全文获取类型
收费全文 | 331821篇 |
免费 | 3777篇 |
国内免费 | 1203篇 |
专业分类
电工技术 | 6756篇 |
综合类 | 305篇 |
化学工业 | 48325篇 |
金属工艺 | 12508篇 |
机械仪表 | 9732篇 |
建筑科学 | 8007篇 |
矿业工程 | 1099篇 |
能源动力 | 8088篇 |
轻工业 | 29749篇 |
水利工程 | 2671篇 |
石油天然气 | 3412篇 |
武器工业 | 12篇 |
无线电 | 44582篇 |
一般工业技术 | 62275篇 |
冶金工业 | 67158篇 |
原子能技术 | 5526篇 |
自动化技术 | 26596篇 |
出版年
2021年 | 1941篇 |
2019年 | 2008篇 |
2018年 | 3060篇 |
2017年 | 3115篇 |
2016年 | 3258篇 |
2015年 | 2441篇 |
2014年 | 4175篇 |
2013年 | 13816篇 |
2012年 | 7180篇 |
2011年 | 10068篇 |
2010年 | 8024篇 |
2009年 | 9359篇 |
2008年 | 10109篇 |
2007年 | 10406篇 |
2006年 | 9350篇 |
2005年 | 8817篇 |
2004年 | 8667篇 |
2003年 | 8469篇 |
2002年 | 8268篇 |
2001年 | 8693篇 |
2000年 | 8076篇 |
1999年 | 8600篇 |
1998年 | 21444篇 |
1997年 | 14909篇 |
1996年 | 11832篇 |
1995年 | 9006篇 |
1994年 | 7956篇 |
1993年 | 7850篇 |
1992年 | 5819篇 |
1991年 | 5606篇 |
1990年 | 5495篇 |
1989年 | 5360篇 |
1988年 | 4967篇 |
1987年 | 4184篇 |
1986年 | 4217篇 |
1985年 | 4912篇 |
1984年 | 4387篇 |
1983年 | 4062篇 |
1982年 | 3806篇 |
1981年 | 3860篇 |
1980年 | 3485篇 |
1979年 | 3387篇 |
1978年 | 3295篇 |
1977年 | 3951篇 |
1976年 | 5126篇 |
1975年 | 2871篇 |
1974年 | 2683篇 |
1973年 | 2669篇 |
1972年 | 2222篇 |
1971年 | 1982篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
G. P. Kurbskii G. P. Kayukova G. M. Usacheva R. I. Mutalapova E. V. Lifanova T. N. Yusupva G. V. Romanov 《Chemistry and Technology of Fuels and Oils》1992,28(6):309-313
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 6, pp. 7–9, June, 1992. 相似文献
992.
993.
The effects of 2 alternative modeling strategies (using multiple scenarios and combining negative and positive model displays) on outcomes of a behavior modeling training program were explored. Trainees (N?=?72) participated in a program on assertive communication structured to allow for a controlled experimental design that crossed scenario variability (1 vs multiple scenarios) with model display variability (positive model displays vs positive and negative model displays). Outcomes assessed included trainee reactions, learning, and retention and behavioral measures of reproduction and generalization. The effects of multiple scenarios were negligible, but the positive and negative combination of model displays had a significant positive effect on trainee generalization and a significant negative effect on reproduction. Implications for future modeling research and practice are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
Abatzoglou T.J. Mendel J.M. Harada G.A. 《Signal Processing, IEEE Transactions on》1991,39(5):1070-1087
The constrained total least squares (CTLS) method is a natural extension of TLS to the case when the noise components of the coefficients are algebraically related. The CTLS technique is developed, and some of its applications to superresolution harmonic analysis are presented. The CTLS problem is reduced to an unconstrained minimization problem over a small set of variables. A perturbation analysis of the CTLS solution is derived, and from it the root mean-square error (RMSE) of the CTLS solution, which is valid for small noise levels, is obtained in closed form. The complex version of the Newton method is derived and applied to determine the CTLS solution. It is also shown that the CTLS problem is equivalent to a constrained parameter maximum-likelihood problem. The CTLS technique is applied to estimate the frequencies of sinusoids in white noise and the angle of arrival of narrowband wavefronts at a linear uniform array. In both cases the CTLS method shows superior or similar accuracy to other advanced techniques 相似文献
995.
An analysis is made of the spatial evolution of quasiperiodic regimes in a chain of coupled circle maps. Mechanisms for the
appearance of strange nonchaotic dynamics and the properties of irregular attractors are analyzed.
Pis’ma Zh. Tekh. Fiz. 23, 73–79 (April 12, 1997) 相似文献
996.
During the winter of 1988/1989, the relationships between the prevalence of work-related health and indoor climate complaints and a number of building, management, workplace and personal characteristics have been investigated in a study in more than 60 office buildings located throughout the Netherlands. To collect the information, a questionnaire was prepared on health and indoor climate complaints and personal and workplace characteristics. A checklist was used to obtain information on building characteristics More than 7000 questionnaires were completed by the regular users of the buildings investigated. The results showed that the prevalence of symptoms was higher in air-conditioned buildings than in naturally or mechanically ventilated buildings. some other variables were also related with most work-related complaints after adjustment for selected management, personal, workplace and job characteristics. These included gender, work satisfaction in general, presence of allergies and/or respiratory symptoms, and personal control over temperature at the workplace. No differences were found in symptom prevalences between buildings with spray and steam humidification. The combination of air-conditioning and humidification did not lead to further increases in the prevalence of complaints as compared to buildings with only airconditioning or only humidification. 相似文献
997.
The behavior during creep in shear of eutectic indium-tin joints on copper and nickel substrates was examined in order to
determine the effect of creep deformation on the microstructure of the alloy. Primary creep was absent in all the samples
tested. The stress exponent at 20° C was much higher for samples on nickel than for those on copper, indicating a different
creep deformation mechanism. Also, the microstructure within the indium-tin joints differed significantly with a change of
substrate. Samples with a nickel substrate showed a colony microstructure that was not observed in those with a copper substrate.
Thus, eutectic morphology is important in determining deformation mechanism during creep. The microstructure within the joints
in tested and untested regions of the samples was effectively the same. This is quite distinct from the behavior of eutectic
lead-tin observed in previous work. Lead-tin formed a recrystallized band of material along a region of concentrated shear
deformation. While the deformation pattern in the indium-tin samples appeared to be the same as for lead-tin, the microstructural
changes did not occur. This implies that the behavior observed in lead-tin is not universal to eutectic alloys. 相似文献
998.
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
999.
The phenolic diterpene carnosic acid appears to be the main substance for general oxidation leading to artifacts with gamma- or delta-lactone structure in extracts of Rosmarinus officinalis and Salvia officinalis. Until now it was only possible to prepare carnosic acid by hydrogenolysis of carnosol. A semipreparative HPLC method has been developed isolating carnosic acid among other phenolic diterpenes. The separated substances were identified by 13C-nuclear magnetic resonance (NMR), 1H-NMR, mass and IR spectroscopy. Conversion of carnosic acid and carnosol to other phenolic diterpenes was investigated by HPLC. 相似文献
1000.