全文获取类型
收费全文 | 2740篇 |
免费 | 512篇 |
国内免费 | 403篇 |
专业分类
化学 | 2064篇 |
晶体学 | 17篇 |
力学 | 153篇 |
综合类 | 22篇 |
数学 | 308篇 |
物理学 | 1091篇 |
出版年
2024年 | 8篇 |
2023年 | 58篇 |
2022年 | 106篇 |
2021年 | 66篇 |
2020年 | 114篇 |
2019年 | 114篇 |
2018年 | 116篇 |
2017年 | 101篇 |
2016年 | 147篇 |
2015年 | 123篇 |
2014年 | 173篇 |
2013年 | 189篇 |
2012年 | 221篇 |
2011年 | 233篇 |
2010年 | 175篇 |
2009年 | 170篇 |
2008年 | 206篇 |
2007年 | 147篇 |
2006年 | 157篇 |
2005年 | 159篇 |
2004年 | 110篇 |
2003年 | 102篇 |
2002年 | 109篇 |
2001年 | 76篇 |
2000年 | 58篇 |
1999年 | 63篇 |
1998年 | 49篇 |
1997年 | 28篇 |
1996年 | 35篇 |
1995年 | 43篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有3655条查询结果,搜索用时 296 毫秒
941.
Coupled atomic-molecular condensates in a double-well potential: decaying molecular oscillations 总被引:1,自引:0,他引:1
H. Jing S. Gu M. Zhan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(2):271-275
We present a four-mode model that describes coherent
photo-association (PA) in a double-well Bose-Einstein condensate,
focusing on the average molecular populations in certain
parameters. Our numerical results predict an interesting
strong-damping effect of molecular oscillations by controlling the
particle tunnellings and PA light strength, which may provide a
promising way for creating a stable molecular condensate via
coherent PA in a magnetic double-well potential. 相似文献
942.
943.
Xiaoyun Liu Guozhu Zhan Yingfeng Yu Shanjun Li 《Journal of Polymer Science.Polymer Physics》2006,44(21):3102-3108
The structural transition in the polyethersulfone (PES)‐modified bismaleimide resin, 4,4′‐bismaleimidodiphenylmethane (BDM), during isothermal curing was studied by using rheological technique, different scanning calorimetry (DSC), and time resolved light scattering (TRLS). Comparing with the cure of neat bismaleimide, two separate tan δ crossover points were observed because of the phase separation during curing the blends of PES/BDM. These two structural transitions stemmed from the fixing of phase structure of the system and the chemical crosslinking of bismaleimide, respectively. The effect of curing temperature and the PES content on structural transition was discussed and found that the occurrence of two structural transition exhibited the different dependency of curing temperature and PES content. The relaxation exponent n and gel strength S were also found to be temperature‐dependent and composition‐dependent. Moreover, the relaxation exponent n of the second structural transition is much lower than that of the first structural transition in the PES/bismaleimide blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3102–3108, 2006 相似文献
944.
将Feshbach-Kerman-Koonin(FKK)量子多步复合(MSC)理论推广至核子自旋为1/2,靶核自旋任意,在j-j表象严格处理角动量耦合,得到自旋为1/2的FKK-MSC公式.进一步用光学模型吸收代替门态强度函数,以及用复合核衰变宽度代替平衡态的逃逸宽度,给出了FKK-MSC理论与复合核反应Hauser-Feshbach模型(HFM)的一个统一表达式.这一公式将MSC和HFM与光学模型相联系,对核反应给出自洽和一致的描述.利用上述工作对一些典型的核反应实验进行了初步地分析,计算结果合理,与实验数据符合尚好. 相似文献
945.
946.
We study the optimal control of an assembly system that produces one assembled-to-order final product with multiple made-to-stock components and sells it at variable price. It is shown that a threshold control on component production, product price, and product orders maximizes total discounted profit over an infinite horizon. 相似文献
947.
Based on geometry picture of gravitational gauge theory, the cosmological constant is determined theoreti-cally. The cosmological constant is related to the average energy density of gravitational gauge field. Because the energydensity of gravitational gauge field is negative, the cosmological constant is positive, which generates repulsive force onstars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of theorder of about 10-52m-2, which is well consistent with experimental results. 相似文献
948.
酞菁锌掺杂二氧化硅凝胶基质的光谱学特征 总被引:1,自引:1,他引:0
利用溶胶凝胶技术将四磺化酞菁锌 (ZnPcS4)成功地引入到了二氧化硅凝胶基质中 ,制备了均匀掺杂的有机 /无机复合干凝胶。研究ZnPcS4分子在溶胶凝胶过程中紫外可见吸收光谱的变化规律以探索其在复合体系中的存在状态。实验表明 ,在溶胶阶段 ,随着时间的延长 ,紫外可见吸收光谱中单体的吸收峰强度增大 ,说明凝胶中酞菁单体的浓度增大 ;而形成凝胶后 ,随着时间的延长 ,紫外可见吸收光谱中单体的吸收峰强度减小 ,二聚体的吸收峰强度增大 ,说明由于体系结构和微化学环境的变化 ,酞菁分子趋向于聚合。 相似文献
949.
A novel route was proposed for preparation of zwitterionic membranes, and it comprises (1) free radical polymerization between glycidylmethacrylate (GMA) and acrylic acid (AA) monomers and (2) subsequent ring-opening of epoxide and quaternary amination with trimethylamine hydrochloride. The reaction products were confirmed by FTIR spectra. The cation-exchange capacities (CIECs) and anion-exchange capacities (AIECs) of these zwitterionic membranes are within the range of (5.4–9.3) × 10−2 and (30.6–11.1) × 10−2 mmol g−1, respectively. In addition, the CIEC increases as AA content increases, but the AIEC generally decreases. TGA and DrTGA measurements reveal that their thermal stabilities can arrive at as high as 380 °C. The water uptake is independent of pH. As for membrane potential and streaming potential, they both suggest that these membranes possess the characteristics of anion-exchange membranes and no IEP is observed. Permeation experiments of mixed KCl and glucose solution indicate that the transport behavior of ions is dependent on the membrane’s charge density. 相似文献
950.
Z. L. Xiao D. Liu C. F. Wang Z. Cao X. F. Zhan Z. L. Yin Q. Y. Chen H. L. Liu F. Xu L. X. Sun 《Journal of Thermal Analysis and Calorimetry》2009,95(2):513-515
The effect of mechanical alloying on Zn-Sb alloy system is investigated with X-ray diffraction (XRD), laser grain size analysis
and differential scanning calorimetry (DSC) respectively. The results of laser particle size analysis shows that the particle
size decreases with increasing of the grinding time between 0 and 24 h. XRD and DSC results indicate that longer the grinding
time of Zn-Sb is, the more content of Zn4Sb3 become in the product in this process. 相似文献