全文获取类型
收费全文 | 14575篇 |
免费 | 1257篇 |
国内免费 | 545篇 |
专业分类
电工技术 | 817篇 |
技术理论 | 1篇 |
综合类 | 776篇 |
化学工业 | 2543篇 |
金属工艺 | 756篇 |
机械仪表 | 906篇 |
建筑科学 | 1041篇 |
矿业工程 | 374篇 |
能源动力 | 451篇 |
轻工业 | 978篇 |
水利工程 | 235篇 |
石油天然气 | 915篇 |
武器工业 | 94篇 |
无线电 | 1964篇 |
一般工业技术 | 1856篇 |
冶金工业 | 682篇 |
原子能技术 | 101篇 |
自动化技术 | 1887篇 |
出版年
2024年 | 48篇 |
2023年 | 257篇 |
2022年 | 441篇 |
2021年 | 632篇 |
2020年 | 418篇 |
2019年 | 362篇 |
2018年 | 416篇 |
2017年 | 442篇 |
2016年 | 420篇 |
2015年 | 577篇 |
2014年 | 743篇 |
2013年 | 918篇 |
2012年 | 910篇 |
2011年 | 1074篇 |
2010年 | 885篇 |
2009年 | 817篇 |
2008年 | 840篇 |
2007年 | 752篇 |
2006年 | 810篇 |
2005年 | 713篇 |
2004年 | 443篇 |
2003年 | 375篇 |
2002年 | 312篇 |
2001年 | 288篇 |
2000年 | 293篇 |
1999年 | 409篇 |
1998年 | 360篇 |
1997年 | 274篇 |
1996年 | 263篇 |
1995年 | 190篇 |
1994年 | 177篇 |
1993年 | 114篇 |
1992年 | 102篇 |
1991年 | 69篇 |
1990年 | 58篇 |
1989年 | 35篇 |
1988年 | 28篇 |
1987年 | 9篇 |
1986年 | 24篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
141.
142.
143.
144.
Shu Liang Cheng Peng Zeng Liao Yong Wang 《International journal of systems science》2014,45(10):2203-2212
Approximations for general fractional order dynamic systems are of much theoretical and practical interest. In this paper, a new approximate method for fractional order integrator is proposed. The poles of the approximate model are unrelated to the order of integrator. This feature shows benefits on extending the algorithm to the systems containing various fractional orders. Then a unified approximate method is derived for general fractional order linear or nonlinear dynamic systems via combining the proposed new method with the distributed frequency model approach. Numerical examples are given to show the wide applicability of our method and to illustrate the acceptable accuracy for approximations as well. 相似文献
145.
Juncong Lin Xing Gao Minghong Liao Jiazhi Xia Guilin Li Ying He 《Computers & Electrical Engineering》2014
Releasing sky lanterns is a popular way of celebrating festivals and ceremonies in the Asian countries. This paper presents a computer-aided approach to help novice users to design flyable sky lantern with desired shape. Given a closed up-right 3D model with a user-specified cutting on the bottom, our system optimizes the shape by regularizing the boundary, smoothing the geometry and improving the volume-to-area ratio to make it feasible for flying. The optimized shape is then approximated by a set of developable patches. Next, through a physical analysis step that tests the flying condition and determines the optimal size, the approximated shape is flattened into 2D patches, which can be printed out and glued together to form the airbag. Finally, the user can attach the airbag to a bamboo frame and assemble the fuel cell. We successfully apply our prototype system to design and construct real sky lanterns. 相似文献
146.
Summary Poly(1-methyl-1-phenyl-1-silapentane) (I) has been prepared by the chemical reduction of the carbon-carbon double bonds of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene (cis-II) with diimide, which was generatedin-situ by the thermal decomposition ofp-toluenesulfonhydrazide in refluxing toluene. At lower temperature (100°C),cis-II is isomerized byp-toluenesulfinic acid to lower molecular weight poly(1-methyl-1-phenyl-1-sila-cis andtrans-pent-3-ene) (cis/trans-II). Protodesilation of I with trifluoromethanesulfonic acid yields poly(1-methyl-1-trifluoromethanesulfonyl-1-silapentane) (III). The structures of I andcis/trans-II have been characterized by1H,13C and29Si NMR, GPC, TGA and elemental analysis. The structure of I has been characterized spectroscopically by1H,13C,19F and29Si NMR. 相似文献
147.
148.
This paper introduces the use of conditional-value-at-risk (CVaR) as a criterion for stochastic scheduling problems. This criterion has the tendency of simultaneously reducing both the expectation and variance of a performance measure, while retaining linearity whenever the expectation can be represented by a linear expression. In this regard, it offers an added advantage over traditional nonlinear expectation-variance-based approaches. We begin by formulating a scenario-based mixed-integer program formulation for minimizing CVaR for general scheduling problems. We then demonstrate its application for the single machine total weighted tardiness problem, for which we present both a specialized l-shaped algorithm and a dynamic programming-based heuristic procedure. Our numerical experimental results reveal the benefits and effectiveness of using the CVaR criterion. Likewise, we also exhibit the use and effectiveness of minimizing CVaR in the context of the parallel machine total weighted tardiness problem. We believe that minimizing CVaR is an effective approach and holds great promise for achieving risk-averse solutions for stochastic scheduling problems that arise in diverse practical applications. 相似文献
149.
本文阐述了高温矿床火区开采特高温炮孔的装药爆破安全技术。提出了掌握炸药安全使用温度,采取隔离、隔热包装,降低孔温及提高临界温度等安全措施。 相似文献
150.