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   6162篇
  免费   39篇
  国内免费   3篇
电工技术   14篇
化学工业   268篇
金属工艺   29篇
机械仪表   26篇
建筑科学   82篇
矿业工程   14篇
能源动力   59篇
轻工业   145篇
水利工程   16篇
石油天然气   15篇
武器工业   3篇
无线电   257篇
一般工业技术   283篇
冶金工业   4676篇
原子能技术   26篇
自动化技术   291篇
  2022年   11篇
  2021年   18篇
  2019年   17篇
  2018年   25篇
  2017年   15篇
  2016年   27篇
  2015年   22篇
  2014年   26篇
  2013年   105篇
  2012年   45篇
  2011年   74篇
  2010年   39篇
  2009年   43篇
  2008年   69篇
  2007年   60篇
  2006年   59篇
  2005年   52篇
  2004年   38篇
  2003年   53篇
  2002年   45篇
  2001年   31篇
  2000年   39篇
  1999年   184篇
  1998年   1541篇
  1997年   875篇
  1996年   554篇
  1995年   321篇
  1994年   292篇
  1993年   297篇
  1992年   66篇
  1991年   78篇
  1990年   81篇
  1989年   74篇
  1988年   77篇
  1987年   69篇
  1986年   57篇
  1985年   74篇
  1984年   34篇
  1983年   32篇
  1982年   27篇
  1981年   38篇
  1980年   53篇
  1979年   18篇
  1978年   28篇
  1977年   109篇
  1976年   178篇
  1975年   19篇
  1974年   11篇
  1973年   22篇
  1971年   14篇
排序方式: 共有6204条查询结果,搜索用时 9 毫秒
41.
Absorbability of Calcium From Common Beans   总被引:4,自引:0,他引:4  
Absorption of calcium from white, red, and pinto beans, labeled with 45Ca, was measured in 24 women in a three-way randomized design using a calcium load of 72 mg and milk as the referent. Fractional absorption for the three beans averaged 0.219 ± 0.047 and did not differ by type. Milk calcium absorption at the same load was more than two times higher, 0.451 ± 0.088 (P < 0.001). Oxalate content averaged 0.34%, and phytate averaged 1.7%, a stoichiometric excess relative to calcium. To evaluate the relation of phytate to reduced absorbability, labeled pinto beans were pre-treated with phytase and fed to 10 subjects. Fractional absorption rose, averaging 0.318 ± 0.071, (P <0.01 vs. untreated beans), but was significantly below that of milk. The difference was partly accounted for by phytate, with the remainder probably due to relatively high oxalate.  相似文献   
42.
43.
Lactate clearance and survival following injury   总被引:1,自引:0,他引:1  
Previous reports cite optimization of O2 delivery (DO2) to 660 mL/min/m2, O2 consumption (VO2) to 170 mL/min/m2, and cardiac index (CI) of 4.5 L/min as predicting survival. We prospectively evaluated 76 consecutive patients with multiple trauma admitted directly to the ICU from the operating room or emergency department. Patients had serum lactate levels and oxygen transport measured on ICU admission and at 8, 16, 24, 36, and 48 hours. Patients were analyzed with respect to survival (S) versus nonsurvival (NS), lactate clearance to normal (< or = 2 mmol/L) by 24 and 48 hours, hemodynamic optimization as defined above, as well as Injury Severity Score (ISS), ICU stay (LOS), and admission blood pressure. All patients achieved non-flow-dependent VO2. There was no difference in CI, DO2, VO2, or ISS when S was compared with NS. All 27 patients whose lactate level normalized in 24 hours survived. If lactate levels cleared to normal between 24 and 48 hours, the survival rate was 75%. Only 3 of the 22 patients who did not clear their lactate level to normal by 48 hours survived. Ten of the 25 nonsurvivors (40%) achieved the above arbitrary optimization criteria. Fifteen of the survivors never achieved any of these criteria. Optimization alone does not predict survival. However, the time needed to normalize serum lactate levels is an important prognostic factor for survival in severely injured patients.  相似文献   
44.
A simple method was developed for the determination of dietary fiber in multicomponent foods. The method involves dispersing the sample into pH 7.4 phosphate buffer and adding bile and pancreatic enzyme as described. Results were comparable to AOAC methods with correlation coefficients of 86% for multicomponent dinners and 89% for breakfast foods. Coefficients of variation ranged from 7.4 to 20.0% for multicomponent foods and 1.0 to 3.6% for single component foods. In addition, blind duplicate samples had a correlation of 0.99. The described method required less time, labor, and manipulation than AOAC methods.  相似文献   
45.
46.
47.
48.
Two-dimensional gel electrophoresis separates several hundred protein molecules in one single experiment and is efficiently used to study the products expressed by different genomes. Low-copy-number gene products are invisible on a stained two-dimensional map and must be enriched such that sufficient amounts are present for visualization and identification. We investigated the enrichment of proteins of the bacterium Haemophilus influenzae by chromatography on immobilized heparin which has affinity for growth and protein biosynthesis factors. Total soluble proteins of the microorganism were fractionated on Heparin-Actigel which resulted in enrichment of approximately 160 proteins. The eluates, representing about 40% of the applied proteins, were analyzed by two-dimensional gel electrophoresis and the protein spots were characterized by amino acid composition analysis and matrix-assisted laser desorption ionization mass spectrometry. The proteins enriched by chromatography on the heparin gel were not exclusively low-copy-number gene products and they did not exclusively belong to one single class of proteins. The proteins that bound to the heparin gel are indicated in a two-dimensional protein map which includes more than 110 newly identified proteins.  相似文献   
49.
Examines, in the context of cancer illness, S. E. Taylor and J. D. Brown's (see record 1988-16903-001) claim that mental health is to a degree predicated on illusory beliefs about the self, one's control, and the future. The Heroic Model (HM), a stance toward cancer characterized by belief that positive thoughts and feelings, a fighting spirit, and an optimistic outlook will promote cancer remission, is presented as paradigmatic of Taylor and Brown's thesis. Strong and weak formulations of the HM (the former affirming a direct influence of mental states over physical processes, and the latter affirming indirect effects only) are examined with respect to their potential adaptive value as true or false beliefs, with different consequences for well-being. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
50.
This study demonstrates that invertebrate acoustic signals can provide information about male phenotypic attributes, and that females can use this acoustic information in mate choice to select a phenotypically superior mate. I investigated the relationships between a male acoustic sexual signal, the phenotype of the signaller, and the female response to signal variation. I recorded and analysed the calling songs of male house crickets, Acheta domesticus. The analyses showed that chirps convey information about male size. With the exception of amplitude, the mean number of pulses per chirp was the best predictor of male size. I performed a laboratory tape-playback experiment to determine female preference during phonotaxis. Females preferred tapes playing the chirps of large males, specifically chirps with a greater number of pulses per chirp. Selection on the female preference is discussed.Copyright 1997 The Association for the Study of Animal Behaviour  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