全文获取类型
收费全文 | 44557篇 |
免费 | 2616篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 318篇 |
综合类 | 32篇 |
化学工业 | 8528篇 |
金属工艺 | 766篇 |
机械仪表 | 903篇 |
建筑科学 | 1410篇 |
矿业工程 | 81篇 |
能源动力 | 888篇 |
轻工业 | 6180篇 |
水利工程 | 410篇 |
石油天然气 | 182篇 |
武器工业 | 4篇 |
无线电 | 2555篇 |
一般工业技术 | 7780篇 |
冶金工业 | 10605篇 |
原子能技术 | 206篇 |
自动化技术 | 6364篇 |
出版年
2024年 | 83篇 |
2023年 | 405篇 |
2022年 | 396篇 |
2021年 | 1037篇 |
2020年 | 892篇 |
2019年 | 818篇 |
2018年 | 1669篇 |
2017年 | 1679篇 |
2016年 | 1778篇 |
2015年 | 1312篇 |
2014年 | 1687篇 |
2013年 | 3261篇 |
2012年 | 2766篇 |
2011年 | 2487篇 |
2010年 | 1944篇 |
2009年 | 1773篇 |
2008年 | 1983篇 |
2007年 | 1739篇 |
2006年 | 1316篇 |
2005年 | 1059篇 |
2004年 | 991篇 |
2003年 | 861篇 |
2002年 | 790篇 |
2001年 | 514篇 |
2000年 | 492篇 |
1999年 | 641篇 |
1998年 | 3376篇 |
1997年 | 2026篇 |
1996年 | 1312篇 |
1995年 | 779篇 |
1994年 | 665篇 |
1993年 | 651篇 |
1992年 | 217篇 |
1991年 | 233篇 |
1990年 | 225篇 |
1989年 | 221篇 |
1988年 | 198篇 |
1987年 | 171篇 |
1986年 | 184篇 |
1985年 | 218篇 |
1984年 | 186篇 |
1983年 | 132篇 |
1982年 | 165篇 |
1981年 | 176篇 |
1980年 | 154篇 |
1979年 | 130篇 |
1978年 | 118篇 |
1977年 | 198篇 |
1976年 | 418篇 |
1975年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Schr?der HF Tambosi JL Sena RF Moreira RF José HJ Pinnekamp J 《Water science and technology》2012,65(5):833-839
Pharmaceutical compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics have been detected in sewage treatment plant (STP) effluents, surface and ground water and even in drinking water all over the world, and therefore have developed as compounds of concern. Membrane bioreactor (MBR) treatment has gained significant popularity as an advanced wastewater treatment technology and might be effective for an advanced removal of these pollutants. This paper evaluates the treatment of wastewater containing three NSAIDs (acetaminophen, ketoprofen and naproxen) and three antibiotics (roxithromycin, sulfamethoxazole and trimethoprim) performed in two MBRs with sludge retention times (SRTs) of 15 (MBR-15) and 30 (MBR-30) days over a period of four weeks. It was observed that NSAIDs were removed with higher efficiencies than the antibiotics for both MBRs, and the MBR-30 presented higher removal efficiencies for all the compounds than obtained by MBR-15. Removal rates ranged from 55% (sulfamethoxazole) up to 100% (acetaminophen, ketoprofen). Besides mineralisation biological transformation products of ketoprofen and naproxen produced by wastewater biocoenosis were identified in both MBR permeates using liquid chromatography coupled with mass spectrometry (LC-MS). The results indicated the importance of investigating the environmental fate of pharmaceuticals and their transformation products reaching the environment. 相似文献
992.
Alves RM Pereira BF Pitol DL Senhorini JA Rocha Rde C Caetano FH 《Microscopy research and technique》2012,75(5):615-619
The adipose fin is small, nonpared, and usually located medially between the dorsal and caudal fin. Its taxonomic occurrence is very restrict; thus, it represents an important trace for taxon distinction. As it does not play a known vital physiological roll and it is easily removed, it is commonly used in marking and recapture studies. The present study characterizes the adipose fin of Prochilodus lineatus, as it is poorly explored by the literature. The adipose fin consists basically of a loose connective core, covered by a stratified epithelium supported by collagen fibers. At the epithelium, pigmented cells and alarm substance cells are found. Despite the name, adipocytes or lipid droplets are not observed on the structure of the fin. 相似文献
993.
Barry U Choubert JM Canler JP Héduit A Robin L Lessard P 《Water science and technology》2012,65(7):1172-1178
This work suggests a procedure to correctly calibrate the parameters of a one-dimensional MBBR dynamic model in nitrification treatment. The study deals with the MBBR configuration with two reactors in series, one for carbon treatment and the other for nitrogen treatment. Because of the influence of the first reactor on the second one, the approach needs a specific calibration strategy. Firstly, a comparison between measured values and simulated ones obtained with default parameters has been carried out. Simulated values of filtered COD, NH(4)-N and dissolved oxygen are underestimated and nitrates are overestimated compared with observed data. Thus, nitrifying rate and oxygen transfer into the biofilm are overvalued. Secondly, a sensitivity analysis was carried out for parameters and for COD fractionation. It revealed three classes of sensitive parameters: physical, diffusional and kinetic. Then a calibration protocol of the MBBR dynamic model was proposed. It was successfully tested on data recorded at a pilot-scale plant and a calibrated set of values was obtained for four parameters: the maximum biofilm thickness, the detachment rate, the maximum autotrophic growth rate and the oxygen transfer rate. 相似文献
994.
Greenhouse gas (GHG) emissions (CO(2), CH(4)) from pilot-scale algal and duckweed-based ponds (ABP and DBP) were measured using the static chamber methodology. Daylight and nocturnal variations of GHG and wastewater characteristics (e.g. chemical oxygen demand (COD), pH) were determined via sampling campaigns during midday (12:30-15:30) and midnight (00:30-03:30) periods. The results showed that under daylight conditions in ABP median emissions were -232 mg CO(2) m(-2) d(-1) and 9.9 mg CH(4) m(-2) d(-1), and in DBP median emissions were -1,654.5 mg CO(2) m(-2) d(-1) and 71.4 mg CH(4) m(-2) d(-1), respectively. During nocturnal conditions ABP median emissions were 3,949.9 mg CO(2) m(-2) d(-1), 12.7 mg CH(4) m(-2) d(-1), and DBP median emissions were 5,116 mg CO(2) m(-2) d(-1), 195.2 mg CH(4) m(-2) d(-1), respectively. Once data measured during daylight were averaged together with nocturnal data the median emissions for ABP were 1,566.8 mg CO(2) m(-2) d(-1) and 72.1 mg CH(4) m(-2) d(-1), whilst for DBP they were 3,016.9 mg CO(2) m(-2) d(-) and 178.9 mg CH(4) m(-2) d(-1), respectively. These figures suggest that there were significant differences between CO(2) emissions measured during daylight and nocturnal periods (p < 0.05). This shows a sink-like behaviour for both ABP and DBP in the presence of solar light, which indicates the influence of photosynthesis in CO(2) emissions. On the other hand, the fluxes of CH(4) indicated that DBP and ABP behave as net sources of CH(4) during day and night, although higher emissions were observed from DBP. Overall, according to the compound average (daylight and nocturnal emissions) both ABP and DBP systems might be considered as net sources of GHG. 相似文献
995.
The hitting time of a classical random walk (Markov chain) is the time required to detect the presence of—or equivalently, to find—a marked state. The hitting time of a quantum walk is subtler to define; in particular, it is unknown whether the detection and finding problems have the same time complexity. In this paper we define new Monte Carlo type classical and quantum hitting times, and we prove several relationships among these and the already existing Las Vegas type definitions. In particular, we show that for some marked state the two types of hitting time are of the same order in both the classical and the quantum case. Then, we present new quantum algorithms for the detection and finding problems. The complexities of both algorithms are related to the new, potentially smaller, quantum hitting times. The detection algorithm is based on phase estimation and is particularly simple. The finding algorithm combines a similar phase estimation based procedure with ideas of Tulsi from his recent theorem (Tulsi A.: Phys. Rev. A 78:012310 2008) for the 2D grid. Extending his result, we show that we can find a unique marked element with constant probability and with the same complexity as detection for a large class of quantum walks—the quantum analogue of state-transitive reversible ergodic Markov chains. Further, we prove that for any reversible ergodic Markov chain P, the quantum hitting time of the quantum analogue of P has the same order as the square root of the classical hitting time of P. We also investigate the (im)possibility of achieving a gap greater than quadratic using an alternative quantum walk. In doing so, we define a notion of reversibility for a broad class of quantum walks and show how to derive from any such quantum walk a classical analogue. For the special case of quantum walks built on reflections, we show that the hitting time of the classical analogue is exactly the square of the quantum walk. 相似文献
996.
Design and behavior study of a grammar-guided genetic programming algorithm for mining association rules 总被引:2,自引:1,他引:1
This paper presents a proposal for the extraction of association rules called G3PARM (Grammar-Guided Genetic Programming for Association Rule Mining) that makes the knowledge extracted more expressive and flexible. This algorithm allows a context-free grammar to be adapted and applied to each specific problem or domain and eliminates the problems raised by discretization. This proposal keeps the best individuals (those that exceed a certain threshold of support and confidence) obtained with the passing of generations in an auxiliary population of fixed size n. G3PARM obtains solutions within specified time limits and does not require the large amounts of memory that the exhaustive search algorithms in the field of association rules do. Our approach is compared to exhaustive search (Apriori and FP-Growth) and genetic (QuantMiner and ARMGA) algorithms for mining association rules and performs an analysis of the mined rules. Finally, a series of experiments serve to contrast the scalability of our algorithm. The proposal obtains a small set of rules with high support and confidence, over 90 and 99% respectively. Moreover, the resulting set of rules closely satisfies all the dataset instances. These results illustrate that our proposal is highly promising for the discovery of association rules in different types of datasets. 相似文献
997.
Exploratory tools that are sensitive to arbitrary statistical variations in spike train observations open up the possibility of novel neuroscientific discoveries. Developing such tools, however, is difficult due to the lack of Euclidean structure of the spike train space, and an experimenter usually prefers simpler tools that capture only limited statistical features of the spike train, such as mean spike count or mean firing rate. We explore strictly positive-definite kernels on the space of spike trains to offer both a structural representation of this space and a platform for developing statistical measures that explore features beyond count or rate. We apply these kernels to construct measures of divergence between two point processes and use them for hypothesis testing, that is, to observe if two sets of spike trains originate from the same underlying probability law. Although there exist positive-definite spike train kernels in the literature, we establish that these kernels are not strictly definite and thus do not induce measures of divergence. We discuss the properties of both of these existing nonstrict kernels and the novel strict kernels in terms of their computational complexity, choice of free parameters, and performance on both synthetic and real data through kernel principal component analysis and hypothesis testing. 相似文献
998.
This article presents a method for rectifying and stabilising video from cell-phones with rolling shutter (RS) cameras. Due to size constraints, cell-phone cameras have constant, or near constant focal length, making them an ideal
application for calibrated projective geometry. In contrast to previous RS rectification attempts that model distortions in
the image plane, we model the 3D rotation of the camera. We parameterise the camera rotation as a continuous curve, with knots
distributed across a short frame interval. Curve parameters are found using non-linear least squares over inter-frame correspondences
from a KLT tracker. By smoothing a sequence of reference rotations from the estimated curve, we can at a small extra cost,
obtain a high-quality image stabilisation. Using synthetic RS sequences with associated ground-truth, we demonstrate that
our rectification improves over two other methods. We also compare our video stabilisation with the methods in iMovie and
Deshaker. 相似文献
999.
A multi-objective evolutionary algorithm for an effective tuning of?fuzzy logic controllers in?heating, ventilating and air conditioning systems 总被引:5,自引:5,他引:0
This paper focuses on the use of multi-objective evolutionary algorithms to develop smartly tuned fuzzy logic controllers
dedicated to the control of heating, ventilating and air conditioning systems, energy performance, stability and indoor comfort
requirements. This problem presents some specific restrictions that make it very particular and complex because of the large
time requirements needed to consider multiple criteria (which enlarge the solution search space) and the long computation
time models required in each evaluation. 相似文献
1000.