全文获取类型
收费全文 | 66804篇 |
免费 | 7566篇 |
国内免费 | 2975篇 |
专业分类
电工技术 | 6293篇 |
技术理论 | 3篇 |
综合类 | 6017篇 |
化学工业 | 4899篇 |
金属工艺 | 3102篇 |
机械仪表 | 5039篇 |
建筑科学 | 13214篇 |
矿业工程 | 2605篇 |
能源动力 | 2048篇 |
轻工业 | 3648篇 |
水利工程 | 3590篇 |
石油天然气 | 4244篇 |
武器工业 | 1447篇 |
无线电 | 4793篇 |
一般工业技术 | 5870篇 |
冶金工业 | 2250篇 |
原子能技术 | 763篇 |
自动化技术 | 7520篇 |
出版年
2025年 | 517篇 |
2024年 | 1200篇 |
2023年 | 1326篇 |
2022年 | 1939篇 |
2021年 | 2304篇 |
2020年 | 2595篇 |
2019年 | 2098篇 |
2018年 | 1872篇 |
2017年 | 2401篇 |
2016年 | 2640篇 |
2015年 | 2731篇 |
2014年 | 4170篇 |
2013年 | 3911篇 |
2012年 | 4958篇 |
2011年 | 5023篇 |
2010年 | 3859篇 |
2009年 | 3778篇 |
2008年 | 3400篇 |
2007年 | 4128篇 |
2006年 | 3698篇 |
2005年 | 3242篇 |
2004年 | 2650篇 |
2003年 | 2202篇 |
2002年 | 1871篇 |
2001年 | 1616篇 |
2000年 | 1301篇 |
1999年 | 1061篇 |
1998年 | 872篇 |
1997年 | 670篇 |
1996年 | 655篇 |
1995年 | 539篇 |
1994年 | 410篇 |
1993年 | 295篇 |
1992年 | 257篇 |
1991年 | 160篇 |
1990年 | 158篇 |
1989年 | 116篇 |
1988年 | 76篇 |
1987年 | 50篇 |
1986年 | 43篇 |
1985年 | 25篇 |
1980年 | 65篇 |
1979年 | 47篇 |
1965年 | 26篇 |
1964年 | 34篇 |
1960年 | 23篇 |
1959年 | 36篇 |
1957年 | 23篇 |
1956年 | 33篇 |
1955年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A Review of the Application of Meta-Heuristic Algorithms to 2D Strip Packing Problems 总被引:4,自引:0,他引:4
This paper is a review of the approachesdeveloped to solve 2D packing problems withmeta-heuristic algorithms. As packing tasks arecombinatorial problems with very large searchspaces, the recent literature encourages theuse of meta-heuristic search methods, inparticular genetic algorithms. The objective ofthis paper is to present and categorise thesolution approaches in the literature for 2Dregular and irregular strip packing problems.The focus is hereby on the analysis of themethods involving genetic algorithms. Anoverview of the methods applying othermeta-heuristic algorithms including simulatedannealing, tabu search, and artificial neuralnetworks is also given. 相似文献
22.
As a novel parallel hip joint simulator, the 3SPS+1PS bionic parallel test platform with 4 degrees of freedom including three rotations and one translation is proposed. SPS denotes the spherical-prismatic-spherical leg and PS denotes the prismatic-spherical leg where only the prismatic joint is actuated and hence underlined. By means of the unit quaternion method, the formulae for solving the inverse/forward displacement, the inverse/forward velocity and the inverse/forward acceleration kinematics are derived. Using the unit quaternion to represent the position and orientation of a moving platform, singularities caused by Euler angles can be avoided. Combining the topological structure characteristics of the 3SPS+1PS bionic parallel test platform and letting the three-dimensional (3-D) motion of a human hip joint as its output movement, the displacement trajectories of three active legs are constructed based on the inverse displacement kinematics. The forward kinematic tests whose data are recorded by a 3-D orientation capture system are carried out on the developed parallel hip joint simulator. Moreover, the results of the forward kinematic tests prove that the 3SPS+1PS bionic parallel test platform can approximately represent human hip joint motion and provide more reliable experimental data for hip joint prostheses in clinical application. 相似文献
23.
《Ergonomics》2012,55(6):1012-1021
For decades, research to quantify the effects of firefighting activities and personal protective equipment on physiology and biomechanics has been conducted in a variety of testing environments. It is unknown if these different environments provide similar information and comparable responses. A novel Firefighting Activities Station, which simulates four common fireground tasks, is presented for use with an environmental chamber in a controlled laboratory setting. Nineteen firefighters completed three different exercise protocols following common research practices. Simulated firefighting activities conducted in an environmental chamber or live-fire structures elicited similar physiological responses (max heart rate: 190.1 vs 188.0 bpm, core temperature response: 0.047°C/min vs 0.043°C/min) and accelerometry counts. However, the response to a treadmill protocol commonly used in laboratory settings resulted in significantly lower heart rate (178.4 vs 188.0 bpm), core temperature response (0.037°C/min vs 0.043°C/min) and physical activity counts compared with firefighting activities in the burn building.Practitioner Summary: We introduce a new approach for simulating realistic firefighting activities in a controlled laboratory environment for ergonomics assessment of fire service equipment and personnel. Physiological responses to this proposed protocol more closely replicate those from live-fire activities than a traditional treadmill protocol and are simple to replicate and standardise. 相似文献
24.
为满足实验室单克隆抗体的制备研究,本实验特对实验室常用的制备单抗的模拟抗原(Ac-NK16-Ahx-3)进行ELISA间接法检测,进而建立一种高效的检测方法。通过对不同稀释度待测抗体的免疫吸附测定,检测出它的最终灵敏度为0.078mg/mL,最佳二抗稀释倍数为300倍,其最佳拟合曲线为y=-0.0732x+0.6875,R2=0.8619。并且,通过统计学方法进行统计分析,确定出各实验组的相关性及变异系数,从而排除实验中的操作误差,最终可确定最佳的实验条件,并保证实验的准确性。 相似文献
25.
The work presented in this paper focuses on improving coal loading performance of shear drum.Employing the similarity theory,we carried out a dimensional analysis of the correlation parameters which in... 相似文献
26.
学生成绩评定方法研究 总被引:2,自引:0,他引:2
分别用x2拟合检验法、直方图和Q-Q分布图从直观和理论两方面出发验证学生成绩是否呈正态分布,通过图象与应用概率统计知识有机结合,运用数学软件对数据进行处理,达到验证研究的目的。 相似文献
27.
由于缺乏正规的标准,铝电解槽能量平衡测试中存在着一些概念混淆、计算方法和公式错误的情况,应引起测试工作者的注意,在测试计算前应认真制订方案,多查一些参考资料,核实所用公式、数据,避免发生失误。同时对于类似计算,由于计算机的应用,应尽可能采取精确算法。没必要采取一些非常粗糙的近似算法和经验值。 相似文献
28.
用比较原则及莱布尼兹判别法对函数f(x)=(1+x)α的马克劳林级数在x=±1的敛散情形给予讨论. 相似文献
29.
Super-highly reinforced concrete tube in tube structure is a developing structure system of high-rise building. The more reasonable derivation process of the multi-vertical-line-element model stiffness matrix is given.On the premise of pointing out the problems of present multi-spring element model, combined with present multivertical-line-element model for analyzing on shear wall, the model is expanded to spatial one, and the stiffness matrix of which is derived. Combined with hysteretic axial model and hysteretic shear model, it is suitable for columns,wall limbs and beams with all kinds of section form. Some examples are calculated and compared with test results,which shows that the models have relatively good accuracy. On the base of the experimental phenomenon and failure mechanism for tube in tube structure specimen, nonlinear seismic responses analysis program on the basis of the advantaged element model for tube in tube structure is developed. Calculation results are in good agreement with those of the pseudo-dynamic tests and the failure mechanism can be well reflected. 相似文献
30.
Performance of Alcohol and Safer Sex Change Rulers Compared With Readiness to Change Questionnaires.
LaBrie Joseph W.; Quinlan Thomas; Schiffman Jason E.; Earleywine Mitchell E. 《Canadian Metallurgical Quarterly》2005,19(1):112
As part of a larger intervention study, the authors hypothesized that change rulers created for alcohol and safer sex would be equivalent to longer questionnaires. Ninety-six male college students completed rulers and questionnaires for assessing behavior change readiness. Participants' scores on the rulers significantly correlated with their scores on the questionnaires (r = .77 for alcohol; r = .77 for safer sex). In both domains, the rulers outperformed the questionnaires in predicting behavioral intentions, suggesting that the rulers had at least comparable concurrent criterion validity. This finding is the first of its kind in the safe sex literature and suggests that quick assessments of readiness to change are possible. Because the rulers are a continuous measure, the results are consistent with the idea that the change process is continuous rather than a series of discrete stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献