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   1707篇
  免费   44篇
  国内免费   1篇
电工技术   17篇
综合类   1篇
化学工业   302篇
金属工艺   37篇
机械仪表   43篇
建筑科学   60篇
矿业工程   43篇
能源动力   24篇
轻工业   158篇
水利工程   15篇
无线电   123篇
一般工业技术   263篇
冶金工业   501篇
原子能技术   24篇
自动化技术   141篇
  2021年   38篇
  2020年   22篇
  2019年   18篇
  2018年   21篇
  2017年   21篇
  2016年   20篇
  2015年   30篇
  2014年   32篇
  2013年   56篇
  2012年   49篇
  2011年   81篇
  2010年   47篇
  2009年   67篇
  2008年   62篇
  2007年   74篇
  2006年   52篇
  2005年   42篇
  2004年   26篇
  2003年   38篇
  2002年   31篇
  2001年   31篇
  2000年   26篇
  1999年   42篇
  1998年   141篇
  1997年   92篇
  1996年   57篇
  1995年   48篇
  1994年   31篇
  1993年   40篇
  1992年   23篇
  1991年   15篇
  1990年   17篇
  1989年   16篇
  1988年   13篇
  1987年   13篇
  1986年   11篇
  1985年   20篇
  1984年   10篇
  1983年   13篇
  1982年   25篇
  1980年   12篇
  1979年   12篇
  1978年   13篇
  1977年   26篇
  1976年   34篇
  1975年   14篇
  1974年   9篇
  1973年   13篇
  1971年   8篇
  1970年   10篇
排序方式: 共有1752条查询结果,搜索用时 15 毫秒
81.
In 2 experiments, participants learned bone anatomy by using a handheld controller to rotate an on-screen 3-dimensional bone model. The on-screen bone either included orientation references, which consisted of visible lines marking its axes (orientation reference condition), or did not include such references (no–orientation reference condition). The learning task involved rotating the on-screen bone to match target orientations. Learning outcomes were assessed by asking participants to identify anatomical features from different orientations. On the learning task, the orientation reference group performed more accurately, directly, and quickly than did the control group, and high-spatial-ability individuals outperformed low-spatial-ability individuals. Assessments of anatomy learning indicated that under more challenging conditions, orientation references elevated learning by low-spatial-ability individuals to a level near that of high-spatial-ability individuals. The authors propose that orientation references assist this learning process by defining the object’s main axes or providing distinguishable features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
82.
An individual's cumulative life decisions help determine that person's well-being. To make good decisions requires knowing something about who one is and who one wants to be. It seems plausible that personality may draw on a specifically tailored intelligence that supports its own self-understanding and contributes to such life decisions. This personal intelligence (PI) helps the individual meet his or her own personal needs and to fit in with (or stand out from) the environment. What are people high in PI actually like relative to those lower in the skills? Drawing on a 2008 theory of PI-related abilities, the author reviews several literatures to examine what features distinguish the behavior of people high in PI from those lower in such skills. The feature list sets the stage for future research in distinguishing high-PI individuals from low-PI individuals according to their life expressions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
Objective: To evaluate cognitive-behavioral therapy to enhance medication adherence and reduce depression (CBT-AD) in individuals with HIV. Design: A two arm, randomized, controlled, cross-over trial comparing CBT-AD to enhanced treatment as usual only (ETAU). ETAU, which both groups received, included a single-session intervention for adherence and a letter to the patient's provider documenting her or his continued depression. The intervention group also received 10 to 12 sessions of CBT-AD. Main Outcome Measures: Adherence to antiretroviral therapy as assessed by Medication Event Monitoring Systems (MEMs) and depression as assessed by blinded structured evaluation. Results: At the acute outcome assessment (3-months), those who received CBT-AD evidenced significantly greater improvements in medication adherence and depression relative to the comparison group. Those who were originally assigned to the comparison group who chose to cross over to CBT-AD showed similar improvements in both depression and adherence outcomes. Treatment gains for those in the intervention group were generally maintained at 6- and 12-month follow-up assessments. By the end of the follow-up period, those originally assigned CBT-AD demonstrated improvements in plasma HIV RNA concentrations, though these differences did not emerge before the cross-over, and hence there were not between-groups differences. Conclusions: CBT-AD is a potentially efficacious approach for individuals with HIV struggling with depression and adherence. Replication and extension in larger efficacy trials are needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
84.
搅拌摩擦点焊(FSSw)是一种最近研究开发出来的新焊接技术.同目前的电阻点焊相比,该方法是具有节能、设备简单、焊点强度高、变形小、焊前表面清理简单,可以焊接厚度差别大的材料,特别适用于高强度铝合金的焊接.重点介绍该技术的基本原理、优缺点、焊接设备,对几种典型铝合金的焊接工艺参数、接头强度和组织等进行了比较详细的分析,从而对该技术有一个全面的了解.  相似文献   
85.
This article is a review of the mechanisms responsible for collisional activation of ions in mass spectrometers. Part I gives a general introduction to the processes occurring when a projectile ion and neutral target collide. The theoretical background to the physical phenomena of curve‐crossing excitation (for electronic and vibrational excitation), impulsive collisions (for direct translational to vibrational energy transfer), and the formation of long‐lived collision intermediates is presented. Part II highlights the experimental and computational investigations that have been made into collisional activation for four experimental conditions: high (>100 eV) and intermediate (1–100 eV) center‐of‐mass collision energies, slow heating collisions (multiple low‐energy collisions) and collisions with surfaces. The emphasis in this section is on the derived post‐collision internal energy distributions that have been found to be typical for projectile ions undergoing collisions in these regimes. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:608–639, 2009  相似文献   
86.
Nuclear magnetic resonance (NMR) spectroscopy has been used effectively in the analysis of elastomeric, soft materials and has been proven to be both sensitive to micro- and macroscopic changes associated with “aging” mechanisms. Traditional analyses, however, rely on empirical formulae containing a large number of (often arbitrary) independent variables. The resulting ambiguity can be circumvented largely by developing models of NMR observables that are based on basic polymer physics. We compare two such models, one previously published and one derived herein, along with two empirical expressions that describe the proton transverse magnetization decay associated with complex polymer networks. One particular extracted parameter, the proton-proton residual dipolar coupling (RDC), can be directly related to network topology, and a comparison of the extracted RDCs reveals high consistency among the models. An expression derived from the properties of a static Gaussian chain can minimize the number of parameters necessarily to describe the solid-like, networked proton population to a single independent parameter, the average RDC, Davg. The distribution of RDCs derived via this methodology is qualitatively similar to those derived from previously published multiple quantum techniques, although quantitative differences between the derived RDCs persist, suggesting that further analysis is necessary.  相似文献   
87.
The synthesis of the bis-cyclometalated complex [{Ir(μ-Cl)(ccpz)2}2] (1, cppz = 1-chloro-4-(4-chlorophenyl)-phthalazine) from hydrated iridium(III) chloride and the ligand ccpz in refluxing ethoxyethanol is described. Compound 1 was characterized by spectroscopic means and the crystal structure was determined by X-ray crystallography. The absorption and emission spectra exhibit the new compound as a red-emitting phosphorescent complex.  相似文献   
88.
Four varieties (Zutano, Bacon, Fuerte, Lula) of avocado (Persea americana) have been investigated for their unsaponifiable matter (UM) in mature and immature fruits. The UM content in crude oil was always higher in immature fruits (15–40%vs. 4–9%). The UM was fractionated by high-performance liquid chromatography for the determination of total sterols and tocopherol. The sterol content in the oil was always higher in immature (1.1–6.2%) than in mature (0.8–2.0%) fruits. The tocopherol content differed with the varieties (10.2–25.0 mg/100 g UM), and the levels in the oil were higher in immature (20.1–45.6 mg/100 g oil) than in mature (5.7–10.3 mg/100 g oil) fruits.  相似文献   
89.
Participatory modeling workshops were held in Sonora, México, with the goal of developing water resources management strategies in a water-stressed basin. A model of the water resources system, consisting of watershed hydrology, water resources infrastructure, and groundwater models, was developed deliberatively in the workshops, along with scenarios of future climate and development. Participants used the final version of the water resources systems model to select management strategies. The performance of the strategies was based on the reliability of meeting current and future demands at a daily time scale over a year’s period. Pre- and post-workshop surveys were developed and administered. The survey questions focused on evaluation of participants’ modeling capacity and the utility and accuracy of the models. The selected water resources strategies and the associated, expected reliability varied widely among participants. Most participants could be clustered into three groups with roughly equal numbers of participants that varied in terms of reliance on expanding infrastructure vs. demand modification; expectations of reliability; and perceptions of social, environmental, and economic impacts. The wide range of strategies chosen and associated reliabilities indicate that there is a substantial degree of uncertainty in how future water resources decisions could be made in the region. The pre- and post-survey results indicate that participants believed their modeling abilities increased and beliefs in the utility of models increased as a result of the workshops.  相似文献   
90.
This paper describes the use of the dual isotope method involving δ(15)N and δ(18)O measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Klju? groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9‰ and δ(18)O(NO(3)) values varied from -2.3 to +5.0‰. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8‰ for δ(15)N) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e.g. via septic systems, yielding δ(15)N values of +9.9 to +11.9‰ and elevated nitrate concentrations of 31.2-245.8 mg/L. The occurrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.  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