全文获取类型
收费全文 | 26160篇 |
免费 | 4404篇 |
国内免费 | 2424篇 |
专业分类
化学 | 17017篇 |
晶体学 | 861篇 |
力学 | 1245篇 |
综合类 | 233篇 |
数学 | 1029篇 |
物理学 | 12603篇 |
出版年
2024年 | 46篇 |
2023年 | 190篇 |
2022年 | 589篇 |
2021年 | 611篇 |
2020年 | 761篇 |
2019年 | 726篇 |
2018年 | 727篇 |
2017年 | 916篇 |
2016年 | 1149篇 |
2015年 | 1132篇 |
2014年 | 1283篇 |
2013年 | 2686篇 |
2012年 | 1561篇 |
2011年 | 1696篇 |
2010年 | 1401篇 |
2009年 | 1503篇 |
2008年 | 1493篇 |
2007年 | 1545篇 |
2006年 | 1500篇 |
2005年 | 1282篇 |
2004年 | 1279篇 |
2003年 | 1131篇 |
2002年 | 1165篇 |
2001年 | 855篇 |
2000年 | 850篇 |
1999年 | 722篇 |
1998年 | 601篇 |
1997年 | 497篇 |
1996年 | 470篇 |
1995年 | 440篇 |
1994年 | 327篇 |
1993年 | 288篇 |
1992年 | 268篇 |
1991年 | 200篇 |
1990年 | 164篇 |
1989年 | 123篇 |
1988年 | 134篇 |
1987年 | 121篇 |
1986年 | 107篇 |
1985年 | 87篇 |
1984年 | 84篇 |
1983年 | 45篇 |
1982年 | 57篇 |
1981年 | 34篇 |
1980年 | 34篇 |
1979年 | 40篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
43.
单晶光纤损耗谱测量装置 总被引:4,自引:1,他引:3
本文描述了一套用以测量单晶光纤损耗谱的装置。本装置由卤钨灯,单色仪,积分球,AgORbCs光电倍增管以及数据采集,处理和控制系统组成。可测量300~1150nm的光谱范围。利用本装置可获得单晶光纤的吸收光谱,透过率谱,散射光谱以及散射位置谱。 相似文献
44.
45.
Timur Zharnikov Alexander Yakovlev Semion Kuchanov 《Journal of Polymer Science.Polymer Physics》2003,41(9):892-902
The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free‐radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 892–902, 2003 相似文献
46.
G. N. Merrill 《Journal of Physical Organic Chemistry》2007,20(1):19-29
Ab initio molecular orbital calculations were carried out on epibromohydrin (EBH) and epichlorohydrin (ECH) in an attempt to elucidate their reactivity with respect to a hard nucleophile, hydroxide. These systems were modeled in both the gas phase and a polar solvent under basic conditions. In the gas phase, it was determined that a direct displacement mechanism (nucleophilic attack at the C1 position) was operative for EBH, while an indirect pathway (nucleophilic attack at the C3 position and subsequent intramolecular displacement) was followed for ECH. In an acetone solution, only the indirect displacement mechanism was found to occur. An electrostatic argument is advanced to account for this behavior in polar solution. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
47.
T. K. Melik-Barkhudarov 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2007,42(5):173-177
An approach is discussed which allows one to describe within the framework of the single model the aggregative states of a system of atoms obeying the Fermi statistics. A phase diagram is obtained containing both the critical point where the distinctions between the liquid and vapor vanish and the triple point where the liquid, vapor, and crystal are in equilibrium. 相似文献
48.
We study phase separation in a system of hard-core particles driven by a fluctuating two-dimensional self-affine potential landscape which evolves through Kardar–Parisi–Zhang (KPZ) dynamics. We find that particles tend to cluster together on a length scale which grows in time. The final phase-separated steady state is characterized by an unusual cusp singularity in the scaled correlation function and a broad distribution for the order parameter. Unlike the one-dimensional case studied earlier, the cluster-size distribution is asymmetric between particles and holes, reflecting the broken reflection symmetry of the KPZ dynamics, and has a contribution from an infinite cluster in addition to a power law part. A study of the surface in terms of coarse-grained depth variables helps understand many of these features. 相似文献
49.
Small‐Angle Neutron Scattering has been performed from poly(ethylene oxide) in deuterated water at temperature ranging from 10 to 80 °C. A simple fitting model was used to obtain a correlation length and a Porod exponent. The correlation length L characterizes the average distance between entanglements in the semidilute region and is proportional to the individual coil sizes in the dilute region. L was found to increase with temperature in the semidilute region but it decreases with temperature in the dilute region. This decrease is the precursor to the single‐chain collapse which applies to very dilute polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2196–2200, 2007 相似文献
50.
J.L. Shui 《Applied Surface Science》2006,253(5):2379-2385
Spongy-like reticular structure is a unique morphology fabricated by electrostatic spray deposition (ESD) technique. The effects of solvent, substrate temperature, precursor feeding rate, static electric field strength, and deposition time on tailoring the reticular structure were investigated. Scanning electron microscopy was used to observe the film morphology. MnOx or LiMn2O4 were selected as the model materials. It is found that in addition to the conventional solvent butyl carbitol, other kinds of solvents such as ethylene glycol and propylene glycol can also be used to obtain reticular films at a suitable substrate temperature. Porous films with a low cross-linking degree pore structure can be prepared by increasing precursor feeding rate or decreasing substrate temperature. Increasing the deposition time or the electric field strength helps to obtain reticular films with more homogeneous pore size distribution. In addition, the addition of a high boiling-point solvent in mixed alcohol solvent results in the increase of proper substrate temperature. It is concluded that the fluidity of the spray droplets on the surface of a hot substrate is an important factor to form a reticular film. 相似文献