全文获取类型
收费全文 | 7655篇 |
免费 | 429篇 |
国内免费 | 61篇 |
专业分类
化学 | 5770篇 |
晶体学 | 67篇 |
力学 | 154篇 |
数学 | 738篇 |
物理学 | 1416篇 |
出版年
2023年 | 31篇 |
2022年 | 28篇 |
2021年 | 148篇 |
2020年 | 127篇 |
2019年 | 142篇 |
2018年 | 121篇 |
2017年 | 122篇 |
2016年 | 254篇 |
2015年 | 233篇 |
2014年 | 279篇 |
2013年 | 479篇 |
2012年 | 583篇 |
2011年 | 655篇 |
2010年 | 407篇 |
2009年 | 305篇 |
2008年 | 522篇 |
2007年 | 468篇 |
2006年 | 473篇 |
2005年 | 379篇 |
2004年 | 363篇 |
2003年 | 299篇 |
2002年 | 269篇 |
2001年 | 145篇 |
2000年 | 135篇 |
1999年 | 91篇 |
1998年 | 69篇 |
1997年 | 56篇 |
1996年 | 57篇 |
1995年 | 56篇 |
1994年 | 53篇 |
1993年 | 41篇 |
1992年 | 40篇 |
1991年 | 32篇 |
1990年 | 36篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 45篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 29篇 |
1981年 | 30篇 |
1980年 | 21篇 |
1979年 | 34篇 |
1978年 | 22篇 |
1977年 | 26篇 |
1976年 | 26篇 |
1975年 | 20篇 |
1973年 | 32篇 |
排序方式: 共有8145条查询结果,搜索用时 15 毫秒
11.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
12.
13.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals. 相似文献
14.
The fuzzification of convex sets in median algebras is considered, and some of their properties are investigated. A characterization of finite valued fuzzy convex set is given. 相似文献
15.
Time-domain numerical computation of noise reduction by diffraction and finite impedance of barriers
Chang Woo Lim 《Journal of sound and vibration》2003,268(2):385-401
A new time-domain numerical method is presented for the estimation of noise reduction by the diffraction and finite impedance of barriers. High order finite difference schemes conventionally used for computational aeroacoustics, and time-domain impedance boundary conditions are utilized for the development of the time-domain method. Compared with other methods, this method can be applied more easily to the problems related to nonlinear noise propagation such as impulsive noise and broadband noise. Linearized Euler equations in Cartesian co-ordinates are considered and solved numerically. Straight and T-shaped barriers with and without surface admittance are calculated. In order to assess the accuracy of this time-domain method, comparison with the results of SYSNOISE software (Ver. 5.3) are made. There are very good agreements between the results of the present time-domain numerical method and the boundary element method of the SYSNOISE software. 相似文献
16.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
17.
18.
Tae Young Kim Dong Myung Kim Won Jung Kim Tae Hee Lee Kwang S. Suh 《Journal of Polymer Science.Polymer Physics》2004,42(15):2813-2820
The effect of the triblock copolymer poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) on the formation of the space charge of immiscible low‐density polyethylene (LDPE)/polystyrene (PS) blends was investigated. Blends of 70/30 (wt %) LDPE/PS were prepared through melt blending in an internal mixer at a blend temperature of 220 °C. The amount of charge that accumulated in the 70% LDPE/30% PS blends decreased when the SEBS content increased up to 10 wt %. For compatibilized and uncompatibilized blends, no significant change in the degree of crystallinity of LDPE in the blends was observed, and so the effect of crystallization on the space charge distribution could be excluded. Morphological observations showed that the addition of SEBS resulted in a domain size reduction of the dispersed PS phase and better interfacial adhesion between the LDPE and PS phases. The location of SEBS at a domain interface enabled charges to migrate from one phase to the other via the domain interface and, therefore, resulted in a significant decrease in the amount of space charge for the LDPE/PS blends with SEBS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2813–2820, 2004 相似文献
19.
Yang Woo Shin 《Operations Research Letters》2004,32(4):364-373
We consider a single server queue with disasters where the arrivals of customers and disasters are correlated. When a disaster occurs, it removes all the customers in the system and there requires repair time for the system to be operated normally. The stationary queue length distribution at the embedded points and at an arbitrary time are presented. 相似文献
20.
Man Young Kim Seung Wook Baek 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,90(3-4):377-388
Radiative heat transfer in an axisymmetric enclosure with absorbing, emitting, and scattering medium is studied here by using the different methods such as MDOM, FVM, and MFVM with emphasis on the treatment of angular derivative term, which appears in curvilinear coordinates due to angular redistribution. After final discretization equation for MFVM is introduced by using the step scheme and directional weights, the present approach is validated by applying it to three different benchmarking problems with absorbing, emitting, and scattering medium. All of the results presented here support its accuracy as well as moderate efficiency. Finally, the present approaches are applied to a truncated cone-shaped enclosure as a body-fitted geometry case. 相似文献