全文获取类型
收费全文 | 30661篇 |
免费 | 1393篇 |
国内免费 | 114篇 |
学科分类
工业技术 | 32168篇 |
出版年
2023年 | 168篇 |
2022年 | 256篇 |
2021年 | 887篇 |
2020年 | 620篇 |
2019年 | 706篇 |
2018年 | 784篇 |
2017年 | 860篇 |
2016年 | 829篇 |
2015年 | 651篇 |
2014年 | 984篇 |
2013年 | 1655篇 |
2012年 | 1461篇 |
2011年 | 1807篇 |
2010年 | 1339篇 |
2009年 | 1369篇 |
2008年 | 1251篇 |
2007年 | 1092篇 |
2006年 | 879篇 |
2005年 | 917篇 |
2004年 | 970篇 |
2003年 | 866篇 |
2002年 | 846篇 |
2001年 | 717篇 |
2000年 | 565篇 |
1999年 | 546篇 |
1998年 | 2050篇 |
1997年 | 1334篇 |
1996年 | 936篇 |
1995年 | 615篇 |
1994年 | 481篇 |
1993年 | 542篇 |
1992年 | 220篇 |
1991年 | 283篇 |
1990年 | 229篇 |
1989年 | 194篇 |
1988年 | 208篇 |
1987年 | 158篇 |
1986年 | 165篇 |
1985年 | 182篇 |
1984年 | 131篇 |
1983年 | 95篇 |
1982年 | 119篇 |
1981年 | 125篇 |
1980年 | 115篇 |
1979年 | 91篇 |
1978年 | 73篇 |
1977年 | 143篇 |
1976年 | 225篇 |
1975年 | 81篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
AG Niessen JG Bollemeijer RJ de Keizer PH de Meijer 《Canadian Metallurgical Quarterly》1994,138(15):770-775
OBJECTIVE: To assess how often the aetiology is established in patients with uveitis, what systemic disease are found and what is the contribution of the internist to the diagnostic process. DESIGN: Retrospective study. SETTING: University Hospital Leiden, the Netherlands. METHOD: From January 1987 to April 1992, 342 patients presented with uveitis. All patients underwent a standard ophthalmological examination. Referral to an internist and individualised laboratory screening followed in patients with recurrent, chronic, bilateral or panuveitis. Recorded were: ophthalmological data, results of laboratory screening, results of analysis by the internist, final diagnosis and presence of systemic disease. RESULTS: 149 (44%) patients were examined by the internist, 18 (5.2%) were seen by another specialist. In 169 (49%) patients a specific diagnosis was made. 74 (22%) had a systemic disease, 74 a primary ocular disease. In 28 (8%) a systemic disease was presumed (5% were HLA-B27 positive, 3% had abnormal laboratory results); 5 (1%) patients had endophthalmitis as a complication of a septic process. CONCLUSION: In approximately 1/3 of the patients with uveitis a systemic disease was found. Examination by the internist tailored to the individual patient is essential in the evaluation of uveitis patients. 相似文献
72.
73.
A. P. J. Voncken A. F. J. Hammen A. T. A. M. de Waele 《Journal of Low Temperature Physics》1996,102(3-4):335-348
In this paper we describe the effect of the vicinity of a liquid3He-vacuum interface on the behavior of a vibrating wire viscometer. It was found that in the fluid near the liquid interface the quality factor is lower than in the bulk liquid. We further report on the observation of a doubling of the resonance peak of the wire in a saturated3He-4He mixture. The frequencies and amplitudes of the two peaks strongly depend on the distance between the phase boundary and the vibrating wire; the temperature and the velocity of the phase boundary have no significant influence on the peak frequencies. The observed peak doubling is attributed to the coupling of the vibrating wire with a standing second-sound wave in the dilute phase where the volume of the dilute phase can be regarded as a resonating cavity for second sound. 相似文献
74.
75.
76.
Classical parameter-extraction programs rely on the minimisation of the relative current deviation. However, since, especially for analogue applications, the slope of the IDS/VDS curve in the saturation region is at least equally important, a new fit strategy has been developed. This new fit strategy extracts a parameter set which optimises the current residual as well as the slope residual at every point. 相似文献
77.
From visual data exploration to visual data mining: a survey 总被引:8,自引:0,他引:8
Ferreira de Oliveira M.C. Levkowitz H. 《IEEE transactions on visualization and computer graphics》2003,9(3):378-394
We survey work on the different uses of graphical mapping and interaction techniques for visual data mining of large data sets represented as table data. Basic terminology related to data mining, data sets, and visualization is introduced. Previous work on information visualization is reviewed in light of different categorizations of techniques and systems. The role of interaction techniques is discussed, in addition to work addressing the question of selecting and evaluating visualization techniques. We review some representative work on the use of information visualization techniques in the context of mining data. This includes both visual data exploration and visually expressing the outcome of specific mining algorithms. We also review recent innovative approaches that attempt to integrate visualization into the DM/KDD process, using it to enhance user interaction and comprehension. 相似文献
78.
Norris Fran H.; Murphy Arthur D.; Baker Charlene K.; Perilla Julia L.; Rodriguez Francisco Gutiérrez; Rodriguez José de Jesús Gutiérrez 《Canadian Metallurgical Quarterly》2003,112(4):646
Prevalence rates of trauma and posttraumatic stress disorder (PTSD) were estimated from a probability sample of 2,509 adults from 4 cities in Mexico. PTSD was assessed according to Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) criteria using the Composite International Diagnostic Interview (CIDI; WHO, 1997). Lifetime prevalence of exposure and PTSD were 76% and 11.2%, respectively. Risk for PTSD was highest in Oaxaca (the poorest city), persons of lower socioeconomic status, and women. Conditional risk for PTSD was highest following sexual violence, but nonsexual violence and traumatic bereavement had greater overall impact because of their frequency. Of lifetime cases, 62% became chronic; only 42% received medical or professional care. The research demonstrates the importance of expanding the epidemiologic research base on trauma to include developing countries around the world. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
The dynamical systems theory developed by Zufiria [1], Zufiria and Guttalu [2, 3], and Guttalu and Zufiria [4] is applied to the stability analysis of control systems in which the feedback control law requires in real time the solution of a set of nonlinear algebraic equations. Since a small sampling period is assumed, the stability and performance of the controlled process can be studied with a continuous-time formulation. A singularly perturbed system is used to model both the dynamics of the system being controlled and a numerical iterative algorithm required to compute the control law. An updating control procedure has been proposed based on the iterative nature of the control algorithm. The results obtained by Zufiria [1] regarding the behavior of a dynamical system that models the numerical algorithms lead to a considerable simplification in the analysis. For the case of a control problem involving inverse kinematics, the numerical algorithm that solves for inverse kinematics can be considered as an observer (or an estimator) of the state-space variables. The study provides an estimate of the required speed of computations to preserve the stability of the controller.Recommended by E .P. Ryan 相似文献
80.
A digital signal processor-based control system for the permanent magnet-assisted reluctance synchronous machine, with the emphasis on dynamic performance, is proposed. A classical design approach is used to design the current and speed controllers for the machine. The stator current of the machine is controlled in such a way that the current angle in the dq synchronous reference frame is constant. The load-torque is estimated using a state space observer and compensation current based on the estimated load is used to improve the dynamic performance of the drive. The control system design is machine specific as it relies on data from finite-element analysis. Simulated and measured results on a 110-kW power level show that the resulting control system is stable and robust with good dynamic performance 相似文献