全文获取类型
收费全文 | 6420篇 |
免费 | 169篇 |
国内免费 | 20篇 |
专业分类
化学 | 3999篇 |
晶体学 | 34篇 |
力学 | 236篇 |
综合类 | 5篇 |
数学 | 817篇 |
物理学 | 1518篇 |
出版年
2024年 | 8篇 |
2023年 | 49篇 |
2022年 | 202篇 |
2021年 | 188篇 |
2020年 | 151篇 |
2019年 | 170篇 |
2018年 | 196篇 |
2017年 | 147篇 |
2016年 | 271篇 |
2015年 | 187篇 |
2014年 | 238篇 |
2013年 | 411篇 |
2012年 | 407篇 |
2011年 | 479篇 |
2010年 | 348篇 |
2009年 | 338篇 |
2008年 | 424篇 |
2007年 | 374篇 |
2006年 | 315篇 |
2005年 | 228篇 |
2004年 | 214篇 |
2003年 | 152篇 |
2002年 | 157篇 |
2001年 | 118篇 |
2000年 | 86篇 |
1999年 | 73篇 |
1998年 | 64篇 |
1997年 | 56篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 54篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 25篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 7篇 |
排序方式: 共有6609条查询结果,搜索用时 0 毫秒
1.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
2.
3.
4.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
5.
Marcelo Queiroz Joaquim Jú dice Carlos Humes Jr.. 《Mathematics of Computation》2004,73(248):1849-1863
In this paper the Eigenvalue Complementarity Problem (EiCP) with real symmetric matrices is addressed. It is shown that the symmetric (EiCP) is equivalent to finding an equilibrium solution of a differentiable optimization problem in a compact set. A necessary and sufficient condition for solvability is obtained which, when verified, gives a convenient starting point for any gradient-ascent local optimization method to converge to a solution of the (EiCP). It is further shown that similar results apply to the Symmetric Generalized Eigenvalue Complementarity Problem (GEiCP). Computational tests show that these reformulations improve the speed and robustness of the solution methods.
6.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
7.
Lígia M. Rodrigues 《Tetrahedron》2004,60(40):8929-8936
Tetrapeptides containing one of a set of four different α,α-dialkyl glycines at the C-terminus were synthesized by conventional methods in solution and their conformational behavior investigated by 1H NMR spectroscopy in connection with molecular mechanics calculations. The results were consistent with conformations stabilized by a γ-turn in the case of compounds with alkyl groups larger than methyl, while the corresponding Aib derivative did not exhibit intramolecular hydrogen bonding. 相似文献
8.
Biosorption of Chromium(III) by Biomass of Seaweed Sargassum sp. in a Fixed-Bed Column 总被引:2,自引:0,他引:2
Eneida Sala Cossich Edson Antonio da Silva Célia Regina Granhen Tavares Lúcio Cardozo Filho Teresa Massako Kakuta Ravagnani 《Adsorption》2004,10(2):129-138
This work aimed at modeling chromium biosorption using the biomass of seaweed Sargassum sp. in a fixed-bed column. The mathematical model used was obtained from the mass balance of the component in the liquid phase and in the biosorbent material. The effects of both axial dispersion in the column and the resistance to mass transfer in the solid were considered for the solution of the partial differential equations of the model, using the Galerkin method on finite elements. To represent the equilibrium data of the batch system the Langmuir isotherm were used. The chromium ion adsorption capacity of the seaweed Sargassum sp., at a temperature of 30°C and pH 3.5, was 2.61 mmol/g. The model performance was evaluated from experimental data obtained at 30°C for flow rates of 2, 6 and 8 mL/min. The parameters of the model, mass transfer and axial dispersion coefficients, were adjusted from these experimental data. The model proved adequate to describe chromium biosorption dynamics in fixed-bed columns. 相似文献
9.
Marcelo Do Amaral Steven Van Es Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):3936-3946
The production of high‐solid‐content, low‐viscosity latexes is an active field in both industry and academia. The viscosity of polymer dispersions has a clear dependence on the particle size distribution (PSD). An example is the rule of thumb that a bimodal PSD enables the reduction of the viscosity with respect to monomodal systems. Despite important progress in theoretical work, not much has been done to quantitatively predict the low shear viscosity of aqueous polymer dispersions as a function of the complex PSD. In this work, the capability of a low‐shear‐viscosity equation to quantitatively account for the influence of both the PSD and the physicochemical characteristics of the dispersions is experimentally assessed. An analysis, consistent with theoretical concepts, of the data with semiempirical correlations is proposed. Next, with values of the parameters of the viscosity equation obtained experimentally, the effect of a latex with a 70% solid content on the low shear viscosity is examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3936–3946, 2004 相似文献
10.
New heuristics for over-constrained flight to gate assignments 总被引:1,自引:0,他引:1
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results. 相似文献