全文获取类型
收费全文 | 47089篇 |
免费 | 4659篇 |
国内免费 | 3163篇 |
专业分类
电工技术 | 3538篇 |
技术理论 | 8篇 |
综合类 | 6116篇 |
化学工业 | 4384篇 |
金属工艺 | 1878篇 |
机械仪表 | 4541篇 |
建筑科学 | 4063篇 |
矿业工程 | 1591篇 |
能源动力 | 1703篇 |
轻工业 | 1194篇 |
水利工程 | 1237篇 |
石油天然气 | 1208篇 |
武器工业 | 713篇 |
无线电 | 4144篇 |
一般工业技术 | 6056篇 |
冶金工业 | 2643篇 |
原子能技术 | 404篇 |
自动化技术 | 9490篇 |
出版年
2024年 | 221篇 |
2023年 | 776篇 |
2022年 | 1048篇 |
2021年 | 1299篇 |
2020年 | 1538篇 |
2019年 | 1345篇 |
2018年 | 1417篇 |
2017年 | 1615篇 |
2016年 | 1700篇 |
2015年 | 1784篇 |
2014年 | 2714篇 |
2013年 | 3349篇 |
2012年 | 2956篇 |
2011年 | 3360篇 |
2010年 | 2587篇 |
2009年 | 2771篇 |
2008年 | 2782篇 |
2007年 | 3085篇 |
2006年 | 2865篇 |
2005年 | 2423篇 |
2004年 | 1982篇 |
2003年 | 1664篇 |
2002年 | 1448篇 |
2001年 | 1174篇 |
2000年 | 1008篇 |
1999年 | 872篇 |
1998年 | 740篇 |
1997年 | 651篇 |
1996年 | 549篇 |
1995年 | 497篇 |
1994年 | 415篇 |
1993年 | 333篇 |
1992年 | 316篇 |
1991年 | 227篇 |
1990年 | 187篇 |
1989年 | 193篇 |
1988年 | 151篇 |
1987年 | 82篇 |
1986年 | 100篇 |
1985年 | 78篇 |
1984年 | 80篇 |
1983年 | 49篇 |
1982年 | 61篇 |
1981年 | 42篇 |
1980年 | 34篇 |
1979年 | 36篇 |
1978年 | 30篇 |
1977年 | 30篇 |
1964年 | 26篇 |
1955年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
ABSTRACT Postmortem structural changes in titin and nebulin filaments were investigated by incubating isolated myofibrils in a solution containing 0.1 mM calcium ions and various concentrations of a protease inhibitor. The inhibition curves showed 2 abnormal steps with increases in the concentration of leupeptin or calpastatin domain I. While the amounts of unchanged titin and nebulin were constant in the 1st step, the 2nd occurred at higher protease inhibitor concentrations. These facts indicated that excess amounts of leupeptin and calpastatin domain I caused deterioration in titin and nebulin properties, thus interfering with the binding of calcium ions. We concluded that the severance of titin and nebulin filaments in the 1st step were induced by calcium ions at 0.1 mM. 相似文献
33.
Using boundary element based three dimensional modelling for linear fracture mechanics, we present an analysis of cracking in a homogeneous medium subject to contact load. The proposed iterative solution procedure allows a simultaneous treatment of a reasonable number of partially closed cracks. It is shown that the most probable direction of propagation of a vertical internal crack is strongly dependent on its size compared to the contact radius and its location with respect to the axis of maximum normal load. 相似文献
34.
Chouping Luo Marek Klisinski 《International journal for numerical methods in engineering》2004,61(2):159-188
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
35.
The theoretical-and-experimental investigation has been performed on the stability of smooth cylindrical shells of steel with a single local dent. All the shells manufactured using the same process were tested with the fulfillment of identical conditions for observations and measurements. Theoretical calculations were carried out by the mesh method with the use of the nonlinear theory of shells. A comparison of the experimental and theoretical values of the critical loads has been made. The theoretical-and-experimental approach proposed enables one to evaluate the quality of shells by studying local dents and other specific imperfections. 相似文献
36.
This study investigates the relationship between the critical surface tension of wetting of celestite and agglomeration recovery as well as the zeta potential in dependence of pH and amount of collector (Na‐Oleate). For this purpose, effects of pH and collector amount on the agglomeration recovery are investigated and zeta potential measurements and Fourier Transform Infrared Spectrophotometer (FTIR) analyses are carried out to determine the adsorption type of Na‐Oleate on celestite surface. The sessile drop technique is used for the measurement of contact angle and determination of the critical surface tension of wetting (YC) of celestite. The maximum agglomeration recovery is obtained at pH 7. The critical surface tension of wetting of celestite is very close to the surface tension of kerosene, which is 25.95 mN/m. Furthermore, at the optimum Na‐Oleate amount of 10 kg/ton, the critical surface tension of wetting of celestite is approximately equal to the surface tension of kerosene. 相似文献
37.
张泽民 《河南机电高等专科学校学报》2004,12(5):19-20
马克思主义理论课教师世界观的要求就是辩证唯物主义和历史唯物主义的思想体系和方法论;其价值观的要求就是以大公无私为特征的价值判断标准。马克思主义理论课所具有的知识性和思想性、科学性和实践性相统一的特点,要求马克思主义理论课教师,不仅要有扎实的化知识,而且必须加强其世界观和价值观的修养。许多事实证明,只有这样才能真正提高马克思主义理论课的教学实效。 相似文献
38.
官泓 《有色冶金设计与研究》2003,24(3):49-51
阐述水厂设计中对水厂规模、水源地、净水厂位置及净水工艺的确定过程,根据原水的特点,通过分析对无阀滤池进行改良。 相似文献
39.
阐述了电接点压力表补水泵定压系统的一些应用问题 ,给出了电接点压力表定压点的上、下限计算公式 ,并提出了该系统补给水泵、补给水箱及安全阀的设计选型方法 相似文献
40.
Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献