全文获取类型
收费全文 | 19975篇 |
免费 | 3314篇 |
国内免费 | 2501篇 |
专业分类
化学 | 10714篇 |
晶体学 | 228篇 |
力学 | 851篇 |
综合类 | 117篇 |
数学 | 1481篇 |
物理学 | 5658篇 |
无线电 | 6741篇 |
出版年
2024年 | 50篇 |
2023年 | 473篇 |
2022年 | 617篇 |
2021年 | 811篇 |
2020年 | 863篇 |
2019年 | 758篇 |
2018年 | 693篇 |
2017年 | 701篇 |
2016年 | 923篇 |
2015年 | 1022篇 |
2014年 | 1279篇 |
2013年 | 1516篇 |
2012年 | 1723篇 |
2011年 | 1831篇 |
2010年 | 1406篇 |
2009年 | 1377篇 |
2008年 | 1469篇 |
2007年 | 1358篇 |
2006年 | 1274篇 |
2005年 | 1084篇 |
2004年 | 732篇 |
2003年 | 606篇 |
2002年 | 552篇 |
2001年 | 461篇 |
2000年 | 375篇 |
1999年 | 340篇 |
1998年 | 235篇 |
1997年 | 223篇 |
1996年 | 211篇 |
1995年 | 167篇 |
1994年 | 131篇 |
1993年 | 113篇 |
1992年 | 106篇 |
1991年 | 73篇 |
1990年 | 60篇 |
1989年 | 47篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
71.
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
72.
Ming Jiang Qiang Ji Bruce F McEwen 《IEEE transactions on information technology in biomedicine》2006,10(3):608-617
We propose a model-based automated approach to extracting microtubules from noisy electron tomography volume. Our approach consists of volume enhancement, microtubule localization, and boundary segmentation to exploit the unique geometric and photometric properties of microtubules. The enhancement starts with an anisotropic invariant wavelet transform to enhance the microtubules globally, followed by a three-dimensional (3-D) tube-enhancing filter based on Weingarten matrix to further accentuate the tubular structures locally. The enhancement ends with a modified coherence-enhancing diffusion to complete the interruptions along the microtubules. The microtubules are then localized with a centerline extraction algorithm adapted for tubular objects. To perform segmentation, we novelly modify and extend active shape model method. We first use 3-D local surface enhancement to characterize the microtubule boundary and improve shape searching by relating the boundary strength with the weight matrix of the searching error. We then integrate the active shape model with Kalman filtering to utilize the longitudinal smoothness along the microtubules. The segmentation improved in this way is robust against missing boundaries and outliers that are often present in the tomography volume. Experimental results demonstrate that our automated method produces results close to those by manual process and uses only a fraction of the time of the latter. 相似文献
73.
Qiang Xu Nicolici N. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(11):1275-1285
Extensive research has been carried out for test planning of core-based system-on-a-chip devices. Most of the prior work assumes that all of the embedded cores are wrapped for test purpose. However, some designs may contain user-defined logic or cores that cannot be wrapped due to area constraints or timing violations. This paper discusses how these unwrapped logic blocks can be tested rapidly by adapting the TestRail architecture, which uses only the test control mechanism and the test instructions available through the IEEE 1500 standard for embedded core test. A new test scheduling algorithm, which facilitates a concurrent test of both unwrapped logic blocks and IEEE 1500-wrapped cores, is proposed, and experiments show that it outperforms a previous approach when the available number of tester channels and/or the number of unwrapped logic blocks are small. 相似文献
74.
In this paper, we present a numerical scheme for solving the coupled system of compressible miscible displacement problem in porous media. The flow equation is solved by the mixed finite element method, and the transport equation is approximated by a discontinuous Galerkin method. The scheme is continuous in time and a priori hp error estimates is presented. 相似文献
75.
本文介绍了电炉冶炼计时装置的设计与开发过程,详细介绍了系统软硬件及抗干扰设计.对同类产品开发具有参考意义. 相似文献
76.
崔光耀 《信息安全与通信保密》2006,(2):23-24
联想网御内部的一次人事变动,不仅牵动了业界的神经,也引起了社会各方的高度关注。信息安全的影响力透过这一事件再次显现。 相似文献
77.
崔光耀 《信息安全与通信保密》2006,(1):13-14
2005年信息安全领域发生了哪些变化,这些变化对信息安全有哪些影响?是抽苗还是拔穗,表面平静的2005年实在值得人们细细咀嚼。 相似文献
78.
崔光耀 《信息安全与通信保密》2005,(12):24-25
在国外做生意更容易 当诸多信息安全公司苦斗域内之 时,这些国内公司似乎并没有发现海外 这一更大的天地会是信息安全产品的另 一淘金宝地。在盘点2005年的业务时, 飞天诚信公司黄煜总经理给出了一个令 人吃惊的数据:今年飞天的整体业务 中,海外市场的销售占三分之一的份 相似文献
79.
利用SIMS和变温霍尔测量手段对P型Hg0.77Gd0.23Te液相外延材料的Ag掺杂技术、机理及掺杂碲镉汞材料的性能进行了研究。结果表明采用AgNO3溶液直接浸泡方式对该材料进行掺Ag是成功的,掺杂浓度与被掺杂材料中的汞空位浓度是一致的,掺杂后,P型碲镉汞材料的受主能级比掺杂前有明显的减小,从实验结果可看到掺Ag碲镉汞材料的电学性能在室温下保持稳定。 相似文献
80.