全文获取类型
收费全文 | 584614篇 |
免费 | 9640篇 |
国内免费 | 2048篇 |
专业分类
电工技术 | 10585篇 |
综合类 | 526篇 |
化学工业 | 86988篇 |
金属工艺 | 19590篇 |
机械仪表 | 16608篇 |
建筑科学 | 16282篇 |
矿业工程 | 1274篇 |
能源动力 | 16242篇 |
轻工业 | 62045篇 |
水利工程 | 4651篇 |
石油天然气 | 3383篇 |
武器工业 | 16篇 |
无线电 | 76599篇 |
一般工业技术 | 106292篇 |
冶金工业 | 111542篇 |
原子能技术 | 7684篇 |
自动化技术 | 55995篇 |
出版年
2021年 | 3946篇 |
2020年 | 2849篇 |
2019年 | 3618篇 |
2018年 | 5618篇 |
2017年 | 5704篇 |
2016年 | 6202篇 |
2015年 | 4927篇 |
2014年 | 8246篇 |
2013年 | 27690篇 |
2012年 | 14700篇 |
2011年 | 21224篇 |
2010年 | 16348篇 |
2009年 | 18615篇 |
2008年 | 19827篇 |
2007年 | 20150篇 |
2006年 | 18316篇 |
2005年 | 16864篇 |
2004年 | 16306篇 |
2003年 | 15981篇 |
2002年 | 15253篇 |
2001年 | 15589篇 |
2000年 | 14318篇 |
1999年 | 15325篇 |
1998年 | 36188篇 |
1997年 | 25906篇 |
1996年 | 20006篇 |
1995年 | 15501篇 |
1994年 | 13692篇 |
1993年 | 13315篇 |
1992年 | 9721篇 |
1991年 | 9258篇 |
1990年 | 8747篇 |
1989年 | 8381篇 |
1988年 | 8089篇 |
1987年 | 6709篇 |
1986年 | 6560篇 |
1985年 | 8082篇 |
1984年 | 7474篇 |
1983年 | 6626篇 |
1982年 | 6100篇 |
1981年 | 6164篇 |
1980年 | 5742篇 |
1979年 | 5456篇 |
1978年 | 5064篇 |
1977年 | 6152篇 |
1976年 | 8133篇 |
1975年 | 4268篇 |
1974年 | 4045篇 |
1973年 | 3969篇 |
1972年 | 3121篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R. Sankarasubramanian C. S. Jog T. A. Abinandanan 《Metallurgical and Materials Transactions A》2002,33(4):1083-1090
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems
under a plane-strain condition with the principal misfit strain components ε*
xx
and ε*
yy
. For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε*
yy
/ε*
xx
. We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For
systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems
with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant
line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness;
moreover, the transition is also forbidden when the particle stiffness is greater than a critical value. 相似文献
992.
Chang-Ho Lee Sutono A. Sangwoo Han Kyutae Lim Pinel S. Tentzeris E.M. Laskar J. 《Advanced Packaging, IEEE Transactions on》2002,25(3):374-384
Presents design, implementation, and measurement of a three-dimensional (3-D)-deployed RF front-end system-on-package (SOP) in a standard multi-layer low temperature co-fired ceramic (LTCC) technology. A compact 14 GHz GaAs MESFET-based transmitter module integrated with an embedded bandpass filter was built on LTCC 951AT tapes. The up-converter MMIC integrated with a voltage controlled oscillator (VCO) exhibits a measured up-conversion gain of 15 dB and an IIP3 of 15 dBm, while the power amplifier (PA) MMIC shows a measured gain of 31 dB and a 1-dB compression output power of 26 dBm at 14 GHz. Both MMICs were integrated on a compact LTCC module where an embedded front-end band pass filter (BPF) with a measured insertion loss of 3 dB at 14.25 GHz was integrated. The transmitter module is compact in size (400 /spl times/ 310 /spl times/ 35.2 mil/sup 3/), however it demonstrated an overall up-conversion gain of 41 dB, and available data rate of 32 Mbps with adjacent channel power ratio (ACPR) of 42 dB. These results suggest the feasibility of building highly SOP integrated RF front ends for microwave and millimeter wave applications. 相似文献
993.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present. 相似文献
994.
螺旋槽管强化传热原理及在石化装置上的应用前景 总被引:3,自引:0,他引:3
李治滨 《石油化工设备技术》2002,23(2):8-10
详细介绍了螺旋槽管换热器的强化传热原理 ,阐明了在无相变和有相变两种工况下 ,螺旋槽管换热器的强化作用 ,并介绍了螺旋槽管换热器的设计计算方法。说明了在石油化工装置上应用的必要性 相似文献
995.
A Symbolic Pole/Zero Extraction Methodology Based on Analysis of Circuit Time-Constants 总被引:1,自引:0,他引:1
O. Guerra J. D. Rodríguez-García F. V. Fernández A. Rodríguez-Vázquez 《Analog Integrated Circuits and Signal Processing》2002,31(2):101-118
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits. 相似文献
996.
雷达系统中天线控制电路完成上位机的初始化和扫描角度控制,要求具有高可靠性和低静态电流,用专用集成电路进行设计具有明显优势.采用Verilog HDL语言描述了系统的逻辑功能,超前进位结构的加/减法器提高了电路的工作速度.利用0.6 μm CMOS工艺完成了天线控制电路的物理实现,芯片面积为1.695 mm×1.631 mm. 相似文献
997.
998.
Summary The equilibrium water contents of linear poly(acrylic acid) sodium salts with different degrees of neutralisation were found to be dependent on temperature and relative humidity. An octahedral model for the primary hydration of poly(acrylic acid) sodium salts (HIRAOKA and YOKOYAMA 1980) was critically evaluated in the light of these findings and an anomaly in the water uptake versus neutralisation curve at approximately 33% neutralisation was explained by the counterion condensation theory. (MANNING 1979). 相似文献
999.
1000.
Bounds on the number of samples needed for neural learning. 总被引:1,自引:0,他引:1
The relationship between the number of hidden nodes in a neural network, the complexity of a multiclass discrimination problem, and the number of samples needed for effect learning are discussed. Bounds for the number of samples needed for effect learning are given. It is shown that Omega(min (d,n) M) boundary samples are required for successful classification of M clusters of samples using a two-hidden-layer neural network with d-dimensional inputs and n nodes in the first hidden layer. 相似文献