全文获取类型
收费全文 | 91376篇 |
免费 | 16452篇 |
国内免费 | 9271篇 |
专业分类
化学 | 61900篇 |
晶体学 | 964篇 |
力学 | 5831篇 |
综合类 | 549篇 |
数学 | 10265篇 |
物理学 | 37590篇 |
出版年
2024年 | 344篇 |
2023年 | 2045篇 |
2022年 | 3308篇 |
2021年 | 3524篇 |
2020年 | 3938篇 |
2019年 | 3522篇 |
2018年 | 3229篇 |
2017年 | 2898篇 |
2016年 | 4600篇 |
2015年 | 4393篇 |
2014年 | 5371篇 |
2013年 | 6826篇 |
2012年 | 8281篇 |
2011年 | 8459篇 |
2010年 | 5588篇 |
2009年 | 5443篇 |
2008年 | 5872篇 |
2007年 | 5147篇 |
2006年 | 4843篇 |
2005年 | 3895篇 |
2004年 | 2996篇 |
2003年 | 2314篇 |
2002年 | 2128篇 |
2001年 | 1835篇 |
2000年 | 1650篇 |
1999年 | 1846篇 |
1998年 | 1592篇 |
1997年 | 1577篇 |
1996年 | 1565篇 |
1995年 | 1324篇 |
1994年 | 1155篇 |
1993年 | 1000篇 |
1992年 | 864篇 |
1991年 | 789篇 |
1990年 | 643篇 |
1989年 | 503篇 |
1988年 | 375篇 |
1987年 | 310篇 |
1986年 | 324篇 |
1985年 | 261篇 |
1984年 | 151篇 |
1983年 | 121篇 |
1982年 | 100篇 |
1981年 | 58篇 |
1980年 | 42篇 |
1979年 | 15篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
Zhang Si-Wei Yan Shi-Ping Liao Dai-Zheng Jiang Zong-Hui Wang Geng-Lin Liu Yong-Jiang 《Transition Metal Chemistry》1997,22(1):42-45
Four new NiII–NiII–NiII homotrinuclear complexes namely [Ni(-BD)2{NiL2}](ClO4)2 [L = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (5-NO2-phen), 2,2-bipyridyl (bpy) or 4,4-dimethyl-2,2bipyridyl (Me2bpy) and (-BD)– = -benzyldioximato ion] have been prepared and characterized. Based on elemental analyses, i.r. spectra, conductivity measurements, extended -benzyldioximato-bridged systems consisting of three nickel(II) ions in which the central nickel(II) ion has a square-planar environment and the end capped two nickel(II) ions have a distorted octahedral environment are proposed for these structures. The temperature dependence of the magnetic susceptibility for complexes (1) (phen), (2) (5-NO2-phen), (3) (bpy) and (4) (Me2bpy) were measured over the 77–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H^ = –2JS^1S^2), giving the exchange integral J = –13.31 cm–1 for (1), J = –7.37 cm–1 for (2), J = –8.96 cm–1 for (3) and J = –7.33 cm–1 for (4) These results indicate a weak antiferromagnetic spin exchange interaction between the two terminal nickel(II) io 相似文献
962.
用高效液相色谱法优化苯与对氯氯苄烷基化反应催化剂刘红霞张书胜袁倬斌*(郑州大学分析测试中心郑州)(中国科学技术大学研究生院北京100039)关键词氯-二苯甲烷,制备,三氯化铝,硝基苯,硝基乙烷,高效液相色谱法1997-03-31收稿,1997-09-... 相似文献
963.
[structure: see text] The chiral monocinchona derivative shown, synthesized in one step from two efficiently prepared chiral building blocks, was designed under mechanistic guidance as a catalyst for the enantio- and position-selective dihydroxylation of the terminal isopropylidene group of polyisoprenoids. Its efficacy as a synthetic reagent for this purpose was demonstrated for several different substrates. 相似文献
964.
Zhang YZ Gao S Sun HL Su G Wang ZM Zhang SW 《Chemical communications (Cambridge, England)》2004,(17):1906-1907
Cyano-bridged corrugated ladder-like chains are connected by mu(1,1)-N(3) (end-on, EO) bridges to form a layered coordination polymer, [Mn(N(3))(CH(3)OH)[Cr(phen)(CN)(4)].CH(3)OH (2), which is the first mixed cyano-azide bridged compound, and shows metamagnetism below 21.8 K, a temperature much higher than that (3.4 K) of the crossed double chain [Cr(phen)(CN)(4)](2) [Mn(H(2)O)(2)].4H(2)O (1) based on the same building block [Cr(phen)(CN)(4)](-). 相似文献
965.
Desorption/ionization on silicon mass spectrometry (DIOS-MS) is a matrix-free technique that allows for the direct desorption/ionization of low-molecular-weight compounds with little or no fragmentation of analytes. This technique has a relatively high tolerance for contaminants commonly found in biological samples. DIOS-MS has been applied to determine the activity of immobilized enzymes on the porous silicon surface. Enzyme activities were also monitored with the addition of a competitive inhibitor in the substrate solution. It is demonstrated that this method can be applied to the screening of enzyme inhibitors. Furthermore, a method for peptide mapping analysis by in situ digestion of proteins on the porous silicon surface modified by trypsin, combined with matrix-assisted laser desorption/ionization-time of flight-MS has been developed. 相似文献
966.
A general and efficient Cu(I)-catalyzed cross-coupling reaction of terminal alkynes and monooxalyl chloride for the synthesis of 2-oxo-3-butynoates and 2-oxo-3-butynoamides was developed. Readily available starting materials, the mild reaction conditions, wide functional group tolerance, and the obviation of stoichiometric organolithium or magnesium reagents combine to highlight this reaction. 相似文献
967.
For the first time, a new method is described for the determination of scandium based on the cathodic adsorptive stripping of the scandium-alizarin red S complex onto a carbon paste electrode. The second-order derivative linear scan voltammograms of the complex are recorded by use of model JP-303 polarographic analyzer from 0.0 to -1.0 V (versus SCE). Optimum conditions are found to be: an acetic acid (0.36 mol l(-1))-potassium biphthalate (0.064 mol l(-1)) buffer solution (pH 4.0) containing 2.0x10(-5) mol l(-1) alizarin red S, a preconcentration potential of 0.0 V, a preconcentration time of 60 s, a rest time of 10 s and a scan rate of 100 mV s(-1). The results show that the complex can be adsorbed on the surface of a carbon paste electrode, yielding one peak at -0.58 V, corresponding to the reduction of alizarin red S in the complex at the electrode. The detection limit is found to be 6.0x10(-10) mol l(-1) for 3 min of preconcentration time. The linear range is 1.0x10(-9) to 4.0x10(-7) mol l(-1). Application of the procedure to the determination of scandium in the ore samples gave good results. 相似文献
968.
969.
JPC – Journal of Planar Chromatography – Modern TLC - A new bonded RP-18 sintered silica gel plate for use in reversed-phase planar electrochromatography has been prepared in our... 相似文献
970.
Wang M Wang BM Shi L Tu YQ Fan CA Wang SH Hu XD Zhang SY 《Chemical communications (Cambridge, England)》2005,(44):5580-5582
A quinine/Selectfluor combination inducing rearrangement reaction of allylic alcohols was discovered, which involved a moderate yield with good enantioselective construction of alpha-quaternary carbon center and beta-fluoro aldehyde under base condition. 相似文献