全文获取类型
收费全文 | 397524篇 |
免费 | 3939篇 |
国内免费 | 869篇 |
专业分类
电工技术 | 6835篇 |
综合类 | 307篇 |
化学工业 | 61952篇 |
金属工艺 | 21368篇 |
机械仪表 | 14571篇 |
建筑科学 | 7565篇 |
矿业工程 | 4868篇 |
能源动力 | 7974篇 |
轻工业 | 21308篇 |
水利工程 | 6029篇 |
石油天然气 | 16373篇 |
武器工业 | 52篇 |
无线电 | 37310篇 |
一般工业技术 | 93137篇 |
冶金工业 | 59490篇 |
原子能技术 | 14050篇 |
自动化技术 | 29143篇 |
出版年
2021年 | 4254篇 |
2019年 | 4118篇 |
2018年 | 7740篇 |
2017年 | 7992篇 |
2016年 | 8557篇 |
2015年 | 4796篇 |
2014年 | 8066篇 |
2013年 | 17040篇 |
2012年 | 11548篇 |
2011年 | 14280篇 |
2010年 | 11668篇 |
2009年 | 13017篇 |
2008年 | 13132篇 |
2007年 | 12668篇 |
2006年 | 10562篇 |
2005年 | 9451篇 |
2004年 | 8948篇 |
2003年 | 8646篇 |
2002年 | 8377篇 |
2001年 | 8274篇 |
2000年 | 8092篇 |
1999年 | 7595篇 |
1998年 | 16348篇 |
1997年 | 12073篇 |
1996年 | 9150篇 |
1995年 | 7090篇 |
1994年 | 6402篇 |
1993年 | 6691篇 |
1992年 | 5388篇 |
1991年 | 5460篇 |
1990年 | 5398篇 |
1989年 | 5205篇 |
1988年 | 5115篇 |
1987年 | 4800篇 |
1986年 | 4759篇 |
1985年 | 5200篇 |
1984年 | 4973篇 |
1983年 | 4771篇 |
1982年 | 4434篇 |
1981年 | 4465篇 |
1980年 | 4525篇 |
1979年 | 4718篇 |
1978年 | 4839篇 |
1977年 | 5032篇 |
1976年 | 5776篇 |
1975年 | 4451篇 |
1974年 | 4467篇 |
1973年 | 4562篇 |
1972年 | 4056篇 |
1971年 | 3707篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
S V Bhat 《Bulletin of Materials Science》1994,17(7):1271-1285
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT
c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon
can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even
in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination
of material parameters of interest such asJ
c andH
c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The
details of these aspects are discussed. 相似文献
93.
An instrument is proposed for continuously tracking the Sun and measuring its height by the use of a laser gyrometer as measuring
converter. The accuracy in photoelectric sighting on the Sun is improved by greatly reducing the light fluxes to be compared
by screening out the central part of the Sun's image in the focal plane.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 7–9, March, 1994. 相似文献
94.
A. A. Kovalev A. F. Kotyuk B. N. Levinskii A. A. Liberman 《Measurement Techniques》1994,37(2):151-158
The authors survey published results on the application of metal diffraction gratings as laser power or energy dividers when the laser beam is split into two approximately equal pans. The normal incidence of laser radiation on metal diffraction gratings of various profiles in the case of three propagating diffraction orders n=0, ±1 is discussed, along with the case of oblique incidence with only two propagating diffraction orders n=0 and n =–1.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 22–26, February, 1994. 相似文献
95.
A method is given for calculating the monitoring reliability parameters (MRP) for an engineering system with allowance for the drift in the measurement error of the means of measurement (MM). The approach is based on introducing a biased MM error distribution into the traditional formulas for the conditional probabilities of spurious and unobserved failure. The bias at the center of the distribution is determined by the systematic error at the given instant. An example is given to illustrate the performance in MRP calculation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–13, January, 1994. 相似文献
96.
A.S. Fomichev I. David S.M. Lukyanov Yu.E. Penionzhkevich N.K. Skobelev O.B. Tarasov 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1994,350(3):605-607
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval. 相似文献
97.
Carroll R.D. Merritt S.W. Branciforte E.J. Tanski W.J. Cullen D.E. Sacks R.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):416-418
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal 相似文献
98.
MA Nowak AL Lloyd GM Vasquez TA Wiltrout LM Wahl N Bischofberger J Williams A Kinter AS Fauci VM Hirsch JD Lifson 《Canadian Metallurgical Quarterly》1997,71(10):7518-7525
Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus. 相似文献
99.
Based on a variational analysis, the authors demonstrate that the noise-induced Gordon-Haus timing jitter in a dispersion-managed soliton transmission system can be substantially reduced by appropriate placement of the amplifiers 相似文献
100.