全文获取类型
收费全文 | 4062篇 |
免费 | 537篇 |
国内免费 | 397篇 |
专业分类
化学 | 2861篇 |
晶体学 | 33篇 |
力学 | 178篇 |
综合类 | 45篇 |
数学 | 594篇 |
物理学 | 1285篇 |
出版年
2024年 | 12篇 |
2023年 | 77篇 |
2022年 | 134篇 |
2021年 | 136篇 |
2020年 | 145篇 |
2019年 | 157篇 |
2018年 | 152篇 |
2017年 | 125篇 |
2016年 | 197篇 |
2015年 | 184篇 |
2014年 | 259篇 |
2013年 | 294篇 |
2012年 | 330篇 |
2011年 | 315篇 |
2010年 | 231篇 |
2009年 | 214篇 |
2008年 | 256篇 |
2007年 | 208篇 |
2006年 | 205篇 |
2005年 | 168篇 |
2004年 | 140篇 |
2003年 | 122篇 |
2002年 | 145篇 |
2001年 | 125篇 |
2000年 | 71篇 |
1999年 | 70篇 |
1998年 | 61篇 |
1997年 | 41篇 |
1996年 | 38篇 |
1995年 | 43篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 34篇 |
1991年 | 41篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1971年 | 5篇 |
1962年 | 3篇 |
排序方式: 共有4996条查询结果,搜索用时 15 毫秒
81.
A novel near infrared (NIR) modeling method—Laplacian regularized least squares regression (LapRLSR) was presented, which can take the advantage of many unlabeled spectra to promote the prediction performance of the model even if there are only few calibration samples. Using LapRLSR modeling, NIR spectral analysis was applied to the online monitoring of the concentration of salvia acid B in the column separation of Salvianolate. The results demonstrated that LapRLSR outperformed partial least squares (PLS) significantly, and NIR online analysis was applicable. 相似文献
82.
Zengshun Jiang Xingqi An Yuqin Zhang Xuan Liu Xifeng Qin Yanjie Zhao Huilin Wang Guiyuan Liu Hongsheng Song 《中国光学快报(英文版)》2021,(4):56-61
After the three-dimensional self-affine fractal random surface simulation, we use the optical scattering theory to calculate the deep Fresnel region speckle(DFRS) under consideration of the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution are studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area. 相似文献
83.
84.
85.
The (2+1)-dimensional Boiti–Leon–Manna–Pempinelli (BLMP) equation is an important integrable model. In this paper, we obtain the breather molecule, the breather-soliton molecule and some localized interaction solutions to the BLMP equation. In particular, by employing a compound method consisting of the velocity resonance, partial module resonance and degeneration of the breather techniques, we derive some interesting hybrid solutions mixed by a breather-soliton molecule/breather molecule and a lump, as well as a bell-shaped soliton and lump. Due to the lack of the long wave limit, it is the first time using the compound degeneration method to construct the hybrid solutions involving a lump. The dynamical behaviors and mathematical features of the solutions are analyzed theoretically and graphically. The method introduced can be effectively used to study the wave solutions of other nonlinear partial differential equations. 相似文献
86.
应用改进分析型嵌入原子方法(MAEAM)计算fcc金属的结构稳定性和声子谱.考虑更远邻原子之间的相互作用,提出新的两体势函数,并采用新的截尾处理函数和加强光滑连接条件.通过拟合单空位迁移能、结合能、三个独立弹性常数及晶体平衡条件,确定了模型参数.在体积不变条件下,计算金属不同结构的能量,说明Ag、Al、Au、Cu、Ir、Ni、Pd、Pt和Rh的fcc结构比较稳定.它们的能量-体积曲线与Rose方程结果基本-致,进-步说明了体积变化时的结构稳定性.同时发现[100]、[110]和[111]三个方向声子谱的计算结果符合实验值和其它计算结果. 相似文献
87.
Wenyu Zhao Shengli An Bin Fan Songbo Li 《Applied Physics A: Materials Science & Processing》2014,116(3):987-991
Tm3+ and In3+ co-doped LaAlO3 phosphors were prepared by a Pechini sol–gel method and characterized by X-ray diffraction, scanning electron microscope, and cathodoluminescence spectrum. The phosphor is composed of slightly aggregated particles with approximately spherical shape and a narrow size range of 1.0–1.5 μm. Under voltage electron beam excitation, the phosphor shows the characteristic emissions of Tm3+. All the color purity, radiant efficiency, luminous efficiency, and stability of the optimum LaAlO3:0.01Tm3+, 0.04In3+ phosphor are superior to these of commercial ZnS:Ag,Cl phosphor. These tests suggest that it could be a potential candidate as a blue phosphor for field emission displays. 相似文献
88.
89.
Damla Durak Anıl Delikanlı Cahit Demetgül İbrahim Kani Selahattin Serin 《Transition Metal Chemistry》2013,38(2):199-206
An unsymmetrical tetradentate Schiff base (H2L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H2L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance. 相似文献
90.
Montmorillonite K10 was found to catalyze the Michael addition of indoles or pyrrole with nitroalkenes efficiently under solventless condition. The short reaction time, simple workup, and excellent yields were noteworthy. The green catalyst could be reused for three runs without considerable variation in yield. 相似文献