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   16405篇
  免费   746篇
  国内免费   27篇
电工技术   218篇
综合类   19篇
化学工业   3542篇
金属工艺   289篇
机械仪表   418篇
建筑科学   595篇
矿业工程   56篇
能源动力   511篇
轻工业   998篇
水利工程   163篇
石油天然气   58篇
武器工业   2篇
无线电   1329篇
一般工业技术   3501篇
冶金工业   2858篇
原子能技术   123篇
自动化技术   2498篇
  2023年   176篇
  2022年   432篇
  2021年   508篇
  2020年   361篇
  2019年   340篇
  2018年   397篇
  2017年   354篇
  2016年   469篇
  2015年   395篇
  2014年   577篇
  2013年   880篇
  2012年   825篇
  2011年   1089篇
  2010年   786篇
  2009年   688篇
  2008年   817篇
  2007年   791篇
  2006年   644篇
  2005年   550篇
  2004年   463篇
  2003年   441篇
  2002年   443篇
  2001年   260篇
  2000年   243篇
  1999年   256篇
  1998年   513篇
  1997年   381篇
  1996年   288篇
  1995年   236篇
  1994年   212篇
  1993年   221篇
  1992年   145篇
  1991年   109篇
  1990年   128篇
  1989年   108篇
  1988年   108篇
  1987年   96篇
  1986年   122篇
  1985年   110篇
  1984年   94篇
  1983年   84篇
  1982年   76篇
  1981年   72篇
  1980年   68篇
  1979年   56篇
  1978年   72篇
  1977年   90篇
  1976年   129篇
  1975年   67篇
  1974年   48篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The authors examined heterogeneity in symptom trajectories among youths following psychiatric crises as well as the psychosocial correlates and placement outcomes associated with identified trajectories. Using semiparametric mixture modeling with 156 youths approved for psychiatric hospitalization, the authors identified 5 trajectories based on symptoms over the 16 months following crisis: high improved, high unimproved, borderline improved, borderline unimproved, and subclinical. Membership in unimproved symptom groups was associated with less suicidality, younger age, more youth hopelessness, and more caregiver empowerment. Improved symptom group membership predicted long-term decreases in days in out-of-home placements. More important, and in contrast with general impressions from the existing literature, findings suggest that a substantive proportion of youths with serious emotional disturbance sustain high levels of symptomatology following intensive mental health services. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
2.
The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput.  相似文献   
3.
A fast and efficient numerical method based on the Gauss-Jacobi quadrature is described that is suitable for solving Fredholm singular integral equations of the second kind that are frequently encountered in fracture and contact mechanics. Here we concentrate on the case when the unknown function is singular at both ends of the interval. Quadrature formulae involve fixed nodal points and provide exact results for polynomials of degree 2n − 1, where n is the number of nodes. Finally, an application of the method to a plane problem involving complete contact is presented.  相似文献   
4.
Recently it has been discovered that a nano-porous main group oxide 12CaO·7Al2O3 (C12A7) can be converted from a wide-gap insulator to a good transparent conductor. Using ab initio modelling we explain good conductivity of this material by very small barriers for hopping of localised electrons between neighbouring positive cages. We show that optical absorption of C12A7 in infrared region and at energies higher than 2.7 eV is due to inter-cage and intra-cage electron transitions, respectively. The proposed mechanisms can be useful in further search for conducting transparent media.  相似文献   
5.
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   
6.
Changes in clinical and laboratory measures of disease activity were studied prospectively in 12 European centers. Altogether 282 rheumatoid patients were evaluated during 6 months of therapy with slow-acting drugs. Patients' global assessment was taken to indicate overall response. The number of swollen joints and number of tender joints correlated highly with this. The erythrocyte sedimentation rate (ESR) correlated less well but was more uniform across centers. Grip strength, C-reactive protein and hemoglobin performed poorly between centers. There were cultural and linguistic difficulties using the Health Assessment Questionnaire in a European setting. Physician's global assessments were similar to the patient's global assessments and provided redundant information. The best measures are: the number of swollen joints, the number of tender joints, the ESR, and the patient's global assessment. It may also help to measure articular pain.  相似文献   
7.
8.
9.
During large scale wildfires, suppression activities are carried out under the direction of an Incident Management Team (IMT). The aim of the research was to increase understanding of decision processes potentially related to IMT effectiveness. An IMT comprises four major functions: Command, Operations, Planning, and Logistics. Four methodologies were used to study IMT processes: computer simulation experiments; analyses of wildfire reports; interviews with IMT members; and cognitive ethnographic studies of IMTs. Three processes were important determinants of IMT effectiveness: information management and cognitive overload; matching component function goals to overall goals; and team metacognition to detect and counter task‐disruptive developments. These processes appear to be complex multi‐person analogues of individual Incident Command processes identified previously. The findings have implications for issues such as: creating IMTs; training IMTs; managing IMTs; and providing decision support to IMTs.  相似文献   
10.
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach. A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that is needed to cause tensile failure of a specimen.  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