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   1531篇
  免费   40篇
  国内免费   3篇
电工技术   36篇
综合类   2篇
化学工业   155篇
金属工艺   17篇
机械仪表   29篇
建筑科学   45篇
矿业工程   1篇
能源动力   26篇
轻工业   68篇
水利工程   4篇
石油天然气   28篇
无线电   241篇
一般工业技术   213篇
冶金工业   539篇
原子能技术   12篇
自动化技术   158篇
  2022年   9篇
  2021年   25篇
  2020年   15篇
  2019年   19篇
  2018年   21篇
  2017年   22篇
  2016年   29篇
  2015年   25篇
  2014年   34篇
  2013年   47篇
  2012年   50篇
  2011年   44篇
  2010年   37篇
  2009年   34篇
  2008年   50篇
  2007年   49篇
  2006年   46篇
  2005年   55篇
  2004年   21篇
  2003年   30篇
  2002年   36篇
  2001年   22篇
  2000年   21篇
  1999年   33篇
  1998年   119篇
  1997年   118篇
  1996年   65篇
  1995年   30篇
  1994年   46篇
  1993年   44篇
  1992年   18篇
  1991年   9篇
  1990年   12篇
  1989年   19篇
  1988年   14篇
  1987年   13篇
  1985年   20篇
  1984年   15篇
  1983年   15篇
  1982年   16篇
  1981年   24篇
  1980年   19篇
  1979年   20篇
  1978年   16篇
  1977年   22篇
  1976年   41篇
  1975年   11篇
  1973年   5篇
  1969年   8篇
  1963年   6篇
排序方式: 共有1574条查询结果,搜索用时 169 毫秒
1.
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations.  相似文献   
2.
On the basis of observations that endemic fluorosis occurs more often in malnourished populations, a series of studies tested the hypothesis that deficient dietary intake of calcium, protein or energy affects fluoride metabolism so that the margin of safe fluoride exposure may be reduced. The objective of the investigation was to determine whether changes in fluoride metabolism in nutritionally deficient rats resulted in manifestation of any extraskeletal toxic fluoride effects not observed in healthy animals. This investigation included two studies, one that monitored the effect of calcium deficiency on the effects of chronic fluoride exposure, and a second study that observed fluoride effects in rats that were deficient either in protein or in energy and total nutrient intake. Control and experimental rats received drinking water containing 0, 0.26 (5), 0.79 (15) or 2.63 (50) mmol fluoride/L (mg/L) for 16 or 48 wk. Control rats were fed optimal diets and experimental rats were fed diets deficient in calcium (Study 1) or protein (Study 2). An additional group of experimental rats (Study 2) was provided with a restricted amount of diet; thus these rats were deficient in energy and total nutrient intake. The intake, excretion and retention of fluoride were monitored; after the rats were killed, tissue fluoride levels and biochemical markers of tissue function were analyzed. Bone marrow cells were harvested from some of the rats, after 48 wk of treatment, for determining the frequency of sister chromatid exchange, a marker of genetic damage. Although there were significant differences among fluoride treatment groups in fluoride excretion and retention that resulted in significantly greater fluoride levels in tissues of the experimental rats, we were unable to detect any harmful, extraskeletal biochemical, physiologic or genetic effects of fluoride in the nutritionally deficient rats.  相似文献   
3.
测井新技术在四川油气勘探开发中的应用   总被引:1,自引:0,他引:1  
综述随着四川盆地油气勘探深入所面临的油气领域复杂和困难的技术问题,介绍应用测井新技术为四川油气开发解决了大量的技术难题,特别是在复杂缝,洞型储层的评价,井旁地质构造形态精细分析和地质,测井,地震多学科结合储层横向预测等3个方面所取得的良好应用效果。  相似文献   
4.
The perception and discrimination of rapidly changing texture stimuli by pigeons was examined in a target localization task. Five experienced pigeons were rewarded for finding and pecking at a randomly placed odd target block of small repeated elements embedded in a larger rectangular array of contrasting distractor elements. On dynamic color test trials, the color of the target, distractor, or both of these regions changed at rates of 100, 250, 500, or 1000 ms per frame. The number of colors appearing within such trials also varied. Pigeons performed well above chance in all test conditions, with target-associated changes producing the best discrimination. The results suggest: (a) global relational information can exclusively guide target localization behavior, (b) pigeons can perceptually group and segregate colored textured differences quite rapidly (< or = 100 ms), and (c) pigeons may possess automatic search control processes that can be captured by stimulus-driven changes in the display.  相似文献   
5.
HIV arthritis     
Whether reexposure of varicella-immune persons to varicella-zoster virus would protect against or predispose to development of zoster was analyzed. The rate of zoster in 511 leukemic recipients of varicella vaccine who had 1 or > 1 dose of varicella vaccine and in those who did or did not have a household exposure to varicella was determined. A Kaplan-Meier life-table analysis revealed that the incidence of zoster was lower in those given > 1 dose of vaccine (P < .05). A Cox proportional hazards analysis showed that both household exposure to varicella and receipt of > 1 dose of vaccine were highly protective (P < .01) against zoster. Thus, the risk of zoster is decreased by reexposure to varicella-zoster virus, either by vaccination or by close exposure to varicella.  相似文献   
6.
Genomic signal processing (GSP) concerns the processing of genomic signals. It may be defined as the analysis, processing, and use of genomic signals to gain biological knowledge and the translation of that knowledge into systems-based applications. In this article, the authors discuss the key research issues for GSP. It is important to recognize that "genomic signal processing" is not a name for genomic bioinformatics nor for the application of signal processing methods in genomics. We note that the research issues pertaining to GSP fit within the overall challenges confronting research in the area of multimodal biomedical systems.  相似文献   
7.
In this paper, mobility parameters for enhancement-mode N-channel 4H SiC MOSFETs are extracted and implemented into 2-D device simulation program and SPICE circuit simulator. The experimental data were obtained from lateral N-channel 4H SiC MOSFETs with nitrided oxide–semiconductor interfaces, exhibiting normal mobility behavior. The presence of increasing interface-trap density (Dit) toward the edge of the conduction band is included during the 2-D device simulation. Using measured distribution of interface-trap density for simulation of the transfer characteristics leads to a good agreement with the experimental transfer characteristic.  相似文献   
8.
9.
10.
Early thrombolytic therapy gives maximum benefit in acute myocardial infarction. In remote rural areas with no mobile intensive care service there is a significant delay between onset of symptoms and administration of thrombolytic therapy which has a critical impact on revascularization. Thrombolytic therapy with streptokinase 1,500,000 U was given in a primary care rural clinic to 2 patients with evolving myocardial infarction 45-50 minutes from onset of symptoms. In both patients, who were transported to hospital after the therapy, there were clinical signs of reperfusion. There were no complications during treatment or transportation. We conclude that thrombolytic therapy given for evolving myocardial infarction in a rural primary care clinic is possible and safe.  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