全文获取类型
收费全文 | 7231篇 |
免费 | 679篇 |
国内免费 | 356篇 |
专业分类
电工技术 | 555篇 |
综合类 | 472篇 |
化学工业 | 1897篇 |
金属工艺 | 345篇 |
机械仪表 | 441篇 |
建筑科学 | 333篇 |
矿业工程 | 174篇 |
能源动力 | 725篇 |
轻工业 | 221篇 |
水利工程 | 145篇 |
石油天然气 | 611篇 |
武器工业 | 73篇 |
无线电 | 438篇 |
一般工业技术 | 896篇 |
冶金工业 | 331篇 |
原子能技术 | 305篇 |
自动化技术 | 304篇 |
出版年
2024年 | 22篇 |
2023年 | 96篇 |
2022年 | 170篇 |
2021年 | 213篇 |
2020年 | 203篇 |
2019年 | 185篇 |
2018年 | 205篇 |
2017年 | 221篇 |
2016年 | 237篇 |
2015年 | 250篇 |
2014年 | 359篇 |
2013年 | 509篇 |
2012年 | 462篇 |
2011年 | 524篇 |
2010年 | 361篇 |
2009年 | 395篇 |
2008年 | 354篇 |
2007年 | 468篇 |
2006年 | 413篇 |
2005年 | 340篇 |
2004年 | 302篇 |
2003年 | 246篇 |
2002年 | 226篇 |
2001年 | 190篇 |
2000年 | 182篇 |
1999年 | 166篇 |
1998年 | 148篇 |
1997年 | 119篇 |
1996年 | 113篇 |
1995年 | 88篇 |
1994年 | 88篇 |
1993年 | 60篇 |
1992年 | 59篇 |
1991年 | 43篇 |
1990年 | 60篇 |
1989年 | 46篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1959年 | 5篇 |
1951年 | 1篇 |
排序方式: 共有8266条查询结果,搜索用时 15 毫秒
1.
2.
采用DSC对不同分子量的聚醚酰亚胺的等温及动态热焓松弛行为进行了研究,并以KWW方程对实验数据进行了非线性拟合。结果表明,分子量对热焓松弛的影响是由高分子端基引起自由体积的差异所致。不同分子量的聚醚酰亚胺分子具有不同数量的端基,淬冷时端基数目的差异将产生不同数量的过剩自由体积,从而影响松弛热焓及松弛速率、低分子量的聚醚酰亚胺松弛相对较快,且起始热焓高,松弛的表观活化能亦较小。 相似文献
3.
Michael E. G. Ferguson Peter L. Spedding 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):262-278
Experimental data for air–water two-phase co-current flow in two different pipe diameters were used to test the prediction of pressure drop by a number of existing theories and correlations. Several models are shown to be useful for prediction, particularly with the stratified regimes which have proved difficult to handle in the past. The model suggested by Olujic proved to be of particular value. 相似文献
4.
A motivational model of rural students' intentions to persist in, versus drop out of, high school. 总被引:1,自引:0,他引:1
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
从汽轮机回热系统的实际情况出发,运用非线性规划理论和计算机技术,解决了给水焓升设计中的最优分配问题。结合具体实例,针对国产200MW汽轮机回热系统给水焓升的分配进行了说明。 相似文献
6.
J. Gajdoš Kljusurić 《Sadhana》2003,28(6):991-998
This work is an experimental study of the differential scanning calorimetry characterisation of polymer materials used in
food packaging materials, such as polypropylene (0.03 mm), polyethylene (0.1 and 0.03 mm), poly(D-(-)-Β-hydroxybutyrate) (powder),
two-layered polypropylene (0.064 mm), and two-layered polypropylene with poly-vinylidene-chloride (0.012/0.021). The polymer
stability was checked by simulation of conditions during food preparation in microwave ovens, sterilisation or rapid freezing.
The materials were tested in the temperature range from 40 to 200‡C at different scan rates from 2 to 30°C min−1 during heating or cooling. The enthalpies show a high correlation coefficient (0.964) with scan rate. All samples undergo
phase change in the temperature range from 107 to 173°C during heating and enthalpies are in the range from 31.8 to 71.1Jg−1. Upon subsequent cooling from 200°C, the temperature range of phase changes is shifted to lower temperatures from 86 to 102°C
with enthalpies ranging from 30.4 to 57.8 J g−1.
Experiments with exposure of polymers to microwave radiation and freezing prove that the phase change considering the temperature
range is very similar in all experiments. 相似文献
7.
Sipra Mahapatra Turaga P. Prasad 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,53(2):201-203
Hydrolysis of Fe(OH)SO4 was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe2O3 and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol. 相似文献
8.
FLOW OF NEWTONIAN FLUIDS THROUGH SINUSOID ALLY CONSTRICTED TUBES. NUMERICAL AND EXPERIMENTAL RESULTS
J. A. Deiber Mb. Peirotti R. A. Bortolozzi R. J. Durelli 《Chemical Engineering Communications》1992,117(1):241-262
Numerical and experimental predictions of pressure drops in the flow of Newtonian fluids through sinusoidally constricted tubes (SCT) are carried out. The numerical evaluations analyzed in this work are obtained from the following methods: Geometric Iteration (GJM), Geometric Iteration with First and Second Upwinds (GIM1, GIM2), Successive Over Relaxation by Line (SORBLM), Global Galerkin Spectral Method (GGSM), Collocation (CM) and Dufort-Frankel (DFM). The GIM1, GIM2 and SORBLM are applied to SCT and explained in this work. The other methods have been previously reported in the literature with the same purpose. Experiments are accomplished for constrictions of approximately 40,60 and 80% of the average tube diameter and results compare well with numerical predictions of the steady flow. It is concluded that special attention should be given to evaluations of the friction factor ƒ for Reynolds numbers Re between the onsets of flow separation and turbulence due to flow instability. Finally, the SCT as a model for porous media (PM) is discussed. 相似文献
9.
部分种子成分的特征X射线在等效生物材料中衰减的测定 总被引:6,自引:5,他引:1
用Si(Li)探测器实现了Na、Mg、S、Cl的特征X射线在有机膜中的相对衰减以及与O、K元素的特征X射线能量相当的X射线或轫致辐射在有机膜中的相对衰减,分别得出了它们减的数学描述,并把实验得到不同能量的X射线在有机膜中的质量吸收系数与Berkeley的OCG软件计算出的结果相比,相关都小于30%。 相似文献
10.
通过分析和计算及实例,从允许电压降范围和电动机母线电压校验两方面叙述了电动机起动时如何合理地选择起动的方式。 相似文献