全文获取类型
收费全文 | 18548篇 |
免费 | 2505篇 |
国内免费 | 2957篇 |
专业分类
化学 | 14739篇 |
晶体学 | 292篇 |
力学 | 780篇 |
综合类 | 269篇 |
数学 | 2023篇 |
物理学 | 5907篇 |
出版年
2024年 | 39篇 |
2023年 | 196篇 |
2022年 | 481篇 |
2021年 | 495篇 |
2020年 | 540篇 |
2019年 | 597篇 |
2018年 | 493篇 |
2017年 | 457篇 |
2016年 | 744篇 |
2015年 | 807篇 |
2014年 | 976篇 |
2013年 | 1349篇 |
2012年 | 1516篇 |
2011年 | 1560篇 |
2010年 | 1189篇 |
2009年 | 1146篇 |
2008年 | 1405篇 |
2007年 | 1286篇 |
2006年 | 1169篇 |
2005年 | 982篇 |
2004年 | 915篇 |
2003年 | 827篇 |
2002年 | 926篇 |
2001年 | 743篇 |
2000年 | 572篇 |
1999年 | 447篇 |
1998年 | 278篇 |
1997年 | 286篇 |
1996年 | 236篇 |
1995年 | 211篇 |
1994年 | 187篇 |
1993年 | 174篇 |
1992年 | 158篇 |
1991年 | 114篇 |
1990年 | 104篇 |
1989年 | 87篇 |
1988年 | 50篇 |
1987年 | 52篇 |
1986年 | 42篇 |
1985年 | 36篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The decay process J/ψ→p X X→p P,where p,p and P are the proton,antiproton and pseudoscalar states,respectively,has been studied in terms of the angular distribution and the generalized moment analysis methods.The result shows that we can identify the spin,but cannot determine the parity of the baryon resonance state X produced in the process J/ψ→p X X→p P. 相似文献
72.
新型X射线靶设计为:由SiO2和TiO2组成具有12个周期的一维光子晶体,在它的中间嵌入光靶材料层作为缺陷层,SiO2,TiO2和光靶层的光学厚度分别为λ4、λ4和λ2,λ为抽运激光波长.与普通平板光靶相比,当抽运光垂直照射到这种光靶时,靶层内部的光强将提高2个数量级,所以抽运激光的阈值强度将降低2个数量级,这有利于X射线激光的小型化.在同样的抽运激光照射下,X射线激光的强度将提高4个数量级,转换效率也将提高约4个数量级.由于平均电离度随抽运激光强度的提高而提高,所以采用这种光靶有利于使X射线激光向短波长推进.
关键词:
X射线激光
光子晶体
光波局域 相似文献
73.
74.
基础房价的相关指标及其走势一直是大众关心的热门话题.本文通过对上海基础房价相关指标的分析,建立了市场房价走势的两个数学模型.模型一:在相关性分析的基础上利用主成分分析消除指标间的共线性,再用回归拟合房价模型并进行预测;模型二:在相关性分析的基础上利用核估计方法预测出房价.继呵对2005年下半年的房价走势进行了预测,得出的结果与实际情况相吻合. 相似文献
75.
ICP-AES测定饮用水源中的Cu、Mn、Pb、Cd、Zn 总被引:7,自引:2,他引:5
用ICP-AES法同时测定饮用水源中的Cu、Mn、Pb、Cd、Zn等重金属元素,具有基体效应小、测量范围宽等优点。检出限为0.2-4.0μg/L,回收率为91.5%-103.9%,相对标准偏差为0.29%-1.5%,测定密码样与实际样品,结果令人满意。 相似文献
76.
Yah ZHAO Xiao Qing LIU Hong You ZHU Zi Ming YANG Rong HUANG 《中国化学快报》2006,17(12):1543-1546
Bridged bis(β-cyclodextrin)s (CDs), as a very important family of CD derivatives, have been known that they can significantly alter the molecular binding ability and selectivity toward a variety of guests in comparison with parent cyclodextrin. Their two… 相似文献
77.
Qiu Hong WU He Xiang WANG Kun GAO State Key Laboratory of Applied Organic Chemistry College of Chemistry Chemical Engineering Lanzhou University Lanzhou 《中国化学快报》2006,17(2)
Many Ligularia species have long been used as traditional folk medicine for theirantibiotic, antiphlogistic and antitussive activities1, and were found to be an importantsource of eremophilane. In the course of our search for bioactive sesquiterpenoids, w… 相似文献
78.
连通图的离散度是用s(G)来表示的,s(G)=max{ω(G-S)-|S|:ω(G-S)>1,SV(G)}.给出了两个完全图乘积的和一个完全图与路的乘积的离散度.还给出了两个完全图乘积的坚韧度. 相似文献
79.
Yong LU Hong WANG Ye LIU Ming Yuan HE 《中国化学快报》2006,17(10):1397-1400
Recently, miniature H2 generator to power fuel cells for portable/micro electronic devices and passenger propulsion has been the focus of intense research activities1-3. One of the strategies is to find simple CO-free H2 production with novel microreactor… 相似文献
80.
Methods to synthesize magnetic Fe3O4 nanoparticles and to modify the surface of particles are presented in the present investigation. Fe3O4 magnetic nanoparticles were prepared by the co-precipitation of Fe3+ and Fe2+, NH3·H2O was used as the precipitating agent to adjust the pH value, and the aging of Fe3O4 magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe3O4 magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe3O4 crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe3O4 magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe3O4 nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe3O4 nanoparticles. The dispersion of Fe3O4 in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe3O4/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe3O4 magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe3O4 nanoparticles. The Fe3O4 magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10−8 and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe3O4 nanoparticles in the fluid was 36.19 nm. 相似文献