全文获取类型
收费全文 | 35762篇 |
免费 | 5122篇 |
国内免费 | 3572篇 |
专业分类
化学 | 20696篇 |
晶体学 | 344篇 |
力学 | 1153篇 |
综合类 | 188篇 |
数学 | 2520篇 |
物理学 | 8711篇 |
无线电 | 10844篇 |
出版年
2024年 | 129篇 |
2023年 | 689篇 |
2022年 | 922篇 |
2021年 | 1277篇 |
2020年 | 1238篇 |
2019年 | 1236篇 |
2018年 | 1095篇 |
2017年 | 1058篇 |
2016年 | 1556篇 |
2015年 | 1623篇 |
2014年 | 1903篇 |
2013年 | 2552篇 |
2012年 | 2886篇 |
2011年 | 2973篇 |
2010年 | 2198篇 |
2009年 | 2211篇 |
2008年 | 2486篇 |
2007年 | 2215篇 |
2006年 | 2043篇 |
2005年 | 1814篇 |
2004年 | 1453篇 |
2003年 | 1349篇 |
2002年 | 1445篇 |
2001年 | 1023篇 |
2000年 | 780篇 |
1999年 | 704篇 |
1998年 | 512篇 |
1997年 | 464篇 |
1996年 | 379篇 |
1995年 | 336篇 |
1994年 | 249篇 |
1993年 | 223篇 |
1992年 | 233篇 |
1991年 | 195篇 |
1990年 | 144篇 |
1989年 | 113篇 |
1988年 | 93篇 |
1987年 | 71篇 |
1986年 | 72篇 |
1985年 | 82篇 |
1984年 | 51篇 |
1983年 | 39篇 |
1982年 | 42篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1975年 | 23篇 |
1970年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
A new numerical method called linearized and rational approximation method is presented to solve non‐linear evolution equations. The utility of the method is demonstrated for the case of differentiation of functions involving steep gradients. The solution of Burgers' equation is presented to illustrate the effectiveness of the technique for the solution of non‐linear evolution equations exhibiting nearly discontinuous solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
262.
263.
Do Young Kim Ji Sim Jung Young Rae Jang Kun Ho Yoo Jin Jang 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):400
We studied the growth of nanocrystalline silicon (nc-Si) thin film exhibiting a strong room temperature photoluminescence (PL) at 1.81–2.003 eV. The amorphous silicon was crystallized by Ni silicide mediated crystallization (Ni SMC) and then Secco-etched to exhibit the PL. The PL peak energy and intensity increase with increasing the metal density on the a-Si because of the reduction in the grain size down to 2 nm. The photoluminescence energy and peak intensity depend strongly on the Secco etch time because the grain size is reduced by etching the grain boundaries. 相似文献
264.
Jun Jiao Lifeng Dong Sean Foxley Catherine L Mosher David W Tuggle 《Microscopy and microanalysis》2003,9(6):516-521
In this article, we report a technique for growing carbon nanotubes in a more controllable fashion, which enables us to synthesize nanotubes directly in various forms of designed patterns. This nanofabrication process is based on a combination of focused ion beam (FIB) and chemical vapor deposition (CVD) techniques. In this process, arrays of conductive patterns were first deposited on silicon substrates by directing a gaseous compound (C(9)H(16)Pt) via the capillary needle-sized nozzles within a FIB system. The substrates were then coated with catalyst and further modified by the FIB to localize the position of the catalyst. Finally, the growth of carbon nanotubes on the designed substrates was carried out by CVD of hydrocarbon gases. This fabrication technique has the advantage of positioning carbon nanotubes in selected locations. This may open up opportunities for the direct synthesis of carbon nanotubes onto almost any substrate material, thus allowing fabrication of carbon nanotube-based devices. 相似文献
265.
Diode lasers used to pump high average power solid-state lasers typically have broad spectral width so that most of the pump light is not at the peak of the gain medium's absorption feature. However, the long absorption length in these lasers enables even weakly absorbed light to pump efficiently. The result is that high absorption efficiency and improved pump distribution uniformity are possible when using realistic pump diodes. In addition, both quantities are nearly independent of the pump center wavelength. 相似文献
266.
Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献
267.
268.
Summary The stability constants of Eu3+ and Am3+ with the site specific humic acid (YKHA) have been determined. The humic acid has been extracted from the soil of Yongkwang
area belonging geologically to the Okchon Basin of the Korean Peninsula, where the nuclear power plant is located. The total
carboxylate capacity, the acidity constant (pKa), and the binding constants with Eu3+ and Am3+ have been determined for humic acid. 相似文献
269.
利用熔融KOH和Co3O4在较低温度(480℃)下反应制备出K0.36CoO2,然后用高锰酸钾溶液和饱和的过硫酸钾溶液进行氧化处理.氧化的同时伴随有水分子嵌入.K0.36CoO2用高锰酸钾和过硫酸钾溶液处理后分别得到K0.12CoO2·0.8H2O和K0.16CO2·0.6H2O.这两种化合物都属于六角晶系,表现出金属行为,脱水后主相变为正交结构并且呈现出半导体特性.K0.16CoO2·0.6H2O在56K附近可能存在自旋玻璃转变行为或其他涨落.随着钾含量的减少和水含量的增多,样品的自旋玻璃行为受到抑制或发生磁性相分离.样品K0.12CoO2·0.8H2O在零场冷却和有场冷却曲线上的分叉现象基本上消失.还讨论了产生KxCoO2与NaxCoO2体系结构和物性差别的原因. 相似文献
270.
The polycrystalline sample of layered compound FePS_3 has been investigated by using M?ssbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below T_N=120.5±1K. The M?ssbauer spectra below T_N indicate that the magnetization axis is perpendicular to the layer of FePS_3, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect. 相似文献