全文获取类型
收费全文 | 54683篇 |
免费 | 5682篇 |
国内免费 | 3269篇 |
专业分类
电工技术 | 1474篇 |
综合类 | 4164篇 |
化学工业 | 10427篇 |
金属工艺 | 5856篇 |
机械仪表 | 5676篇 |
建筑科学 | 2987篇 |
矿业工程 | 1880篇 |
能源动力 | 1488篇 |
轻工业 | 7687篇 |
水利工程 | 1511篇 |
石油天然气 | 1517篇 |
武器工业 | 517篇 |
无线电 | 4470篇 |
一般工业技术 | 7711篇 |
冶金工业 | 1893篇 |
原子能技术 | 537篇 |
自动化技术 | 3839篇 |
出版年
2024年 | 356篇 |
2023年 | 1139篇 |
2022年 | 1598篇 |
2021年 | 1923篇 |
2020年 | 2153篇 |
2019年 | 1945篇 |
2018年 | 1969篇 |
2017年 | 2293篇 |
2016年 | 2271篇 |
2015年 | 2329篇 |
2014年 | 3034篇 |
2013年 | 3870篇 |
2012年 | 3944篇 |
2011年 | 4070篇 |
2010年 | 2827篇 |
2009年 | 2846篇 |
2008年 | 2650篇 |
2007年 | 3334篇 |
2006年 | 3034篇 |
2005年 | 2479篇 |
2004年 | 2018篇 |
2003年 | 1711篇 |
2002年 | 1549篇 |
2001年 | 1270篇 |
2000年 | 1165篇 |
1999年 | 971篇 |
1998年 | 784篇 |
1997年 | 738篇 |
1996年 | 655篇 |
1995年 | 483篇 |
1994年 | 440篇 |
1993年 | 367篇 |
1992年 | 297篇 |
1991年 | 198篇 |
1990年 | 210篇 |
1989年 | 139篇 |
1988年 | 136篇 |
1987年 | 64篇 |
1986年 | 82篇 |
1985年 | 67篇 |
1984年 | 59篇 |
1983年 | 46篇 |
1982年 | 44篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1959年 | 7篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Robert R. Gillies Jayne Brim Box Jürgen Symanzik Eli J. Rodemaker 《Remote sensing of environment》2003,86(3):411-422
Impervious surface area (ISA) was derived for a period from 1979 to 1997 from Landsat MSS and TM data for the Line Creek watershed that lies to the south of the city of Atlanta, GA. The change in ISA is presented as an ecological indicator to examine the cumulative water resource impacts on mussel population in three sub-watersheds of Line Creek—namely, Line, Flat, and Whitewater creeks. The satellite analysis shows that ISA expansion occurred substantially from 1987 to 1997 and is predominantly in industrial, commercial, and shopping center (ICS) complexes but also in smaller lot-size residential development. Evidence of mussel habitat degradation is indicated and loss of species (in the region of 50 to 70%) is present in areas where ISA expansion is observed—specifically in ICS complex development in and around Peachtree City that drains directly into the Line and Flat creeks. This is in marked contrast to Whitewater Creek where overall development of ISA is less and no major loss of mussel species is observed. 相似文献
42.
Water turbidity, surface temperature and circulation of Barton and Wroxham Broads, two of the Norfolk Broads, were studied using one reflective (TM1) and the thermal (TM6) TM band. The results indicated that the through-flowing path of the River Ant in Barton Broad is the major influence on the distribution of these parameters. In Wroxham Broad, both turbidity and surface temperature displayed a uniform distribution. This could be explained by the absence of a predominant direction of flow. 相似文献
43.
链烷烃的表面张力与内压 总被引:1,自引:0,他引:1
对Davis和Rosseinsky提出的关系检验表明,液体的表面张力σ与P1Vm1/3之比不仅取决于温度,还与液体的种类有关,据此,建立了一个能由链烷烃的分子结构准确预测其表面张力的方法。 相似文献
44.
45.
46.
Shihong XU Pengshou XU Mingrong JI Xianming LIU Maosheng MA Jingsheng ZHU Yuheng ZHANG Structure Research Laboratory University of Science Technology of China Hefei ChinaZhenjia XU Institute of Semiconductor Academia Sinica Beijing China 《材料科学技术学报》1993,9(6):437-440
The alkali-metal Na adsorption on Si(100)2×1 surface and its promoted oxidation and Si oxidegrowth have been investigated by means of thermal desorption,work function,Auger electronspectroscopy and photoemission electron spectroscopy.The experimental data showed that therewas a new state,interface electron state,near the Fermi level after the deposition of Na atoms.It wasfound that the presence of Na always caused an increase of the oxygen initial uptake whereas thepromotion of Si oxide growth was observed only at the coverage of Na greater than 0.5 ML.A newmechanism of Na-promoted Si oxide growth is suggested in this paper. 相似文献
47.
离子注入对Cr12MoV钢表面组织结构和力学性能的影响 总被引:1,自引:0,他引:1
研究了Cr12MoV钢离子注入层的显微组织特征及其对表面性能的影响。结果表明,离子注入使Cr12MoV钢的表面硬度和耐磨性能得到显著改善,且存在着一个最佳的注入剂量,约为3×10^1^7N^+/cm^2左右。离了注入在Cr12MoV钢表面层中形成了大量细小弥散的第二相粒子,并使α-Fe晶格发生严重畸变,从而引起材料表面强化。 相似文献
48.
Wu Ting M. Badaye T. Morishita N. Koshizuka S. Tanaka 《Journal of Superconductivity》1996,9(6):637-645
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T
c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films. 相似文献
49.
Inverse surface design problems from light transport behavior specification usually represent extremely complex and costly processes, but their importance is well known. In particular, they are very interesting for lighting and luminaire design, in which it is usually difficult to test design decisions on a physical model in order to avoid costly mistakes. In this survey, we present the main ideas behind these kinds of problems, characterize them, and summarize existing work in the area, revealing problems that remain open and possible areas of further research. 相似文献
50.
钢纤维混凝土在南钢大道工程中的应用 总被引:1,自引:0,他引:1
钢纤维混凝土是一种性能优良的新型复合材料,与普通混凝土相比,其抗拉、抗弯、抗裂及耐磨、耐冲击、耐疲劳等性能都有显著提高,它不仅可使路面厚度减薄,工程缝间距加大,改善路面的使用性能,延长路面使用寿命,而且还可节省工程造价,缩短施工工期。文中结合南钢大道路面工程实际,主要介绍了钢纤维混凝土的施工及质量控制要点。 相似文献