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   7443篇
  免费   785篇
  国内免费   5篇
电工技术   63篇
综合类   5篇
化学工业   2045篇
金属工艺   81篇
机械仪表   210篇
建筑科学   294篇
矿业工程   15篇
能源动力   163篇
轻工业   1663篇
水利工程   73篇
石油天然气   20篇
无线电   467篇
一般工业技术   1216篇
冶金工业   362篇
原子能技术   16篇
自动化技术   1540篇
  2024年   32篇
  2023年   92篇
  2022年   124篇
  2021年   297篇
  2020年   243篇
  2019年   242篇
  2018年   383篇
  2017年   392篇
  2016年   444篇
  2015年   321篇
  2014年   413篇
  2013年   761篇
  2012年   698篇
  2011年   634篇
  2010年   419篇
  2009年   407篇
  2008年   387篇
  2007年   381篇
  2006年   267篇
  2005年   197篇
  2004年   186篇
  2003年   156篇
  2002年   151篇
  2001年   73篇
  2000年   58篇
  1999年   44篇
  1998年   61篇
  1997年   55篇
  1996年   39篇
  1995年   41篇
  1994年   27篇
  1993年   29篇
  1992年   22篇
  1991年   18篇
  1990年   8篇
  1989年   14篇
  1988年   12篇
  1987年   6篇
  1986年   9篇
  1985年   15篇
  1984年   14篇
  1983年   6篇
  1982年   7篇
  1981年   11篇
  1979年   7篇
  1978年   3篇
  1976年   4篇
  1908年   2篇
  1905年   2篇
  1899年   2篇
排序方式: 共有8233条查询结果,搜索用时 15 毫秒
31.
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro.  相似文献   
32.
A new process of management of waste of composite materials from Sheet Moulding Compounds (SMC), as reinforcing fillers for thermoplastic materials, including both mechanical and chemical processes is proposed in this paper. Communited SMC being composed of coated glass fibres intimately mixed with calcium carbonate powder, their reinforcing power is low. First, the fibrous part was increased by partial dissolution of calcium carbonate present in the crushed products SMC. Second, a process of partial solvolysis was developed aiming at strong increasing the interfacial mechanical properties by functionalising of SMC load incorporated into polypropylene/grafted maleic anhydride polypropylene (PP/PPgma). At this effect, we investigated a treatment with a hot triamine (diethylenetriamine, DETA) in order to create a functionalisation, after scission of the bond ester of unsaturated polyester, as bridging amino-succinimide.The effect of this recycling way by partial solvolysis was checked from the mechanical properties of the resulting reinforced PP/PPgma material: Although a lower of Young modulus, better yield stress and especially resilience were observed.  相似文献   
33.
A rate 1/n binary generic convolutional encoder is a shift-register circuit where the inputs are information bits and the outputs are blocks of n bits generated as linear combinations on the appropriate shift register contents. The decoding of the outputs of a convolutional encoder can be carried out by the well-known Viterbi algorithm. The communication pattern of the Viterbi Algorithm is given as a graph, called trellis, associated to the state diagram of the corresponding encoder. In this paper we present a methodology that permits the efficient mapping of the Viterbi algorithm onto a column of an arbitrary number of processors. This is done through the representation of the data flow by using mathematical operators which present an inmediate hardware projection. A single operator string has been obtained to represent a generic encoder through the study of the data flow of free-forward encoders and feed-back encoders. The formal model developed is employed for the partitioning of the computations among an arbitrary number of processors in such a way that the data are recirculated opimizing the use of the processors and the communications. As a result, we obtain a highly regular and modular architecture suitable for VLSI implementation.  相似文献   
34.
This article proposes a scheme for the on-line adjustment of three mode controller settings based on experimental measurements of closed-loop performance. It uses a recently developed heuristic tuning procedure to identify estimated process parameters. This method may give rise to conflicting estimates. Fuzzy Set theory is applied to manage the situation in terms of a fuzzy conjunction to combine the various estimates. PID control was chosen because of its wide use in the industrial environment due to driving simplicity and robustness. The article shows design, development, and computer simulation aspects.  相似文献   
35.
The purpose of this study was to examine whether anxiety-related cognitive bias for threat is stronger for threatening pictures than for threatening words. Spider-phobic participants (n?=?31 ) and control participants (n?=?33) performed a pictorial and linguistic spider Stroop task. Spider-phobic participants showed a marked bias for threat. However, this bias was similar for pictures and for words, although the spider-phobic group evaluated the pictures as being more aversive. The results suggest that automatic processing of threatening information in people with phobias is triggered in an on-off fashion, independent of subjective threat of the stimuli. This lack of distinction in automatic processing of weak and strong predictors of danger may be fundamental to the irrational nature of anxiety disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
36.
37.
There are more than 20,000 uncontrolled sanitary landfill areas in Brazil. The paper reports an integrated study undertaken to develop an environmental assessment of the uncontrolled sanitary landfill area of the city of Po?os de Caldas, State of Minas Gerais, Brazil. A number of remedial alternatives were evaluated. The USGS modular 3D finite difference groundwater flow model (Modflow) and Modular 3D Finite Difference Mass Transport Model (MT3D) software were used to simulate groundwater flow and contaminant transport modelling, as well as to predict changes due to the proposed remediation measures. The remedial alternatives considered for normal conditions from 20 to 40 year periods were waste removal, vertical cut-off barriers, extraction wells and top capping. The results indicated that extraction wells and waste removal are the best alternatives because they significantly reduce both the extension and levels of the contamination plume even after 5 years. The extraction well proved a less expensive remedial alternative than waste removal.   相似文献   
38.
The purpose of this study was to analyse the validity and the economic efficiency of a portable monitor of respiratory parameters (PMRP), used in a home setting for the diagnosis of sleep apnoea/hypopnoea syndrome (SAHS). Eighty nine patients with suspected SAHS were studied in two settings: in the sleep laboratory using full-polysomnography (full-PSG); and at the patient's home using a PMRP. In the home setting, 50 patients were assisted by a technician and 39 set up the equipment themselves. SAHS (apnoea/hypopnoea index (AHI) >10 events x h(-1) by means of full-PSG) was diagnosed in 75 of the 89 patients. An acceptable agreement was obtained between the AHI measured by full-PSG and PMRP, according to the Bland and Altman method of concordance (mean bias 2.56; 95% confidence interval 3.25). Sensitivity and specificity of PMRP were adequate for diagnostic purposes; however, their values rely on the prior PMRP-AHI cut-off point selected with reference to full-PSG-AHI >10. The clinical therapeutic decision taken after PMRP agreed with that taken with full-PSG in 79 patients (89%). Although 10% of the studies with an individual set-up needed repetition, both of the domiciliary modalities (with and without a technician's intervention) were, economically, about three times more efficient than full-PSG. In conclusion, we believe that patients with a suspected sleep apnoea/hypopnoea syndrome should initially be studied in a home setting with a portable monitor of respiratory parameters, since it is a reliable method with an acceptable cost-effective profile.  相似文献   
39.
Detailed analyses and comparisons of urban travel forecasts prepared by applying the state-of-practice sequential procedure and the solution of a combined network equilibrium model are presented. The sequential procedure for solving the trip distribution, mode choice and assignment problems with feedback is the current practice in most transportation planning agencies, although its important limitations are well known. The solution of a combined model, in contrast, results from a single mathematical formulation, which ensures a well-converged and consistent result. Using a real network, several methods for solving the sequential procedure with feedback are compared to the solution of the combined model ESTRAUS. The results of these methods are shown to have various levels of instability. The paper concludes with a call for a new paradigm of travel forecasting practice based on an internally consistent model formulation that can be solved to a level of precision suitable for comparing alternative scenarios.  相似文献   
40.
Individual yeast cells can be successfully isolated and recultured on plates with a new isolation method making use of optical trapping with infrared laser light. The cells can be selected on morphological criteria by high resolution microscopy. The isolation device is constructed from two coverslips separated by spacers, in which selected cells are transferred to a plastic capillary, using the optical trap. To test the procedure, selection experiments were done with a mixture of two Saccharomyces cerevisiae strains, distinguishable both in fluorescence microscopy and on agar plates. These experiments showed that only selected cells were isolated, and close to 100% of the isolated stationary-phase cells formed colonies on agar plates, indicating a high recovery. A lower recovery was obtained with exponential-phase cells, possibly because of a higher sensitivity to laser irradiation. Applications for this method may include the isolation of mutants with altered morphology and the isolation of subpopulations of yeast cultures, for their separate investigation or for the initiation of pure cultures.  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