全文获取类型
收费全文 | 3509篇 |
免费 | 37篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 35篇 |
综合类 | 1篇 |
化学工业 | 606篇 |
金属工艺 | 74篇 |
机械仪表 | 57篇 |
建筑科学 | 135篇 |
矿业工程 | 11篇 |
能源动力 | 47篇 |
轻工业 | 219篇 |
水利工程 | 14篇 |
石油天然气 | 29篇 |
无线电 | 207篇 |
一般工业技术 | 497篇 |
冶金工业 | 1055篇 |
原子能技术 | 43篇 |
自动化技术 | 527篇 |
出版年
2022年 | 22篇 |
2021年 | 29篇 |
2019年 | 32篇 |
2018年 | 26篇 |
2017年 | 42篇 |
2016年 | 40篇 |
2015年 | 28篇 |
2014年 | 43篇 |
2013年 | 195篇 |
2012年 | 101篇 |
2011年 | 126篇 |
2010年 | 82篇 |
2009年 | 105篇 |
2008年 | 129篇 |
2007年 | 116篇 |
2006年 | 121篇 |
2005年 | 121篇 |
2004年 | 113篇 |
2003年 | 94篇 |
2002年 | 82篇 |
2001年 | 81篇 |
2000年 | 63篇 |
1999年 | 87篇 |
1998年 | 158篇 |
1997年 | 86篇 |
1996年 | 74篇 |
1995年 | 89篇 |
1994年 | 69篇 |
1993年 | 76篇 |
1992年 | 42篇 |
1991年 | 33篇 |
1990年 | 55篇 |
1989年 | 53篇 |
1988年 | 48篇 |
1987年 | 60篇 |
1986年 | 48篇 |
1985年 | 61篇 |
1984年 | 53篇 |
1983年 | 52篇 |
1982年 | 43篇 |
1981年 | 59篇 |
1980年 | 39篇 |
1979年 | 60篇 |
1978年 | 54篇 |
1977年 | 49篇 |
1976年 | 38篇 |
1975年 | 39篇 |
1974年 | 43篇 |
1973年 | 27篇 |
1972年 | 20篇 |
排序方式: 共有3557条查询结果,搜索用时 0 毫秒
1.
2.
David J. Lawrence Brianna L. Smith Cameron D. Collard Keyton A. Elliott Kyle L. Fakhoury Jeffery D. Mangold Anna N. Soyka 《International Journal of Hydrogen Energy》2021,46(2):1642-1655
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices. 相似文献
3.
Lawrence K. Forbes Graeme C. Hocking Simon Wotherspoon 《Journal of Engineering Mathematics》2004,48(1):69-91
Rainwater can collect in a lens-shaped region within the rock of a tropical island, and may be separated from the underlying salt water by a sharp interface. This paper presents a nonlinear theory for determining the shape of this interface. The island is assumed to be saturated with rain, and provision is made for the outflow of rain-water through the sides of the island. The effect of a bore well on the shape of the interface is investigated, and the problem is solved using a spectral method. An integral-equation method is also presented for the case when the island has infinite width. 相似文献
4.
Saravi A. Lawrence P.D. Lam F. 《IEEE transactions on instrumentation and measurement》2004,53(2):284-292
The most accurate way of determining the strength of lumber requires destructive testing. An intelligent mechanics-based lumber-grading system was developed to provide a better estimation of the strength of a board nondestructively. This system processed X-ray-extracted geometric features (of 1080 boards that eventually underwent destructive strength testing) by using finite element methods to generate associated stress fields. The stress fields were then fed to a feature-extracting-processor, which produced 26 strength predicting features. The best strength predicting features were determined from the coefficient of determination (correlation r/sup 2/) between the features and actual strengths of the boards. The coefficients of determination of each feature (or combination of features), with the actual strength of the board, were calculated and compared. A coefficient of determination of 0.4158 was achieved by using a longitudinal (along the local grain angle) maximum stress concentration (MSC) feature to predict the estimated strength of lumber. 相似文献
5.
Krenz William Robin Michael Barez Shirin Stark Lawrence 《IEEE transactions on bio-medical engineering》1985,(10):817-825
A model of the pathways controlling the size of the human pupil is presented. Computer simulation of this model demonstrates the role played by each of the elements in the pupil pathways. Simulations of the effects of drugs and a few common abnormalities in the system also help to illustrate the workings of the internal processes. Computer models of this type can be used as teaching aids or as tools for testing of hypotheses regarding the system. 相似文献
6.
Brown Michael T.; White Michael J.; Gerstein Lawrence H. 《Canadian Metallurgical Quarterly》1989,36(2):183
Examined the association between self-monitoring and occupational preferences. 237 undergraduates completed Snyder and Gangestad's (1986) revised self-monitoring scale and Holland's (1977) Vocational Preference Inventory (VPI). Regression analyses showed that men who valued congruence between their beliefs and behavior (i.e., low self-monitors) preferred social occupations. Men who were inclined to modify their behavior to fit social situations (i.e., high self-monitors) preferred enterprising occupations. In contrast, high self-monitoring women preferred artistic occupations. It is argued that these gender-neutral occupations permit high self-monitoring women to use their social skills but without the constraints found in male dominated enterprising occupations. Results support the assumption that people prefer occupations compatible with their social skills. Implications for career counseling and further research are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
8.
Summary The magnetohydrodynamic (MHD) boundary layer flow over a flat plate is examined here for two cases, viz. a uniform free-stream velocity and a uniform hydrostatic pressure. The nonlinear boundary layer equations are solved using a reliable finite-difference method. The boundary layer physical parameters such as skin-friction coefficient, displacement, momentum and energy thicknesses of the boundary layer are determined. It is found that the normal surface velocity gradient decreases with the local magnetic interaction parameter for the cases of a uniform hydrostatic pressure, whereas in the case of a uniform free-stream volocity it increases with the interaction parameter. 相似文献
9.
School-based condom distribution programs have generated considerable controversy across the country. In the present study 249 sexually active African American adolescents who did (n = 119) and did not (n = 130) use a condom during their initial sexual experience were compared to assess whether condom use at the onset of sexual activity was associated with later differences in sexual behavior. The results indicated that youths who used a condom from the onset of sexual activity were more likely to have used a condom in the most recent intercourse occasion, less likely to be diagnosed with a sexually transmitted disease (STD) or to combine substance use with sexual activity, endorsed more positive attitudes toward condoms, and were older when they initiated sexual activity. The findings have implications for condom availability programs and indicate that initial condom use was not associated with earlier onset of sexual activity and was associated with higher rates of precautionary behavior among sexually active minority adolescents. 相似文献
10.
During a study of natural food colours, a simple and reliable high-performance liquid chromatography system was developed for use with cochineal and annato. An isocratic mobile phase, consisting of methanol and 6% aqueous acetic acid, resolved bixin and norbixin, while a gradient system was used to separate carminic acid and the annato compounds. The carminic acid contents of cochineal extract, carmine and carmine hydrosoluble were determined using an isocratic mobile phase (40:60, v/v). The detection limit for carminic acid in the various products was approximately 100 ng/g. Carminic acid was determined quantitatively in fruit beverages, yogurt and candies. It was demonstrated that, because of decomposition, carminic acid was not suitable for use in candies when manufacturing temperatures above 100 degrees C were required. Most membrane filters are not suitable for use with cochineal solutions, but a cellulose membrane filter did not adsorb carminic acid and was used successfully to remove impurities from water-based cochineal products and food extracts containing carminic acid. 相似文献