全文获取类型
收费全文 | 6816篇 |
免费 | 1517篇 |
国内免费 | 603篇 |
专业分类
电工技术 | 495篇 |
综合类 | 605篇 |
化学工业 | 1582篇 |
金属工艺 | 208篇 |
机械仪表 | 544篇 |
建筑科学 | 434篇 |
矿业工程 | 113篇 |
能源动力 | 252篇 |
轻工业 | 905篇 |
水利工程 | 175篇 |
石油天然气 | 145篇 |
武器工业 | 214篇 |
无线电 | 732篇 |
一般工业技术 | 905篇 |
冶金工业 | 800篇 |
原子能技术 | 147篇 |
自动化技术 | 680篇 |
出版年
2024年 | 33篇 |
2023年 | 149篇 |
2022年 | 518篇 |
2021年 | 555篇 |
2020年 | 375篇 |
2019年 | 348篇 |
2018年 | 364篇 |
2017年 | 370篇 |
2016年 | 448篇 |
2015年 | 389篇 |
2014年 | 534篇 |
2013年 | 529篇 |
2012年 | 530篇 |
2011年 | 533篇 |
2010年 | 345篇 |
2009年 | 393篇 |
2008年 | 336篇 |
2007年 | 364篇 |
2006年 | 342篇 |
2005年 | 259篇 |
2004年 | 205篇 |
2003年 | 170篇 |
2002年 | 141篇 |
2001年 | 93篇 |
2000年 | 102篇 |
1999年 | 72篇 |
1998年 | 61篇 |
1997年 | 63篇 |
1996年 | 42篇 |
1995年 | 47篇 |
1994年 | 39篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有8936条查询结果,搜索用时 0 毫秒
1.
2.
Biological information is stored in DNA, RNA and protein sequences, which can be understood as genotypes that are translated into phenotypes. The properties of genotype–phenotype (GP) maps have been studied in great detail for RNA secondary structure. These include a highly biased distribution of genotypes per phenotype, negative correlation of genotypic robustness and evolvability, positive correlation of phenotypic robustness and evolvability, shape-space covering, and a roughly logarithmic scaling of phenotypic robustness with phenotypic frequency. More recently similar properties have been discovered in other GP maps, suggesting that they may be fundamental to biological GP maps, in general, rather than specific to the RNA secondary structure map. Here we propose that the above properties arise from the fundamental organization of biological information into ‘constrained'' and ‘unconstrained'' sequences, in the broadest possible sense. As ‘constrained'' we describe sequences that affect the phenotype more immediately, and are therefore more sensitive to mutations, such as, e.g. protein-coding DNA or the stems in RNA secondary structure. ‘Unconstrained'' sequences, on the other hand, can mutate more freely without affecting the phenotype, such as, e.g. intronic or intergenic DNA or the loops in RNA secondary structure. To test our hypothesis we consider a highly simplified GP map that has genotypes with ‘coding'' and ‘non-coding'' parts. We term this the Fibonacci GP map, as it is equivalent to the Fibonacci code in information theory. Despite its simplicity the Fibonacci GP map exhibits all the above properties of much more complex and biologically realistic GP maps. These properties are therefore likely to be fundamental to many biological GP maps. 相似文献
3.
Dynamics of liquid-filled spacecraft 总被引:1,自引:0,他引:1
A method is presented for simulating coupled liquid-solid dynamics. An important example of a coupled liquid-solid system is a satellite carrying fuel. The dynamics of the satellite and the onboard fuel influence each other, which may lead to satellite motion that is uncontrollable. For better understanding of the complex dynamics of coupled systems, a numerical model is developed. The model consists of two parts. The first part that solves the liquid motion is only briefly discussed here. The focus in this paper is on the way in which the dynamics of the liquid and the solid body are coupled. For this, the governing equations are presented in which terms appear that represent the force and torque on the solid body due to the sloshing liquid. The governing equations are rewritten such that the discrete approximation of these equations can be integrated in a stable manner for arbitrary liquid/solid mass ratios. Results are presented demonstrating the stability of the present model. A grid-refinement study and a time-step analysis are performed. Finally, the flat-spin motion of a satellite, partially filled with liquid, that flew in 1992 as part of the Wet Satellite Model experiment is studied. Results from the simulation are compared with the actual flight data. 相似文献
4.
噪声测量作为筛选光电耦合器件的一种方法 总被引:2,自引:2,他引:0
本文针对目前用于光电耦合器件筛选方法的不足,提出了用测量耦合器件噪声功率谱的方法来筛选掉噪声值大的器件,给出一批光电耦合器件的测量统计结果及在不同工作点时的噪声功率谱,并给出相应的筛选标准,实验结果表明,这种方法是有效、可行的。 相似文献
5.
CCD器件已经广泛地应用于各个研究领域中 ,对其信号的具体处理方法是各种各样的。我们针对所研究的对象采取了一定的降低噪声的措施 ,取得了较好的结果 ,本文将对此进行阐述 相似文献
6.
两栖装甲装备新型防腐材料的研究 总被引:1,自引:0,他引:1
沿海地区特殊海洋环境造成装甲装备的严重腐蚀,为了研制一种新型的耐蚀有机涂层,该文作者研究了有机硅改性环氧树脂的化学反应,并对改性树脂的性能进行了测试分析.结果表明,改性树脂克服了环氧树脂的耐温性差、亲水性强以及盐水渗透率高的性能缺陷,为进一步制备该地区装甲装备防腐涂料奠定基础. 相似文献
7.
8.
Optimal Operation of Reservoir Systems using Simulated Annealing 总被引:5,自引:0,他引:5
A stochastic search technique, simulated annealing (SA), is used to optimize the operation of multiple reservoirs. Seminal application of annealing technique in general to multi-period, multiple-reservoir systems, along with problem representation and selection of different parameter values used in the annealing algorithm for specific cases is discussed. The search technique is improved with the help of heuristic rules, problem-specific information and concepts from the field of evolutionary algorithms. The technique is tested for application to a benchmark problem of four-reservoir system previously solved using a linear programming formulation and its ability to replicate the global optimum solution is examined. The technique is also applied to a system of four hydropower generating reservoirs in Manitoba, Canada, to derive optimal operating rules. A limited version of this problem is solved using a mixed integer nonlinear programming and results are compared with those obtained using SA. A better objective function value is obtained using simulated annealing than the value from a mixed integer non-linear programming model developed for the same problem. Results obtained from these applications suggest that simulated annealing can be used for obtaining near-optimal solutions for multi-period reservoir operation problems that are computationally intractable. 相似文献
9.
This paper deals with a new boundary element method for analysis of the quasistatic problems in coupled thermoelasticity. Through some mathematical manipulation of the Navier equation in elasticity, the heat conduction equation is transformed into a simpler form, similar to the uncoupled-type equation with the modified thermal conductivity which shows the coupling effects. This procedure enables us to treat the coupled thermoelastic problems as an uncoupled one, A few examples are computed by the proposed BEM, and the results obtained are compared with the analytical ones available in the literature, whereby the accuracy and versatility of the proposed method are demonstrated. 相似文献
10.