全文获取类型
收费全文 | 358258篇 |
免费 | 29318篇 |
国内免费 | 15291篇 |
专业分类
电工技术 | 21542篇 |
技术理论 | 25篇 |
综合类 | 22511篇 |
化学工业 | 58162篇 |
金属工艺 | 19253篇 |
机械仪表 | 22103篇 |
建筑科学 | 28181篇 |
矿业工程 | 9337篇 |
能源动力 | 10632篇 |
轻工业 | 24036篇 |
水利工程 | 6642篇 |
石油天然气 | 18930篇 |
武器工业 | 2595篇 |
无线电 | 44209篇 |
一般工业技术 | 43713篇 |
冶金工业 | 18443篇 |
原子能技术 | 3822篇 |
自动化技术 | 48731篇 |
出版年
2024年 | 1224篇 |
2023年 | 5443篇 |
2022年 | 10055篇 |
2021年 | 14506篇 |
2020年 | 10642篇 |
2019年 | 8665篇 |
2018年 | 9885篇 |
2017年 | 11196篇 |
2016年 | 10152篇 |
2015年 | 13610篇 |
2014年 | 17630篇 |
2013年 | 22112篇 |
2012年 | 23521篇 |
2011年 | 25455篇 |
2010年 | 22201篇 |
2009年 | 21149篇 |
2008年 | 20500篇 |
2007年 | 19241篇 |
2006年 | 19527篇 |
2005年 | 16720篇 |
2004年 | 11247篇 |
2003年 | 9716篇 |
2002年 | 8995篇 |
2001年 | 8003篇 |
2000年 | 8062篇 |
1999年 | 8969篇 |
1998年 | 8028篇 |
1997年 | 6645篇 |
1996年 | 6161篇 |
1995年 | 5070篇 |
1994年 | 4126篇 |
1993年 | 3093篇 |
1992年 | 2400篇 |
1991年 | 1881篇 |
1990年 | 1442篇 |
1989年 | 1198篇 |
1988年 | 981篇 |
1987年 | 629篇 |
1986年 | 523篇 |
1985年 | 385篇 |
1984年 | 310篇 |
1983年 | 221篇 |
1982年 | 219篇 |
1981年 | 186篇 |
1980年 | 175篇 |
1979年 | 129篇 |
1978年 | 89篇 |
1977年 | 106篇 |
1976年 | 118篇 |
1975年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 921 毫秒
961.
Tramadol hydrochloride is a centrally acting synthetic analgesic in widespread clinical use. Despite different degrees of opioid-like characteristics in preclinical tests, it is characterized by lack of full naloxone reversibility or naloxone-precipitated withdrawal in humans. To investigate this apparent discrepancy, the present study measured the affinity of tramadol (and its enantiomers) and an active O-desmethyl metabolite (M1) (and its enantiomers) to cloned human opioid receptors of the mu, delta and kappa type stably expressed in HN9.10 neuroblastoma cells. At mu sites, the Ki values for tramadol, its (+) and (-) enantiomers, M1, and its (+) and (-) enantiomers were 17000, 15700, 28800, 3190, 153 and 9680 nM, respectively, compared to 7.1 nM for morphine. These results are consistent with the suggestion of a non-opioid contribution to the clinical profile of tramadol. 相似文献
962.
M Yaono R Hasegawa K Kato J Kimura C Lin M Tada T Shirai 《Canadian Metallurgical Quarterly》1996,98(2):145-149
We attempted to purify endogenous growth factors of chick embryonal retinal pigment epithelial cells from bovine neural retina. Ammonium sulfate precipitation, gel filtration, and anion exchange column chromatography were used. Though only partially purification, bovine retinal extract had two effects, growth and transformation, on chick embryonal pigment epithelial cells. We think that these purified factors may be novel from the estimation of their molecular weight by gel filtration. 相似文献
963.
964.
A technique for SiO2 formation by liquid-phase deposition (LPD) at nearly room temperature for low-temperature processed (LTP) polysilicon thin-film transistor (poly-Si TFT) was developed. LPD SiO2 film with a lower P-etch rate shows a dense structure. LPD SiO2 also exhibits good electrical characteristics. LTP poly-Si thin-film transistors (TFTs) with LPD SiO 2 as the gate insulator have been fabricated and investigated. Their characteristics indicate performance adequate for their use as pixel transistors in liquid crystal displays (LCDs) 相似文献
965.
通过对抽样检验方法的研究,确立了区间估计的下限公式,用来在已知样本值的情况下确定导弹单发命中概率出现在该区间内的置信水平和精确度。 相似文献
966.
Ferrite is a potential sorbent for flue gases such as CO2, H2S and SO2. This paper discusses the adsorption and decomposition of CO2 into carbon by hydrogen-activated waste ferrites prepared from Berkeley Pit acid mine water (Butte, MT). The decomposition effectiveness of these waste ferrites was studied at 300 °C and compared with the synthetic magnetite obtained from ferrous sulfate solution in our laboratory. The decomposition was measured by two methods: indirectly by measuring the adsorption rate of CO2 and directly by analysing the carbon deposited on the samples. The results indicated that the mixed waste ferrite had good affinity for the adsorption and decomposition. The CO2 decomposition data of both sorbents fitted the first-order reaction kinetics. Even though the surface area of the magnetite was higher than that of waste ferrite, the CO2 decomposition rate of the waste ferrite was estimated to be 2.5 times higher than that of magnetite under identical conditions. The carbon analysis deposited on the sample indicated that the CO2 was 100% decomposed into carbon and other carbon/hydrogen compounds by the waste ferrite, whereas the conversion was 43% by the magnetite. In terms of specific adsorption of carbon, ferrite was three to five times more efficient than magnetite. 相似文献
967.
旋风分离器是一种应用离心力进行粉体分离的设备。低温粉碎系统应用它分离粉体并起集粉作用。它的效率决定了物质回收率。本文从离心加速度与重力加速度的比值,筒体的高低,筒体直径,进口速度叙述对分离器效率的影响。着重叙述筒体直径确定方法,以及我们设计造长筒形旋风分离器的具体结构和令人满意的试验结果。 相似文献
968.
969.
970.
Transdermal Iontophoretic Delivery of Thyrotropin-Releasing Hormone Across Excised Rabbit Pinna Skin
Enhanced transport of a model peptide drug thyrotropin-releasing hormone (TRH), a tripeptide of molar mass 362 g and a pKa 6.2, through excised rabbit pinna skin was achieved by means of iontophoresis with continuous current or monophase periodically pulsed current. The resulting flux in the steady state was proportional to the applied current density. In the transdermal iontophoretic delivery of TRH, the pulsed iontophoretic flux exceeded that obtained with a continuous current. At a low ionic strength, an increased degree of protonation in TRH increased the rate of permeation. The flux of TRH in a buffer at pH 4 is greater than that at pH 8 when the ionic strength is 0.1 M. At a greater ionic strength, the trend is reversed. The enhanced flux of unprotonated TRH during transdermal iontophoresis is attributed largely to electro-osmotic volume flow. An increased rate of permeation of TRH crossing the skin is achieved at low ionic strength, moderate pH, and a large duly cycle of current; the frequency of pulsed current had no significant influence on the rate of transdermal iontophoretic delivery of TRH. 相似文献