全文获取类型
收费全文 | 898篇 |
免费 | 21篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 31篇 |
综合类 | 4篇 |
化学工业 | 262篇 |
金属工艺 | 29篇 |
机械仪表 | 9篇 |
建筑科学 | 11篇 |
能源动力 | 69篇 |
轻工业 | 78篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 79篇 |
一般工业技术 | 174篇 |
冶金工业 | 82篇 |
原子能技术 | 19篇 |
自动化技术 | 71篇 |
出版年
2022年 | 10篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 39篇 |
2013年 | 45篇 |
2012年 | 49篇 |
2011年 | 53篇 |
2010年 | 45篇 |
2009年 | 49篇 |
2008年 | 47篇 |
2007年 | 48篇 |
2006年 | 52篇 |
2005年 | 34篇 |
2004年 | 24篇 |
2003年 | 22篇 |
2002年 | 27篇 |
2001年 | 20篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 36篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有923条查询结果,搜索用时 0 毫秒
851.
Satoshi KANECO Hiroaki KITANAGA Hideyuki KATSUMATA Tohru SUZUKI 《Frontiers of Chemical Science and Engineering》2012,6(4):432
In the present work, a new preconcentration method of trace elements by adsorption onto a niobium wire has been developed for electrothermal atomization atomic absorption spectrometry (ETAAS) with a tungsten tube atomizer. Detection limits (pg·mL–1) by this method combined with ETAAS were 45 for bismuth, 7.0 for cadmium, 20 for copper, 1.3 for gold, 36 for lead, 65 for manganese, 9.5 for rhodium and 19 for silver. 相似文献
852.
Kawagucci S Tsunogai U Kudo S Nakagawa F Honda H Aoki S Nakazawa T Gamo T 《Analytical chemistry》2005,77(14):4509-4514
We developed a simple measurement system for delta17O in nanomole quantities of CO2 using continuous flow isotope ratio mass spectrometry (CF-IRMS). The analytical system consisted of a sample injection system, a helium-purged CO2 purification line, a capillary GC, a combustion unit, and CF-IRMS. A unique feature of the system is that we use molecular CO2 to determine the isotopic compositions including delta17O. The delta17O of CO2 in a sample is calculated from the mass ratios of both 45/44 and 46/44 of two different kinds of CO2, which have been purified quantitatively from different aliquots of a sample. While one aliquot (rCO2) flows into IRMS directly, the other (eCO2) flows through a CuO unit (900 degrees C) prior to injection into IRMS, to exchange oxygen atoms in the sample CO2 molecules with those in CuO for which we can assume Delta17O = 0. In our system, we introduce both rCO2 and eCO2 alternately to IRMS repeatedly by using an automatic multianalytical system to improve analytical precision statistically. The standard deviation of 0.35 per thousand for Delta17O can be realized using as little as 8.7 nmol CO2 in a approximately 3-h analysis. Based on this system, we have quantified delta17O in the stratospheric CO2 over Japan. 相似文献
853.
We have developed a high-speed confocal laser microscope. A microlens-array disk set in front of a pinhole-array disk improved optical efficiency more than ten times compared with that of conventional Nipkow confocal microscopy. This new microscope achieves a high-speed measurement of 1 frame/ms. We expect that it will be used for measuring biological and industrial active samples. 相似文献
854.
855.
Kuwahara H. Amemiya S. Murano K. 《Selected Areas in Communications, IEEE Journal on》1986,4(8):1367-1372
This paper proposes an alternative to the passive bus realization of the current CCITT ISDN user-network interface. Our new approach is termed phase aligned passive bus (PAB) scheme. An automatic phase adjusting mechanism using a monitor bit is employed in the terminal equipment. This scheme enables the terminals to operate in complete phase synchronization on a passive bus. The advantages that result from this technique are: 1) Eliminates, in principle, the bus length limitation due to round-trip delay time. If line bit rate of 192 kbit/s is kept, then a practical bus length is about 700 m with no limitation on terminal distribution. 2) Allows various extended bus configurations, such as simple repeatered extention, connection of optical link, and multibranched passive bus. 3) Provides spare bit transmission capability to facilitate intrabus communication and maintenance. As an alternative it keeps the general framework of the current CCITT I-series standard such asB + B + D channel structure and LAP-D protocol. Experiments realizing long passive buses are shown to confirm the feasibility of the proposed scheme. This concept is also shown to be applicable to a 2-wire full duplex user-network interface, advantageous in the existing office environment, employing time compression transmission. 相似文献
856.
857.
An optimisation scheme is proposed for the optical-filter bandwidth in an optical preamplifier for a given tolerance in the signal-wavelength and a given filter profile. The optimised bandwidth is 3.46 times the conceivable detuning for a Lorentzian-shaped filter profile. Preamplifiers with optimised bandwidth can operate with the lowest noise figure at maximum detuning.<> 相似文献
858.
859.
Benchmark experiments of thermal neutron distributions within the shield materials, graphite pile and pure water, were performed by using 252Cf fission neutrons and gold foil activation detectors, and, to these results, the estimates obtained by using the discrete ordinate code ANISN and the Monte Carlo code MCNP5 with two different cross-section libraries, ENDF/B-VI and the Japanese new version of JENDL-3.3, were compared. The results revealed that the MCNP5 calculations with the two libraries closely agree with the experiments and that there are slight differences between the MCNP5 and the ANISN calculations. The differences are caused mainly by the overestimation of the thermal neutron absorption cross sections constructed in NJOY99. The ANISN calculations with the modified absorption cross sections reproduced the results of the MCNP5 fairly well. 相似文献
860.
Tanisako A Hori A Okumura A Miyata C Kuzuryu C Obi T Yoshimura H 《Journal of electron microscopy》2005,54(4):379-383
The projection X-ray microscope utilises a very small X-ray source emitted from a thin (0.1-3 microm) target metal film excited by the focused electron beam of a scanning electron microscope. When an object is placed just below the target metal film, the diverging X-rays enlarge the shadow of the object. Because no X-ray optics such as a zone-plate is used, the focal depth is, in principle, infinitely large. We exploited this to apply projection X-ray microscopy to three-dimensional (3-D) structure analysis by means of cone-beam computed tomography. The projection images of a small arthropod (Pseudocneorhinus bifasciatus, 5 mm in length), was recorded at 3 degrees increments over the whole range (360 degrees) of a stepping-motor-controlled sample rotator. A 3-D image was reconstructed from corn-beam projections using a filtered back-projection algorithm. The reconstructed 3-D image showed in detail the internal structure of an opaque object. 相似文献