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   1830篇
  免费   122篇
  国内免费   3篇
电工技术   31篇
综合类   2篇
化学工业   441篇
金属工艺   20篇
机械仪表   51篇
建筑科学   74篇
矿业工程   1篇
能源动力   69篇
轻工业   224篇
水利工程   19篇
石油天然气   4篇
无线电   185篇
一般工业技术   301篇
冶金工业   204篇
原子能技术   4篇
自动化技术   325篇
  2024年   3篇
  2023年   15篇
  2022年   22篇
  2021年   109篇
  2020年   54篇
  2019年   61篇
  2018年   74篇
  2017年   56篇
  2016年   84篇
  2015年   63篇
  2014年   85篇
  2013年   128篇
  2012年   109篇
  2011年   124篇
  2010年   119篇
  2009年   119篇
  2008年   109篇
  2007年   77篇
  2006年   65篇
  2005年   66篇
  2004年   39篇
  2003年   57篇
  2002年   51篇
  2001年   31篇
  2000年   16篇
  1999年   28篇
  1998年   28篇
  1997年   19篇
  1996年   14篇
  1995年   18篇
  1994年   18篇
  1993年   8篇
  1992年   8篇
  1991年   7篇
  1990年   4篇
  1989年   8篇
  1988年   4篇
  1987年   3篇
  1986年   2篇
  1985年   6篇
  1984年   6篇
  1983年   4篇
  1982年   5篇
  1981年   8篇
  1980年   4篇
  1978年   3篇
  1976年   2篇
  1975年   3篇
  1964年   2篇
  1946年   1篇
排序方式: 共有1955条查询结果,搜索用时 15 毫秒
61.
The effects of serotonergic agonists were examined in intact and spinal fetuses, using an in vivo fetal rat preparation. On Gestational Day 20, fetuses were prepared with a midthoracic or sham spinal transection. Dose-response curves were obtained for quipazine (nonselective 5-hydroxytryptamine [5-HT] agonist; 1.0-10.0 mg/kg), CGS-12066A (5-HT1B agonist; 1.0-30.0 mg/kg), and α-methylserotonin (α-Me-5-HT; 5-HT? agonist; 0.2-15.0 mg/kg). During a 10-min test, each of the agonists (delivered via intraperitoneal injection) influenced fetal behavior: They increased the occurrence of head movements, mouthing, and hindlimb stepping. Quipazine and α-Me-5-HT also promoted hindlimb activity in spinal fetuses. Thus, stimulation of the fetal 5-HT system modulates motor activity at multiple levels of the developing central nervous system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
J-integral has been calculated along the free-of-stress border of deep and shallow rounded notches under torsion, under the hypothesis of a linear elastic behaviour of the material. Two exact closed-form solutions have been obtained which make it explicit the influence of the notch opening angle and the notch root radius. When the notch root radius tends to zero the proposed solution matches the expression for the corresponding pointed V-notch case.  相似文献   
63.
Prostate cancer (PCa) is globally the second most diagnosed cancer type and the most common cause of cancer-related deaths in men. Family history of PCa, hereditary breast and ovarian cancer (HBOC) and Lynch syndromes (LS), are among the most important risk factors compared to age, race, ethnicity and environmental factors for PCa development. Hereditary prostate cancer (HPCa) has the highest heritability of any major cancer in men. The proportion of PCa attributable to hereditary factors has been estimated in the range of 5–15%. To date, the genes more consistently associated to HPCa susceptibility include mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2) and homologous recombination genes (BRCA1/2, ATM, PALB2, CHEK2). Additional genes are also recommended to be integrated into specific research, including HOXB13, BRP1 and NSB1. Importantly, BRCA1/BRCA2 and ATM mutated patients potentially benefit from Poly (ADP-ribose) polymerase PARP inhibitors, through a mechanism of synthetic lethality, causing selective tumor cell cytotoxicity in cell lines. Moreover, the detection of germline alterations in MMR genes has therapeutic implications, as it may help to predict immunotherapy benefits. Here, we discuss the current knowledge of the genetic basis for inherited predisposition to PCa, the potential target therapy, and the role of active surveillance as a management strategy for patients with low-risk PCa. Finally, the current PCa guideline recommendations are reviewed.  相似文献   
64.
The association between nonalcoholic fatty liver disease (NAFLD) and chronic kidney disease has attracted interest and attention over recent years. However, no data are available in children. We determined whether children with NAFLD show signs of renal functional alterations, as determined by estimated glomerular filtration rate (eGFR) and urinary albumin excretion. We studied 596 children with overweight/obesity, 268 with NAFLD (hepatic fat fraction ≥5% on magnetic resonance imaging) and 328 without NAFLD, and 130 healthy normal-weight controls. Decreased GFR was defined as eGFR < 90 mL/min/1.73 m2. Abnormal albuminuria was defined as urinary excretion of ≥30 mg/24 h of albumin. A greater prevalence of eGFR < 90 mL/min/1.73 m2 was observed in patients with NAFLD compared to those without liver involvement and healthy subjects (17.5% vs. 6.7% vs. 0.77%; p < 0.0001). The proportion of children with abnormal albuminuria was also higher in the NAFLD group compared to those without NAFLD, and controls (9.3% vs. 4.0% vs. 0; p < 0.0001). Multivariate logistic regression analysis revealed that NAFLD was associated with decreased eGFR and/or microalbuminuria (odds ratio, 2.54 (confidence interval, 1.16–5.57); p < 0.05) independently of anthropometric and clinical variables. Children with NAFLD are at risk for early renal dysfunction. Recognition of this abnormality in the young may help to prevent the ongoing development of the disease.  相似文献   
65.
A closed form solution for the stress fields around a rigid nanoparticle under uniaxial tensile load is provided. The work explicitly accounts for the presence, around the nanoparticle, of an interphase of thickness comparable to the particle size and different elastic properties from those of the matrix. The solution allows one to determine, in closed form, the stress concentration around nanoparticles relevant for fracture and strength assessments of polymer nanocomposites.  相似文献   
66.
We propose an exact mathematical mapping that can be useful for making an analog quantum simulator that uses ion-based systems to realize the many-body electron–electron Coulomb interaction of an electron gas. This exact mathematical mapping allows us to deal with a system that is difficult to solve and control using a potentially more experimentally feasible setup. We show that ions can efficiently simulate electronic Coulomb interactions by using a unitary dilatation transform. The transformation does not need to be physically implemented if only the energy spectrum is desired, eliminating the complexity overhead. This proposal works in any number of dimensions and could be used to simulate different topological phases of electrons in graphene-like structures, by using ions confined in honeycomb lattices.  相似文献   
67.
Rollout methodology is a constructive metaheuristic algorithm and its main characteristics are its modularity, the adaptability to different objectives and constraints and the easiness of implementation. Multi-heuristic Rollout extends the Rollout by incorporating several constructive heuristics in the Rollout framework and it is able to easily incorporate human experience inside its research patterns to fulfil complex requirements dictated by the application at hand. However, a drawback for both Rollout and multi-heuristic Rollout is often represented by the required computation time. This paper proposes some alternatives of the full multi-heuristic Rollout algorithm aimed at improving the efficiency by reducing the computational effort while preserving the effectiveness. Namely, we propose dynamic heuristics pruning and candidates reduction strategies. As illustrative case studies, we analyse complex deterministic identical parallel machine scheduling problems showing how Rollout procedures can be used to tackle several additional constraints arising in real contexts. More specifically, we considered both standard (batch production, family set-ups, release, due dates, etc.) and non-standard (machine unavailabilities, maximum campaign size) scheduling constraints. An extensive campaign of computational experiments shows the behaviour of the multi-heuristic Rollout approach and the effectiveness of the different proposed speed-up methods.  相似文献   
68.
The scale of shot, i.e. the apparent distance of the camera from the main subject of a scene, is one of the main stylistic and narrative functions of audiovisual products, conveying meaning and inducing the viewer’s emotional state. The statistical distribution of different shot scales in a film may be an important identifier of an individual film, an individual author, and of various narrative and affective functions of a film. In order to understand at which level shot scale distribution (SSD) of a movie might become its fingerprint, it is necessary to produce automatic recognition of shot scale on a large movie corpus. In our work we propose an automatic framework for estimating the SSD of a movie by using inherent characteristics of shots containing information about camera distance, without the need to recover the 3D structure of the scene. In the experimental investigation, the comparison of obtained results with manual SSD annotations proves the validity of the framework. Experiments conducted on movies by Michelangelo Antonioni taken from different stylistic periods (1950–57, 1960–64, 1966–75, 1980–82) show a strong similarity in shot scale distributions within each period, thus opening interesting research lines regarding the possible aesthetic and cognitive sources of such a regularity.  相似文献   
69.
We present the calculation results of optimal texture geometries which maximize the supported load for a three-dimensional thrust bearing pad. By making use of the recently developed mean field theory of texture hydrodynamics, we develop an efficient multigrid optimization procedure based on the sequential genetic and conjugate gradient optimization. We show that our model allows to determine optimal solutions based on a two-scale hierarchy of structures, and the existence of particularly effective optimal geometries is presented and discussed.  相似文献   
70.
Molecular relaxation and polarization phenomena of twelve single-ion-conducting nanocomposite polymer electrolytes (nCPEs) are studied using Broadband Electrical Spectroscopy (BES). The electrolytes are obtained by combining PEG400 oligomers with increasing amounts of anionic nanofiller comprised of fluorinated-TiO2 associated with Li+ cations (LiFT®), resulting in [PEG400/(LiFT)y] systems with 0 ≤ y ≤ 26.4. This new class of [PEG400/(LiFT)y] electrolytes allows us to achieve a significant single-ion conductivity (1.1·10−5 S cm−1 at 30 °C for nLi/nO = 0.113) without the addition of lithium salts. To the best of our knowledge, this is the highest conductivity value reported for this class of electrolytes. This study, in conjunction with the results reported in Part 1, leads us to hypothesize a conduction mechanism in terms of two types of long-range charge-transfer processes. The first charge-transfer occurs at the interface between the filler nanoparticles and filler-PEG domains, while the second occurs through the PEG400 matrix with the assistance of polymer segmental motion. The measured Li+ transference numbers confirm that the studied materials are single-ion conductors.  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