全文获取类型
收费全文 | 25639篇 |
免费 | 2500篇 |
国内免费 | 1857篇 |
专业分类
电工技术 | 1983篇 |
技术理论 | 1篇 |
综合类 | 2715篇 |
化学工业 | 1673篇 |
金属工艺 | 1639篇 |
机械仪表 | 3823篇 |
建筑科学 | 2685篇 |
矿业工程 | 3326篇 |
能源动力 | 976篇 |
轻工业 | 443篇 |
水利工程 | 3154篇 |
石油天然气 | 1833篇 |
武器工业 | 243篇 |
无线电 | 471篇 |
一般工业技术 | 1897篇 |
冶金工业 | 1105篇 |
原子能技术 | 390篇 |
自动化技术 | 1639篇 |
出版年
2024年 | 103篇 |
2023年 | 272篇 |
2022年 | 541篇 |
2021年 | 689篇 |
2020年 | 828篇 |
2019年 | 585篇 |
2018年 | 630篇 |
2017年 | 739篇 |
2016年 | 880篇 |
2015年 | 960篇 |
2014年 | 1558篇 |
2013年 | 1684篇 |
2012年 | 2309篇 |
2011年 | 2122篇 |
2010年 | 1556篇 |
2009年 | 1507篇 |
2008年 | 1263篇 |
2007年 | 1663篇 |
2006年 | 1598篇 |
2005年 | 1360篇 |
2004年 | 1124篇 |
2003年 | 1006篇 |
2002年 | 884篇 |
2001年 | 751篇 |
2000年 | 631篇 |
1999年 | 491篇 |
1998年 | 375篇 |
1997年 | 296篇 |
1996年 | 301篇 |
1995年 | 289篇 |
1994年 | 225篇 |
1993年 | 144篇 |
1992年 | 147篇 |
1991年 | 100篇 |
1990年 | 79篇 |
1989年 | 74篇 |
1988年 | 46篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 23篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 18篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1964年 | 2篇 |
1959年 | 13篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
ETRⅠ-30调速器是瑞士爱舍维斯工厂生产的具有PID调节规律的电液调速器。本文对其液压控制系统作了较详细的介绍,供有关人员参考。 相似文献
42.
J.M Mäkynen J.K Jokiniemi P.P Ahonen E.I Kauppinen R Zilliacus 《Nuclear Engineering and Design》1997,178(1):74
Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper. 相似文献
43.
水力喷砂割缝增产增注技术的作用原理及展望 总被引:11,自引:2,他引:9
本文对从俄罗斯引进的水力喷砂割缝技术的发展过程、工作原理及该技术在大庆油田的试验情况做了详细的阐述。并对它的改进及其将来的推广与发展前景做了展望。 相似文献
44.
45.
46.
文章论述了井塔拆除爆破中,把框架承重立柱的裸露钢筋骨架失稳看作为压杆失稳以及井塔在倾斜撞地时下部不解体破坏的估算。 相似文献
47.
M. Bennahmias H. B. Radousky T. J. Goodwin R. N. Shelton 《Journal of Electronic Materials》1993,22(10):1189-1193
Magnetic characterization has been performed on the members of the cuprateniobate RBa2Cu2NbO8 (R = Pr, Nd, and La) series and R1.5Ce0.5Sr2Cu2NbO10 (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K.
The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition
is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of
the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting
NdCSCNO, SmCSCNO, and EuCSCNO compounds. 相似文献
48.
49.
针对稠油黏度高、密度大、驱替效率低,常规方法开采困难等问题,开展了稠油开采装置研究。介绍了全液压稠油开采装置在原油开采过程中的加热功能,分析了采油装置系统井下流体流动及传热过程。结合理论研究方法和热力学计算,建立了井下流体热交换的物理和数学模型,并对模型进行了分析、矫正和求解。以实际油井参数和液压油的流量、温度为输入参数,通过计算机仿真模拟了井下热交换参数之间的关系,从而改进了已获得的热交换理论方程和模型,并得出了原油的产量与液压油的输入量之间的关系,以及保温提采原油所需要的最小液压油输入量。该模型的建立为进一步研究不同井况和不同输入状态下的流体传热提供了理论依据。 相似文献
50.
Mamata Mukhopadhyay Sameer V Dalvi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(4):445-454
A supercritical antisolvent (SAS) process is employed for production of solid nanoparticles from atomized droplets of dilute solution in a flowing supercritical carbon dioxide (SC CO2) stream by attaining extremely high, very rapid, and uniform supersaturation. This is facilitated by a two‐way mass transfer of CO2 and solvent, to and from the droplet respectively, rendering rapid reduction in equilibrium solubility of the solid solute in the ternary solution. The present work analyses the degree of supersaturation and nucleation kinetics in a single droplet of cholesterol solution in acetone during its flight in a flowing SC CO2 stream. Both temperature and composition are assumed to be uniform within the droplet, and their variations with time are calculated by balancing the heat and mass transfer fluxes to and from the droplet. The equilibrium solubility of cholesterol with CO2 dissolution has been predicted as being directly proportional to the Partial Molar Volume Fraction (PMVF) of acetone in the binary (CO2–acetone) system. The degree of supersaturation has been simulated up to the time required to attain almost zero cholesterol solubility in the droplet for evaluating the rate of nucleation and the size of the stable critical nuclei formed. The effects of process parameters have been analysed in the pressure range of 7.1–35.0 MPa, temperature range of 313–333 K, SC CO2 flow rate of 0.1136–1.136 mol s?1, the ratio of the volumetric flow rates of CO2‐to‐solution in the range of 100–1000, and the initial mole fraction of cholesterol in acetone solution in the range of 0.0025–0.010. The results confirm an extremely high and rapid increase in degree of supersaturation, very high nucleation rates and stable critical nucleus diameter of the order of a nanometre. Copyright © 2005 Society of Chemical Industry 相似文献