全文获取类型
收费全文 | 3542篇 |
免费 | 184篇 |
国内免费 | 18篇 |
专业分类
化学 | 2441篇 |
晶体学 | 13篇 |
力学 | 77篇 |
数学 | 603篇 |
物理学 | 610篇 |
出版年
2023年 | 31篇 |
2022年 | 40篇 |
2021年 | 62篇 |
2020年 | 79篇 |
2019年 | 76篇 |
2018年 | 70篇 |
2017年 | 77篇 |
2016年 | 178篇 |
2015年 | 138篇 |
2014年 | 124篇 |
2013年 | 230篇 |
2012年 | 266篇 |
2011年 | 284篇 |
2010年 | 163篇 |
2009年 | 118篇 |
2008年 | 232篇 |
2007年 | 194篇 |
2006年 | 167篇 |
2005年 | 171篇 |
2004年 | 152篇 |
2003年 | 140篇 |
2002年 | 126篇 |
2001年 | 39篇 |
2000年 | 30篇 |
1999年 | 37篇 |
1998年 | 37篇 |
1997年 | 27篇 |
1996年 | 40篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 15篇 |
排序方式: 共有3744条查询结果,搜索用时 15 毫秒
41.
Summary We prove that every mixing
d
by automorphisms of a compact, connected, abelian group is mixing of all orders.Oblatum 5-II-1992The second author gratefully acknowledges support from NSF grant DMS-91-03056 at the Ohio State University 相似文献
42.
研究了基于微芯片电泳分离和电感耦合等离子体质谱的连接技术,并对不同形态的Cu和As进行了快速分离和检测. 相似文献
43.
New boracites containing nitrato- or fluoroanions that appear to be true low-pressure phases have been synthesized at superatmospheric pressures. The M3B7O13NO3 compounds (M = Co, Ni, Cu, Zn, Cd) transform rapidly and reversibly in the temperature region 300–500°C between probable orthorhombic and face centered cubic symmetry, while the M3B7O13F compounds (M = Mg, Mn, Fe, Co, Zn) appear to maintain rhombohedral symmetry up to their decomposition temperatures of 800–900°C. True high-pressure boracite-like phases containing F and Cr, Mn, Fe, or Co that decompose upon heating to M3B7O13F have also been isolated. 相似文献
44.
45.
Close DM Crespo-Hernández CE Gorb L Leszczynski J 《The journal of physical chemistry. A》2005,109(41):9279-9283
In the present study the ionization energy thresholds (IET's) of uracil and thymine have been calculated (with the B3LYP, PMP2, and P3 levels of theory using the standard 6-31++G(d,p) basis set) with one to three water molecules placed in the first hydration shell. Then (B3LYP) polarizable continuum model (PCM) calculations were performed with one to three waters of the hydration shell included. Calculations show there is a distinct effect of microhydration on uracil and thymine. For uracil, one added water results in a decrease in the IET of about 0.15 eV. The second and third water molecules cause a further decrease by about 0.07 eV each. For thymine, the first water molecule is seen to decrease the IET by about 0.1 eV, while the second and third water molecules cause a further decrease of less than 0.1 eV each. The changes in IET calculated here for thymine with one to three waters of hydration are smaller than the experimental values determined by Kim et al. (Kim, S. K.; Lee, W.; Herschbach, D. R. J. Phys. Chem. 1996, 100, 7933). Preliminary results presented here indicate that the experimental results may involve keto-enol tautomers of thymine. The results of placing the microhydrated structures of uracil and thymine in a PCM cavity was seen to make very little difference in the IET when compared to the IET of ordinary uracil or thymine in a PCM cavity. The implications are that accurate calculations of the IET's of uracil and thymine can be obtained by simply considering long-range solvation effects. 相似文献
46.
With the use of the tritium monitoring network the samples of river water, air humidity and precipitation are collected and analysed for HTO in the vicinity of Temelín nuclear power plant. 相似文献
47.
A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules. 相似文献
48.
Metal-catalyzed di-tert-butylsilylene transfer was developed as a mild, operationally simple, functional-group-tolerant method for silacyclopropane formation. Di-tert-butylsilylene was transferred from cyclohexene silacyclopropane 1 to an alkene through the use of a metal salt. Silacyclopropanation occurred at temperatures as low as -27 degrees C when AgOTf or AgOC(O)CF(3) were used as catalysts. Complex silacyclopropanes were formed stereospecifically and diastereoselectively from functionalized alkenes. Silacyclopropanes reacted with various carbonyl compounds, including aldehydes, ketones, formate esters, and formamides, in an overall process that efficiently converts alkenes into oxasilacyclopentanes with defined stereochemistry. 相似文献
49.
K.D. Franz H. Tom Dieck U. Krynitz I.W. Renk 《Journal of organometallic chemistry》1973,64(3):361-366
Glyoxal- and diacetyl-bis(imine)metal tetracarbonyls (RNCR′CR′NR)M(CO)4 (M = Cr, Mo, W) are reduced with potassium in DME to give paramagnetic mono-anions. Their high-resolutior, ESR spectra show the hyperfine splittings of the magnetically active ligand atoms as well as the satellites of the metal isotopes 53Cr,95,97Mo and 183W. The coupling constants are discussed with respect to π-bonding mechanisms. 相似文献
50.
The flavonoid composition of broccoli inflorescences has been studied by LC/UV-DAD/ESI-MSn. A large number of hydroxycinnamic acid esters of kaempferol and quercetin glucosides has been characterised. The structures of the flavonoid glycosides were analysed after alkaline hydrolysis, and were identified as 3-sophoroside/sophorotrioside-7-glucoside/sophoroside of kaempferol, quercetin and isorhamnetin (this last found in trace amount). These complex quercetin and isorhamnetin glucosides have not been previously characterised in nature. In addition, several less complex glucosides based on the same aglycones have been identified. The effect of sugar substitution and acylation on chromatographic mobility and ESI ionisation and fragmentation are discussed. 相似文献