全文获取类型
收费全文 | 27911篇 |
免费 | 2673篇 |
国内免费 | 1457篇 |
专业分类
电工技术 | 405篇 |
综合类 | 1580篇 |
化学工业 | 11874篇 |
金属工艺 | 1492篇 |
机械仪表 | 359篇 |
建筑科学 | 713篇 |
矿业工程 | 350篇 |
能源动力 | 3397篇 |
轻工业 | 2774篇 |
水利工程 | 127篇 |
石油天然气 | 1587篇 |
武器工业 | 272篇 |
无线电 | 1135篇 |
一般工业技术 | 2947篇 |
冶金工业 | 1132篇 |
原子能技术 | 616篇 |
自动化技术 | 1281篇 |
出版年
2024年 | 315篇 |
2023年 | 907篇 |
2022年 | 1152篇 |
2021年 | 1240篇 |
2020年 | 1262篇 |
2019年 | 1176篇 |
2018年 | 1038篇 |
2017年 | 1126篇 |
2016年 | 1018篇 |
2015年 | 879篇 |
2014年 | 1359篇 |
2013年 | 1654篇 |
2012年 | 1582篇 |
2011年 | 1786篇 |
2010年 | 1305篇 |
2009年 | 1397篇 |
2008年 | 1271篇 |
2007年 | 1566篇 |
2006年 | 1378篇 |
2005年 | 1191篇 |
2004年 | 1064篇 |
2003年 | 946篇 |
2002年 | 815篇 |
2001年 | 725篇 |
2000年 | 645篇 |
1999年 | 575篇 |
1998年 | 436篇 |
1997年 | 371篇 |
1996年 | 340篇 |
1995年 | 287篇 |
1994年 | 274篇 |
1993年 | 207篇 |
1992年 | 153篇 |
1991年 | 114篇 |
1990年 | 97篇 |
1989年 | 67篇 |
1988年 | 55篇 |
1987年 | 52篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1980年 | 11篇 |
1964年 | 9篇 |
1963年 | 5篇 |
1961年 | 5篇 |
1957年 | 8篇 |
1955年 | 8篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
?smail Dinçer 《Advances in Engineering Software》2011,42(4):160-171
Determination of deformation modulus and coefficient of subgrade reaction of soils have major importance, whether the projects are in design, and construction or compaction assessment stage of earth filling structures. Plate load test is one of the frequently used method to directly determine the parameters but the method is both costly and time consuming. For this reason, this paper is concerned with the applications of artificial neural networks (ANN) and simple-multiple regression analysis to predict deformation modulus and coefficient of subgrade reaction of compacted soils from compaction parameters (such as maximum dry density (MDD) and optimum moisture content (OMC), field dry density (FDD), and field moisture content (FMC)). Regression analysis and artificial neural network estimation indicated that there are acceptable correlations between deformation modulus and coefficient of subgrade reaction and these parameters. Artificial neural networks model exhibits higher performance than traditional statistical model for predicting deformation modulus and coefficient of subgrade reaction. 相似文献
42.
Binary oxides of manganese and vanadium have been synthesized by solid state sintering, in which the mass ratio of the individual components Mn2O3 and VO2 have been varied from 90:10 to 5:95. The bulk ceramic samples were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray analysis. The initial compositions either rich in Mn2O3 or in equi-proportion by mass with VO2 yield β-Mn2V2O7 or a new crystalline form of Mn2V2O7, with unit cell parameters: a = 7.73091 Å, b = 6.640788 Å, c = 6.70779 Å α = γ = 90° and β = 98.7086° which is designated as γ-Mn2V2O7. The compositions, richer in VO2 produce MnV2O6 co-existing with V2O5 the proportion of which increases with increase in VO2. The surface microanalysis shows a spherical-granular morphology in Mn2V2O7 structure and plate/rod-like structures co-existing with granular morphology in case of MnV2O6 together with V2O5. The electrical parameters of the negative temperature coefficient thermistors were determined. Depending on the constituent oxide composition, the NTC thermistors showed room temperature resistivity in the range of 6.52 × 102 to 6.1 × 106 Ω-cm. The thermistor constant and activation energy are in the range of 0.12–0.458 eV and 1393–4801 K, respectively. 相似文献
43.
This paper addresses the explicit synchronisation of heterogeneous dynamics networks via three-layer communication framework. The main contribution is to propose an explicit synchronisation algorithm, in which the synchronisation errors of all the agents are decoupled. By constructing a three-layer node model, the proposed algorithm removes the assumptions that the topology is fixed and the synchronisation process is coupled. By introducing appropriate assumptions, the algorithm leads to a class of explicit synchronisation protocols based on the states of agents in different layers. It is proved in the sense of Lyapunov that, if the dwell time is larger than a threshold, the explicit synchronisation can be achieved for closed-loop heterogeneous dynamics networks under switching topologies. The results are further extended to the cases in which the switching topologies are only frequently but not always connected. Simulation results are presented with four single-link manipulators to verify the theoretical analysis. 相似文献
44.
针对选煤厂生产调度的自身特点,以大屯选煤厂生产调度的实际情况为背景,介绍了基于CSCW的选煤生产调度管理系统,并对此系统的安全性和异构为数据库的访问做了阐述。 相似文献
45.
Miguel López-Portugués Jesús A. López-Fernández Jonatan Menéndez-Canal Alberto Rodríguez-Campa José Ranilla 《Journal of Parallel and Distributed Computing》2012
In this paper, we present a heterogeneous parallel solver of a high frequency single level Fast Multipole Method (FMM) for the Helmholtz equation applied to acoustic scattering. The developed solution uses multiple GPUs to tackle the compute bound steps of the FMM (aggregation, disaggregation, and near interactions) while the CPU handles a memory bound step (translation) using OpenMP. The proposed solver performance is measured on a workstation with two GPUs (NVIDIA GTX 480) and is compared with that of a distributed memory solver run on a cluster of 32 nodes (HP BL465c) with an Infiniband network. Some energy efficiency results are also presented in this work. 相似文献
46.
Aviles Fredy; Earleywine Mitchell; Pollock Vicki; Stratton Joy; Miller Norman 《Canadian Metallurgical Quarterly》2005,19(1):108
The authors examined alcohol's effect on triggered displaced aggression, the hostile reaction to a second provoking person after provocation from a first. Participants consumed an alcoholic or a nonalcoholic beverage. Subsequently, one individual provoked all of them with moderate intensity. Then, 2 groups were studied: those who received or who failed to receive a second provocation of minimal intensity. Consistent with prior research, participants who received a second, minimal provocation displayed more aggression than those who did not. After participants drank alcohol, the magnitude of this difference was significantly greater, indicating that alcohol increases triggered displaced aggression. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
47.
48.
以一直径138cm的聚乙烯球作为中子慢化剂与全吸收探测器,采用全吸收法测量了钒球的14MeV中子的泄漏倍增率。用1支与H对热中子具有相同1/V吸收规律的^6Li玻璃探测器的测量子全吸收体的径向中子计数率分布。实验得到了钒球中心D-T中子时的Al、Fe、In和V一组阈探测器的绝对活化反应率的分布。用MCNP/4A程序、ENDF/B-Ⅵ和FENDL-2核数据进行了模拟计算。与实验结果相比较可知:用ENDF/B-Ⅵ库数据的计算结果与实验结果符合良好,而用FENDL-2库数据的计算结果比实验结果约高4%。 相似文献
49.
A new approach, called the “variational theory of complex rays” has been developed in order to calculate the vibrations of slightly damped elastic plates in the medium-frequency range. The resolution of a small system of equations which does not result from a fine spatial discretization of the structure leads to the evaluation of effective quantities (deformation energy, vibration amplitude,…). Here, we extend this approach, which was already validated for assemblies of homogeneous substructures, to the case of heterogeneous substructures. 相似文献
50.
苯基金属试剂对乳醇立体选择性反应的研究 总被引:1,自引:0,他引:1
(±)4,10-二氧杂三环[5,2,1,02,6]-癸-8-烯-3-醇在ZnBr2催化下与格氏试剂反应得S-二醇4a,而与街进制AT(OPr-i)3单独作用则得R-H醇4b。探讨了反应机理,并提出了合成不同构型乳醇的新方法。 相似文献