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   1882篇
  免费   59篇
  国内免费   8篇
电工技术   19篇
综合类   2篇
化学工业   417篇
金属工艺   65篇
机械仪表   33篇
建筑科学   37篇
矿业工程   1篇
能源动力   96篇
轻工业   118篇
水利工程   5篇
石油天然气   2篇
无线电   247篇
一般工业技术   500篇
冶金工业   164篇
原子能技术   7篇
自动化技术   236篇
  2023年   23篇
  2022年   24篇
  2021年   48篇
  2020年   32篇
  2019年   38篇
  2018年   53篇
  2017年   43篇
  2016年   46篇
  2015年   38篇
  2014年   73篇
  2013年   119篇
  2012年   83篇
  2011年   96篇
  2010年   71篇
  2009年   87篇
  2008年   87篇
  2007年   77篇
  2006年   51篇
  2005年   52篇
  2004年   38篇
  2003年   53篇
  2002年   41篇
  2001年   40篇
  2000年   36篇
  1999年   40篇
  1998年   40篇
  1997年   33篇
  1996年   25篇
  1995年   38篇
  1994年   31篇
  1993年   30篇
  1992年   24篇
  1991年   28篇
  1990年   21篇
  1989年   15篇
  1988年   23篇
  1987年   15篇
  1986年   17篇
  1985年   31篇
  1984年   26篇
  1983年   20篇
  1982年   20篇
  1981年   18篇
  1980年   15篇
  1979年   14篇
  1978年   10篇
  1977年   9篇
  1976年   15篇
  1975年   10篇
  1971年   7篇
排序方式: 共有1949条查询结果,搜索用时 15 毫秒
41.
Site selection is a key factor in any aquaculture operation, affecting both success and sustainability as well as solving land or water use conflicts. This study was conducted to identify suitable sites for carp farming development in urban water bodies (UWBs) of Chittagong, Bangladesh using Geographical Information Systems (GIS) based MultiCriteria Evaluation (MCE) of water, soil and infrastructure database. ASTER imagery and 14 thematic layers were analyzed with ENVI and GIS capabilities, and developed a series of GIS models to identify and prioritize the appropriate UWBs for carp farming. The study identified 487 UWBs occupying 362 ha and revealed 280 ha (77%) is the most suitable, 36 ha (10%) is moderately suitable and 46 ha (13%) is not suitable which was consistent with field verification. The results are encouraging for extension of carp culture and diversify the economic activities of the urban dwellers.  相似文献   
42.
43.

This study presents a comprehensive analysis of the entropy of condensed phases, its temperature, pressure, and composition dependence on a macroscopic correlative platform. Two principal contributions to total nonconfiguration entropy (ST) are outlined. They are: (i) the pure thermal (Sth) contribution arising from the isochoric temperature dependence of Gibbs energy (GT) and (ii) the elastic contribution (Sel) representing the dilatational volume effects. It is then argued that entropy variation among a group of alloy phases can be exclusively related to molar volume, only when both thermal pressure (pth) and thermal entropy terms assume common values for all members. This argument is extended to establish a linear relationship between transformation entropy (ΔStr) and transformation-induced volumetric strain (ΔVtr/V). The temperature and pressure dependencies of entropy have been discussed in terms of the complementing roles of Sth and Sel and simple approximations to these effects are suggested. A macroscopic power law relation for systematizing the standard entropy variation using a composite scaling parameter (MV2/3/Tm) has been proposed, and its validity is demonstrated for both solid and liquid metals. This power law correlation has been exploited to deduce the following outcome: (i) a simple approximation for the initial slope (dp/dTm) of pTm melting curve, (ii) self-consistent correlation of entropy with specific heat and Debye temperature, (iii) estimation of entropy of metastable phases, and (iv) correlating dilute solution entropy with volume effects of alloying.

  相似文献   
44.
Seventy-two pearl millet genotypes were water stressed at panicle development and grain filling stages. Neither grain yields, yield components, protein percent nor total protein per unit area were affected by water deficit during panicle development but protein content per grain was increased. When plants were water stressed during grain filling, grain yield, grains per unit area and 1000 grain weight were reduced, but grain protein percentage increased. Total protein per unit area was reduced primarily due to lower grain yield. The protein content per grain was unaffected by stress, suggesting that the apparent increase in protein percentage is due to reduced carbohydrate accumulation under stress.  相似文献   
45.
A field experiment was conducted with tea cultivar UPASI‐9 over a period of 9 years to evaluate the long‐term effects of nitrogen (N) and potassium (K) fertilizers on yield, biochemical parameters, soil and leaf nutrient status. The yield increase was as high as 66% over the control for N application of 450 kg ha?1 year?1. Polyphenol and amino acid contents increased with increase in K application rate. Positive and significant correlation was found between nitrate reductase activity and the amino acid content of the tea shoots. While ammoniacal nitrogen in the soil was not affected by the application of fertilizer, ammonium acetate extractable K increased. The failure to apply fertilizer resulted in depletion of the organic matter status of the soil. Although increased rate of nitrogen application increased the overall yield of made tea (kg ha?1 year?1), the specific yield (kg kg?1 N) declined. The soil tended to become acidic from frequent application of high doses of nitrogenous fertilizer. The leaf NK status was significantly influenced by the various treatments. Copyright © 2004 Society of Chemical Industry  相似文献   
46.
A systematic study was conducted using reversed‐phase thin‐layer chromatography wherein unsaponifiable matter of samples namely, pure cow and buffalo milk fats, vegetable oils (groundnut oil, soya bean oil and sunflower oil) and milk fats adulterated with vegetable oils (≥1%) were run along with the reference standards using two new solvent systems to detect adulteration in milk fat. The results of the study revealed that adulteration at even a 1% level could easily be detected using this rapid, reliable and reproducible method based on the presence of β‐sitosterol as a marker and some additional spots ascribable to their occurrence in vegetable oils only.  相似文献   
47.
Pancreatic ductal adenocarcinoma (PDAC), a highly aggressive malignancy with a poor prognosis is usually detected at the advanced stage of the disease. The only US Food and Drug Administration-approved biomarker that is available for PDAC, CA 19-9, is most useful in monitoring treatment response among PDAC patients rather than for early detection. Moreover, when CA 19-9 is solely used for diagnostic purposes, it has only a recorded sensitivity of 79% and specificity of 82% in symptomatic individuals. Therefore, there is an urgent need to identify reliable biomarkers for diagnosis (specifically for the early diagnosis), ascertain prognosis as well as to monitor treatment response and tumour recurrence of PDAC. In recent years, proteomic technologies are growing exponentially at an accelerated rate for a wide range of applications in cancer research. In this review, we discussed the current status of biomarker research for PDAC using various proteomic technologies. This review will explore the potential perspective for understanding and identifying the unique alterations in protein expressions that could prove beneficial in discovering new robust biomarkers to detect PDAC at an early stage, ascertain prognosis of patients with the disease in addition to monitoring treatment response and tumour recurrence of patients.  相似文献   
48.
The current work explores the usage of novel synthesized Deep Eutectic Solvent (DES) as a catalyst cum solvent media for the thermal dehydrogenation of chemical hydrides, namely Ammonia Borane (AB) and Ethylene diamine bisborane (EDAB). In the first instance, the quantum chemistry based COSMO-SAC (COnductor like Screening MOdel Segment Activity Coefficient) model was used for the selection of the pertinent solvent. 1-Butyl-3-methylimidazolium methanesulfonate: Imidazole ([BMIM][MeSO3]:[Im]) turned out to be an ideal eutectic mixture with the highest predicted solubility with amine boranes. The DES was synthesized by combining the Hydrogen Bond Acceptor (HBA), namely 1-Butyl-3-methylimidazolium methanesulfonate and Imidazole as Hydrogen Bond Donor (HBD) at a molar ratio of 1:2 and T = 70 °C. The formation of DES was confirmed by recording the NMR spectra. Further, the thermal dehydrogenation study was performed at a vacuum of 4 × 10?2 mbar (gauge pressure) of AB/DES and EDAB/DES systems at 105 °C, where a hydrogen equivalent of 1.40 and 2.55 was produced, respectively. The residual samples were further analyzed through 1H NMR analysis for the reaction mechanism and to confirm the role of Ionic Liquid-based DES as catalyst cum solvent media.  相似文献   
49.
Li+ conductive solid polymeric electrolytes (SPEs) have been prepared by complexing Li salts LiX (X = I, SCN, CLO4, CF3SO3) with poly(vinyl butyral) (PVB) an amorphous polymer with a low Tg value and well known for its outstanding laminating properties. These self-supporting SPEs have been prepared by the solution cast technique using cyclohexanone, tetrahydrofuran, and n-butyl alcohol as solvents. The XRD and DSC investigations correlated to measured ionic conductivities have revealed that in addition to the amorphous nature of the resulting complex, its Tg value, the concentration and the values of the lattice energies of the complexing salts, the solvent used in making the SPEs also govern the value of ionic conductivity. Highest ionic conductivity values attained in SPEs made with n-butyl alcohol are explained in terms of the interception of the hydrogen bonding due to solvation.  相似文献   
50.
Excipients form a major component of pharmaceutical formulations and are classified as any ingredient other than the active ingredient which is included within the product formulation to improve drug product performance. Functional uses of excipients include improving solubility and stability, safety and efficacy, as bulking agents in lyophilized formulations, tonicity agents, and aiding in controlled or prolonged drug delivery. Parenteral formulations are sterile, pyrogen-free; free of particulate matter and by-pass the body’s natural defense mechanisms. Excipients may demonstrate a synergistic effect when combined with an active ingredient but may also lead to unwanted reactions with the drugs and packaging components. Ideal excipients are required to be considered safe, inert and multifunctional. Contrary to the past, safety of excipients needs to be well established in order for their use in the pharmaceutical formulations. Therefore, careful consideration should be given while selecting an excipient. This review article provides an overview of the excipients used exclusively in small molecule and biological parenteral products including solutions, suspensions, and lyophilized formulations, information on the possible drug-excipient and drug-packaging interactions and the regulatory requirements for the use of pharmaceutical excipients. The readers will be able to have a comprehensive understanding of the excipients used in parenteral formulations.  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