全文获取类型
收费全文 | 249023篇 |
免费 | 1667篇 |
国内免费 | 265篇 |
专业分类
电工技术 | 4039篇 |
综合类 | 91篇 |
化学工业 | 40347篇 |
金属工艺 | 15143篇 |
机械仪表 | 10061篇 |
建筑科学 | 4175篇 |
矿业工程 | 3759篇 |
能源动力 | 3872篇 |
轻工业 | 9710篇 |
水利工程 | 4088篇 |
石油天然气 | 13006篇 |
武器工业 | 28篇 |
无线电 | 20186篇 |
一般工业技术 | 62751篇 |
冶金工业 | 32145篇 |
原子能技术 | 11136篇 |
自动化技术 | 16418篇 |
出版年
2021年 | 2754篇 |
2019年 | 2730篇 |
2018年 | 5430篇 |
2017年 | 5710篇 |
2016年 | 6044篇 |
2015年 | 3051篇 |
2014年 | 5323篇 |
2013年 | 10082篇 |
2012年 | 7304篇 |
2011年 | 8928篇 |
2010年 | 7295篇 |
2009年 | 8106篇 |
2008年 | 8173篇 |
2007年 | 7858篇 |
2006年 | 6361篇 |
2005年 | 5567篇 |
2004年 | 5483篇 |
2003年 | 5299篇 |
2002年 | 5134篇 |
2001年 | 4949篇 |
2000年 | 4938篇 |
1999年 | 4254篇 |
1998年 | 7175篇 |
1997年 | 5835篇 |
1996年 | 4423篇 |
1995年 | 3655篇 |
1994年 | 3422篇 |
1993年 | 3623篇 |
1992年 | 3214篇 |
1991年 | 3359篇 |
1990年 | 3481篇 |
1989年 | 3371篇 |
1988年 | 3267篇 |
1987年 | 3260篇 |
1986年 | 3156篇 |
1985年 | 3315篇 |
1984年 | 3253篇 |
1983年 | 3147篇 |
1982年 | 2993篇 |
1981年 | 3047篇 |
1980年 | 3071篇 |
1979年 | 3257篇 |
1978年 | 3490篇 |
1977年 | 3460篇 |
1976年 | 3912篇 |
1975年 | 3210篇 |
1974年 | 3293篇 |
1973年 | 3341篇 |
1972年 | 2987篇 |
1971年 | 2754篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The present study has been divided into two sets. In the first set, the aim of the experiments was to investigate the dose-response effect of selective serotonin re-uptake inhibitor (SSRI) citalopram on rat exploratory behaviour in the elevated plus-maze. In the second set of experiments, the effect of cholecystokinin (CCK) CCKA and CCKB receptor antagonists, devazepide and L 365260, on citalopram-induced decrease of exploratory behaviour in the elevated plus-maze was studied. Citalopram (5 and 10 mg/kg) decreased the number of open and total arm entries, line crossings on open arms, and percentage of time spent exploring in open arm. Dose 15 mg/kg was without any effect on rat exploratory behaviour. Devazepide (0.01 and 1.0 mg/kg) failed to modify any of the citalopram-induced changes observed. L 365260 (1.0 mg/kg) reversed most of the effects of citalopram: the numbers of open and total arm entries, the number of line crossings, and the percentage of time spent exploring in open arms. L 365260 at dose level 0.01 mg/kg was ineffective. These results support the involvement of the CCKB receptor subtype in SSRI-induced anxiogenic-like effects in rodents. 相似文献
32.
The metabolism of the poly(A) tail is a process important for the translational regulation of maternal mRNAs in Xenopus laevis oocytes and early embryos. Two poly(A) nuclease (PAN) activities have been described in Xenopus embryo or activated egg extracts (Legagneux et al (1995) RNA 1, 1001-1008). These activities (default PAN and EgPAN) are distinguishable by their deadenylation kinetics and their substrate specificities. In this report, we show that these activities display different sensitivities to biochemical treatments. Urea and, to a lesser extent, spermidine, inhibit EgPAN at concentrations which have no effect on default PAN. Heparin activates default PAN but inhibits EgPAN. When extracts are fractionated by ultracentrifugation, the default activity is recovered in one unique fraction, whereas two fractions must be combined to reconstitute the EgPAN activity. Moreover, these two deadenylation activities are separable by size exclusion chromatography under native conditions. We conclude that these two deadenylation activities are mediated by two protein complexes. 相似文献
33.
Known examples of the positive influence of electrohydroimpulse treatment on the quality of weld joints of various steels, particularly including an increase in their long-term and cyclic strength and also corrosion resistance, are analyzed. It is shown that in this case there is a reduction in residual macro- and micro-stresses and also a change in the parameters of the dislocation structure of the joint metal in the direction of stabilization of it.Translated from Problemy Prochnosti, No. 4, pp. 119–123, April, 1996. 相似文献
34.
Biryukov S.V. Polevoi V.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(6):1160-1170
For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths 相似文献
35.
The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994. 相似文献
36.
M.E.W. Eggenkamp V. A. Shvarts R. Blaauwgeers A. Storm R. Jochemsen G. Frossati 《Journal of Low Temperature Physics》1998,110(1-2):299-304
This paper focuses on the hydrodynamics of third sound on a superfluid
3
He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range. 相似文献
37.
38.
A method is described for experimentally determining the dose rate created in building bricks by incorporated natural radionuclides.
It was established using the thermoluminescence dosimetry method that the measured dose rate depends on the detector thickness,
the mass of the ceramic product investigated, and the irradiation geometry. The contributions to the measured dose of weakly
penetrating α and β radiation and hard ψ radiation are separated, the ratio between them depending on the experimental conditions.
Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–66, July, 1996. 相似文献
39.
40.
N Sobel V Prabhakaran JE Desmond GH Glover EV Sullivan JD Gabrieli 《Canadian Metallurgical Quarterly》1997,78(1-2):115-123
A method for generating olfactory stimuli for humans within a functional magnetic resonance imaging (fMRI) experimental design is described. The system incorporates a nasal-mask in which the change from odorant to no-odorant conditions occurs in less than 500 ms and is not accompanied by visual, auditory, tactile, or thermal cues. The mask provides an ordorant-free environment following prolonged ordorant presence. Specific imaging parameters that are conducive to the study of the human olfactory system are described. In a pilot study performed using these methods, the specific patterns of activation observed converged with published experimental and clinical findings. 相似文献