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861.
The purpose of the paper is to propose an efficient method to compute propagation modes in helicoidal waveguides. An helicoidal system of co-ordinates is introduced to define the structure and to set up the problem. These co-ordinates, albeit non-orthogonal, preserve the translational invariance in a way that allows a two-dimensional finite element model similar to that of classical straight waveguides 相似文献
862.
The paper proposes a novel method of forecasting short-term electricity price based on a two-stage hybrid network of self-organised map (SOM) and support-vector machine (SVM). In the first stage, a SOM network is applied to cluster the input-data set into several subsets in an unsupervised manner. Then, a group of SVMs is used to fit the training data of each subset in the second stage in a supervised way. With the trained network, one can predict straightforwardly the next-day hourly electricity prices. To confirm its effectiveness, the proposed model has been trained and tested on the data of historical energy prices from the New England electricity market. 相似文献
863.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
864.
R. Oliva A. L. Gemal A. W. N brega A. C. P. Araú jo 《Food Additives & Contaminants》2003,20(8):758-763
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables. 相似文献
865.
We consider the dynamics of a dark soliton in an elongated harmonically trapped Bose-Einstein condensate. A central question
concerns the behavior at finite temperatures, where dissipation arises due to the presence of a thermal cloud. We study this
problem using coupled Gross-Pitaevskii and N-body simulations, which include the mean field coupling between the condensate and thermal cloud. We find that the soliton
decays relatively quickly even at very low temperatures, with the decay rate increasing with rising temperature. 相似文献
866.
A phenomenological model is developed for describing the kinetics of the crystallite size refinement process of Cu powder
under mechanical treatment conditions. Based on the evidence that collisions represent the elementary events of energy transfer,
the rate of crystallite size decrease is related on a statistical basis to the amount of powder trapped at each collision,
to the number of collisions and to the collision energy. The mathematical approach allows for identifying the approximate
functional form of the kinetic curves obtained at largely different impact energies. The values of the apparent kinetic constants
and of the model parameters involved can be thus estimated by fitting the model curves to the experimental data. The results
obtained provide a deeper insight into the details of the crystallite size refinement process. 相似文献
867.
The hydrolysis and condensation reactions of γ-APS have been studied in different acid content aqueous solution by using Fourier
Transform infrared (FT-IR) spectroscopy. The hydrolysis of γ-APS under the studied conditions can be followed by the increase
of the ethanol band located at 882 cm−1 and the decrease of the band due to the ρ(CH3) of γ-APS molecules located at 959 cm−1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of γ-APS are used. The increase of the vibrational band located at 1146 cm−1 shows that condensation of the hydrolysed γ-APS molecules take place forming linear chains in poorly cross-linked structures.
Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water
and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric
hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except
for samples with the lowest H2O content. 相似文献
868.
Alexander Chroneos Nicholas J. Ashley Kaajal H. Desai John F. Maguire R. W. Grimes 《Journal of Materials Science》2007,42(6):2024-2029
The structures of a number of hydroxide and oxyhydroxide minerals have previously been reported without the hydrogen positions
explicitly defined. Here we use two atomic scale computer simulation techniques, one based on classical ionic potentials,
the other on density functional theory (DFT), to predict these positions. The aim is not only to provide data that can be
used as the basis for future experimental structure optimizations but also model parameters that can be used to predict complex
hydroxide structures. The efficacy of the approach is demonstrated through the comparison of predicted and experimental data
for minerals whose hydrogen positions are known. 相似文献
869.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
870.
Tanu Sharma Sanjeev Aggarwal Shyam Kumar V. K. Mittal P. C. Kalsi V. K. Manchanda 《Journal of Materials Science》2007,42(4):1127-1130
The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu
Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening
as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated
CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct
band gap. 相似文献