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   388326篇
  免费   4605篇
  国内免费   1663篇
电工技术   7218篇
综合类   2589篇
化学工业   54758篇
金属工艺   20442篇
机械仪表   15662篇
建筑科学   9624篇
矿业工程   1782篇
能源动力   8135篇
轻工业   28460篇
水利工程   3849篇
石油天然气   3241篇
武器工业   3篇
无线电   45585篇
一般工业技术   77048篇
冶金工业   59183篇
原子能技术   5168篇
自动化技术   51847篇
  2021年   1698篇
  2019年   1535篇
  2018年   22372篇
  2017年   21990篇
  2016年   15194篇
  2015年   3078篇
  2014年   3680篇
  2013年   11686篇
  2012年   10679篇
  2011年   23582篇
  2010年   20619篇
  2009年   18306篇
  2008年   19359篇
  2007年   22017篇
  2006年   7558篇
  2005年   11282篇
  2004年   9215篇
  2003年   8892篇
  2002年   7485篇
  2001年   6682篇
  2000年   6212篇
  1999年   6640篇
  1998年   16853篇
  1997年   11817篇
  1996年   9174篇
  1995年   6847篇
  1994年   6082篇
  1993年   5901篇
  1992年   4199篇
  1991年   4152篇
  1990年   3689篇
  1989年   3639篇
  1988年   3546篇
  1987年   3023篇
  1986年   2948篇
  1985年   3535篇
  1984年   3192篇
  1983年   2853篇
  1982年   2657篇
  1981年   2657篇
  1980年   2512篇
  1979年   2359篇
  1978年   2308篇
  1977年   2902篇
  1976年   4268篇
  1975年   1980篇
  1974年   1878篇
  1973年   1852篇
  1972年   1514篇
  1971年   1356篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
2.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
3.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  相似文献   
4.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
5.
6.
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa.  相似文献   
7.
Journal of Inorganic and Organometallic Polymers and Materials - In this work, a borosilicate glass sample (5SiO2–45B2O3–20Na2O–25CaO–5Ag2O) was added to nano-sized...  相似文献   
8.
An improved glucose-chelator-albumin bioconjugate (GluCAB) derivative, GluCAB-2Mal, has been synthesized and studied for in vivo 64Cu-PET/CT imaging in breast cancer mice models together with its first-generation analogue GluCAB-1Mal. The radioligand works on the principle of tumor targeting through the enhanced permeability and retention (EPR) effect with a supportive role played by glucose metabolism. [64Cu]Cu-GluCAB-2Mal (99 % RCP) exhibited high serum stability with immediate binding to serum proteins. In vivo experiments for comparison between tumor targeting of [64Cu]Cu-GluCAB-2Mal and previous-generation [64Cu]Cu-GluCAB-1Mal encompassed microPET/CT imaging and biodistribution analysis in an allograft E0771 breast cancer mouse model. Tumor uptake of [64Cu]Cu-GluCAB-2Mal was clearly evident with twice as much accumulation as compared to its predecessor and a tumor/muscle ratio of up to 5 after 24 h. Further comparison indicated a decrease in liver accumulation for [64Cu]Cu-Glu-CAB-2Mal.  相似文献   
9.
10.
The SAFT-γ Mie group-contribution equation of state is used to represent the fluid-phase behavior of aqueous solutions of a variety of linear, branched, and cyclic amines. New group interactions are developed in order to model the mixtures of interest, including the like and unlike interactions between alkyl primary, secondary, and tertiary amine groups (NH2, NH, N), cyclic secondary and tertiary amine groups (cNH, cN), and cyclic methine-amine groups (cCHNH, cCHN) with water (H2O). The group-interaction parameters are estimated from appropriate experimental thermodynamic data for pure amines and selected mixtures. By taking advantage of the group-contribution nature of the method, one can describe the fluid-phase behavior of mixtures of molecules comprising those groups over broad ranges of temperature, pressure, and composition. A number of aqueous solutions of amines are studied including linear, branched aliphatic, and cyclic amines. Liquid–liquid equilibria (LLE) bounded by lower critical solution temperatures (LCSTs) have been reported experimentally and are reproduced here with the SAFT-γ Mie approach. The main feature of the approach is the ability not only to represent accurately the experimental data employed in the parameter estimation, but also to predict the vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria, and LCSTs with the same set of parameters. Pure compound and binary phase diagrams of diverse types of amines and their aqueous solutions are assessed in order to demonstrate the main features of the thermodynamic and fluid-phase behavior.  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