全文获取类型
收费全文 | 3095篇 |
免费 | 277篇 |
国内免费 | 457篇 |
专业分类
化学 | 216篇 |
晶体学 | 3篇 |
力学 | 73篇 |
综合类 | 96篇 |
数学 | 3162篇 |
物理学 | 279篇 |
出版年
2024年 | 4篇 |
2023年 | 37篇 |
2022年 | 37篇 |
2021年 | 42篇 |
2020年 | 56篇 |
2019年 | 79篇 |
2018年 | 84篇 |
2017年 | 90篇 |
2016年 | 123篇 |
2015年 | 64篇 |
2014年 | 138篇 |
2013年 | 266篇 |
2012年 | 137篇 |
2011年 | 152篇 |
2010年 | 164篇 |
2009年 | 196篇 |
2008年 | 225篇 |
2007年 | 254篇 |
2006年 | 196篇 |
2005年 | 172篇 |
2004年 | 167篇 |
2003年 | 181篇 |
2002年 | 176篇 |
2001年 | 140篇 |
2000年 | 111篇 |
1999年 | 99篇 |
1998年 | 100篇 |
1997年 | 79篇 |
1996年 | 64篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 18篇 |
1992年 | 24篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有3829条查询结果,搜索用时 31 毫秒
101.
Johnny Henderson 《Journal of Difference Equations and Applications》2013,19(7):1005-1018
We study the existence and non-existence of positive solutions of a system of nonlinear second-order difference equations with eigenvalues subject to multi-point boundary conditions. 相似文献
102.
In the present investigation we define a new class of meromorphic functions on the punctured unit disk △*:= {z ∈ C : 0 < |z| < 1} by making use of the generalized Dziok-Srivastava operator H l m [α1 ]. Coefficient inequalities, growth and distortion inequalities, as well as closure results are obtained. We also establish some results concerning the partial sums of meromorphic functions and neighborhood results for functions in new class. 相似文献
103.
On the existence of positive solutions of the p‐Laplacian dynamic equations on time scales
下载免费PDF全文
![点击此处可从《Mathematical Methods in the Applied Sciences》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Abdulkadir Dogan 《Mathematical Methods in the Applied Sciences》2017,40(12):4385-4399
In this paper, we investigate the existence of positive solutions for a nonlinear m‐point boundary value problem for the p‐Laplacian dynamic equations on time scales, by applying a Krasnosel'skii's fixed point theorem. As an application, an example is included to demonstrate the main results. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
104.
In this paper, we propose a fast algorithm for computing the spectral radii of symmetric nonnegative tensors. In particular, by this proposed algorithm, we are able to obtain the spectral radii of weakly reducible symmetric nonnegative tensors without requiring the partition of the tensors. As we know, it is very costly to determine the partition for large‐sized weakly reducible tensors. Numerical results are reported to show that the proposed algorithm is efficient and also able to compute the spectral radii of large‐sized tensors. As an application, we present an algorithm for testing the positive definiteness of Z‐tensors. By this algorithm, it is guaranteed to determine the positive definiteness for any Z‐tensor. 相似文献
105.
Phosphate esters are important commercial products that have been used both as flame retardants and as plasticizers. To analyze these compounds by gas chromatographic mass spectrometry, it is important to understand the mass spectra of these compounds using various ionization modes. This paper is a systematic overview of the electron impact (EI), electron capture negative ionization (ECNI) and positive chemical ionization (PCI) mass spectra of 13 organophosphate esters. These data are useful for developing and optimizing analytical measurements. The EI spectra of these 13 compounds are dominated by ions such as H4PO4+, (M ? Cl)+, (M ? CH2Cl)+ or (M)+ depending on specific chemical structures. The ECNI spectra are generally dominated by (M ? R)?. The PCI spectra are mainly dominated by the protonated molecular ion (M + H)+. The branching of the alkyl substituents, the halogenation of the substituents and, for aromatic phosphate esters, ortho alkylation of the ring are all significant factors controlling the details of the fragmentation processes. EI provides the best sensitivity for the quantitative measurement of these compounds, but PCI and ECNI both have considerable qualitative selectivity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
106.
107.
Yanjun Wang Shaoyun Chen Heng Chen Xingzhou Yuan Yongchun Zhang 《Journal of Energy Chemistry》2013,22(6):902-906
Removal of carbonyl sulfide (COS) from CO2 stream is significant for the production and utilization of food grade CO2. This study investigates the adsorption performance of Ag/NaZSM-5 as adsorbent prepared by incipient wetness impregnation for the removal of COS from a CO2 stream in a fixed-bed adsorption apparatus. Effects of various conditions on the preparation of adsorbent, adsorption and desorption were intensively examined. The results revealed that COS can be removed to below 1×10?9 from a CO2 stream (1000 ppm COS/CO2) using Ag/NaZSM-5 (10 wt% AgNO3) with an adsorption capacity of 12.86 mg-g?1. The adsorbent can be fully regenerated using hot air at 450 °C. The adsorption ability remained stable even after eight cycles of regeneration. 相似文献
108.
In this paper, as a first step to study the global structure of solution, we treat a class of reaction–diffusion systems with competitive interaction, and discuss a uniqueness theorem of radially symmetric solutions for the system. To do this, the comparison principle and the shooting method are employed, and the spatial profile is investigated. 相似文献
109.
On doubling metric measure spaces endowed with a strongly local regular Dirichlet form, we show some characterisations of pointwise upper bounds of the heat kernel in terms of global scale-invariant inequalities that correspond respectively to the Nash inequality and to a Gagliardo–Nirenberg type inequality when the volume growth is polynomial. This yields a new proof and a generalisation of the well-known equivalence between classical heat kernel upper bounds and relative Faber–Krahn inequalities or localised Sobolev or Nash inequalities. We are able to treat more general pointwise estimates, where the heat kernel rate of decay is not necessarily governed by the volume growth. A crucial role is played by the finite propagation speed property for the associated wave equation, and our main result holds for an abstract semigroup of operators satisfying the Davies–Gaffney estimates. 相似文献
110.
We consider the following system of fractional differential equations where is the Riemann‐Liouville fractional derivative of order α,f,g : [0,1] × [0, ∞ ) × [0, ∞ ) → [0, ∞ ). Sufficient conditions are provided for the existence of positive solutions to the considered problem. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献