全文获取类型
收费全文 | 43658篇 |
免费 | 6692篇 |
国内免费 | 3096篇 |
专业分类
电工技术 | 4006篇 |
技术理论 | 2篇 |
综合类 | 4722篇 |
化学工业 | 3589篇 |
金属工艺 | 1719篇 |
机械仪表 | 3340篇 |
建筑科学 | 4319篇 |
矿业工程 | 2429篇 |
能源动力 | 2146篇 |
轻工业 | 4327篇 |
水利工程 | 2028篇 |
石油天然气 | 3158篇 |
武器工业 | 675篇 |
无线电 | 6652篇 |
一般工业技术 | 3805篇 |
冶金工业 | 2042篇 |
原子能技术 | 973篇 |
自动化技术 | 3514篇 |
出版年
2024年 | 339篇 |
2023年 | 876篇 |
2022年 | 1707篇 |
2021年 | 1934篇 |
2020年 | 2136篇 |
2019年 | 1663篇 |
2018年 | 1454篇 |
2017年 | 1815篇 |
2016年 | 2004篇 |
2015年 | 2063篇 |
2014年 | 2938篇 |
2013年 | 2737篇 |
2012年 | 3431篇 |
2011年 | 3623篇 |
2010年 | 2692篇 |
2009年 | 2619篇 |
2008年 | 2175篇 |
2007年 | 2637篇 |
2006年 | 2313篇 |
2005年 | 2026篇 |
2004年 | 1615篇 |
2003年 | 1421篇 |
2002年 | 1118篇 |
2001年 | 977篇 |
2000年 | 909篇 |
1999年 | 750篇 |
1998年 | 590篇 |
1997年 | 450篇 |
1996年 | 423篇 |
1995年 | 385篇 |
1994年 | 329篇 |
1993年 | 283篇 |
1992年 | 195篇 |
1991年 | 156篇 |
1990年 | 144篇 |
1989年 | 102篇 |
1988年 | 74篇 |
1987年 | 60篇 |
1986年 | 39篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1966年 | 7篇 |
1964年 | 14篇 |
1962年 | 6篇 |
1959年 | 14篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
72.
Organic photovoltaic solar cells bear an important potential of development in the search for low-cost modules for the production of domestic electricity. One of the main differences between inorganic and organic solar cells is that photo-excitation in these materials does not automatically lead to the generation of free charge carriers, but to bind electron–hole pairs (exciton) with a binding energy of about 0.4 eV. Till now various numerical methods using approximations have been reported to study different aspects of organic solar cells. For the first time an accurate method using Lambert W-function is presented to study different parameters of organic solar cells. 相似文献
73.
This article introduces the basic structure of a symmetric self-electrooptic effect device (S-SEED), and applies the Kirchoff' s current law and a purely equivalent capacitive model, to analyze S-SEED's switch characteristics. Linear approximation and N-segment approximation are utilized to obtain S-SEED's voltage-time (V-T) and characteristics. Theoretical analysis is verified by simulations, and the results demonstrate that the precision of S-SEED's switch time can satisfy the requirement in applications with linear approximation. Moreover, the simulations compare S-SEED's switch characteristics with different input powers and input contrast ratios, which reveal that increasing input contrast ratio is an effective way to improve S-SEED's switch characteristics. 相似文献
74.
75.
LIJuan HUAYu-lin WANGChang-sheng XIONGShao-zhen 《半导体光子学与技术》2004,10(1):41-43,47
The white organic light emitting device (OLED) with single-structure using a polymer blend as the light emitting layer is fabricated. Heat treatment is used to control the ratio between the intensities of main electroluminescent spectral peaks. The electroluminescent spectrum of our device is quite similar to that of white inorganic LED produced by Nichia Corporation after being annealed, and its turn-on voltage can be decreased by 1V. 相似文献
76.
It is well recognized that performance changes over time. However, the effect of these changes on overall assessments of performance is largely unknown. In a laboratory experiment, we examined the influence of salient Gestalt characteristics of a dynamic performance profile on supervisory ratings. We manipulated performance trend (flat, linear-improving, linear-deteriorating, U-shaped, and ∩-shaped), performance variation (small, large), and performance mean (negative, zero, positive) within subjects and display format (graphic, tabular) between subjects. Participants received and evaluated information about the weekly performance of different employees over a simulated 26-week period. Results showed strong main effects on performance ratings of both performance mean and performance trend, as well as interactions with display format. Theoretical and practical implications of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
77.
Nusslock Robin; Abramson Lyn Y.; Harmon-Jones Eddie; Alloy Lauren B.; Hogan Michael E. 《Canadian Metallurgical Quarterly》2007,116(1):105
On the basis of the behavioral approach system (BAS) dysregulation theory of bipolar disorder, this study examined the relation between occurrence of a BAS activation-relevant life event--goal striving--and onset of hypomanic and depressive episodes and symptoms. In particular, the authors examined the relation between preparing for and completing final exams (a goal-striving event) and onset of bipolar spectrum episodes and symptoms in college students with bipolar II disorder or cyclothymia (i.e., "soft" bipolar spectrum conditions). One hundred fifty-nine individuals with either a bipolar spectrum disorder (n=68) or no major affective psychopathology (controls; n=91) were further classified on the basis of whether they were college students (i.e., completed final exams). Consistent with the BAS dysregulation theory, preparing for and completing final exams was associated with an increase in hypomanic but not depressive episodes and symptoms in individuals with a soft bipolar spectrum diagnosis. Furthermore, self-reported BAS sensitivity moderated the presence of certain hypomanic symptoms during final exams. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
In its policy rationale for evidence-based practice in psychology (EBPP), the APA Presidential Task Force on Evidence-Based Practice (see record 2006-05893-001) claims to have constituted itself with "scientists and practitioners from a wide range of perspectives and traditions, reflecting the diverse perspectives within the field" (p. 273). We applaud this attention to diversity but contend that an entire perspective of the debate was omitted in the Task Force's newly approved policy and its underlying report. The failure to consider a philosophy of science perspective led the Task Force to make a number of epistemological assumptions that are not based on evidence or rationale and that thus violate the very spirit of evidence-based decision making. In this comment, we reveal a few of these assumptions and discuss their detrimental consequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
Hitsman Brian; Borrelli Belinda; McChargue Dennis E.; Spring Bonnie; Niaura Raymond 《Canadian Metallurgical Quarterly》2003,71(4):657
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
80.