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11.
International scientific collaboration is very sensitive to political and economic changes in a country or a geopolitical region. Collaboration in research is reflected by the corresponding coauthorship of the published results which can be analysed with the help of bibliometric methods. Based on data from theScience Citation Index (SCI), the change of annual international coauthorship patterns ofBulgaria, Czechoslovakia, Hungary, Poland andRomania have been analysed for the periods 1981–1985 and 1984–1993, respectively. It is shown that international collaboration was not developing similarly in the countries under study. Whilst scientific communities of Hungary and Poland have already been opening in the early 80s, the international collaboration of the other East-European countries was still dominated by COMECON relations till 1989. As expected, since 1990 an increasing scientific collaboration with highly developed countries can be observed in all five countries. At the same time, scientific collaboration with the former communist countries shows a clear decline. The great share of international co-authorship links is some countries reflect various tendencies part of which are interpreted with the help of a cardiologic model. 相似文献
12.
It is demonstrated that glassy carbon powder can be thermochemically activated. During activation, a film with open pores is created on the glassy carbon particles. This film has a large internal surface area, which is accessible to liquids and gases. A simple model for the evolution of the internal surface area in glassy carbon powder during thermochemical gas-phase oxidation is also presented and compared with experimental data. Experimental results are in qualitative agreement with the model. We found that a sharp particle size distribution is desirable with regard to potential technical applications. 相似文献
13.
Gerd Breitbach 《Nuclear Engineering and Design》1989,114(1)
At very high temperatures loaded metallic structures undergo creep deformations. The generated creep strains are connected with stress relaxations, stress redistributions and/or progressive deformations.In mainly load controlled situations the behaviour of the material can be described by a nonlinear viscous flow law (Norton power law).A stress-deformation analysis of complex structures can be carried out by finite element codes in which the mentioned constitutive equation is implemented. The code PERMAS-VISCOUS was used to analyse the stress state of a notched tension bar and the deformation behaviour of a tube under external pressure undergoing a creep collapse. The relation to experimental findings is also given. 相似文献
14.
DePriest C.M. Yilmaz T. Braun A. Abeles J. Delfyett P.J. Jr. 《Quantum Electronics, IEEE Journal of》2002,38(4):380-389
We report on the development of an ultralow-noise, external-cavity, actively mode-locked semiconductor diode laser for application in next-generation photonic sampling systems. A summary of harmonically mode-locked noise characteristics in a 65-MHz ring cavity is presented through the range of pulse repetition frequencies between 130 MHz and 8.3 GHz (2nd-128th harmonic). Important implications regarding the use of gain-versus-loss modulation as the active modelocking mechanisms are discussed. We also report what are, to our knowledge, the lowest noise characteristics achieved to date for a semiconductor diode laser operating at 10 GHz. Individually optimized results of 0.12% rms amplitude noise (10 Hz-10 MHz), and 43 fs rms residual phase jitter (10 Hz-10 MHz) provide a theoretical resolution of 8.6 bits in a 10-GSPS optical analog-to-digital converter. We have also achieved dispersion-compensated pulsewidths; as short as 1.2 ps, and shown successful operation of a novel phase-locked-loop capable of reducing the rms; residual phase noise by as much as 91% within its response bandwidth. Finally, the first measurements of residual phase noise out to the Nyquist frequency (5 GHz) are presented, providing an upper bound on the rms residual phase jitter of 121 fs (10 Hz-5 GHz) 相似文献
15.
Minimum shift keying (MSK) is a digital modulation scheme which is suited to demanding applications requiring good bandwidth efficiency and error performance. It can be regarded as continuous phase frequency shift keying (CPFSK) with two signalling frequencies. In general, there is no unique mapping from the input data polarity to the particular signalling frequency during a given bit interval. The simplest formulation maps zeros of the data (marks) to the lower frequency, and ones (spaces) to the higher frequency. Other formulations of MSK employ more complex mappings. The article summarises the most commonly encountered mappings, then shows how to convert from one formulation to another by manipulating the input or output data. It is, therefore, possible to establish communication between different MSK modems employing different formulations of MSK by simple processing of the data 相似文献
16.
17.
On the stress corrosion cracking behaviour of recrystallized 8090-T81 Sheets The stress corrosion cracking behaviour of a recrystallized sheet of the Al-Li-Cu-Mg-Zr alloy 8090-T81 was studied performing accelerated tests under constant deformation, constant load, and slow strain rate conditions. The used electrolytes were an aqueous 3.5% NaCl solution, an aqueous solution of 2% NaCl + 0.5% Na2CrO4 at pH = 3, and synthetic seawater according to ASTM D1141. Alternately immersed in 3.5% NaCl solution according to ASTM G44 the investigated alloy was found to be susceptible to stress corrosion cracking was not promoted by continuous immersion in aerated 3.5% NaCl solution, 3.5% NaCl solution saturated with carbon dioxide, and in acid chromate inhibited 2% NaCl solution. Using the slow strain rate technique with continuously immersed flat tensile specimens stress corrosion cracking was only observed in synthetic seawater. Under specific environmental conditions hydrogen embrittlement can occur in the investigated material. 相似文献
18.
Recent advances in the realization of individual molecular‐scale devices [1,2] highlight the integration of individual devices into large‐scale functional circuits as the major challenge. DNA‐programmed assembly is a promising avenue in that direction due to the large amount of information that can be coded into the molecules and the ability to translate that information into physical constructs [3]. Large‐scale DNA‐templated electronics require, however, complex manipulation of double‐stranded DNA (dsDNA) molecules, as well as patterning of the electrical properties instilled to them by, e.g., metallization. To that end, sequence‐specific molecular lithography on single DNA molecules has been developed [4]. This was achieved by harnessing the exquisite homologous recombination process of the RecA protein. Sequence‐specific patterning of the metal coating of DNA molecules, localization of arbitrary labeled molecular objects at any desired dsDNA address without prior modifications, and generation of molecularly accurate stable dsDNA‐dsDNA junctions are demonstrated. The information encoded in the DNA molecules directs the lithographic process in analogy to the masks used in conventional microelectronics. The RecA protein provides the assembling capabilities, as well as the resist function. 相似文献
19.
Inactivation of phage T5 by lysed cells after phage multiplication is prevented by a phage-encoded lipoprotein (Llp) that inactivates the FhuA outer membrane receptor protein (K. Decker, V. Krauel, A. Meesmann, and K. Heller, Mol. Microbiol. 12:321-332, 1994). Using FhuA derivatives carrying insertions of 4 and 16 amino acid residues and point mutations, we determined whether FhuA inactivation is caused by binding of Llp to FhuA and which regions of FhuA are important for inactivation by Llp. Cells expressing Llp were resistant not only to phage T5 but to all FhuA ligands tested, such as phage phi 80, colicin M, and albomycin, and they were strongly reduced in the uptake of ferrichrome. Most of the FhuA derivatives which were not affected by Llp were, according to a previously published FhuA transmembrane topology model, located in periplasmic turns and in the TonB box close to the periplasm. Since the ligands bind to the cell surface, interaction of FhuA with Llp in the periplasm may induce a FhuA conformation which impairs binding of the ligands. This conclusion was supported by the increase rather than decrease of colicin M sensitivity of two mutants in the presence of Llp. The only Llp-resistant FhuA derivatives with mutations at the cell surface contained insertions of 16 residues in the loop that determines the permeability of the FhuA channel and serves as the principal binding site for all FhuA ligands. This region may be inactivated by steric hindrance in that a portion of Llp penetrates into the channel. Outer membranes prepared with 0.25% Triton X-100 from cells expressing Llp contained inactivated FhuA, suggesting Llp to be an outer membrane protein whose interaction with FhuA was not abolished by Triton X-100. Llp solubilized in 1.1% octylglucoside prevented T5 inactivation by FhuA dissolved in octylglucoside. 相似文献
20.