全文获取类型
收费全文 | 21815篇 |
免费 | 1448篇 |
国内免费 | 190篇 |
专业分类
电工技术 | 366篇 |
综合类 | 97篇 |
化学工业 | 5704篇 |
金属工艺 | 535篇 |
机械仪表 | 827篇 |
建筑科学 | 811篇 |
矿业工程 | 37篇 |
能源动力 | 1479篇 |
轻工业 | 2041篇 |
水利工程 | 350篇 |
石油天然气 | 332篇 |
武器工业 | 9篇 |
无线电 | 2270篇 |
一般工业技术 | 3905篇 |
冶金工业 | 681篇 |
原子能技术 | 156篇 |
自动化技术 | 3853篇 |
出版年
2024年 | 102篇 |
2023年 | 435篇 |
2022年 | 884篇 |
2021年 | 1402篇 |
2020年 | 1200篇 |
2019年 | 1397篇 |
2018年 | 1584篇 |
2017年 | 1449篇 |
2016年 | 1406篇 |
2015年 | 841篇 |
2014年 | 1351篇 |
2013年 | 2226篇 |
2012年 | 1441篇 |
2011年 | 1579篇 |
2010年 | 1070篇 |
2009年 | 947篇 |
2008年 | 645篇 |
2007年 | 521篇 |
2006年 | 444篇 |
2005年 | 296篇 |
2004年 | 275篇 |
2003年 | 208篇 |
2002年 | 171篇 |
2001年 | 117篇 |
2000年 | 111篇 |
1999年 | 101篇 |
1998年 | 158篇 |
1997年 | 132篇 |
1996年 | 118篇 |
1995年 | 86篇 |
1994年 | 61篇 |
1993年 | 74篇 |
1992年 | 56篇 |
1991年 | 54篇 |
1990年 | 55篇 |
1989年 | 44篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
In this note we present a proof to the conjecture given in the above paper, and therefore establish the equivalence of characterizations of fixed modes for the general case. 相似文献
32.
33.
Compact WLAN disc antennas 总被引:1,自引:0,他引:1
McEwan N.J. Abd-Alhameed R.A. Ibrahim E.M. Excell P.S. Ali N.T. 《Antennas and Propagation, IEEE Transactions on》2002,50(12):1862-1864
A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes. 相似文献
34.
It has been previously reported that Bryostatin 1 (Bryo1) induces differentiation of the human acute lymphoblastic leukemia (ALL) cell line, Reh, to a monocytoid B-cell stage. In this study we demonstrate that a novel protein, ubiquitin COOH-terminal hydrolase (UCH-L1), is associated with this differentiation. Reh cells were treated with 200 nmol/l of Bryo1 for 72 h and analyzed for changes in morphology, surface immunophenotype, acid phosphatase and terminal deoxynucleotidyl transferase. Protein patterns of the parent and differentiated cells, by two-dimensional polyacrylamide gel electrophoresis (2D PAGE), were studied. Bryo1-treated cells expressed morphologic, phenotypic and enzymatic features of the monocytoid B-cell stage. The UCH-L1 enzyme (MW-pl 34-5.3) was detected by 2 D PAGE in the differentiated, but not in parent cells. The presence of UCH-L1 in the Bryo1-treated cells was further confirmed by immunoblotting of 2 D PAGE using UCH-L1 polyclonal antibody. Ubiquitin expression was studied in parent and Bryo1-treated cells and was compared with 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells. Both agents, TPA and Bryo1, increased the level of ubiquitin expression as detected by flow cytometry. Sodium borohydride, an inhibitor of UCH-L1, inhibited the Bryo1-induced differentiating effect on Reh cells. To date, the mechanism by which Bryo1, exerts its B-cell differentiating effect is not fully understood. This study shows that UCH-L1 expression may play a major role in Bryo1-induced differentiation in pre-B-ALL. 相似文献
35.
Progress and prospects of group-III nitride semiconductors 总被引:1,自引:0,他引:1
We review recent progress in the group-III nitride and related materials, and electronic and optical devices based on them. Blue and UV (e.g. ultra violet) emitters and detectors, and high temperature/high power electronics which has long been coveted are beginning to be realized either in the laboratory or in the commercial arena, due in part to the breathtaking progress made in the last few years in the art and science of GaN, InN, AlN and their salloys. With brief references to the historical aspect of the relevant developments, this review concerns itself primarily with the current status of wide bandgap gallium nitride and related semiconductors from both the materials and devices points of view. Following a discussion of the structural properties of these materials, their electrical and optical properties are described in detail. The available data on metal contacts, the properties of which are indeed very conducive for the devices mentioned, from the points of view of ohmic contacts and Schottky barriers, are elaborated on. Recent progress on processing issues such as etching are reviewed. The review then embarks on an indash;depth discussion and analysis of field effect transistors, bipolar transistors, light emitting diodes, laser and photo detectors. 相似文献
36.
37.
38.
Hong Jin Mohammad S. Uddin Yu L. Huang Wah K. Teo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(1):67-72
High level expression of recombinant human tumour necrosis factor β (rh TNF-β) in Escherichia coli results in the formation of two portions of protein, namely soluble active protein and insoluble protein which is inactive and aggregates in the form of inclusion bodies (IBs). In this study, a procedure for purification and renaturation of rh TNF-β from inclusion bodies has been designed and verified experimentally with a product purity of more than 90% and a recovery of about 30%. The procedure includes washing of IBs with specific wash buffer (Triton X-100/EDTA/lysozyme/PMSF), their solubilization with 8 mol dm?3 alkaline urea, purification with ion-exchange columns, refolding with renaturation buffer and finally concentration and desalination with an ultrafiltration membrane. The characteristics of the renatured protein were identical with those of purified protein from the soluble fraction as demonstrated by (1) SDS-PAGE, (2) cytotoxic activity on mouse L929 cells, (3) N-terminal amino acid sequence, and (4) gel filtration chromatography. 相似文献
39.
BATCH SEQUENCING 总被引:1,自引:0,他引:1
Consider the single machine scheduling problem where there are a number of part types to be processed. A part type is defined as follows: Two parts are of the same part type if the machine does not require a setup in between the processing of these parts. The problem investigated in this paper is to find a sequence of batches of parts (if there are any) where all the requirements for parts are met. A heuristic and an exact algorithm are developed, and computational analysis is performed to measure the performance of the heuristic. The time complexity function of the heuristic is O(n2), and the exact algorithm runs in polynomial time given a fixed upper bound on the number of setups. 相似文献
40.
Akon Mohammad Mursalin Asaduzzaman Shah Rahman Md. Saidur Matsumoto Mitsuji 《Telecommunication Systems》2004,25(3-4):287-298
A routing protocol chooses one of the several paths (routes) from a source node to a destination node in the computer network, to send a packet of information. In this paper, we propose a new routing protocol, which we call st-routing protocol, based on st-numbering of a graph. The protocol fits well in noisy environments where robustness of routing using alternative paths is a major issue. The proposed routing protocol provides a systematic way to retry alternative paths without generating any duplicate packets. The protocol works for only those networks that can be represented by biconnected graphs. 相似文献