全文获取类型
收费全文 | 466852篇 |
免费 | 11706篇 |
国内免费 | 5614篇 |
专业分类
电工技术 | 13163篇 |
技术理论 | 4篇 |
综合类 | 5523篇 |
化学工业 | 68609篇 |
金属工艺 | 20099篇 |
机械仪表 | 17846篇 |
建筑科学 | 13666篇 |
矿业工程 | 4462篇 |
能源动力 | 13281篇 |
轻工业 | 33066篇 |
水利工程 | 5862篇 |
石油天然气 | 11045篇 |
武器工业 | 1007篇 |
无线电 | 56934篇 |
一般工业技术 | 88906篇 |
冶金工业 | 77601篇 |
原子能技术 | 10043篇 |
自动化技术 | 43055篇 |
出版年
2022年 | 4948篇 |
2021年 | 7170篇 |
2020年 | 5322篇 |
2019年 | 5616篇 |
2018年 | 8494篇 |
2017年 | 8758篇 |
2016年 | 8944篇 |
2015年 | 7361篇 |
2014年 | 10796篇 |
2013年 | 24312篇 |
2012年 | 16568篇 |
2011年 | 20605篇 |
2010年 | 16971篇 |
2009年 | 18330篇 |
2008年 | 18536篇 |
2007年 | 17800篇 |
2006年 | 16150篇 |
2005年 | 14263篇 |
2004年 | 12577篇 |
2003年 | 11791篇 |
2002年 | 11112篇 |
2001年 | 10838篇 |
2000年 | 10149篇 |
1999年 | 10342篇 |
1998年 | 24800篇 |
1997年 | 17140篇 |
1996年 | 13195篇 |
1995年 | 9867篇 |
1994年 | 8600篇 |
1993年 | 8571篇 |
1992年 | 6228篇 |
1991年 | 5799篇 |
1990年 | 5770篇 |
1989年 | 5379篇 |
1988年 | 5097篇 |
1987年 | 4456篇 |
1986年 | 4333篇 |
1985年 | 4826篇 |
1984年 | 4432篇 |
1983年 | 4003篇 |
1982年 | 3665篇 |
1981年 | 3743篇 |
1980年 | 3444篇 |
1979年 | 3330篇 |
1978年 | 3336篇 |
1977年 | 3750篇 |
1976年 | 4849篇 |
1975年 | 2850篇 |
1974年 | 2665篇 |
1973年 | 2732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
A Gopal G Li Mandri DL King C Marboe S Homma 《Canadian Metallurgical Quarterly》1994,105(6):1885-1887
Cardiac papillary fibroelastomas are unusual, frond-like growths typically found on cardiac valves, diagnosed incidentally on autopsy or cardiac surgery, but rarely during life. We report a rare case of an aortic valve papillary fibroelastoma detected by transthoracic echocardiography and confirmed by histologic study. 相似文献
182.
Ubiquitin has been shown by immunohistochemical studies to be a component of many of the filamentous inclusion bodies that are known in neuropathology. In the current study, we examined the expression of ubiquitin in 14 cases of typical inclusion body myositis, in skeletal muscle specimens from four cases of typical amyotrophic lateral sclerosis, and in muscle specimens from three normal controls. In the cases of inclusion body myositis, rimmed vacuoles were ubiquitin immunoreactive in all cases. Intrasarcoplasmic inclusions were positive in the nine cases that had them. In four cases, there were positive intranuclear inclusions, and in seven, there was homogeneous staining of nuclei. Atrophic fibers and necrotic fibers were positive in 11 and nine cases, respectively. In the cases of amyotrophic lateral sclerosis, atrophic fibers were positive in three cases, and focal nuclear staining was seen in two. In one of the three control cases, a few atrophic fibers had faint sarcoplasmic positivity; no other staining was seen. We conclude that ubiquitin is a component of the inclusions that characterize inclusion body myositis. However, ubiquitin expression in skeletal muscle disease is not pathognomonic of inclusion body myositis. 相似文献
183.
The state of the surface of n-GaAs crystals upon high-vacuum microwave plasmachemical (HVMWPC) etching in various gas mixtures and the influence of the semiconductor surface condition on the photoelectric characteristics of related metal-semiconductor-metal structures with double Schottky barrier (MSMDSB structures) are investigated. Dependence of the HVMWPC etching rate of the GaAs surface on the gas mixture composition and substrate temperature is determined. It is shown that the HVMWPC etching regime strongly influences the photoelectric properties of MSMDSB structures: the treatment can lead to either growth or drop in photosensitivity of the samples. Optimum etching regimes are established for which good semiconductor surface quality and high photosensitivity of the MSMDSB structures are retained at a high etching rate. 相似文献
184.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
185.
The properties of a spinel copper cobaltite obtained by thermal decomposition of mixed nitrates of both metals at 350°C and normal pressure are described. It has been shown that the maximum copper content (x) in the spinel CuxCo3?xO4 does not exceed 0.9. When the copper amount in the initial mixture is higher a second phase CuO is formed. The copper ions are distributed over the A- and the B-sites of the spinel lattice, i.e. the spinel is partially inverted. Such a model explains well the data obtained about the lattice parameter, IR-absorption and the magnetic susceptibility of the samples with different x. 相似文献
186.
A. A. Konstantinov N. V. Kurenkov A. B. Malinin T. E. Sazonova S. V. Sepman 《Atomic Energy》1989,67(3):696-698
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989. 相似文献
187.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
188.
189.
190.
A narrow linewidth has been obtained in a new 1.5 ?m distributed feedback laser integrated monolithically with a tunable external cavity. The linewidth of 18 MHz has been achieved by tuning the current in the external cavity, and the FM response was flat from 100 kHz to 500 MHz. 相似文献