全文获取类型
收费全文 | 4258篇 |
免费 | 83篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 47篇 |
综合类 | 2篇 |
化学工业 | 572篇 |
金属工艺 | 106篇 |
机械仪表 | 56篇 |
建筑科学 | 121篇 |
矿业工程 | 27篇 |
能源动力 | 59篇 |
轻工业 | 308篇 |
水利工程 | 23篇 |
石油天然气 | 4篇 |
无线电 | 320篇 |
一般工业技术 | 608篇 |
冶金工业 | 1721篇 |
原子能技术 | 40篇 |
自动化技术 | 332篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 57篇 |
2020年 | 34篇 |
2019年 | 52篇 |
2018年 | 58篇 |
2017年 | 55篇 |
2016年 | 53篇 |
2015年 | 39篇 |
2014年 | 68篇 |
2013年 | 156篇 |
2012年 | 108篇 |
2011年 | 147篇 |
2010年 | 112篇 |
2009年 | 104篇 |
2008年 | 110篇 |
2007年 | 95篇 |
2006年 | 109篇 |
2005年 | 80篇 |
2004年 | 73篇 |
2003年 | 81篇 |
2002年 | 80篇 |
2001年 | 73篇 |
2000年 | 65篇 |
1999年 | 104篇 |
1998年 | 496篇 |
1997年 | 315篇 |
1996年 | 246篇 |
1995年 | 131篇 |
1994年 | 131篇 |
1993年 | 136篇 |
1992年 | 51篇 |
1991年 | 42篇 |
1990年 | 44篇 |
1989年 | 66篇 |
1988年 | 44篇 |
1987年 | 43篇 |
1986年 | 41篇 |
1985年 | 38篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 30篇 |
1977年 | 55篇 |
1976年 | 119篇 |
1975年 | 30篇 |
1974年 | 19篇 |
排序方式: 共有4346条查询结果,搜索用时 15 毫秒
91.
Peter Nuhn Ekkehard Schilling Günther Wagner 《Advanced Synthesis \u0026amp; Catalysis》1976,318(2):291-297
Immunosuppressant-Antigen Conjugates. VIII. Preparation of 6-Thiopurine-Protein Conjugates by the Azide Method 6-Carboxymethyl-thiopurine was coupled with human serum albumin (HSA) and bovine serum globuline in the presence of a water soluble carbodiimide. Under these conditions, reaction of HSA with the carbodiimide led to electrophoretically detectable changes. Therefore, further conjugates were prepared by the azide method. The used azides, N-(6-benzylthiopurin- and 6-methylthiopurin-9-yl)-acetyl azide, were obtained from the hydrazides. The prepared conjugates contained upto 4.2% thiopurine, determined by spectrophotometry. It was not possible to obtain an azide from purinyl-(6)-thioacethydrazide. 相似文献
92.
Leonardo Rocha Fernando Mourão Hilton Mota Thiago Salles Marcos André Gonçalves Wagner Meira Jr. 《Information Systems》2013
The management of a huge and growing amount of information available nowadays makes Automatic Document Classification (ADC), besides crucial, a very challenging task. Furthermore, the dynamics inherent to classification problems, mainly on the Web, make this task even more challenging. Despite this fact, the actual impact of such temporal evolution on ADC is still poorly understood in the literature. In this context, this work concerns to evaluate, characterize and exploit the temporal evolution to improve ADC techniques. As first contribution we highlight the proposal of a pragmatical methodology for evaluating the temporal evolution in ADC domains. Through this methodology, we can identify measurable factors associated to ADC models degradation over time. Going a step further, based on such analyzes, we propose effective and efficient strategies to make current techniques more robust to natural shifts over time. We present a strategy, named temporal context selection, for selecting portions of the training set that minimize those factors. Our second contribution consists of proposing a general algorithm, called Chronos, for determining such contexts. By instantiating Chronos, we are able to reduce uncertainty and improve the overall classification accuracy. Empirical evaluations of heuristic instantiations of the algorithm, named WindowsChronos and FilterChronos, on two real document collections demonstrate the usefulness of our proposal. Comparing them against state-of-the-art ADC algorithms shows that selecting temporal contexts allows improvements on the classification accuracy up to 10%. Finally, we highlight the applicability and the generality of our proposal in practice, pointing out this study as a promising research direction. 相似文献
93.
Reinvestigation of the Lewis acid catalyzed rearrangement of some open-chain permethyloligosilanes with the Al(Fe)Cl(3) catalyst system exhibited several cases of additional reactivity: namely, a fragmentation/cyclization reaction. Introduction of (trimethylsilyl)methyl substituents into the oligosilane substrates strongly facilitated this reaction, yielding cyclic or bicyclic carbacyclosilanes. Investigations concerning the composition of the catalyst system indicated that the incorporation of about 0.1% FeCl(3) into the AlCl(3) lattice provided an effective catalyst. 相似文献
94.
95.
96.
J. Sch?nenberger T. Momose B. Wagner W. H. Leong V. R. Tarnawski 《International Journal of Thermophysics》2012,33(2):342-362
Forty Canadian soils were laboratory tested for the presence of quartz and other minerals using X-ray diffraction/X-ray fluorescence techniques. On average, the highest quartz content was observed in soil samples from sites in Nova Scotia followed by Prince Edward Island sites, whereas soil sample from British Columbia sites had the lowest quartz content. The second most abundant mineral was albite that mainly occurred in soil samples from Ontario and Quebec sites. Illite was the third most abundant and prevailed in soils mainly from British Columbia and New Brunswick sites. Soil samples from British Columbia sites had the highest combined clay and silt content and were composed of illite, albite, kaolinite, and chlorite. The lowest clay content was found in the samples from the Quebec sites. The highest microcline (a potassium feldspar) content was observed in Quebec, Ontario, and Prince Edward Island sites. In contrast to other provinces, samples from Quebec and Ontario sites also included amphibole. Soil samples from Saskatchewan and Manitoba sites also comprised carbonates, i.e., calcite and dolomite. Iron oxides (e.g., goethite) were present in all soils, except the Quebec sites, but their occurrence was rather insignificant. 相似文献
97.
K H Hellmuth A Wagner E Fischer 《Zeitschrift für Lebensmittel-Untersuchung und -Forschung》1989,188(4):317-323
In a field investigation (1983-1985) comprising eight places of the most important viticultural regions in the Federal Republic of Germany, the contents of the radionuclides tritium (3H), carbon-14 (14C), strontium-90 (90Sr), and cesium-137 (137Cs) in air, soils, leaves of the vine, grapes and wine were measured and site-specific transfer factors were calculated. Data concerning soil parameters, climatic conditions, cultivation and vinification were collected. The tritium content of all samples was 10 Bq/l water of combustion, independent of location and year. The specific activity of 14C in the atmosphere and in biological material was 0.22 Bq/g carbon, independent of site and year. 90Sr contents of soils fluctuated between 0.7 and 3.5 Bq/kg dry matter. The mean content of leaves was 2 Bq/kg fresh material, of grapes 0.035 Bq/kg and of wine 0.008 Bq/l. 137Cs content of soils fluctuated between 1.3 and 7.9 Bq/kg dry matter. The mean content of leaves was 0.098 Bq/kg fresh material, of grapes 0.021 Bq/kg and of wine 0.0085 Bq/l. A relation between transfer of radionuclides and soil parameters and between the contents of grapes and wine was not recognizable. While cultivar-specific differences were not observed in grapes, red wines contained somewhat more 137Cs than white wines. Transfer factors soil grapes were 0.027 for 90Sr and 0.0057 for 137Cs. Site-specific influences such as soil parameters, climate, cultivation, vinification and differences between years led to a relatively small fluctuation of values. An influence of the nuclear power station Neckarwestheim has not been found in any of the radionuclides. 相似文献
98.
The surface growth kinetics of CdTe and HgTe have been investigated during molecular and metalorganic molecular beam epitaxy.
The surface growth kinetics was studied through in-situ measurements of the growth rate as a function of flux ratio and substrate
temperature on the (001), (111)B, and (211)B CdTe surface orientations. For the (001) and (111)B CdTe growth kinetics, the
existence of low binding energy surface precursor sites was proposed for both molecular and atomic growth species before lattice
incorporation. Intensity oscillations were observed during HgTe growth on misoriented (111)B surfaces and during CdTe growth
on the (211)B orientation. The (211)B surface reconstructions displayed both vicinal and singular surface characteristics,
depending on the growth flux ratio. 相似文献
99.
H. Wolf F. Wagner Th Wichert R. Grill E. Belas Isolde Collaboration 《Journal of Electronic Materials》2006,35(6):1350-1353
Anomalous diffusion profiles of Ag in single crystalline CdTe were observed using the radiotracer 111Ag. The diffusion anneals were performed at 800 K under Cd or Te vapor and in vacuum with low Ag concentrations. The measured
Ag profiles directly reflect the distribution of the self-interstitials and vacancies of the Cd sublattice and are the result
of chemical self-diffusion which describes the variation of the deviation from stoichiometry of the binary crystal as a function
of depth and time. It turned out that the spread of the Ag dopant essentially is determined by the drift of the charged defects
within the electric field caused by the distribution of the extrinsic and intrinsic defects. 相似文献
100.
Brandon Wagner Pankaj Ghildiyal Prithwish Biswas Mahbub Chowdhury Michael R. Zachariah Lorenzo Mangolini 《Advanced functional materials》2023,33(21):2212805
Magnesium is a promising candidate as a solid fuel for energetic applications, however, the diffusion-controlled oxidation mechanism impedes its reaction with an oxidizer, often resulting in diminished performance. In this study, non-thermal plasma processing is implemented to modify the surface of magnesium nanoparticles with silicon in-flight, in the gas-phase to enhance the rate of interfacial reactions and tune the ignition pathways. Allowing the silicon coating to partially oxidize provides direct contact between the fuel and oxidizer, resulting in a nanostructured thermite system at the single particle level. The proximal distance between oxidizer and fuel directly impacts the ignition temperature and, therefore, the combustion kinetics. An intermetallic reaction occurs within the magnesium/silicon system to supplement the heating of the magnesium fuel to initiate its reaction with the oxidizer, resulting in highly reduced ignition thresholds. The ignition temperature is lowered significantly from ≈740 °C for magnesium particles with a native oxide layer to ≈520 °C for particles coated via the in-flight plasma process. 相似文献