全文获取类型
收费全文 | 81581篇 |
免费 | 6195篇 |
国内免费 | 3110篇 |
专业分类
电工技术 | 4419篇 |
技术理论 | 6篇 |
综合类 | 4915篇 |
化学工业 | 14110篇 |
金属工艺 | 4347篇 |
机械仪表 | 5246篇 |
建筑科学 | 5705篇 |
矿业工程 | 2585篇 |
能源动力 | 2552篇 |
轻工业 | 5537篇 |
水利工程 | 1138篇 |
石油天然气 | 5592篇 |
武器工业 | 523篇 |
无线电 | 8687篇 |
一般工业技术 | 10596篇 |
冶金工业 | 4256篇 |
原子能技术 | 862篇 |
自动化技术 | 9810篇 |
出版年
2024年 | 321篇 |
2023年 | 1363篇 |
2022年 | 2320篇 |
2021年 | 3217篇 |
2020年 | 2440篇 |
2019年 | 2200篇 |
2018年 | 2526篇 |
2017年 | 2764篇 |
2016年 | 2362篇 |
2015年 | 2994篇 |
2014年 | 3903篇 |
2013年 | 4745篇 |
2012年 | 4890篇 |
2011年 | 5489篇 |
2010年 | 4747篇 |
2009年 | 4437篇 |
2008年 | 4332篇 |
2007年 | 4158篇 |
2006年 | 4167篇 |
2005年 | 3826篇 |
2004年 | 2541篇 |
2003年 | 2343篇 |
2002年 | 2148篇 |
2001年 | 1905篇 |
2000年 | 1986篇 |
1999年 | 2204篇 |
1998年 | 1892篇 |
1997年 | 1532篇 |
1996年 | 1470篇 |
1995年 | 1263篇 |
1994年 | 1020篇 |
1993年 | 769篇 |
1992年 | 589篇 |
1991年 | 450篇 |
1990年 | 349篇 |
1989年 | 275篇 |
1988年 | 238篇 |
1987年 | 148篇 |
1986年 | 124篇 |
1985年 | 100篇 |
1984年 | 76篇 |
1983年 | 50篇 |
1982年 | 50篇 |
1981年 | 42篇 |
1980年 | 30篇 |
1979年 | 16篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The main purpose of this paper is to find the mixed-mode stress intensity factors of composite materials using the crack opening displacement (COD). First, a series solution of the composite material with a crack was used to evaluate COD values. Then, the least-squares method was used to calculate mixed-mode stress intensity factors. This algorithm can be applied to any method that generates or measures COD values. The major advantage of this method is that COD values very near the crack tip are not necessary. Both finite element simulations and laboratory experiments were applied to validate this least-squares method with acceptable accuracy if the even terms of the series solution are removed. 相似文献
102.
Single-crystalline 3C-SiC nanowires have been synthesized in large scale through a one-step autoclave route by the reaction of SiCl4, (C5H5)2Fe and metallic Na at 500 °C. Electron microscopy investigations show that the nanowires have typical diameters of 15-50 nm, lengths up to several tens of micrometers and grow along the [111] direction. The possible growth mechanism of the nanowires is discussed. 相似文献
103.
Sanghyun Ju Jianye Li Pimparkar N. Alam M.A. Chang R.P.H. Janes D.B. 《Nanotechnology, IEEE Transactions on》2007,6(3):390-395
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold 相似文献
104.
孙进 《石油化工管理干部学院学报》2003,(3):40-42
引入劳动力市场价位是企业薪酬制度改革的必然趋势。系统研究和分析了劳动力市场价位的基本特征;提出企业在引入劳动力市场价位过程中应该遵循的基本原则。 相似文献
105.
减少GPS接收机多径干扰的办法是采用特殊天线和在接收机中采取一定的措施。文中针对窄相关技术展开分析。重点分析影响接收机多径误差的因素及窄相关的性能,并给出仿真及分析结果。 相似文献
106.
An alternative method to compute the component fractions in the geometrical optical model: visual computing method 总被引:1,自引:0,他引:1
Hong-Bo Su Ren-Hua Zhang Xin-Zhai Tang Xiao-Min Sun Zhi-Lin Zhu Zhao-Liang Li 《Geoscience and Remote Sensing, IEEE Transactions on》2003,41(3):719-724
A method called visual computing was used to solve angular four-components' proportions and directional vegetation cover fraction for discrete canopies and continuous row-planted plants. It proved effective to predict the angular characteristics on pixel scale. The method could be an alternative way to a classical solution of geometrical optical models. A visual computing method would be effective especially when the canopies' spatial distribution and shapes were irregular and could not be described statistically. 相似文献
107.
LiNi0.5Mn1.5O4 powder was synthesized via sol-gel method and coated with ZnO in order to test the electrochemical cyclability of the material as a cathode for the secondary Li battery in the 5 V range at 55 °C. The ZnO-coated LiNi0.5Mn1.5O4 powder nearly maintained its initial capacity of 137 mA h g−1 after 50 cycles whereas the uncoated powder was able to retain no more than 10% of the initial capacity after 30 cycles. TEM analysis of the cycled cathodes suggests that the formation of the graphitic surface phase, hindering the Li migration, may be responsible for the rapid capacity loss of the uncoated material while no such phase was observed on the surface of the ZnO coated LiNi0.5Mn1.5O4 powder. 相似文献
108.
立方相GaN的持续光电导 总被引:1,自引:1,他引:0
研究了金属有机物化学气相外延 (MOVPE)方法生长的非故意掺杂的立方相 Ga N的持续光电导效应 .在六方相 Ga N中普遍认为持续光电导效应与黄光发射有关 ,而实验则显示在立方 Ga N中 ,持续光电导效应与其中的六方相 Ga N夹杂有关系 ,而与黄光发射没有关系 .文中提出 ,立方相 Ga N与其中的六方相 Ga N夹杂之间的势垒引起的空间载流子分离是导致持续光电导现象的物理原因 .通过建立势垒限制复合模型 ,解释了立方相 Ga N的持续光电导现象的物理过程 ,并对光电导衰减过程的动力学作了分析 .对实验数据拟合的结果证明以上的模型和推导是与实验相符的 . 相似文献
110.
Five new salts based on 1-alkyl-2-methyl pyrrolinium ion are reported, two involving the iodide ion and three involving the bis(trifluoromethanesulfonyl) amide ion. The iodide salts have melting points around 100 °C, while the amide salts have melting points around room temperature. Two of the amide salts can be easily quenched into the glassy state and exhibit glass transition temperatures around −70 °C. The 2-methyl pyrrolinium cation bears structural similarities to the aromatic imidazolium cations on one hand and the cyclic ammonium cation family based on the pyrrolidinium cation on the other. The properties of the salts reported here are compared within these two related families of salts. 相似文献