全文获取类型
收费全文 | 1530693篇 |
免费 | 25684篇 |
国内免费 | 6995篇 |
专业分类
电工技术 | 35137篇 |
综合类 | 6401篇 |
化学工业 | 274785篇 |
金属工艺 | 66264篇 |
机械仪表 | 45131篇 |
建筑科学 | 46555篇 |
矿业工程 | 11784篇 |
能源动力 | 50403篇 |
轻工业 | 113656篇 |
水利工程 | 15435篇 |
石油天然气 | 38376篇 |
武器工业 | 141篇 |
无线电 | 199001篇 |
一般工业技术 | 290746篇 |
冶金工业 | 163305篇 |
原子能技术 | 34494篇 |
自动化技术 | 171758篇 |
出版年
2021年 | 15657篇 |
2020年 | 11930篇 |
2019年 | 14690篇 |
2018年 | 18561篇 |
2017年 | 18227篇 |
2016年 | 22669篇 |
2015年 | 17684篇 |
2014年 | 28847篇 |
2013年 | 88450篇 |
2012年 | 36345篇 |
2011年 | 50739篇 |
2010年 | 45143篇 |
2009年 | 53527篇 |
2008年 | 46812篇 |
2007年 | 44629篇 |
2006年 | 44691篇 |
2005年 | 40788篇 |
2004年 | 42122篇 |
2003年 | 41684篇 |
2002年 | 40676篇 |
2001年 | 37117篇 |
2000年 | 35560篇 |
1999年 | 34574篇 |
1998年 | 43649篇 |
1997年 | 38824篇 |
1996年 | 35044篇 |
1995年 | 30562篇 |
1994年 | 28671篇 |
1993年 | 28541篇 |
1992年 | 26250篇 |
1991年 | 23359篇 |
1990年 | 23708篇 |
1989年 | 22873篇 |
1988年 | 21356篇 |
1987年 | 19561篇 |
1986年 | 18951篇 |
1985年 | 22276篇 |
1984年 | 22416篇 |
1983年 | 20369篇 |
1982年 | 19326篇 |
1981年 | 19446篇 |
1980年 | 18055篇 |
1979年 | 18547篇 |
1978年 | 17824篇 |
1977年 | 17745篇 |
1976年 | 18821篇 |
1975年 | 16107篇 |
1974年 | 15560篇 |
1973年 | 15660篇 |
1972年 | 13151篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Results are reported of a detailed optical and electron metallographic study of the effects of variations in quenching rate from the β-phase and aging temperature in the + ZrCr2 phase region, on the recrystallization and grain growth characteristics of Zr-1.14 wt% Cr-0.08 wt% Fe alloy used for nuclear fuel sheathing. It is shown that certain quenching rates, which produce a mixed martensitic-Widmanstätten structure, should be avoided during the fabrication of fuel sheathing, since recrystallization and grain growth occurs at a much lower temperature than a material quenched at such a rate that the structure is wholly Widmanstätten or wholly martensitic. Preaging at 350 or 450°C prior to the high-temperature (700–750°C) aging reduces the incidence of recrystallization and grain growth. 相似文献
952.
Noel E. Sharkey 《Robotics and Autonomous Systems》1997,22(3-4):345-359
It is time to locate connectionist representation theory in the new wave of robotics research. The utility of representations developed in artificial neural networks (ANNs) during learning has been demonstrated in cognitive science research since the 1980s. The research reported here puts learned representations to work in a decentered control task, the disembodied arm problem, in which a mobile robot operates an arm fixed to a table to pick up objects. There is no physical linkage between the arm and the robot and so the robot's point of view must be decentered. This is done by developing a modular Artificial Neural Net system in three stages: (i) a classifier net is trained with laser scan data to output transformationally invariant position classes; (ii) an arm net is trained for picking up objects; (iii) an inter net is trained to communicate and coordinate the sensing and acting. The completed system is shown to create new nonsymbolic transformationally invariant representations in order to perform the effective generalization of decentered viewpoints. 相似文献
953.
C Di Biasi M Accorinti G Trasimeni P Pivetti Pezzi A Melone G Gualdi 《Canadian Metallurgical Quarterly》1997,93(4):348-351
OBJECTIVE: To evaluate the relationships between patient and physician pretreatment expectations of pain relief and subsequent pain relief reported by chronic pain patients immediately after treatment. DESIGN: Prospective study of consecutive patients undergoing a procedure in a pain clinic for treatment of chronic pain. Patients rated their current pain level and their expectation of pain relief immediately prior to undergoing a procedure (e.g., intravenous drug infusion, nerve block) for the treatment of chronic pain. Simultaneously and independently, the treating physician completed a similar questionnaire. At completion of the procedure, patients rated their current pain level and degree of pain relief. SETTING: University of Washington Multidisciplinary Pain Center procedure suite. PATIENTS: Forty-six consecutive chronic pain patients. INTERVENTION: Intravenous drug infusions and nerve blocks. OUTCOME MEASURES: Current pain and pain relief ratings. RESULTS: Patients' pain relief expectation ratings were not correlated significantly with their postprocedure pain relief ratings or pre-post procedure changes in pain ratings. However, a statistically significant correlation was found between physician expectations of pain relief and patient pain relief ratings and patient pre-post procedure changes in pain. CONCLUSIONS: The results of this study suggest that physicians are better predictors than are patients of patients responses to these procedures and/or that physicians may somehow subtly communicate their expectations to patients during the procedure, and these expectations then influence patient response. Patient pretreatment expectations may not always play a significant role in nonspecific treatment effects. 相似文献
954.
This study describes the derivatization of the pseudooligosaccharide acarbose and its main metabolite, component 2, with 7-aminonaphthalene-1,3-disulfonic acid (ANDS) in human urine. Their efficient separation was possible by means of capillary zone electrophoresis, using a capillary tube of fused-silica containing 100 mM triethylammonium phosphate buffer, pH 1.5. On column laser-induced fluorescence allowed the detection of the pseudooligosaccharides in human urine in the nanomolar range. With this method, acarbose and component 2 were quantified in human urine after application of 300 mg of acarbose. 相似文献
955.
This paper is concerned with partially observed stochastic optimal control problems when nonlinearities enter the dynamics of the unobservable state and the observations as gradients of potential functions. Explicit representations for the information state are derived in terms of a finite number of sufficient statistics. Consequently, the partially observed problem is recast as one of complete information with a new state generated by a modified version of the Kalman filter. When the terminal cost is quadratic in the unobservable state and includes the integral of the nonlinearities, the optimal control laws are explicitly computed, similar to linear-exponential-quadratic-Gaussian (LEQG) and linear-quadratic-Gaussian (LQG) tracking problems. The results are applicable to filtering and control of Hamiltonian systems 相似文献
956.
Lauren P.D. Nandhakumar N. 《IEEE transactions on pattern analysis and machine intelligence》1997,19(5):417-430
The ability to determine the viewing parameters of objects from their projections has enabled well established tomographic techniques to be employed in the 3D reconstruction of objects from images obtained via modalities where the orientation of the objects cannot be controlled. A method is described for the determination of the viewing parameters of randomly acquired projections of asymmetric objects. It extends upon the common lines algorithm by determining the relative orientation of projections from the location of lines of intersection among the Fourier transforms of the projections in 3D Fourier space. A new technique for finding the lines of intersection in the presence of translational displacement, and for subsequently finding the translational displacement, is presented. The complete algorithm is described and its efficacy is demonstrated using real data. A new technique for dealing with noise is also discussed 相似文献
957.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
958.
959.
960.
N Sobel V Prabhakaran JE Desmond GH Glover EV Sullivan JD Gabrieli 《Canadian Metallurgical Quarterly》1997,78(1-2):115-123
A method for generating olfactory stimuli for humans within a functional magnetic resonance imaging (fMRI) experimental design is described. The system incorporates a nasal-mask in which the change from odorant to no-odorant conditions occurs in less than 500 ms and is not accompanied by visual, auditory, tactile, or thermal cues. The mask provides an ordorant-free environment following prolonged ordorant presence. Specific imaging parameters that are conducive to the study of the human olfactory system are described. In a pilot study performed using these methods, the specific patterns of activation observed converged with published experimental and clinical findings. 相似文献