加氢, 苯的低温加氢, 以及乙炔的选择性加氢等反应中的应用. 最后, 讨论了利用金属碳化物代替贵金属Pt以减少双金属催化剂中Pt用量的可能性. 相似文献
93.
We have produced nanophase metal clusters, (Fe)n, (Cr)n, (Mo)n and (W)n, by multiphoton decomposition of the corresponding metal carbonyls with a 10.6 μm CO2 laser in the presence of Ar and SF6. The size distribution was narrow and the average diameter was 6, 3.5, 2 and 1 nm for Fe, Cr, Mo and W clusters, respectively. The structure was found to be bcc for both Fe and Cr clusters, fcc for Mo clusters, and amorphous for W clusters (note that all the bulk metals have bcc structure). Considering the cluster sizes (9630, 1870, 230 and 30 for Fe, Cr, Mo and W clusters, respectively) estimated from their average diameters, it is likely that there exists a structural transition from fcc to bulk bcc with increasing cluster size in these metal clusters. 相似文献
94.
Valfredo Azevedo Lemos Douglas Gonalves da Silva Anaildes Lago de Carvalho Dbora de Andrade Santana Geisiane dos Santos Novaes Adenilde Souza dos Passos 《Microchemical Journal》2006,84(1-2):14-21
A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through –N=C– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as packing for the minicolumn in an on-line system preconcentration system for cadmium, cobalt, copper and nickel determination. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer–burner system of the flame atomic absorption spectrometer (FAAS). Elution of all metals from minicolumn can be made with 0.50 mol L− 1 HCl or HNO3. The enrichment factors obtained were 16 (Cd), 24 (Co), 15 (Cu) and 19 (Ni), for 60 s preconcentration time, and 39 (Cd), 69 (Co), 36 (Cu) and 41 (Ni), if used 180 s preconcentration time. Under the optimum conditions, the proposed procedure allowed the determination of cadmium, cobalt, copper and nickel with detection limits of 0.31, 0.32, 0.39 and 1.64 μg L− 1, respectively, when used preconcentration periods of 180 s. The accuracy of the developed procedure was sufficient and evaluated by the analysis of the certified reference materials NIST 1515 apple leaves and NIST 1570a spinach leaves. The method was applied to the analysis of food samples (spinach, black tea and rice flour). 相似文献
95.
Metal(II) tetranitro phthalocyanines of cobalt, nickel and copper are synthesized in pure state by a novel modified method. The complexes are characterized using elemental, electronic and IR spectral studies. Pure metal(II) tetra-amino phthalocyanines of cobalt, nickel and copper are synthesized by reducing the nitro groups of the above complexes using sodium sulphide. These complexes are also characterized by elemental, electronic, IR spectral and magnetic susceptibility measurements. The nature of the electrical conductivities of the above three metal(II) tetra-amino phthalocyanine derivatives are studied in the temperature range 303-473 K and the data are presented. Among the effect of various substituent groups on the electrical conducting property of phthalocyanine, amine group substituent on the peripheral benzene ring of the phthalocyanine molecule has been found to increase electrical conductivity to a greatest extent. These complexes showed about 105-106 times higher electrical conductivities compared to their parent phthalocyanine compounds. 相似文献
96.
The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2 eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance factor. (2) When A is one of the heavier alkaline earth metals (Ca, Sr, Ba) and B a transition metal, stable compounds ABH3 result only when B is from the Fe, Co, or Ni groups. This stability trend is basically determined by effects associated with d band filling of both the transition metal and the hydride. In contrast to group (1) perovskites, the transition metal-containing compounds are metals. The synthesis of CaNiH3 and its structure determination from CaNiD3 is reported. This compound is a type (2) perovskite hydride with a fully occupied hydrogen position (CaNiD3: a=3.551(4) Å, dNi-D=1.776(2) Å). Its stability is discussed with respect to transition metal hydrides with complex anions (e.g., Mg2NiH4, Na2PdH2, Sr2PdH4). 相似文献
97.
Development in the area of UV-crosslinkable solvent-based pressure-sensitive adhesives with excellent shrinkage resistance 总被引:1,自引:0,他引:1
Zbigniew Czech 《European Polymer Journal》2004,40(9):2221-2227
Solvent-based UV-crosslinkable pressure-sensitive adhesives (PSA) present a new class of products that offers the potential to produce a novel generation of ultraviolet cured self-adhesive products with excellent shrinkage resistance. A variety of solvent-based pressure-sensitive adhesives were prepared by synthesis in ethyl acetate with solid content on 50 wt.% with 2-ethylhexyl acrylate, methyl acrylate, acrylic acid, N-vinyl caprolactam and unsaturated photoinitiators: 4-acryloyloxy benzophenone, allyl benzoine and phenyl-(1-acryloyloxy)-cyclohexyl ketone. The main emphasis is given to the influence of viscosity and molecular mass of synthesized adhesive on their shrinkage. Further trials show the effect of the UV-crosslinking process with UV-lamp and comparison with acrylics PSA crosslinked with metal chelates aluminium acetylacetonate and titanium acetylacetonate on shrinkage. Further examinations describe the influence of various factors such as UV exposure time and UV dose on very relevant PSA performance such as shrinkage on coated PVC carrier. 相似文献
98.
Cadmium colloids have been prepared by Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming, stable liquid colloids are formed with particle size ranging between 25–100 Å. Zeta potentials were calculated according to the conversion of Hunter and the Hückel equation, for ethanol and dimethyl sulphoxide. UV/VIS measurement of most of the black colloids showed absorption band around 280 nm. For comparison, we prepared CdS colloid with size 400–625 Å. The colloids are stable to oxidation in air and/or oxygen bubbling. The synthesis of colloids and films from Cd with acetone, 2-butanone, ethanol, 2-propanol, 2-methoxyethanol, DMF and DMSO is reported. Transmission Electron Microscopy (TEM) allows us to determine particle size. 相似文献
99.
The absorption spectra and emission spectral band shapes of several polypyridine-ligand (PP) bridged bis-ruthenium(II) complexes imply that the Ru(II)/Ru(III) electronic coupling is weak in their lowest energy metal to ligand charge transfer (MLCT) excited states. Many of these PP-bridging ligands contain pyrazine moieties and the weak electronic coupling of the excited states contrasts to the strong electronic coupling inferred for the correlated mixed-valence ground states. Although the bimetallic complexes emit at significantly lower energy than their monometallic analogs, the vibronic contributions to their 77 K emission spectra are much stronger than expected based on comparison to the monometallic analogs (around twofold in some complexes) and this feature is characteristic of bimetallic complexes in which the mixed-valence excited states are electronically localized. The weaker excited state than ground state donor/acceptor electronic coupling in this class of complexes is attributed to PP-mediated super-exchange coupling in which the mediating orbital of the bridging ligand (PP-LUMO) is partly occupied in the MLCT excited states, but is unoccupied in the ground states; therefore, the vertical Ru(III)-PP− (MLCT) energy is larger and the mixing coefficient smaller in these excited states than is found for Ru(II)-PP in the corresponding ground states. 相似文献
100.
Chains, ladders and sheets of d metal–organic polymers generated from the flexible bipyridyl ligands
Yaqiong Gong Ruihu Wang Daqiang Yuan Weiping Su Yougui Huang Chengyang Yue Feilong Jiang Maochun Hong 《Polyhedron》2007,26(18):5309-5316
By use of the three-layer diffusion method, reactions of flexible bipyridyl ligands (4,4′-bpp or 3,3′-bpp) with M(II) salts (M = Zn, Cd) and multi-carboxylate ligands resulted in the formation of four interesting d10 metal–organic coordination polymers: [Zn(μ-4,4′-bpp)Br2]n (1), [Zn(μ-4,4′-bpp)(1,2-bdc)]n · nH2O (2), [Zn(μ-3,3′-bpp)(1,3-bdc)]n · nCH3OH · 2nH2O (3) and [Cd(μ-3,3′-bpp)(C4H2O4)]n · 3nH2O (4) (4,4′-bpp = 2,2′-bis(4-pyridylmethyleneoxy)-1,1′-biphenylene; 3,3′-bpp = 2,2 ′-bis(3-pyridylmethyleneoxy)-1,1′-biphenylene; bdc=benzenedicarboxylate, C4H4O4 = fumaric acid). Complex 1 has a 2D sheet structure consisting of two unusual zigzag Zn(II) chains which are nearly perpendicular to each other. Complex 2 is comprised of two-leg ladders, in which [Zn(4,4′-bpp)] chains serve as the side rails and 1,2-bdc ligands serve as the cross rungs. In complex 3, every two 1,3-bdc ligands connect the neighbouring Zn(II)-3,3′-bpp dimetallic rings in η1 coordination modes into an interesting chain structure. Complex 4 consists of an anionic macrocycle-containing cadmium dicarboxylate sheets that are separated by 3,3′-bpp. These d10 metal complexes exhibit high thermal stabilities and strong luminescence efficiencies. 相似文献