全文获取类型
收费全文 | 922篇 |
免费 | 137篇 |
国内免费 | 90篇 |
专业分类
化学 | 420篇 |
晶体学 | 10篇 |
力学 | 226篇 |
综合类 | 7篇 |
数学 | 211篇 |
物理学 | 275篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 37篇 |
2018年 | 29篇 |
2017年 | 38篇 |
2016年 | 28篇 |
2015年 | 36篇 |
2014年 | 55篇 |
2013年 | 79篇 |
2012年 | 63篇 |
2011年 | 59篇 |
2010年 | 46篇 |
2009年 | 52篇 |
2008年 | 59篇 |
2007年 | 44篇 |
2006年 | 62篇 |
2005年 | 47篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 32篇 |
2001年 | 39篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 12篇 |
1995年 | 18篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 0 毫秒
81.
通过保持非耗散介观LC电路的固有频率不变,而使电路参数作阶跃函数变化,就可将介观LC电路由初始的偶相干态制备到压缩偶相干态;在压缩偶相干态下,介观电路系统不仅有非经典的量子压缩效应,而且有非经典的反聚束效应.
关键词:
介观LC电路
单位阶跃函数
压缩算符
压缩偶相干态 相似文献
82.
83.
Uniform-sized molecularly imprinted polymer (MIP) beads were prepared using a one-step swelling and polymerization method. The obtained sulfamethazine (SMZ)-imprinted polymer showed high affinity and selectivity toward SMZ and other structurally related sulfonamides in acetonitrile or water-acetonitrile mobile phases, particularly in high aqueous systems. The column performance of the MIPs for SMZ and its analogues could be improved by elevating the column temperature and optimizing the flow rate. The hydrogen-bonding effect plays a significant role in the recognition process of SMZ-imprinted polymer systems in organic media, while the ion-exchange effect, as well as hydrophobic effect, dominates the retention mechanism in aqueous-rich media, in addition to shape recognition. 相似文献
84.
In this paper, we apply the two‐step Newton method to solve inverse eigenvalue problems, including exact Newton, Newton‐like, and inexact Newton‐like versions. Our results show that both two‐step Newton and two‐step Newton‐like methods converge cubically, and the two‐step inexact Newton‐like method is super quadratically convergent. Numerical implementations demonstrate the effectiveness of new algorithms. 相似文献
85.
A two‐step method was used to fabricate the hydroxyapatite (HAP)/silk fibroin (SF) scaffolds, i.e. the nano‐sized HAP/SF composite powders were prepared by co‐precipitation, which were then blended with SF solution to fabricate the HAP/SF composite scaffolds. The obtained scaffolds showed a 3D porous structure. The porosity was higher than 90% with the average macropore size of 214.2 µm. Moreover, the nano‐sized HAP/SF composite powders were uniformly dispersed in the silk fibroin matrix, which provided the scaffolds enhanced compressive properties. The cell culture assay showed that the scaffolds fabricated by the two‐step method could improve the cell proliferation and osteogenic differentiation when compared with those prepared by the conventional one‐step blending method. The results suggested that the two‐step method could promote the uniform dispersion of HAP in the SF matrix and efficient combination between the HAP and the matrix, which may provide a potential application in the composite scaffold preparation for tissue engineering. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
86.
受非均匀调制演变随机激励结构响应快速精确计算 总被引:5,自引:4,他引:5
本文假定结构受到非均匀调制的演变随机激励,亦即其调制函数是时间与频率二者的函数,导出了有关的虚拟激励算法,并采用精细逐步积分格式,进行时变功率谱计算,获得了很高的计算效率和精度。 相似文献
87.
W. B. Tsai W. W. Lin C.‐C. Chieng 《Numerical Methods for Partial Differential Equations》2001,17(5):454-474
A design of varying step size approach both in time span and spatial coordinate systems to achieve fast convergence is demonstrated in this study. This method is based on the concept of minimization of residuals by the Bi‐CGSTAB algorithm, so that the convergence can be enforced by varying the time‐step size. The numerical results show that the time‐step size determined by the proposed method improves the convergence rate for turbulent computations using advanced turbulence models in low Reynolds‐number form, and the degree of improvement increases with the degree of the complexity of the turbulence models. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 454–474, 2001. 相似文献
88.
讨论光通信中脉冲的准单色光光场的正负频表示,正负频形式的傅里叶变换,正负频形式的非线性薛定谔方程及它们之间的关系.尤其在脉冲频谱的求解问题中,如果采用负频形式的非线性薛定谔方程则必须选取负频形式的傅里叶变换;如果采用正频形式的非线性薛定谔方程则必须选取正频形式的傅里叶变换.采用分步傅里叶法对具体实例进行数值求解,验证了讨论结果. 相似文献
89.
Multicomponent reactions (MCRs) have inherent advantages in pot, atom, and step economy (PASE). This important green synthetic approach has gained increasing attention due to high efficiency, minimal waste, saving resources, and straightforward procedures. Presented in this review article are the recent development on 5-compoment reactions (5CRs) of the following six types: (I) five different molecules A + B + C + D + E; pseudo-5CRs including (II) 2A + B + C + D, (III) 2A + 2B + C, (IV) 3A + B + C, (V) 3A + 2B, and (VI) 4A + B. 5CRs with more than five-reaction centers are also included. 相似文献
90.
Yu Nagao Akinori Takasu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(19):4207-4218
Click Cu(I)‐catalyzed polymerizations of diynes that contained ester linkages and diazides were performed to produce polyesters (click polyesters) of large molecular weights [(~1.0–7.0 ) × 104], that contained main‐chain 1,4‐disubstitued triazoles in excellent yields. Incorporation of triazole improved the thermal properties and magnified the even‐odd effect of the methylene chain length. We also found that, by changing the positions of the triazole rings, the thermal properties of the polyesters could be controlled. The use of in situ azidation was a safe reaction, as explosive diazides are not used. In addition, the microwave heating was found to accelerate the polymerization rates. This is the first study that has applied click chemistry for the synthesis of a series of polyesters. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4207–4218, 2010 相似文献