全文获取类型
收费全文 | 205434篇 |
免费 | 27118篇 |
国内免费 | 8293篇 |
专业分类
电工技术 | 12289篇 |
技术理论 | 12篇 |
综合类 | 11128篇 |
化学工业 | 43119篇 |
金属工艺 | 9425篇 |
机械仪表 | 11487篇 |
建筑科学 | 15370篇 |
矿业工程 | 4869篇 |
能源动力 | 5678篇 |
轻工业 | 18133篇 |
水利工程 | 3755篇 |
石油天然气 | 8685篇 |
武器工业 | 1509篇 |
无线电 | 27232篇 |
一般工业技术 | 30187篇 |
冶金工业 | 8416篇 |
原子能技术 | 2016篇 |
自动化技术 | 27535篇 |
出版年
2024年 | 806篇 |
2023年 | 2804篇 |
2022年 | 5450篇 |
2021年 | 7464篇 |
2020年 | 6683篇 |
2019年 | 7307篇 |
2018年 | 7698篇 |
2017年 | 8674篇 |
2016年 | 8575篇 |
2015年 | 10493篇 |
2014年 | 12471篇 |
2013年 | 15185篇 |
2012年 | 14211篇 |
2011年 | 14237篇 |
2010年 | 13235篇 |
2009年 | 12721篇 |
2008年 | 11774篇 |
2007年 | 11239篇 |
2006年 | 10971篇 |
2005年 | 9225篇 |
2004年 | 6636篇 |
2003年 | 5866篇 |
2002年 | 5437篇 |
2001年 | 4756篇 |
2000年 | 4731篇 |
1999年 | 4238篇 |
1998年 | 3322篇 |
1997年 | 2683篇 |
1996年 | 2437篇 |
1995年 | 2064篇 |
1994年 | 1671篇 |
1993年 | 1200篇 |
1992年 | 961篇 |
1991年 | 740篇 |
1990年 | 582篇 |
1989年 | 514篇 |
1988年 | 421篇 |
1987年 | 242篇 |
1986年 | 216篇 |
1985年 | 159篇 |
1984年 | 130篇 |
1983年 | 91篇 |
1982年 | 90篇 |
1981年 | 71篇 |
1980年 | 64篇 |
1979年 | 50篇 |
1978年 | 27篇 |
1977年 | 50篇 |
1976年 | 37篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
In this paper, the moving least-squares differential quadrature (MLSDQ) method is employed for free vibration of thick antisymmetric laminates based on the first-order shear deformation theory. The generalized displacements of the laminates are independently approximated with the centered moving least-squares (MLS) technique within each domain of influence. The MLS nodal shape functions and their partial derivatives are computed quickly through back-substitutions after only one LU decomposition. Subsequently, the weighting coefficients in the MLSDQ discretization are determined with the nodal partial derivatives of the MLS shape functions. The MLSDQ method combines the merits of both the differential quadrature and meshless methods which can be conveniently applied to complex domains and irregular discretizations without loss of implementation efficiency and numerical accuracy. The natural frequencies of the laminates with various edge conditions, ply angles, and shapes are calculated and compared with the existing solutions to study the numerical accuracy and stability of the MLSDQ method. Effects of support size, order of completeness of basis functions, and node irregularity on the numerical accuracy are investigated in detail. 相似文献
23.
低温脂肪酶产生菌的筛选、鉴定及其部分酶学性质 总被引:15,自引:1,他引:14
从南极乔治王岛冻土来源的76株低温细菌中筛选到13株低温脂肪酶产生菌,对其中的BTsl0022菌株进行鉴定。通过生理生化特征、16s rDNA基因序列的同源性和系统发育分析发现,菌株RTsl0022属于假单胞菌属(Pseudomonas),但与已定名的假单胞菌有一定的差异,与未定名的Pseudomonas sp.PsB的亲缘关系最接近,故将其暂定名为Pseudomonas sp.BTsl0022。对该菌脂肪酶的酶学性质初步研究表明,酶的最适作用温度为24℃,对热敏感,60℃处理30min仅残留25%酶活性,酶的适宜作用pH范围在7.0~9.0,最适pH为8.0。 相似文献
24.
25.
26.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
27.
28.
Yang C.W. Fang Y.K. Lin C.S. Tsair Y.S. Chen S.M. Wang W.D. Wang M.F. Cheng J.Y. Chen C.H. Yao L.G. Chen S.C. Liang M.S. 《Electronics letters》2003,39(21):1499-1501
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V. 相似文献
29.
N. Jongen M. Donnet P. Bowen J. Lemaître H. Hofmann R. Schenk C. Hofmann M. Aoun‐Habbache S. Guillemet‐Fritsch J. Sarrias A. Rousset M. Viviani M.T. Buscaglia V. Buscaglia P. Nanni A. Testino J.R. Herguijuela 《化学工程与技术》2003,26(3):303-305
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production. 相似文献
30.