全文获取类型
收费全文 | 16865篇 |
免费 | 1431篇 |
国内免费 | 607篇 |
学科分类
工业技术 | 18903篇 |
出版年
2024年 | 20篇 |
2023年 | 184篇 |
2022年 | 234篇 |
2021年 | 491篇 |
2020年 | 405篇 |
2019年 | 409篇 |
2018年 | 505篇 |
2017年 | 443篇 |
2016年 | 574篇 |
2015年 | 558篇 |
2014年 | 749篇 |
2013年 | 1094篇 |
2012年 | 947篇 |
2011年 | 1155篇 |
2010年 | 944篇 |
2009年 | 967篇 |
2008年 | 994篇 |
2007年 | 836篇 |
2006年 | 834篇 |
2005年 | 679篇 |
2004年 | 606篇 |
2003年 | 614篇 |
2002年 | 686篇 |
2001年 | 578篇 |
2000年 | 480篇 |
1999年 | 406篇 |
1998年 | 484篇 |
1997年 | 347篇 |
1996年 | 294篇 |
1995年 | 231篇 |
1994年 | 176篇 |
1993年 | 130篇 |
1992年 | 102篇 |
1991年 | 87篇 |
1990年 | 89篇 |
1989年 | 91篇 |
1988年 | 64篇 |
1987年 | 54篇 |
1986年 | 61篇 |
1985年 | 43篇 |
1984年 | 35篇 |
1983年 | 35篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 29篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
11.
Yejun Wu Bowen Yan Juan Zhou Huizhang Lian Xiaojun Yu Jianxin Zhao Hao Zhang Wei Chen Daming Fan 《Journal of food science》2020,85(10):3282-3292
12.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
13.
14.
Yang Yang Yibei Zhou Juan Ren Qiaoji Zheng Kwok Ho Lam Dunmin Lin 《Journal of the European Ceramic Society》2018,38(2):557-566
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response. 相似文献
15.
GIS在深圳市三防指挥信息系统中的应用 总被引:1,自引:0,他引:1
深圳市三防指挥信息系统利用GIS技术,结合水利(水务)、防汛、抗旱的具体业务,建立了水情遥测数据处 理分系统、工况监测数据处理分系统、水务行业三防信息管理分系统、决策支持分系统、水源优化调度分 系统,提高了现代化管理水平。 相似文献
16.
17.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
黄骅坳陷新生代断裂构造系统研究 总被引:5,自引:2,他引:3
黄骅坳陷断裂构造极为发育,其新生代构造系统主要为伸展构造系统,以铲形正断层或坡坪式正断层为主干伸展断层,以不同尺度的北东一北东东向正断层和具调节性质的北西一北西西向断层为特征。经过对黄骅坳陷新生代构造应力场的分析,黄骅坳陷盖层中极难出现明确的走滑断裂,其雁列状排列的断层应为倾斜滑动断层;黄骅坳陷中不同凹陷或断块之间不同的伸展程度往往为横向地垒状凸起、鼻状凸起或鼻状背斜所调节,在横向凸起和凹陷之间伴生北西向正断层,它们与挤压变形体系中具有走滑性质的横向变换断层又有本质上的不同。 相似文献
19.
对走向长壁俯仰斜连续综放开采技术进行了实践,积累了大量的技术数据,针对回采过程中遇到的问题,提出了切实可行的技术措施,经济技术效果显著。 相似文献
20.
When quadrature error exists, the shape of the M‐ary phase shift keying (MPSK) signal constellation becomes skewed‐elliptic. Each MPSK symbol takes on a different symbol error probability (SEP) value. The analytical results presented thus far have been derived from studies which examined the SEP problem assuming that the SEP of each MPSK symbol is equally likely; therefore, those results should not be treated as offering a complete solution. In this letter, we present a new and more complete solution to the SEP problem of MPSK by relaxing the above assumption and finding the expressions for the average as well as individual SEP in the presence of quadrature error. 相似文献