全文获取类型
收费全文 | 102882篇 |
免费 | 1345篇 |
国内免费 | 1230篇 |
专业分类
电工技术 | 1924篇 |
综合类 | 138篇 |
化学工业 | 10489篇 |
金属工艺 | 5456篇 |
机械仪表 | 3187篇 |
建筑科学 | 2033篇 |
矿业工程 | 159篇 |
能源动力 | 2959篇 |
轻工业 | 6059篇 |
水利工程 | 704篇 |
石油天然气 | 668篇 |
武器工业 | 15篇 |
无线电 | 15941篇 |
一般工业技术 | 21755篇 |
冶金工业 | 25246篇 |
原子能技术 | 1382篇 |
自动化技术 | 7342篇 |
出版年
2022年 | 452篇 |
2021年 | 698篇 |
2020年 | 522篇 |
2019年 | 676篇 |
2018年 | 1129篇 |
2017年 | 1093篇 |
2016年 | 1173篇 |
2015年 | 924篇 |
2014年 | 1489篇 |
2013年 | 4668篇 |
2012年 | 2569篇 |
2011年 | 3840篇 |
2010年 | 3097篇 |
2009年 | 3718篇 |
2008年 | 3893篇 |
2007年 | 4079篇 |
2006年 | 3689篇 |
2005年 | 3325篇 |
2004年 | 3177篇 |
2003年 | 3024篇 |
2002年 | 2670篇 |
2001年 | 2970篇 |
2000年 | 2718篇 |
1999年 | 3075篇 |
1998年 | 9437篇 |
1997年 | 6154篇 |
1996年 | 4761篇 |
1995年 | 3162篇 |
1994年 | 2787篇 |
1993年 | 2723篇 |
1992年 | 1628篇 |
1991年 | 1593篇 |
1990年 | 1518篇 |
1989年 | 1322篇 |
1988年 | 1172篇 |
1987年 | 861篇 |
1986年 | 887篇 |
1985年 | 916篇 |
1984年 | 803篇 |
1983年 | 698篇 |
1982年 | 699篇 |
1981年 | 681篇 |
1980年 | 567篇 |
1979年 | 476篇 |
1978年 | 414篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 276篇 |
1973年 | 256篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Gaussian multiterminal source coding 总被引:4,自引:0,他引:4
Oohama Y. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1997,43(6):1912-1923
In this paper, we consider the problem of separate coding for two correlated memoryless Gaussian sources. We determine the rate-distortion region in the special case when one source provides partial side information to the other source. We also show that the previously obtained inner region of the rate-distortion region is partially tight. A rigorous proof of the direct coding theorem is also given 相似文献
993.
A wide variety of speech recognition distortion measures have been proposed and tested, including some especially effective ones. It is shown that there is a general framework, based on the concepts of information theory, linking most of these measures. The distortion measure between any two speech spectra can be defined in terms of the distortions between the associated probability distributions. This general framework defines three broad families of distortion measures for speech recognition and provides a consistent way of combining the energy and the spectral information of a phonetic event. In addition, the cepstral-domain representation for several distortion measures is derived, allowing comparison of these measures in a domain that also yields convenient equations for their practical implementation 相似文献
994.
A practical configuration for an amplified distributed reflective N -star coupler using 2×2 3-dB fiber couplers and minimum numbers of erbium-doped fibers, pump lasers, and standard fibers is presented. The constitution and characteristics of this coupler are investigated. Besides a tremendous amount of saving of the required standard fibers, this distributed coupler is more efficient, more reliable, more flexible for future expansion, and more cost-effective for application in optical networks 相似文献
995.
The propagation and dispersion characteristics of picosecond electrical pulses in a suspended coplanar waveguide (SCPW) are investigated, and it is shown that the SCPW is a very promising transmission structure for ultrashort pulses. Numerical results for the modal dispersion of the SCPW are presented and compared to those of the conventional CPW, and a field-coupling theory is used to explain the evolution in the dispersion behavior. An evaluation based on the numerical analysis shows that a SCPW with properly controlled dispersion can exhibit a five times improvement in pulse transmission capability compared to the conventional CPW. Both computer simulations and experimental measurements show a substantial suppression in pulse distortion as well, compared to conventional CPWs 相似文献
996.
Y Segawa N Takigawa K Mandai Y Maeda I Takata N Fujimoto K Jinno 《Canadian Metallurgical Quarterly》1997,16(2-3):229-238
Serum p53 protein levels were measured in 36 patients with small cell lung cancer (SCLC) and 35 patients with benign lung diseases in order to evaluate the relationship of these levels to clinicopathological features of SCLC. Serum levels of p53 protein were measured by an enzyme-linked immunosorbent assay, p53 protein level was 23.92 +/- 6.78 pg/ml in patients with SCLC, and similar to that (17.47 +/- 2.86 pg/ml) in patients with benign lung diseases. By the clinical stage of SCLC, the mean level of p53 protein was 16.68 +/- 4.62 pg/ml in 21 patients with limited disease, and lower than that in 15 patients with extensive disease (34.05 +/- 14.84 pg/ml) (P = 0.23). The levels of p53 protein were not correlated with age, smoking index, or presence of cancer history for patients with SCLC. However, immunohistochemical examination disclosed a mild correlation between the expression of p53 protein by SCLC tumor and p53 protein serum level (r = 0.45, P = 0.02). Two patients with SCLC had an elevated serum level of p53 protein (> 2 S.D. above the mean for benign lung diseases). However, measurement of p53 protein serum level was not found to be clinically useful for detection of SCLC. 相似文献
997.
Segman J. Rubinstein J. Zeevi Y.Y. 《IEEE transactions on pattern analysis and machine intelligence》1992,14(12):1171-1183
A method for the analysis of deformed patterns is presented and analyzed. The image is transformed into a new set of coordinates in which the deformation has a particular simple form. A number of deformations are considered. The practical implementation of the method is discussed. Similar aspects of biological vision are also considered 相似文献
998.
The 3DP (3-Dimensional Processor), a parallel-computing architecture that targets problems that have a 3-D numerical structure and require numerous calculations on 3-D vectors, is described. The 3DP architecture differs from traditional scalar architectures in that it operates directly on vectors. It differs from general parallel architectures in that it can solve problems that predict the behavior of highly coupled systems, and it differs from vector architectures in that it runs efficiently on length-3 vectors. Object-oriented programming on the 3DP and programming the 3DP in C++ are discussed. 3DP performance is reviewed, and the current implementation of the 3DP architecture, as an attached processor that plugs directly into Sun host VMEbus, is described 相似文献
999.
1000.
F Davodeau MA Peyrat A Necker R Dominici F Blanchard C Leget J Gaschet P Costa Y Jacques A Godard H Vie A Poggi F Romagné M Bonneville 《Canadian Metallurgical Quarterly》1997,158(12):5603-5611
Several studies have demonstrated the existence of a murine NK1.1+ alphabeta T cell subset expressing V alpha14+ TCR alpha-chains with highly conserved invariant junctional sequences and able to secrete Th2 cytokines when exposed to CD1+ stimulator cells. In humans, alphabeta T cells carrying invariant V alpha24+ TCR alpha-chains highly homologous to those expressed by murine NK1.1 cells have been recently described. Here we show that these cells (referred to as V alpha24inv T cells) and murine NK1.1+ alphabeta T cells resemble each other in several ways. First, like their murine counterparts, T cells expressing high levels of V alpha24inv TCRs can be either CD4- CD8- double negative (DN) or CD4+, but they never express heterodimeric CD8 molecules. Second, most V alpha24inv T cells are brightly stained by NKRP1-specific mAb but not by mAb directed against other type II transmembrane proteins of the NK complex. Third, DN and particularly CD4+ V alpha24inv T cells are greatly enriched for IL-4 producers. The concomitant expression of highly conserved TCRs of a particular set of NK markers and of Th2 cytokines in human and murine alphabeta T cells suggests a coordinate acquisition of these phenotypic and functional properties. Furthermore, the relatively high frequency of human V alpha24inv T cells, which are presently shown to represent on average 1/500 PBL, and the high interindividual variations of the size of this cell subset under physiologic conditions go for a major role played by alphabeta T cells carrying invariant TCR in a large array of immune responses. 相似文献