全文获取类型
收费全文 | 3470篇 |
免费 | 101篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 41篇 |
综合类 | 6篇 |
化学工业 | 877篇 |
金属工艺 | 124篇 |
机械仪表 | 80篇 |
建筑科学 | 48篇 |
矿业工程 | 3篇 |
能源动力 | 299篇 |
轻工业 | 185篇 |
水利工程 | 22篇 |
石油天然气 | 7篇 |
无线电 | 340篇 |
一般工业技术 | 802篇 |
冶金工业 | 470篇 |
原子能技术 | 25篇 |
自动化技术 | 264篇 |
出版年
2023年 | 38篇 |
2022年 | 81篇 |
2021年 | 109篇 |
2020年 | 86篇 |
2019年 | 86篇 |
2018年 | 142篇 |
2017年 | 77篇 |
2016年 | 83篇 |
2015年 | 77篇 |
2014年 | 112篇 |
2013年 | 217篇 |
2012年 | 159篇 |
2011年 | 195篇 |
2010年 | 157篇 |
2009年 | 143篇 |
2008年 | 121篇 |
2007年 | 117篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 67篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 68篇 |
1998年 | 154篇 |
1997年 | 99篇 |
1996年 | 93篇 |
1995年 | 50篇 |
1994年 | 53篇 |
1993年 | 53篇 |
1992年 | 36篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有3593条查询结果,搜索用时 15 毫秒
161.
P. Venkata Ramana G. Madhusudhan Reddy T. Mohandas A.V.S.S.K.S. Gupta 《Materials & Design》2010,31(2):749-760
The influence of parent metal heat treatment condition on the residual stress distribution in dissimilar metal welds of maraging steel to quenched and tempered medium alloy medium carbon steel has been investigated. It has been observed that the residual stress distribution would be more compressive if the maraging steel is in soft condition. This is attributed to stress absorbing nature of highly yielding soft maraging steel. 相似文献
162.
Devendrasinh Darbar M.R. Anilkumar Vijayaraghavan Rajagopalan Indranil Bhattacharya Hendry Izaac Elim T. Ramakrishnappa F.I. Ezema Rajan Jose M.V. Reddy 《Ceramics International》2018,44(5):4630-4639
Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo2O4 (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 °C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 °C, 550 °C and 750 °C; whereas FeCo2O4 and NiCo2O4 contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo2O4 and ZnCo2O4, submicron sized particles of FeCo2O4 and agglomerated submicron particle of NiCo2O4 are observed. Galvanostatic cycling has been conducted in the voltage range 0.005–3.0 V vs. Li at a current density of 60 mA g?1 up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo2O4 – 365 mA h g?1 (750 °C); ZnCo2O4 – 516 mA h g?1 (550 °C); FeCo2O4 – 480 mA h g?1 (550 °C); NiCo2O4 – 384 mA h g?1 (750 °C); and Co3O4 – 675 mA h g?1 (350 °C). The Co3O4 showed the highest reversible capacity of 675 mA h g?1; the NiO present in NiCo2O4 acts as a buffer layer that results in improved cycling stability; the ZnCo2O4 with long needle-like shows good cycling stability. 相似文献
163.
Sreeraj Gopi Augustine Amalraj Karthik Varma Shintu Jude Prakash B. Reddy Chandradhara Divya 《国际聚合物材料杂志》2018,67(9):581-588
A phytogenic feed additive (PFA) formulation was prepared with bioactive molecules—curcuminoids, gingerol, and carvacrol by encapsulating in nanofiber isolated from turmeric spent (turmeric nanofiber, TNF). This formulation was completely characterized by scanning electron microscope, ultra performance liquid chromatography, and gas chromatography and evaluated for its efficacy. PFA-encapsulated TNF (PFA@TNF) considerably increased mean body weight, decreased cholesterol level, mortality rate, and reduced Escherichia coli content of broilers than antibiotic growth promoter (AGP). The depth of crypts in the ileum of broilers was considerably reduced by the inclusion of PFA@TNF in diets compared with the AGP. 相似文献
164.
The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas‐fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
165.
A diffractive optical element is described that can be used to implement a very simple self-aligning electronic speckle-pattern interferometer and holographic interferometer that requires only a laser source and a camera in the optical setup. 相似文献
166.
G. Chattopadhyay V. Reddy P.-O. Larsson-Kråik 《International Transactions in Operational Research》2005,12(6):545-558
Rail players around the world have been increasing axle loads to improve the productivity of freight and heavy haul operations. This has increased the risk of surface cracks at curves because of rolling contact fatigue. Rail grinding has been considered an effective process for controlling these cracks and reducing risks of rail breaks. The complexity of deciding the optimal rail grinding intervals for improving the reliability and safety of rails is because of insufficient understanding of the various factors involved in the crack initiation and propagation process. This paper focuses on identifying the factors influencing rail degradation, developing models for rail failures and analyzing the costs of various grinding intervals for economic decision making. Various costs involved in rail maintenance, such as rail grinding, downtime, inspection, rail failures and derailment, and replacement of worn‐out rails, are incorporated into the total cost model developed in this paper. Field data from the rail industry have been used for illustration. 相似文献
167.
Balaji T Acharya RN Nair AG Reddy AV Rao KS Naidu GR Manohar SB 《The Science of the total environment》2000,253(1-3):75-79
The concentrations of some elements in a few varieties of cereals and pulses are determined by Instrumental Neutron Activation Analysis using a single comparator method (k0-standardised NAA method). A total of 15 elements are measured. The method was validated by analysing the Standard Reference Material (SRM-1571) of NIST; the results are within +/-10% of the reported values for the majority of the elements. The measured concentrations of major and minor elements are analysed in terms of the average intake of mineral content and the role of these elements in terms of the nutritional value. 相似文献
168.
A. V. Ramana Reddy G. Ranga Mohan D. Ravinder B. S. Boyanov 《Journal of Materials Science》1999,34(13):3169-3176
The dielectric constant () and complex dielectric constant () of zinc substituted cobalt ferrites have been measured at room temperature in the high frequency range 100 kHz to 1 MHz. The values of dielectric loss tangent (tan ) have been computed from and . Plots of dielectric constant () versus frequency show a normal dielectric behaviour of the spinel ferrites. The frequency dependence of dielectric loss tangent (tan ) is found to be abnormal, giving a peak at certain frequency for all the ferrites under investigation. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. The dielectric constant for these mixed ferrites is approximately inversely proportional to the square root of the resistivity. A plot of dielectric constant versus temperature shows a transition near the Curie temperature. An attempt is made to explain the possible mechanism for this observation. 相似文献
169.
Induction of apoptosis and apoptotic mediators in balb/C splenic lymphocytes by dietary n−3 and n−6 fatty acids 总被引:5,自引:0,他引:5
The present study was designed to investigate the effect of diatery n−6 and n−3 polyunsaturated fatty acids (PUFA) on anti-CD3
and anti-Fas antibody-induced apoptosis and its mediators in mouse spleen cells. Nutritionally adequate semipurified diets
containing either 5% w/w corn oil (n−6 PUFA) or fish oil (n−3 PUFA) were fed to weanling female Balb/C mice, and 24 wk later
mice were sacrificed. In n−3 PUFA-fed mice, serum and splenocyte lipid peroxides were increased by 20 and 28.3% respectively,
compared to n−6 PUFA-fed mice. Further, serum vitamin F levels were decreased by 50% in the n−3 PUFA-fed group, whereas higher
anti0Fas- and anti-CD3-induced apoptosis (65 and 66%) and necrosis (17 and 25%), compared to the n−6 PUFA-fed group, were
found when measured with Annexin V and propidium iodide staining, respectively. In addition, decreased Bcl-2 and increased
Fas-ligand (Fas-L) also were observed in the n−3 PUFA-fed group compared to the n−6 PUFA-fed group. No difference in the ratio
of splenocyte subsets nor their Fas expression was observed between the n−3 PUFA-fed and n−6 PUFA-fed groups, whereas decreased
proliferation of splenocytes was found in n−3 PUFA-fed mice compared to n−6 PUFA-fed mice. In conclusion, our results indicate
that dietary n−3 PUFA induces higher apoptosis by increasing the generation of lipid peroxides and elevating Fas-L expression
along with decreasing Bcl-2 expression. A reduced proliferative response of immune cells also was observed in n−3 PUFA-fed
mice. 相似文献
170.
This paper analyses two queueing models consisting of two units I and II connected in series, separated by a finite buffer of size N. In both models, unit I has only one exponential server capable of serving customers one at a time and unit II consist of c parallel exponential servers, each of them serving customers in groups according to general bulk service rules. When the queue length in front of unit II is less than the minimum of batch size, the free servers take a vacation. On return from vacation, if the queue length is less than the minimum, they leave for another vacation in the first model, whereas in the second model they wait in the system until they get the minimum number of customers and then start servicing. The steady-state probability vector of the number of customers waiting and receiving service in unit I and waiting in the buffer is obtained for both the models, using the modified matrix geometric method. Numerical results are also presented. 相似文献