全文获取类型
收费全文 | 304414篇 |
免费 | 7745篇 |
国内免费 | 1865篇 |
专业分类
电工技术 | 5727篇 |
技术理论 | 5篇 |
综合类 | 1280篇 |
化学工业 | 51897篇 |
金属工艺 | 11794篇 |
机械仪表 | 8708篇 |
建筑科学 | 8106篇 |
矿业工程 | 1765篇 |
能源动力 | 6668篇 |
轻工业 | 34230篇 |
水利工程 | 3337篇 |
石油天然气 | 6189篇 |
武器工业 | 247篇 |
无线电 | 29981篇 |
一般工业技术 | 56445篇 |
冶金工业 | 54398篇 |
原子能技术 | 5781篇 |
自动化技术 | 27466篇 |
出版年
2022年 | 2086篇 |
2021年 | 3962篇 |
2020年 | 2762篇 |
2019年 | 3328篇 |
2018年 | 5170篇 |
2017年 | 5105篇 |
2016年 | 5566篇 |
2015年 | 4224篇 |
2014年 | 6404篇 |
2013年 | 15093篇 |
2012年 | 10694篇 |
2011年 | 13064篇 |
2010年 | 10381篇 |
2009年 | 10747篇 |
2008年 | 11443篇 |
2007年 | 11314篇 |
2006年 | 9775篇 |
2005年 | 8477篇 |
2004年 | 7649篇 |
2003年 | 7137篇 |
2002年 | 6988篇 |
2001年 | 6859篇 |
2000年 | 6399篇 |
1999年 | 6401篇 |
1998年 | 15226篇 |
1997年 | 11142篇 |
1996年 | 8301篇 |
1995年 | 6127篇 |
1994年 | 5575篇 |
1993年 | 5434篇 |
1992年 | 4137篇 |
1991年 | 3912篇 |
1990年 | 3942篇 |
1989年 | 3909篇 |
1988年 | 3674篇 |
1987年 | 3155篇 |
1986年 | 3163篇 |
1985年 | 3540篇 |
1984年 | 3431篇 |
1983年 | 3154篇 |
1982年 | 2796篇 |
1981年 | 3036篇 |
1980年 | 2764篇 |
1979年 | 2910篇 |
1978年 | 2799篇 |
1977年 | 3022篇 |
1976年 | 4016篇 |
1975年 | 2511篇 |
1974年 | 2345篇 |
1973年 | 2380篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
L De Petrocellis P Orlando M Gavagnin M Ventriglia G Cimino V Di Marzo 《Canadian Metallurgical Quarterly》1996,52(9):874-877
Five novel 1,2-sn-diacylglycerols with diterpenoid acyl moieties in the sn-1 position were isolated and characterized, together with the corresponding 1,3-sn-diacylglycerols, from three species of dorid nudibranchs molluscs. Their potent activity as morphogens in vivo in the Hydra tentacle regeneration assay and their parallel activity as activators of rat brain protein kinase C (PKC) in vitro are reported here. Our findings promote the use of these compounds as useful molecular probes for both in vivo and in vitro studies on the participation of PKC in cell development. 相似文献
952.
EK Yeong R Mann M Goldberg L Engrav D Heimbach 《Canadian Metallurgical Quarterly》1996,40(6):956-61; discussion 961-2
The utility of the laser Doppler for determining burn depth has been questioned because of problems with technology and methodology. This study prospectively evaluates the ability of a new laser Doppler technique to predict burn healing time. Using the Periflux System 4000 laser Doppler, readings were taken on 305 burns (147 patients) on postburn day 3 or 4. Sixty-six wounds were used to derive a predictive function (phase I) and 152 wounds were used to test the function (phase II). Blood flow dynamics (flux), microvascular dilation capacity of the wounds to beat stress, and flow motion wave pattern (vasomotion) were studied using the laser Doppler, and seven parameters were evaluated to determine their relative contribution to the prediction of healing time. These parameters are hyperemic flux (flux value after heating to 42 degrees C), average hyperemic wave amplitude (AHWA), number of average flux units >100(F100), number readings with wave amplitude 75 (A5), average flux change (AFC), percentage of average flux increase, and relative flow capacity (RFC = AFC/average hyperemic flux). After readings were made, the wounds were observed and divided into two groups: those that healed in less than 14 days and those that healed or were grafted after 14 days. A step-wise discriminant analysis was used to assess the relative contribution of the Doppler-derived measures to healing time prediction. AHWA, F100, and RFC were included in the final discriminant function explaining 72% of the healing time variance (Wilks' lambda value 0.28; p value <0.0001). Predicted outcome = 0.05(AHWA) + 0.31(F100) + 5.0(RFC) - 2.3. With this derived function, there is 94% accuracy in the prediction of burn wound healing time compared with a physician predictive accuracy of 70%. 相似文献
953.
S. Bismo P. Duverneuil L. Pibouleau S. Domenech J. -P. Couderc 《Materials and Manufacturing Processes》1995,10(2):241-266
This paper presents the results of our work on a new type of CVD reactor, annular reactor. This equipment is able to deposit pure silicon and also in-situ phosphorus doped silicon on a large number of substrates 相似文献
954.
This paper presents an artificial intelligence approach of using evolutionary programming to estimate the transient and subtransient parameters of a generator under normal operation. The estimation using evolutionary programming is compared with that using a corrected extended Kalman filter. The comparisons with both simulation and micromachine test results show that evolutionary programming is robust to search the real values of parameters even when the data are highly contaminated by noise, while with the extended Kalman filter, the estimation tends to diverge with such data 相似文献
955.
956.
Control of calcium hexaluminate grain morphology in in-situ toughened ceramic composites 总被引:2,自引:0,他引:2
The influence of processing conditions on the morphology of calcium hexaluminate (CA6) grains in Al2O3: 30 vol% CaO·6Al2O3 (CA6) ceramic composites was investigated. Specimens were prepared by in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA6 grains developed a platelike morphology when CaCO3 was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA6 grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA6 reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.Cement Nomenclature C
CaO
- A
Al2O3 相似文献
957.
This study assesses the growth, the patterns of development and the complexity of research in the field of ecology from 1976 to 1993 in Spain and the five Spanish speaking countries of the Caribbean. Using as a yardstick of research and development in that field, the dissertation titles were counted for each region. The total length, the key words per title were recorded and analysed statistically. Results show that the growth of research in ecology is greater in Spain and peaked earlier than in the Caribbean countries. However, the titles in the latter region were more complex than those in Spain. 相似文献
958.
A melt-extraction technique, using a sharpened molybdenum wheel, has been used to produce fine oxide ceramic fibres. Wetting of the molybdenum wheel by molten ceramic is a key parameter in the melt-extraction process. Two types of fibre are generally obtained, depending on the extraction speed. At very low wheel speed, fine and uniform fibres of high quality are produced. However, when the wheel speed exceeds a critical velocity, Rayleigh waves are formed on the free surface of the fibres. Moreover, the average fibre thickness first increases with the wheel velocity, then passes through a maximum, decreasing at high velocity. This thickness variation is discussed in terms of both surface tension and viscosity of the liquid ceramics. 相似文献
959.
960.