全文获取类型
收费全文 | 4644篇 |
免费 | 221篇 |
国内免费 | 1篇 |
专业分类
化学 | 3242篇 |
晶体学 | 39篇 |
力学 | 73篇 |
数学 | 702篇 |
物理学 | 810篇 |
出版年
2023年 | 40篇 |
2022年 | 22篇 |
2021年 | 56篇 |
2020年 | 82篇 |
2019年 | 71篇 |
2018年 | 98篇 |
2017年 | 101篇 |
2016年 | 173篇 |
2015年 | 154篇 |
2014年 | 163篇 |
2013年 | 330篇 |
2012年 | 375篇 |
2011年 | 423篇 |
2010年 | 203篇 |
2009年 | 163篇 |
2008年 | 306篇 |
2007年 | 319篇 |
2006年 | 260篇 |
2005年 | 266篇 |
2004年 | 204篇 |
2003年 | 174篇 |
2002年 | 135篇 |
2001年 | 131篇 |
2000年 | 104篇 |
1999年 | 61篇 |
1998年 | 44篇 |
1997年 | 23篇 |
1996年 | 49篇 |
1995年 | 34篇 |
1994年 | 32篇 |
1993年 | 33篇 |
1992年 | 40篇 |
1991年 | 22篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有4866条查询结果,搜索用时 0 毫秒
51.
Jianyuan Xu Xudong Pan Yuefeng Li Guanglin Wang R. Martínez 《Journal of Difference Equations and Applications》2019,25(9-10):1255-1269
ABSTRACTThe single input single output (SISO) system with known strong interference is widely used in various occasions. Due to its strong interference, the control accuracy is hard to guarantee. To solve this problem, an improved generalized predictive control (IGPC) algorithm is developed. The IGPC firstly builds the difference equation CARIMA (Controlled Auto-Regressive Integrated Moving-Average) model of the SISO system and then treats the system as a two input single output (TISO) system and calculates its predictive vector, then transforms it into a SISO system and uses the TISO system predictive vector to calculate the SISO system control increment. A new parameter called phase coefficient is added to inhibit the control lag. Simulations are performed to make the comparison among the traditional GPC, PID control, velocity synchronization control (VSC), fuzzy adaptive PID control (FAPID), model-based robust PID control (BPID) and the IGPC. Results show that IGPC has best performance compared to the others. Finally, experiments are developed which proved that the IGPC algorithm has a higher accuracy in the SISO system with known strong interference than that of VSC. 相似文献
52.
Dr. María Jose Capitán Dr. Jesús Álvarez Dr. Yang Wang Dr. Roberto Otero Dr. Manuel Alcamí Prof. Fernando Martín Prof. Rodolfo Miranda 《Chemphyschem》2013,14(14):3294-3302
The structure and stability of adenine crystals and thin layers has been studied by using scanning tunneling microscopy, X‐ray diffraction, and density functional theory calculations. We have found that adenine crystals can be grown in two phases that are energetically quasi‐degenerate, the structure of which can be described as a pile‐up of 2D adenine planes. In each plane, the structure can be described as an aggregation of adenine dimers. Under certain conditions, kinetic effects can favor the growth of the less stable phase. These results have been used to understand the growth of adenine thin films on gold under ultra‐high vacuum conditions. We have found that the grown phase corresponds to the α‐phase, which is composed of stacked prochiral planes. In this way, the adenine nanocrystals exhibit a surface that is enantiopure. These results could open new insight into the applications of adenine in biological, medical, and enantioselective or pharmaceutical fields. 相似文献
53.
M. Rosario De La Fuente Enrique Martín Miguel Ángel Pérez Jubindo Carmen Artal Blanca Ros José Luis Serrano 《Liquid crystals》2013,40(1):151-155
We present an achiral diacrylate that shows a phase transition from the synclinic smectic C phase (SmC) to the anticlinic smectic C (SmCalt). This last phase has been previously reported only for swallow-tailed or dimeric compounds. Our studies using differential scanning calorimetry, X-ray diffraction, polarizing optical microscopy and broad band dielectric spectroscopy suggest the existence of this mesophase in this bifunctional smectogen. 相似文献
54.
The aim of work is to study the adsorption of a common volatile organic compound such as toluene using activated carbons prepared by chemical activation with phosphoric acid of a lignocellulosic precursor, almond shell, under different conditions. The Impregnation ratio, temperature and time of activation were modified to obtain activated carbons with different characteristics. Regarding the characteristics of the activated carbons, the effects of porous structure and surface chemistry on the toluene adsorption capacity from toluene isotherms have been analysed. Results show that the control of properties of the activated carbons, particularly porous structure, highly dependent on the preparation conditions, plays a decisive role on the toluene adsorption capacity of the activated carbons. Concerning the experiments of toluene adsorption conducted in dynamic mode, activated carbons prepared at low temperatures of activation show higher breakthrough times than those obtained for activated carbons prepared at higher activation temperatures. The amount of toluene adsorbed in presence of water vapor in the gas stream lead to a decrease ranging from 33 to 46 % except for carbons prepared at higher temperatures activated that show only a slight decrease in the amount of toluene adsorbed. Activated carbons can be regenerated with soft heat treatment showing a slight decrease in the adsorption capacity. The high toluene adsorption capacities as well as the high breakthrough times obtained in presence of water vapor make these activated carbons suitable for commercial applications. 相似文献
55.
56.
57.
Juan Enrique Martínez-Legaz 《Optimization》2015,64(1):87-96
This article surveys the main contributions of K.-H. Elster to the theory of generalized conjugate functions and its applications to duality in nonconvex optimization. 相似文献
58.
Multiresidue method for the fast determination of pesticides in nutraceutical products (Camellia sinensis) by GC coupled to triple quadrupole MS 下载免费PDF全文
Gerardo Martínez‐Domínguez Patricia Plaza‐Bolaños Roberto Romero‐González Antonia Garrido Frenich 《Journal of separation science》2014,37(6):665-674
A method based on QuEChERS (quick, easy, cheap, effective, rugged, and safe) has been developed and validated for the determination and quantification of more than 140 pesticides in nutraceutical products obtained from green tea (Camellia sinensis). Extraction was performed with acidified acetonitrile (acetic acid 1%, v/v) and a clean‐up step using primary secondary amine (50 mg), graphitized black carbon (100 mg) and magnesium sulfate (200 mg) was needed. Pesticide determination was achieved utilizing GC coupled to triple quadrupole MS/MS using the selective‐reaction monitoring mode. The total run time was 23 min. Pesticides were quantified using matrix‐matched calibration. Recoveries ranged from 70 to 120% and relative SD was lower than 25% at 10, 50, and 100 μg/kg. LOQs were lower than 10 μg/kg. 148 pesticides were validated. The validated method was applied to commercial nutraceutical products, detecting 4,4‐dichlorobenzophenone (28 μg/kg), o,p′‐dicofol (38 μg/kg) and p,p‐dicofol (44 μg/kg) in a few samples. 相似文献
59.
Víctor García-Vázquez Alba Carretero Cerdán Dr. Amparo Sanz-Marco Prof. Enrique Gómez-Bengoa Prof. Belén Martín-Matute 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202201000
In this paper, we present an unprecedented and general umpolung protocol that allows the functionalization of silyl enol ethers and of 1,3-dicarbonyl compounds with a large range of heteroatom nucleophiles, including carboxylic acids, alcohols, primary and secondary amines, azide, thiols, and also anionic carbamates derived from CO2. The scope of the reaction also extends to carbon-based nucleophiles. The reaction relies on the use of 1-bromo-3,3-dimethyl-1,3-dihydro-1λ3[d][1,2]iodaoxole, which provides a key α-brominated carbonyl intermediate. The reaction mechanism has been studied experimentally and by DFT, and we propose formation of an unusual enolonium intermediate with a halogen-bonded bromide. 相似文献
60.
Aguilar T. Carrillo-Berdugo I. Martínez-Merino P. Yasinskiy A. Rodríguez-Fernández M. Navas J. 《Journal of Thermal Analysis and Calorimetry》2021,144(3):895-905
Journal of Thermal Analysis and Calorimetry - Nanofluids are considered a promising alternative to the classic fluids used in heat transfer processes. One interesting application of nanofluids is... 相似文献