首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5765篇
  免费   157篇
  国内免费   11篇
电工技术   353篇
综合类   14篇
化学工业   1299篇
金属工艺   174篇
机械仪表   183篇
建筑科学   110篇
能源动力   196篇
轻工业   545篇
水利工程   18篇
石油天然气   1篇
无线电   501篇
一般工业技术   1036篇
冶金工业   924篇
原子能技术   206篇
自动化技术   373篇
  2023年   20篇
  2022年   55篇
  2021年   99篇
  2020年   43篇
  2019年   68篇
  2018年   89篇
  2017年   66篇
  2016年   83篇
  2015年   70篇
  2014年   155篇
  2013年   273篇
  2012年   211篇
  2011年   308篇
  2010年   207篇
  2009年   260篇
  2008年   249篇
  2007年   242篇
  2006年   211篇
  2005年   208篇
  2004年   168篇
  2003年   187篇
  2002年   165篇
  2001年   133篇
  2000年   105篇
  1999年   150篇
  1998年   390篇
  1997年   258篇
  1996年   201篇
  1995年   132篇
  1994年   141篇
  1993年   97篇
  1992年   52篇
  1991年   73篇
  1990年   69篇
  1989年   61篇
  1988年   57篇
  1987年   55篇
  1986年   54篇
  1985年   62篇
  1984年   39篇
  1983年   40篇
  1982年   42篇
  1981年   39篇
  1980年   44篇
  1979年   26篇
  1978年   22篇
  1977年   27篇
  1976年   51篇
  1975年   15篇
  1974年   15篇
排序方式: 共有5933条查询结果,搜索用时 15 毫秒
71.
72.
Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are disorders that are common and disturbing to uremic patients. The treatment of these is problematic. Eight patients on chronic hemodialysis and continuous peritoneal dialysis completed a double-blind placebo-controlled crossover study using incremental doses of pergolide up to 0.25 mg at bedtime for treatment of RLS and sleep disruption. Five patients (62.5%) noted subjective improvement in restless legs symptoms and sleep quality. Objective results were improved only slightly by treatment. The percentage of the first hour in bed during which leg movements occurred decreased from 20.5 +/- 6.0 to 11.5 +/- 3.3, p < 0.05. However, findings during sleep were less positive. The following measures were not significant between placebo and treatment: leg movements per hour of sleep [53.7 +/- 22.3 vs 35.8 +/- 11.8 (p = 0.2)]; and percentage of sleep time spent with leg movements [5.5% +/- 3.2 vs 4.4% +/- 1.4 (p = 0.37)]. Patients continued to have very disrupted sleep, and we could not document an objective improvement in sleep architecture. Thus, although pergolide at the dose of 0.25 mg at bedtime provided subjective improvement in symptoms of restless legs and quality of sleep, and objectively decreased leg movements during the first hour in bed, objectively sleep continued to be disrupted. In this small patient group, the response to pergolide was not uniform, and further investigation is required to test effectiveness at higher doses.  相似文献   
73.
CsB3O5 has been found to be phase matchable for SFG down to 0.185 μm by mixing the fifth harmonic of a Nd:YAG laser at 1.0642 μm and the output of a KTP parametric oscillator pumped by the second harmonic of the same Nd:YAG laser at 20.0°C. Improved Sellmeier's equations and nonlinear optical constant of this crystal are reported  相似文献   
74.
Infectious mononucleosis (IM) syndrome is typically caused by EBV, but also by drugs and other organisms such as CMV and HBV. It demonstrates a wide range of clinical and laboratory characteristics, presumably depending on the age of onset. However, associations of laboratory abnormalities with the clinical features have not been well documented. We evaluated here, the associations among patients with IM syndrome using of multiple regression (MR) and multiple logistic regression (MLR) analyses. We examined 90 (40 males, 50 females) patients, who were admitted to our hospital with IM syndrome. The diagnostic criteria were fever and presence of atypical lymphocytes (> 5% of the WBC or the count including monocytes > 5000/microliter), and at least 3 of 7 clinical features: tonsillitis, lymphadenopathy, skin rash, hepato-, spleno-megaly, hepatic dysfunction. The diagnosis of EBV was serologically confirmed in 41 cases. MR revealed that the higher age group tended to have lower platelet counts, and that lower platelet counts were associated with higher ALT levels. In addition, MLR revealed that patients with skin rash tended not to have splenomegaly. The frequency of splenomegaly was not related to age, contrary to the findings of previous reports. These findings are useful to differentiate IM syndrome based on laboratory data.  相似文献   
75.
The efficacy of collagen-sponge to reduce postoperative scar formation was investigated in 65 Japanese white rabbits that received laminectomy in the 7th and 8th thoracic vertebra. The defect after laminectomy was filled by collagen-sponge in 25 rabbits, by free fat in 20 rabbits, and by nothing in 20 rabbits as controls. The animals were sacrificed 2, 4, 8 and 12 weeks and additional 5 rabbits of which defects were filled with collagen-sponge were sacrificed after 24 weeks. All the defects were examined histologically. At 4 weeks after laminectomy, the defects filled by collagen-sponge showed that fibrous tissue had invaded into the sponge, but there was no remarkable adhesion to the dura mater. At 8 weeks, the defect with collagen sponge showed foaming cells, and no thickening of the dura mater was observed. At 12 weeks, the grouping of foaming cells was partially replaced by fat cells. At 24 weeks, most of the foaming cells were replaced by fat cells, and the defect was then similar to that filled by free fat at 12 weeks. In contrast, the defect with no interposed membrane was already filled with fibrous tissue at 4 weeks, and adhesion to the dura mater was observed. Although the free-fat graft at 12 weeks postoperatively showed no remarkable adhesion around the dura mater, infiltration of fat tissue into the spinal canal was observed in 2 of 5 rabbits. These results indicated that collagen-sponge can be utilized as a new biomaterial to effectively prevent scar formation after laminectomy.  相似文献   
76.
Applied Intelligence - A multi-agent system (MAS) is expected to be applied to various real-world problems where a single agent cannot accomplish given tasks. Due to the inherent complexity in the...  相似文献   
77.
Stationary projectors mainly used in system applications have recently gained a wider application range, including general presentations in halls and large conference rooms and being used, for example, in digital signage and for monitoring purposes. Consequently, they are required to meet new market demands for durability, reliability, and flexibility in installation in addition to their conventional basic performance such as especially high brightness. To achieve especially high brightness, a new optical system with two lamps is proposed; the profile of the cover glass that prevents the glass from scattering is made aspherical, the profile of the beam‐combining mirror is improved with its position optimized, and the size of the incident plane of the integrator rod is made larger (1.1 times). These measures resulted in an optical system of an even higher efficiency with 7000 lm, which is the highest in its class (according to a June 2010 investigation). Also, the arrangement of two parallel lamps completely eliminated the effect of heat passing from one lamp to the other, which helped secure durability, reliability, and flexibility in installation. Furthermore, the combined use of the unique non‐telecentric optical system, adopted from the conventional single‐lamp model, helps maintain the class‐highest contrast ratio.1,2  相似文献   
78.
This is an extensive overview of the core and special space?Ctime and Arbitrary Lagrangian?CEulerian (ALE) techniques developed by the authors?? research teams for patient-specific cardiovascular fluid?Cstructure interaction (FSI) modeling. The core techniques are the ALE-based variational multiscale (ALE-VMS) method, the Deforming-Spatial-Domain/Stabilized Space?CTime formulation, and the stabilized space?Ctime FSI technique. The special techniques include methods for calculating an estimated zero-pressure arterial geometry, prestressing of the blood vessel wall, a special mapping technique for specifying the velocity profile at an inflow boundary with non-circular shape, techniques for using variable arterial wall thickness, mesh generation techniques for building layers of refined fluid mechanics mesh near the arterial walls, a recipe for pre-FSI computations that improve the convergence of the FSI computations, the Sequentially-Coupled Arterial FSI technique and its multiscale versions, techniques for the projection of fluid?Cstructure interface stresses, calculation of the wall shear stress and oscillatory shear index, arterial-surface extraction and boundary condition techniques, and a scaling technique for specifying a more realistic volumetric flow rate. With results from earlier computations, we show how these core and special FSI techniques work in patient-specific cardiovascular simulations.  相似文献   
79.
The computational challenges posed by fluid–structure interaction (FSI) modeling of parachutes include the lightness of the parachute canopy compared to the air masses involved in the parachute dynamics, in the case of “ringsail” parachutes the geometric complexities created by the construction of the canopy from “rings” and “sails” with hundreds of ring “gaps” and sail “slits”, and in the case of parachute clusters the contact between the parachutes. The Team for Advanced Flow Simulation and Modeling () has successfully addressed these computational challenges with the Stabilized Space–Time FSI (SSTFSI) technique, which was developed and improved over the years by the and serves as the core numerical technology, and a number of special techniques developed in conjunction with the SSTFSI technique. The quasi-direct and direct coupling techniques developed by the , which are applicable to cases with incompatible fluid and structure meshes at the interface, yield more robust algorithms for FSI computations where the structure is light and therefore more sensitive to the variations in the fluid dynamics forces. The special technique used in dealing with the geometric complexities of the rings and sails is the Homogenized Modeling of Geometric Porosity, which was developed and improved in recent years by the . The Surface-Edge-Node Contact Tracking (SENCT) technique was introduced by the as a contact algorithm where the objective is to prevent the structural surfaces from coming closer than a minimum distance in an FSI computation. The recently-introduced conservative version of the SENCT technique is more robust and is now an essential technology in the parachute cluster computations carried out by the . We provide an overview of the core and special techniques developed by the , present single-parachute FSI computations carried out for design-parameter studies, and report FSI computation and dynamical analysis of two-parachute clusters.  相似文献   
80.
The temperature dependence of the electrical resistivity and Seebeck coefficient was measured on single crystals of La1–x Ca x MnO3(0 <x 0.3) and La1–x Sr x MnO 3 (0 <x 0.4) grown by the arc-image floating zone method. The electrical conduction for La1–x crystals withx 0.2 was of the activation type aboveT c and of the degenerate type belowT c, while that for the crystal withx = 0.1 was of the activation type over the whole measured temperature range between –170 and 400°C. The conduction behaviour of La1– x Sr x MnO3 was essentially the same as that of La1–x Ca x MnO3 except that the conduction of the crystals withx = 0.3 and 0.4 was of the degenerate type aboveT c. A distinct difference in Seebeck data was observed between the calcium and the strontium compounds.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号