全文获取类型
收费全文 | 1641篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 213篇 |
金属工艺 | 14篇 |
机械仪表 | 22篇 |
建筑科学 | 73篇 |
矿业工程 | 4篇 |
能源动力 | 18篇 |
轻工业 | 220篇 |
水利工程 | 5篇 |
石油天然气 | 1篇 |
无线电 | 81篇 |
一般工业技术 | 196篇 |
冶金工业 | 619篇 |
原子能技术 | 7篇 |
自动化技术 | 189篇 |
出版年
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 11篇 |
2017年 | 24篇 |
2016年 | 27篇 |
2015年 | 15篇 |
2014年 | 31篇 |
2013年 | 85篇 |
2012年 | 52篇 |
2011年 | 61篇 |
2010年 | 56篇 |
2009年 | 52篇 |
2008年 | 80篇 |
2007年 | 60篇 |
2006年 | 43篇 |
2005年 | 46篇 |
2004年 | 45篇 |
2003年 | 41篇 |
2002年 | 53篇 |
2001年 | 42篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 90篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 57篇 |
1994年 | 30篇 |
1993年 | 46篇 |
1992年 | 31篇 |
1991年 | 13篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 24篇 |
1986年 | 30篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 26篇 |
1978年 | 12篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1973年 | 9篇 |
1970年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有1677条查询结果,搜索用时 15 毫秒
1.
Diane M. Hopkins Alan D. Jackson Kenneth Oates 《Microscopy research and technique》1991,18(2):176-182
The standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X-ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X-ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together. 相似文献
2.
KL Hopkins PK Dickson TI Ball RR Ricketts PA O'Shea CR Abramowsky 《Canadian Metallurgical Quarterly》1997,32(10):1476-1479
Fetus-in-fetu is an unusual condition in which a vertebrate fetus is enclosed within the abdomen of another fetus. These occurrences are usually benign. This report describes an instance of malignant recurrence after resection of a fetus-in-fetu. 相似文献
3.
4.
The purpose of this study was to assess the use, in computer-mediated communication, of the strategic message structuring tactic known as framing. Interlocutors in computer-mediated environments have software supported systemic resources facilitative of constructing messages using framing tactics in their argumentative discourse. It is hypothesized that framing strategies are related to the emotional tenor of a disputant's message and that a speaker's emotional involvement with an issue should be curvilinearly related to the appropriation of framing as an argumentative discourse strategy. Results from the analysis of 3000 messages, obtained from a diverse sampling of computer-mediated discussion groups and forums, provided support for the primary hypothesized relationship. A speaker's emotional involvement was significantly and curvilinearly related to two message framing devices (message dependency and coalition building) and a measure of conciliatory face-saving moves. 相似文献
5.
R. D. Dupuis J. C. Bean J. M. Brown A. T. Macrander R. C. Miller L. C. Hopkins 《Journal of Electronic Materials》1987,16(1):69-77
We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical
vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge
and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied,
the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal
X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission
electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial
layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth
of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of
a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped
AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates. 相似文献
6.
Diane M. Moran F. S. Richardson
M. Koralewski
B. M. Wanklyn
《Journal of Alloys and Compounds》1992,180(1-2):171-175Chiroptical luminescence and circular dichroism measurements are reported for single crystals of Ho2Ge2O7. These crystals belong to the tetragonal space group P4,2,2 (or P43212) with Z=4. Each Ho3+ ion in the crystal structure is coordinated to seven oxygens to form a distorted pentagonal bipyramid. The Ho3+ ions exhibit luminescence from several excited multiplet levels; chiroptical luminescence spectra are reported for 6I8 → 6F6, 6S2, and 6F3 at a sample temperature of 10 K. Room-temperature absorption and circular dichroism measurements are reported for the 6I8 → 6F6, 5S2, 6F4, and 6F3 transition regions. 相似文献
7.
Diane J. Cook 《Applied Intelligence》1991,1(2):133-144
Analogical planning provides a means of solving engineering problems where other machine learning methods fail. Unlike many machine learning paradigms, analogy does not require numerous previous examples or a rich domain theory. Instead, analogical planners adapt knowledge of solved problems in similar domains to the current problem. Unfortunately, the analogical planning task is an expensive one. While the process of forming correspondences between a known problem and a new problem is complex, the problem of selecting a base case for the analogy is virtually intractable.This paper addresses the issue of efficiently forming analogical plans. The Anagram planning system is described, which takes advantage of the massively parallel architecture of the Connection Machine to perform base selection and map formation. Anagram provides a tractable solution to analogical planning, with a complexity that is sublinear in the size of the plans.This paper describes the Anagram system and its parallel algorithms. The paper also presents theoretical analyses and empirical results of testing the system on a large database of plans from the domain of automatic programming. 相似文献
8.
Hopkins William D.; Morris Robin D.; Savage-Rumbaugh E. Sue; Rumbaugh Duane M. 《Canadian Metallurgical Quarterly》1992,106(3):575
Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time (RT) paradigm. Ss were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from 2 semantic categories: food and tools. A 3rd set of warning stimuli were familiar geometric symbols. Dependent measures included RT and the number of false-positive responses. RT data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when Ss responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
We evaluated the influence of supplemental dietary NaHCO3 on K metabolism of young dairy calves. Thirty-two Holstein and Jersey male and female calves were blocked at 56 to 70 d after birth according to breed, sex, and age and assigned randomly to a 2 x 2 factorial arrangement of dietary treatments for 8 wk: .4% K with 0% NaHCO3, .4% K with 2% NaHCO3, .6% K with 0% NaHCO3, and .6% K with 2% NaHCO3. Feed intake was not affected by dietary KCl or NaHCO3 supplementation, but average daily gain increased with increased K and tended to be reduced by dietary NaHCO3. Plasma K was elevated by increased dietary K but generally was unaffected by NaHCO3. Urinary Ca excretion appeared to be reduced by NaHCO3; urine pH increased with supplemental NaHCO3. Results indicate 1) the K requirement of the growing calf is between .40 and .55% of diet DM, 2) because urinary K excretion was elevated by dietary NaHCO3, the K requirement may be increased when the diet is supplemented with NaHCO3, and 3) average daily gain and plasma K are sensitive indicators of dietary K in the growing calf. 相似文献
10.
Liping Wang Ramana V. Grandhi Dale A. Hopkins 《International journal for numerical methods in engineering》1995,38(10):1721-1738
The objective of this paper is to conduct reliability-based structural optimization in a multidisciplinary environment. An efficient reliability analysis is developed by expanding the limit functions in terms of intermediate design variables. The design constraints are approximated using multivariate splines in searching for the optimum. The reduction in computational cost realized in safety index calculation and optimization are demonstrated through several structural problems. This paper presents safety index computation, analytical sensitivity analysis of reliability constraints and optimization using truss, frame and plate examples. 相似文献