全文获取类型
收费全文 | 41694篇 |
免费 | 2468篇 |
国内免费 | 2513篇 |
专业分类
化学 | 19709篇 |
晶体学 | 155篇 |
力学 | 886篇 |
综合类 | 782篇 |
数学 | 16407篇 |
物理学 | 8736篇 |
出版年
2023年 | 298篇 |
2022年 | 455篇 |
2021年 | 1439篇 |
2020年 | 829篇 |
2019年 | 976篇 |
2018年 | 702篇 |
2017年 | 792篇 |
2016年 | 978篇 |
2015年 | 986篇 |
2014年 | 1420篇 |
2013年 | 2653篇 |
2012年 | 1558篇 |
2011年 | 1938篇 |
2010年 | 1815篇 |
2009年 | 2365篇 |
2008年 | 2512篇 |
2007年 | 2697篇 |
2006年 | 2031篇 |
2005年 | 1372篇 |
2004年 | 1290篇 |
2003年 | 1345篇 |
2002年 | 3803篇 |
2001年 | 1454篇 |
2000年 | 1018篇 |
1999年 | 809篇 |
1998年 | 716篇 |
1997年 | 566篇 |
1996年 | 592篇 |
1995年 | 485篇 |
1994年 | 487篇 |
1993年 | 491篇 |
1992年 | 464篇 |
1991年 | 327篇 |
1990年 | 279篇 |
1989年 | 222篇 |
1988年 | 244篇 |
1987年 | 216篇 |
1986年 | 215篇 |
1985年 | 343篇 |
1984年 | 253篇 |
1983年 | 174篇 |
1982年 | 310篇 |
1981年 | 491篇 |
1980年 | 449篇 |
1979年 | 482篇 |
1978年 | 381篇 |
1977年 | 282篇 |
1976年 | 238篇 |
1974年 | 77篇 |
1973年 | 150篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Early stages of rare-earth metal (Yb and Eu) growth on a vicinal, single-domain Si(1 0 0)2 × 1 surface have been studied in the coverage range of 0.1-0.3 monolayer (ML) by low energy electron diffraction, scanning tunneling microscopy, and synchrotron radiation photoemission spectroscopy. We show that Yb induces the 2 × 3 periodicity in the whole range of coverage studied. The 2 × 3 reconstruction coexists with the local 3 × 2/4 × 2 structure at about 0.2 ML of Yb. In contrast, Eu forms the 3 × 2 periodicity at 0.1-0.2 ML, whereas this structure is converted into the 2 × 3 phase at about 0.3 ML. The atomic arrangement and electronic properties of these reconstructions and the adsorbate-mediated modification of surface morphology are investigated. 相似文献
92.
93.
YaoKui ChenZhixiang 《分析论及其应用》2003,19(2):115-120
This paper gives the weighted Lp convergence rate estimations of the Gruenwald interpolatory polynomials based on the zeros of Chebyshev polymomials of the first kind,and proves that the order of the estimations is optimal for p≥1. 相似文献
94.
本文对一般微分代数方程给出了几类可解集的概念,并讨论了多项式微分代数方程的可解集,得到子多项式系统具有唯一解。特别是有多于一个的解的条件,并得到了低次多项式在一定意义下的充分必要条件。 相似文献
95.
We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series. 相似文献
96.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
97.
本文考虑广义C-R组^[1](H)的解f=u iv jw∈C^2的一些性质,提出与之相关的两个边值问题,用积分方程方法和调和函数性质证明了边值问题解的存在唯一性,并写出解的积分表达式. 相似文献
98.
Lígia M. Rodrigues 《Tetrahedron》2004,60(40):8929-8936
Tetrapeptides containing one of a set of four different α,α-dialkyl glycines at the C-terminus were synthesized by conventional methods in solution and their conformational behavior investigated by 1H NMR spectroscopy in connection with molecular mechanics calculations. The results were consistent with conformations stabilized by a γ-turn in the case of compounds with alkyl groups larger than methyl, while the corresponding Aib derivative did not exhibit intramolecular hydrogen bonding. 相似文献
99.
The glow curve structures for LiF:Mg,Cu,Na,Si TL detectors with various dopant concentrations and sintering temperatures were investigated for the improvement of the glow curve structure and sensitivity of the TL detector. The dopant concentrations were varied over the following ranges: Mg (0–0.25 mol%), Cu (0–0.07 mol%), Na and Si (0–1.5 mol%). With increasing Cu concentration, the intensity of the main peak was intensified and reached a maximum at a concentration of 0.05 mol%. The high-temperature peak was reduced. The dependency of the main peak intensity on the Mg concentration exhibits a sharp maximum at 0.2 mol%. The intensity of the high-temperature peak tends to rise slightly with increasing Mg concentration. It was found that the optimum concentrations of the dopants in the LiF:Mg,Cu,Na,Si TL material are Mg: 0.2 mol%, Cu: 0.05 mol%, Na and Si: 0.9 mol%. The dependency of the main peak intensity on sintering temperature exhibits a very sharp maximum at 830°C. The high-temperature peak was rapidly reduced after 825°C. 相似文献
100.
Jie Da Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2004,42(2):360-373
The synthesis is reported of copolymers of N,N‐dimethylacrylamide (DMA) and methacrylates containing 2,2′‐dihydroperfluorodecanoyl (RF) groups separated from the methacrylate by long polyethylene glycol (PEG) tether groups (between 1000 and 14,000 Da). At concentrations of between 1 and 8 wt % the copolymers with macromonomer contents of 1 mol % or less give gels in organic solvents such as dioxane, THF, or methanol, as well as in water. Given the low molecular weights, this indicates very efficient association of very low numbers of RF groups. Association and gel formation is enormously enhanced in the presence of longer PEG tethers. This is consistent with smaller poly(N,N,‐dimethylacrylamide) (PDMA) intermolecular excluded volume effects that are mediated by the longer PEG tethers and possibly by the incompatibility of PEG and PDMA that may lead to the formation of PEG microdomains. This increases the local concentrations of the RF groups in the PEO domains that are not diluted by the PDMA chains, as would be the case in the absence of PEG tethers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 360–373, 2004 相似文献