全文获取类型
收费全文 | 291185篇 |
免费 | 3492篇 |
国内免费 | 1025篇 |
专业分类
化学 | 161992篇 |
晶体学 | 4857篇 |
力学 | 11939篇 |
综合类 | 9篇 |
数学 | 29092篇 |
物理学 | 87813篇 |
出版年
2016年 | 3335篇 |
2015年 | 2510篇 |
2014年 | 3506篇 |
2013年 | 11793篇 |
2012年 | 7938篇 |
2011年 | 10041篇 |
2010年 | 6543篇 |
2009年 | 6348篇 |
2008年 | 9126篇 |
2007年 | 9258篇 |
2006年 | 9029篇 |
2005年 | 8486篇 |
2004年 | 7633篇 |
2003年 | 6863篇 |
2002年 | 6730篇 |
2001年 | 8339篇 |
2000年 | 6384篇 |
1999年 | 5171篇 |
1998年 | 4194篇 |
1997年 | 4232篇 |
1996年 | 4107篇 |
1995年 | 3928篇 |
1994年 | 3618篇 |
1993年 | 3459篇 |
1992年 | 4165篇 |
1991年 | 3985篇 |
1990年 | 3853篇 |
1989年 | 3880篇 |
1988年 | 3872篇 |
1987年 | 3871篇 |
1986年 | 3614篇 |
1985年 | 4916篇 |
1984年 | 5017篇 |
1983年 | 4177篇 |
1982年 | 4589篇 |
1981年 | 4394篇 |
1980年 | 4357篇 |
1979年 | 4483篇 |
1978年 | 4809篇 |
1977年 | 4563篇 |
1976年 | 4557篇 |
1975年 | 4319篇 |
1974年 | 4191篇 |
1973年 | 4386篇 |
1972年 | 2779篇 |
1971年 | 2258篇 |
1969年 | 2159篇 |
1968年 | 2760篇 |
1967年 | 3013篇 |
1966年 | 2585篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
241.
S. Mohri D. Amutha Rani Y. Yamamoto Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2004,42(2):238-245
Syndiotactic polystyrene (sPS) has various crystalline forms such as α, β, γ, and δ forms, and a mesophase depending on the preparation method. In this study, we focused on the mesophase with the molecular cavity of sPS, which is obtained by step‐wise extraction of the guest molecules from the sPS δ form. To prepare the mesophase containing different shapes and sizes of the cavity, two kinds of the sPS δ form membrane cast from either toluene or chloroform solution were first prepared and then the guest molecules were removed by a step‐wise extraction method using acetone and methanol. We could succeed in the preparation of two kinds of mesophase with different shapes and sizes of the molecular cavity. Either toluene or chloroform vapor sorption to the sPS mesophase membranes was examined at 25 °C. Sorption analysis indicates that the mesophase with large molecular cavities can mainly sorb large molecules; on the other hand, the mesophase with small cavities can sorb only the small molecules, and is unable to sorb a large amount of large molecule because the cavity was too small to sorb the large molecules. Therefore, the sPS mesophase membrane has sorption selectivity based on the size of the molecular cavity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 238–245, 2004 相似文献
242.
Beeranahally H Doreswamy Madegowda Mahendra Hirihally C Devarajegowda Venkatesh B Devaru Sridhar M Anandalwar Javaregowda S Prasad 《Analytical sciences》2004,20(2):407-408
The title compound was extracted from a natural product and its structure was characterized by an X-ray diffraction method. It crystallizes in the tetragonal space group P41 with cell parameters a = 15.832(10)A, c = 11.622(10)A, Z = 4; the final residual factor is R1 = 0.0769. The structure has both intra and intermolecular hydrogen bonds. 相似文献
243.
The photocatalytic degradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid (2,4-D, 1), has been investigated in aqueous suspensions of titanium dioxide. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time in the presence of UV light source. The degradation kinetics was investigated under a variety of conditions, such as different types of TiO2, pH, catalyst and substrate concentrations. Higher photonic efficiencies were observed with Degussa P25 as compared with other photocatalysts. The degradation products were analysed by GC-MS and probable pathways for the formation of different products were proposed. 相似文献
244.
Jérôme Gualbert Patrick Shahgaldian Adina Lazar Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(1-2):37-44
Solid Lipid Nanoparticles (SLNs) have been prepared fromc-2,c-8,c-14,c-20-tetraundecyl-4,6,10,12,16,18,22,24-octahydroxyresorc[4]areneas colloidal suspensions. Photon Correlation Spectroscopy studies revealed aparticle hydrodynamic diameter of 150 nm. Non-contact mode Atomic ForceMicroscopy allows observation of the particles as slightly flattened sphericalobjects of 236 (±40) nm diameter and 145 (±40) nm height. Thestudy of the preparation parameters showed that shear force does not affectthe hydrodynamic size of the SLNs. In contrast, the viscosity and the pH ofthe aqueous phase, the amphiphile concentration in the organic phase and thevolume of organic phase used, all lead to variation in the size of the particles.In term of post preparation parameters only the ionic strength has been shownto affect significantly the particle size; while the pH of the storing solution,microwave, ultrasonic and thermal treatments do not. Short and long-termstability studies have been performed to measure the effect of the ionic strengthon the stability of the particles. The use of carbohydrate cryoprotectants does notallow re-dispersion of the colloidal suspension after freeze-drying. 相似文献
245.
H. William Bosch Sre
o D. kapin Egon Matijevi 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):43-50
Controlled precipitation of the diagnostic imaging agent ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate has been used to produce fine particles of various sizes, morphologies, and degrees of crystallinity, which depended on experimental conditions. In addition, two distinct polymorphic forms of the drug have been fully characterized by single crystal X-ray diffraction studies, and evidence for a third polymorph was also observed. Some of the so prepared dry particles were coated with a thin layer of silica. 相似文献
246.
247.
248.
249.
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
250.
W Y Hung S Kucherenko N J Samsatli N Shah 《The Journal of the Operational Research Society》2004,55(8):801-813
In this paper, we present a new modelling approach for realistic supply chain simulation. The model provides an experimental environment for informed comparison between different supply chain policies. A basic simulation model for a generic node, from which a supply chain network can be built, has been developed using an object-oriented approach. This generic model allows the incorporation of the information and physical systems and decision-making policies used by each node. The object-oriented approach gives the flexibility in specifying the supply chain configuration and operation decisions, and policies. Stochastic simulations are achieved by applying Latin Supercube Sampling to the uncertain variables in descending order of importance, which reduces the number of simulations required. We also present a case study to show that the model is applicable to a real-life situation for dynamic stochastic studies. 相似文献