全文获取类型
收费全文 | 410493篇 |
免费 | 5260篇 |
国内免费 | 1371篇 |
专业分类
电工技术 | 7641篇 |
综合类 | 319篇 |
化学工业 | 61169篇 |
金属工艺 | 16566篇 |
机械仪表 | 13601篇 |
建筑科学 | 8679篇 |
矿业工程 | 2187篇 |
能源动力 | 11726篇 |
轻工业 | 29070篇 |
水利工程 | 4311篇 |
石油天然气 | 7939篇 |
武器工业 | 17篇 |
无线电 | 49729篇 |
一般工业技术 | 83962篇 |
冶金工业 | 76906篇 |
原子能技术 | 9256篇 |
自动化技术 | 34046篇 |
出版年
2022年 | 2599篇 |
2021年 | 3937篇 |
2020年 | 2982篇 |
2019年 | 3866篇 |
2018年 | 6538篇 |
2017年 | 6539篇 |
2016年 | 7016篇 |
2015年 | 4398篇 |
2014年 | 7242篇 |
2013年 | 20408篇 |
2012年 | 11610篇 |
2011年 | 15513篇 |
2010年 | 12369篇 |
2009年 | 13948篇 |
2008年 | 14325篇 |
2007年 | 14087篇 |
2006年 | 12668篇 |
2005年 | 11333篇 |
2004年 | 10699篇 |
2003年 | 10585篇 |
2002年 | 10029篇 |
2001年 | 9871篇 |
2000年 | 9269篇 |
1999年 | 9658篇 |
1998年 | 24555篇 |
1997年 | 16919篇 |
1996年 | 12957篇 |
1995年 | 9661篇 |
1994年 | 8521篇 |
1993年 | 8526篇 |
1992年 | 6186篇 |
1991年 | 5770篇 |
1990年 | 5790篇 |
1989年 | 5412篇 |
1988年 | 5145篇 |
1987年 | 4508篇 |
1986年 | 4405篇 |
1985年 | 4949篇 |
1984年 | 4563篇 |
1983年 | 4107篇 |
1982年 | 3761篇 |
1981年 | 3852篇 |
1980年 | 3511篇 |
1979年 | 3419篇 |
1978年 | 3416篇 |
1977年 | 3857篇 |
1976年 | 4977篇 |
1975年 | 2963篇 |
1974年 | 2725篇 |
1973年 | 2802篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Rothschild M. Forte A.R. Horn M.W. Kunz R.R. Palmateer S.C. Sedlacek J.H.C. 《IEEE journal of selected topics in quantum electronics》1995,1(3):916-923
The trend in microelectronics toward printing features 0.25 μm and below has motivated the development of lithography at the 193-nm wavelength of argon fluoride excimer lasers. This technology is in its early stages, but a picture is emerging of its strengths and limitations. The change in wavelength from 248 to 193 nm will require parallel progress in projection systems, optical materials, and photo-resist chemistries and processes. This paper reviews the current status of these various topics as they have been engineered under a multiyear program at MIT Lincoln Laboratory 相似文献
992.
The definition of the curl operator in terms of an integral is shown to lead to a method for numerical solutions that facilitates the use of mixtures of cells having different shapes and different dielectric properties. The derivation is followed by examples for, waveguides, mixtures of different cells, and a method for increasing the accuracy when an equation is known for the field on the outer boundary. Thus, these results suggest that the formal definition of the curl operator has more than pedagogical value. This definition is taught in an undergraduate class at Florida International University 相似文献
993.
Ku T.K. Chen S.H. Yang C.D. She N.J. Wang C.C. Chen C.F. Hsieh I.J. Cheng H.C. 《Electron Device Letters, IEEE》1996,17(5):208-210
Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities 相似文献
994.
The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity. 相似文献
995.
D Pende R Biassoni C Cantoni S Verdiani M Falco C di Donato L Accame C Bottino A Moretta L Moretta 《Canadian Metallurgical Quarterly》1996,184(2):505-518
Human natural killer (NK) cells express inhibitory receptors that are specific for different groups of HLA-C or HLA-B alleles. The majority of these receptors belong to the immunoglobulin (Ig) superfamily and are characterized by two or three extracellular Ig-like domains. Here we describe a novel inhibitory NK receptor that is specific for a group of HLA-A alleles. The HLA-A3-specific NK cell clone DP7 has been used for mice immunization. Two mAbs, termed Q66 and Q241, bound to the immunizing clone and stained only a subset of NK cell populations or clones. Among Q66 mAb-reactive clones, we further selected those that did not express any of the previously identified HLA-class I-specific NK receptors. These clones did not lyse HLA-A3+ (or -A11+) target cells, but lysis of these targets could be detected in the presence of Q66 or Q241 mAbs. On the other hand, target cells expressing other HLA-A alleles, including -A1, -A2, and -A24, were efficiently lysed. Moreover, none of the HLA-C or HLA-B alleles that were tested exerted a protective effect. Q66+, but not Q66- NK cell clones, expressed messenger RNA coding for a novel 3 Ig domain protein homologous to the HLA-C (p58) and HLA-B (p70) receptors. The corresponding cDNA (cl.1.1) was used to generate transient and stable transfectants in COS7 and NIH3T3 cell lines, respectively. Both types of transfectants were specifically stained by Q66 and Q241 mAbs. Since the cytoplasmic tail of Q66-reactive molecules was at least 11 amino acid longer than the other known p58/p70 molecules, we could generate an antiserum specific for the COOH-terminus of Q66-reactive molecules, termed PGP-3. PGP-3 immunoprecipitated, only from Q66+ NK cells, molecules displaying a molecular mass of 140 kD, under nonreducing conditions, which resolved, under reducing conditions, in a 70-kD band. Thus, differently from the other p58/p70 receptors, Q66-reactive molecules appear to be expressed as disulphide-linked dimers and were thus termed p140. The comparative analysis of the amino acid sequences of p58, p70, and p140 molecules revealed the existence of two cysteins proximal to the transmembrane region, only in the amino acid sequence of p140 molecules. 相似文献
996.
997.
The feasibility of applying a chemical method based on the formation of 2-alkylcyclobutanone to samples of irradiated soft cheese (Brie and Camembert) was investigated. Significant quantities of 2-dodecylcyclobutanone (DCB) and 2-tetradecylcyclobutanone (TCB) were detected in both types of irradiated cheese and are proposed as qualitative markers. Other members of the cyclobutanone family (decyl- and tetradecenyl-) are also thought to be present but could not be substantiated due to a lack of authentic standards. These compounds were absent from the unirradiated samples. Results also show a significant linear relationship between the irradiation dose (1 to 8 kGy) and the amount of DCB and TCB detected in the cheese. 相似文献
998.
999.
WKB近似下的Fourier衍射成象方法 总被引:1,自引:0,他引:1
对于介质目标微波衍射成象,本文引入了WKB近似来模拟目标内部总场。基于这种近似,我们导出了Fourier衍射公式,并采用了广义滤波逆传播方法由目标空间谱实现目标特性的重建。计算机模拟结果表明采用WKB近似重建目标特性较Born近似有明显改善。 相似文献
1000.
S. Bismo P. Duverneuil L. Pibouleau S. Domenech J. -P. Couderc 《Materials and Manufacturing Processes》1995,10(2):241-266
This paper presents the results of our work on a new type of CVD reactor, annular reactor. This equipment is able to deposit pure silicon and also in-situ phosphorus doped silicon on a large number of substrates 相似文献