全文获取类型
收费全文 | 14657篇 |
免费 | 1550篇 |
国内免费 | 942篇 |
专业分类
化学 | 1723篇 |
晶体学 | 26篇 |
力学 | 1317篇 |
综合类 | 190篇 |
数学 | 11100篇 |
物理学 | 2793篇 |
出版年
2024年 | 12篇 |
2023年 | 126篇 |
2022年 | 152篇 |
2021年 | 224篇 |
2020年 | 410篇 |
2019年 | 422篇 |
2018年 | 389篇 |
2017年 | 423篇 |
2016年 | 485篇 |
2015年 | 367篇 |
2014年 | 700篇 |
2013年 | 1548篇 |
2012年 | 720篇 |
2011年 | 817篇 |
2010年 | 697篇 |
2009年 | 904篇 |
2008年 | 859篇 |
2007年 | 988篇 |
2006年 | 836篇 |
2005年 | 718篇 |
2004年 | 662篇 |
2003年 | 649篇 |
2002年 | 583篇 |
2001年 | 469篇 |
2000年 | 459篇 |
1999年 | 410篇 |
1998年 | 339篇 |
1997年 | 316篇 |
1996年 | 234篇 |
1995年 | 165篇 |
1994年 | 158篇 |
1993年 | 91篇 |
1992年 | 123篇 |
1991年 | 86篇 |
1990年 | 64篇 |
1989年 | 47篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 56篇 |
1984年 | 61篇 |
1983年 | 28篇 |
1982年 | 42篇 |
1981年 | 44篇 |
1980年 | 34篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1977年 | 26篇 |
1976年 | 25篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
采用自主设计搭建的雾化辅助化学气相沉积系统设备,开展了Ga2O3薄膜制备及其特性研究工作。通过X射线衍射研究了沉积温度、系统沉积压差对Ga2O3薄膜结晶质量的影响。结果表明,Ga2O3在425~650 ℃温度区间存在物相转换关系。随着沉积温度从425 ℃升高至650 ℃,薄膜结晶分别由非晶态、纯α-Ga2O3结晶状态向α-Ga2O3、β-Ga2O3两相混合结晶状态改变。通过原子力显微镜表征探究了生长温度对Ga2O3薄膜表面形貌的影响,从475 ℃升高至650 ℃时,薄膜表面粗糙度由26.8 nm下降至24.8 nm。同时,高分辨X射线衍射仪测试表明475 ℃、5 Pa压差条件下的α-Ga2O3薄膜样品半峰全宽仅为190.8″,为高度结晶态的单晶α-Ga2O3薄膜材料。 相似文献
4.
5.
6.
Yves Pomeau 《Comptes Rendus Mecanique》2018,346(3):184-197
The equations for a self-similar solution to an inviscid incompressible fluid are mapped into an integral equation that hopefully can be solved by iteration. It is argued that the exponents of the similarity are ruled by Kelvin's theorem of conservation of circulation. The end result is an iteration with a nonlinear term entering a kernel given by a 3D integral for a swirling flow, likely within reach of present-day computational power. Because of the slow decay of the similarity solution at large distances, its kinetic energy diverges, and some mathematical results excluding non-trivial solutions of the Euler equations in the self-similar case do not apply. 相似文献
7.
《Mathematical Methods in the Applied Sciences》2018,41(14):5691-5710
We consider a 2 time scale nonlinear system of ordinary differential equations. The small parameter of the system is the ratio ϵ of the time scales. We search for an approximation involving only the slow time unknowns and valid uniformly for all times at order O(ϵ2). A classical approach to study these problems is Tikhonov's singular perturbation theorem. We develop an approach leading to a higher order approximation using the renormalization group (RG) method. We apply it in 2 steps. In the first step, we show that the RG method allows for approximation of the fast time variables by their RG expansion taken at the slow time unknowns. Next, we study the slow time equations, where the fast time unknowns are replaced by their RG expansion. This allows to rigorously show the second order uniform error estimate. Our result is a higher order extension of Hoppensteadt's work on the Tikhonov singular perturbation theorem for infinite times. The proposed procedure is suitable for problems from applications, and it is computationally less demanding than the classical Vasil'eva‐O'Malley expansion. We apply the developed method to a mathematical model of stem cell dynamics. 相似文献
8.
Nasrollah Hamidi 《Journal of Macromolecular Science: Physics》2019,58(2):219-247
The thermal decomposition of post-consumer samples of a carbonated water bottle made of poly(ethylene terephthalate), PC-PET, was examined by linear temperature programing under an argon atmosphere to determine its mass loss kinetics. A simple kinetic model, called the first order pseudo single-component model, was used. The total weight-loss of each sample assumed to be in two periods, with each period corresponding to a one step decomposition of the PC-PET to volatiles. Three methods for determining the kinetic parameters by thermal gravimetric analysis were examined: differential analysis at a constant heating rate (differential), temperatures of a given conversion at a number of heating rates (isoconversional), and the maximum rate at multiple heating rates (peak temperature). The latter two multiple heating rates methods results were comparable to each other but they were not in agreement with the results from the differential method. The results of the differential method were insensitive to the heating rate and consistent with kinetics data reported in the literature for PET. 相似文献
9.
Jamil Chaker 《Mathematische Nachrichten》2019,292(11):2316-2337
We consider systems of stochastic differential equations of the form for with continuous, bounded and non‐degenerate coefficients. Here are independent one‐dimensional stable processes with . In this article we research on uniqueness of weak solutions to such systems by studying the corresponding martingale problem. We prove the uniqueness of weak solutions in the case of diagonal coefficient matrices. 相似文献
10.
Awatif Alqahtani Mohamed Jleli Bessem Samet 《Mathematical Methods in the Applied Sciences》2019,42(3):861-870
In this paper, some nonlocal in time differential inequalities of Sobolev type are considered. Using the nonlinear capacity method, sufficient conditions for the nonexistence of nontrivial global classical solutions are provided. 相似文献