全文获取类型
收费全文 | 22914篇 |
免费 | 2247篇 |
国内免费 | 1186篇 |
专业分类
电工技术 | 613篇 |
综合类 | 1893篇 |
化学工业 | 4498篇 |
金属工艺 | 1820篇 |
机械仪表 | 3754篇 |
建筑科学 | 944篇 |
矿业工程 | 1389篇 |
能源动力 | 1113篇 |
轻工业 | 789篇 |
水利工程 | 391篇 |
石油天然气 | 525篇 |
武器工业 | 609篇 |
无线电 | 634篇 |
一般工业技术 | 3197篇 |
冶金工业 | 1065篇 |
原子能技术 | 321篇 |
自动化技术 | 2792篇 |
出版年
2024年 | 140篇 |
2023年 | 486篇 |
2022年 | 855篇 |
2021年 | 978篇 |
2020年 | 898篇 |
2019年 | 750篇 |
2018年 | 699篇 |
2017年 | 910篇 |
2016年 | 979篇 |
2015年 | 951篇 |
2014年 | 1424篇 |
2013年 | 1482篇 |
2012年 | 1421篇 |
2011年 | 1740篇 |
2010年 | 1098篇 |
2009年 | 1258篇 |
2008年 | 1109篇 |
2007年 | 1387篇 |
2006年 | 1241篇 |
2005年 | 968篇 |
2004年 | 898篇 |
2003年 | 756篇 |
2002年 | 626篇 |
2001年 | 557篇 |
2000年 | 458篇 |
1999年 | 405篇 |
1998年 | 329篇 |
1997年 | 269篇 |
1996年 | 224篇 |
1995年 | 184篇 |
1994年 | 162篇 |
1993年 | 129篇 |
1992年 | 105篇 |
1991年 | 97篇 |
1990年 | 63篇 |
1989年 | 95篇 |
1988年 | 56篇 |
1987年 | 31篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1959年 | 8篇 |
1956年 | 2篇 |
1955年 | 5篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
An experimental study of the gas-dynamic aspects of the high-velocity oxyfuel (HVOF) thermal spray process has been performed
using commercially available HVOF equipment (Hobart-Tafa JP-5000, Ho-bart-Tafa Technologies, Inc., Concord, NH). Optical diagnostic
techniques, including microsecond-expo-sure schlieren and shadowgraph imaging, were applied to visualize the hot supersonic
jet produced by this equipment without particle injection. Rapid turbulent mixing of the jet with the surrounding atmos-phere
was observed, which is an issue of concern in coating quality due to the possibility of oxidation of sprayed particles. This
mixing appears to be a function of the ratio of densities of the hot jet and the cold atmosphere as well as a function of
the velocity of the jet, rather than one of combustion-chamber pres-sure or barrel length. The supersonic core of the HVOF
jet dissipates rapidly due to the mixing, so that the jet is no longer supersonic when it impinges on the target surface being
sprayed. Secondary issues also observed in this study include strong jet-noise radiation from the HVOF plume and the entrainment
and induced bulk motion of the surrounding air. 相似文献
92.
Experimental investigations of machining characteristics and removal mechanisms of advanced ceramics in high speed deep grinding 总被引:1,自引:0,他引:1
Machining characteristics and surface integrity of advanced ceramics, including alumina, alumina–titania, and yttria partially stabilized tetragonal zirconia, were studied under high speed deep grinding conditions. Material removal mechanisms involved in the grinding processes were explored. The material removal in the grinding of alumina and alumina–titania was dominated by grain dislodgement or lateral cracking along grain boundaries. The removal for zirconia was via both local micro fracture and ductile cutting. It was found that under a feed rate of 500 mm/min and for all the wheel speeds used, an increase in the wheel depth of cut (DOC) from 0.1–2 mm slightly improved the ground surface finish, but greatly prolonged the wheel life. This increase did not deepen the subsurface damage layer for the alumina and alumina–titania, but resulted in a slightly deeper damage layer for the zirconia. 相似文献
93.
The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional
computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and
compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of
acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through
an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate.
The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including
the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent
chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as
source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions
and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances
whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the
global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made
to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared
satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated
injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference
code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal
heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations
compared fairly well with experimental results obtained with the optical DPV2000 system. 相似文献
94.
ANALYSISOFDISSIPATIVESTRUCTUREINMATERIAL COMMINUTIONZhang;Zhitie(DepartmentofMechanicalEngineering,CentralSouthUniversityofTe... 相似文献
95.
Interactive high-performance computing is doubtlessly beneficial for many computational science and engineering applications whenever simulation results should be visually processed in real time, i.e. during the computation process. Nevertheless, interactive HPC entails a lot of new challenges that have to be solved – one of them addressing the fast and efficient data transfer between a simulation back end and visualisation front end, as several gigabytes of data per second are nothing unusual for a simulation running on some (hundred) thousand cores. Here, a new approach based on a sliding window technique is introduced that copes with any bandwidth limitations and allows users to study both large and small scale effects of the simulation results in an interactive fashion. 相似文献
96.
采用计算流体力学(CFD)软件FLUENT,以用户自定义函数(UDF)添加化学反应和反应热,对实验室带有陶瓷膜管分散器的催化柴油管式液相加氢脱硫反应器进行模拟计算,得出反应床层不同部位的硫化物含量分布和温度分布状况。从反应床层的入口到出口,催化柴油的硫化物含量逐渐下降,且下降速度趋缓。在压力6.5 MPa、混氢量0.84%(m)、空速2 h~(-1)、进口温度633 K的条件下,位于床层高度0.15 m处出现最高温度点643.8 K,径向温差最大2.1 K,表明催化柴油管式液相加氢脱硫反应器催化剂装填合适的高径比为4~6。工艺条件的模拟结果表明:随着进口温度上升、混氢量增加、空速减小脱硫率提高,与实验数据吻合程度较好,说明模拟研究过程中采用的模型和控制方程准确性较高。 相似文献
97.
用户击键行为作为一种生物特征,具有采集成本低、安全性高的特点。然而,现有的研究方法和实验环境都是基于实验室数据,并不适用于极度不平衡的真实数据。比如,在实验室数据上效果出色的分类算法在真实数据上却无法应用。针对此问题,提出了基于真实击键行为数据的用户识别算法。该方法将聚类算法和距离算法结合起来,通过比较新来的击键行为和历史击键行为相似度以实现用户识别。实验结果表明,该算法在100名用户的3015条真实击键记录组成的数据集上准确率达到88.22%,在投入实际应用后,随着样本集的增大算法的准确率还可以进一步提升。 相似文献
98.
Aspergillus niger is an industrially important microorganism used in the production of citric acid. It is a common cause of food spoilage and represents a health issue for patients with compromised immune systems. Recent studies on Aspergillus niger have revealed details on the isocitrate lyase (ICL) superfamily and its role in catabolism, including (2R, 3S)-dimethylmalate lyase (DMML). Members of this and related lyase super families are of considerable interest as potential treatments for bacterial and fungal infections, including Tuberculosis. In our efforts to better understand this class of protein, we investigate the catalytic mechanism of DMML, studying five different substrates and two different active site metals configurations using molecular dynamics (MD) and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. We show that the predicted barriers to reaction for the substrates show good agreement with the experimental kcat values. This results help to confirm the validity of the proposed mechanism and open up the possibility of developing novel mechanism based inhibitors specifically for this target. 相似文献
99.
Dengue virus is a major issue of tropical and sub-tropical regions. Dengue virus has been the cause behind the major alarming epidemics in the history with mass causalities from the decades. Unavailability of on-shelf drugs for the prevention of further proliferation of virus inside the human body results in immense number of deaths each year. This issue necessitates the design of novel anti-dengue drug. The protease enzyme pathway is the critical target for drug design due to its significance in the replication, survival and other cellular activities of dengue virus. Therefore, approximately eighteen million compounds from the ZINC database have been virtually screened against nonstructural protein 3 (NS3). The incremental construction algorithm of Glide docking program has been used with its features high throughput virtual screening (HTVS), standard precision (SP), extra precision (XP) and in combination of Prime module, induced fit docking (IFD) approach has also been applied. Five top-ranked compounds were then selected from the IFD results with better predicted binding energies with the catalytic triad residues (His51, Asp75, and Ser135) that may act as potential inhibitors for the underlying target protease enzyme. The top-ranked compounds ZINC95518765, ZINC44921800, ZINC71917414, ZINC39500661, ZINC36681949 have shown the predicted binding energies of −7.55, −7.36, −8.04, −8.41, −9.18 kcal/mol, respectively, forming binding interactions with three catalytically important amino acids. Top-docking poses of compounds are then used in molecular dynamics (MD) simulations. In computational studies, our proposed compounds confirm promising results against all the four serotypes of dengue virus, strengthening the opportunity of these compounds to work as potential on-shelf drugs against dengue virus. Further experimentation on the proposed compounds can result in development of strong inhibitors. 相似文献
100.
Adaptive output feedback tracking control of stochastic nonlinear systems with dynamic uncertainties 下载免费PDF全文
In this paper, adaptive output feedback tracking control is developed for a class of stochastic nonlinear systems with dynamic uncertainties and unmeasured states. Neural networks are used to approximate the unknown nonlinear functions. K‐filters are designed to estimate the unmeasured states. An available dynamic signal is introduced to dominate the unmodeled dynamics. By combining dynamic surface control technique with backstepping, the condition in which the approximation error is assumed to be bounded is avoided. Using It ô formula and Chebyshev's inequality, it is shown that all signals in the closed‐loop system are bounded in probability, and the error signals are semi‐globally uniformly ultimately bounded in mean square or the sense of four‐moment. Simulation results are provided to illustrate the effectiveness of the proposed approach. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献