全文获取类型
收费全文 | 20065篇 |
免费 | 483篇 |
国内免费 | 437篇 |
专业分类
化学 | 3941篇 |
晶体学 | 972篇 |
力学 | 385篇 |
综合类 | 44篇 |
数学 | 11942篇 |
物理学 | 3701篇 |
出版年
2023年 | 55篇 |
2022年 | 144篇 |
2021年 | 149篇 |
2020年 | 185篇 |
2019年 | 369篇 |
2018年 | 393篇 |
2017年 | 269篇 |
2016年 | 328篇 |
2015年 | 323篇 |
2014年 | 599篇 |
2013年 | 1361篇 |
2012年 | 526篇 |
2011年 | 1581篇 |
2010年 | 1388篇 |
2009年 | 1281篇 |
2008年 | 1383篇 |
2007年 | 1360篇 |
2006年 | 1022篇 |
2005年 | 904篇 |
2004年 | 796篇 |
2003年 | 608篇 |
2002年 | 632篇 |
2001年 | 419篇 |
2000年 | 399篇 |
1999年 | 371篇 |
1998年 | 382篇 |
1997年 | 293篇 |
1996年 | 334篇 |
1995年 | 336篇 |
1994年 | 318篇 |
1993年 | 244篇 |
1992年 | 248篇 |
1991年 | 173篇 |
1990年 | 183篇 |
1989年 | 172篇 |
1988年 | 106篇 |
1987年 | 124篇 |
1986年 | 89篇 |
1985年 | 158篇 |
1984年 | 114篇 |
1983年 | 68篇 |
1982年 | 91篇 |
1981年 | 121篇 |
1980年 | 107篇 |
1979年 | 61篇 |
1978年 | 108篇 |
1977年 | 91篇 |
1976年 | 90篇 |
1975年 | 39篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
111.
V.B. Nalbandyan 《Journal of Physics and Chemistry of Solids》2004,65(6):1201
The irreproducibility of electrical properties of Na0.88Li0.12NbO3 solid solution on thermal cycling reported by M.A.L. Nobre and S. Lanfredi is explained by gradual decomposition of the supersaturated solid solution below ca. 800 °C. 相似文献
112.
Deependra Das Mulmi Nozomi Kamiya Yutaka Murakami 《Journal of Physics and Chemistry of Solids》2004,65(6):1181-1185
Nb-doped anatase TiO2 single crystal has been grown by chemical vapour transport method. Raman spectra shows that the obtained crystal with Nb of 0.08 wt% has typical anatase structure. An absorption band was observed at around 2.2 eV, which seems to be due to the d-d transition in the conduction band. The electron paramagnetic resonance and electric resistivity measurements show that the doped niobium makes quite shallow donor level whose orbital is dxy-like centered at the titanium position of anatase. 相似文献
113.
The cation distribution in spinel-related titanium-substituted lithium ferrite, Li0.5+0.5xFe2.5−1.5xTixO4 has been explored using interatomic potential and ab initio calculations. The results suggest that the cation distribution with Ti4+ substituting for Fe3+ on octahedral B sites and excess Li+ substituting for Fe3+ on tetrahedral A sites is stabilised by the formation of clusters of two octahedrally coordinated Ti4+ ions and one tetrahedrally coordinated Li+ ion linked through a common oxygen. 相似文献
114.
Margarete O. Machado 《Journal of Physics and Chemistry of Solids》2004,65(10):1697-1703
The crystalline lamellar compound, VOPO4·2H2O, was employed as host to react with a long monoamine aliphatic chain, dodecylamine, and with an aromatic derivative, nicotinamide, using two distinct synthetic approaches: in the solid state and from aqueous solution. The resulting compounds were characterized by elemental analysis, infrared spectroscopy, X-ray diffractometry, thermogravimetry and SEM microscopy. From X-ray diffraction patterns, the calculated increase of the interlayer distance was 2.05 nm for the dodecylamine, containing product, which is in agreement with the intercalation process, and was observed with both reactions routes. On the contrary, the guest nicotinamide molecule was not inserted into the lamellar cavity. The reaction in the solid state caused a small modification of the phosphate microstructure, in comparison with the solution procedure. The aliphatic amine molecules are oriented in a bilayer inside the host cavity by forming an angle of 67° with the inorganic lamella. The thermal decomposition for both series of synthesized compounds did not demonstrate any difference in behavior. 相似文献
115.
Electron paramagnetic resonance (EPR) investigations has been carried out on the new family of molybdenum doped vanadium sesquioxides (V1−xMox)2−δO3. The oxidation effects were monitored from the rate of paramagnetic V4+ created when the sample is exposed to the air. The effects of the oxidation time, sample temperature, and annealing at 1000 °C under a diluted hydrogen atmosphere on the EPR signal features are analyzed. The V4+ concentration in the oxidized samples is determined and the relaxation effects driven by the conduction electrons are pointed out from the thermal behaviour of the EPR line features. EPR spectra of all the oxidized samples also reveal a small ferromagnetic contribution strongly correlated with the V4+ content. 相似文献
116.
117.
Fan Chung 《Annals of Combinatorics》2005,9(1):1-19
We consider Laplacians for directed graphs and examine their eigenvalues. We introduce a notion of a circulation in a directed graph and its connection with the Rayleigh quotient. We then define a Cheeger constant and establish the Cheeger inequality for directed graphs. These relations can be used to deal with various problems that often arise in the study of non-reversible Markov chains including bounding the rate of convergence and deriving comparison theorems.Received September 8, 2004 相似文献
118.
As predicted by Haldane, spin, S=1 one-dimensional (1D) Heisenberg antiferromagnet (HAF) has an energy gap between the singlet ground state and first excited triplet. On application of magnetic field, the triplet state Zeeman splits and the energy of one of the triplet state becomes zero at a critical field, Hc. Above Hc the system recovers magnetism. Then, we expect that a quasi-1D HAF will show a magnetic long-range ordering (LRO) at low temperatures due to the inter-chain coupling. This field-induced LRO has not been observed before due to complication of the crystal structure in the materials studied so far and/or technical difficulty.From a heat capacity measurement on a single crystal of an S=1 quasi-Q1D HAF, Ni(C5H14N2)2N3(PF6), we found an anomaly at a temperature in finite fields indicating a field-induced phase transition. A magnetic LRO is confirmed by a neutron diffraction measurement on the same sample. The temperature versus magnetic field phase diagram of this compound is constructed and discussed. 相似文献
119.
We synthesized a new intercalation compound, 1,5-diaminonaphathalene(DAN)-saponite where intercalated DAN molecules were shown to have a formal charge of +0.67 The measurement of optical diffuse reflectance spectra revealed the formation of electronic bands with a gap of ca. 1 eV suggesting semiconducting behaviour of this system. From ESR measurements, the radical formation in DAN-saponite was confirmed and the spin concentration was determined to be 1 spin per 200 and 300 DAN-molecules at 290 and 7.9 K, respectively. This temperature dependence of the spin density also implies the semiconductive nature of DAN-saponite. 相似文献
120.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献