全文获取类型
收费全文 | 12507篇 |
免费 | 2166篇 |
国内免费 | 1303篇 |
专业分类
化学 | 8553篇 |
晶体学 | 112篇 |
力学 | 892篇 |
综合类 | 110篇 |
数学 | 1713篇 |
物理学 | 4596篇 |
出版年
2024年 | 27篇 |
2023年 | 252篇 |
2022年 | 283篇 |
2021年 | 405篇 |
2020年 | 475篇 |
2019年 | 464篇 |
2018年 | 429篇 |
2017年 | 399篇 |
2016年 | 608篇 |
2015年 | 578篇 |
2014年 | 697篇 |
2013年 | 907篇 |
2012年 | 1056篇 |
2011年 | 1134篇 |
2010年 | 778篇 |
2009年 | 738篇 |
2008年 | 862篇 |
2007年 | 681篇 |
2006年 | 718篇 |
2005年 | 542篇 |
2004年 | 454篇 |
2003年 | 372篇 |
2002年 | 377篇 |
2001年 | 326篇 |
2000年 | 261篇 |
1999年 | 258篇 |
1998年 | 242篇 |
1997年 | 213篇 |
1996年 | 205篇 |
1995年 | 180篇 |
1994年 | 168篇 |
1993年 | 147篇 |
1992年 | 125篇 |
1991年 | 110篇 |
1990年 | 105篇 |
1989年 | 77篇 |
1988年 | 58篇 |
1987年 | 44篇 |
1986年 | 42篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 904 毫秒
991.
本文利用文[2]提供的方法,得到了代数特征值反问题解几乎处处扰动存在及连续性的结论。 相似文献
992.
There is relatively little information on glasses based on chlorides, bromides and iodides. Because of the recent interest in fluoride it is the objective of this paper to evaluate the potential for preparing new halide glasses and to offer some predictions on the properties of glasses based on chlorides, bromides and iodides. The predictions of glass-forming tendency, viscosity, chemical durability and structures are discussed. 相似文献
993.
The free vibration of a functionally graded material hollow sphere submerged in a compressible fluid medium is exactly analyzed.
The sphere is assumed to be spherically isotropic with material constants being inhomogeneous along the radial direction.
By employing a separation technique as well as the spherical harmonics expansion method, the governing equations are simplified
to an uncoupled second-order ordinary differential equation, and a coupled system of two such equations. Solutions to these
equations are given when the elastic constants and the mass density are power functions of the radial coordinate. Numerical
examples are finally given to show the effect of the material gradient on the natural frequencies.
The project is supported by the National Natural Sciences Foundation of China(No. 19872060). 相似文献
994.
1 Besicovitch Inner ProductIll this paper, we consider Dirichlet serie8where an, tL = 1, 2,' ', are complex nunlbers. They are Besicovitch almost periodic functionsWe see the 8ystenl {e.(t); e.(t) = e--it Iog 1l, 71 = l, 2,' .} fOrnis a1l orthollor11la1 systelll witl1respect to tI1e BesicovitcI1 iIl1ler productThell we call fOrm the gelleralized trigouolnetrical polynolIlialsAccording to tl1e idea developed il1 [l],[2], auy Dirichlet seriesis weakly convergent over K witll respect to … 相似文献
995.
Yizhe An 《Journal of luminescence》2005,111(3):131-138
The time dependence of thermalization between the 3P0 and 3P1 electronic states of Pr3+ in symmetrical Pr3+-Gd3+ pairs in CsCdBr3, following pulsed laser excitation into either state, is reflected in the time dependence of the luminescence from both states. The 3P0 and 3P1 states achieve thermal equilibrium in the microsecond time domain over the temperature range of study (215-340 K). Because the 3P0-3P1 energy gap is larger than the phonon cutoff in CsCdBr3, thermalization occurs via multiphonon processes. A rate-equation model for the thermalization process is presented, and the temperature dependence of the rate constants for 3P1←3P0 multiphonon absorption and 3P1→3P0 multiphonon emission is reported from 215-340 K. In contrast to CsCdBr3, the analogous thermalization kinetics in Pr3+-Gd3+ pairs in isostructural CsMgCl3 is not discernable in the 3P0 and 3P1 luminescence, because thermalization is instantaneous within the time resolution of our experiments (∼20 ns). The difference in the thermalization kinetics in the two lattices is attributed to the difference in the number of phonons required to bridge the 3P0-3P1 energy gap. 相似文献
996.
通过微量CH3CN(36Pa)与He(660Pa)混合气体交流Penning辉光放电获得CN自由基分子,采用光外差-磁旋转-浓度调制光谱技术,在可见光波段16850~17480cm^-1进行了转动分辨光谱测量,分别标识了CN分子红带A^2Πi-X^2Σ^ (6,1)和(7,2)138条和118条的转动光谱(其余光谱为C2自由基及CN红带(8,3)带光谱)。理论拟合分子常数时考虑电子态间的微扰作用,采用有效哈密顿量矩阵对角化获得了A^2Πi(v=6,7)态更精确的分子常数及电子态A^2Πi(v=7)与X^2Σ^ (v=11)之间的微扰常数ξ,η,总体拟合方差均小于实验误差0.007cm^-1,表明拟合结果是非常精确的。 相似文献
997.
The thermally activated morphological evolution of an N,N’-di(naphthalene-1-yl)-N,N’-diphthalbenzidine (NPB) thin film on an ITO-coated glass/copper phthalocyanine (CuPc) underlying layer has been studied in situ by exploiting variable-temperature tapping mode atomic force microscopy (VT-AFM) in detail. The morphological change, assumed as an apparent glass transition of the NPB thin film, was observed to initially occur at ∼60 °C, and the transition finished at about 95 °C. Crystallization of the NPB thin film from the glassy state quickly appeared at about 135 °C in N2. The NPB thin film gradually melted and disappeared with an increase in temperature, and simultaneously revealed the ITO/CuPc underlying layer. The morphological variations of the NPB thin film have been verified by micro-Raman spectra. Moreover, it has been found that heating history and moisture seriously affect the degradation evolution of the NPB layer. These observations should shed light on the thermally activated degradation pathways and the long-term operation stability and reliability of NPB-based organic light-emitting diodes. PACS 68.55.Jk; 85.60.Jb; 64.70.Kb; 68.37.Ps 相似文献
998.
Renhua Qiu Guoping Zhang Xinhua Xu Kangbin Zou Lingling Shao Dawei Fang Yinhui Li Akihiro Orita Ryosuke Saijo Hidetaka Mineyama Tomoyoshi Suenobu Shunichi Fukuzumi Delie An Junzo Otera 《Journal of organometallic chemistry》2009,694(9-10):1524-1528
Zirconocene and titanocene bis(perfluorooctanesulfonate)s were synthesized. In contrast to the corresponding triflates and perchlorates, these compounds are air- and water-stable. They were proved to be ionic on the basis of conductivity measurements and X-ray analysis, allowing these complexes to be stored for months. The strong Lewis acidity of these cationic metallocene species, which was proved by ESR study, enabled catalytic glycosylation. 相似文献
999.
A fourth-order variational inequality of the second kind arising in a plate frictional bending problem is considered. By using regularization method, the original problem can be formulated as a differentiable variational equation, and the corresponding discrete FEM variational equation is presented afterwards. Abstract error estimates and error estimates of the approximation are derived in terms of energy norm and L^2-norm. 相似文献
1000.
Huming Ren Yanhuai Ding Yong Jiang Fu Xu Zhilin Long Ping Zhang 《Journal of Sol-Gel Science and Technology》2009,52(2):287-290
ZnO nanofibers were prepared from zinc acetate/polyvinyl alcohol (PVA) by electrospun method. The morphological features,
crystallinity, mechanical and optical properties of the ZnO nanofibers were studied. The results show the specific surface
area of the ZnO nanofibers was influenced by the electrospun conditions. The specific surface area reached 389.7 m2g−1 as the average diameter was 232 nm. The XRD date reveals the nanofibers consist of a single phase of well-crystallized ZnO
with hexagonal structure. The elastic modulus of a single ZnO nanofiber was also characterized by nano-scale three-point bending
test. 相似文献