全文获取类型
收费全文 | 384739篇 |
免费 | 5294篇 |
国内免费 | 1340篇 |
专业分类
电工技术 | 7640篇 |
综合类 | 510篇 |
化学工业 | 57652篇 |
金属工艺 | 14840篇 |
机械仪表 | 12425篇 |
建筑科学 | 9864篇 |
矿业工程 | 1417篇 |
能源动力 | 9671篇 |
轻工业 | 36669篇 |
水利工程 | 3513篇 |
石油天然气 | 4432篇 |
武器工业 | 72篇 |
无线电 | 50628篇 |
一般工业技术 | 73355篇 |
冶金工业 | 67344篇 |
原子能技术 | 7203篇 |
自动化技术 | 34138篇 |
出版年
2021年 | 2685篇 |
2019年 | 2744篇 |
2018年 | 4351篇 |
2017年 | 4479篇 |
2016年 | 4787篇 |
2015年 | 3224篇 |
2014年 | 5549篇 |
2013年 | 16892篇 |
2012年 | 9167篇 |
2011年 | 12676篇 |
2010年 | 9940篇 |
2009年 | 11289篇 |
2008年 | 12452篇 |
2007年 | 12579篇 |
2006年 | 11344篇 |
2005年 | 10416篇 |
2004年 | 10092篇 |
2003年 | 9812篇 |
2002年 | 9591篇 |
2001年 | 9557篇 |
2000年 | 9115篇 |
1999年 | 9213篇 |
1998年 | 19822篇 |
1997年 | 14602篇 |
1996年 | 11801篇 |
1995年 | 9384篇 |
1994年 | 8490篇 |
1993年 | 8189篇 |
1992年 | 6757篇 |
1991年 | 6354篇 |
1990年 | 6122篇 |
1989年 | 5876篇 |
1988年 | 5597篇 |
1987年 | 4929篇 |
1986年 | 4821篇 |
1985年 | 5703篇 |
1984年 | 5316篇 |
1983年 | 4865篇 |
1982年 | 4567篇 |
1981年 | 4601篇 |
1980年 | 4300篇 |
1979年 | 4179篇 |
1978年 | 3967篇 |
1977年 | 4690篇 |
1976年 | 5803篇 |
1975年 | 3655篇 |
1974年 | 3490篇 |
1973年 | 3523篇 |
1972年 | 2848篇 |
1971年 | 2671篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Mobile Networks and Applications - Public cloud system offers Infrastructure-as-a-Service (IaaS) to deliver the computational resources on demand. Resource requirements of a cloud environment are... 相似文献
92.
Kozhitov L. V. Kiselev B. G. Raykova T. B. Popkova A. V. Kostishin V. G. Muratov D. G. Yakushko E. V. Kosushkin V. G. Bebenin V. G. 《Russian Microelectronics》2019,48(8):599-612
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical... 相似文献
93.
Breslavs’kyi D. V. Metel’yov V. O. Morachkovs’kyi O. K. Tatarinova O. A. 《Strength of Materials》2019,51(5):753-760
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A... 相似文献
94.
D.R. Santos‐Peñate C.M. Campos‐Rodríguez J.A. Moreno‐Pérez 《International Transactions in Operational Research》2019,26(1):340-363
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included. 相似文献
95.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for... 相似文献
96.
Dr. Iain J. W. McKean Prof. Paul A. Hoskisson Prof. Glenn A. Burley 《Chembiochem : a European journal of chemical biology》2020,21(20):2890-2897
This Concept article describes the latest developments in the emerging area of late-stage biocatalytic alkylation. Central to these developments is the ability to efficiently prepare S-adenosyl methionine (SAM) cofactor analogues and couple this with enzymatic alkyl transfer. Recent developments in the enzymatic synthesis of SAM cofactor analogues are summarized first, followed by their application as alkyl transfer agents catalyzed by methyltransferases (MTases). Second, innovative methods to regenerate SAM cofactors by enzymatic cascades is reported. Finally, future opportunities towards establishing a generalized platform for late-stage alkylation are described. 相似文献
97.
98.
99.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
100.
Titania-based ceramics with adjustable anatase-rutile fractions were obtained by milling of anatase, quartz and corundum precursors, uniaxial pressing and firing at 1100?°C. The influence of silica and alumina, combined with milling time and compaction pressure, was studied by design of experiments. The L9 orthogonal array with a three-level noise factor was employed. Firing of pure titania at 1100?°C yielded complete anatase to rutile transformation (ART), whereas stabilized samples show that an optimum amount of 9% silica and 33% alumina reduces phase transformation to only about 5?wt% rutile. An extended correlation matrix combined with analysis of variance (ANOVA) was applied to assess the combined effects of quartz, alumina, milling time and uniaxial compressing pressure on relative density, and anatase to rutile transformation. Results show absence of ART after milling, and controlled partial conversion of anatase to rutile after firing. Very good fitting was obtained by multivariate analysis on considering first and second order terms for dependence on silica contents and interactions between silica and each of the remaining factors, including milling time. This empirical dependence could be interpreted on a sound physicochemical basis, allowing the prediction of suitable compositions and processing conditions to obtain rutile-free samples by conventional ceramic processing, and to design ceramic samples with controlled fractions of anatase and rutile. 相似文献