全文获取类型
收费全文 | 3371篇 |
免费 | 85篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 37篇 |
综合类 | 7篇 |
化学工业 | 707篇 |
金属工艺 | 62篇 |
机械仪表 | 45篇 |
建筑科学 | 157篇 |
矿业工程 | 12篇 |
能源动力 | 110篇 |
轻工业 | 203篇 |
水利工程 | 12篇 |
石油天然气 | 15篇 |
无线电 | 249篇 |
一般工业技术 | 478篇 |
冶金工业 | 956篇 |
原子能技术 | 30篇 |
自动化技术 | 390篇 |
出版年
2022年 | 30篇 |
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 32篇 |
2018年 | 37篇 |
2017年 | 45篇 |
2016年 | 39篇 |
2015年 | 41篇 |
2014年 | 57篇 |
2013年 | 268篇 |
2012年 | 83篇 |
2011年 | 108篇 |
2010年 | 115篇 |
2009年 | 105篇 |
2008年 | 112篇 |
2007年 | 98篇 |
2006年 | 85篇 |
2005年 | 78篇 |
2004年 | 73篇 |
2003年 | 69篇 |
2002年 | 58篇 |
2001年 | 51篇 |
2000年 | 41篇 |
1999年 | 57篇 |
1998年 | 182篇 |
1997年 | 121篇 |
1996年 | 94篇 |
1995年 | 90篇 |
1994年 | 75篇 |
1993年 | 78篇 |
1992年 | 46篇 |
1991年 | 55篇 |
1990年 | 63篇 |
1989年 | 39篇 |
1988年 | 47篇 |
1987年 | 46篇 |
1986年 | 53篇 |
1985年 | 44篇 |
1984年 | 44篇 |
1983年 | 43篇 |
1982年 | 53篇 |
1981年 | 60篇 |
1980年 | 34篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 40篇 |
1976年 | 36篇 |
1975年 | 46篇 |
1974年 | 25篇 |
1973年 | 25篇 |
排序方式: 共有3470条查询结果,搜索用时 15 毫秒
991.
Louis A. Merlin 《Journal of the American Planning Association. American Planning Association》2013,79(4):501-510
Shared mobility and ride-hailing have not apparently promoted transportation sustainability to date. Evidence suggests ride-hailing increases congestion and primarily serves the advantaged, and services that encourage pooled rides have not taken off. However, simulation research into automated vehicle ride-hailing systems indicates greater ride pooling may be the key to major improvements in transportation sustainability. Though the results are widely varying, the common finding is pooled ride mobility systems could offer substantial benefits if they are able to attain sufficient market share. Moreover, such systems do not require self-driving vehicles but merely centralized fleet coordination, achievable with today’s technologies. 相似文献
992.
Øyvind Berle Bjørn Egil AsbjørnslettJames B. Rice 《Reliability Engineering & System Safety》2011,96(6):696-705
World trade increasingly relies on longer, larger and more complex supply chains, where maritime transportation is a vital backbone of such operations. Long and complex supply chain systems are more prone to being vulnerable, though through reviews, no specific methods have been found to assess vulnerabilities of a maritime transportation system. Most existing supply chain risk assessment frameworks require risks to be foreseen to be mitigated, rather than giving transportation systems the ability to cope with unforeseen threats and hazards. In assessing cost-efficiency, societal vulnerability versus industrial cost of measures should be included.This conceptual paper presents a structured Formal Vulnerability Assessment (FVA) methodology, seeking to transfer the safety-oriented Formal Safety Assessment (FSA) framework into the domain of maritime supply chain vulnerability. To do so, the following two alterations are made: (1) The focus of the assessment is defined to ensure the ability of the transportation to serve as a throughput mechanism of goods, and to survive and recover from disruptive events. (2) To cope with low-frequency high-impact disruptive scenarios that were not necessarily foreseen, two parallel tracks of risk assessments need to be pursued—the cause-focused risk assessment as in the FSA, and a consequence-focused failure mode approach. 相似文献
993.
Khalaf M Kohl SD Klumpp E Rice JA Tombácz E 《Environmental science & technology》2003,37(13):2855-2860
Humic acid was fractionated into eight different molecular size components using ultrafiltration. Solid-state CPMAS 13C NMR demonstrated that fractions larger than 100,000 Daltons were primarily aliphatic in character, while fractions smaller than 30,000 Daltons were predominantly aromatic in character. Solid-state 19F NMR examination of the sorptive uptake of hexafluorobenzene (HFB) by HA and each of the fractions gave spectroscopic evidence for the existence of at least three sorption sites in the smaller molecular size fractions, while two predominant sorption sites could be established in the larger molecular size fractions. Sorbed HFB displayed higher mobility in the smaller, more aromatic fractions while HFB in the larger, more aliphatic fractions displayed lower mobility. The relative mobilities of HFB in each sorption domain suggest that the rigid domain may be composed of aliphatic carbon rather than aromatic carbon moieties. In larger size fractions, this domain may be the result of rigid, glassy regions composed of aliphatic molecules or side chains. 相似文献
994.
不少欧美玩具公司成功开发出各种环保型的玩具。近两年来,经济因素减缓了绿色玩具在大众零售市场的需求。但在专卖店渠道中,凭借着具有环保意识的消费者基础,环保玩具有别于其它类型的产品却继续获得大力追捧。随着去年年底全球气候变化高峰会在丹麦哥本哈根召开。选择环保产品的可能性和必要性更加受到关注。 相似文献
995.
The microbial quality of livestock drinking water was evaluated in 473 cattle water troughs located at 99 different cattle operations. The mean log10-transformed coliform and Escherichia coli concentrations per milliliter of trough water were 1.76 +/- 1.25 (SD) and 0.98 +/- 1.06 (SD), respectively. The degree of E. coli contamination was positively associated with the proximity of the water trough to the feedbunk, protection of the trough from direct sunlight, lower concentrations of protozoa in the water, and warmer weather. Salmonella sp. were isolated from 2/235 (0.8%) troughs and shigatoxigenic-E. coli O157 was recovered from 6/473 (1.3%) troughs. Four experimental microcosms simulating cattle water troughs were used to further evaluate the effects of protozoal populations on the survival of E. coli O157 in cattle water troughs. Escherichia coli O157 of bovine fecal origin proliferated in all microcosms. Reduction of protozoal populations by treatment with cycloheximide was associated with increased persistence of E. coli O157 concentrations in the microcosms. Water troughs are a major source of exposure of cattle to enteric bacteria, including a number of foodborne pathogens, and this degree of bacterial contamination appeared to be associated with potentially controllable factors. 相似文献
996.
该研究主要利用Gini系数来探讨镜质体反射率量测上不均性的结果,由单一煤样之水洗样(Y2)及富集壳质组之样品(Y3),与原始样(Y1)作Gini系数的比较。分析显示水洗样Y2之镜质体反射率有向平均值集中的情形,而富集样Y3之Gini系数则有向平均值两端分布的趋势;向高值端的部分系受水洗的影响,而向低值端的发展,系受壳质组富集的影响。由Gini系数特性的研究可推广至已知再沉积材料之镜质体反射率的量测上,以取得一个可靠之Gini系数分布范围,作为将来分析样品时的参考。 相似文献
997.
Jeremy Rice Amir Faghri Baki Cetegen 《International Journal of Heat and Mass Transfer》2005,48(25-26):5192-5204
A detailed analysis of the liquid film characteristics and the accompanying heat transfer of a free surface controlled liquid impinging jet onto a rotating disk are presented. The computations were run on a two-dimensional axi-symmetric Eulerian mesh while the free surface was calculated with the volume of fluid method. Flow rates between 3 and 15 lpm with rotational speeds between 50 and 200 rpm are analyzed. The effects of inlet temperature on the film thickness and heat transfer are characterized. The evaporative effects are captured when the fluid impinges on the disk at saturated conditions. The conjugate heating effect is modeled, and was found to effect the heat transfer results the most at both the inner and outer edges of the heated surface. The heat transfer was enhanced with both increasing flow rate and increasing rotational speeds. When evaporative effects were modeled, the evaporation was found to increase the heat transfer at the lower flow rates the most because of a fully developed thermal field that was achieved. The evaporative effects did not significantly enhance the heat transfer at the higher flow rates. 相似文献
998.
Xi Long W Louis Cleveland Y Lawrence Yao 《IEEE transactions on information technology in biomedicine》2005,9(3):407-412
In this paper, we describe a novel strategy for combining fisher's linear discriminant (FLD) preprocessing with a feedforward neural network to classify cultured cells in bright field images. This technique was applied to various experimental scenarios utilizing different imaging environments, and the results were compared with those for the traditional principal component analysis (PCA) preprocessing. Our FLD preprocessing was shown to be more effective than PCA due in large part to the fact that FLD maximizes the ratio of between-class to within-class scatter. The new cell recognition algorithm with FLD preprocessing improves accuracy while the speed is suitable for practical applications. 相似文献
999.
We present an overview and analysis of existing work in the design of online testable reversible logic circuits, as well as propose new approaches for the design of such circuits. We explain how previously proposed approaches are unnecessarily high in overhead and in many cases do not provide adequate fault coverage. Proofs of the correctness of our approaches are provided, and discussions of the advantages and disadvantages of each design approach are given. Experimental results comparing our approaches to existing work are presented as well. Both approaches that we propose have better fault coverage and significantly lower overheads than previous approaches. 相似文献
1000.
Sandip Bhattacharya Mohammed Imran Hussain John Ajayan Shubham Tayal Louis Maria Irudaya Leo Joseph Sreedhar Kollem Usha Desai Syed Musthak Ahmed Ravichander Janapati 《ETRI Journal》2023,45(5):910-921
In this study, we designed a 6T-SRAM cell using 16-nm CMOS process and analyzed the performance in terms of read-speed latency. The temperature-dependent Cu and multilayered graphene nanoribbon (MLGNR)-based nano-interconnect materials is used throughout the circuit (primarily bit/bit-bars [red lines] and word lines [write lines]). Here, the read speed analysis is performed with four different chip operating temperatures (150K, 250K, 350K, and 450K) using both Cu and graphene nanoribbon (GNR) nano-interconnects with different interconnect lengths (from 10 μm to 100 μm), for reading-0 and reading-1 operations. To execute the reading operation, the CMOS technology, that is, the16-nm PTM-HPC model, and the16-nm interconnect technology, that is, ITRS-13, are used in this application. The complete design is simulated using TSPICE simulation tools (by Mentor Graphics). The read speed latency increases rapidly as interconnect length increases for both Cu and GNR interconnects. However, the Cu interconnect has three to six times more latency than the GNR. In addition, we observe that the reading speed latency for the GNR interconnect is ~10.29 ns for wide temperature variations (150K to 450K), whereas the reading speed latency for the Cu interconnect varies between ~32 ns and 65 ns for the same temperature ranges. The above analysis is useful for the design of next generation, high-speed memories using different nano-interconnect materials. 相似文献