全文获取类型
收费全文 | 173542篇 |
免费 | 11053篇 |
国内免费 | 6137篇 |
专业分类
电工技术 | 7647篇 |
技术理论 | 3篇 |
综合类 | 8971篇 |
化学工业 | 24703篇 |
金属工艺 | 9612篇 |
机械仪表 | 9117篇 |
建筑科学 | 8788篇 |
矿业工程 | 3153篇 |
能源动力 | 3943篇 |
轻工业 | 11147篇 |
水利工程 | 3493篇 |
石油天然气 | 4038篇 |
武器工业 | 1038篇 |
无线电 | 21638篇 |
一般工业技术 | 26690篇 |
冶金工业 | 6084篇 |
原子能技术 | 1592篇 |
自动化技术 | 39075篇 |
出版年
2024年 | 351篇 |
2023年 | 1420篇 |
2022年 | 2815篇 |
2021年 | 4309篇 |
2020年 | 3096篇 |
2019年 | 2568篇 |
2018年 | 17006篇 |
2017年 | 16207篇 |
2016年 | 12762篇 |
2015年 | 4693篇 |
2014年 | 5397篇 |
2013年 | 6618篇 |
2012年 | 10469篇 |
2011年 | 16810篇 |
2010年 | 14974篇 |
2009年 | 12048篇 |
2008年 | 12940篇 |
2007年 | 13576篇 |
2006年 | 5450篇 |
2005年 | 5450篇 |
2004年 | 4317篇 |
2003年 | 3779篇 |
2002年 | 3223篇 |
2001年 | 2335篇 |
2000年 | 1725篇 |
1999年 | 1196篇 |
1998年 | 978篇 |
1997年 | 725篇 |
1996年 | 629篇 |
1995年 | 483篇 |
1994年 | 361篇 |
1993年 | 250篇 |
1992年 | 233篇 |
1991年 | 176篇 |
1990年 | 130篇 |
1989年 | 134篇 |
1988年 | 74篇 |
1987年 | 70篇 |
1986年 | 44篇 |
1985年 | 48篇 |
1984年 | 39篇 |
1968年 | 44篇 |
1966年 | 45篇 |
1965年 | 44篇 |
1959年 | 50篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 35篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
应用油藏地球化学的方法对塔河油田的成藏期次进行了探讨。塔河油田稠油正构烷烃分布完整,但色谱基线不同程度抬升;原油非烃和沥青质碳同位素偏轻,族组成碳同位素发生倒转;原油中普遍含有25-降藿烷。这些特征表明该区油藏经历了至少两期成藏过程,早期充注原油遭受生物降解作用后又受到高成熟原油充注。塔河油田天然气为典型的油型气,成熟度较高,为成熟—过成熟阶段产物,亦显示了两期充注的特征:早期充注的为典型的原油伴生气,充注时间与后期原油的充注时间相同;晚期充注的为高温裂解气,充注方向为自东向西。因此,塔河油田至少存在着3次油气充注过程。 相似文献
102.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth
century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more
rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the
basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving
sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less
successfully in constructive concept formation itself.
The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for
his projected voluminousOrganon der gesamten Analysis.
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
103.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
104.
105.
针对不同地质目标的叠前时间偏移成像解释评价 总被引:3,自引:0,他引:3
随着计算机硬件和地震勘探成像技术的发展,叠前时间偏移正逐步替代常规的NMO加DMO加叠后时间偏移成为地震数据成像处理方法的主流。但对于不同的地质目标,叠前时间偏移的成像效果是否优于常规NMO加DMO加叠后时间偏移的成像效果呢?为此,从地震数据成像处理方法、处理流程和处理参数等方面进行了讨论,并基于某地区三维数据常规处理结果和叠前时间偏移处理结果,针对不同地质目标进行了剖析与评价。认为:叠前时间偏移成像的垂向分辨率较常规处理明显降低,但对于空间波阻抗变化明显的河流和断层,叠前时间偏移成像的空间分辨率要高于常规处理;对于小于1/4波长的叠置薄储层,叠前时间偏移成像的垂向和空间分辨率低于常规处理结果。 相似文献
106.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
107.
108.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
109.
110.
2.4GHz动态CMOS分频器的设计 总被引:1,自引:0,他引:1
对现阶段的主流高速CMOS分频器进行分析和比较,在此基础上设计一种采用TSPC(truesingle phase clock)和E-TSPC(extended TSPC)技术的前置双模分频器电路.该分频器大大提高了工作频率,采用0.6μm CMOS工艺参数进行仿真的结果表明,在5V电源电压下,最高频率达到3GHz,功耗仅为8mW. 相似文献