全文获取类型
收费全文 | 341208篇 |
免费 | 2260篇 |
国内免费 | 1368篇 |
专业分类
电工技术 | 5995篇 |
综合类 | 579篇 |
化学工业 | 49619篇 |
金属工艺 | 13834篇 |
机械仪表 | 10493篇 |
建筑科学 | 7807篇 |
矿业工程 | 1971篇 |
能源动力 | 8600篇 |
轻工业 | 27950篇 |
水利工程 | 3777篇 |
石油天然气 | 7519篇 |
武器工业 | 49篇 |
无线电 | 39396篇 |
一般工业技术 | 69686篇 |
冶金工业 | 61198篇 |
原子能技术 | 8970篇 |
自动化技术 | 27393篇 |
出版年
2021年 | 2978篇 |
2020年 | 2382篇 |
2019年 | 2923篇 |
2018年 | 4814篇 |
2017年 | 4903篇 |
2016年 | 5373篇 |
2015年 | 3246篇 |
2014年 | 5577篇 |
2013年 | 14902篇 |
2012年 | 8917篇 |
2011年 | 11940篇 |
2010年 | 9416篇 |
2009年 | 10857篇 |
2008年 | 11188篇 |
2007年 | 11184篇 |
2006年 | 9585篇 |
2005年 | 8793篇 |
2004年 | 8634篇 |
2003年 | 8371篇 |
2002年 | 8076篇 |
2001年 | 8159篇 |
2000年 | 7812篇 |
1999年 | 8035篇 |
1998年 | 19294篇 |
1997年 | 13728篇 |
1996年 | 10525篇 |
1995年 | 8105篇 |
1994年 | 7091篇 |
1993年 | 7081篇 |
1992年 | 5173篇 |
1991年 | 4954篇 |
1990年 | 4900篇 |
1989年 | 4878篇 |
1988年 | 4489篇 |
1987年 | 4031篇 |
1986年 | 4023篇 |
1985年 | 4486篇 |
1984年 | 4083篇 |
1983年 | 3824篇 |
1982年 | 3565篇 |
1981年 | 3596篇 |
1980年 | 3586篇 |
1979年 | 3357篇 |
1978年 | 3360篇 |
1977年 | 3782篇 |
1976年 | 4876篇 |
1975年 | 2906篇 |
1974年 | 2825篇 |
1973年 | 2833篇 |
1972年 | 2420篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The program LMSMVE performs robust regression analysis by using the method of the least median of squares. It also computes robust distances to locate leverage points, that is, outliers with respect to the set of independent variables. LMSMVE constructs plots of least median of squares residuals against robust distances. Both methods can tolerate up to half the data being outliers before they fail to give results that describe the bulk of the data. A complete system that operates directly on SYSTAT files is available for the IBM PC and compatibles; it includes a utility that converts ASCII files to SYSTAT format. 相似文献
992.
A. E. Gorodetskii A. V. Markin V. N. Chernikov A. P. Zakharov T. A. Burtseva I. V. Mazul N. N. Shipkov G. D. Tolstolutskaya V. F. Rybalko 《Atomic Energy》1997,82(6):448-462
Conclusions The conditions have been proposed for performing modeling experiments making it possible to predict the accumulation of hydrogen
isotopes in carbon materials which are in contact with a tokamak plasma acting as a source of particles having a flux density
of between 3×1016 and 3×1019 cm−2·sec−1. By analyzing the reemission fluxes formed in the stopping zone of the particles implanted from the plasma it is suggested
that the action of the plasma as regards the sorption of hydrogen is identical to that of annealing the material in an atmosphere
of hydrogen isotopes at a pressure of 1–103 Pa and a temperature of 1200–1700 K. The quantity of absorbed deuterium in POCO, UAM, RGT-B, and USB increases as the temperature
is lowered and the pressure is raised (1500 K, 0.66 Pa→1200 K, 133 Pa). As regards their sorption of deuterium, POCO, UAM,
and RGT behave similarly. There is a tendency for the sorption capacity of materials doped with boron to be reduced. In a
class of itself is the isotropic material USB, whose sorption capacity is a factor of 10–100 lower than that of undoped graphite.
The introduction into these materials of radiation-induced defects (T=300 K) by means of ion irradiation in the range 0.1–1 dpa results in a continuous rise in the deuterium sorption capacity
by a factor of 10–100 (up to 10−2 atomic fraction). The USB graphite demonstrates record low increments in the sorption capacity. In the fluence range identical
to 1–10 dpa the sorption capacity of carbon materials for hydrogen is almost constant. The process of the sorption of hydrogen
isotopes can be described as the filling of two ensembles of traps, deep traps which are difficult to access and readily accessible
Langmuir traps. In the RGT-B materials containing 0.1% of boron, the traps introduced by irradiation with 300-keV neon ions
vanish on annealing in a vacuum (T=1800 K, t=1 min).
Institute of Physical Chemistry, Russian Academy of Sciences.
SINTEZ Scientific and Technical Center, Scientific-Research Institute of Electrophysical Apparatus.
Graphite Scientific-Research Institute.
National Scientific Center, Kharkov Physicotechnical Institute. Translated from Atomnaya énergiya, Vol. 82, No. 6, pp. 448–464,
June, 1997. 相似文献
993.
994.
Yu. E. Pivinskii P. V. Dyakin Ya. Yu. Pivinskii S. V. Vikhman 《Refractories and Industrial Ceramics》2003,44(5):309-313
General aspects (including terminology) related to the use of ultradisperse particulates (nanosystems) are discussed. The important role of nanoparticles in the technology of highly concentrated binding suspensions (HCBS) and refractory castables is emphasized. Using nanoparticles provides a route toward improving the rheotechnologic properties of HCBS and HCBS-based molding mixtures as well as the structure and service properties of the end product. 相似文献
995.
Novel compounds RETSb2 have been prepared and characterized for T Cu (RE rare earth from La to Lu), Ni (RE La to Ho), Pd (RE La to Tb) and Au (RE La to Sm). From X-ray powder diffraction analyses all compounds were found to crystallize as the ZrCuSi2 type. Magnetic susceptibilities were generally measured in the temperature range from 4 to 100 K. YCuSb2 and LaTSbz are temperature-independent paramagnets. RETSb2 compounds are found to order antiferromagnetically below T = 20 K. PrPdSb2 and TbPdSb2 undergo metamagnetic transitions, whereas PrCuSb2 and ErCuSb2 are simple ferromagnets. The Sm-containing compounds are typical Van Vleck paramagnets owing to the closely spaced multiplets. 相似文献
996.
A Kurtaran J Preitfellner P Schaffarich C Scheuba B Niederle I Virgolini E Havlik 《Canadian Metallurgical Quarterly》1997,36(6):202-204
AIM: The aim of the present study was to estimate the additional radiation exposure to personnel, other patients and members of the family caused by patients who had been injected with 99mTc-Sestamibi (Cardiolite DuPONT PHARMA) for preoperative localization of parathyroid adenoma. METHODS: Dose rates were measured from 16 patients who had received an intravenous injection of 600 +/- 50 MBq 99mTc-Sestamibi. All measurements were performed with a portable dosimeter (Berthold LB 133) at 3 different distances (0.5, 1 and 2 m) at 10 min, 180-200 min and 24 h after administration of the tracer. RESULTS: The dose rates amounted to 20.5 microSv/h at 0.5 m, 5.25 microSv/h at 1 m and 1.55 microSv/h at 2 m distance from patients respectively. The biological half-life was 54 h. The calculated maximal dose to other persons in the waiting area was 31.2 microSv, to family members 27.6 microSv and to nurses in a ward 31.2 microSv. CONCLUSION: Our results indicate that the calculated maximal radiation exposure for personnel, family members and other patients even under very unfavourable conditions was below the maximal allowed dose for non-professionally exposed persons. 相似文献
997.
Internet information services replicate their servers to improve availability, response time, and fault tolerance. Traditional replication algorithms do not address the scale and administrative decentralization of today's internetworks. We have proposed and implemented a scalable and efficient tool to replicate wide-area, autonomously managed services. We target replication degrees of thousands of weakly consistent replicas. The main goal of our replication tool is to make traditional replication services scale in today's exponentially growing, autonomously managed internetworks. Our tool, which we call flood-d, allows servers to be organized in multiple replication groups. For each replication group, flood-d builds a logical update topology that is resilient to server failure, and tries to minimize the communication cost and propagation time needed to transmit updates. Flood-d's logical topologies are computed based on communication latency and available network bandwidth. This paper describes flood-d, and presents simulation results obtained when using flood-d to extend existing replication algorithms. Our results show the gains of organizing service replicas into multiple, smaller replication groups, and using network-cognizant logical topologies to propagate updates. We argue that existing as well as emerging Internet information services can benefit from flood-d's services 相似文献
998.
999.
1000.
Shunt active power filters are connected in parallel with the electricity supply network. If the AC mains has a neutral conductor, it is desirable to compensate the mains harmonic currents zero-sequence components. This can be achieved with a four-wire pulsewidth modulation voltage converter connected to the AC mains. In this case, the three-phase and the neutral AC currents must be controlled. A generalization of the space-vector-based current controller in the αβo coordinate system is presented in this paper. With this current controller, all the current harmonic systems of positive, negative, and zero sequence can be injected by the converter and, thus, compensated on the AC mains. The system is also useful to compensate unbalanced currents of fundamental frequency. A useful benefit of this system is that it is possible to control the converter four-wire currents with equal hysteresis errors. Simulation and experimental results are presented 相似文献