首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1464篇
  免费   93篇
  国内免费   1篇
电工技术   9篇
综合类   3篇
化学工业   551篇
金属工艺   17篇
机械仪表   22篇
建筑科学   53篇
矿业工程   4篇
能源动力   30篇
轻工业   250篇
水利工程   13篇
石油天然气   1篇
无线电   63篇
一般工业技术   220篇
冶金工业   194篇
原子能技术   6篇
自动化技术   122篇
  2024年   4篇
  2023年   28篇
  2022年   89篇
  2021年   119篇
  2020年   62篇
  2019年   48篇
  2018年   50篇
  2017年   73篇
  2016年   56篇
  2015年   38篇
  2014年   47篇
  2013年   93篇
  2012年   92篇
  2011年   96篇
  2010年   71篇
  2009年   65篇
  2008年   71篇
  2007年   68篇
  2006年   61篇
  2005年   37篇
  2004年   37篇
  2003年   19篇
  2002年   23篇
  2001年   6篇
  2000年   15篇
  1999年   10篇
  1998年   14篇
  1997年   11篇
  1996年   16篇
  1995年   17篇
  1994年   9篇
  1993年   17篇
  1992年   6篇
  1991年   5篇
  1990年   4篇
  1989年   8篇
  1987年   3篇
  1985年   10篇
  1984年   6篇
  1983年   7篇
  1982年   5篇
  1981年   6篇
  1980年   4篇
  1979年   6篇
  1977年   3篇
  1976年   5篇
  1975年   2篇
  1973年   3篇
  1968年   2篇
  1964年   2篇
排序方式: 共有1558条查询结果,搜索用时 15 毫秒
121.
The objective of the research was to characterize the quality of damaged and undamaged jojoba seeds. The study was performed on jojoba seeds grown in La Rioja, Argentina. Proximal composition, fatty acid composition, acid value, peroxide value, conjugated dienes and trienes and protein electrophoresis profiles were determined in undamaged (JS) and damaged jojoba seeds (DJS). The fat content (wax) was lower in DJS (39.11%) than in JS (50.82%). The values of acid, peroxide, conjugated dienes and trienes were higher in DJS than in JS. No difference in fatty acid composition was observed between DJS and JS. The protein content was not significantly different between JS and DJS. However, DJS had lower soluble protein values. In the electrophoresis profiles, the band located at 50 kDa disappeared in DJS and the intensity of the band located at 25 kDa decreased. The deterioration process in jojoba kernels significantly affects the chemical quality of their proteins and waxes.  相似文献   
122.
123.
Wine ageing in wood barrels is a traditional practice in quality wine-making areas. It is generally believed that the organoleptic characteristics of wines aged in barrels are deeply influenced by wood geographical origin, as well as by age of barrels (new or used).  相似文献   
124.
Evaluated the degree of sex-role stereotyping in TV commercials using both a verbal response mode and a content analysis. A total of 120 commercials (60 daytime and 60 primetime), each depicting an adult male–female dyad verbally interacting, were drawn from a larger sample of commercials aired between October 1983 and January 1984 on the major North American networks. Results of the 2 analyses reveal a more sex-stereotyped pattern of male–female differences in daytime than in primetime commercials. It is concluded that sex-role stereotyping still exists in TV commercials and is present at subtle as well as obvious levels of analysis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
125.
Three levels (0%, 1% and 2%) of conjugated linoleic acid (CLA) were combined with two levels of monounsaturated fatty acids (MUFA) (low: 19% and high: 39%) for pig feeding. The fatty acid profile of neutral lipids (NL) and polar lipids (PL) of loin and liver and their oxidative susceptibility were studied. A dose-dependent enrichment in cis-9, trans-11 CLA and trans-10, cis-12 CLA in NL and PL of loin and liver was obtained. This effect was independent of the MUFA supplementation (except for NL of loin in which the CLA accumulation was higher at high MUFA levels). Regardless of the MUFA supplementation, dietary CLA increased the ratio of saturated fatty acids (SFA) to unsaturated fatty acids in both tissues and lipid fractions. The interaction between CLA and MUFA affected the SFA and polyunsaturated fatty acids contents of PL from loin. Regardless of the MUFA level of the diets, CLA supplementation decreased the induced peroxidation values in liver and did not change those of loin.  相似文献   
126.
The effects of outpatient group behavioral therapy including aerobic exercise (BE), behavioral therapy only (B), and aerobic exercise only (E) on pain and physical and psychosocial disability were evaluated and compared in a group of mildy disabled chronic low-back-pain patients. Ninety-six Ss were randomly assigned to the 3 treatments and a waiting-list control (WL) condition and assessed on a variety of patient self-report, spouse-rated, and direct observational measures at pretreatment, posttreatment, and 6- and 12-month follow-ups. Patients in the BE condition, but not the B or E conditions, improved significantly more pretreatment to posttreatment than did WL patients on the patient self-report and observer-rated measures. At both follow-ups, all 3 treatment groups remained significantly improved from pretreatment, with no significant differences among treatments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
127.
Many packaging decisions are routine, but require a high level of expertise. The research described in this paper explores the use of expert systems for automating routine package development tasks. It begins with a general discussion of expert systems and outlines some feasible packaging applications in design, prediction, problem diagnosis, and management control. A PC-based prototype system is described, which is composed of six modules related to the following tasks: performance requirements, packaging solutions, testing specifications, testing results analysis, vendor specifications and procurement.  相似文献   
128.
Bridged ureasil precursors were synthesized by the reaction of either ethylenediamine (1 mol) or m‐xylylenediamine (1 mol) with isocyanatepropyltriethoxysilane (2 mol). Transparent polysilsesquioxane films were obtained by the hydrolytic condensation of the pure precursors or their co‐condensation in a 50:50 molar ratio. Films based on pure ureasil precursors showed a blue photoluminescent emission band assigned to the photoinduced proton‐transfer among H‐bonded urea groups and the subsequent radiative recombination of ionized groups. Films synthesized by the co‐condensation of both precursors exhibited a significant red‐shift of their absorption, excitation, and emission spectra, associated to de‐localization of H‐bonds, and a high absorption of UV‐radiation.

  相似文献   

129.
130.
The Santa Ana River (SAR), CA and adjacent wetlands have been identified as potential sources of fecal indicator bacteria (FIB) to the surf zone at Huntington Beach, CA. A suite of fecal steroids, including coprostanol (COP), epicoprostanol (eCOP), cholesterol (CHOE), cholestanol (CHOA), alpha-cholestanone (aONE), beta-cholestanone (bONE), beta-sitosterol (bSIT), stigmasterol (STIG), stigmastanol (STAN), and campesterol (CAM), were used as chemical markers to examine whether sewage was a significant source of FIB within the lower Santa Ana River watershed. A total of 54 water samples were collected from three locations in the intertidal zone near the mouth of the Santa Ana River at different tidal stages. Steroid ratios in SAR samples were different from those found in raw and treated sewage from a local wastewater treatment plant or in nearby effluent plume and did not appear to be influenced by the sampling location, daily tides, and spring/neap tidal cycle. The characteristics of steroid ratios suggested a diagenetic ratherthan a biogenic source forthe COP content of the samples. The log-based concentrations of COP and FIB in the SAR samples were not significantly correlated, inconsistent with sewage being the source of FIB in the study area. In addition, multivariate statistical analysis showed that the concentrations of FIB were better correlated with bird fecal steroids than with the typical sewage sterols. The results implied that sewage was not a significant source of fecal steroids, and therefore perhaps FIB to the study area. Instead, birds may be one possible source of the intermittently high levels of FIB observed in the lower Santa Ana River watershed and the nearby surf zone.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号