全文获取类型
收费全文 | 253586篇 |
免费 | 3072篇 |
国内免费 | 869篇 |
专业分类
电工技术 | 4824篇 |
综合类 | 228篇 |
化学工业 | 36340篇 |
金属工艺 | 9528篇 |
机械仪表 | 7554篇 |
建筑科学 | 6182篇 |
矿业工程 | 884篇 |
能源动力 | 7263篇 |
轻工业 | 21206篇 |
水利工程 | 2205篇 |
石油天然气 | 3230篇 |
武器工业 | 15篇 |
无线电 | 34332篇 |
一般工业技术 | 50143篇 |
冶金工业 | 48596篇 |
原子能技术 | 5077篇 |
自动化技术 | 19920篇 |
出版年
2021年 | 2199篇 |
2020年 | 1589篇 |
2019年 | 1938篇 |
2018年 | 3287篇 |
2017年 | 3328篇 |
2016年 | 3441篇 |
2015年 | 2245篇 |
2014年 | 3995篇 |
2013年 | 11530篇 |
2012年 | 6272篇 |
2011年 | 8647篇 |
2010年 | 6971篇 |
2009年 | 7940篇 |
2008年 | 8466篇 |
2007年 | 8358篇 |
2006年 | 7421篇 |
2005年 | 6549篇 |
2004年 | 6309篇 |
2003年 | 6583篇 |
2002年 | 6055篇 |
2001年 | 6532篇 |
2000年 | 5984篇 |
1999年 | 6409篇 |
1998年 | 16492篇 |
1997年 | 11422篇 |
1996年 | 8799篇 |
1995年 | 6612篇 |
1994年 | 5908篇 |
1993年 | 5848篇 |
1992年 | 4135篇 |
1991年 | 4031篇 |
1990年 | 3860篇 |
1989年 | 3652篇 |
1988年 | 3562篇 |
1987年 | 3018篇 |
1986年 | 2943篇 |
1985年 | 3210篇 |
1984年 | 2931篇 |
1983年 | 2828篇 |
1982年 | 2638篇 |
1981年 | 2544篇 |
1980年 | 2464篇 |
1979年 | 2307篇 |
1978年 | 2109篇 |
1977年 | 2608篇 |
1976年 | 3564篇 |
1975年 | 1764篇 |
1974年 | 1731篇 |
1973年 | 1666篇 |
1972年 | 1466篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
221.
Mandal Tarun K.; Mukhopadhyay Chaitali 《Protein engineering, design & selection : PEDS》2002,15(12):979-986
Galectins show remarkable binding specificity towards ß-galactosides.A recently developed method for calculating binding free energiesbetween a protein and its substrates has been used to evaluatethe binding specificity of galectin-3. Five disaccharides anda tetrasaccharide were used as the substrates. The calculatedbinding free energies agree quite well with the experimentaldata and the ranking of binding affinities is well reproduced.For all the six proteinligand complexes it was observedthat electrostatic interactions oppose binding whereas the non-polarcontributions drive complex formation. The observed bindingspecificity of galectin-3 for galactosides rather than glucosidesis discussed in light of our results. 相似文献
222.
Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed. 相似文献
223.
Hyun-Goo Kim Wha-Nam Myung K. Sumiyama K. Suzuki 《Journal of Alloys and Compounds》2002,340(1-2):270-274
We report upon the chemical leaching and magnetic properties of nanoscale crystalline Al0.6(Co25Cu75)0.4 alloy powders produced by rod milling. X-Ray diffractometry (XRD), transmission electron microscopy, differential scanning calorimetry, vibrating sample magnetometry, and superconducting quantum interference device magnetometry were used to characterize the as-milled and leached specimens. After 400 h of milling, only the b.c.c. phase of the intermetallic compound γ-Al3.892Cu6.10808 was detected by XRD. After annealing the leached specimen at 600 °C for 1 h, the nanoscale crystalline phase was transformed into the f.c.c. Cu phase, and this was accompanied by a change in the magnetic properties. The peaks of the magnetization shifted towards lower temperature with increasing external field. The temperature behavior at Tf (45 K) for direct current (d.c.) magnetic susceptibility measurements was quite different for field cooling and zero-field cooling. After cooling the leached specimen from 800 °C, magnetization increased gradually. 相似文献
224.
J. Suutarinen K. Honkapää R.-L. Heiniö A. Mustranta H. Liukkonen-Lilja M. Mokkila 《Journal of food science》2002,67(3):1240-1248
ABSTRACT: :
Different calcium chloride (CaCl2 ) and pectin methylesterase (PME) prefreezing treatments in a vacuum were used to clarify the most effective prefreezing factors for strawberries and traditional jams. Fractional factorial design and modeling were used. CaCl2 had the greatest effect on the majority of the 15 studied responses ( p < 0.001). The pretreatment time should be short (about 5 to 10 min), the temperature low (less than 20 °C), the vacuum level high (pressure less than 10 kPa), the CaCl2 concentration moderate (about 1%) and the dosage of PME comparatively low (about 50 to 100 nkat/g) in order to yield high quality frozen strawberries for jam making. 相似文献
Different calcium chloride (CaCl
225.
K. A. Abdikalikov V. K. Zadiraka O. S. Kondratenko S. S. Mel'nikova 《Cybernetics and Systems Analysis》1991,27(3):414-419
A fast algorithm is proposed for estimating the auto- and cross-correlation functions of a large signal. The algorithm is based on the sectioning method by the fast Fourier transform. We determine the optimal length of the portion of data read from external memory into RAM which achieves Tmin—a minimum processing time. An estimate of Tmin is obtained.Translated from Kibernetika, No. 3, pp. 78–81, May–June, 1991. 相似文献
226.
227.
Statistics on the backscatter coefficient σ0 from the Ku -band Seasat-A Satellite Scatterometer (SASS) collected over the world's land surfaces are presented. This spaceborne scatterometer provided data on σ0 between latitude 80° S and 80° N at incidence angles up to 70°. The global statistics of vertical (V ) and horizontal (H ) polarization backscatter coefficients for 10° bands in latitude are presented for incidence angles between 20° and 70° and compared with the Skylab and ground spectrometer results. Global images of the time-averaged V polarization σ0 at a 45° incidence angle and its dependence on the incidence angle are presented and compared to a generalized map of the terrain type. Global images of the differences between the V an H polarization backscatter coefficients are presented and discussed. The most inhomogeneous region, which contains the deserts of North Africa and the Arabian Peninsula, is studied in greater detail and compared with the terrain type 相似文献
228.
Shamansky H.T. Dominek A.K. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1989,37(8):1019-1025
The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth 相似文献
229.
Emmerich M.T.M. Giannakoglou K.C. Naujoks B. 《Evolutionary Computation, IEEE Transactions on》2006,10(4):421-439
This paper presents and analyzes in detail an efficient search method based on evolutionary algorithms (EA) assisted by local Gaussian random field metamodels (GRFM). It is created for the use in optimization problems with one (or many) computationally expensive evaluation function(s). The role of GRFM is to predict objective function values for new candidate solutions by exploiting information recorded during previous evaluations. Moreover, GRFM are able to provide estimates of the confidence of their predictions. Predictions and their confidence intervals predicted by GRFM are used by the metamodel assisted EA. It selects the promising members in each generation and carries out exact, costly evaluations only for them. The extensive use of the uncertainty information of predictions for screening the candidate solutions makes it possible to significantly reduce the computational cost of singleand multiobjective EA. This is adequately demonstrated in this paper by means of mathematical test cases and a multipoint airfoil design in aerodynamics. 相似文献
230.