全文获取类型
收费全文 | 12957篇 |
免费 | 607篇 |
国内免费 | 98篇 |
专业分类
电工技术 | 287篇 |
综合类 | 34篇 |
化学工业 | 2724篇 |
金属工艺 | 281篇 |
机械仪表 | 339篇 |
建筑科学 | 349篇 |
矿业工程 | 37篇 |
能源动力 | 790篇 |
轻工业 | 1213篇 |
水利工程 | 146篇 |
石油天然气 | 195篇 |
武器工业 | 4篇 |
无线电 | 1546篇 |
一般工业技术 | 2537篇 |
冶金工业 | 995篇 |
原子能技术 | 144篇 |
自动化技术 | 2041篇 |
出版年
2024年 | 38篇 |
2023年 | 284篇 |
2022年 | 672篇 |
2021年 | 929篇 |
2020年 | 611篇 |
2019年 | 651篇 |
2018年 | 771篇 |
2017年 | 588篇 |
2016年 | 634篇 |
2015年 | 400篇 |
2014年 | 564篇 |
2013年 | 992篇 |
2012年 | 643篇 |
2011年 | 723篇 |
2010年 | 471篇 |
2009年 | 394篇 |
2008年 | 375篇 |
2007年 | 342篇 |
2006年 | 286篇 |
2005年 | 233篇 |
2004年 | 185篇 |
2003年 | 179篇 |
2002年 | 179篇 |
2001年 | 113篇 |
2000年 | 112篇 |
1999年 | 139篇 |
1998年 | 277篇 |
1997年 | 235篇 |
1996年 | 167篇 |
1995年 | 150篇 |
1994年 | 112篇 |
1993年 | 106篇 |
1992年 | 76篇 |
1991年 | 66篇 |
1990年 | 62篇 |
1989年 | 76篇 |
1988年 | 70篇 |
1987年 | 57篇 |
1986年 | 60篇 |
1985年 | 70篇 |
1984年 | 74篇 |
1983年 | 69篇 |
1982年 | 38篇 |
1981年 | 34篇 |
1980年 | 39篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 37篇 |
1976年 | 53篇 |
1972年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
M. S. Rizk Y. M. Issa M. A. Ahmed S. M. Shaaban 《Journal of Materials Science: Materials in Electronics》1993,4(2):109-112
The charge transfer complexes produced by the reaction between picric acid and some aniline derivatives were prepared. The prepared charge transfer complexes (CTC) were investigated using infrared and nuclear magnetic resonance spectroscopy aiming to throw more light on their molecular structure. It was proved that a proton transfer interaction takes place between PiOH and x-Ph.NH2 leading to the formation of PiO} and x-Ph.NH3
+ ions. The normal -1 electronic interaction takes place by transferring an electron from the aniline ring to the picric acid. The semiconducting properties of the CTC were investigated. All the prepared complexes were proved to have a semiconducting character within the temperature range investigated. 相似文献
32.
This paper examines some of the special considerations which apply to the development of such software for minicomputers. These are treated under the following general categories:
- loading and throughput
- the external interfaces of the system software
- the internal structure of the system software
- developing the software
33.
Chengkun Xu Richard Killmeyer McMahan L. Gray Shahed U.M. Khan 《Applied catalysis. B, Environmental》2006,64(3-4):312-317
The present research focused on wet process synthesis of visible light active carbon-modified (CM)-n-TiO2 nanoparticles and their photocatalytic activity. The CM-n-TiO2 was synthesized by hydrolysis of TiCl4 in the presence of tetrabutylammonium hydroxide and also in the presence of glucose and sodium hydroxide. UV–vis spectra, X-ray diffraction (XRD), and FT-IR were used to characterize these photocatalysts. It was found that the CM-n-TiO2 nanoparticles synthesized by hydrolysis with tetrabutylammonium hydroxide or with sodium hydroxide and glucose when subjected to extended aging and subsequent calcinations absorb well into the visible to near infrared region up to 800 nm and exhibit enhanced visible light photocatalytic activity on degradation of 4-chlorophenol. CM-n-TiO2 synthesized using glucose as the carbon source generated 13-fold increase in the initial rate of photodegradation of 4-chlorophenol compared to those by regular n-TiO2, whereas, it increased only eight-fold when tetrabutylammonium hydroxide was used as the carbon source. 相似文献
34.
The second Egyptian research reactor ET-RR-2 went critical on the 27th of November 1997. The National Center of Nuclear Safety and Radiation Control (NCNSRC) has the responsibility of the evaluation and assessment of the safety of this reactor. The purpose of this paper is to present an approach to optimization of the fuel element plate. For an efficient search through the solution space we use a multi objective genetic algorithm which allows us to identify a set of Pareto optimal solutions providing the decision maker with the complete spectrum of optimal solutions with respect to the various targets. The aim of this paper is to propose a new approach for optimizing the fuel element plate in the reactor. The fuel element plate is designed with a view to improve reliability and lifetime and it is one of the most important elements during the shut down. In this present paper, we present a conceptual design approach for fuel element plate, in conjunction with a genetic algorithm to obtain a fuel plate that maximizes a fitness value to optimize the safety design of the fuel plate. 相似文献
35.
Numerical simulations were performed to determine the effect of Reynolds number and orifice to pipe diameter ratio (do/d) on the wall mass transfer rate downstream of an orifice. The simulations were performed for do/d of 0.475 for Reynolds number up to 70,000. The effect of do/d was determined by performing simulations at a Reynolds number of 70,000 for do/d of 0.375, 0.475 and 0.575. The momentum and mass transport equations were solved using the Low Reynolds Number (LRN) K-? turbulence model. The Sherwood number (Sh) profile downstream of the orifice was in relatively good agreement with existing experimental results. The Sh increases sharply downstream of the orifice, reaching a maximum within 1–2 diameters downstream of the orifice, before relaxing back to the fully developed pipe flow value. The Sh number well downstream of the orifice was in good agreement with results for fully developed pipe flow estimated from the correlation of Berger and Hau (1977). The peak Sh numbers from the simulations were higher than that predicted from Tagg et al. (1979) and Coney (1980). 相似文献
36.
M. A. Khan M. Mannan L. L. Lee K. E. Starling 《International Journal of Thermophysics》1990,11(2):373-380
This paper discusses theoretical models for the composition dependence of equations of state and compares the quality of predictions against experimental thermodynamic property data. The mean density approximation (MDA) and the van der Waals one-fluid (VDW1) model are compared with hybrid mixing rules (HMR), in which rigorous composition dependence is used for the second and third virial coefficients and the conformai solution model is used for equation-of-state density terms beyond the third virial term. It is found that when values of unity are used for all binary and three-body unlike interaction parameters, calculated densities for methane-normal heptane mixtures have average absolute deviations of 3.54% for MDA, 4.04% for VDW1, and 2.59% for HMR. When vapor-liquid equilibrium calculations were performed for the methane-normal heptane system, average absolute deviations of calculatedK values from experimental values were 16.7% for methane and 36.4% for normal heptane using HMR, whereas when conformal solution model (CSM) mixing rules were used, the results were 34.8% for methane and 66.7% for normal heptane. When the binary interaction parameter for the characterization of interaction energies is determined, it is found to be less sensitive to state conditions in the case of HMR than either MDA or VDW1. These preliminary results suggest the potential of mixture equation-of-state methods which utilize rigorous composition dependence for the lower-order virial coefficients.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A. 相似文献
37.
Chunjie Wang Yue Wang Yongliang Cheng Wenzhi Huang Zuhair S. Khan Xizhi Fan Ying Wang Binglin Zou Xueqiang Cao 《Journal of Materials Science》2012,47(10):4392-4399
Rare earth zirconates (Ln2Zr2O7, Ln = La, Nd, Sm, and Gd) with pyrochlore structure were prepared by hydrothermal method with polyethylene glycol as surfactant.
X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy,
Raman spectroscopy, and field emission scanning electron microscopy were utilized to characterize the phase structure, thermal
decomposition, and morphology of the products. Qualitative analysis indicates that the as-prepared zirconates are pyrochlore-type
structures. The specific surface area, lattice parameter, and average crystallite size of the as-prepared products are closely
related to the ionic radius. The activation energy of crystal growth shows an increasing trend with the decrease in ionic
radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties
of Ln2Zr2O7 are descending as the order of La2Zr2O7, Nd2Zr2O7, Sm2Zr2O7, and Gd2Zr2O7. 相似文献
38.
Daniel Villalobos-García Hamdy E. A. Ali Ahmed B. Alarabi Medhat S. El-Halawany Fatima Z. Alshbool Fadi T. Khasawneh 《International journal of molecular sciences》2022,23(10)
Smoking is a risk factor for a variety of deleterious conditions, such as cancer, respiratory disease and cardiovascular disease. Thrombosis is an important and common aspect of several cardiovascular disease states, whose risk is known to be increased by both first- and secondhand smoke. More recently, the residual cigarette smoke that persists after someone has smoked (referred to as thirdhand smoke or THS) has been gaining more attention, since it has been shown that it also negatively affects health. Indeed, we have previously shown that 6-month exposure to THS increases the risk of thrombogenesis. However, neither the time-dependence of THS-induced thrombus formation, nor its sex dependence have been investigated. Thus, in the present study, we investigated these issues in the context of a shorter exposure to THS, specifically 3 months, in male and female mice. We show that the platelets from 3-month THS-exposed mice exhibited enhanced activation by agonists. Moreover, we also show that mice of both sexes exposed to THS have decreased tail bleeding as well as decreased thrombus occlusion time. In terms of the role of sex, intersex disparities in thrombus development and hemostasis as well as in platelet aggregation were, interestingly, observed. Together, our findings show that exposing mice to THS for 3 months is sufficient to predispose them to thrombosis; which seems to be driven, at least in part, by an increased activity in platelets, and that it does not manifest equally in both sexes. 相似文献
39.
Arwa Ishaq A. Khayyat Seema Zargar Tanveer A. Wani Muneeb U. Rehman Azmat Ali Khan 《International journal of molecular sciences》2022,23(10)
Atrazine (ATR) is a herbicide globally used to eliminate undesired weeds. Herbicide usage leads to various adverse effects on human health and the environment. The primary source of herbicides in humans is the food laced with the herbicides. The ATR binding to trypsin (TYP) was investigated in this study to explore its binding potential and toxicity. In vitro interaction of ATR with TYP was studied using multi-spectroscopic methods, molecular docking, and enzyme kinetics to explore the mechanism of binding for the TYP-ATR system. The TYP-ATR complex revealed binding constants (103 M−1), suggesting a moderate binding. The free energy for the TYP-ATR complexes was negative, suggesting a spontaneous interaction. Thermodynamic parameters enthalpy (ΔH) and entropy (ΔS) obtained positive values for the TYP-ATR system suggesting hydrophobic interactions in the binding process. Micro-environmental and conformational changes in TYP molecules were induced on interaction with ATR. Reduced catalytic activity of TYP was observed after interaction with ATR owing to the changes in the secondary structure of the TYP. 相似文献
40.
Oliver Shey-Njila Ahmed F. Hikal Tuhina Gupta Kaori Sakamoto Hind Yahyaoui Azami Wendy T. Watford Frederick D. Quinn Russell K. Karls 《International journal of molecular sciences》2022,23(10)
Copper is required for aerobic respiration by Mycobacterium tuberculosis and its human host, but this essential element is toxic in abundance. Copper nutritional immunity refers to host processes that modulate levels of free copper to alternately starve and intoxicate invading microbes. Bacteria engulfed by macrophages are initially contained within copper-limited phagosomes, which fuse with ATP7A vesicles that pump in toxic levels of copper. In this report, we examine how CtpB, a P-type ATPase in M. tuberculosis, aids in response to nutritional immunity. In vitro, the induced expression of ctpB in copper-replete medium inhibited mycobacterial growth, while deletion of the gene impaired growth only in copper-starved medium and within copper-limited host cells, suggesting a role for CtpB in copper acquisition or export to the copper-dependent respiration supercomplex. Unexpectedly, the absence of ctpB resulted in hypervirulence in the DBA/2 mouse infection model. As ctpB null strains exhibit diminished growth only in copper-starved conditions, reduced copper transport may have enabled the mutant to acquire a “Goldilocks” amount of the metal during transit through copper-intoxicating environments within this model system. This work reveals CtpB as a component of the M. tuberculosis toolkit to counter host nutritional immunity and underscores the importance of elucidating copper-uptake mechanisms in pathogenic mycobacteria. 相似文献