全文获取类型
收费全文 | 61393篇 |
免费 | 11732篇 |
国内免费 | 15144篇 |
专业分类
化学 | 44998篇 |
晶体学 | 1561篇 |
力学 | 3987篇 |
综合类 | 1712篇 |
数学 | 9206篇 |
物理学 | 26805篇 |
出版年
2024年 | 79篇 |
2023年 | 923篇 |
2022年 | 1632篇 |
2021年 | 2018篇 |
2020年 | 2290篇 |
2019年 | 2179篇 |
2018年 | 1995篇 |
2017年 | 2399篇 |
2016年 | 2538篇 |
2015年 | 2953篇 |
2014年 | 3560篇 |
2013年 | 4826篇 |
2012年 | 5107篇 |
2011年 | 5686篇 |
2010年 | 4640篇 |
2009年 | 4805篇 |
2008年 | 5104篇 |
2007年 | 4667篇 |
2006年 | 4458篇 |
2005年 | 3866篇 |
2004年 | 3121篇 |
2003年 | 2331篇 |
2002年 | 2363篇 |
2001年 | 2374篇 |
2000年 | 2362篇 |
1999年 | 1606篇 |
1998年 | 1006篇 |
1997年 | 858篇 |
1996年 | 837篇 |
1995年 | 731篇 |
1994年 | 701篇 |
1993年 | 608篇 |
1992年 | 545篇 |
1991年 | 451篇 |
1990年 | 420篇 |
1989年 | 405篇 |
1988年 | 282篇 |
1987年 | 252篇 |
1986年 | 257篇 |
1985年 | 173篇 |
1984年 | 173篇 |
1983年 | 146篇 |
1982年 | 93篇 |
1981年 | 99篇 |
1980年 | 70篇 |
1979年 | 60篇 |
1978年 | 33篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1965年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
11.
Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by 18O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts. 相似文献
12.
对晶体硅(c-Si)太阳能电池而言, 氧化铝(AlOx)是一种广泛使用的钝化材料, 因为它具有优异的沉积保形性和良好的钝化质量. 为了确保AlOx发挥其良好的钝化效果, 在沉积后退火并氢化处理是必不可少的. 通过在AlOx薄膜上沉积氢化氮化硅(SiNx:H)来实现氢化, 利用开尔文探针力显微镜研究了在不同热处理和氢化作用下, AlOx/SiNx:H双层薄膜功函数的变化, 并基于沉积薄膜所含氢与固定电荷展开了讨论. 发现钝化质量和功函数之间有相关性, 影响因素包括薄膜厚度、氢化与热处理顺序. 相似文献
13.
14.
A graphic sequence π =(d1, d2,..., dn) is said to be forcibly k-edge-connected if every realization of π is k-edge-connected. In this paper, we obtain a new sufficient degree condition for π to be forcibly k-edgeconnected. We also show that this new sufficient degree condition implies a strongest monotone degree condition for π to be forcibly 2-edge-connected and a conjecture about a strongest monotone degree condition for π to be forcibly 3-edge-connected due to... 相似文献
15.
16.
Donglei Wei Huili Li Chuanqing Yang Jianmin Fu Hou Chen Liangjiu Bai Wenxiang Wang Huawei Yang Lixia Yang Ying Liang 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1588-1594
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst. 相似文献
17.
In this article,we study the initial boundary value problem of coupled semi-linear degenerate parabolic equations with a singular potential term on manifolds with corner singularities.Firstly,we introduce the corner type weighted p-Sobolev spaces and the weighted corner type Sobolev inequality,the Poincare′inequality,and the Hardy inequality.Then,by using the potential well method and the inequality mentioned above,we obtain an existence theorem of global solutions with exponential decay and show the blow-up in finite time of solutions for both cases with low initial energy and critical initial energy.Significantly,the relation between the above two phenomena is derived as a sharp condition.Moreover,we show that the global existence also holds for the case of a potential well family. 相似文献
18.
Science China Mathematics - Linear factor models are familiar tools used in many fields. Several pioneering literatures established foundational theoretical results of the quasi-maximum likelihood... 相似文献
19.
Liang Zhao 《Journal of Differential Equations》2019,266(9):5615-5624
In this paper, let be n-dimensional noncompact metric measure space which satisfies Poincaré inequality with some Ricci curvature condition. We obtain a Liouville theorem for positive weak solutions to weighted p-Lichnerowicz equation where are real constants. 相似文献
20.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers. 相似文献