全文获取类型
收费全文 | 18461篇 |
免费 | 2972篇 |
国内免费 | 1445篇 |
专业分类
电工技术 | 2575篇 |
综合类 | 2292篇 |
化学工业 | 2848篇 |
金属工艺 | 333篇 |
机械仪表 | 1084篇 |
建筑科学 | 626篇 |
矿业工程 | 288篇 |
能源动力 | 837篇 |
轻工业 | 761篇 |
水利工程 | 289篇 |
石油天然气 | 627篇 |
武器工业 | 184篇 |
无线电 | 2917篇 |
一般工业技术 | 1601篇 |
冶金工业 | 509篇 |
原子能技术 | 193篇 |
自动化技术 | 4914篇 |
出版年
2024年 | 95篇 |
2023年 | 356篇 |
2022年 | 566篇 |
2021年 | 749篇 |
2020年 | 690篇 |
2019年 | 606篇 |
2018年 | 595篇 |
2017年 | 712篇 |
2016年 | 797篇 |
2015年 | 839篇 |
2014年 | 1162篇 |
2013年 | 1229篇 |
2012年 | 1549篇 |
2011年 | 1535篇 |
2010年 | 1144篇 |
2009年 | 1142篇 |
2008年 | 1080篇 |
2007年 | 1195篇 |
2006年 | 1145篇 |
2005年 | 878篇 |
2004年 | 714篇 |
2003年 | 699篇 |
2002年 | 549篇 |
2001年 | 432篇 |
2000年 | 396篇 |
1999年 | 320篇 |
1998年 | 286篇 |
1997年 | 208篇 |
1996年 | 211篇 |
1995年 | 154篇 |
1994年 | 126篇 |
1993年 | 99篇 |
1992年 | 93篇 |
1991年 | 80篇 |
1990年 | 66篇 |
1989年 | 67篇 |
1988年 | 48篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 33篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 30篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1964年 | 11篇 |
1963年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
根据双点后方交会的图形特点和已知条件,列出了方程组,推导出了双点后方交会直接计算座标的简便公式,同时求出了精度计算公式,以供测量人员参考 相似文献
42.
A remarkable nonlinearity has been observed for electric transport in K-TCNQ (potassium tetracyanoquinodimethane) quasi-one-dimensional
conductor. The negative differential resistance region appears afterV
m (turn over voltage), beyond which voltage goes down with increase of current. A possible mechanism is discussed in terms
of dynamics of charged solitons and domain walls in one-dimensional molecular stacks of these types of crystals. 相似文献
43.
J.M Mäkynen J.K Jokiniemi P.P Ahonen E.I Kauppinen R Zilliacus 《Nuclear Engineering and Design》1997,178(1):74
Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper. 相似文献
44.
The standard deviation of differential pressure fluctuations between pressure taps in a 31.7 mm i.d. vertical downer was found to be proportional to the square root of the distance between the taps when measured under otherwise constant conditions. This finding confirms the prediction of a theoretical model based on the Central Limit Theorem of sampling statistics. Although the paper only presents experimental confirmation for downward flow, the theoretical model should be valid for flows in all orientations. Except at very low solids flows, the pressure gradient was found to be positive in the flow direction, indicating that rise in pressure due to static pressure more than compensated for frictional pressure losses. 相似文献
45.
介绍燕山石化公司为扩大1Mt/a中压加氢改质装置的原料来源,改用大庆减二线油和重油催化裂化柴油组成的混合料开工投产的经验以及装置初期的运行条件。中压加氢改质技术可以生产优质柴油和蒸汽裂解制乙烯的原料,还可增产喷气燃料。 相似文献
46.
通过引入归一化脉宽P和相对脉冲展宽因子q,提出了一个适用于IM/DD系统中各种眼图恶化量x和归一化脉宽P的色散限制改进公式。通过与其它理论的比较、计算机仿真和对实验数据的分析,验证了该公式的正确性,并给出了其它结果的限制条件。研究表明:当眼图恶化量x为1dB左右时,对2.5Gb/;外调制信号(α=0)而言,非色散位移光纤IM/DD系统的色散因子γ约等于0.79,所对应的系统再生中继距离约为900余公里。 相似文献
47.
The present paper demonstrates the applicability of population based search optimization method, namely, Differential Evolution
(DE) to a case study of Mahi Bajaj Sagar Project (MBSP), India. Ten different strategies of DE are employed to assess the
ability of DE for solving higher dimensional problems as an alternative methodology for irrigation planning. The parameters
considered in DE are population size, crossover constant and weighting factor. Linear Programming (LP) is utilized as a comparative
approach to assess the ability of DE. Comparison of results of LP and the 10 DE strategies for the given parameters indicated
that both the results are comparable even for high dimensional problems. Extensive sensitivity analysis studies, performed
for 3,600 combinations of above parameters for the 10 DE strategies suggested that DE/rand-to-best/1/bin strategy is the best
strategy giving maximum benefits taking minimum CPU time. It is concluded that DE can be utilized for efficient planning of
any irrigation system with suitable modifications. 相似文献
48.
关于差阻式仪器的几个技术问题 总被引:1,自引:0,他引:1
本文对差阻式仪器的几个重要问题,如差阻式仪器的国家标准、监测数据的质量控制、长期埋设仪器的现场鉴定、仪器测值异常的分析处理等进行了讨论,并提出了自己的意见,供有关科研人员进一步研究和参考. 相似文献
49.
针对传统的非锐化掩模算法的局限性,依据图像中各像素点及以其为中心的若干相邻像素点的均方差值,提出了自适应图像增强算法的原理,并分析其硬件实现方法,然后给出了该算法与其它算法应用于图像增强的对比结果,最后在FPGA(field programmable gate array)实验板上进行验证.实验结果表明,此算法有效的增强图像的细节区域,防止图像边缘区域出现过冲现象,抑制图像平坦区域的噪声放大.因此,该算法取得了良好的视觉效果,硬件实现简单,适合于实时条件下图像的增强. 相似文献
50.
The goal of comprehension is to build coherent mental representations or structures. These structures represent clauses, sentences, paragraphs, passages, and other meaningful units. Thus, comprehending a clause requires building a mental structure to represent what that clause is about; comprehending a sentence requires building a mental structure to represent what that sentence is about; comprehending a passage requires building a mental structure to represent what that passage is about. In Gernsbacher (1990), I described a simple framework for understanding how comprehenders build mental structures during comprehension. I call this framework, the Structure Building Framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献