首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   138000篇
  免费   15444篇
  国内免费   8553篇
电工技术   11588篇
技术理论   13篇
综合类   10886篇
化学工业   19694篇
金属工艺   8304篇
机械仪表   9213篇
建筑科学   11548篇
矿业工程   4872篇
能源动力   4167篇
轻工业   9506篇
水利工程   3385篇
石油天然气   6699篇
武器工业   1696篇
无线电   17090篇
一般工业技术   14507篇
冶金工业   5500篇
原子能技术   1911篇
自动化技术   21418篇
  2024年   816篇
  2023年   2658篇
  2022年   5562篇
  2021年   7567篇
  2020年   5664篇
  2019年   4273篇
  2018年   4829篇
  2017年   5330篇
  2016年   4757篇
  2015年   7008篇
  2014年   8544篇
  2013年   9952篇
  2012年   11498篇
  2011年   11978篇
  2010年   10483篇
  2009年   9720篇
  2008年   9266篇
  2007年   8299篇
  2006年   7401篇
  2005年   6008篇
  2004年   3979篇
  2003年   2747篇
  2002年   2490篇
  2001年   1942篇
  2000年   1763篇
  1999年   1596篇
  1998年   1116篇
  1997年   929篇
  1996年   899篇
  1995年   673篇
  1994年   549篇
  1993年   387篇
  1992年   309篇
  1991年   219篇
  1990年   168篇
  1989年   128篇
  1988年   123篇
  1987年   71篇
  1986年   55篇
  1985年   38篇
  1984年   25篇
  1983年   15篇
  1982年   25篇
  1981年   21篇
  1980年   31篇
  1979年   21篇
  1977年   4篇
  1976年   11篇
  1959年   22篇
  1951年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
强化会计内部控制促进高校科学管理   总被引:1,自引:0,他引:1  
建立和强化完善的会计内部控制体系,对于高校优化资源,促进科学管理有着重要意义.针对当前高校会计内部控制的不足,提出了若干解决对策.  相似文献   
32.
InGaAs(P)分别限制应变单量子阱激光器的优化设计   总被引:1,自引:0,他引:1  
针对较常用的InGaAs(P)分别限制应变单量子阱激光器,给出了为得到最大净增益的优化设计参数。对于激射波长为1.55μm的无应变激光器,最佳的光限制层波长为1.24μm,厚度为100nm。当阱材料引入压缩应变后.由于价带的有效状态密度减小,量子阱激光器的微分增益变大,阱深的增大对增大线性增益的效果更加明显.所以最佳光限制层的波长将变短,为1.20μm  相似文献   
33.
China has formulated a series of preferential taxation policies for the country 's petroleum enterprises. Those state policies are the important factors influencing reform and development of petroleum enterprises. The taxes turned over to the State by CNPC in 1998, 1999 and 2000 are 31.4 billion yuan, 31.7 billion yuan and 41 billion yuan respectively, accounting for 11.64 percent, 9.06 percent and 10.15 percent of the annual sales income.With China 's entry into WTO, it is necessary for t…  相似文献   
34.
A novel methanol-tolerant oxygen-reduction catalyst, Iridium-selenium (Ir-Se) chalcogenide, was synthesized by chemical precipitation in an organic solvent. Auger electron spectroscopy (AES) analysis confirmed that the synthesized Ir-Se chalcogenide had a chemical formula of Ir4Se. This chalcogenide showed strong catalytic activity towards the oxygen reduction reaction (ORR) and a high methanol tolerance. It was found that most of the oxygen could be directly reduced to water through a four-electron pathway with less than 10% hydrogen peroxide (H2O2) being produced during the ORR. The improvement in catalytic activity of the Ir-Se chalcogenide in comparison with that of pure Ir might be attributed to the effect of a bimetallic interaction.  相似文献   
35.
The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m?3 day?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm3 per dm3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability.  相似文献   
36.
An analysis is given of the performance of the standard forgetting factor recursive least squares (RLS) algorithm when used for tracking time-varying linear regression models. Three basic results are obtained: (1) the ‘P-matrix’ in the algorithm remains bounded if and only if the (time-varying) covariance matrix of the regressors is uniformly non-singular; (2) if so, the parameter tracking error covariance matrix is of the order O(μ + γ2/μ), where μ = 1 - λ, λ is the forgetting factor and γ is a quantity reflecting the speed of the parameter variations; (3) this covariance matrix can be arbitrarily well approximated (for small enough μ) by an expression that is easy to compute.  相似文献   
37.
Xia  Lei  Lv  Jiancheng  Xie  Chunzhi  Yin  Jing 《Applied Intelligence》2021,51(11):8334-8348

In the context of human-robot and robot-robot interactions, the better cooperation can be achieved by predicting the other party’s subsequent actions based on the current action of the other party. The time duration for adjustment is not sufficient provided by short term forecasting models to robots. A longer duration can by achieved by mid-term forecasting. But the mid-term forecasting models introduce the previous errors into the follow-up forecasting and amplified gradually, eventually invalidating the forecasting. A new mid-term forecasting with error suppression based on restricted Boltzmann machine(RBM) is proposed in this paper. The proposed model can suppress the error amplification by replacing the previous inputs with their features, which are retrieved by a deep belief network(DBN). Furthermore, a new mechanism is proposed to decide whether the forecasting result is accepted or not. The model is evaluated with several datasets. The reported experiments demonstrate the superior performance of the proposed model compared to the state-of-the-art approaches.

  相似文献   
38.
初步分析了混沌信号(以Logistic为例)应用于测量中的主要特性。仿真分析了Logistic信号的频谱特性、相关特性、模糊函数。说明了混沌信号在具有较高的距离速度分辨力,同时具备强抗干扰性。对比分析了混沌码和伪随机码的多普勒容限能力。初步分析Logistic信号的抗干扰特性。  相似文献   
39.
Qiu  Jun  Wang  Yueting  Wu  Peng  Jiang  Shan  Cui  Kaibo  Chen  Guowei  Liu  Dongliang  Cui  Guangwen 《Journal of Porous Materials》2021,28(6):1675-1687
Journal of Porous Materials - The dynamics and thermodynamics of adsorption of hexadecyl ammonium with different numbers of carbon chains in montmorillonite (Mt) with different layer charge density...  相似文献   
40.
The microstructure,alloying reaction and sintering behavior of the powder produced by Mechanical Al-loying(MA)for 8 h from 64 wt.-% Ti powder and 36 wt.-% Al powder were studied by scanning electronmicroscopy,optical microscopy,X-ray diffractometry,differential scanning calorimetry(DSC)and dilatometry.The mechanically alloyed powder partictes are Ti-Al composite particles.Thus,titanium aluminides can formeasily in the powder through diffusion during heat treatment.It is shown that the sintering behavior of this pow-der,different from the behaviors of TiAl alloy powder and mixed powder of 64 wt.-% Ti powder and 36 wt.-%Al powder,changes from expansion at temperatures below 1000℃ to shrinkage at temperatures above 1000℃.Homogeneously alloyed TiAl material with a density over 96% of the theoretical density can be produced fromthe mechanically alloyed powder by compaction-sintering.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号