全文获取类型
收费全文 | 14253篇 |
免费 | 1349篇 |
国内免费 | 539篇 |
专业分类
电工技术 | 807篇 |
综合类 | 699篇 |
化学工业 | 2754篇 |
金属工艺 | 604篇 |
机械仪表 | 661篇 |
建筑科学 | 1124篇 |
矿业工程 | 317篇 |
能源动力 | 359篇 |
轻工业 | 1075篇 |
水利工程 | 314篇 |
石油天然气 | 305篇 |
武器工业 | 116篇 |
无线电 | 1359篇 |
一般工业技术 | 2083篇 |
冶金工业 | 688篇 |
原子能技术 | 125篇 |
自动化技术 | 2751篇 |
出版年
2024年 | 72篇 |
2023年 | 300篇 |
2022年 | 547篇 |
2021年 | 745篇 |
2020年 | 520篇 |
2019年 | 417篇 |
2018年 | 503篇 |
2017年 | 487篇 |
2016年 | 526篇 |
2015年 | 650篇 |
2014年 | 803篇 |
2013年 | 990篇 |
2012年 | 1034篇 |
2011年 | 1108篇 |
2010年 | 916篇 |
2009年 | 851篇 |
2008年 | 852篇 |
2007年 | 786篇 |
2006年 | 658篇 |
2005年 | 567篇 |
2004年 | 429篇 |
2003年 | 366篇 |
2002年 | 394篇 |
2001年 | 309篇 |
2000年 | 220篇 |
1999年 | 165篇 |
1998年 | 141篇 |
1997年 | 128篇 |
1996年 | 102篇 |
1995年 | 89篇 |
1994年 | 67篇 |
1993年 | 62篇 |
1992年 | 52篇 |
1991年 | 38篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 22篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 25篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
可溶高分子负载钯催化剂对于硝基苯加氢反应催化性能的研究 总被引:3,自引:1,他引:2
以醇或水溶性高分子(聚乙烯吡咯烷酮,PVP;乙基纤维素,EC;聚乙烯醇,PVA;羧甲基纤维素钠,CMCNa)为载体,制备了四种可溶高分子负载钯催化剂。无机碱的存在对反应呈明显的加速效应。在少量K2CO3存在下,EC-PdCl2和PVP-PdCl2对于硝基苯的催化加氢具有非常高的活性,最高活性>230molH2/molPd·min,即大于5150mlH2/mmolPd·min,该数值是已知文献报道的最好结果。详细考察了各种碱、K2CO3用量、溶剂以及反应温度对PVP-PdCl2催化硝基苯加氢性能的影响。 相似文献
912.
Stefan Reisch 《Acta Informatica》1980,13(1):59-66
Summary For many games, the decision problem of whether a player in a given situation has a winning strategy has been shown to be PSPACE-complete. Following the PSPACE-completeness results of Even and Tarjan [1] for generalized Hex on graphs and of Schaefer [6] for a variety of combinatorial games, the decision problems were shown to be PSPACE-hard for generalizations of Go and Checkers. In this paper a corresponding theorem is proved for the board-game Gobang, a variant of Go. Since the decision problem for Gobang states-of-play itself lies in PSPACE, it can be shown that Gobang is in fact PSPACE-complete. 相似文献
913.
Two phenolic acids were identified in the collembolan Ceratophysella denticulata: 3-hydroxy-4,5 dimethoxy benzoic acid and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid). These are localized on or in the integument of the springtail, in field-collected animals, in a ratio of 47:100 (v/v). Springtails kept under different temperature regimes showed differences in production and ratio of the benzoic acid derivatives. At 20 degrees C, C. denticulata produced only syringic acid, whereas at 10 degrees C both isomers in a ratio of 100:61 (v/v) were detected. Bioassays with C. denticulata as well as with the specialized collembolan predator Stenus comma (Staphylinidae) were carried out. Staphylinid beetles topically treated with the acids try to clean their mouthparts by rubbing them on the ground significantly more often than do control beetles. Both compounds individually and as a natural mixture have deterrent effects towards the predator S. comma. 相似文献
914.
This paper addresses one of the controversial issues in the current comparative studies of the environmental and health impacts of energy systems, i.e. the treatment of severe accidents. The work covers technical aspects of severe accidents and thus primarily reflects an engineering perspective on the energy-related risk issues, though some social implications are also touched upon. The assessment concerns fossil energy sources (coal, oil and gas), nuclear power and hydro power. The scope is not limited to the power production (conversion) step of these energy chains but, whenever applicable, also includes exploration, extraction, transports, processing, storage and waste disposal. With the exception of the nuclear chain the focus of the work has been on the evaluation of the historical experience of accidents. The basis used for this evaluation is a comprehensive database ENSAD (Energy-related Severe Accident Database), established by the Paul Scherrer Institut (PSI). For hypothetical nuclear accidents the probabilistic technique has also been employed and extended to cover the assessment of economic consequences of such accidents. The broader picture obtained by coverage of full energy chains leads on the world-wide basis to aggregated immediate fatality rates being much higher for the fossil chains than what one would expect if only power plants were considered. Generally, the immediate fatality rates are for all considered energy carriers significantly higher for the non-OECD countries than for OECD countries. In the case of hydro and nuclear the difference is in fact dramatic. The presentation of results is not limited to the aggregated values specific for each energy chain. Also frequency-consequence curves are provided. They reflect implicitly the ranking based on the aggregated values but include also such information as the observed or predicted chain-specific maximum extents of damages. This perspective on severe accidents may lead to different system rankings, depending on the individual risk aversion. 相似文献
915.
Aspects of decision support in water management--example Berlin and Potsdam (Germany) I--spatially differentiated evaluation 总被引:2,自引:0,他引:2
Decisions about sustainable development demand spatially differentiated evaluations. As an example, we demonstrate the evaluation of water management strategies in the cities of Berlin and Potsdam (Germany) with respect to their ecological effects in 14 sections of the surface water system. Two decision support systems were compared, namely PROMETHEE, which is designed to obtain a clear decision (linear ranking), and Hasse Diagram Technique (HDT), normally providing more than one favourable solution (partial order). By PROMETHEE, the spatial differentiation had unwanted effects on the result, negating the stakeholders determined weighting of indicators. Therefore, the stakeholder can barely benefit from the convenience of obtaining a clear decision (linear ranking). In contrast, the result obtained by HDT was not influenced by spatial differentiation. Furthermore, HDT provided helpful tools to analyse the evaluation result, such as the concept of antagonistic indicators to discover conflicts in the evaluation process. 相似文献
916.
High-spatial resolution mass spectrometric imaging of peptide and protein distributions on a surface
For the first time macromolecular ion microscope images have been recorded using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Single-shot, mass-resolved images of the spatial distributions of intact peptide and protein ions over an area of 200 microm in diameter were obtained in less than 1 ms at a repetition rate of 12 Hz. The magnifying ion optics of the ion microscope allowed ion images to be obtained with a lateral resolution of 4 microm. These results prove the concept of high-resolution MALDI-MS imaging in microscope mode without the need for a tight laser focus and the accompanying sensitivity losses. The ion microscopy approach offers an improvement of several orders of magnitude in speed of acquisition compared to the conventional (microprobe) approach to MALDI-MS imaging. 相似文献
917.
Etienne M Schulte A Mann S Jordan G Dietzel ID Schuhmann W 《Analytical chemistry》2004,76(13):3682-3688
Constant-distance mode scanning potentiometry was established by integrating potentiometric microsensors as ion-selective scanning probes into a SECM setup that was equipped with a piezoelectric shear force-based tip-to-sample distance control. The combination of specially designed micrometer-sized potentiometric tips with an advanced system for tip positioning allowed simultaneous acquisition of both topographic and potentiometric information at solid/liquid interfaces with high spatial resolution. The performance of the approach was evaluated by applying Ca(2+)-selective constant-distance mode potentiometry to monitor the dissolution of calcium carbonate occurring either at the (104) surface of calcite crystals or in proximity to the more complex surface of cross sections of a calcium carbonate shell of Mya arenaria exposed to slightly acidic aqueous solutions. Micrometer-scale heterogeneities in the apparent calcium activity profiles have successfully been resolved for both samples. 相似文献
918.
We present a procedure using continuous wavelet transforms (CWTs) to extract the phase information from moiré interferograms. The relationship between precise ridge detection of the two-dimensional CWT magnitude map and accurate phase extraction is detailed. A cost function is introduced for the adaptive selection of the ridge, and a computationally inexpensive implementation of the cost function ridge detection algorithm is explored with dynamic programming optimization. The results of the proposed ridge detection algorithm on actual interferograms are illustrated. Moreover, the resulting extracted phase is demonstrated to be smooth and accurate. As a result, the sensitivity of the moiré interferometry method is improved to obtain a pixel-by-pixel in-plane strain distribution map. 相似文献
919.
The aim of this study was to determine the feasibility of minimally invasive glucose concentration measurement of a body fluid within the physiologically important range below 100 nL with a number of samples such as interstitial fluid, plasma, or whole blood using mid-infrared spectroscopy, but starting with preliminary measurements on samples of simple aqueous glucose solutions. The Fourier transform infrared spectrometer was equipped with a Golden Gate single reflection diamond attenuated total reflection (ATR) accessory and a room-temperature pyroelectric detector. As the necessary detection limits can be achieved only for dried samples within the spectrometric conditions realized by a commercial instrument, the work focused on the optimization of such ATR measurements. We achieved quantification of samples with volumes as low as 7 nL between 10 and 600 mg/dL. The standard error of prediction (SEP) for the concentration range 10-100 mg/dL is 3.2 mg/dL with full interval data between 1180 and 940 cm(-1). The performance of the prediction is given by a coefficient of variation of prediction (CV(pred) ) of 6.2%. When all samples within the whole concentration range are included, the SEP increases to 20.2 mg/dL, and hence the CV(pred) to 10.6% due to a nonlinear signal dependence on glucose concentration. A detection limit for glucose of 0.7 ng with a signal-to-noise ratio of 10 was obtained. 相似文献
920.
Container terminal operation and operations research - a classification and literature review 总被引:23,自引:11,他引:12
In the last four decades the container as an essential part of a unit-load-concept has achieved undoubted importance in international sea freight transportation. With ever increasing containerization the number of seaport container terminals and competition among them have become quite remarkable. Operations are nowadays unthinkable without effective and efficient use of information technology as well as appropriate optimization (operations research) methods. In this paper we describe and classify the main logistics processes and operations in container terminals and present a survey of methods for their optimization.
Correspondence to: Stefan Voß 相似文献