全文获取类型
收费全文 | 967篇 |
免费 | 50篇 |
国内免费 | 47篇 |
专业分类
化学 | 682篇 |
晶体学 | 5篇 |
力学 | 36篇 |
数学 | 108篇 |
物理学 | 233篇 |
出版年
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 46篇 |
2012年 | 71篇 |
2011年 | 102篇 |
2010年 | 42篇 |
2009年 | 45篇 |
2008年 | 65篇 |
2007年 | 54篇 |
2006年 | 66篇 |
2005年 | 49篇 |
2004年 | 47篇 |
2003年 | 34篇 |
2002年 | 30篇 |
2001年 | 26篇 |
2000年 | 39篇 |
1999年 | 20篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1935年 | 4篇 |
排序方式: 共有1064条查询结果,搜索用时 0 毫秒
81.
Chun-Che Huang Tzu-Liang Tseng Fuhua Jiang Yu-Neng Fan Chih-Hua Hsu 《Annals of Operations Research》2014,216(1):163-189
Rough set theory is a new data mining approach to manage vagueness. It is capable to discover important facts hidden in the data. Literature indicate the current rough set based approaches can’t guarantee that classification of a decision table is credible and it is not able to generate robust decision rules when new attributes are incrementally added in. In this study, an incremental attribute oriented rule-extraction algorithm is proposed to solve this deficiency commonly observed in the literature related to decision rule induction. The proposed approach considers incremental attributes based on the alternative rule extraction algorithm (AREA), which was presented for discovering preference-based rules according to the reducts with the maximum of strength index (SI), specifically the case that the desired reducts are not necessarily unique since several reducts could include the same value of SI. Using the AREA, an alternative rule can be defined as the rule which holds identical preference to the original decision rule and may be more attractive to a decision-maker than the original one. Through implementing the proposed approach, it can be effectively operating with new attributes to be added in the database/information systems. It is not required to re-compute the updated data set similar to the first step at the initial stage. The proposed algorithm also excludes these repetitive rules during the solution search stage since most of the rule induction approaches generate the repetitive rules. The proposed approach is capable to efficiently and effectively generate the complete, robust and non-repetitive decision rules. The rules derived from the data set provide an indication of how to effectively study this problem in further investigations. 相似文献
82.
Fu-Shiang Tseng Yingchieh Yeh 《The Journal of the Operational Research Society》2014,65(11):1760-1769
Under a maintenance outsourcing contract, an external contractor receives a fixed payment from a manufacturer for periodically performing preventive maintenance and for performing minimal repairs whenever process failures occur. If the contractor’s maintenance policy results in a process uptime above a target level specified in the contract, the contractor receives a bonus payment based on the difference between the uptime and the target levels. We study the optimal designs of maintenance outsourcing contracts for achieving channel coordination when the contractor is risk averse towards uncertain repair costs caused by process failures. We find cases in which channel coordination cannot be achieved because of the contractor’s risk preference. Furthermore, the contractor’s risk preference may make channel coordination more difficult or easier, depending on the parameters considered in the model. 相似文献
83.
The validation of causal relationship between two groups of multivariate time series data often requires the precedence knowledge of all variables. However, in practice one finds that some variables may be negligible in describing the underlying causal structure. In this article we provide an explicit definition of “non-informative variables” in a two-group causal relationship and introduce various automatic computer-search algorithms that can be utilized to extract informative variables based on a hypothesis testing procedure. The result allows us to represent a simplified causal relationship by using minimum possible information on two groups of variables. 相似文献
84.
Fatemeh Zehtabi Hossein Montazerian Reihaneh Haghniaz Kaylee Tseng Neda Mohaghegh Kalpana Mandal Behnam Zamanian Mehmet Remzi Dokmeci Mohsen Akbari Alireza Hassani Najafabadi Han-Jun Kim Ali Khademhosseini 《Macromolecular bioscience》2023,23(1):2200333
Shear-thinning biomaterials (STBs) based on gelatin-silicate nanoplatelets (SNs) are emerging as an alternative to conventional coiling and clipping techniques in the treatment of vascular anomalies. Improvements in the cohesion of STB hydrogels pave the way toward their translational application in minimally invasive therapies such as endovascular embolization repair. In the present study, sodium phytate (Phyt) additives are used to tune the electrostatic network of SNs-gelatin STBs, thereby promoting their mechanical integrity and facilitating injectability through standard catheters. We show that an optimized amount of Phyt enhances storage modulus by approximately one order of magnitude and reduces injection force by ≈58% without compromising biocompatibility and hydrogel wet stability. The Phyt additives are found to decrease the immune responses induced by SNs. In vitro embolization experiments suggest a significantly lower rate of failure in Phyt-incorporated STBs than in control groups. Furthermore, the addition of Phyt leads to accelerated blood coagulation (reduces clotting time by ≈45% compared to controls) due to the contributions of negatively charged phosphate groups, which aid in the prolonged durability of STB in coagulopathic patients. Therefore, the proposed approach is an effective method for the design of robust and injectable STBs for minimally invasive treatment of vascular malformations. 相似文献
85.
C. -W. Chang Y. -C. Chou J. -M. Tseng M. -Y. Liu C. -M. Shu 《Journal of Thermal Analysis and Calorimetry》2009,95(2):639-643
Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics
regarding stability would represent potential hazards during the production or utilization stage and could be determined by
calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate
the thermokinetic parameters for MWNTs at various compositions.
Thermoanalytical curves showed that the average heat of decomposition (ΔH
d) of the MWNTs samples in a manufacturing process was about 31,723 J g−1, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence
of sulfuric acid (H2SO4). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch
addition with reactants of H2SO4. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation
or accident. 相似文献
86.
Der-Jang Liaw Been-Yang Liaw Jeng-Ming Tseng 《Journal of polymer science. Part A, Polymer chemistry》1999,37(14):2629-2635
A series of novel soluble poly(amide-imide)s were prepared from the diimide-dicarboxylic acid, 2,2-bis[N-(4-carboxyphenyl)-phthalimidyl]hexafluoropropane, with various diamines by the direct polycondensation in N-methyl-2-pyrrolidinone containing CaCl2 using triphenyl phosphite and pyridine as condensing agents. All the polymers were obtained in quantitative yields with inherent viscosities of 0.78–1.63 dL g−1. The polymers were amorphous and readily soluble in aprotic polar solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide as well as in less polar solvents such as pyridine and γ-butyrolactone, and also in tetrahydrofuran. The polymer films had tensile strength of 84–129 MPa, an elongation at break range of 6–22%, and a tensile modulus range of 2.0–2.7 GPa. The glass transition temperatures of the polymers were determined by DSC method and they were in the range of 240–282°C. These polymers were fairly stable up to a temperature around or above 400°C, and lose 10% weight in the range of 450–514°C and 440–506°C in nitrogen and air, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2629–2635, 1999 相似文献
87.
An unprecedented C,C-linked dimeric norcembranoid (sinulochmodin A, 1), a novel isocembranoid (sinulochmodin B, 2), and a novel yonarane norditerpenoid (sinulochmodin C, 3) were isolated from the soft coral Sinularia lochmodes. The structures of these metabolites were elucidated by extensive spectroscopic analysis and on the basis of the absolute structures of two related norditerpenoids (4 and 5), which were determined for the first time by a modified Mosher method. A plausible pathway for the biosynthesis of 1 and 3-5 from 2 was postulated. [structure: see text] 相似文献
88.
In this paper a parallel algorithm to solve the stable marriage problem is given. The worst case performance of this algorithm is stated. A theoretical analysis shows that the probability of the occurrence of this worst case is extremely small. For instance, if there are sixteen men and sixteen women involved, then the probability that the worst case occurs is only 10–45. Possible future research is also discussed in this paper. 相似文献
89.
SynthesisandCrystalStructureofMnSm_4(SiO_4)_3O¥ChiLi-Sheng;DengShui-Quan;ZhuangHong-Hui;HuangJin-Shun;(StateHeylaboratoryofStr?.. 相似文献
90.