全文获取类型
收费全文 | 206804篇 |
免费 | 15373篇 |
国内免费 | 7807篇 |
专业分类
电工技术 | 11245篇 |
技术理论 | 14篇 |
综合类 | 11215篇 |
化学工业 | 35710篇 |
金属工艺 | 10539篇 |
机械仪表 | 11999篇 |
建筑科学 | 16408篇 |
矿业工程 | 4942篇 |
能源动力 | 5853篇 |
轻工业 | 12682篇 |
水利工程 | 3211篇 |
石油天然气 | 11072篇 |
武器工业 | 1345篇 |
无线电 | 25484篇 |
一般工业技术 | 26717篇 |
冶金工业 | 11982篇 |
原子能技术 | 2114篇 |
自动化技术 | 27452篇 |
出版年
2024年 | 881篇 |
2023年 | 3262篇 |
2022年 | 5827篇 |
2021年 | 7927篇 |
2020年 | 5796篇 |
2019年 | 5013篇 |
2018年 | 5414篇 |
2017年 | 6200篇 |
2016年 | 5693篇 |
2015年 | 7290篇 |
2014年 | 9520篇 |
2013年 | 12278篇 |
2012年 | 12225篇 |
2011年 | 13871篇 |
2010年 | 11611篇 |
2009年 | 11460篇 |
2008年 | 10872篇 |
2007年 | 10467篇 |
2006年 | 10857篇 |
2005年 | 9629篇 |
2004年 | 6564篇 |
2003年 | 5776篇 |
2002年 | 5253篇 |
2001年 | 4723篇 |
2000年 | 4869篇 |
1999年 | 5662篇 |
1998年 | 5600篇 |
1997年 | 4500篇 |
1996年 | 4075篇 |
1995年 | 3375篇 |
1994年 | 2826篇 |
1993年 | 2258篇 |
1992年 | 1709篇 |
1991年 | 1296篇 |
1990年 | 1036篇 |
1989年 | 900篇 |
1988年 | 695篇 |
1987年 | 514篇 |
1986年 | 402篇 |
1985年 | 342篇 |
1984年 | 212篇 |
1983年 | 201篇 |
1982年 | 166篇 |
1981年 | 150篇 |
1980年 | 141篇 |
1979年 | 97篇 |
1978年 | 66篇 |
1977年 | 92篇 |
1976年 | 154篇 |
1975年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
221.
中厚板矫直技术的发展 总被引:13,自引:0,他引:13
本文介绍中厚板产生不平直度的原因,中厚板矫直机的种类,3各种新型矫直机,矫直机产能的确认及中厚板矫直技术的发展。 相似文献
222.
The precise integration and differential quadrature methods are two new unconditionally stable numerical schemes to approximate
time derivative with more than the second order accuracy. Recent studies showed that compared with the Houbolt and Newmark
methods, they produced more accurate solutions with large time step for the problems where response is primarily dominated
by low and intermediate frequency modes. This paper aims to investigate these time schemes in the context of the dual reciprocity
BEM (DRBEM) formulation of various shock-excited scalar elastic wave problems, where high modes have important affect on traction
response. The Houbolt method was widely recommended in many literatures for such DRBEM dynamic formulations. However, this
study found that the damped Newmark algorithm was the most efficient and accurate for impact traction analysis in conjunction
with the DRBEM. The precise integration and differential quadrature methods are shown inapplicable for such shock-excited
problems due to the absence of numerical damping. On the other hand, we also found that to achieve the same order of accuracy,
the differential quadrature method required much less computing effort than the precise integration method due to the use
of the Bartels–Stewart algorithm solving the resulting Lyapunov matrix analogization equation.
Received 6 November 2000 相似文献
223.
秦山核电厂气载放射性释放的环境影响 总被引:3,自引:1,他引:2
本文评价了秦山核电厂气载放射性流出物对环境的影响。应用现场及风洞大气扩释实验结果和厂址周围的人口与食谱调查资料,估算了秦山核电厂在正常运行和事故条件下释放的气载放射性流出物对公众产生的个人有效剂量当量和集体有效剂量当量。计算结果表明,正常运行时厂址边界(0.5km)处的最大个人有效剂量当量为2.7×10~(-2)mSv/a,该剂量的大部分来自~(137)Cs 的食入(主要由地表湿沉积引起);80km 范围内的集体有效剂量当量为1.1人·Sv/a,归一化集体有效剂量当量为3.7人·Sv/GW(e)·a。文中还给出了事故情况下剂量估算结果。 相似文献
224.
在行骨骼活检时,穿刺针的选择非常重要,甚至直接影响着活检的成功与否。笔者根据多次实践,应用环锯和Ackerman钻取外替代传统的活检方法取得了较好的效果。 相似文献
225.
A direct method for transient stability analysis of a multimachine power system is presented. Emphasis is placed on the detailed development and evaluation of the proposed method in transient stability assessment. An energy-type Lyapunov function, taking into account the effect of transfer conductance, is introduced first. The potential energy boundary surface method is then adopted to determine the critical energy value quickly. The main computational burden in the direct method lies in the reduction of the admittance matrices. In this paper, an efficient reduction technique incorporating the sparsity technique and compensation theory is developed. Finally, the proposed method was tested on the Taipower system, which is the only power system in Taiwan. The results obtained confirm the validity and accuracy of the proposed method, and hence demonstrate the superiority and potential of the direct method in real power system applications. 相似文献
226.
Juin-Hung Chen Hen-Wai Tsao 《Lightwave Technology, Journal of》1998,16(7):1137-1148
This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method 相似文献
227.
Forty-three patients with spastic quadriplegia (mean age 7.9 years, range 3.3 to 17.2 years) underwent bone mineral density (BMD) measurement of the lumbar spine and were evaluated between 2.6 and 5.5 years (mean 3.8) later to determine whether this measurement had predicted risk of fracture over the subsequent period of observation. Other potential risk factors that were evaluated include body weight z score, serum vitamin D levels, previous fracture, and hip spica casting. The baseline measurements showed that BMD falls further below normal with increasing age and was more than one standard deviation below age-matched normal mean in 38 of the 43 patients. Fracture rate did not differ between those with low and those with very low spinal BMD. Similarly, serum vitamin D levels and body weight z scores were not predictive of fracture. However, fracture rate was over fourfold greater following spica casting and more than threefold greater following an initial fracture. Fracture rates in the study group were similar to those reported for age- and sex-matched normal children, though generally the location of the fractures and mechanisms of injury differed. 相似文献
228.
229.
T. -Y. Chen 《Structural and Multidisciplinary Optimization》1992,4(3-4):179-185
A design optimization procedure using a sequential linear programming technique is proposed in this paper to design minimum weight structures subjected to frequency response and static displacement constraints. The merit of the proposed approach is that the reanalyses of the static and dynamic responses, as well as the computations of the static and dynamic sensitivity data, are performed in a reduced approximate model. A significant saving of computer time for large scale structures is expected. Two numerical examples show good results of this method. 相似文献
230.
Haitao Zhang Zonghai Chen Yongji Wang Ming Li Ting Qin 《International Journal of Adaptive Control and Signal Processing》2006,20(2):53-76
Laguerre Functional Model has many advantages such as good approximation capability for the variances of system time‐delay, order and other structural parameters, low computational complexity, and the facility of online parameter identification, etc., so this model is suitable for complex industrial process control. A series of successful applications have been gained in linear and non‐linear predictive control fields by the control algorithm based on Laguerre Functional Model, however, former researchers have not systemically brought forward the theoretical analyses of the stability, robustness, and steady‐state performance of this algorithm, which are the keys to guarantee the feasibility of the control algorithm fundamentally. Aimed at this problem, we introduce the principles of the Incremental Mode Linear Laguerre Predictive Control (IMLLPC) algorithm, and then systemically propose the theoretical analyses and proofs of the stability and robustness of the algorithm, in addition, we also put forward the steady‐state performance analysis. At last, the control performances of this algorithm on two different physical industrial plants are presented in detail, and a number of experimental results validate the feasibility and superiority of IMLLPC algorithm. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献