全文获取类型
收费全文 | 2329篇 |
免费 | 128篇 |
国内免费 | 6篇 |
专业分类
化学 | 1404篇 |
晶体学 | 24篇 |
力学 | 41篇 |
数学 | 423篇 |
物理学 | 571篇 |
出版年
2023年 | 20篇 |
2022年 | 18篇 |
2021年 | 39篇 |
2020年 | 53篇 |
2019年 | 43篇 |
2018年 | 50篇 |
2017年 | 76篇 |
2016年 | 138篇 |
2015年 | 95篇 |
2014年 | 85篇 |
2013年 | 154篇 |
2012年 | 154篇 |
2011年 | 202篇 |
2010年 | 118篇 |
2009年 | 98篇 |
2008年 | 99篇 |
2007年 | 80篇 |
2006年 | 67篇 |
2005年 | 50篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1988年 | 11篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1973年 | 12篇 |
1968年 | 11篇 |
1959年 | 23篇 |
1958年 | 33篇 |
1957年 | 34篇 |
1956年 | 16篇 |
1955年 | 12篇 |
1954年 | 22篇 |
排序方式: 共有2463条查询结果,搜索用时 328 毫秒
41.
V. Spěvá?ková J. Jhn M. Pra?ská 《Journal of Radioanalytical and Nuclear Chemistry》1983,80(1-2):115-120
The determination of uranium in natural waters by XRF analysis after its preconcentration with some organic precipitants is described.109Cd source is used for the excitation of L-series X-rays of uranium. Separation yield, kinetics of coprecipitation and the possibility of preparing thin-layer samples for XRF analysis were studied in detail for uranium concentration with α-nitroso-β-naphtol, methylene blue with ammonium thiocyanate, tannin with urotropine and other precipitants. A procedure using coprecipitation of uranium with α-nitroso-β-naphtol from 500 ml samples of surface or waste, waters is proposed. 相似文献
42.
Vlastimil Matějec Ivan Kašík Daniela Berková Miloš Hayer Jiří Kaňka 《Journal of Sol-Gel Science and Technology》1998,13(1-3):617-621
Optical cores of preforms for drawing optical fibers doped with Er3+ and Yb3+ were fabricated by the sol-gel method with the aim of increasing the thickness of glass layers coated in a single coating cycle and to determine the relation between the preparation conditions and optical properties of the fibers. Al2O3-P2O5-SiO2 and TiO2-P2O5-SiO2 glasses have been studied as matrices for entrapping the rare-earth elements. Input sols have been prepared from silicon and titanium alkoxides, AlCl3, ErCl3, YbCl3, POCl3, water and a modifier under acidic catalysis of HCl. The sols were coated on the inner wall of a silica substrate tube and the gel layers were sintered at high temperatures up to 2000°C after which the tube was collapsed into the preform. Continuous and homogenous glass films with the maximum thickness of about 8 m were fabricated. The influence of high-temperature heat treatment of the layers on their composition and optical attenuation was observed. The amplified stimulated emission of Er3+ around 1.55 m was measured under the excitation of the fibers by an Nd : YAG laser at 1.064 m. 相似文献
43.
Summary Unsaturated hexenoic acids are important compounds due to their utilization for specific aromatic alcohol (leaf alcohols)
preparation. The influences of the reaction conditions on the sorbic acid hydrogenation to cis-hex-3-enoic acid are given.
[Cp*Ru(sorbic acid)]CF3SO3 was used as a catalyst in two-phase hydrogenation. 相似文献
44.
Ivan Němec Zorka Machá?ková Ivana Císa?ová Zdeněk Mi?ka 《Journal of solid state chemistry》2004,177(12):4655-4664
Aminoguanidinium(1+) dihydrogen phosphate was prepared by crystallization from aqueous solution. On the basis of the results of DSC measurements, X-ray structural analysis was carried out at temperatures of 160, 215 and 293 K for three aminoguanidinium(1+) dihydrogen phosphate phases ( |Z=2|non-ferroic |melting point 408 K; II |201-222 K|(2) |Z=2|non-ferroic|-; III |<201 K|(2)|Z=4|non-ferroic|-). The triclinic unit cell dimensions (a=6.8220(2), b=7.1000(2), c=7.4500(2) Å, α=86.925(2)°, β=80.731(2)°, γ=79.630(2)°, V=350.21(2) Å3—phase I) are similar for all three structural phases with the exception of phase III, where doubling of the c-axis length leads to an increase in the volume to 692.34(3) Å3. The crystal structure of all three modifications consists of parallel layers of dihydrogen phosphate anions that are interconnected by aminoguanidinium(1+) cations through hydrogen bonds of the N-H…O type. The planar aminoguanidinium(1+) cations are oriented almost parallel to each other and are perpendicular to the anion layers. The primary differences amongst phases I, II and III lie in the location of the H atom in the short O-H…O bonds connecting the dihydrogen phosphate anions in layers. The FTIR and FT Raman spectra of natural and deuterated compounds were recorded and interpreted. The FTIR spectra were studied down to a temperature of 90 K. 相似文献
45.
46.
Influence of Coriolis coupling on excitation of some Nilsson states in155Gd,157Gd and167Er by inelastic scattering of 12·1 MeV deuterons is analysed. Expanded Nilsson potential with hexadecapolar deformation is used for the model calculations. Theoretical values of reduced transition probability,B(E2) are compared with experimental ones. 相似文献
47.
The structural and magnetic properties of the Pr1?xMn1+xO3 perovskites were studied. The increase of x (i.e., ) leads to the decrease of the orthorhombic deformation and of the Néel temperature and, simultaneously, to an increase of the ferromagnetic contribution. The latter effect is explained from the suggested distribution of the cations (Pr3+1?xMn2+x)A(Mn3+1?xMn4+x)O2?3 by the double exchange of Mn3+Mn4+ pairs at the B—sublattice. 相似文献
48.
A method of determination of adsorbed and absorbed hydrogen on palladium catalysts with carbon carriers is suggested and verified. The method allows Had and Hab to be determined with an accuracy of about 10% using catalysts containing at least 5% Pd.
- . . . 10% , , - , 5% Pd.相似文献
49.
Trávníček Zdeněk Machala Viktor Szüčová Lucie Maloň Michal Marek Jaromír 《Transition Metal Chemistry》2004,29(4):352-357
A series of new [NiX(S2P{O-c-Hex}2)(PPh3)](X = Cl–, Br–, I– and NCS–)(1)–(4) and [Ni(NCS)(S2P{OR}2)(PPh3)][R =n-Pr (5), i-Pr (6)] complexes has been synthesized and characterized by elemental analyses, f.i.r., i.r., u.v.–vis., 1H-, 13C{1H}- and 31P{1H}-n.m.r. spectra, magnetochemical and conductivity measurements. A single crystal X-ray analysis of [Ni(NCS)(S2P{O-n-Pr}2)(PPh3)](5) reveals the molecular structure of the complex and confirms a square-planar geometry around the central atom of nickel with the NCS anion coordinated via the nitrogen atom. 相似文献
50.
Daniela Walterová Zdeně;K Stránský Vladimír Preininger Prof. Dr. Vilím Šimánek 《Electrophoresis》1985,6(3):128-132
The isotachophoretic behavior of quaternary benzo/c/phenanthridine, protoberberine and aporphine alkaloids in different electrolyte systems is described. The concentration of the leading ion and the pH value of the leading electrolyte affect the relative effective mobilities of the alkaloids. The system of pH 4.7, containing the leading ion K+ (0.005 M) counter ion acetate, and the terminating ion β-alanine (0.02 M), has been selected for the quantitative determination of the studied alkaloids in model mixtures and plant extracts. 相似文献