全文获取类型
收费全文 | 5821篇 |
免费 | 304篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 96篇 |
综合类 | 13篇 |
化学工业 | 1195篇 |
金属工艺 | 125篇 |
机械仪表 | 155篇 |
建筑科学 | 202篇 |
矿业工程 | 9篇 |
能源动力 | 198篇 |
轻工业 | 364篇 |
水利工程 | 35篇 |
石油天然气 | 24篇 |
无线电 | 1047篇 |
一般工业技术 | 1088篇 |
冶金工业 | 497篇 |
原子能技术 | 38篇 |
自动化技术 | 1065篇 |
出版年
2024年 | 9篇 |
2023年 | 103篇 |
2022年 | 198篇 |
2021年 | 314篇 |
2020年 | 240篇 |
2019年 | 227篇 |
2018年 | 255篇 |
2017年 | 209篇 |
2016年 | 297篇 |
2015年 | 191篇 |
2014年 | 252篇 |
2013年 | 395篇 |
2012年 | 305篇 |
2011年 | 349篇 |
2010年 | 249篇 |
2009年 | 244篇 |
2008年 | 235篇 |
2007年 | 204篇 |
2006年 | 162篇 |
2005年 | 140篇 |
2004年 | 116篇 |
2003年 | 94篇 |
2002年 | 81篇 |
2001年 | 92篇 |
2000年 | 62篇 |
1999年 | 74篇 |
1998年 | 221篇 |
1997年 | 107篇 |
1996年 | 96篇 |
1995年 | 80篇 |
1994年 | 55篇 |
1993年 | 77篇 |
1992年 | 46篇 |
1991年 | 41篇 |
1990年 | 27篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1975年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有6151条查询结果,搜索用时 15 毫秒
21.
22.
Hayden J.D. Taft R.C. Kenkare P. Mazure C. Gunderson C. Nguyen B.-Y. Woo M. Lage C. Roman B.J. Radhakrishna S. Subrahmanyan R. Sitaram A.R. Pelley P. Lin J.-H. Kemp K. Kirsch H. 《Electron Devices, IEEE Transactions on》1994,41(12):2318-2325
An advanced, high-performance, quadruple well, quadruple polysilicon BiCMOS technology has been developed for fast 16 Mb SRAM's. A split word-line bitcell architecture, using four levels of polysilicon and two self-aligned contacts, achieves a cell area of 8.61 μm2 with conventional I-line lithography and 7.32 μm2 with I-line plus phase-shift or with deep UV lithography. The process features PELOX isolation to provide a 1.0 μm active pitch, MOSFET transistors designed for a 0.80 μm gate poly pitch, a double polysilicon bipolar transistor with aggressively scaled parasitics, and a thin-film polysilicon transistor to enhance bitcell stability. A quadruple-well structure improves soft error rate (SER) and allows simultaneous optimization of MOSFET and bipolar performance 相似文献
23.
An experimental investigation under cold condition was made to study the effects of some operating/design parameters and non-mechanical L valve configuration on the solid circulation rate in a 4.5 m tall, 0.15 m diameter circulating fluidized bed with riser flow rate varying from 1400 litres/min to 2000 litres/min and bed inventory from 15 kg to 25 kg of sand of average sizes 200 μm, 400 μm and 500 μm. Solid circulation rate was estimated by measuring velocity of sand particle travelling through a vertical Perspex tube section at the bottom of the return leg. It was found to be in the range of 2.8 to 12.3kg/m2s, 0.07 to 9.1kg/m2s and 0.12 to 2.23kg/m2s for sand sizes of 200 μm, 400 μm and 500 μm, respectively for a horizontal L valve. Two mathematical correlations have been developed from the experimental results to predict solid circulation rate as a function of riser flow rate, aeration flow rate, total bed inventory and particle size used. 相似文献
24.
Digital filter bank design quadratic-constrained formulation 总被引:5,自引:0,他引:5
Formulate the filter bank design problem as an quadratic-constrained least-squares minimization problem. The solution of the minimization problem converges very quickly since the cost function as well as the constraints are quadratic functions with respect to the unknown parameters. The formulations of the perfect-reconstruction cosine-modulated filter bank, of the near-perfect-reconstruction pseudo-QMF bank, and of the two-channel biorthogonal linear-phase filter bank are derived using the proposed approach. Compared with other design methods, the proposed technique yields PR filter banks with much higher stopband attenuation. The proposed technique can also be extended to design multidimensional filter banks 相似文献
25.
26.
In the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH3)2? Si? O? Si? (CH3)2H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry 相似文献
27.
The main purpose of this study is to evaluate the computational efficiency of algorithms for calculating shortest paths when they are correctly coded by using the C programming language. The eight algorithms that we selected for this experiment are the most efficient, either measured in terms of worst-case bounds or marked as such from previous computational studies; they include the redistributive heap algorithm. We suggest computer implementations that use the full power of C. In particular, the network representation and the various data structures used to keep the scan eligible list may be managed by using only additions and no multiplications, while it is not possible with FORTRAN. These capabilities, unique to C, yield several interesting conclusions: one may expect to speed up a shortest path algorithm by a factor of 20%; in some cases, this factor may reach 30%. Interestingly, the level of programming difficulty required to achieve these benefits is not greater than that required by implementations using arrays. 相似文献
28.
Ngoc-Anh T. Nguyen Mickey L. Wells David C. Cooper 《Drug development and industrial pharmacy》1995,21(14):1671-1682
To identify factors affecting the chemical stability and preservative efficacy of lamivudine oral liquid formulations, an optimization study using a central composite design was performed. In this design, five factors, each at three levels, were investigated: pH (4.5, 5.5, and 73, sucrose (5%, 20%. and 50% w/v), propylene glycol (0% 2%, and 5% w/v), glycerin (4% 8%, and 12% w/v). and EDTA (0.100. 0.175, and 0.250 mg/mL). All formulations contained a constant concentration of lamivudine, parabens, and artificial strawberry and banana flavors. All formulations were evaluated for preservative effectiveness against USP and BP standards and for chemical stability at 30°C and 40°C for three months. All formulations were effective against bacteria and yeasts, but indicated reduced preservative effectiveness against the mold Aspergillus niger. Preservative effectiveness improved with increasing pH (4.5 to 7.5) and to a lesser extent with increasing EDTA concentration (0.100 to 0.250 mg/mL). Increasing glycerin concentration (4% to 12% w/v) slightly decreased preservative effectiveness. Over the concentration ranges tested, no change in preservative effectiveness was noted with concentration changes in sucrose or propylene glycol. The pH was the main factor influencing the chemical stability of the drug and preservatives in this study. Lamivudine chemical stability increased with increasing pH from 4.5 to 7.5. Methyl and propylparaben showed extensive degradation at pH 7.5. 相似文献
29.
DiPietro Janet A.; Caulfield Laura; Costigan Kathleen A.; Merialdi Mario; Nguyen Ruby H. N.; Zavaleta Nelly; Gurewitsch Edith D. 《Canadian Metallurgical Quarterly》2004,40(3):445
Longitudinal neurobehavioral development was examined in 237 fetuses of low-risk pregnancies from 2 distinct populations-Baltimore, Maryland, and Lima. Peru-at 20. 24. 28. 32, 36. and 38 weeks gestation. Data were based on digitized Doppler-based fetal heart rate (FHR) and fetal movement (FM). In both groups. FHR declined while variability, episodic accelerations, and FM-FHR coupling increased, with discontinuities evident between 28 and 32 weeks gestation. Fetuses in Lima had higher FHR and lower variability, accelerations, and FM-FHR coupling. Declines in trajectories were typically observed 1 month sooner in Lima, which magnified these disparities. Motor activity differences were less consistent. No sex differences in fetal neurobehaviors were detected. It is concluded that population factors can influence the developmental niche of the fetus. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
WL Flejter D Finlinson S Root W Nguyen AR Brothman D Viskochil 《Canadian Metallurgical Quarterly》1996,66(3):276-280
Ring (19) chromosomal mosaicism has been identified in a 14-month-old girl referred for cytogenetic evaluation due to microcephaly and developmental delay with autistic-like mannerisms. An analysis of her peripheral blood lymphocytes showed a 46,XX,r(19) cell line in 119/121 of cells examined. Of the two remaining cells, one had a normal female chromosome complement and the other showed loss of one of the chromosome 19 homologs. Further analysis by fluorescence in situ hybridization using an all human telomere probe showed the presence of a single hybridization signal on the r(19) chromosome. Subsequent cytogenetic characterization of cells derived from the patient's phenotypically normal mother also demonstrated the presence of a ring 19 chromosome in 4/100 cells. The remaining cells had a normal female chromosome complement. These findings represent the first reported case of familial ring 19 mosaicism. The cytogenetic and clinical findings in these two individuals are discussed in relation to six previously reported cases of de novo ring chromosome 19 mosaicism. 相似文献