全文获取类型
收费全文 | 88243篇 |
免费 | 6590篇 |
国内免费 | 8505篇 |
专业分类
化学 | 31924篇 |
晶体学 | 354篇 |
力学 | 7308篇 |
综合类 | 1541篇 |
数学 | 38772篇 |
物理学 | 23439篇 |
出版年
2023年 | 747篇 |
2022年 | 1085篇 |
2021年 | 1569篇 |
2020年 | 1781篇 |
2019年 | 2069篇 |
2018年 | 1832篇 |
2017年 | 2109篇 |
2016年 | 2261篇 |
2015年 | 2044篇 |
2014年 | 3056篇 |
2013年 | 6264篇 |
2012年 | 3405篇 |
2011年 | 3991篇 |
2010年 | 3452篇 |
2009年 | 4892篇 |
2008年 | 5425篇 |
2007年 | 5839篇 |
2006年 | 5305篇 |
2005年 | 4554篇 |
2004年 | 4147篇 |
2003年 | 4201篇 |
2002年 | 3936篇 |
2001年 | 3281篇 |
2000年 | 3125篇 |
1999年 | 2848篇 |
1998年 | 2548篇 |
1997年 | 2141篇 |
1996年 | 1859篇 |
1995年 | 1686篇 |
1994年 | 1549篇 |
1993年 | 1303篇 |
1992年 | 1240篇 |
1991年 | 944篇 |
1990年 | 767篇 |
1989年 | 676篇 |
1988年 | 616篇 |
1987年 | 499篇 |
1986年 | 420篇 |
1985年 | 516篇 |
1984年 | 479篇 |
1983年 | 244篇 |
1982年 | 400篇 |
1981年 | 449篇 |
1980年 | 336篇 |
1979年 | 314篇 |
1978年 | 251篇 |
1977年 | 216篇 |
1976年 | 170篇 |
1974年 | 114篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
为了获得纯度更高的碳纳米管膜, 保证材料发热稳定性, 需要对通过化学气相沉积法得到的碳纳米管膜进行二次纯化. 通过使用高温纯化炉, 在真空状态下, 从1700℃到3200℃分7挡温度对碳纳米管进行纯化, 并对其含碳量和方块电阻进行比较. 结果表明, 高温纯化后的碳纳米管膜含碳量从95.0%提高到99.9%, 解决了含碳量低的问题. 同时, 在高温纯化中发现碳纳米管膜方块电阻从纯化前3Ω降低到0.5Ω, 方块电阻的降低对碳纳米管膜具有十分重要的意义, 同样对碳纳米管膜后续产品的开发也有重要作用. 相似文献
2.
3.
Rose Morris-Wright 《Journal of Pure and Applied Algebra》2021,225(1):106468
Parabolic subgroups are the building blocks of Artin groups. This paper extends previous results of Cumplido, Gebhardt, Gonzales-Meneses and Wiest, known only for parabolic subgroups of finite type Artin groups, to parabolic subgroups of FC-type Artin groups. We show that the class of finite type parabolic subgroups is closed under intersection. We also study an analog of the curve complex for mapping class group constructed by Cumplido et al. using parabolic subgroups. We extend the construction of this complex, called the complex of parabolic subgroups, to FC-type Artin groups. We show that this simplicial complex is, in most cases, infinite diameter and conjecture that it is δ-hyperbolic. 相似文献
4.
Dominik Vítek Prof. Aleš Růžička Lise Vermeersch Dr. Libor Dostál Dr. Jan Turek Prof. Roman Jambor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202639
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed. 相似文献
5.
6.
《Operations Research Letters》2022,50(2):137-144
In mine planning problems, cutoff grade optimization defines a threshold at every time period such that material above this value is processed, and the rest is considered waste. In orebodies with multiple minerals, which occur in practice, the natural extension is to consider a cutoff surface. We show that in two dimensions the optimal solution is a line, and in n dimensions it is a hyperplane. 相似文献
7.
《Discrete Mathematics》2022,345(10):112984
Let G be a generalized dicyclic group with identity 1. An inverse closed subset S of is called minimal if and there exists some such that . In this paper, we characterize distance-regular Cayley graphs of G under the condition that S is minimal. 相似文献
8.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献
9.
10.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献