全文获取类型
收费全文 | 11685篇 |
免费 | 851篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 130篇 |
综合类 | 8篇 |
化学工业 | 2688篇 |
金属工艺 | 431篇 |
机械仪表 | 567篇 |
建筑科学 | 272篇 |
矿业工程 | 10篇 |
能源动力 | 391篇 |
轻工业 | 1157篇 |
水利工程 | 37篇 |
石油天然气 | 21篇 |
无线电 | 1593篇 |
一般工业技术 | 2350篇 |
冶金工业 | 1698篇 |
原子能技术 | 130篇 |
自动化技术 | 1074篇 |
出版年
2023年 | 96篇 |
2022年 | 169篇 |
2021年 | 280篇 |
2020年 | 206篇 |
2019年 | 262篇 |
2018年 | 298篇 |
2017年 | 343篇 |
2016年 | 401篇 |
2015年 | 352篇 |
2014年 | 498篇 |
2013年 | 775篇 |
2012年 | 661篇 |
2011年 | 825篇 |
2010年 | 594篇 |
2009年 | 561篇 |
2008年 | 561篇 |
2007年 | 434篇 |
2006年 | 350篇 |
2005年 | 326篇 |
2004年 | 318篇 |
2003年 | 303篇 |
2002年 | 262篇 |
2001年 | 213篇 |
2000年 | 196篇 |
1999年 | 226篇 |
1998年 | 552篇 |
1997年 | 395篇 |
1996年 | 241篇 |
1995年 | 174篇 |
1994年 | 175篇 |
1993年 | 191篇 |
1992年 | 114篇 |
1991年 | 97篇 |
1990年 | 93篇 |
1989年 | 93篇 |
1988年 | 67篇 |
1987年 | 53篇 |
1986年 | 57篇 |
1985年 | 76篇 |
1984年 | 68篇 |
1983年 | 45篇 |
1982年 | 45篇 |
1981年 | 45篇 |
1980年 | 42篇 |
1979年 | 38篇 |
1978年 | 32篇 |
1977年 | 57篇 |
1976年 | 101篇 |
1975年 | 41篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We have previously observed that bovine papillomavirus type 1 (BPV-1) induces the appearance of five cellular proteins in C127 mouse fibroblasts, four of which appear to arise by altered processing of resident endoplasmic reticulum proteins. Studies of various cell lines revealed that expression of the 3' end of the BPV early region was sufficient for induction of these changes. To identify the BPV gene responsible, we have utilized the simian virus 40 (SV40)/BPV-1 recombinant virus Pava-1, which expresses the 3' end of the BPV early region behind an SV40 early promoter. C127 cells infected with Pava-1 for 48 h show the expected BPV-associated alterations, as do cells infected with Pava constructs mutated in the E5 or E2 genes. However, a mutation in the start codon of a previously ignored open reading frame extending from nucleotides 4013 to 4170 (E5B) eliminated the BPV-associated changes. Similar results were obtained with COS cells infected with the Pava mutants and C127 cells transformed by full-length mutated BPV. Despite its influence on the processing of cellular endoplasmic reticulum proteins, this mutation in E5B did not alter BPV-transforming efficiency or the ability of transformants to form colonies in soft agar. The E5B open reading frame encodes a hydrophobic 52-amino-acid polypeptide that shares structural similarities with HPV6 E5A and HPV16 E5. Speculations on a role for E5B in the viral life cycle are discussed. 相似文献
32.
33.
Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement. 相似文献
34.
Previous research has shown that a combination of feed restriction and dietary 1,3-butanediol starting at 14 d post-partum resulted in fatty liver and ketosis. Sixteen multiparous Holstein cows were used to determine effects of feed restriction or 1,3-butanediol as separate treatments. Treatments during d 14 to 42 postpartum were 1) control (ad libitum intake), 2) 20% feed restriction, or 3) control plus dietary 1,3-butanediol (5.5% of DM). From d 43 to 56, cows assigned to treatments 2 and 3 received a combination of feed restriction and butanediol. One cow on treatment 2 developed ketosis, but not fatty liver, after only 4 d of feed restriction. No other cows developed fatty liver or ketosis. Both treatments decreased milk production compared with controls. Feed restriction increased the extent of negative energy balance and caused transient increases in concentrations of NEFA, acetate, and beta-hydroxybutyrate in plasma. Concentrations of beta-hydroxybutyrate and insulin in plasma were increased by butanediol, which is a potent ketone body precursor. Concentration of glycogen in liver was less in feed-restricted cows, whereas glycogen and total lipid were greater in cows given butanediol separately. Gluconeogenic capacity of liver slices was not different among groups. Addition of 1,3-butanediol to in vitro incubation media decreased oxidation of propionate to CO2. Neither feed restriction nor dietary 1,3-butanediol as separate treatments induced the fatty liver and ketosis observed in earlier experiments in which the two treatments were given together. 相似文献
35.
Mansfield C. Newson D.J. Birdsall P. Quayle J.A. Young R. MacBean M.D.A. Merrett R.P. 《Electronics letters》1991,27(18):1632-1633
Four-channel receiver arrays have been fabricated by monolithically integrating diffused InGaAs JFET-based electronics with InGaAs pin photodiodes. Cascode and simple inverter transimpedance amplifier circuits have been produced, both of which use a micro-FET as a tunable feedback element to vary bandwidth between 20 and 800 MHz. A sensitivity of -28.2 dBm was achieved at 1.25 Gbit/s with crosstalk between adjacent channels of -50 dB (electrical).<> 相似文献
36.
Coating of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO3 (SRO) metallic oxide electrodes on SrTiO3 (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed. 相似文献
37.
38.
39.
Woo Yong Sung Seung Min Lee Wal Jun Kim Jong Girl Ok Ho Young Lee Yong Hyup Kim 《Diamond and Related Materials》2008,17(6):1003-1007
Complementary electroplating combined with electrophoresis enhanced the field emission characteristics of emitters by improving the adhesions between CNT emitters and substrate. The emitting current of the CNT emitters prepared by our combined method increased nine times higher than that of CNT emitters prepared by electrophoresis only, since electroplating improved the adhesion of CNT emitters. During the life-time measurement for 10 h, the emitting current of CNT emitters fabricated by electrophoresis only was drastically decreased to 13% of the initial current, while that prepared by the combination of electrophoresis and successive electroplating decreased to 64% of the initial current. We suggest that our method is a promising approach for the efficient fabrication of reliable CNT emitters. 相似文献
40.