全文获取类型
收费全文 | 11859篇 |
免费 | 1574篇 |
国内免费 | 873篇 |
专业分类
化学 | 3779篇 |
晶体学 | 58篇 |
力学 | 971篇 |
综合类 | 83篇 |
数学 | 3889篇 |
物理学 | 5526篇 |
出版年
2024年 | 14篇 |
2023年 | 109篇 |
2022年 | 268篇 |
2021年 | 303篇 |
2020年 | 365篇 |
2019年 | 345篇 |
2018年 | 337篇 |
2017年 | 360篇 |
2016年 | 452篇 |
2015年 | 352篇 |
2014年 | 578篇 |
2013年 | 1139篇 |
2012年 | 669篇 |
2011年 | 758篇 |
2010年 | 595篇 |
2009年 | 685篇 |
2008年 | 690篇 |
2007年 | 759篇 |
2006年 | 655篇 |
2005年 | 556篇 |
2004年 | 451篇 |
2003年 | 432篇 |
2002年 | 432篇 |
2001年 | 364篇 |
2000年 | 371篇 |
1999年 | 260篇 |
1998年 | 255篇 |
1997年 | 208篇 |
1996年 | 161篇 |
1995年 | 169篇 |
1994年 | 140篇 |
1993年 | 144篇 |
1992年 | 118篇 |
1991年 | 100篇 |
1990年 | 84篇 |
1989年 | 66篇 |
1988年 | 64篇 |
1987年 | 48篇 |
1986年 | 51篇 |
1985年 | 76篇 |
1984年 | 68篇 |
1983年 | 29篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 21篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
P. Paasche T. Valenzuela D. Biswas C. Angelescu G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):295-300
We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation
is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the
number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation
of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass
resonance suggests that it is a parametric instability of a Mathieu type equation of motion.
Received 11 July 2001 and Received in final form 12 November 2001 相似文献
52.
可提前还款的定期贷款是隐含着期权的利率衍生物,本文建立CIR利率模型下可提前还款的定期贷款的数学模型,通过离散偏微分方程,建立了模型的计算方法,讨论了随机利率对提前还贷的影响. 相似文献
53.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献
54.
Long JIANG 《数学年刊B辑(英文版)》2006,27(5):553-564
Abstract
Under the Lipschitz assumption and square integrable assumption on g, the author proves that Jensen’s inequality holds for backward stochastic differential equations with generator g if and only if g is independent of y, g(t, 0) ≡ 0 and g is super homogeneous with respect to z. This result generalizes the known results on Jensen’s inequality for g- expectation in [4, 7–9].
*Project supported by the National Natural Science Foundation of China (No.10325101) and the Science Foundation of China University
of Mining and Technology. 相似文献
55.
56.
Mark E. Filipkowski Edwin E. Hach III Michael Offenbacker 《Journal of magnetism and magnetic materials》2006
We show, via a straightforward calculation, that it is feasible to detect nuclear spin echoes in a ferromagnetic thin film by electrical means. The detection scheme is based on the deflection of the electronic magnetization when the nuclear magnetization reforms during an echo. This deflection is observed as a time-dependent magnetoresistive signal. 相似文献
57.
用硼氢化钠作还原剂,制备出两种相对稳定的含银纳米颗粒的水溶胶,用透射电镜(TEM)和光学吸收谱对这些颗粒进行了表征.当被还原的银离子较少时,所形成的银纳米颗粒较小,吸收峰呈现二极等离子体共振吸收峰.当被还原的银离子较多时,银纳米颗粒尺寸变大,并出现二极和四极共振吸收峰.在Ag纳米颗粒形成后,对其溶液稀释,发现其峰形保持不变,而峰位会出现红移,最大红移量可达到10 nm.透射电镜研究表明,低浓度溶胶中的Ag纳米颗粒尺寸较为均匀,平均直径12 nm.高浓度溶胶中的纳米颗粒尺寸呈双尺寸分布特点,少量颗粒直径小于14 nm,大部分颗粒直径大于20 nm. 相似文献
58.
《Magnetic resonance in chemistry : MRC》2003,41(8):585-588
A novel, radical responsive MRI contrast agent based on a gadolinium chelate conjugated to a liposome through a disulfide linker was synthesized, with the aim of pursuing the in vivo mapping of radicals. The liposome was prepared by incorporating a thiol‐activated phospholipid, which was subsequently reacted with a gadolinium chelate containing a free thiol group. The long reorientational motion of the supramolecular adduct endows the paramagnetic agent with a relaxivity significantly higher than that of the free complex. The disulfide bond represents a radical‐sensitive moiety and a large decrease in contrast efficacy (T1 relaxivity) is shown upon its cleavage. A preliminary assessment of the system was made by means of in vitro gamma‐irradiation and thiol–disulfide bond exchange with dithiothreitol. Both methods showed a clear dose‐dependent decrease in T1‐relaxivity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
59.
Electron paramagnetic resonance (EPR) investigations has been carried out on the new family of molybdenum doped vanadium sesquioxides (V1−xMox)2−δO3. The oxidation effects were monitored from the rate of paramagnetic V4+ created when the sample is exposed to the air. The effects of the oxidation time, sample temperature, and annealing at 1000 °C under a diluted hydrogen atmosphere on the EPR signal features are analyzed. The V4+ concentration in the oxidized samples is determined and the relaxation effects driven by the conduction electrons are pointed out from the thermal behaviour of the EPR line features. EPR spectra of all the oxidized samples also reveal a small ferromagnetic contribution strongly correlated with the V4+ content. 相似文献
60.
In this article, we define stochastic dynamics for a system coupled to reservoirs. The rules for forward and backward transitions are related by a generalized detailed balance identity involving the system and its reservoirs. We compare the variation of information and of entropy. We define the Carnot dissipation and prove that it can be expressed in terms of cyclic transformations. Lower bounds for partial dissipations are also studied, as well as the effect of switching off certain reservoirs. We also study the near degeneracy of the stochastic matrix, relate it to phase transitions and we show that the reduced dynamics on the set of phases is a permutation. Finally, we relate these concepts to heat, work and more generally to the dissipation and creation of resources, in general systems. 相似文献