全文获取类型
收费全文 | 1335篇 |
免费 | 294篇 |
国内免费 | 114篇 |
专业分类
化学 | 214篇 |
晶体学 | 2篇 |
力学 | 367篇 |
综合类 | 18篇 |
数学 | 293篇 |
物理学 | 849篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 50篇 |
2020年 | 44篇 |
2019年 | 42篇 |
2018年 | 34篇 |
2017年 | 53篇 |
2016年 | 57篇 |
2015年 | 64篇 |
2014年 | 84篇 |
2013年 | 119篇 |
2012年 | 59篇 |
2011年 | 104篇 |
2010年 | 86篇 |
2009年 | 83篇 |
2008年 | 94篇 |
2007年 | 98篇 |
2006年 | 90篇 |
2005年 | 73篇 |
2004年 | 69篇 |
2003年 | 58篇 |
2002年 | 51篇 |
2001年 | 35篇 |
2000年 | 34篇 |
1999年 | 33篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1743条查询结果,搜索用时 965 毫秒
31.
Hiroshi Sakamoto 《Journal of Discrete Algorithms》2005,3(2-4):416-430
A linear-time approximation algorithm for the grammar-based compression is presented. This is an optimization problem to minimize the size of a context-free grammar deriving a given string. For each string of length n, the algorithm guarantees approximation ratio without suffix tree construction. 相似文献
32.
对轴线起爆式螺线管型爆磁压缩发生器进行了理论模型研究,建立了爆炸管的一维爆轰驱动模型、螺线管内空间磁场强度分布模型、爆炸管外表面磁压力模型和发生器系统的等效电路模型等,对此类发生器的物理过程进行系统描述。在此基础上,编制了相应的零维数值模拟程序CEMG 1.0,利用该程序分别对四种不同模型参数的发生器进行了理论计算和参数优化,并对其中一模型发生器爆炸管外表面的磁压力及其引起的剩余电感进行了计算,给出了剩余电感与初始输入条件及负载电感的关系,从而得到该模型的输出性能极限。对理论模型的正确性进行了实例验算证明。 相似文献
33.
I. J. Gnip V. I. Kersulis S. I. Vaitkus S. A. Veyelis 《Mechanics of Composite Materials》2005,41(6):535-540
Data obtained in investigating the creep of expanded polystyrene in compression are discussed. An analysis of the results
of creep tests 65–608 days long showed that the creep can be predicted for 50 years based on experiments of less duration
than the 605 days indicated in EN 13163. For this purpose, it is suggested to employ a 95-fold extrapolation in time if the
creep curves are described by a power function (as recommended by EN 13163) or a 50-fold extrapolation if the exponential
equation proposed in the present paper is used.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 795–802, November–December, 2005. 相似文献
34.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
35.
脉冲离散效应对光纤中基于交叉相位调制的脉冲压缩的影响 总被引:4,自引:1,他引:3
通过数值模拟,分析了脉冲离散效应对单模光纤正群速色区基于暗孤子交叉不相位调制的脉冲压缩的影响,并提出了减轻这种影响的办法,作者发现,即使暗孤子与被压缩脉冲的中心波长相差很小,离散效应对脉冲压缩的影响也很大,离散效应不仅导致脉冲压缩比的减小和压缩后脉冲峰值功率的降低,而且还导致脉冲压缩所需最佳光纤长度的增加以及压缩后的脉冲呈现不对称性,还发现,若采取本文提出了的非同步耦合法,则可以明显地弥补离散效应 相似文献
36.
成像光谱技术中机上实时数据压缩方法研究 总被引:2,自引:0,他引:2
根据成像光谱仪的特点用一系列串行的一维压缩实现二维图像压缩.提出了在机上对原始数据从光谱方向进行实时压缩的“二真值线性预测方法”.该法可做到压缩/复原后光谱特征信息不丢失.实验表明,对大多数光谱数据在1%的重建精度下,至少可获得2:1的压缩比.从总体而言,压缩后原始数据率可降低3~4倍.文中还对压缩数据的编码和误差进行了讨论. 相似文献
37.
I. Esteban-Díez 《Analytica chimica acta》2006,555(1):84-95
Orthogonal WAVElet correction (OWAVEC) is a pre-processing method aimed at simultaneously accomplishing two essential needs in multivariate calibration, signal correction and data compression, by combining the application of an orthogonal signal correction algorithm to remove information unrelated to a certain response with the great potential that wavelet analysis has shown for signal processing. In the previous version of the OWAVEC method, once the wavelet coefficients matrix had been computed from NIR spectra and deflated from irrelevant information in the orthogonalization step, effective data compression was achieved by selecting those largest correlation/variance wavelet coefficients serving as the basis for the development of a reliable regression model. This paper presents an evolution of the OWAVEC method, maintaining the first two stages in its application procedure (wavelet signal decomposition and direct orthogonalization) intact but incorporating genetic algorithms as a wavelet coefficients selection method to perform data compression and to improve the quality of the regression models developed later. Several specific applications dealing with diverse NIR regression problems are analyzed to evaluate the actual performance of the new OWAVEC method. Results provided by OWAVEC are also compared with those obtained with original data and with other orthogonal signal correction methods. 相似文献
38.
Changes in the physicochemical properties of transferrin upon chemical derivatization with ceramides
M. A. Egea M. L. García M. A. Alsina C. Mestres F. Reig 《Colloid and polymer science》1994,272(5):570-576
The interaction of native and derivatized transferrin with lecithin, cholesterol and their mixtures was studied using monomolecular layers of phospholipids. Moreover, the thermodynamic parameters corresponding to these interactions: the mixing excess free energy, interaction energy, and interaction parameter were also calculated.The ability of these two proteins to insert into monolayers was studied working at constant area.The formation of aggregates or secondary structures in solution was determined by the fluorescence and polarization values of ANS (anilinonaphthalene sulfonate), measured at different protein/ANS relationships.Abbreviations TF
Transferrin
- DTF
derivatized transferrin
- PC
lecithin
- CHOL
cholesterol
- CER
ceramides
- ANS
anilinonaphthalene sulfonate
- TNBS
trinitro benzenesulfonate method 相似文献
39.
离散小波变换-遗传算法-交互检验法用于近红外光谱数据的高倍压缩与变量筛选 总被引:11,自引:0,他引:11
用遗传算法(GA)与交互检验(CV)相结合建立了一种用于对近红外光谱(NIR)数据及其离散小波变换(DWT)系数进行变量筛选的方法,并应用于烟草样品中总挥发碱和总氮的同时测定。结果表明:NIR数据经DWT压缩为原始大小的3.3%时基本没有光谱信息的丢失;有效的变量筛选可以极大地减少模型中的变量个数,降低模型的复杂程度,改善预测的准确度。 相似文献
40.
Improved quantification limits in chiral capillary electrochromatography by peak compression effects
The peak compression effect has been applied to improve quantification limits in chiral capillary electrochromatography (CEC). A stationary phase based on the chiral selector vancomycin (Chirobiotic V) was used for separations of the enantiomers of mianserin. By adding solvents with a low dielectric constant, e.g. 2-propanol or tetrahydrofuran, to the sample solution, peak compression could be induced. The plate numbers for the minor enantiomer increased from approximately 100,000 to 1.4-1.6 million plates/m, when the composition of the mobile phase was adjusted so that the analyte eluted within either one of two system zones originating from the sample solution. A 10-fold improvement in the quantification limit for the minor enantiomer was obtained compared to elution under non-focused conditions. 相似文献