全文获取类型
收费全文 | 7058篇 |
免费 | 361篇 |
国内免费 | 53篇 |
专业分类
电工技术 | 133篇 |
综合类 | 26篇 |
化学工业 | 1788篇 |
金属工艺 | 118篇 |
机械仪表 | 211篇 |
建筑科学 | 277篇 |
矿业工程 | 6篇 |
能源动力 | 462篇 |
轻工业 | 725篇 |
水利工程 | 76篇 |
石油天然气 | 115篇 |
无线电 | 653篇 |
一般工业技术 | 1142篇 |
冶金工业 | 337篇 |
原子能技术 | 83篇 |
自动化技术 | 1320篇 |
出版年
2024年 | 24篇 |
2023年 | 151篇 |
2022年 | 317篇 |
2021年 | 405篇 |
2020年 | 295篇 |
2019年 | 335篇 |
2018年 | 416篇 |
2017年 | 358篇 |
2016年 | 355篇 |
2015年 | 236篇 |
2014年 | 320篇 |
2013年 | 641篇 |
2012年 | 356篇 |
2011年 | 505篇 |
2010年 | 350篇 |
2009年 | 326篇 |
2008年 | 288篇 |
2007年 | 217篇 |
2006年 | 201篇 |
2005年 | 140篇 |
2004年 | 111篇 |
2003年 | 117篇 |
2002年 | 90篇 |
2001年 | 64篇 |
2000年 | 73篇 |
1999年 | 50篇 |
1998年 | 77篇 |
1997年 | 41篇 |
1996年 | 49篇 |
1995年 | 40篇 |
1994年 | 36篇 |
1993年 | 44篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1974年 | 12篇 |
排序方式: 共有7472条查询结果,搜索用时 9 毫秒
891.
Xing-Gang Jiang Susan T. Yang James C. Earthman Farghalli A. Mohamed 《Metallurgical and Materials Transactions A》1996,27(4):863-872
In this investigation, the ductility and cavitation behavior of five grades of the superplastic Zn-22 pct Al were studied
under identical conditions of grain size, temperature, and initial strain rate. These five grades were prepared from high-purity
Al and Zn using the same procedure but different Fe impurity levels; grades A, B, C, D, and E contain 1, 40, 120, 400, and
1460 ppm of Fe, respectively. A comparison between the present results and those reported earlier for the creep behavior of
the five grades of Zn 22 pct Al demonstrates that while the presence of Fe has no noticeable effect on the steady-state creep
rates during deformation in the superplastic region (where maximum ductility occurs), it has a pronounced effect on the ductility
and fracture behavior of the alloy. The experimental data show that there is a significant drop in the average elongation
to fracture when Fe concentration exceeds 125 ppm, and that the ductility of grade E is approximately 50 pct of grade A for
initial strain rates less than 10−2 s−1. In addition, the data reveal two important findings regarding cavitation behavior. First, neither the initial grain size
nor the occurrence of grain growth has an effect on cavitation that is as significant as that arising from the presence of
excessive impurities. Second, the presence of other impurities in addition to Fe in Zn-22 pct Al has the effect of enhancing
cavitation. The effect of Fe, alone or in the presence of other impurities, on ductility and cavitation in Zn 22 pct Al is
examined in terms of phenomena associated with impurity segregation at boundaries.
Formerly Research Associate, Materials Section, Department of Mechanical and Aerospace Engineering, University of California,
Irvine, CA
Formerly Graduate Research Assistant, Materials Science & Engineering, Department of Chemical and Biochemical Engineering,
University of California, Irvine, CA
This article is based on a presentation made at the “High Temperature Fracture Mechanisms in Advanced Materials” symposium,
as a part of the 1994 Fall meeting of TMS, October 2-6, 1994, in Rosemont, Illinois, under the auspices of the ASM/SMD Flow
and Fracture Committee. 相似文献
892.
B Sammak B Yousef M Abd El Bagi M Al Karawi A Mohamed M Gali M Al Shahed 《Canadian Metallurgical Quarterly》1998,45(22):1097-1099
We report two cases of needle track seeding in the subcutaneous tissue and intercostal muscles following percutaneous ethanol injection for the treatment of hepatocellular carcinoma. In one patient, tumor seeding was observed 11 months after a total of 12 alcohol injections, and in the other patient, tumor seeding was observed 30 months after a total of 18 alcohol injections. The cases reported in the literature are discussed. 相似文献
893.
J.A. Hendry L.M. Delves J. Mohamed 《Computer Methods in Applied Mechanics and Engineering》1982,35(3):271-283
A previous paper [4]discussed in detail techniques for setting up the defining equations for the Global Element Method for elliptic partial differential equations, and sketched an iterative method for their solution. For a calculation in two-dimensions using M elements (with a basis of degree N - 1 in each element), operation counts of O(MN4) were achieved for both set-up and solution phases. Timings were included demonstrating this count for the set-up, but not the solution, phase. In this paper we describe a modified and simpler version of the iterative solution scheme and report timings obtained with an exploratory implementation of the scheme. These demonstrate the rapid convergence and O(MN4) behaviour predicted for it. 相似文献
894.
895.
El-Deek M. El-Sayed Mohamed N. Morsy 《International journal for numerical methods in engineering》1984,20(12):2213-2220
The transmission-line-matrix (t.l.m.) numerical analysis technique is used in this paper to evaluate resonant frequencies and field parameters of the generated modes in microwave ovens loaded with lossy process materials. Analysis is made for the variation of resonant frequencies with the loss factor of the loading material. Temperature rise profile through the load is predicted from the calculated results of field parameters of sustained modes. The demonstrated data are for the dimensional parameters of a rectangular cavity of a commercial microwave oven operating at the standard heating frequency 915 MHz. 相似文献
896.
El-Ibiary Mohamed Yousif El-Kharadly Laila A. 《IEEE transactions on nuclear science》1976,23(3):1275-1282
A generalized analysis of zero cross-over timing systems is developed and applied to the case of germanium planar detectors to determine operating parameters which give smallest timing dispersion under the constraints of available charge-sensitive preamplifier risetimes. Charts are given using normalized values to indicate these parameters. The conclusions are verified by experimental results published elsewhere. 相似文献
897.
Adsorption of IPC, CIPC, Linuron, Neburon and Vitavax on bentonite clays (H-, Fe- and Ca-forms) was investigated. Adsorption was found to conform with Freundlich's equation and to depend on the nature of saturating cation as well as the chemical structure of phenylamides. Considerable amounts of bentonite are needed to bring about effective removal of these pesticides from polluted water. The role of suspended clay minerals in the decontamination of surface waters will be rather limited. 相似文献
898.
Phase diagrams for Tm2O3-H2O-CO2. Yb2O3-H2O-CO2 and Lu2O3-H2O-CO2 systems at 650 and 1300 bars have been investigated in the temperature range of 100–800°C. The phase diagrams are far more complex than those for the lighter lanthanides. The stable phases are Ln(OH)3, Ln2(CO3)3.3H2O (tengerite phase), orthorhombic-LnOHCO3, hexagonal-Ln2O2CO3. LnOOH and cubic-Ln2O3. Ln(OH)3 is stable only at very low partial pressures of CO2. Additional phases stabilised are Ln2O(OH)2CO3and Ln6(OH)4(CO3)7 which are absent in lighter lanthanide systems. Other phases, isolated in the presence of minor alkali impurities, are Ln6O2(OH)8(CO3)3. Ln4(OH)6(CO3)3 and Ln12O7(OH)10,(CO3)6. The chemical equilibria prevailing in these hydrothermal systems may be best explained on the basis of the four-fold classification of lanthanides. 相似文献
899.
Three nonlinear-distortion sources are analysed separately for polarity and magnitude of harmonics. If magnitudes are small, the resultant harmonic from these sources is the vector sum of its separated magnitudes. Universal charts are computed, to design amplifier circuits with simultaneous zero second and third harmonics. Experiments on an OC44 confirmed the theory, giving 2.5 mW with second to sixth harmonics better than ?75 dB, power gain 40 dB, and no feedback or push-pull. 相似文献
900.
Bromination of palmitoleic or palmitelaidic acid proceeds bytrans addition and yields dibrominated products which cannot undergo β-oxidation when incubated with mitochondria isolated from
hamster brown adipose tissue. These mitochondria were selected because they have a high capacity for oxidation of C16 fatty acids and because they are readily uncoupled by an excess of free fatty acids of this chain length. The only metabolites
which could be recovered from the incubation mixtures were dibromopalmitoylcarnitine and dibromopalmitoyl CoA. Free fatty
acid was also recovered. Addition of synthetic carnitine or CoA esters of brominated fatty acids did not interfere with subsequent
oxidation of palmitoylcarnitine. Addition of the free brominated fatty acids did significantly increase the rate of oxidation
of subsequent additions of palmitoylcarnitine, as did other known synthetic uncouplers. These results are consistent with
observations by others that feeding brominated oils leads to brominated fatty acid incorporation into tissue lipids, and indicate
why this is so. They also provide a possible explanation for the hepatic damage noted in feeding experiments. 相似文献