全文获取类型
收费全文 | 30203篇 |
免费 | 3819篇 |
国内免费 | 2500篇 |
专业分类
电工技术 | 1629篇 |
综合类 | 3995篇 |
化学工业 | 2927篇 |
金属工艺 | 2738篇 |
机械仪表 | 1625篇 |
建筑科学 | 7120篇 |
矿业工程 | 875篇 |
能源动力 | 667篇 |
轻工业 | 1263篇 |
水利工程 | 1496篇 |
石油天然气 | 905篇 |
武器工业 | 330篇 |
无线电 | 2007篇 |
一般工业技术 | 5303篇 |
冶金工业 | 1153篇 |
原子能技术 | 168篇 |
自动化技术 | 2321篇 |
出版年
2024年 | 128篇 |
2023年 | 448篇 |
2022年 | 766篇 |
2021年 | 1002篇 |
2020年 | 1132篇 |
2019年 | 1107篇 |
2018年 | 1015篇 |
2017年 | 1295篇 |
2016年 | 1318篇 |
2015年 | 1301篇 |
2014年 | 1851篇 |
2013年 | 2085篇 |
2012年 | 2220篇 |
2011年 | 2447篇 |
2010年 | 1719篇 |
2009年 | 1790篇 |
2008年 | 1799篇 |
2007年 | 1909篇 |
2006年 | 1753篇 |
2005年 | 1441篇 |
2004年 | 1185篇 |
2003年 | 989篇 |
2002年 | 830篇 |
2001年 | 789篇 |
2000年 | 666篇 |
1999年 | 605篇 |
1998年 | 497篇 |
1997年 | 425篇 |
1996年 | 330篇 |
1995年 | 314篇 |
1994年 | 250篇 |
1993年 | 215篇 |
1992年 | 213篇 |
1991年 | 138篇 |
1990年 | 102篇 |
1989年 | 122篇 |
1988年 | 62篇 |
1987年 | 59篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
纵横波测井资料在储层评价中的应用 总被引:5,自引:1,他引:4
将弹性波基础理论,Gasman理论,Biot理论和实验研究结果相结合,探讨了沉积岩地层中速度和弹性模量,弹性模量和孔隙度,剪切模量和孔隙度,速度和孔隙度,孔隙度和Biot系数之间的关系,利用从各种声学测井资料中提取出的P波和S波时差(或速度)定量评价地层孔隙度和骨架物质,辅以泥质指示测井曲线,可以计算地层孔隙度,饱和度,岩性等参数,在M,Krief方法的基础上,采用优化算法寻求适合于任何岩性地层的孔隙度与Biot系数之间的关系式,提高了Biot系数的计算精度,该评价方法有坚实的实验基础和理论基础,评价结果与实验室岩心分析数据吻合。 相似文献
52.
53.
On the basis of generalization of the results of investigation of the operation of rodlike elements of composite materials, we make a conclusion that the influence of various factors on the deformability of these elements is studied incompletely. The comparison of the stress-strain states for different models of concrete and reinforced-concrete elements makes it possible to describe the effect of longitudinal reinforcement (coefficient of reinforcement, strength and deformation characteristics) on the critical level of strains in the cross section. According to the results of our investigations, we give recommendations concerning the evaluation of the critical value of the coefficient of reinforcement above which one may observe the effect of reinforcement on the deformability of the analyzed sections. It is shown that the compression strength of the brittle base of the composite with inhomogeneous structure decreases as a result of the fracture processes. It is also demonstrated that the existing procedure used for the evaluation of the indicated decrease in strength requires significant improvement. The problem of evaluation of the ultimate value of the coefficient of reinforcement is also analyzed. 相似文献
54.
B. Bereqvist 《Strain》1987,23(1):7-13
The design and performance of precision bending equipment for testing straight beams with constant rectangular section under a pure bending moment is described. Part 1 deals with the loading arrangements and Part 2 with the rig for measuring beam deflection. The methods for recording deflection of strain gauges applied on the beam have been described elsewhere.1–4
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2Gcim ), is about ± 25 x. 10-4% , for 23 tests with a steel beam with 15 mm × 75 mm cross sectional dimensions, loaded to 1-1.5 mm/m strain.
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 104% for about 10 reproduced, not repeated, tests with the same steel beam. The deflection for such a beam is of the order of 2 to 4 mm. 相似文献
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2G
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 10
55.
56.
天然河流的横断面多为由主槽和漫滩组成的复式断面,水流在这种断面中比在单一断面中受到更多因素影响,流态也更加复杂。通过将明渠横断面上微元体在水流方向的N-S控制方程沿水深积分,得出描述垂线平均流速和边界剪切应力横向分布的模型,并通过对实验数据的验证,确定了模型的实用性。 相似文献
57.
谌行星 《湖南冶金职业技术学院学报》2006,6(2):262-264
在用基本不等式求最值时,大家都熟悉一个口诀:"一正二定三相等",但是有许多学生在怎样保证定值和相等时不知道该如何变形.为了解决学生的困难和困惑,我根据自己的经验,概括为两句口诀:"一正二定三相等,巧变四数定乾坤". 相似文献
58.
The effects of the uncertainties associated ith the apparent strain and gauge factor data, given by the manufacturer, in the evaluation of principal strains are examined. Principal strains are obtained by a reduction of the strains measured ith electrical resistance strain gauge rectangular or delta rosettes. The theoretical analysis points out the relevance of the effects caused. 相似文献
59.
Yue Fang 《时间序列分析杂志》2005,26(4):527-541
Abstract. We analyze, by simulation, the finite‐sample properties of goodness‐of‐fit tests based on residual autocorrelation coefficients (simple and partial) obtained using different estimators frequently used in the analysis of autoregressive moving‐average time‐series models. The estimators considered are unconditional least squares, maximum likelihood and conditional least squares. The results suggest that although the tests based on these estimators are asymptotically equivalent for particular models and parameter values, their sampling properties for samples of the size commonly found in economic applications can differ substantially, because of differences in both finite‐sample estimation efficiencies and residual regeneration methods. 相似文献
60.
碾压混凝土穿透型诱导缝不同扩展阶段的强度指标试验研究 总被引:2,自引:0,他引:2
在不同削弱度碾压混凝土轴拉试件的穿透型诱导缝周围粘贴了应变片,得到在不同应力状态下诱导缝应变发展规律为:在加载初期,离缝端不同距离的应变发展较为均匀,数值上相差不突出;随着荷载的增加,应变开始出现不均匀发展,离缝端越远,应变变化越缓慢;当接近最大荷载的阶段,缝端应变急速发展,试件瞬间断裂。应变从均匀发展变为不均匀发展,实质上隐含了诱导缝起裂、稳定发展、失稳断裂的整个过程,针对这一试验现象,结合断裂力学理论,建立了诱导缝不同开裂阶段的远场温度应力强度指标模型。 相似文献