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   1643篇
  免费   72篇
  国内免费   1篇
电工技术   37篇
化学工业   317篇
金属工艺   36篇
机械仪表   17篇
建筑科学   38篇
矿业工程   1篇
能源动力   51篇
轻工业   256篇
水利工程   13篇
石油天然气   3篇
无线电   172篇
一般工业技术   213篇
冶金工业   290篇
原子能技术   6篇
自动化技术   266篇
  2023年   12篇
  2022年   21篇
  2021年   25篇
  2020年   24篇
  2019年   36篇
  2018年   43篇
  2017年   43篇
  2016年   51篇
  2015年   26篇
  2014年   55篇
  2013年   85篇
  2012年   77篇
  2011年   90篇
  2010年   77篇
  2009年   56篇
  2008年   75篇
  2007年   73篇
  2006年   59篇
  2005年   50篇
  2004年   58篇
  2003年   40篇
  2002年   37篇
  2001年   31篇
  2000年   36篇
  1999年   39篇
  1998年   117篇
  1997年   73篇
  1996年   54篇
  1995年   26篇
  1994年   25篇
  1993年   30篇
  1992年   15篇
  1991年   16篇
  1990年   14篇
  1989年   12篇
  1988年   13篇
  1987年   7篇
  1986年   9篇
  1985年   3篇
  1984年   10篇
  1983年   12篇
  1982年   8篇
  1981年   4篇
  1980年   5篇
  1979年   4篇
  1978年   4篇
  1976年   13篇
  1975年   4篇
  1974年   3篇
  1973年   5篇
排序方式: 共有1716条查询结果,搜索用时 0 毫秒
91.
An algorithm is proposed for estimating soil moisture over vegetated areas. The algorithm uses in situ and remote sensing information and statistical tools to estimate soil moisture at 1 km spatial resolution and at 20 cm depth over Puerto Rico. Soil moisture within the study region is characterized by spatial and temporal variability. The temporal variability for a given area exhibits long- and short-term variations that can be expressed by two empirical models. The average monthly soil moisture exhibits the long-term variability and is modelled by an artificial neural network (ANN), whereas the short-term variability is determined by hourly variation and is represented by a nonlinear stochastic transfer function model. Monthly vegetation index, land surface temperature, accumulated rainfall and soil texture are the major drivers of the ANN to estimate the monthly soil moisture. Radar, satellite and in situ observations are the major sources of information of the soil moisture empirical models. A self-organized ANN was also used to identify spatial variability to be able to determine a similar transfer function that best resembles the properties of a particular grid point and estimate the hourly soil moisture across the island. Validation techniques reveal an average absolute error of 3.34% of volumetric water content and this result shows that the proposed algorithm is a potential tool for estimating soil moisture over vegetated areas.  相似文献   
92.
Objective: Hematopoietic stem cell transplant (HSCT) survivors who are 1 to 3 years posttransplant are challenged by the need to resume valued social roles and activities—a task that may be complicated by enduring transplant-related psychological distress common in this patient population. The present study investigated whether transplant survivors who receive adequate social support from their spouse or intimate partner experience lower distress. Method: Effects of receiving a greater quantity of partner support (a common approach to studying enacted support) were compared with effects of receiving more effective partner support (i.e., support that more closely matches their needs in terms of its quantity and quality). Men and women (N = 230) who were 1 to 3 years posttransplant completed measures of partner support quantity (Manne & Schnoll, 2001), partner social support effectiveness (Rini & Dunkel Schetter, 2010), and psychological distress (Brief Symptom Inventory; Derogatis & Spencer, 1982). Potential medical and sociodemographic confounds were controlled in analyses. Results: As hypothesized, survivors reported less distress when they received more effective partner support (p  相似文献   
93.
The tremendous development of nanotechnology is bringing us closer to the dream of clinical application of nanoparticles in photothermal therapies of tumors. This requires the use of specific nanoparticles that must be highly biocompatible, efficient light‐to‐heat converters and fluorescent markers. Temperature reading by the heating nanoparticles during therapy appears of paramount importance to keep at a minimum the collateral damage that could arise from undesirable excessive heating. In this work, this thermally controlled therapy is possible by using Nd3+ ion‐doped LaF3 nanocrystals. Because of the particular optical features of Nd3+ ions at high doping concentrations, these nanoparticles are capable of in vivo photothermal heating, fluorescent tumor localization and intratumoral thermal sensing. The successful photothermal therapy experiments here presented highlight the importance of controlling therapy parameters based on intratumoral temperature measurements instead of on the traditionally used skin temperature measurements. In fact, significant differences between intratumoral and skin temperatures do exist and could lead to the appearance of excessive collateral damage. These results open a new avenue for the real application of nano­particle‐based photothermal therapy at clinical level.  相似文献   
94.
Some chemotherapeutic agents, as well as TNF and Fas, induce apoptotic cell death in tumor cells, but the cellular components involved in the process have not yet been identified. Interleukin 1 beta converting enzyme (ICE) is a mammalian homolog of CED-3, a protein required for programmed cell death in nematode Caenorhabditis elegans. We found that a selective inhibitor of ICE/ced 3 family proteases, benzyloxycarbonyl Asp CH2OC(O) 2 6,-dichlorobenzene (Z-Asp-CH2-DCB). completely blocked the apoptotic cell death of human leukemia cells caused by etoposide, camptothecin, 1-beta-D-arabinofuranosyl cytosine (Ara-C) and adriamycin. Moreover, in antitumor agent-treated U937 cells, an ICE-like (CPP32-like) protease was strongly activated. These results indicate that ICE/ ced 3 family proteases are involved in antitumor agent-induced apoptosis. Activation of ICE family proteases plays a key role in apoptosis. However, the subsequent mechanisms resulting in apoptosis are largely unknown. We identified actin as a substrate of ICE family proteases. Cleavage of actin and other substrate proteins by ICE family proteases could be critical in the ongoing process of antitumor agent-induced apoptosis in tumor cells.  相似文献   
95.
Groups of castrate male Criollo goats were slaughtered at 12, 16, 20 and 24 kg liveweights after being reared on natural rangeland with concentrate supplementation.

After slaughter the carcasses were chilled for 24 h at 2°C, and the total lean was dissected from the left halves of the carcasses. The total lean was subjected to a proximate analysis. M. biceps femoris and M. longissimus dorsi muscles were dissected out of the right halves of the carcasses. Various physical and chemical quality parameters, such as Warner-Bratzler shear values and tristimulus colour values, were measured on these muscles in addition to hydroxy proline analysis, for the estimation of collagen content.

The moisture content of the total lean decreased steadily with increasing slaughter weight to a level of approximately 76% in the heaviest group. Ash and protein content tended to fall, with intramuscular fat increasing to approximately 16% of the wet tissue weight. The ultimate pH of the two muscles was high in all the slaughter groups, being usually higher than 6·0. Generally, shear values did not change between the slaughter groups in the two muscles.

The data indicate that slaughtering castrate male Criollo goats at 24 kg instead of 8 kg does not exert deleterious effects on the parameters of physical and chemical quality investigated.  相似文献   

96.
This paper adapts some literature results on stabilizing discrete time-varying input delay systems to the case of having a predictor-based controller. The objective of the paper is showing that the incorporation of predictors to the referred results is relatively simple and, by means of such predictors, robustness against delay mismatch in the input channel may be improved. In this way, larger delay variation margins are proved with predictors when compared to standard memoryless state feedback, as intuitively expected, due to the extra past information available.  相似文献   
97.
This paper introduces two original equations for biasing the common-emitter bipolar-junction transistor (BJT-CE) amplifier. These equations permit placing both Q-point coordinates (i.e. current and voltage) within known bounds in the presence of transistor parameter variations. An illustrative design example is provided  相似文献   
98.
99.
Islanding of a utility-interactive photovoltaic (UIPV) system occurs if the UIPV system continues to power a section of the utility system after that section has been disconnected from the utility source. Since islanding creates hazards for personnel and equipment, UIPV systems are required to detect and prevent it. It is desirable to have a simplified method of determining which islanding detection methods (IDMs) are most effective. In this paper, a previously described method for finding the nondetection zones (NDZs) of IDMs is experimentally verified. This method is used to determine the NDZs of several common IDMs. These results indicate that, of the IDMs discussed in this paper: (1) Sandia Frequency Shift (SFS) is most effective; and (2) the worst-case loads are low-power loads that are near resonance at the line frequency and have a large capacitance and small inductance (a high value of the quality factor Q)  相似文献   
100.
Preculture incubation, preculture freezing, and increased plate inoculation volumes were tested in an attempt to increase the recovery rate of pathogens in milk from cases of clinical bovine mastitis. Culture of milk from 291 cases of clinical bovine mastitis was performed using standard milk culture techniques (.01 ml of fresh milk streaked on trypticase soy agar plates with 5% sheep blood and .1% esculin). The sensitivity of this method was compared with that of cultures performed using augmented techniques: 4 and 18 h of preculture incubation; preculture freezing of samples overnight at -20 degrees C; and increasing the plate inoculation volume to .05 and .1 ml for fresh, incubated, and frozen samples. Preculture incubation and larger plate inoculation volumes significantly increased the recovery rate of bacterial pathogens over the standard culture method. The greatest improvement in sensitivity without a concomitant increase in contamination was achieved when samples were incubated for 4 h and plates were inoculated with .1 ml of the sample. Recovery was enhanced significantly by this method for several organisms, including environmental streptococci and coliform bacteria. Freezing milk before culture yielded a significantly higher positive culture rate overall, but freezing did not affect the positive culture rate of any individual bacterial species.  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