全文获取类型
收费全文 | 10911篇 |
免费 | 419篇 |
国内免费 | 117篇 |
专业分类
电工技术 | 252篇 |
综合类 | 193篇 |
化学工业 | 2207篇 |
金属工艺 | 376篇 |
机械仪表 | 403篇 |
建筑科学 | 355篇 |
矿业工程 | 103篇 |
能源动力 | 437篇 |
轻工业 | 682篇 |
水利工程 | 118篇 |
石油天然气 | 163篇 |
武器工业 | 16篇 |
无线电 | 1244篇 |
一般工业技术 | 2501篇 |
冶金工业 | 1172篇 |
原子能技术 | 120篇 |
自动化技术 | 1105篇 |
出版年
2023年 | 106篇 |
2022年 | 236篇 |
2021年 | 282篇 |
2020年 | 252篇 |
2019年 | 191篇 |
2018年 | 330篇 |
2017年 | 259篇 |
2016年 | 257篇 |
2015年 | 238篇 |
2014年 | 340篇 |
2013年 | 704篇 |
2012年 | 450篇 |
2011年 | 550篇 |
2010年 | 452篇 |
2009年 | 444篇 |
2008年 | 427篇 |
2007年 | 385篇 |
2006年 | 346篇 |
2005年 | 308篇 |
2004年 | 272篇 |
2003年 | 229篇 |
2002年 | 226篇 |
2001年 | 190篇 |
2000年 | 226篇 |
1999年 | 232篇 |
1998年 | 309篇 |
1997年 | 272篇 |
1996年 | 236篇 |
1995年 | 203篇 |
1994年 | 191篇 |
1993年 | 171篇 |
1992年 | 153篇 |
1991年 | 150篇 |
1990年 | 103篇 |
1989年 | 108篇 |
1988年 | 113篇 |
1987年 | 112篇 |
1986年 | 90篇 |
1985年 | 131篇 |
1984年 | 122篇 |
1983年 | 134篇 |
1982年 | 96篇 |
1981年 | 99篇 |
1980年 | 84篇 |
1979年 | 91篇 |
1978年 | 76篇 |
1977年 | 66篇 |
1976年 | 72篇 |
1975年 | 57篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
V. Rao S. Pramanik C. R. Tewari S. R. Singh O. N. Mohanty 《Journal of Materials Science》1989,24(11):4088-4093
Phase transformation studies have been made of the Mn-Al alloys with compositions near the equiatomic range with or without small amounts of carbon, copper and nickel, using differential thermal analysis, X-ray diffraction and optical and electron microscopy. The high temperature hexagonal phase obtained by quenching, transforms to the ferromagnetic phase between 500 and 550° C and on further heating transforms back to the hexagonal phase between 750 and 950° C. Also, on controlled cooling of the phase from about 900° C, the ferromagnetic phase is formed between 800 and 670° C. TEM studies have shown the presence of the B19 ordered phase, ferromagnetic phase and Mn5Al8 precipitates even in quenched alloys. 相似文献
142.
Given a planar setS ofn points,maxdominance problems consist of computing, for everyp S, some function of the maxima of the subset ofS that is dominated byp. A number of geometric and graph-theoretic problems can be formulated as maxdominance problems, including the problem of computing a minimum independent dominating set in a permutation graph, the related problem of finding the shortest maximal increasing subsequence, the problem of enumerating restricted empty rectangles, and the related problem of computing the largest empty rectangle. We give an algorithm for optimally solving a class of maxdominance problems. A straightforward application of our algorithm yields improved time bounds for the above-mentioned problems. The techniques used in the algorithm are of independent interest, and include a linear-time tree computation that is likely to arise in other contexts.The research of this author was supported by the Office of Naval Research under Grants N00014-84-K-0502 and N00014-86-K-0689, and the National Science Foundation under Grant DCR-8451393, with matching funds from AT&T.This author's research was supported by the National Science Foundation under Grant DCR-8506361. 相似文献
143.
A study has been conducted on the microbiology of sheep carcasses processed in a modern abattoir. The data revealed that careful handling at the different stages of processing of sheep reduced the level of microbial contamination of carcasses. Processing steps such as evisceration and washing did not increase the microbial counts on the carcass surface. Sources of microbial contamination in the abattoir were examined. It was observed that skin, floor washings, intestinal contents and gambrels were the major sources of microbial contamination. Seasonality did not have any effect on the microbial contamination of carcasses. The study revealed that total plate counts in 86·6% of the carcasses ranged between 3·0–4·9log/cm2. The counts of coliforms, staphylococci, enterococci and psychrotrophs were low. Pathogens such as Salmonella were not detected. The microbial counts were well within the generally acceptable levels. These findings demonstrated hygienic handling of carcasses. Shoulder and neck are the critical points for microbiological sampling as these sites showed higher microbial counts. Micrococcus and Staphylococcus predominated among microorganisms associated with carcasses. It was noted that differences occurred in microbial types of carcasses processed in tropical and temperate climates. The data generated in a model facility procided useful information for improving meat handling practices. 相似文献
144.
The effect of end-over-end rotation on heat transfer rate to canned Newtonian liquids was studied with two cans (length: diameter ) over the range 0–38·6 r.p.m. and radius of rotation 0–14·9 cm. Data were obtained with water, glycerine and 30%, 50%, and 60% sucrose solutions. The agitation induced oscillations of the centre temperature about an increasing average value. The oscillations were more pro-nounced in viscous liquids. The heat transfer coefficient (HTC) was found to be independent of the radius of rotation and . Head space volume between 3 and 9% did not affect the HTC. A correlation was developed in terms of Nusselt, rotational Reynolds, and Prandtl numbers to predict the HTC: The characteristic dimension in Nu and Re was the radius of rotation. This correlation, with R2 = 92%, is valid for Re: 83 ? 2·1 × 105 and Pr: 2·8 ? 49. Attempts to improve the correlation by incorporating the Grashof number, and head space volume as well as other characteristic dimensions were not successful. 相似文献
145.
X-ray spectroscopy which is a combination of two techniques, namely x-ray absorption near edge structure (xanes) and extended x-ray absorption fine structure (EXAFS) analyses, is a unique technique for the study of local structures in glasses. Availability of synchrotron radiation sources
has made the technique quite attractive and useful because the photon flux from synchrotrons is very intense and polarized.
In this article, a brief summary ofxanes andEXAFS techniques is given along with a few applications to the study of local structures in glasses.
Communication No. 323 from Solid State and Structural Chemistry Unit. 相似文献
146.
This paper presents the analysis of a parallel formulation of depth-first search. At the heart of this parallel formulation is a dynamic work-distribution scheme that divides the work between different processors. The effectiveness of the parallel formulation is strongly influenced by the work-distribution scheme and the target architecture. We introduce the concept of isoefficiency function to characterize the effectiveness of different architectures and work-distribution schemes. Many researchers considered the ring architecture to be quite suitable for parallel depth-first search. Our analytical and experimental results show that hypercube and shared-memory architectures are significantly better. The analysis of previously known work-distribution schemes motivated the design of substantially improved schemes for ring and shared-memory architectures. In particular, we present a work-distribution algorithm that guarantees close to optimal performance on a shared-memory/-network-with-message-combining architecture (e.g. RP3). Much of the analysis presented in this paper is applicable to other parallel algorithms in which work is dynamically shared between different processors (e.g., parallel divide-and-conquer algorithms). The concept of isoefficiency is useful in characterizing the scalability of a variety of parallel algorithms.This work was supported by Army Research Office Grant No. DAAG29-84-K-0060 to the Artificial Intelligence Laboratory, and Office of Naval Research Grant N00014-86-K-0763 to the Computer Science Department at the University of Texas at Austin. 相似文献
147.
Satya Gopal Rao P. Venkatehwarlu K. Siripuram Rajesh Sripada Suresh 《Glass Physics and Chemistry》2021,47(4):308-320
Glass Physics and Chemistry - The growth of nanocrystalization in TeO2–SeO2–Na2O glasses is achieved by the conventional heat treatment method. The influence of Na2O concentration on... 相似文献
148.
Impact of communication time delays on
combined LFC and AVR of a multi-area
hybrid system with IPFC-RFBs coordinated
control strategy
下载免费PDF全文
![点击此处可从《电力系统保护与控制》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, the impact of communication time delays (CTDs) on combined load frequency control (LFC) and
automatic voltage regulation (AVR) of a multi-area system with hybrid generation units is addressed. Investigation
reveals that CTDs have significant effect on system performance. A classical PID controller is employed as a
secondary regulator and its parametric gains are optimized with a differential evolution - artificial electric field
algorithm (DE-AEFA). The superior performance of the presented algorithm is established by comparing with
various optimization algorithms reported in the literature. The investigation is further extended to integration of
redox flow batteries (RFBs) and interline power flow controller (IPFC) with tie-lines. Analysis reveals that IPFC and
RFBs coordinated control enhances system dynamic performance. Finally, the robustness of the proposed control
methodology is validated by sensitivity analysis during wide variations of system parameters and load. 相似文献
149.
Abid Ali Lina Song Jiankun Hu Jingxian Jiang Qingqing Rao Muhammad Shoaib Shah Fahad Yongjie Cai Xiaoli Zhan Fengqiu Chen Qinghua Zhang 《中国化学工程学报》2021,34(6):299-306
In this work,a degradable polyurethane composed of caprolactone(CL)and L-Lactide(LLA)as soft seg-ments,and 4,4'-methylenebis(cyclohexyl isocyanate)(H12MDI)and polytetramethylene ether glycol(PTMEG)as hard segments,was prepared.Hydrolytic degradation experiment revealed that the degrad-able polyurethane(PU)could be degraded in artificial seawater.It also showed that caprolactone-co-polyurethane(CL-PU)copolymer with higher crystallinity degraded much slower in artificial seawater.However,the introduction of LLA resulted in an increase in the hydrophilicity and reduction in the crys-tallinity of degradable PU,as demonstrated by the contact angle analysis.The result of the scanning elec-tron microscope showed that the surface of degradable PU renewed under static condition.Moreover,degradable PU was able to be used as a carrier,and it controlled the release rate of 4,5-dichloro-2-octyl-isothiazolone(DCOIT).The anti-diatom(Navicula incerta)test demonstrated that the(caprolactone-co-L-lactide)-co-polyurethane 4(CL/LAx-PU4)with DCOIT contents prevented the adhe-sion of diatom Navicula incerta(88.37%reduction)due to their self-polishing and the release of antifou-lants.Therefore,the degradable PU consisted of CL,LLA,and DCOIT could be a durable resin with good antifouling activity for the application in the marine anti-biofouling field. 相似文献
150.
The oxide films formed during early stage of oxidation at 800 °C on dendritic and interdendritic regions of the cast Fe–16Al–1C (wt.%) alloy were studied using scanning Auger electron spectroscopy. Microhardness measurement and elemental depth profiles by Auger spectroscopy reveal that the carbide, Fe3AlC0.69, is the major constituent of the interdendritic region, while dendrites are predominantly Fe3Al phase. Between the two, the interdendritic region is found to be more prone to oxidation than the dendritic region, which was attributed to presence of carbides with low-Al content. In spite of the difference in oxide film thickness exhibited by both the phases, they consist of an inner aluminium oxide layer and an outer iron oxide layer. 相似文献