全文获取类型
收费全文 | 33690篇 |
免费 | 5709篇 |
国内免费 | 4992篇 |
专业分类
化学 | 25387篇 |
晶体学 | 456篇 |
力学 | 1698篇 |
综合类 | 303篇 |
数学 | 3302篇 |
物理学 | 13245篇 |
出版年
2024年 | 129篇 |
2023年 | 701篇 |
2022年 | 1275篇 |
2021年 | 1381篇 |
2020年 | 1392篇 |
2019年 | 1406篇 |
2018年 | 1238篇 |
2017年 | 1235篇 |
2016年 | 1725篇 |
2015年 | 1774篇 |
2014年 | 2115篇 |
2013年 | 2651篇 |
2012年 | 3240篇 |
2011年 | 3163篇 |
2010年 | 2279篇 |
2009年 | 2088篇 |
2008年 | 2299篇 |
2007年 | 2102篇 |
2006年 | 1921篇 |
2005年 | 1578篇 |
2004年 | 1136篇 |
2003年 | 917篇 |
2002年 | 959篇 |
2001年 | 807篇 |
2000年 | 640篇 |
1999年 | 700篇 |
1998年 | 500篇 |
1997年 | 471篇 |
1996年 | 419篇 |
1995年 | 368篇 |
1994年 | 293篇 |
1993年 | 278篇 |
1992年 | 210篇 |
1991年 | 177篇 |
1990年 | 181篇 |
1989年 | 146篇 |
1988年 | 91篇 |
1987年 | 79篇 |
1986年 | 82篇 |
1985年 | 72篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1957年 | 6篇 |
1930年 | 2篇 |
1916年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
22.
23.
24.
Jing Cheng 《量子光学学报》2006,12(B08):71-72
The effect of finite control beam on the transverse spatial profile of the slow light propagation in an electromagnetically induced transparency medium is studied. From the second-order wave equation and linear response of an EIT medium to the signal field, we find it is possible to produce an effective waveguide for the signal field. The existence and properties of a set of localized, stationary transverse modes are demonstrated. Especially, by carefully manipulating the profile of the control beam, we can realize single-mode propagation for the signal field, which may be important for potential applications. 相似文献
25.
采用光学显微镜和扫描电子显微镜等手段,对某轻型汽车40Cr后桥半轴断裂件的组织及断口特征进行了分析结果表明:半轴在调质处理时的淬火温度不够高,使其表层和心部组织中存在较多的铁素体相,造成了工件最终的硬度和疲劳强度不足,导致半轴在使用中发生扭转疲劳断裂. 相似文献
26.
Let X be a metric space, B the σ-algebra of Borel subsets of X, and μ a probability measure on (X,B). In this note, for a measure-preserving map T (respectively a measure-preserving semi-flow φ) on (X,B,μ), we prove that if suppμ=X, and T (respectively φ) is weak-mixing, then T (respectively φ) has sensitive dependence. 相似文献
27.
Bing-sheng He Zhen-hua Yang Xiao-ming Yuan 《Journal of Mathematical Analysis and Applications》2004,300(2):139-374
Proximal point algorithms (PPA) are attractive methods for monotone variational inequalities. The approximate versions of PPA are more applicable in practice. A modified approximate proximal point algorithm (APPA) presented by Solodov and Svaiter [Math. Programming, Ser. B 88 (2000) 371–389] relaxes the inexactness criterion significantly. This paper presents an extended version of Solodov–Svaiter's APPA. Building the direction from current iterate to the new iterate obtained by Solodov–Svaiter's APPA, the proposed method improves the profit at each iteration by choosing the optimal step length along this direction. In addition, the inexactness restriction is relaxed further. Numerical example indicates the improvement of the proposed method. 相似文献
28.
Zhimin He 《Journal of Mathematical Analysis and Applications》2004,296(1):97-109
In this paper, by means of a new twin fixed-point theorem in a cone, the existence of at least two positive solutions of m-point boundary value problem for second order dynamic equations on time scales is considered. 相似文献
29.
30.
Benzoic acid as a source of proton is widely used in the technology of manufacture of proton exchanged ( PE) waveguide .But the diffusing speed of proton is too fast to make the waveguide stable in the pure benzoic acid. The characteristic of waveguide is improved with mixture of benzoic acid and lithium benzoate . 相似文献