全文获取类型
收费全文 | 89731篇 |
免费 | 10554篇 |
国内免费 | 7517篇 |
专业分类
电工技术 | 8201篇 |
技术理论 | 20篇 |
综合类 | 2997篇 |
化学工业 | 12260篇 |
金属工艺 | 6921篇 |
机械仪表 | 2611篇 |
建筑科学 | 6042篇 |
矿业工程 | 4136篇 |
能源动力 | 6128篇 |
轻工业 | 5357篇 |
水利工程 | 3789篇 |
石油天然气 | 12402篇 |
武器工业 | 1044篇 |
无线电 | 7685篇 |
一般工业技术 | 9461篇 |
冶金工业 | 6870篇 |
原子能技术 | 1243篇 |
自动化技术 | 10635篇 |
出版年
2024年 | 472篇 |
2023年 | 3181篇 |
2022年 | 4439篇 |
2021年 | 4921篇 |
2020年 | 5499篇 |
2019年 | 4294篇 |
2018年 | 3515篇 |
2017年 | 4432篇 |
2016年 | 4835篇 |
2015年 | 4674篇 |
2014年 | 6469篇 |
2013年 | 7374篇 |
2012年 | 9082篇 |
2011年 | 7881篇 |
2010年 | 5541篇 |
2009年 | 5448篇 |
2008年 | 3006篇 |
2007年 | 4374篇 |
2006年 | 4064篇 |
2005年 | 2100篇 |
2004年 | 1121篇 |
2003年 | 1061篇 |
2002年 | 1059篇 |
2001年 | 1012篇 |
2000年 | 859篇 |
1999年 | 909篇 |
1998年 | 588篇 |
1997年 | 451篇 |
1996年 | 513篇 |
1995年 | 438篇 |
1994年 | 370篇 |
1993年 | 260篇 |
1992年 | 292篇 |
1991年 | 255篇 |
1990年 | 229篇 |
1989年 | 213篇 |
1988年 | 335篇 |
1987年 | 688篇 |
1986年 | 654篇 |
1985年 | 158篇 |
1984年 | 135篇 |
1983年 | 98篇 |
1982年 | 93篇 |
1981年 | 101篇 |
1980年 | 93篇 |
1979年 | 65篇 |
1978年 | 47篇 |
1976年 | 36篇 |
1959年 | 34篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《Calphad》2015
The total energies of Laves phases in the Cr–Nb and Zr–Cr systems have been calculated by the pseudo-potential VASP code with a full relaxation of all structural parameters. The special quasirandom structures (SQSs) have been constructed and their total energies have been calculated by the VASP code to predict the enthalpies of mixing for bcc and hcp solid solution phases. The phonon calculations for the C14 and C15 Laves phases have been performed to analyze the phase stability at elevated temperatures. The experimental study on the Zr–Cr system has been carried out at different temperatures to determine the phase boundaries. Based on these results, thermodynamic models of Cr–Nb and Zr–Cr with extension to the ternary Zr–Nb–Cr systems have been developed in this work by using the CALPHAD approach. 相似文献
2.
Characteristics and formation mechanism of porosities in CFRP during laser joining of CFRP and steel
An experimental investigation on the mechanism of porosity formation during the laser joining of carbon fiber reinforced polymer (CFRP) and steel is presented. The porosity morphology and distribution were characterized by optical and scanning electron microscopy, and the thermal pyrolysis behaviors were investigated by thermal analysis and designed back-side cooling experiments. The results show that there are two types of porosities in CFRP. Porosity I only appears when the heat input is more than 77.8 J/mm. It has a smooth inner wall and distributes near the bonding interface between CFRP and steel at the central area of melted zone, which is caused by gaseous products such as CO2, NH3, H2O, and hydrocarbons produced by the pyrolysis of CFRP. Porosity II can be seen under all joining conditions. It has a rough inner wall and distributes far away from the bonding interface, concentrating at the final solidification locations. Porosity II is caused by the shrinkage of melted CFRP during solidification stage. 相似文献
3.
Rectangular section control technology(RSCT)was introduced to achieve high-precision profile control during silicon steel rolling.The RSCT principle and method were designed,and the whole RSCT control strategy was developed.Specifically,RSCT included roll contour design,rolling technology optimization,and control strategy development,aiming at both hot strip mills(HSMs)and cold strip mills(CSMs).Firstly,through the high-performance variable crown(HVC)work roll optimization design in the upper-stream stands and the limited shifting technology for schedule-free rolling in the downstream stands of HSMs,a hot strip with a stable crown and limited wedge,local spot,and single wave was obtained,which was suitable for cold rolling.Secondly,an approximately rectangular section was obtained by edge varying contact(EVC)work roll contour design,edge-drop setting control,and closed loop control in the upper-stream stands of CSMs.Moreover,complex-mode flatness control was realized by coordinating multiple shape-control methods in the downstream stands of CSMs.In addition,the RSCT approach was applied in several silicon-steel production plants,where an outstanding performance and remarkable economic benefits were observed. 相似文献
4.
High dimensionality in real-world multi-reservoir systems greatly hinders the application and popularity of evolutionary algorithms, especially for systems with heterogeneous units. An efficient hierarchical optimization framework is presented for search space reduction, determining the best water distributions, not only between cascade reservoirs, but also among different types of hydropower units. The framework is applied to the Three Gorges Project (TGP) system and the results demonstrate that the difficulties of multi-reservoir optimization caused by high dimensionality can be effectively solved by the proposed hierarchical method. For the day studied, power output could be increased by 6.79 GWh using an optimal decision with the same amount of water actually used; while the same amount of power could be generated with 2.59 × 107 m3 less water compared to the historical policy. The methodology proposed is general in that it can be used for other reservoir systems and other types of heterogeneous unit generators. 相似文献
5.
We investigated the resistive switching characteristics of a polystyrene:ZnO–graphene quantum dots system and its potential application in a one diode-one resistor architecture of an organic memory cell. The log–log I–V plot and the temperature-variable I–V measurements revealed that the switching mechanism in a low-current state is closely related to thermally activated transport. The turn-on process was induced by a space-charge-limited current mechanism resulted from the ZnO–graphene quantum dots acting as charge trap sites, and charge transfer through filamentary path. The memory device with a diode presented a ∼103 ION/IOFF ratio, stable endurance cycles (102 cycles) and retention times (104 s), and uniform cell-to-cell switching. The one diode-one resistor architecture can effectively reduce cross-talk issue and realize a cross bar array as large as ∼3 kbit in the readout margin estimation. Furthermore, a specific word was encoded using the standard ASCII character code. 相似文献
6.
The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu2O3 (LuAG:Ce + Lu2O3), are described. Powders of a novel material LuAG:Ce + Lu2O3 were synthesized by co-precipitation method. The introduction of Lu2O3 into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties. 相似文献
7.
《低温学》2015
He-3 is generally recognized for its ability to provide more excellent thermophysical performance than He-4, especially in the 4 K temperature range. However, this was not always the case in our preliminary experiments on a three-stage Stirling-type pulse tube cryocooler (SPTC). Our ongoing studies, as reported in this paper, demonstrate that the different working fluids also affect the performance through their phase shifting capability. This feature has been passed over in large part by researchers considering refrigerant substitution. Unlike previous theoretical analyses that focus primarily on regenerator losses, this report investigates the effects of the working fluid on the phase angle at the cold end in order to quantitatively reveal the relationship between the lowest attainable temperature and the cooling capacity. The analysis agrees well with our experimental results on a three-stage SPTC. While running with the operating parameters optimized for He-3, the lowest temperature of the SPTC decreased from 5.4 K down to 4.03 K. This is the lowest refrigeration temperature ever achieved with a three-stage SPTC. 相似文献
8.
The proposed work involves the multiobjective PSO based adaption of optimal neural network topology for the classification of multispectral satellite images. It is per pixel supervised classification using spectral bands (original feature space). This paper also presents a thorough experimental analysis to investigate the behavior of neural network classifier for given problem. Based on 1050 number of experiments, we conclude that following two critical issues needs to be addressed: (1) selection of most discriminative spectral bands and (2) determination of optimal number of nodes in hidden layer. We propose new methodology based on multiobjective particle swarm optimization (MOPSO) technique to determine discriminative spectral bands and the number of hidden layer node simultaneously. The accuracy with neural network structure thus obtained is compared with that of traditional classifiers like MLC and Euclidean classifier. The performance of proposed classifier is evaluated quantitatively using Xie-Beni and β indexes. The result shows the superiority of the proposed method to the conventional one. 相似文献
9.
《Intermetallics》2015
The site preferences of co-alloying elements (Mo–Ta, Mo–Re, Mo–Cr) in Ni3Al are studied using first-principles calculations, and the effects of these alloying elements on the elastic properties of Ni3Al are evaluated by elastic property calculations. The results show that the Mo–Ta, Mo–Re and Mo–Cr atom pairs all prefer Al–Al sites and the spatial neighbor relation of substitution sites almost has no influence on the site preference results. Furthermore, the Young's modulus of Ni3Al increases much higher by substituting Al–Al sites with co-alloying atoms, among which Mo–Re has the best strengthening effect. The enhanced chemical bondings between alloying atoms and their neighbor host atoms are considered to be the main strengthening mechanism of the alloying elements in Ni3Al. 相似文献
10.
An Intermediate Bulk Container (IBC) was punctured during its handling, releasing oil onto soil at an environmentally-sensitive region of Australia. The telehandler did not pierce the plastic of the IBC directly (as was expected) but rather one of the tynes had caught on the underside of the metal base plate, despite numerous controls being in place at time of spill, revealing a previously unreported mechanism for a fluid spill from handling of petroleum hydrocarbons. The diverse investigation team used a root cause analysis (RCA) technique to identify the underlying cause: the inspection process was inadequate with contributing factors of not using a spotter and design of IBC did not anticipate conditions. Engineering controls were put in place as part of the change management process to help prevent spills from occurring from piercing from telehandler tynes on the current project site. 相似文献