全文获取类型
收费全文 | 1328篇 |
免费 | 34篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 15篇 |
综合类 | 7篇 |
化学工业 | 296篇 |
金属工艺 | 20篇 |
机械仪表 | 42篇 |
建筑科学 | 66篇 |
矿业工程 | 8篇 |
能源动力 | 24篇 |
轻工业 | 182篇 |
水利工程 | 18篇 |
石油天然气 | 3篇 |
武器工业 | 1篇 |
无线电 | 116篇 |
一般工业技术 | 194篇 |
冶金工业 | 248篇 |
原子能技术 | 13篇 |
自动化技术 | 116篇 |
出版年
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 18篇 |
2017年 | 16篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 70篇 |
2012年 | 38篇 |
2011年 | 55篇 |
2010年 | 49篇 |
2009年 | 44篇 |
2008年 | 61篇 |
2007年 | 50篇 |
2006年 | 40篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 38篇 |
2002年 | 20篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 22篇 |
1998年 | 85篇 |
1997年 | 52篇 |
1996年 | 43篇 |
1995年 | 34篇 |
1994年 | 41篇 |
1993年 | 31篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 28篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1966年 | 9篇 |
排序方式: 共有1369条查询结果,搜索用时 15 毫秒
31.
PJ Oefner SP Hunicke-Smith L Chiang F Dietrich J Mulligan RW Davis 《Canadian Metallurgical Quarterly》1996,24(20):3879-3886
Based on a high-performance liquid chromatographic pump, we have built a device that allows recirculation of DNA through a 63-microm orifice with ensuing fractionation to a minimum fragment size of approximately 300 base pairs. Residence time of the DNA fragments in the converging flow created by a sudden contraction was found to be sufficiently long to allow extension of the DNA molecules into a highly extended conformation and, hence, breakage to occur at midpoint. In most instances, 30 passages sufficed to obtain a narrow size distribution, with >90% of the fragments lying within a 2-fold size distribution. The shear rate required to achieve breakage was found to be inversely proportional to the 1.0 power of the molecular weight. Compared with a restriction digest, up to 40% of all fragments could be cloned directly, with only marginal improvements in cloning efficiency having been observed upon prior end repair with Klenow, T4 polymerase or T4 polynucleotide kinase. Sequencing revealed a fairly random distribution of the fragments. 相似文献
32.
VG Kolupaeva TV Pestova CU Hellen IN Shatsky 《Canadian Metallurgical Quarterly》1998,273(29):18599-18604
A complex of eukaryotic initiation factors (eIFs) 4A, 4E, and 4G (collectively termed eIF4F) plays a key role in recruiting mRNAs to ribosomes during translation initiation. The site of ribosomal entry onto most mRNAs is determined by interaction of the 5'-terminal cap with eIF4E; eIFs 4A and 4G may facilitate ribosomal entry by modifying mRNA structure near the cap and by interacting with ribosome-associated factors. eIF4G recruits uncapped encephalomyocarditis virus (EMCV) mRNA to ribosomes without the involvement of eIF4E by binding directly to the approximately 450-nucleotide long EMCV internal ribosome entry site (IRES). We have used chemical and enzymatic probing to map the eIF4G binding site to a structural element within the J-K domain of the EMCV IRES that consists of an oligo(A) loop at the junction of three helices. The oligo(A) loop itself is not sufficient to form stable complexes with eIF4G since alteration of its structural context abolished its interaction with eIF4G. Addition of wild type or trans-dominant mutant forms of eIF4A to binary IRES.eIF4G complexes did not further alter the pattern of chemical/enzymatic modification of the IRES. 相似文献
33.
Taylor H. Gerry; Dietrich Ann; Nuss Kathryn; Wright Martha; Rusin Jerome; Bangert Barbara; Minich Nori; Yeates Keith Owen 《Canadian Metallurgical Quarterly》2010,24(2):148
To investigate postconcussive symptoms (PCS) following pediatric mild traumatic brain injury (mTBI), 8- to 15-year-old children with mTBI (n = 186) and a comparison group with uncomplicated orthopedic injuries (OI, n = 99) were recruited from two emergency departments. Parent and child ratings of PCS and symptom counts were obtained within 3 weeks after injury (baseline) and at 1, 3, and 12 months postinjury. The mTBI group also completed magnetic resonance imaging at baseline. Group differences were examined using growth modeling, controlling for age at injury, sex, socioeconomic status, and (for parent-based measures) preinjury symptom levels. Relative to the OI group, the mTBI group had higher ratings of somatic PCS and parent counts of PCS at the initial assessments, but higher parent ratings of cognitive PCS and child counts of PCS throughout follow-up. Higher levels of PCS in the mTBI group were associated with motor-vehicle-related trauma, loss of consciousness, neuroimaging abnormalities, and hospitalization. The findings validate both transient and persistent PCS in children with mTBI and document associations of symptoms with injury and noninjury factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
34.
A high-pressure diamond anvil pressure technique for x-ray structure investigations at temperatures down to 1.5 K is described. An energy dispersive method in conjunction with a newly developed conical x-ray shutter brings maximum intensity to the adjacent germanium detector. Superconductivity is detected by use of a SQUID. The 4096-channel analyzer data are evaluated on-line by a computer. The precision of the lattice parameter determination is discussed. 相似文献
35.
The reduction of PVC and of copolymers from vinyl chloride and 2-chloropropene with lithium aluminium hydride occurs in a nearly quantitative manner. A selective reduction of the tertiary chlorine atoms in the copolymers, using lithium deuteride, cannot be observed by means of n.m.r. spectroscopy. The amount of CH3-groupins the reduced samples was determined by i.r. spectroscopic compensation against polymethylene. The number of methyl groups determined in the copolymers agrees well with the copolymer composition found by n.m.r. spectroscopy. The experimental results of the determination of branches and of the thermal degradation indicate no tertiary chlorine atoms in PVC; therefore, one can assume another structure of branches in PVC. 相似文献
36.
In this paper, an original direct and non-intrusive technique using Planar Laser Induced Florescence with Inhibition (PLIFI) is proposed to quantify the local mass transfer around a single spherical bubble rising in a quiescent liquid. The new set-up tracks the mass transferred in the bubble wake for a plane perpendicular to the bubble trajectory instead of a parallel plane as in previous works, thus avoiding optical reflection problems. A spherical bubble is formed in a glass column containing fluorescent dye. A camera with a microscopic lens is placed underneath the column to record cross-sections of the transferred oxygen. A high-speed camera is located far from the column to simultaneously record the bubble position, size, shape and velocity. The dissolved gas inhibits the fluorescence so that oxygen concentration fields can be measured. From this, a calculation method is developed to determine mass transfer on the micro-scale. Experimental results are compared to the Sherwood numbers calculated from the Frössling and Higbie models used for fully contaminated and clean spherical bubbles, respectively. Results show that all experimental Sherwood numbers occur between the two models, which gives credence to the measurements. The new technique is then developed for bubble diameters ranging from 0.7 to 2 mm in six hydrodynamic conditions (1<Re<102, 102<Sc<106). 相似文献
37.
38.
Dietrich Goers Michael E. Spahr Antonio Leone Wolfgang Märkle Petr Novák 《Electrochimica acta》2011,(11):A1478
The local current density related to the exfoliation process of graphite negative electrodes in mixed ethylene carbonate/propylene carbonate electrolytes was controlled by a variation of the current applied to lithium half-cells containing either single type graphite electrodes or electrodes consisting of mixtures of an exfoliating and a non-exfoliating graphite. The partial local current density attributed to graphite passivation and its distribution within the volume of the electrode was found to be a key parameter to explain differences in the exfoliation behaviour observed for graphite electrodes. The local current density is related with a local overpotential which may suppress one of several possible electrochemical processes. In a negative electrode consisting of a mixture of a non-exfoliating and an exfoliating graphite component, the exfoliation of the exfoliation-sensitive graphite component can be completely suppressed when increasing the partial local current density attributed to the graphite exfoliation process above a certain threshold, by either decreasing the amount of exfoliating graphite particles in the electrode or by increasing the total current density, i.e., the specific current. The consideration of the local current density distribution for the electrochemical processes throughout the electrode leads to a more general concept for the graphite passivation behaviour during the first lithium insertion in lithium-ion batteries. 相似文献
39.
Dipl.‐Ing. Volker Lenz Dipl.‐Ing. Marian Schenker Dipl.‐Ing. Christian Thiel Prof. Dr. Wolf‐Dietrich Einicke M.Sc. René Bindig Dr. rer. nat. Ulf Roland 《化学,工程师,技术》2011,83(3):371-376
In addition to the reduction of particulate matter, a catalytic supported emission reduction in small scale biomass combustion systems can also enable a conversion of toxic organic components into carbon dioxide and water. For catalyst investigations under practical conditions a special test facility was designed. The results show that products of incomplete combustion like carbon monoxide from stoves can be reduced by catalytic processes. Further developments and studies are necessary to achieve the targeted emission limits. 相似文献
40.
AG Milekhin N Yeryukov AI Toropov D Dmitriev E Sheremet DR Zahn 《Nanoscale research letters》2012,7(1):476
ABSTRACT: We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in the polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing. 相似文献