全文获取类型
收费全文 | 43593篇 |
免费 | 5908篇 |
国内免费 | 5254篇 |
专业分类
化学 | 31946篇 |
晶体学 | 497篇 |
力学 | 2258篇 |
综合类 | 390篇 |
数学 | 5218篇 |
物理学 | 14446篇 |
出版年
2024年 | 127篇 |
2023年 | 705篇 |
2022年 | 1188篇 |
2021年 | 1299篇 |
2020年 | 1440篇 |
2019年 | 1477篇 |
2018年 | 1242篇 |
2017年 | 1152篇 |
2016年 | 1765篇 |
2015年 | 1815篇 |
2014年 | 2216篇 |
2013年 | 2966篇 |
2012年 | 3485篇 |
2011年 | 3739篇 |
2010年 | 2656篇 |
2009年 | 2605篇 |
2008年 | 2918篇 |
2007年 | 2605篇 |
2006年 | 2351篇 |
2005年 | 2149篇 |
2004年 | 1700篇 |
2003年 | 1469篇 |
2002年 | 1532篇 |
2001年 | 1217篇 |
2000年 | 1023篇 |
1999年 | 966篇 |
1998年 | 795篇 |
1997年 | 697篇 |
1996年 | 702篇 |
1995年 | 564篇 |
1994年 | 555篇 |
1993年 | 472篇 |
1992年 | 469篇 |
1991年 | 416篇 |
1990年 | 331篇 |
1989年 | 287篇 |
1988年 | 225篇 |
1987年 | 161篇 |
1986年 | 194篇 |
1985年 | 198篇 |
1984年 | 126篇 |
1983年 | 90篇 |
1982年 | 91篇 |
1981年 | 64篇 |
1980年 | 61篇 |
1979年 | 65篇 |
1978年 | 49篇 |
1976年 | 44篇 |
1974年 | 50篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Ching-Cherng Sun You-Nian Lin Shih-Po Yeh Wei-Chia Su Yuh Ouyang 《Optics & Laser Technology》2002,34(7):523-526
High longitudinal selectivity of the shifting multiplexing with spherical reference wave is proposed and demonstrated. A simplified method based on wave optics is used for calculating the selectivity, and the result fits well the experimental measurement. Under the paraxial condition, a simple formula for the longitudinal selectivity is introduced. With use of an object lens with effective NA=0.817, we obtain that an FWHM of selectivity is as small as 1 μm. 相似文献
92.
用射频磁控溅射结合传统退火的方法制备LiCo0.8M0.2O2 (M=Ni,Zr)阴极薄膜.X射线衍射、拉曼光谱、扫描电子显微镜等手段表征了不同掺杂的LiCo0.8M0.2O2薄膜.结果显示,700℃退火的LiCo0.8M0.2O2薄膜具有类似α-NaFeO2的层状结构.通过对不同掺杂锂钴氧阴极的全固态薄膜锂电池Li/LiPON/LiCo0.8M0.2O2的电化学性能研究表明,电化学活性元素Ni的掺杂使全固态电池具有更大的放电容量(56μAh/cm2μm),而非电化学活性元素Zr的掺杂使全固态电池具有更好的循环稳定性. 相似文献
93.
1引言许多科学和工程计算问题都可以归结为无界区域上的偏微分方程边值问题.而求解椭圆方程边值问题的常用技术是有限元方法,可是对于无界区域,在用有限元方法求解时,往往遇到困难.最简单的办法显然是直接略去区域的无界部分求解,但这样做或者导致过低的计算精度,或者要付出很高的计算代价.边界归化,即将求解偏微分方程边值问题转化为边界积分方程,是求解某些无界区域问题的强有力的手段.自70年代以来,有限元和 相似文献
94.
95.
得到εdx/dt=A(t)x的扰动系统具有指数型二分性一个充分条件,作为应用得到其扰动系统概周期解及有界解的存在性,推广了[1,2,3]的结果。 相似文献
96.
97.
主要讨论了不含k-C-圈的n阶r-一致超图,对不同的k,分别得出了它的极大边数的一个下界,并且得出在有些情况下它的下界是最大的.另外,我们得到了Krn含k-C-圈的一个充分必要条件. 相似文献
98.
A new formulation derived from thermal characters of inclusions and host films for estimating laser induced damage threshold has been deduced. This formulation is applicable for dielectric films when they are irradiated by laser beam with pulse width longer than tens picoseconds. This formulation can interpret the relationship between pulse-width and damage threshold energy density of laser pulse obtained experimentally. Using this formulation, we can analyze which kind of inclusion is the most harmful inclusion. Combining it with fractal distribution of inclusions, we have obtained an equation which describes relationship between number density of inclusions and damage probability. Using this equation, according to damage probability and corresponding laser energy density, we can evaluate the number density and distribution in size dimension of the most harmful inclusions. 相似文献
99.
Chen-Cheng Sun Shih-Chin Lee Yaw-Shyan Fu Yu-Hwe Lee 《Applied Surface Science》2006,252(23):8295-8300
CrNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability and non-sticking properties (low surface free energy). However, few data has been published on the surface free energy (SFE) of CrNx films at temperatures in the range 20-170 °C. In this study CrNx thin films with CrN, Cr(N), Cr2N (and mixture of these phases) were prepared using closed field unbalanced magnetron sputtering at a wide range of Cr+2 emission intensity. The contact angles of water, di-iodomethane and ethylene glycol on the coated surfaces were measured at temperatures in the range 20-170 °C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the CrNx films and their components (e.g., dispersion, polar) were calculated using the Owens-Wendt geometric mean approach. The influences of CrNx film surface roughness and microstructure on the surface free energy were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The experimental results showed that the lowest total SFE was obtained corresponding to CrN at temperature in 20 °C. This is lower than that of Cr(N), Cr2N (and mixture of these phases). The total SFE, dispersive SFE and polar SFE of CrNx films decreased with increasing surface temperature. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. 相似文献
100.
X. Luo F. Y. Shi J. X. Lin 《International Journal of Infrared and Millimeter Waves》1991,12(2):141-147
Detection of COCl2, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN2 cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC 相似文献