全文获取类型
收费全文 | 975522篇 |
免费 | 12375篇 |
国内免费 | 2823篇 |
专业分类
电工技术 | 17993篇 |
综合类 | 1228篇 |
化学工业 | 146432篇 |
金属工艺 | 36351篇 |
机械仪表 | 28816篇 |
建筑科学 | 23561篇 |
矿业工程 | 4474篇 |
能源动力 | 26789篇 |
轻工业 | 81144篇 |
水利工程 | 9527篇 |
石油天然气 | 15952篇 |
武器工业 | 54篇 |
无线电 | 114192篇 |
一般工业技术 | 188143篇 |
冶金工业 | 191444篇 |
原子能技术 | 18954篇 |
自动化技术 | 85666篇 |
出版年
2021年 | 8466篇 |
2020年 | 6397篇 |
2019年 | 8010篇 |
2018年 | 13571篇 |
2017年 | 13301篇 |
2016年 | 14187篇 |
2015年 | 9626篇 |
2014年 | 15912篇 |
2013年 | 45902篇 |
2012年 | 25192篇 |
2011年 | 34857篇 |
2010年 | 27659篇 |
2009年 | 31322篇 |
2008年 | 32064篇 |
2007年 | 31813篇 |
2006年 | 28064篇 |
2005年 | 25618篇 |
2004年 | 24649篇 |
2003年 | 24396篇 |
2002年 | 23181篇 |
2001年 | 23049篇 |
2000年 | 21705篇 |
1999年 | 23036篇 |
1998年 | 58689篇 |
1997年 | 41414篇 |
1996年 | 32049篇 |
1995年 | 24153篇 |
1994年 | 21335篇 |
1993年 | 21006篇 |
1992年 | 15235篇 |
1991年 | 14233篇 |
1990年 | 14152篇 |
1989年 | 13735篇 |
1988年 | 12889篇 |
1987年 | 11434篇 |
1986年 | 11312篇 |
1985年 | 12860篇 |
1984年 | 11771篇 |
1983年 | 10718篇 |
1982年 | 9927篇 |
1981年 | 10128篇 |
1980年 | 9523篇 |
1979年 | 9294篇 |
1978年 | 8923篇 |
1977年 | 10785篇 |
1976年 | 14183篇 |
1975年 | 7832篇 |
1974年 | 7443篇 |
1973年 | 7545篇 |
1972年 | 6251篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---Hn-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data. 相似文献
992.
This paper derives the governing equations for the thermomechanical behaviour of composites. When the basic equations for the thermoelastic behaviour of solids were first derived in the nineteenth century several approximations were made. The effect of these assumptions are discussed and illustrated by the results of a simple laboratory test. The implications of this work on the analysis of impact damaged laminates are then discussed. 相似文献
993.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
994.
Spherical indenters were used to produce elastic-plastic contact damage in a lead lanthanum zirconate titanate (PLZT) under conditions of quasi-static and impact loading. The extent of radial cracking produced under both loading conditions showed good correlation with the response predicted by an earlier fracture mechanics analysis for quasi-static conditions. Calculated radial crack lengths corresponding to conditions of impact loading exhibited excellent agreement with experimentally measured values. The dynamic hardness of the PLZT was determined to be ∼ 1.5 times the quasi-static hardness. Differences in the radial crack lengths produced under the two loading conditions were attributed primarily to this difference in hardness response. 相似文献
995.
R. Baweja 《Drug development and industrial pharmacy》1986,12(14):2431-2442
Dissolution testing was conducted for six non-combination, single entity, modified-release oral solid dosage forms. Dissolution medium was water and 0.1 N hydrochloric acid. USP Apparatus 1 and Apparatus 2 were used arid were rotated at either 50 or 100 rpm. A complete dissolution profile was obtained for all six dosage forms based on their stated dosing interval, D. The three strengths of Theo-dur tablets, Norpace CR 150 mg capsules, and the two strengths of Chlor-trimeton tablets passed the Compendial Case One requirements (USP XXI, 2S, 1906). Thorazine spansules and Quinidex tablets were unable to meet the specifications with water as the dissolution medium; the latter showed improved dissolution character in 0.1 N hydrochloric acid. Tenuate Dospan 75 mg tablets showed good release characteristics in water when the authentic (dosing interval (D = 24 hours) was changed to a modified dosing interval of D* = 12 hours. All dissolution aliquots were assayed by UV absorbance measurements at the absorbance maximum for each drug and were also checked for excipient interference. Newer drugs appearing on the market will be more likely candidates for meeting compendial specifications; modified-release pharmaceuticals that appeared before the new specifications may have to be allocated specifically expanded window percentages. 相似文献
996.
P. K. Yeung S. C. Kot 《International journal for numerical methods in engineering》1985,21(5):929-939
A body-fitted curvilinear co-ordinate system is used to solve the equations of two-dimensional incompressible laminar flow over bluff obstructions by finite differences. Arbitrary conditions at the corner are removed by this method. Results for a backward-facing step are in reasonable agreement with those obtained with conventional mesh systems, and the differences are explained. A treatment of a channel expansion, in comparison with empirical data, is also included. The capability of the present method to handle arbitrary two-dimensional geometries is stressed and demonstrated, using a triangle and a semi-circle as examples. 相似文献
997.
Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<> 相似文献
998.
R. A. Mustafaev D. K. Ganiev D. M. Gabulov 《Journal of Engineering Physics and Thermophysics》1985,48(2):241-242
Dynamic-viscosity measurements are reported for liquid mixtures in the system formed by n-butyraldehyde and isobutyraldehyde.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 321–322, February, 1985. 相似文献
999.
1000.
N Paster J Blumenthal-Yonassi R Barkai-Golan M Menasherov 《International journal of food microbiology》1991,12(2-3):157-165
The production of zearalenone by an isolate of Fusarium equiseti was studied in chemically defined medium and in corn grains stored under modified atmospheres. An increase in the concentrations of sucrose or xylose in Czapek's medium resulted in increased toxin production, while no toxin was produced when lactose was present in the medium. Methionine (10(-2) and 10(-3) M) and cystine (10(-3) M) added to Czapek's medium inhibited zearalenone production. When amino acids or nitrogen salts were added as the sole nitrogen source, only alanine, tryptophan and NH4Cl totally inhibited zearalenone production. Zearalenone production was inhibited almost completely in high-moisture corn grains (27%) kept under atmospheres enriched with high CO2 levels (60%, 40% or 20%) with either 20% or 5% O2. However, a lower amount of CO2 was needed to inhibit fungal development and toxin formation when a reduced O2 level was applied. 相似文献