全文获取类型
收费全文 | 1817篇 |
免费 | 70篇 |
国内免费 | 105篇 |
专业分类
化学 | 225篇 |
晶体学 | 16篇 |
力学 | 49篇 |
综合类 | 4篇 |
数学 | 211篇 |
物理学 | 706篇 |
综合类 | 781篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 27篇 |
2021年 | 22篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 21篇 |
2017年 | 42篇 |
2016年 | 65篇 |
2015年 | 61篇 |
2014年 | 123篇 |
2013年 | 83篇 |
2012年 | 104篇 |
2011年 | 185篇 |
2010年 | 157篇 |
2009年 | 150篇 |
2008年 | 139篇 |
2007年 | 125篇 |
2006年 | 92篇 |
2005年 | 90篇 |
2004年 | 59篇 |
2003年 | 66篇 |
2002年 | 45篇 |
2001年 | 52篇 |
2000年 | 27篇 |
1999年 | 28篇 |
1998年 | 30篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1992条查询结果,搜索用时 0 毫秒
1.
提出TCP/IP在过程控制中的应用. 评价TCP/IP控制系统性能,通过传统控制系统与TCP/IP控制系统的比较,指出采用TCP/IP 控制系统的优缺点. 说明过程控制技术中,采用TCP/IP是一种更好的选择. 相似文献
2.
三峡工程二期围堰是三峡工程最重要的临时建筑物之一,大江截流水深大,流量大;防渗墙深度大,工程量大,工期紧,且还要穿过各种复杂地层,通过试验,研究,采取有效地对策确保大江安全,顺利截流,基坑按三峡总工期目标要求抽干,检查渗漏量仅为设计估计量的1/10。 相似文献
3.
4.
用蜗牛酶处理对数期啤酒酵母和异常汉逊酵母细胞,可以有效地从中分离到原生质体透射电镜观察证明了细胞中周质体的存在,揭示了酵母原生质体的释放机理和蜗牛酶的作用位点。 相似文献
5.
This paper presents a method to estimate reflected and transmitted wave amplitude spectra in a bounded domain such as a wave tank, when available data signals must be shortened due to interferences and wall effects. This paper extends the well known Goda and Suzuki two-probe method to three probes. The paper also suggests solutions to compute reliable transmission and reflection coefficients in spite of problems linked to higher harmonics and to the interference between different wave trains propagating in the tank. To cite this article: G. Duclos, A.H. Clément, C. R. Mecanique 331 (2003). 相似文献
6.
We investigated iron and cobalt films with 20% carbon concentration with nanocrystalline structure. One of the aims of this work is to analyze the physical nature of high-speed structural self-assembling as often happens in explosive crystallization processes in these films. 相似文献
7.
张俊祥 《南京邮电大学学报(自然科学版)》1991,(1)
本文基于PAL信号的频谱特点,分析了由2H延迟线组成的梳状滤波器分离亮度信号的原理,给出了实验电路框图,并简要叙述了误差带来的影响。 相似文献
8.
C. D. Eisenbach A. Göldel M. Terskan-Reinold U. S. Schubert 《Colloid and polymer science》1998,276(9):780-785
Transmission electron microscopy (TEM) studies on bipyridine (bpy) containing block copolymer systems showed the formation
of nanoscopic polymer–ion complexes through complexation with copper(I) ions which segregated to highly ordered columnar domains
of mesoscopic dimensions. The domains, i.e. stacks of [(bpy)2Cu(I)] complex moieties could be visualized by complementary TEM techniques. First, electron energy loss spectra (EELS) showed
the absorption edges of copper and nitrogen, which are specific for the bipyridine copper complexes. The element spectroscopic
imaging (ESI) technique allowed the imaging of the net copper and net nitrogen distribution, and the coinciding pictures exhibited
a microphase separated system in the case of a 3-block copolymer with complexed end segments. High resolution elastic bright
field images showed interference lines with a line to line distance of about 8 A which could be related to the Cu–Cu distance
in staggered Cu(I)–bipyridine complexes.
Received: 6 August 1997 Accepted: 28 April 1998 相似文献
9.
Poly(methyl methacrylate) (PMMA)/silica/titania ternary nanocomposites with covalent bonding interaction between polymer and inorganic phases have been prepared using a novel non-hydrolytic sol-gel method. Transmission electron microscope (TEM) image of silica/titania binary inorganic component indicates a core-shell-like structure. Scanning electron microscope (SEM) images suggest that the well dispersed silica/titania particles in the hybrid are on the nanometer-scale. The transparencies of nanocomposites are maintained in visible region while the absorption band in ultraviolet (UV) region is red shifted with increasing inorganic content. The thermogravimetric analysis (TGA) results show that the thermal stability of PMMA copolymer increases dramatically with the addition of silica/titania moieties both in nitrogen and in air. 相似文献
10.
Igor Djerdj Georg Garnweitner Markus Niederberger 《Journal of solid state chemistry》2007,180(7):2154-2165
The preparation of lanthanum hydroxide and manganese oxide nanoparticles is presented, based on a nonaqueous sol-gel process involving the reaction of La(OiPr)3 and KMnO4 with organic solvents such as benzyl alcohol, 2-butanone and a 1:1 vol. mixture thereof. The lanthanum manganese oxide system is highly complex and surprising results with respect to product composition and morphology were obtained. In dependence of the reaction parameters, the La(OH)3 nanoparticles undergo a shape transformation from short nanorods with an average aspect ratio of 2.1 to micron-sized nanofibers (average aspect ratio is more than 59.5). Although not directly involved, KMnO4 plays a crucial role in determining the particle morphology of La(OH)3. The reason lies in the fact that KMnO4 is able to oxidize the benzyl alcohol to benzoic acid, which presumably induces the anisotropic particle growth in [0 0 1] direction upon preferential coordination to the ±(1 0 0), ±(0 1 0) and ±(−110) crystal facets. By adjusting the molar La(OiPr)3-to-KMnO4 ratio as well as by using the appropriate solvent mixture it is possible to tailor the morphology, phase purity and microstructure of the La(OH)3 nanoparticles. Postsynthetic thermal treatment of the sample containing La(OH)3 nanofibers and β-MnOOH nanoparticles at the temperature of 800 °C for 8 h yielded polyhedral LaMnO3 and worm-like La2O3 nanoparticles as final products. 相似文献