全文获取类型
收费全文 | 2111篇 |
免费 | 422篇 |
国内免费 | 305篇 |
专业分类
化学 | 1312篇 |
晶体学 | 5篇 |
力学 | 175篇 |
综合类 | 10篇 |
数学 | 565篇 |
物理学 | 771篇 |
出版年
2024年 | 11篇 |
2023年 | 52篇 |
2022年 | 101篇 |
2021年 | 107篇 |
2020年 | 149篇 |
2019年 | 121篇 |
2018年 | 103篇 |
2017年 | 97篇 |
2016年 | 123篇 |
2015年 | 112篇 |
2014年 | 152篇 |
2013年 | 157篇 |
2012年 | 133篇 |
2011年 | 170篇 |
2010年 | 110篇 |
2009年 | 120篇 |
2008年 | 97篇 |
2007年 | 94篇 |
2006年 | 108篇 |
2005年 | 66篇 |
2004年 | 80篇 |
2003年 | 52篇 |
2002年 | 62篇 |
2001年 | 60篇 |
2000年 | 35篇 |
1999年 | 39篇 |
1998年 | 48篇 |
1997年 | 37篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有2838条查询结果,搜索用时 15 毫秒
981.
Dai-Qiang Chen Li-Zhi Cheng Fang Su 《Journal of Computational and Applied Mathematics》2011,235(8):2766-2774
We propose a new fast algorithm for solving a TV-based image restoration problem. Our approach is based on merging subspace optimization methods into an augmented Lagrangian method. The proposed algorithm can be seen as a variant of the ALM (Augmented Lagrangian Method), and the convergence properties are analyzed from a DRS (Douglas-Rachford splitting) viewpoint. Experiments on a set of image restoration benchmark problems show that the proposed algorithm is a strong contender for the current state of the art methods. 相似文献
982.
分束器是光纤通信系统中光无源网络和光子集成回路的重要器件.1×2 MMI(multimode interferences)电光有机聚合物分束器是利用自成像效应设计的.分析了1×2 MMI 的工作原理.利用有效折射率方法(effective index method,EIM)计算出1×2 MMI 三维多模脊形波导的有效折射率分布.利用自成像效应的成像规律计算出成像位置并用导模传输分析法(guided-mode propagation analysis,MPA)对输出波导的光强进行模拟.分析表明:在波长为 1.55μm 的情况下,1×2 MMI 的输出波导的光强在未加电极时可以实现预定分束比输出;加上电极之后,由于电光效应可调控有机聚合物波导折射率的改变,利用有限差分光束传播法模拟输出波导的分束比可在7.6 dB 范围内可调. 相似文献
983.
为了在不影响干涉条纹成像质量的基础上通过增大双折射棱镜结构角的方法获得更细致的光谱成分,优化设计了双折射棱镜的结构.通过计算分束角与结构角之间的函数关系,分析得知在传统双折射棱镜后附加一个与第二个楔形同性质的等腰三角形棱镜,使出射棱镜的o光和e光平行于光轴,即分束角α为0°,从而干涉条纹的成像不再受分束角的变化所影响.... 相似文献
984.
基于完全对角化方法(complete diagonalization method, CDM), 研究了6 S(3d5)态离子在三角晶场(包括C3v,D3,D3d点群对称晶场)中零场分裂(zero-field splitting, ZFS)参量D和(a-F)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同
关键词:
6 S(3d5)态离子')" href="#">6 S(3d5)态离子
零场分裂参量
磁相互作用
完全对角化方法 相似文献
985.
986.
A method is presented to facilitate the non-target analysis of data obtained in temperature-programmed comprehensive two-dimensional (2D) gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-ToF-MS). One main difficulty of GC×GC data analysis is that each peak is usually modulated several times and therefore appears as a series of peaks (or peaklets) in the one-dimensionally recorded data. The proposed method, 2DAid, uses basic chromatographic laws to calculate the theoretical shape of a 2D peak (a cluster of peaklets originating from the same analyte) in order to define the area in which the peaklets of each individual compound can be expected to show up. Based on analyte-identity information obtained by means of mass spectral library searching, the individual peaklets are then combined into a single 2D peak. The method is applied, amongst others, to a complex mixture containing 362 analytes. It is demonstrated that the 2D peak shapes can be accurately predicted and that clustering and further processing can reduce the final peak list to a manageable size. 相似文献
987.
Verstraeten M Broeckhoven K Dittmann M Choikhet K Witt K Desmet G 《Journal of chromatography. A》2011,1218(8):1170-1184
We report on a first series of experiments comparing the selectivity and the kinetic performance of constant flow rate and constant pressure mode gradient elution separations. Both water-methanol and water-acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the constant flow rate and the constant pressure mode is a (small) difference in efficiency caused by the difference in average flow rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20-95% water-acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20-40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5-10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained. 相似文献
988.
The peak spreading of DNAs of various sizes [12-mer, 20-mer, 50-mer and 95-mer poly(T)] in linear gradient elution (LGE) chromatography with a thin monolithic disk was investigated by using our method developed for determining HETP in LGE. Electrostatic interaction-based chromatography mode (ion-exchange chromatography, IEC) was used. Polymer-based monolithic disks of two different sizes (12 mm diameter, 3mm thickness and 0.34 mL; 5.2 mm diameter, 4.95 mm thickness and 0.105 mL) having anion-exchange groups were employed. For comparison, a 15-μm porous bead IEC column (Resource Q, 6.4mm diameter, 30 mm height and 0.97 mL) was also used. The peak width did not change with the flow velocity for the monolithic disks where as it became wider with increasing velocity. For the monolithic disks the peak width normalized with the column bed volume was well-correlated with the distribution coefficient at the peak position K(R). HETP values were constant (ca. 0.003-0.005 cm) when K(R)>5. Much higher HETP values which are flow-rate dependent were obtained for the porous bead chromatography. It is possible to obtain 50-100 plates for the 3mm monolithic disk. This results in very sharp elution peaks (standard deviation/bed volume=0.15) even for stepwise elution chromatography, where the peak width is similar to that for LGE of a very steep gradient slope. 相似文献
989.
Xiang C Liu G Kang S Guo X Yao B Weng W Zeng Q 《Journal of chromatography. A》2011,1218(48):8718-8721
Enantioseparation of naproxen was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar alcohol modifier in mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. Two unusual phenomena were observed. One was solvent-induced reversal of elution order for the two enantiomers. Not only the type but also the content of polar alcohol modifier could induce the reversal. Another uncommon phenomenon was peak deformation under some chromatographic conditions. 相似文献
990.