全文获取类型
收费全文 | 213067篇 |
免费 | 3087篇 |
国内免费 | 630篇 |
专业分类
电工技术 | 3617篇 |
综合类 | 159篇 |
化学工业 | 32302篇 |
金属工艺 | 8312篇 |
机械仪表 | 6314篇 |
建筑科学 | 5361篇 |
矿业工程 | 1322篇 |
能源动力 | 5595篇 |
轻工业 | 19290篇 |
水利工程 | 2398篇 |
石油天然气 | 4082篇 |
武器工业 | 8篇 |
无线电 | 23715篇 |
一般工业技术 | 42283篇 |
冶金工业 | 38684篇 |
原子能技术 | 5162篇 |
自动化技术 | 18180篇 |
出版年
2021年 | 2118篇 |
2020年 | 1460篇 |
2019年 | 1921篇 |
2018年 | 3115篇 |
2017年 | 3135篇 |
2016年 | 3300篇 |
2015年 | 2166篇 |
2014年 | 3631篇 |
2013年 | 9818篇 |
2012年 | 5887篇 |
2011年 | 8000篇 |
2010年 | 6277篇 |
2009年 | 7035篇 |
2008年 | 7058篇 |
2007年 | 7078篇 |
2006年 | 6047篇 |
2005年 | 5629篇 |
2004年 | 5328篇 |
2003年 | 5189篇 |
2002年 | 4808篇 |
2001年 | 4850篇 |
2000年 | 4758篇 |
1999年 | 4893篇 |
1998年 | 11948篇 |
1997年 | 8465篇 |
1996年 | 6670篇 |
1995年 | 4834篇 |
1994年 | 4400篇 |
1993年 | 4204篇 |
1992年 | 3288篇 |
1991年 | 3140篇 |
1990年 | 2923篇 |
1989年 | 2995篇 |
1988年 | 2869篇 |
1987年 | 2436篇 |
1986年 | 2351篇 |
1985年 | 2760篇 |
1984年 | 2535篇 |
1983年 | 2377篇 |
1982年 | 2127篇 |
1981年 | 2244篇 |
1980年 | 2059篇 |
1979年 | 2137篇 |
1978年 | 2141篇 |
1977年 | 2402篇 |
1976年 | 3247篇 |
1975年 | 1846篇 |
1974年 | 1776篇 |
1973年 | 1792篇 |
1972年 | 1454篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
K. A. Taylor J. B. Vander Sande M. Cohen 《Metallurgical and Materials Transactions A》1993,24(11):2585-2588
Y. OHMORI and I. TAMURA:Metall. Trans. A, 1992, vol. 23A, 相似文献
992.
Low-loaded vanadia-titania catalysts have been prepared by impregnation of titania P-25 (Degussa). The catalysts were characterized by X-ray diffraction, specific surface area and porosity assessment by nitrogen adsorption at 77 K. For very low vanadia contents the absence of surface acid Brønsted sites leads to dimerization on surface acid Lewis sites, whereas the presence of surface acid Bransted sites when the vanadia content is increased leads to oxidation to carbonyl and carboxylate species. 相似文献
993.
A new scheme based on using an IIR design algorithm is presented to demultiplex critically sampled QPSK channels for onboard processing (OBP) satellites. Comparisons with an existing nonrecursive (FIR) transmultiplexer (TMUX) show that the presented IIR TMUX is also a suitable candidate for consideration in future OBP applications 相似文献
994.
995.
D Crenesse B Fossat F Craffa P Chaland J Porthe-Nibelle JC Poiree J Gugenheim 《Canadian Metallurgical Quarterly》1994,31(6):540-548
Isolated hepatocytes from the rat were used to assess the maintenance of liver cell function in relation to the composition of the preservation medium. After separation by collagenase, they were incubated in Krebs-Ringer-Bicarbonate medium (KRB), Euro-Collins (EC), or University of Wisconsin (UW) solutions. Potassium influx, cell volume, and transaminase release were measured in cells freshly separated from control livers or from livers preserved in vitro up to 12 h in these media or having undergone orthotopic liver transplantation (OLT). While ion exchange levels were retained in all media, cells shrank significantly in UW but were able to restore their volume after 3 h of liver preservation. With regard to in vivo conditions, UW appears to be the best medium to prevent edema and to maintain more stable potassium exchange and enzyme production. These results are of value for liver transplantation in humans. 相似文献
996.
A Guhlmann K Krauss F Oberdorfer T Siegel PH Scheuber J Müller B Csuk-Gl?nzer S Ziegler H Ostertag D Keppler 《Canadian Metallurgical Quarterly》1995,21(6):1568-1575
N-Acetyl-leukotriene E4 has been identified as an endogenous, biologically less active cysteinyl leukotriene metabolite in rodents and humans. To evaluate the ratio of hepatobiliary to renal elimination of leukotrienes noninvasively by positron emission tomography (PET), we synthesized N-[11C]acetyl-leukotriene E4 by chemical N-acetylation of leukotriene E4. After the intravenous injection of N-[11C]acetyl-leukotriene E4 in normal rats and monkey, uptake by the liver and subsequent excretion into bile were largely responsible for its rapid elimination from blood. In the Cynomolgus monkey, renal excretion of the leukotriene into urine was of additional quantitative importance. Kinetic modeling indicated a mean transit time through the liver of 17 minutes and 34 minutes in rat and monkey, respectively; the corresponding hepatic excretion half-times amounted to 8.5 minutes and 16 minutes. In a mutant rat strain deficient in the hepatobiliary excretion of cysteinyl leukotrienes across the canalicular membrane, the apparent mean liver transit time was 54 minutes, and the hepatic excretion half-time was 29 minutes, indicating prolonged organ storage and metabolism. After transport from the liver back into the circulating blood of omega-oxidized and beta-oxidized metabolites of N-[11C]acetyl-leukotriene E4, renal excretion compensated for the impairment of hepatobiliary elimination in the transport mutant. Metabolite analyses in urine after intravenous injection of N-[3H]acetyl-leukotriene E4 indicated the extensive inactivation of N-acetyl-leukotriene E4 by beta-oxidation from the omega-end in the mutants. A similar shift from hepatobiliary to renal cysteinyl leukotriene elimination was monitored in rats with cholestasis due to bile duct obstruction.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
997.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 12, pp. 8–10, December, 1993. 相似文献
998.
999.
The growth structure of MgF2 and NdF3 films grown on polished CaF2(111) substrates deposited by molecular beam deposition has been investigated using transmission electron microscopy (TEM) of microfractographical and surface replications as well as cross-sectional TEM, atomic force microscopy, packing density, and absorption measurements. It has been shown that by taking advantage of ultrahigh vacuum environments and a special stratification property of MgF2 and NdF3 films, the preparation of nanocrystalline films of high packing density and low optical absorption is possible at a substrate temperature of 425 K. 相似文献
1000.
Iron pyrite films prepared by sulfur vapor transport 总被引:4,自引:0,他引:4
Iron films deposited via thermal evaporation, with a thickness between 100 and 250 nm, were converted into FeS2 by open sulfur transport using nitrogen as a gas vector. The films thus obtained constituted a single pyrite phase and were optically highly absorbing. The sulfurization process was optimized. As a result, sample temperature and conversion time were found to be the major determining parameters. The films were characterized using several methods. The crystallinity and phase identification were determined by X-ray diffractometry. Scanning electron microscopy showed a homogeneous surface of both iron and pyrite layers. Optical transmission measurements confirmed the highly absorbing character of FeS2 and allowed the determination of direct (1.35 eV) and indirect (0.82 eV) transitions. 相似文献