全文获取类型
收费全文 | 11048篇 |
免费 | 1207篇 |
国内免费 | 1650篇 |
专业分类
化学 | 6854篇 |
晶体学 | 294篇 |
力学 | 481篇 |
综合类 | 8篇 |
数学 | 2515篇 |
物理学 | 3753篇 |
出版年
2024年 | 20篇 |
2023年 | 257篇 |
2022年 | 429篇 |
2021年 | 385篇 |
2020年 | 409篇 |
2019年 | 255篇 |
2018年 | 295篇 |
2017年 | 370篇 |
2016年 | 438篇 |
2015年 | 491篇 |
2014年 | 650篇 |
2013年 | 813篇 |
2012年 | 960篇 |
2011年 | 1026篇 |
2010年 | 759篇 |
2009年 | 741篇 |
2008年 | 620篇 |
2007年 | 699篇 |
2006年 | 680篇 |
2005年 | 473篇 |
2004年 | 374篇 |
2003年 | 299篇 |
2002年 | 318篇 |
2001年 | 298篇 |
2000年 | 179篇 |
1999年 | 228篇 |
1998年 | 192篇 |
1997年 | 132篇 |
1996年 | 89篇 |
1995年 | 78篇 |
1994年 | 61篇 |
1993年 | 46篇 |
1992年 | 43篇 |
1991年 | 49篇 |
1990年 | 52篇 |
1989年 | 38篇 |
1988年 | 141篇 |
1987年 | 225篇 |
1986年 | 234篇 |
1985年 | 26篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Strong limit-point criteria for singular Hamiltonian differential expressions with complex coefficients are obtained. The main results are extensions of the previous results due to Everitt, Giertz, and Weidmann for scalar differential expressions.
72.
《Colloids and surfaces. A, Physicochemical and engineering aspects》2007,292(1):51-55
The polypseudorotaxanes (PPRs) have been prepared by supramolecular self-assembly of β-cyclodextrins (β-CDs) threaded onto the triblock copolymers (Pluronic F127) in an ionic liquid [1-n-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6)] with two different manners. Structural characterizations of the assembled PPRs are carried out in detail respectively with XRD, 13C CP/MAS NMR, 1H NMR and DSC techniques. The results obtained indicate a channel-type crystalline structure for such produced inclusion complexes (ICs). Which one will finally be included inside β-CD, F127 or bmimPF6, is related to the ethanol amount around the initially β-CD/bmimPF6 ICs. At higher ethanol concentration, F127 may squeeze bmimPF6 molecules out from β-CD and thread themselves instead into the cavity of β-CD and finally precipitate with more CDs being stacked. 相似文献
73.
W. Shi Y.J. Ding C. Fang Q. Pan Q. Gu 《Applied Physics A: Materials Science & Processing》2003,77(3-4):567-570
The optimal corona-poling temperature of polymer films was accurately determined by measuring the temperature dependence of the in situ second-harmonic (SH) intensity profile under the applied poling electric field. The in situ SH intensity profile was first measured by probing both the surface voltages and the poling currents induced by surface/space charges for the corona-poled polymer films. Moreover, charge effects on the stability of the chromophore orientation were first studied by using the thermally stimulated discharge-current technique. PACS 72.20.Jv; 42.65.Ky; 73.61.Ph; 81.40.Tv 相似文献
74.
一类非线性算子方程的多重正解及其应用 总被引:18,自引:5,他引:13
本文利用不动点指数理论对一类非线性算子方程建立了多重正解的存在性定理,并将所获结果应用到Hammerstein积分方程和Sturm Liouvile两点边值问题,得到了新的结论,本质上改进和推广了[2,4,5,6,8-12]的工作. 相似文献
75.
若干有关欧阳不等式的非线性积分不等式和离散不等式 总被引:10,自引:0,他引:10
获得几个非线性的积分不等式及离散不等式.它们和近期Pachpate[1]中欧阳亮不等式[2]的推广有关.作为特殊情形还导出了一些具有幂非线性的新不等式.为说明结果的有用性,讨论了某个非线性差分方程解的有界性. 相似文献
76.
The electronic structure and magnetism of SmCo7-xZrx alloy are investigated using the spin-polarized MS-X. method. The results show that a few of electrons are transferred to the Sm(5d0) orbital due to orbital hybridization between Sm and Co atoms. The exchange interactions between 3d and 5d electrons are more important than the polarization effects of the conductive electrons, thus it is the main reason resulting in the long-range ferromagnetic order in SmCo7-xZrx. The Curie temperature of SmCo7-xZrx is generally lower than that of corresponding pure Co, which may be explained by the weaker average coupling strength between Co lattices due to some negative couplings mainly occurring of 2e site. The calculated results for the Sm5Co32Zr2 cluster may lead to a better understanding of why SmCo7-xZrx is stable phase. Since the spin-up DOS peak of d electrons at EF arises and the bonding of electrons at EF strengthens with increasing Zr concentration, which results in the internal energy of the system decrease, the stable ferromagnetic order forms in SmCo7-xZrx. 相似文献
77.
In this Letter, structural properties of liquid Ni20Al80 have been studied through molecular dynamics (MD) simulations, and results agree well with X-ray experiments. The prepeak in the structure factor manifests the existence of medium-range structural order (MRSO) in liquid Ni20Al80. Analyses in MRSO reveal the dominance of ideal icosahedra and defective icosahedra which, furthermore, form clusters and share common atoms. 相似文献
78.
Meng F. Q. Lu M. K. Yang Z. H. Zeng H. 《Journal of Thermal Analysis and Calorimetry》1998,52(2):609-613
The thermal behavior of two new non-linear optical (NLO) materials, urea-(D) tartaric acid (UDT) and urea-(DL) tartaric acid
(UDLT) were studied by using DSC, TG and TMA. The results show that: 1) The two crystals have different melting points but
similar decomposition temperatures due to the influences of intermolecular forces, which is attributed to the stereo effects
of (D)-tartaric and (DL)-tartaric acid molecules; 2) There was only thermal expansion and no thermal contraction when the
UDT and UDLT crystals were heated; 3) There was no phase transition within the measured temperature range; 4) The thermal
expansion of the UDT and UDLT crystals shows a small anisotropy; 5) The specific heats of UDT and UDLT change linearly with
temperature in the measured temperature range and the value for UDT is 1.321 J g-1 K-1 at 320 K while the specific heat of
UDLT is 1.357 J g-1 K-1 at the same temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
FANG Qi LEI Hong CUI Yuezhi HUANG Zhenli XUE Gang & YU Wentao . State Key Laboratory of Crystal Materials Shandong University Jinan China . School of Information Science Engineering Shandong University Jinan China . Department of Chemical Engineering Light Industry College of Shandong Jinan China . Key Laboratory of Biomedical Photonics Ministry of Education Huazhong University of Science Technology Wuhan China 《中国科学B辑(英文版)》2005,48(3)
Organic nonlinear optics (NLO) is also called mo-lecular nonlinear optics. In recent years organic mate-rials have been intensively studied because of their large NLO coefficients and structural diversities[1―3]. Second harmonic generation (SHG) is a bas… 相似文献
80.
In this paper, we investigate strict stability of differential systems by variational Lyapunov function. We obtain some sufficient conditions and comparison theorems. 相似文献