全文获取类型
收费全文 | 78895篇 |
免费 | 8252篇 |
国内免费 | 7770篇 |
专业分类
化学 | 52898篇 |
晶体学 | 482篇 |
力学 | 2779篇 |
综合类 | 917篇 |
数学 | 10812篇 |
物理学 | 27029篇 |
出版年
2024年 | 121篇 |
2023年 | 748篇 |
2022年 | 1826篇 |
2021年 | 2547篇 |
2020年 | 2108篇 |
2019年 | 2142篇 |
2018年 | 1681篇 |
2017年 | 1951篇 |
2016年 | 2417篇 |
2015年 | 2582篇 |
2014年 | 3335篇 |
2013年 | 5616篇 |
2012年 | 4264篇 |
2011年 | 4682篇 |
2010年 | 4113篇 |
2009年 | 4923篇 |
2008年 | 5135篇 |
2007年 | 5243篇 |
2006年 | 4497篇 |
2005年 | 3524篇 |
2004年 | 3093篇 |
2003年 | 2818篇 |
2002年 | 4985篇 |
2001年 | 2333篇 |
2000年 | 1895篇 |
1999年 | 1642篇 |
1998年 | 1477篇 |
1997年 | 1223篇 |
1996年 | 1163篇 |
1995年 | 1042篇 |
1994年 | 970篇 |
1993年 | 930篇 |
1992年 | 873篇 |
1991年 | 651篇 |
1990年 | 515篇 |
1989年 | 433篇 |
1988年 | 438篇 |
1987年 | 338篇 |
1986年 | 305篇 |
1985年 | 415篇 |
1984年 | 316篇 |
1983年 | 190篇 |
1982年 | 373篇 |
1981年 | 522篇 |
1980年 | 470篇 |
1979年 | 512篇 |
1978年 | 393篇 |
1977年 | 305篇 |
1976年 | 265篇 |
1973年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
861.
A 1Σ u + -X 1Σ g + emission in Na2 is observed following excitation ofB 1π u by various lines of an argon ion laser. The excitation energy ofB 1π u is collisionally transferred to the (2)1Σ g + which then radiatively populates theA 1Σ u + state. The Na vapour is contained in a stainless steel crossed heat pipe with Ar buffer gas and temperature around 600°C. For all laser lines except 4579 Å, the coarse features ofA-X emission are independent of the laser wavelength. However, at high resolution the finer differences between different laser line excitation are explained. Variousv′-v″ transitions in this emission are identified. Computer simulation is presented to help explain some features of this emission. 相似文献
862.
Eugene P. Gross 《Journal of statistical physics》1989,54(1-2):405-427
A study is made of the ground-state energy of a spin-one-half particle in a fieldB and interacting with a phonon bath. The infrared-sensitive case of acoustic phonons with point coupling in three dimensions is characterized by two parameters, a coupling constant andB. Units are used where the high-momentum phonon cutoff is unity. There is a curve (B) separating a symmetry-breaking region with a long-range phonon field from a normal region. Two simple, well-known, approximations are compared. The source theory yields discontinuities in the first derivatives of the energy with respect toB and whenB>e
–1 and an infinite-order transition whenB<e
–1, but is trivial in the large- region. The classical theory yields discontinuities in the second derivatives but is trivial in the small- region. An improved variationally fixed ground-state wave function is analyzed. It gives a new (B) curve with an infinite-order transition with continuous energy derivatives whenB<e/(e
2–1/4) and with discontinuous derivatives whenB is larger than this value. It is nontrivial in the entire (B) plane. The crossover to classical behavior occurs near =1/2 forB1. But the wave function does not describe quantum fluctuations in the large- phase. A second way of combining source and classical effects is described. It yields a second-order transition (near =1/2 forB1) everywhere. These theories are special cases of a symmetry-breaking transformation together with a one-mode treatment of quantum fluctuations. The transition is viewed in terms of a single mode with a variable length, coupled dynamically to the spin. 相似文献
863.
Thomas Unnerstall 《Journal of statistical physics》1989,54(1-2):379-403
The irreversible macroscopic dynamics of the Josephson junction coupled to external wires acting as a current source is derived rigorously from the underlying microscopic Hamiltonian quantum mechanics. The external systems are treated in the singular coupling limit. The use of this limit is explicitly justified via an interpretation of the singular coupling limit in terms of the relative magnitudes of system, reservoir, and coupling energies. The qualitative behavior of the macroscopic dynamical equations is shown to depend sensitively and crucially on the interaction between the wires and the superconductors and on the size of the wires: the dc Josephson effect only happens when one lets Cooper pairs be driven into the junction by collective (i.e., small) reservoirs. 相似文献
864.
Multinuclear magnetic resonance data for the title compounds are presented and discussed. The intramolecular coordination observed in the solid state is shown to be retained in solution. The best probes for the presence or absence of pentacoordination at tin are provided by the various tin-element coupling constants, although chemical shifts are in some cases also informative. A selenium-proton correlated spectrum indicated that the coupling constant 1J(Sn,Se) has a positive sign. 相似文献
865.
866.
本文就薄膜法制样、用X-射线荧光谱法分析稀土样品时,试样面积和厚度对分析结果产生的影响作了定量研究,提出的有关分析条件和参数用于实际样品分析中,获得了满意的分析结果。 相似文献
867.
本文利用表面光电压谱(Surface Photovohage spectroscopy,简称SPS)研究了ZnTPP对TiO_2粉末的光谱敏化,发现用ZnTPP修饰后的TiO_2(金红石和锐钛矿)粉末在可见区420、550和590nm附近有三个光伏响应带,它们分别对应于ZnTPP的Soret、Q(1,0)和Q(0,0)带。经过严格的实验和分析,证明这三个带是由ZnTPP对TiO_2的敏化光电压引起的,而不是ZnTPP自身的光伏响应。在敏化效果上,亚稳的锐钛矿优于金红石。同时,我们对这种光敏表面的光诱导电荷转移机制和SPS作为一种研究光谱敏化方法的可行性进行了讨论。 相似文献
868.
G.?G.?GospodinovEmail author M.?G.?Stancheva 《Journal of Thermal Analysis and Calorimetry》2004,78(3):1057-1063
The solubility isotherm of the Sm2O3-SeO2-H2O system was studied at 100°C. The two compounds obtained in the three-component system were identified by the Schreinemakers method as well as by chemical, thermoanalytical and X-ray diffraction analyses after their isolation in pure state. 相似文献
869.
The nanoparticles of a spirooxazine (SPO) and its photomerocyanine (PMC) were prepared through the reprecipitation method. Two distinct features were observed. One is that the decaying lifetime for PMC nanoparticles was 600 times of that for the dispersed molecules, and the other is that the fluorescence intensity of SPO nanoparticles was enhanced by 240 times of that of the dispersed monomer. 相似文献
870.