全文获取类型
收费全文 | 7491篇 |
免费 | 233篇 |
国内免费 | 71篇 |
专业分类
化学 | 4841篇 |
晶体学 | 56篇 |
力学 | 273篇 |
数学 | 834篇 |
物理学 | 1791篇 |
出版年
2022年 | 40篇 |
2021年 | 92篇 |
2020年 | 110篇 |
2019年 | 89篇 |
2018年 | 66篇 |
2017年 | 75篇 |
2016年 | 147篇 |
2015年 | 130篇 |
2014年 | 185篇 |
2013年 | 379篇 |
2012年 | 369篇 |
2011年 | 433篇 |
2010年 | 252篇 |
2009年 | 285篇 |
2008年 | 379篇 |
2007年 | 350篇 |
2006年 | 348篇 |
2005年 | 312篇 |
2004年 | 301篇 |
2003年 | 283篇 |
2002年 | 273篇 |
2001年 | 205篇 |
2000年 | 210篇 |
1999年 | 124篇 |
1998年 | 99篇 |
1997年 | 92篇 |
1996年 | 114篇 |
1995年 | 117篇 |
1994年 | 106篇 |
1993年 | 107篇 |
1992年 | 94篇 |
1991年 | 74篇 |
1990年 | 76篇 |
1989年 | 90篇 |
1988年 | 75篇 |
1987年 | 71篇 |
1986年 | 64篇 |
1985年 | 95篇 |
1984年 | 78篇 |
1983年 | 80篇 |
1982年 | 93篇 |
1981年 | 69篇 |
1980年 | 65篇 |
1979年 | 55篇 |
1978年 | 59篇 |
1977年 | 53篇 |
1976年 | 69篇 |
1975年 | 78篇 |
1974年 | 47篇 |
1973年 | 54篇 |
排序方式: 共有7795条查询结果,搜索用时 312 毫秒
21.
The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules. 相似文献
22.
Kimin Hong Jungju Lee Jinhan Lee Young-Dong Ko Jin-Seok Chung Jin-Gyu Kim 《Journal of magnetism and magnetic materials》2006
We investigated the change of magnetic properties of the electroplated Cu/Co alloys and multilayers caused by organic additives and high temperature annealing. When plated with a pure Cu/Co electrolyte, the alloy contained ∼25% of Cu and ∼75% of Co. The alloy was made of hcp-Co, fcc-Co and Cu(1 1 1) and was super-paramagnetic at room temperature. As we add a few organic additives in the plating electrolyte, the hcp-Co of the films disappeared. The organic additives contained in the electrolytes changed paramagnetic Cu/Co multilayers to ferromagnets. High-temperature thermal annealing increased coercivity due to the growth of the Co grains. 相似文献
23.
Jaeyoung Chung 《Journal of Mathematical Analysis and Applications》2004,300(2):376-350
We reformulate and prove the Hyers–Ulam–Rassias stability of Cauchy equation in the space of Schwartz tempered distributions and Fourier hyperfunctions. 相似文献
24.
Meisters and Peterson gave an equivalent condition under which the multisensor deconvolution problem has a solution when there are two convolvers, each the characteristic function of an interval. In this article we find additional conditions under which the deconvolution problem for multiple characteristic functions is solvable. We extend the result to the space of Gevrey distributions and prove that every linear operator S, fromthe space of Gevrey functions with compact support onto itself, which commutes with translations can be represented as convolution with a unique Gevrey distribution T of compact support. Finally, we find explicit formula for deconvolvers when the convolvers satisfy weaker conditions than the equivalence conditions using nonperiodic sampling method. 相似文献
25.
Andrew Bach Xinglong Jiang Joseph Mckenna Kapa Prasad Oljan Repic Wen‐Chung Shieh 《Journal of heterocyclic chemistry》2004,41(4):637-640
An efficient approach has been developed for the synthesis of an isofervenulin analogue 1 employing a one‐pot condensation‐substitution reaction of a chlorocarboethoxytriazine (electrophile) with a urea (nucleophile). The resulting cyclization reaction resulted in the synthesis of a pyrimido‐heterocycle in good yield in either acidic or basic media. The former was assisted by utilizing trimethylsilyl chloride. 相似文献
26.
C.H Chung S.D KimH.J Kim F.O AdurodijaK.H Yoon J Song 《Solid State Communications》2003,126(4):185-190
The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering. 相似文献
27.
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
28.
Kyu Hwang Yeon Suk Seong Kim Chung In Um Thomas F. George 《International Journal of Theoretical Physics》2003,42(9):2043-2059
Quantum Hamiltonian systems corresponding to classical systems related by a general canonical transformation are considered. The differential equation to find the unitary operator, which corresponds to the canonical transformation and connects quantum states of the original and transformed systems, is obtained. The propagator associated with their wave functions is found by the unitary operator. Quantum systems related by a linear canonical point transformation are analyzed. The results are tested by finding the wave functions of the under-, critical-, and over-damped harmonic oscillator from the wave functions of the harmonic oscillator, free-particle system, and negative harmonic potential system, using the unitary operator to connect them, respectively. 相似文献
29.
M. C. Caracoche J. A. Martínez P. C. Rivas M. A. Taylor A. F. Pasquevich S. Barolin O. A. de Sanctis 《Hyperfine Interactions》2007,179(1-3):87-93
The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO2 and 20 mol% CaO–HfO2 has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ?1 (CaHf4O9) and ?2 (Ca6Hf19O44) phases. Dynamical effects on the electric field gradient reveal the existence of oxygen vacancies movements in the solid solution. The thermal behavior of the relaxation constant observed in films allowed the determination of activation energies of 0.54 eV and 0.70 eV for the 14 mol% and 20 mol% CaO doped hafnias, respectively. The influence of the microdomains and the stability of the cubic solid solution are discussed. 相似文献
30.