全文获取类型
收费全文 | 106321篇 |
免费 | 11577篇 |
国内免费 | 6525篇 |
学科分类
工业技术 | 124423篇 |
出版年
2024年 | 678篇 |
2023年 | 2268篇 |
2022年 | 4481篇 |
2021年 | 5891篇 |
2020年 | 4303篇 |
2019年 | 3308篇 |
2018年 | 3392篇 |
2017年 | 3813篇 |
2016年 | 3486篇 |
2015年 | 4838篇 |
2014年 | 6133篇 |
2013年 | 6920篇 |
2012年 | 7983篇 |
2011年 | 8517篇 |
2010年 | 7625篇 |
2009年 | 7238篇 |
2008年 | 7201篇 |
2007年 | 6571篇 |
2006年 | 6023篇 |
2005年 | 5020篇 |
2004年 | 3430篇 |
2003年 | 2687篇 |
2002年 | 2634篇 |
2001年 | 2215篇 |
2000年 | 1824篇 |
1999年 | 1398篇 |
1998年 | 920篇 |
1997年 | 723篇 |
1996年 | 679篇 |
1995年 | 551篇 |
1994年 | 403篇 |
1993年 | 269篇 |
1992年 | 217篇 |
1991年 | 177篇 |
1990年 | 121篇 |
1989年 | 102篇 |
1988年 | 90篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1959年 | 11篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
申浩 《苏州科技学院学报(工程技术版)》2015,(2):61-65
解释了跨界借鉴的含义,并阐述了其在建筑立面创新设计中运用的可能性和积极意义。通过案例分析,提出建筑立面跨界借鉴的内容和方式。 相似文献
2.
3.
4.
We propose an analytical model to evaluate the lightpath blocking performance for a single ROADM node with intra-node add/drop contention,in which the number of lightpaths that can be added/dropped with the same wavelength is limited by the add/drop contention factor.Different models of traffic load per nodal degree are considered to validate the effectiveness of the analytical model.The simulation results show that the proposed analytical model is effective in predicting the performance for different values of add/drop contention factor C and for variable offered loads at the node.The add/drop contention factor shows an important impact on the lightpath blocking performance and properly raising the contention factor can significantly improve the lightpath blocking performance.When the add/drop contention factor C exceeds a certain level,the performance of a ROADM with intra-node contention is close to that of a contentionless ROADM. 相似文献
5.
6.
7.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed. 相似文献
8.
9.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
10.