全文获取类型
收费全文 | 7084篇 |
免费 | 656篇 |
国内免费 | 180篇 |
专业分类
化学 | 811篇 |
晶体学 | 7篇 |
力学 | 462篇 |
综合类 | 93篇 |
数学 | 552篇 |
物理学 | 1184篇 |
无线电 | 4811篇 |
出版年
2024年 | 18篇 |
2023年 | 49篇 |
2022年 | 119篇 |
2021年 | 150篇 |
2020年 | 212篇 |
2019年 | 115篇 |
2018年 | 132篇 |
2017年 | 274篇 |
2016年 | 284篇 |
2015年 | 302篇 |
2014年 | 496篇 |
2013年 | 445篇 |
2012年 | 455篇 |
2011年 | 504篇 |
2010年 | 320篇 |
2009年 | 334篇 |
2008年 | 413篇 |
2007年 | 440篇 |
2006年 | 383篇 |
2005年 | 380篇 |
2004年 | 313篇 |
2003年 | 347篇 |
2002年 | 251篇 |
2001年 | 198篇 |
2000年 | 170篇 |
1999年 | 116篇 |
1998年 | 133篇 |
1997年 | 94篇 |
1996年 | 106篇 |
1995年 | 78篇 |
1994年 | 45篇 |
1993年 | 47篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有7920条查询结果,搜索用时 31 毫秒
901.
分析了布尔偏导数与布尔差分的关系,给出了基于布尔偏导数的组合电路双故障测试集的方程,引入了奇集合的概念.在此基础上提出了基于布尔偏导数的组合电路双故障检测的新方法.实例表明该方法具有思路清晰、操作简单及易于掌握的优点. 相似文献
902.
Robert C. Aitken 《Journal of Electronic Testing》1992,3(4):367-375
Recently there has been renewed interest in fault detection in static CMOS circuits through I
DDQ
monitoring. This work shows that, in addition to fault detection, accurate fault diagnosis may be performed using a combination of current and voltage observations. The proposed system combines a simple single fault model for test generation with a more realistic multiple defect model for diagnosis, and as a result requires only minor modifications to existing stuck-at fault ATPG software. The associated hardware is sufficiently simple that on-board implementation is possible. Experimental results demonstrate the effectiveness of the method on a standard-cell ASIC. 相似文献
903.
StephanMorgenthaler RobertG.Staudte 《应用数学学报(英文版)》2005,21(2):247-256
A weight of evidence is a calibrated statistic whose values in [0,1] indicate the degree of agreement between the data and either of two hypothesis, one being treated as the null (H_0) and the other as the alternative (H_1). A value of zero means perfect agreement with the null, whereas a value of one means perfect agreement with the alternative. The optimality we consider is minimal mean squared error (MSE) under the alternative while keeping the MSE under the null below a fixed bound. This paper studies such statistics from a conditional point of view, in particular for location and scale models. 相似文献
904.
欠采样技术是软件无线电的核心技术之一,目前被广泛用于雷达、移动等通信系统中,本文利用SYSTEMVIEW软件对该技术进行了仿真,并通过对AM和FM两种调制信号的欠采样研究,解释了新采样体制对部分系统参数的影响并寻求解决途径。 相似文献
905.
G. Srinubabu K. Jaganbabu B. Sudharani K. Venugopal G. Girizasankar J. V. L. N. S. Rao 《Chromatographia》2006,64(1-2):95-100
A rapid and sensitive RP-HPLC method with UV detection for routine control of pramipexole in tablets was developed. Chromatography
was performed with mobile phase containing a mixture of acetonitrile/phosphate buffer (60/40; v/v) with a flow rate of 0.8
mL min−1. Quantitation was accomplished with the internal standard method; the procedure was validated by linearity (correlation coefficient
= 0.99892), accuracy, robustness and intermediate precision. Limit of quantitation and limit of detection were found to be
4.5 μg and 1.4 μg respectively, which indicates the method is highly sensitive. Experimental design was used during validation
to calculate method robustness and intermediate precision, for robustness test three factors were considered; percentage v/v of acetonitrile, flow rate and pH; an increase in the flow rate results in a decrease of concentration found of the drug,
while the percentage of organic modifier and temperature have no important effect on the response. For intermediate precision
measure the considered variables were: analyst, equipment, days and obtained RSD value (0.56%, n=24) which indicated a good precision of the analytical method. The method was found to be applicable for determination of
the drug in tablet formulations and the results of the developed method were compared with those of the UV spectrophotometric
method to access the active pramipexole content.
Revised: 13 March and 25 April 2006 相似文献
906.
T.S. Arthanari 《Discrete Mathematics》2006,306(14):1474-1492
In this paper we define a combinatorial object called a pedigree, and study the corresponding polytope, called the pedigree polytope. Pedigrees are in one-to-one correspondence with the Hamiltonian cycles on Kn. Interestingly, the pedigree polytope seems to differ from the standard tour polytope, Qn with respect to the complexity of testing whether two given vertices of the polytope are nonadjacent. A polynomial time algorithm is given for nonadjacency testing in the pedigree polytope, whereas the corresponding problem is known to be NP-complete for Qn. We also discuss some properties of the pedigree polytope and illustrate with examples. 相似文献
907.
T. M. Liu H. Q. Xie K. J. O'callaghan A. Rudin W. E. Baker 《Journal of Polymer Science.Polymer Physics》1993,31(10):1347-1362
Blends of t-butylaminoethyl methacrylate grafted polyethylene (PE-g-tBAEMA) with methyl methacrylate-methacrylic acid copolymer (PMMA-MAA) and polymethyl methacrylate (PMMA) were prepared in a Banbury type batch mixer. The effects of component proportions and processing conditions on the melt flow index, morphology, impact, and tensile properties of the resulting polymer blends were investigated. The interfacial chemical reaction was studied using Fourier transform infrared (FTIR) technique. It was observed that the melt index of the blends was reduced with increasing melt processing temperature and mixing time, indicating the formation of PE-g-PMMA block copolymer. New IR bands at 1554, 1628, 1800, and 1019 cm?1 were observed only for PE-g-tBAEMA/PMMA-MAA, the reactive blends, but not for PE-g-tBAEMA/PMMA, the nonreactive blend. These IR bands were attributed to the amide, carboxylate anion and methacrylimide formation resulting from the chemical reaction between the secondary amine on the PE-g-tBAEMA/PMMA moiety and the carboxylic acid on PMMA-MAA segment. The morphology of the blends in various compositions was examined using scanning electron microscopy (SEM) and related to their mechanical properties. All of the blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase. Furthermore, the PE-g-tBAEMA/PMMA-MAA reactive blends were shown to have much finer morphology than the corresponding nonreactive blends. For the reactive polymer blends consisting of brittle particles dispersed in the ductile matrices, the PE-g-tBAEMA/PMMA-MAA, impact and tensile result higher than predicted by the additivity rule were observed. The toughening of polyethylene by PMMA was explained by a “cold-drawing” mechanism. The Young's modulus of the blends and the extent of interfacial adhesion were analyzed with Takayanagi and Sato-Furukawa's theories. © 1993 John Wiley & Sons, Inc. 相似文献
908.
激光精细加工及其质量检测的最新进展 总被引:2,自引:0,他引:2
本文综述了目前激光精细加工的状况及其质量检测的最新发展,指出带有高精度质量检测的激光精细加工系统在工业应用中的重要性。 相似文献
909.
从影响ECL电路高速性能的原因出发,阐述了ECL电路测试及使用中对电源电压、输入偏置、负载范围、外围连线以及接地等一些特殊的要求。本文对这些特殊要求作了一些简略分析,并提出了正确测试和使用高速ECL电路的几种方法。 相似文献
910.