全文获取类型
收费全文 | 2212篇 |
免费 | 174篇 |
国内免费 | 141篇 |
专业分类
化学 | 1471篇 |
晶体学 | 41篇 |
力学 | 76篇 |
综合类 | 12篇 |
数学 | 258篇 |
物理学 | 669篇 |
出版年
2023年 | 27篇 |
2022年 | 34篇 |
2021年 | 32篇 |
2020年 | 51篇 |
2019年 | 48篇 |
2018年 | 39篇 |
2017年 | 45篇 |
2016年 | 83篇 |
2015年 | 54篇 |
2014年 | 82篇 |
2013年 | 117篇 |
2012年 | 150篇 |
2011年 | 158篇 |
2010年 | 91篇 |
2009年 | 86篇 |
2008年 | 107篇 |
2007年 | 126篇 |
2006年 | 102篇 |
2005年 | 106篇 |
2004年 | 74篇 |
2003年 | 61篇 |
2002年 | 63篇 |
2001年 | 49篇 |
2000年 | 53篇 |
1999年 | 41篇 |
1998年 | 22篇 |
1997年 | 36篇 |
1996年 | 42篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1974年 | 9篇 |
1971年 | 9篇 |
排序方式: 共有2527条查询结果,搜索用时 377 毫秒
1.
2.
Studies on metabolism of total glucosides of paeony from Paeoniae Radix Alba in rats by UPLC‐Q‐TOF‐MS/MS 下载免费PDF全文
Wenli Cao Xinguo Wang Haojie Li Xuliang Shi Wencheng Fan Shaohua Zhao Minyan Liu Liying Niu 《Biomedical chromatography : BMC》2015,29(11):1769-1779
Total glucosides of paeony are the active constituents of Paeoniae Radix Alba. In this study, a novel strategy was proposed to find more metabolites and the differences between paeoniflorin, albiflorin and total glucosides of paeony (TGP). This strategy was characterized as follows: firstly, the animals were divided into three groups (paeoniflorin, albiflorin and TGP) to identify the source of TGP metabolites from paeoniflorin or albiflorin; secondly, a generic information‐dependent acquisition scan for the low‐level metabolites was triggered by the multiple mass defect filter and dynamic background subtraction; thirdly, the metabolites were identified with a combination of data‐processing methods including mass defect filtering, neutral loss filtering and product ion filtering; finally, a comparative study was used in the metabolism of paeoniflorin, albiflorin and TGP. Based on the strategy, 18 metabolites of TGP, 10 metabolites of paeoniflorin and 13 metabolites of albiflorin were identified respectively. The results indicated that the hydrolysis, conjugation reaction and oxidization were the major metabolic pathways, and the metabolic sites were the glycosidic linkage, the ester bond and the benzene ring. This study is first to explore the metabolism of TGP, and these findings enhance our understanding of the metabolism and the interactions of paeoniflrin and albiflorin in TGP. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
用分子动力学方法对5%负失配条件下面心立方晶体铝薄膜的原子沉积外延生长进行了三维模拟.铝原子间的相互作用采用嵌入原子法(EAM)多体势计算.模拟结果再现了失配位错的形成现象.分析表明,失配位错在形成之初即呈现为Shockley扩展位错,即由两个伯格斯矢量为〈211〉/6的部分位错和其间的堆垛层错组成,两个部分位错的间距、即层错宽度为1.8 nm,与理论计算结果一致;外延晶体薄膜沉积生长中,位错对会发生滑移,但其间距保持稳定.进一步观察发现,该扩展位错产生于一种类似于“局部熔融-重结晶”的表层局部无序紊乱-
关键词:
失配位错
外延生长
薄膜
分子动力学
铝 相似文献
4.
5.
6.
In this article we use classical formulas involving the K–Bessel function in two variables to express the Poisson kernel on a Riemannian manifold in terms of the heat kernel. We then use the small time asymptotics of the heat kernel on certain Riemannian manifolds to obtain a meromorphic continuation of the associated Poisson kernel to all values of complex time with identifiable singularities. This result reproves in a different setting by different means a well–known theorem due to Duistermaat and Guillemin [DG 75]. Also, we develop analytic expressions for the heat kernel beyond asymptotic expansions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
7.
M. Ferro-Luzzi Z.-L. Zhou J.F.J. van den Brand H.J. Bulten J. Lang H.R. Poolman 《Hyperfine Interactions》1997,110(3-4):239-257
We present data showing hyperfine transitions in an atomic deuterium beam induced by the (476 MHz) radio-frequency field of
a 704 MeV electron beam in a storage ring. A polarized deuterium beam, produced in an atomic beam source, was crossed with
a stored electron beam and analyzed with a Breit--Rabi polarimeter. Electron-beam induced transitions were singled out by
injecting different combinations of hyperfine states. Transition probabilities as high as 70% were measured at large currents
(~ 100 mA). All possible deuterium transitions for a radio-frequency of 476 MHz were observed. In addition, a 1--6 transition
resulting from the first harmonic (952 MHz) was observed.
The effects of these transitions are of general importance for the polarized internal target technique applied in nuclear
and particle physics experiments. The data are reasonably described by numerical estimates. The observed mechanism can be
exploited to create nuclear polarized atoms when injecting electron polarized atoms with no net nuclear polarization into
a storage cell. However, when nuclear polarized atoms are injected, care should be taken to avoid this mechanism, since it
would result in depolarization of the atoms. The studies enabled us to choose the magnetic guide field during our spin-dependent
electron--deuteron scattering experiments, such that electron-beam induced depolarizing effects were avoided.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
提出了用联合变换相关器(JTC)来实现证据理论概率分配函数正交和的光学计算,在理论上对于如何用联合变像相关器实现证据理论分配函数正交和作了详细的讨论,并作了相应的仿真测试,结果显示该方法是可行的。与John Caulfield提出的用声光器件矢量外积实现的正交和计算相比,在该结构中由于采用二进制编码的数值计算,因此其计算精度得到了提高,同时对联合变换相关器输入端二进制编码的数值空间位置的适当调整可以直接得到所需要的证据理论正交和矢量,在处理步骤上得到了简化。 相似文献
9.
It is predicted that resonance coupling between two discrete electron energy levels corresponding to different size-quantization
quantum numbers and different Landau quantum numbers can occur in a quantum well in a quantizing magnetic field. The resonance
coupling is due to the interaction of an electron with LO phonons and results in the formation of polaron states of a new type. It is shown that for a certain value of the magnetic
field, which depends on the splitting of the electron size-quantization levels, the absorption peak and the two-phonon resonance
Raman scattering peak split into two components, the separation between which is determined by the electron-phonon coupling
constant. The resonance coupling between size-quantization levels with the same Landau quantum numbers is also studied. The
splitting of the peaks in this case is virtually independent of the magnetic field and can be observed in much weaker fields.
The experimental observation of the effect will make it possible to determine the relative position of the electronic levels
and the electron-phonon coupling constant.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 511–515 (10 April 1997) 相似文献
10.
Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA. 相似文献