全文获取类型
收费全文 | 265637篇 |
免费 | 32312篇 |
国内免费 | 10988篇 |
专业分类
电工技术 | 15356篇 |
技术理论 | 13篇 |
综合类 | 16047篇 |
化学工业 | 53342篇 |
金属工艺 | 13390篇 |
机械仪表 | 15731篇 |
建筑科学 | 20396篇 |
矿业工程 | 6479篇 |
能源动力 | 7343篇 |
轻工业 | 22286篇 |
水利工程 | 4876篇 |
石油天然气 | 12670篇 |
武器工业 | 1944篇 |
无线电 | 33363篇 |
一般工业技术 | 37273篇 |
冶金工业 | 10825篇 |
原子能技术 | 2665篇 |
自动化技术 | 34938篇 |
出版年
2024年 | 1038篇 |
2023年 | 3808篇 |
2022年 | 7070篇 |
2021年 | 9914篇 |
2020年 | 8535篇 |
2019年 | 8825篇 |
2018年 | 9179篇 |
2017年 | 10585篇 |
2016年 | 10118篇 |
2015年 | 13067篇 |
2014年 | 15183篇 |
2013年 | 18511篇 |
2012年 | 17644篇 |
2011年 | 18729篇 |
2010年 | 17000篇 |
2009年 | 16181篇 |
2008年 | 15482篇 |
2007年 | 14329篇 |
2006年 | 14105篇 |
2005年 | 11980篇 |
2004年 | 8591篇 |
2003年 | 7672篇 |
2002年 | 7633篇 |
2001年 | 6763篇 |
2000年 | 6328篇 |
1999年 | 5714篇 |
1998年 | 4445篇 |
1997年 | 3748篇 |
1996年 | 3454篇 |
1995年 | 3013篇 |
1994年 | 2476篇 |
1993年 | 1823篇 |
1992年 | 1402篇 |
1991年 | 1133篇 |
1990年 | 815篇 |
1989年 | 693篇 |
1988年 | 560篇 |
1987年 | 376篇 |
1986年 | 278篇 |
1985年 | 170篇 |
1984年 | 119篇 |
1983年 | 94篇 |
1982年 | 103篇 |
1981年 | 75篇 |
1980年 | 71篇 |
1979年 | 30篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1959年 | 11篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
本文提出了以通用阵列逻辑器件 GAL 和只读存贮器 EPROM 为核心器件的频率/待测量变换的设计方法。配以数字式传感器及用最小二乘法编制的曲线自动分段拟合程序生成的 EPROM 中的数据,可用于力、温度、光强等非电量的测量显示和控制。这种装置与采用微处理器的电路相比,有相同的测量精度,电路简单,而且保密性好. 相似文献
962.
A general model, based on double film theory, is developed to study absorption with chemical reactions. In the liquid film region, the model is a set of differential equations that describe the mass transfer accompanying several chemical reactions; the resolution of the system is achieved by the finite difference method using an implicit scheme combined with Newton's method. Continuity equations and equilibrium coefficients are exploited in the treatment of the bulk region, which is based on the Newton‐Raphson method; the results are used directly as boundary conditions in the liquid film equations. Maxwell‐Stefan equations have been used as a rigorous approach in this model. 相似文献
963.
Z.Y. Tan X.F. Xu S.L. Sun C. Zhou Y.H. Ao H.X. Zhang Y. Han 《Polymer Engineering and Science》2006,46(10):1476-1484
A series of acrylonitrile–butadiene–styrene (ABS) with different rubber content were prepared by diluting ABS grafting copolymer containing 60% rubber with a styrene–acrylonitrile copolymer. ABS prepared were blended with bisphenol‐A‐polycarbonate (PC) at the ratio of 70/30, 50/50, and 30/70 to prepare PC/ABS blends. Influence of rubber content in ABS on the properties of ABS and PC/ABS blends were investigated. PC/ABS blends with different compositions got good toughness when the rubber in ABS increased to the level that ABS itself got good toughness. The tensile properties and processability of PC/ABS blends decreased with the increase of the total rubber content introduced into the blends. ABS with the rubber content of 30 wt% is most suitable to be used to prepare PC/ABS blends. The rubber content in ABS affected the viscosity of ABS, and subsequently the viscosity ratio of PC to ABS. As a result, the morphology of PC/ABS blends varied. The increase of rubber content in ABS results in finer structure of PC/ABS blends. POLYM. ENG. SCI. 46:1476–1484, 2006. © 2006 Society of Plastics Engineers. 相似文献
964.
965.
In this paper, we present a kernel-based least squares policy iteration (KLSPI) algorithm for reinforcement learning (RL) in large or continuous state spaces, which can be used to realize adaptive feedback control of uncertain dynamic systems. By using KLSPI, near-optimal control policies can be obtained without much a priori knowledge on dynamic models of control plants. In KLSPI, Mercer kernels are used in the policy evaluation of a policy iteration process, where a new kernel-based least squares temporal-difference algorithm called KLSTD-Q is proposed for efficient policy evaluation. To keep the sparsity and improve the generalization ability of KLSTD-Q solutions, a kernel sparsification procedure based on approximate linear dependency (ALD) is performed. Compared to the previous works on approximate RL methods, KLSPI makes two progresses to eliminate the main difficulties of existing results. One is the better convergence and (near) optimality guarantee by using the KLSTD-Q algorithm for policy evaluation with high precision. The other is the automatic feature selection using the ALD-based kernel sparsification. Therefore, the KLSPI algorithm provides a general RL method with generalization performance and convergence guarantee for large-scale Markov decision problems (MDPs). Experimental results on a typical RL task for a stochastic chain problem demonstrate that KLSPI can consistently achieve better learning efficiency and policy quality than the previous least squares policy iteration (LSPI) algorithm. Furthermore, the KLSPI method was also evaluated on two nonlinear feedback control problems, including a ship heading control problem and the swing up control of a double-link underactuated pendulum called acrobot. Simulation results illustrate that the proposed method can optimize controller performance using little a priori information of uncertain dynamic systems. It is also demonstrated that KLSPI can be applied to online learning control by incorporating an initial controller to ensure online performance. 相似文献
966.
Optimal Conditions for Preparing Ultra-Fine CeO2 Powders in A Submerged Circulative Impinging Stream Reactor 总被引:1,自引:0,他引:1
Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO3)3·6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO2) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO3)3 and NH4HCO3 solutions were 0.25 and 0.3 mol·L-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g·L-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r·min-1, 80 ℃, 20 min, 5~6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8~2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point group was O5H-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR). 相似文献
967.
本文在局部凸Hausdorff线性拓扑空间中讨论了一类不可微的凸规划,得到了Kuhn-Tucker最优性条件和对偶定理。 相似文献
968.
969.
基于语法的元程序设计系统的自动生成技术 总被引:4,自引:0,他引:4
本文提出一种基于语法的元程序设计系统的自动生成技术,并开发了一个元程序设计系统的自动生成系统A-MPS。元程序设计系统是一种以程序作为操作对象的有效的程序设计工具,并具有广泛的应用。 相似文献
970.
容错磁盘阵列的性能模型 总被引:1,自引:1,他引:0
本文以排队论为工具,建立了容错磁盘阵列的M/G/1排队模型,并在此基础上分析了RAID的平均响应时间,稳定数据传输率等重要性能指标;比较了同步和异步RAID的性能差异,最后提出了以吞吐率作为衡量RAID性能的综合指标,并给出了确定最大吞吐率的定量。 相似文献