全文获取类型
收费全文 | 51311篇 |
免费 | 9647篇 |
国内免费 | 7942篇 |
专业分类
化学 | 38618篇 |
晶体学 | 713篇 |
力学 | 3226篇 |
综合类 | 549篇 |
数学 | 5802篇 |
物理学 | 19992篇 |
出版年
2024年 | 112篇 |
2023年 | 983篇 |
2022年 | 1680篇 |
2021年 | 1898篇 |
2020年 | 2161篇 |
2019年 | 2207篇 |
2018年 | 1828篇 |
2017年 | 1816篇 |
2016年 | 2470篇 |
2015年 | 2603篇 |
2014年 | 3153篇 |
2013年 | 4066篇 |
2012年 | 4870篇 |
2011年 | 4984篇 |
2010年 | 3556篇 |
2009年 | 3604篇 |
2008年 | 3946篇 |
2007年 | 3292篇 |
2006年 | 3052篇 |
2005年 | 2541篇 |
2004年 | 1941篇 |
2003年 | 1657篇 |
2002年 | 1699篇 |
2001年 | 1374篇 |
2000年 | 1111篇 |
1999年 | 984篇 |
1998年 | 769篇 |
1997年 | 654篇 |
1996年 | 631篇 |
1995年 | 515篇 |
1994年 | 489篇 |
1993年 | 390篇 |
1992年 | 345篇 |
1991年 | 264篇 |
1990年 | 268篇 |
1989年 | 172篇 |
1988年 | 148篇 |
1987年 | 129篇 |
1986年 | 122篇 |
1985年 | 88篇 |
1984年 | 46篇 |
1983年 | 48篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 22篇 |
1977年 | 11篇 |
1957年 | 11篇 |
1936年 | 9篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
111.
U型管内液柱振动的演示实验研究 总被引:1,自引:1,他引:0
根据实验结果,分析了影响U型管中液柱振动的各种因素,给出了获得好的演示效果的改进措施. 相似文献
112.
利用场发射显微镜和四极质谱计研究了充入高纯O2的四极质谱和O2对单壁碳纳米管场发射的影响.单壁碳纳米管经过约1000℃的热处理得到清洁态场发射像后,充入O2,分别测量了O2吸附和脱附后场发射的I V特性.实验观测到在单壁碳纳米管上O2的吸附使场发射电流减小,说明逸出功增加.在10-4Pa的O2压强下对单壁碳纳米管进行约1000℃的热处理,可以产生氧化刻蚀作用,观测到场发射像的变化,并测量了氧化刻蚀产生的I V特性变化.
关键词:
单壁碳纳米管
场发射显微镜
场发射
四极质谱 相似文献
113.
114.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
115.
116.
117.
Ping Li Fei Rong Yibing Xie Van Hu Chunwei Yuan 《Journal of Analytical Chemistry》2004,59(10):939-944
S-naproxen imprinted polymer was prepared with acrylamide as a functional monomer, 1,4-butanediyl diacrylate as a new kind of crossliner, and 2,4,6-trimethylbenzoylphenyl-phosphinic acid ethyl ester as photoinitiator. Their UV and IR spectra were applied to study the interactions between the template and the monomer. Binding experiments showed that the S-naproxen imprinted polymer had better recognition capability for the template than that of a blank polymer. The adsorption distribution coefficient KD of S-naproxen on molecularly-imprinted polymer was 153.2 g/mL, and the separation factor was 1.95 when the initial concentration of substrate was 2.0 mmol/L. Scatchard curves suggested that there were two classes of binding sites in the imprinted polymer and only one class in the blank polymer. Computer simulation using Hyperchem showed the existence of the interactions between the template and the functional monomer as well as the models of the complexes formed by the template and the monomer. 相似文献
118.
119.
The process of single liquid drop impact on thin liquid surface is numerically simulated with moving particle semi‐implicit method. The mathematical model involves gravity, viscosity and surface tension. The model is validated by the simulation of the experimental cases. It is found that the dynamic processes after impact are sensitive to the liquid pool depth and the initial drop velocity. In the cases that the initial drop velocity is low, the drop will be merged with the liquid pool and no big splash is seen. If the initial drop velocity is high enough, the dynamic process depends on the liquid depth. If the liquid film is very thin, a bowl‐shaped thin crown is formed immediately after the impact. The total crown subsequently expands outward and breaks into many tiny droplets. When the thickness of the liquid film increases, the direction of the liquid crown becomes normal to the surface and the crown propagates outward. It is also found that the radius of the crown is described by a square function of time: rC = [c(t ? t0)]0.5. When the liquid film is thick enough, a crown and a deep cavity inside it are formed shortly after the impact. The bottom of the cavity is initially oblate and then the base grows downward to form a sharp corner and subsequently the corner moves downward. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
120.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献