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991.
The stability under illumination of transmission-mode GaAs photocathode sealed in the third generation intensifier is investigated by use of spectral response testing instruments. The variations of spectral response with the illumination times under weak and intense illumination are compared. The variations of photoemission performance parameters are also characterized. The results show that during initial several weak illuminations photocathode behaves no evident decay and a maximum sensitivity is achieved, while under intense illumination the sensitivity of photocathode begin to decrease largely at the first illumination. The calculated performance parameters show that the variation of surface escape probability with illumination times is a direct cause of instability of photocathode. It is also found that under intense illumination peak wavelength is moved towards short-wave and peak response is decreased, which shows that the ability of long-wave response of photocathode is decreased. 相似文献
992.
采用纳米硫化铅作为增感剂对边长为0.8μm的溴化银立方体颗粒进行了化学增感.利用微弱信号的微波吸收相敏检测技术,在超短脉冲激光作用下,获得了立方体溴化银乳剂中自由光电子和浅束缚光电子随增感时间变化的衰减曲线。通过测量溴化银光作用过程的时间分辨谱,讨论了卤化银晶体中电子陷阱对光电子运动行为的影响,分析了电子陷阱效应同增感时间之间的关系以及两个一级衰减区间寿命值同增感时间的关系.通过未增感样品与增感样品的衰减曲线对比,得到了在此实验奈件下的最佳增感时间为60min. 相似文献
993.
稀土节能灯中的荧光粉光衰问题 总被引:3,自引:0,他引:3
分三个方面综述了稀土节能灯中的荧光粉光衰研究方面的进展:1.荧光粉在点灯过程中的老化。2.荧光粉在制灯过程中的劣化。3.荧光粉组成、晶体结构及制备工艺过程造就的荧光粉本身的光衰特性。 相似文献
994.
E. G. Wang B. G. Liu J. Wu M. Z. Li J. X. Zhong John Wendelken Q. Niu Z. Zhang 《Computational Materials Science》2002,23(1-4):197-203
For decades research on thin-film growth has attracted a lot of attention as these kinds of materials have the potential in new generation device application. It is known that the nuclei at initial stage of the islands are more stable than others and certain atoms are inert while others are active. In this paper, we will show that, when a surfactant layer is used to mediate the growth, a counter-intuitive fractal-to-compact island shape transition can be induced by increasing deposition flux or decreasing growth temperature. Specifically, we introduce a reaction-limited aggregation (RLA) theory, where the physical process controlling the island shape transition is the shielding effect of adatoms stuck to stable islands on incoming adatoms. Also discussed are the origin of a transition from triangular to hexagonal then to inverted triangular and the decay characteristics of 3D islands on surface, and connections of our unique predictions with recent experiments. Furthermore, we will present a novel idea to make use of the condensation energy of adatoms to control the island evolution along special direction. 相似文献
995.
Canan Kuscu Manjari Kiran Akram Mohammed Cem Kuscu Sarthak Satpathy Aaron Wolen Elissa Bardhi Amandeep Bajwa James D. Eason Daniel Maluf Valeria Mas Enver Akalin 《International journal of molecular sciences》2021,22(12)
Transplant glomerulopathy develops through multiple mechanisms, including donor-specific antibodies, T cells and innate immunity. This study investigates circulating small RNA profiles in serum samples of kidney transplant recipients with biopsy-proven transplant glomerulopathy. Among total small RNA population, miRNAs were the most abundant species in the serum of kidney transplant patients. In addition, fragments arising from mature tRNA and rRNA were detected. Most of the tRNA fragments were generated from 5′ ends of mature tRNA and mainly from two parental tRNAs: tRNA-Gly and tRNA-Glu. Moreover, transplant patients with transplant glomerulopathy displayed a novel tRNA fragments signature. Gene expression analysis from allograft tissues demonstrated changes in canonical pathways related to immune activation such as iCos-iCosL signaling pathway in T helper cells, Th1 and Th2 activation pathway, and dendritic cell maturation. mRNA targets of down-regulated miRNAs such as miR-1224-5p, miR-4508, miR-320, miR-378a from serum were globally upregulated in tissue. Integration of serum miRNA profiles with tissue gene expression showed that changes in serum miRNAs support the role of T-cell mediated mechanisms in ongoing allograft injury. 相似文献
996.
997.
导爆管雷管消爆空间的研究 总被引:2,自引:1,他引:1
采用YA-16多闪光高速摄影反相拍摄导爆管经过不同的消爆空间后出口流场的动态结构,以及出口火焰在持续时间内的累积照片,从有利于点燃延期药的角度出发,对出口流场进行了研究。结果表明:采用带锥的消爆空间有利于点燃延期药,提高延时精度。 相似文献
998.
Manuel A. S. Santos Chakib El-Adlouni Alison D. Cox Jos M. Luz Gerard Keith Mick F. Tuite 《Yeast (Chichester, England)》1994,10(5):625-636
A new molecular taxonomic method applicable to the identification of medically important Candida species and other yeast species has been developed. It is based on the electrophoretic pattern of total tRNA samples (a ‘tRNA profile’) isolated from Candida species and generated using high-resolution semi-denaturing urea-polyacrylamide gel electrophoresis and methylene blue staining. Species-specific tRNA profiles for the species. C. albicans, C. tropicalis, C. parapsilosis, C. guilliermondii, C. glabrata and Pichia guilliermondii were obtained. Detailed studies with the major human pathogen of the Candida genus, C. albicans, demonstrated that the tRNA profile for a given species was both reproducible and strain-independent; seven different C. albicans strains generated identical tRNA profiles. Minor strain-specific heterogeneities in the tRNA profiles of C. guilliermondii and C. parapsilosis were detected, but in neither case did they significantly alter the species-specific diagnostic tRNA profile. The potential of this method in clarifying taxonomic anomalies was demonstrated by the finding that Type I and Type II strains of C. stellatoidea generate very different tRNA profiles, with that of a Type II strain being identical to the C. albicans tRNA profile. This method offers a number of advantages over current electrophoretic karyotype methods for species identification, both within the Candida genus and with yeast species in general. 相似文献
999.
M. C. Chen L. Colombo J. A. Dodge J. H. Tregilgas 《Journal of Electronic Materials》1995,24(5):539-544
This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg1-xCdxTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τA7
i/τA1
i ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped
with the carrier concentration ranging from 2 x 1015 to 1.5 x 1017 cm-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x
1015 and 8 x 1016 cm-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes
several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The
ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs
temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τA7
i/τA1
i, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier
lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed,
a donor-like SRH recombination center located at midgap (Ev+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting
lifetime vs temperature curves of undoped films. 相似文献
1000.
It is well known that within-wafer nonuniformity (WIWNU) due to the variation in material removal rate (MRR) in chemical mechanical
polishing (CMP) significantly affects the yield of good dies. The process control for a batch CMP operation is further complicated
by wafer-to-wafer nonuniformity (WTWNU) caused by MRR decay when a number of wafers are polished with the same unconditioned
pad. Accordingly, the present work focuses on modeling the WIWNU and WTWNU in CMP processes. Various material removal models
suggest that the MRR is strongly influenced by the interface pressure. It is also well known that the viscoelastic properties
of the pad play an important role in CMP. In the present work, an analytical expression for pressure distribution (and its
associated MRR) at the wafer-pad interface for a viscoelastic pad is developed. It is observed that under constant load, which
is typical during main polishing in CMP, the spatial distribution of the interface pressure profile may change with time from
edge-slow to edge-fast, depending on the combination of wafer curvature, down pressure, and pad properties. For constant displacement
operations, the pressure profile retains its edge-slow or edge-fast characteristics over time. The analytical model predictions
of MRR based on viscoelastic pad properties also correlate very well to existing experimental observations of MRR decay when
an unconditioned pad is used to polish a number of wafers. Based on these observations, it may be conjectured that the viscoelastic
material properties of the pad play a primary role in causing the observed MRR decay. The analytical results obtained in the
present work can also provide an estimation of evolution of thickness removal distribution over the entire wafer. This may
be used for determining the optimum thickness of the overburden material and its polishing time, and for effective control
of CMP processes. 相似文献