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排序方式: 共有1127条查询结果,搜索用时 22 毫秒
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Perminova IV Frimmel FH Kudryavtsev AV Kulikova NA Abbt-Braun G Hesse S Petrosyant VS 《Environmental science & technology》2003,37(11):2477-2485
Recorded molecular weights (MWs) for humic substances (HS) range from a few hundred to millions of daltons. For purposes of defining HS as a specific class of chemical compounds, it is of particular importance to ascertain if this broad range of MWs can be attributed to actual variability in molecular properties or is simply an artifact of the analytical techniques used to characterize HS. The main objectives of this study were (1)to establish if a preferential range of MWs exists for HS and (2) to determine any consistent MW properties of HS. To reach the goal, we have undertaken an approach to measure under standardized conditions the MW characteristics of a large set of HS from different natural environments. Seventy-seven humic materials were isolated from freshwater, soil, peat, and coal, such that each possessed a different fractional composition: humic acid (HA), fulvic acid (FA), and a nonfractionated mixture of HA and FA (HF). Size exclusion chromatography (SEC) was used as the analytical technique to determine molecular weight characteristics. The MW distributions were characterized by number (Mn) and weight (Mw) average MW, and by polydispersity. The complete range of Mw values varied within 4.7-30.4 kDa. The maximum Mw values were observed for peat HF and soil HA, whereas the smallest weights were measured for river water HF. Maximum values of polydispersity (3.5-4.4) were seen for peat HF and soil HA, while much lower values (1.6-3.1) were found for all preparations isolated with XAD-resins. Statistical evaluation showed consistent Mw and Mn variations with the HS source, while polydispersity was mostly a function of the isolation procedure used. A conclusion was made that HS have a preferential range of MW values that could characterize them as a specific class of chemical compounds. 相似文献
66.
A statistical model for identifying proteins by tandem mass spectrometry 总被引:51,自引:0,他引:51
A statistical model is presented for computing probabilities that proteins are present in a sample on the basis of peptides assigned to tandem mass (MS/MS) spectra acquired from a proteolytic digest of the sample. Peptides that correspond to more than a single protein in the sequence database are apportioned among all corresponding proteins, and a minimal protein list sufficient to account for the observed peptide assignments is derived using the expectation-maximization algorithm. Using peptide assignments to spectra generated from a sample of 18 purified proteins, as well as complex H. influenzae and Halobacterium samples, the model is shown to produce probabilities that are accurate and have high power to discriminate correct from incorrect protein identifications. This method allows filtering of large-scale proteomics data sets with predictable sensitivity and false positive identification error rates. Fast, consistent, and transparent, it provides a standard for publishing large-scale protein identification data sets in the literature and for comparing the results obtained from different experiments. 相似文献
67.
O. V. Kasparova Yu. V. Baldokhin A. S. Solomatin N. I. Khokhlov 《Protection of Metals》2003,39(5):429-434
The effect of silicon (0.06 to 4.89%) on the electron density distribution around 57Fe nuclei in quenched boron-containing X20H20 steels is studied with the use of -resonance spectroscopy. Computer treatment of the spectra provided the estimates of the isomeric (chemical) shifts (mm/s) and half-widths (mm/s) of the singlet and doublet spectral lines, as well as the area parts S (%) of each constituent in the summary spectrum and the quadrupole electric splitting eq (mm/s) of the doublet. On the basis of these estimates, both new and earlier obtained experimental data on the peculiarities of the corrosion–electrochemical behavior of silicon-containing austenitic stainless steels are discussed. 相似文献
68.
Wide-aperture,line-focused ultrasonic material characterization system based on lateral scanning 总被引:1,自引:0,他引:1
Titov S Maev R Bogatchenkov A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(8):1046-1056
We present a new wide-aperture, line-focused ultrasonic material characterization system. The foci of the transmitting and receiving transducers are located in the specimen-immersion liquid interface; and the output voltage V(x, t) of the system is recorded as a function of the lateral position of the receiving transducer. The two-dimensional spectrum of V(x, t) can be expressed as a product of the transfer function of the system and the reflectance function of the interface. In comparison with a system based on scanning in the z direction, the angular resolution of the proposed technique increases with decreasing angle of incidence. There are no geometrical restrictions on the length of the recorded spatial data and the angle of incidence in the case of lateral scanning. The temperature coefficient of the measurement error is low because of the constancy of the propagation distance of ultrasound in the immersion fluid during data acquisition. 相似文献
69.
Future trends in data mining 总被引:3,自引:1,他引:3
Hans-Peter Kriegel Karsten M. Borgwardt Peer Kröger Alexey Pryakhin Matthias Schubert Arthur Zimek 《Data mining and knowledge discovery》2007,15(1):87-97
Over recent years data mining has been establishing itself as one of the major disciplines in computer science with growing
industrial impact. Undoubtedly, research in data mining will continue and even increase over coming decades. In this article,
we sketch our vision of the future of data mining. Starting from the classic definition of “data mining”, we elaborate on
topics that — in our opinion — will set trends in data mining. 相似文献
70.
Octavio Pozo Garcia Vesa-Matti Tikkala Alexey Zakharov Sirkka-Liisa Jämsä-Jounela 《Control Engineering Practice》2013,21(6):818-828
The performance of a modern industrial plant can be severely affected by the performance of its key devices, such as valves. In particular, valve stiction can cause poor performance in control loops and can consequently lower the efficiency of the plant and the quality of the product. This paper presents an integrated FDD system for valve stiction which employs various FDD methods in a parallel configuration. A reliability index was integrated into each method in order to estimate their degree of influence in the final diagnosis of the system. Each method and the integrated system were tested using industrial data. 相似文献