全文获取类型
收费全文 | 102886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 | 10493篇 |
金属工艺 | 5456篇 |
机械仪表 | 3186篇 |
建筑科学 | 2033篇 |
矿业工程 | 159篇 |
能源动力 | 2959篇 |
轻工业 | 6061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 | 7341篇 |
出版年
2022年 | 452篇 |
2021年 | 698篇 |
2020年 | 522篇 |
2019年 | 676篇 |
2018年 | 1130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 | 4080篇 |
2006年 | 3689篇 |
2005年 | 3325篇 |
2004年 | 3177篇 |
2003年 | 3025篇 |
2002年 | 2670篇 |
2001年 | 2971篇 |
2000年 | 2719篇 |
1999年 | 3075篇 |
1998年 | 9438篇 |
1997年 | 6153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 | 1171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 0 毫秒
941.
942.
Ito M. Miki T. Hosotani S. Kumamoto T. Yamashita Y. Kijima M. Okuda T. Okada K. 《Solid-State Circuits, IEEE Journal of》1994,29(12):1531-1536
A 10 bit CMOS A/D converter with 3 V power supply has been developed for being integrated into system VLSI's. In this A/D converter, redundant binary encoders named “twin encoders” enhance tolerance to substrate noise, together with employing differential amplifiers in comparators. The bias circuit using a replica of the amplifier is developed for biasing differential comparators with 3 V power supply. Subranging architecture along with a multilevel tree decoding structure improves dynamic performance of the ADC at 3 V power supply. The A/D converter is fabricated in double-polysilicon, double-metal, 0.8 μm CMOS technology. The experimental results show that the ADC operates at 20 MS/s and the twin encoders suppress the influence of substrate noise effectively. This ADC has a single power supply of 3 V, and dissipates 135 mW at 20 MS/s operation 相似文献
943.
Spreading depression (SD) is known to be involved in the N-methyl-D-aspartate receptor-mediated neuronal damage. In urethane-anesthetized rats, we examined the release of adenosine and glutamate during SD induced by microdialysis of high K+ perfusate through the hippocampal CA1 area. The effects of endogenous adenosine upon SD were studied by applying an adenosine antagonist, theophylline (1 mM) and by a simultaneous application of adenosine uptake blockers, dipyridamole (DPR) (100 microM) and nitrobenzylthioinosine (NBI) (50 microM). The dialysates were sampled every 5 or 10 min and analyzed by HPLC. SD was identified by flattening of background EEg and disappearance of population spikes recorded from the pyramidal cell layer of CA1 area by a glass microelectrode. Adenosine and glutamate release was enhanced significantly in association with the occurrence of SD. Theophylline increased the release of glutamate and the incidence of SD and decreased the latency of the SD occurrence. DPR+NBI decreased the release of glutamate and the occurrence of SD, but increased extracellular adenosine concentration. The effects of DPR+NBI were blocked by application of a selective antagonist of adenosine A1 receptor, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM). These findings suggest that endogenous adenosine exerts inhibitory influences upon the development of SD and the glutamate release through the A1 receptor in rat hippocampus. 相似文献
944.
945.
G Pillemer R Yelin M Epstein L Gont Y Frumkin JK Yisraeli H Steinbeisser A Fainsod 《Canadian Metallurgical Quarterly》1998,74(1-2):133-143
Patterning of the marginal zone in the Xenopus embryo has been attributed to interactions between dorsal genes expressed in the organizer and ventral-specific genes. In this antagonistic interplay of activities, BMP-4, a gene that is not expressed in the organizer, provides a strong ventralizing signal. The Xenopus caudal type homeobox gene, Xcad-2, which is expressed around the blastopore with a gap over the dorsal lip, was analyzed as part of the ventral signal. Xcad-2 was shown to efficiently repress during early gastrula stages the dorsal genes gsc, Xnot-2, Otx-2, XFKH1 and Xlim-1, while it positively regulates the ventral genes, Xvent-1 and Xvent-2, with Xpo exhibiting a strong positive response to Xcad-2 overexpression. Xcad-2 was also capable of inducing BMP-4 expression in the organizer region. Support for a ventralizing role for Xcad-2 was obtained from co-injection experiments with the dominant negative BMP receptor which was used to block BMP-4 signaling. Under lack-of-BMP-signaling conditions Xcad-2 could still regulate dorsal and ventral gene expression and restore normal development, suggesting that it can act downstream of BMP-4 signaling or independently of it. Xcad-2 could also inhibit secondary axis formation and dorsalization induced by the dominant negative BMP receptor. Xcad-2 was also shown to efficiently reverse the dorsalizing effects of LiCl. These results place Xcad-2 as part of the ventralizing gene program which acts during early gastrula stages and can execute its ventralizing function in the absence of BMP signaling. 相似文献
946.
After an i.p. transplantation of an allogeneic tumor (Meth A) to C57BL/6 mice, a macrophage (M phi)-rich, non-T, non-NK cell population is induced as the major infiltrate and cytotoxic cells. We here evaluated the role of the M phi s in the rejection of allografted Meth A cells and characterized the M phi s in comparison with other well-known M phi s. At all time intervals after transplantation, the highest cytotoxic activities against Meth A tumor were obtained with the M phi-rich population. In addition, the lymphocyte-rich population had a significant but low cytotoxic activity, whereas two other population types, granulocytes and large granular cells, were inactive. When the M phi-rich or the T cell-depleted M phi-rich population was i.p. transplanted simultaneously with Meth A cells into untreated C57BL/6 mice, the tumor cells were rejected without growth. After specific elimination of M phi s by in vivo application of dichloromethylene diphosphonate-containing liposomes, the cytotoxic activity against Meth A cells was hardly induced at the transplantation site of Meth A cells and the allografted Meth A tumor continued to grow, indicating that a type of M phi is the effector cell essential for the rejection. In contrast to other well-known M phi s, the cytotoxic activity against Meth A cells was cell-to-cell contact dependent and soluble factor (e.g., NO and TNF-alpha) independent. Moreover, the cytotoxic activity of the M phi s (H-2b) against 51Cr-labeled Meth A (H-2d) cells was inhibited by the addition of unlabeled H-2d, but not H-2b, H-2k or H-2h, lymphoblasts as well as Meth A cells, implying the specific interaction of the M phi s with H-2d cells. 相似文献
947.
Y. Murat Elin Mehmet Saak 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(2):174-180
This paper presents the results of urease immobilization onto methacrylic acid–acrylamide grafted poly(ethyleneterephthalate) fibres. The graft yield strongly affected the maximum activity of the immobilized enzyme up to a value of 70·2%. Higher grafting caused a decline in urease activity and led to the degradation of the fibres. The minor changes observed in Km and Vmax demonstrated that the conformational changes existed during immobilization were not extensive. However, 70·2% methacrylic acid–acrylamide-g-fibres containing urease were more stable towards acidic and alkaline pH, high temperature and storage conditions compared with free enzyme. Apart from the increase in stability to heat inactivation, the initial enzymatic activity of the urease–fibre system remained almost unchanged even after 40 repeated assays corresponding to 10 h of operation in 4 months, indicating the excellent durability of the system. 相似文献
948.
A novel diagram which describes the condition of 3 dB coupler is proposed. Using the proposed diagram, the design of a wavelength-flattened 3 dB directional coupler composed of a uniform coupled waveguide is investigated. Normalized waveguide parameters are introduced to characterize a five-layer planar waveguide. This enables us to generalize the discussion and to reduce the number of parameters required for characterizing a coupled waveguide. A broadband 3 dB coupler having 50±5% coupling ratio over a wavelength range of 1.1-1.7 μm is designed 相似文献
949.
950.
Y.X. Gan 《Materials and Manufacturing Processes》1994,9(2):263-280
This paper concerns electrolytic metallic coatings for carbon fibers and the related processes. Plating bath design, electrolyte selection and other aspects were investigated. Experimental results especially in copper electroplating show that the uniformity of metallic coatings on carbon fibers can be improved by the modification of plating bath and the selection of electrolytes. Thus continuous and uniform metallic coatings can be obtained on carbon fibers, even if the cross section of carbon fibers has irregular shape. Polarization tests on different copper baths was performed. Electrodeposition of other metallic layers such as nickel, cobalt, and copper/tin duplex layer was also introduced. A process of two or more than two plating steps in which different electrolytes may be used for same metal deposition was proposed to expedite the coating procedure 相似文献