全文获取类型
收费全文 | 458226篇 |
免费 | 5246篇 |
国内免费 | 2018篇 |
专业分类
电工技术 | 8606篇 |
综合类 | 352篇 |
化学工业 | 67938篇 |
金属工艺 | 18774篇 |
机械仪表 | 15264篇 |
建筑科学 | 9676篇 |
矿业工程 | 2551篇 |
能源动力 | 12846篇 |
轻工业 | 33461篇 |
水利工程 | 4898篇 |
石油天然气 | 9467篇 |
武器工业 | 55篇 |
无线电 | 54296篇 |
一般工业技术 | 94574篇 |
冶金工业 | 84337篇 |
原子能技术 | 11035篇 |
自动化技术 | 37360篇 |
出版年
2022年 | 2928篇 |
2021年 | 4446篇 |
2020年 | 3373篇 |
2019年 | 4292篇 |
2018年 | 7443篇 |
2017年 | 7506篇 |
2016年 | 8060篇 |
2015年 | 4945篇 |
2014年 | 8187篇 |
2013年 | 22548篇 |
2012年 | 13047篇 |
2011年 | 17205篇 |
2010年 | 13819篇 |
2009年 | 15546篇 |
2008年 | 15876篇 |
2007年 | 15612篇 |
2006年 | 13929篇 |
2005年 | 12509篇 |
2004年 | 11838篇 |
2003年 | 11722篇 |
2002年 | 11078篇 |
2001年 | 10984篇 |
2000年 | 10368篇 |
1999年 | 10678篇 |
1998年 | 27096篇 |
1997年 | 18678篇 |
1996年 | 14294篇 |
1995年 | 10669篇 |
1994年 | 9397篇 |
1993年 | 9399篇 |
1992年 | 6803篇 |
1991年 | 6501篇 |
1990年 | 6478篇 |
1989年 | 6133篇 |
1988年 | 5757篇 |
1987年 | 5101篇 |
1986年 | 4980篇 |
1985年 | 5543篇 |
1984年 | 5008篇 |
1983年 | 4574篇 |
1982年 | 4191篇 |
1981年 | 4270篇 |
1980年 | 3959篇 |
1979年 | 3840篇 |
1978年 | 3822篇 |
1977年 | 4369篇 |
1976年 | 5597篇 |
1975年 | 3306篇 |
1974年 | 3102篇 |
1973年 | 3179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
The separate contributions of impellers and stators to suction are studied by means of interaction models. From these, suction can be predicted when interchangeable components are used in any combination, and in either direction of impeller rotation. Methods are devised by which numerical values of the impeller and stator terms can be simply assigned. The resulting model provides good agreement with experiment. The influence of variability in component geometry is reflected in the model parameters. Possible applications of the model are suggested. 相似文献
93.
In the development of a novel freeze-drying technique in a fluidized bed at atmospheric pressure, a parallel study was undertaken using a conventional vacuum equipment. Two kinetically distinct phases were observed during freeze drying of representative Pood samples:
(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure 相似文献
(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure 相似文献
94.
A.O. Lebeck 《Tribology International》1985,18(3):188-189
95.
A. N. Gudkov V. M. Zhivun A. V. Zvonarev V. V. Kovalenko A. B. Koldobskii Yu. F. Koleganov S. V. Krivasheev V. B. Pavlovich N. S. Piven' E. V. Semenova 《Atomic Energy》1989,66(2):115-118
Translated from Atomnaya Énergiya, Vol. 66, No. 2, pp. 100–103, February, 1989. 相似文献
96.
测定钠中杂质的手动阻塞计的研究 总被引:1,自引:1,他引:0
文章介绍了测定钠中杂质浓度的手动阻塞计的原理、装置和实验结果。为了减少测量误差,我们研究了影响准确测定阻塞温度的因素,并且找到了减少测量误差的办法。在同样的杂质饱和温度下,该阻塞计测得的高、低阻塞温度所对应的杂质浓度差是很接近的。对氧其差值为1.03ppm;对氢为0.0763ppm。 相似文献
97.
98.
PCR-based procedures in detection and DNA-fingerprinting of Salmonella from samples of animal origin
A. del Cerro S. M. Soto E. Landeras M. A. Gonzlez-Hevia J. A. Guijarro M. C. Mendoza 《Food microbiology》2002,19(6):567
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment. 相似文献
99.
Results of a numerical investigation of heat and mass transfer at the initial stage of fire within a building in combustion of kerosene, carried out with the use of a three-dimensional mathematical field model, are presented. A comparison of the distribution of the averaged temperatures and velocities along the vertical axis of the convective column and of the mass rates of gas flows through an open opening with the experimental data has been made. Substantial three-dimensional inhomogeneities of the velocities and the temperatures in the near-ceiling layer have been revealed. It has been established that near the opening there is a critical separation zone which influences significantly the parameters of natural gas transfer. 相似文献
100.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy. 相似文献