全文获取类型
收费全文 | 7907篇 |
免费 | 721篇 |
国内免费 | 878篇 |
专业分类
化学 | 2814篇 |
晶体学 | 26篇 |
力学 | 534篇 |
综合类 | 131篇 |
数学 | 4795篇 |
物理学 | 1206篇 |
出版年
2024年 | 10篇 |
2023年 | 70篇 |
2022年 | 142篇 |
2021年 | 229篇 |
2020年 | 222篇 |
2019年 | 231篇 |
2018年 | 211篇 |
2017年 | 218篇 |
2016年 | 266篇 |
2015年 | 228篇 |
2014年 | 402篇 |
2013年 | 579篇 |
2012年 | 371篇 |
2011年 | 412篇 |
2010年 | 356篇 |
2009年 | 510篇 |
2008年 | 493篇 |
2007年 | 541篇 |
2006年 | 479篇 |
2005年 | 385篇 |
2004年 | 369篇 |
2003年 | 335篇 |
2002年 | 333篇 |
2001年 | 290篇 |
2000年 | 286篇 |
1999年 | 188篇 |
1998年 | 190篇 |
1997年 | 160篇 |
1996年 | 166篇 |
1995年 | 144篇 |
1994年 | 122篇 |
1993年 | 80篇 |
1992年 | 75篇 |
1991年 | 63篇 |
1990年 | 41篇 |
1989年 | 27篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 27篇 |
1985年 | 40篇 |
1984年 | 39篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1959年 | 2篇 |
排序方式: 共有9506条查询结果,搜索用时 31 毫秒
1.
Prof. Dr. Peter Hess 《Chemphyschem》2022,23(6):e202100880
In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials. 相似文献
2.
《Indagationes Mathematicae》2021,32(6):1229-1239
3.
Most notable Kinetoplastids are of the genus Trypanosoma and Leishmania, affecting several millions of humans in Africa and Latin America. Current therapeutic options are limited by several drawbacks, hence the need to develop more efficacious inhibitors. An investigation to decipher the mechanism behind greater inhibitory potency of a chroman-4-one derivative (compound 1) in Trypanosoma brucei pteridine reductase 1 (TbPTR1) and Leishmania major pteridine reductase 1 (LmPTR1) was performed. Estimation of ΔGbind revealed that compound 1 had a greater binding affinity in TbPTR1 with a ΔGbind value of −49.0507 Kcal/mol than −29.2292 Kcal/mol in LmPTR1. The ΔGbind in TbPTR1 were predominantly contributed by “strong” electrostatic energy compared to the “weak” van der Waals in LmPTR1. In addition to this, the NADPH cofactor contributed significantly to the total energy of TbPTR1. A characteristic weak aromatic π interaction common in PTR1 was more prominent in TbPTR1 than LmPTR1. The consistent occurrence of high-affinity conventional hydrogen bond interactions as well as a steady interaction of crucial active site residues like Arg14/Arg17, Ser95/Ser111, Phe97/Phe113 in TbPTR1/LmPTR1 with chroman-4-one moiety equally revealed the important role the moiety played in the activity of compound 1. Overall, the structural and conformational analysis of the active site residues in TbPTR1 revealed them to be more rigid than LmPTR1. This could be the mechanism of interaction TbPTR1 employs in exerting a greater potency than LmPTR1. These findings will further give insight that will be assistive in modifying compound 1 for better potency and the design of novel inhibitors of PTR1. 相似文献
4.
5.
文[1]提出了两个DEA的逆问题,并用搜索法来解.而本文根据所证的定理,对每个问题一般只要解二、三个线性规划问题就能得到答案. 相似文献
7.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献
8.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
9.
具有模糊数的模糊多目标群体决策优选模型与方法 总被引:5,自引:0,他引:5
多目标群体决策问题是运筹学的一个重要研究领域,目前已经提出了一些有效的决策方法。但对目标值和权重均为模糊数的模糊多目标群体决策问题却研究不多,本对此类模糊多目标群体决策问题进行了探讨,利用相对正理想方案与相对负理想方案概念定义了相对差异距离,进而建立了模糊多目标群体决策优选模型与方法,并通过战役决心方案的评价说明了该方法是可行、有效的,可作为军事决策与决策支持系统的备选方法。 相似文献
10.
Mariano J. Valderrama 《商业与工业应用随机模型》1991,7(1):93-106
Alternative procedures for representing a stochastic signal as a denumerable series with uncorrelated terms are developed. The study includes considerations about parametric rescaling and its repercussions on the orthogonal expansion, as well as numerical techniques for approaching such an expansion. In addition, applications to the Gaussian characterization of stochastic signals, filtering and stochastic modelling are treated. 相似文献