全文获取类型
收费全文 | 33976篇 |
免费 | 5462篇 |
国内免费 | 2016篇 |
专业分类
电工技术 | 3499篇 |
技术理论 | 2篇 |
综合类 | 3301篇 |
化学工业 | 4460篇 |
金属工艺 | 1407篇 |
机械仪表 | 2267篇 |
建筑科学 | 3753篇 |
矿业工程 | 2343篇 |
能源动力 | 2251篇 |
轻工业 | 3687篇 |
水利工程 | 1857篇 |
石油天然气 | 3582篇 |
武器工业 | 424篇 |
无线电 | 2100篇 |
一般工业技术 | 2364篇 |
冶金工业 | 2207篇 |
原子能技术 | 332篇 |
自动化技术 | 1618篇 |
出版年
2024年 | 320篇 |
2023年 | 818篇 |
2022年 | 1535篇 |
2021年 | 1765篇 |
2020年 | 1931篇 |
2019年 | 1446篇 |
2018年 | 1265篇 |
2017年 | 1464篇 |
2016年 | 1561篇 |
2015年 | 1595篇 |
2014年 | 2361篇 |
2013年 | 2151篇 |
2012年 | 2616篇 |
2011年 | 2708篇 |
2010年 | 2070篇 |
2009年 | 2001篇 |
2008年 | 1555篇 |
2007年 | 1891篇 |
2006年 | 1704篇 |
2005年 | 1479篇 |
2004年 | 1202篇 |
2003年 | 1059篇 |
2002年 | 868篇 |
2001年 | 693篇 |
2000年 | 644篇 |
1999年 | 550篇 |
1998年 | 393篇 |
1997年 | 301篇 |
1996年 | 277篇 |
1995年 | 242篇 |
1994年 | 202篇 |
1993年 | 163篇 |
1992年 | 107篇 |
1991年 | 93篇 |
1990年 | 88篇 |
1989年 | 64篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 22篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1980年 | 14篇 |
1966年 | 7篇 |
1964年 | 14篇 |
1962年 | 6篇 |
1959年 | 10篇 |
1957年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
52.
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
53.
催化裂化汽油脱硫助剂TS-01的工业试验 总被引:3,自引:0,他引:3
中国石油化工股份有限公司九江分公司在I套催化裂化装置进行了TS—0l催化裂化汽油脱硫双功能助剂的工业应用。结果表明:TS—0l剂对催化裂化汽油有较好的脱硫效果。当TS—0l剂注入原料中的量为70μg/g时,对催化裂化汽油的硫脱除率约为20%;注入量为120μg/g时,硫脱除率可达到25%-30%。汽油中脱除的硫主要以硫化氢形态转移至于气、液化气中。TS—01剂对产品分布及产品其它质量无明显影响,该剂亦有良好的金属钝化效果。 相似文献
54.
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
55.
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
56.
57.
用单透镜变换由多模光纤出射的大功率Nd:YAG激光束的特性 总被引:1,自引:0,他引:1
根据理论假设,通过选取单透镜的参数和位置,计算说明了单透镜使经由多模光纤出射的大功率Nd:YAG激光束的发射角压缩,光束聚焦效率提高,光束截面场为高斯分布;文中的计算结果符合已知规律,从而说明了理论假设的正确性。 相似文献
58.
ETRⅠ-30调速器是瑞士爱舍维斯工厂生产的具有PID调节规律的电液调速器。本文对其液压控制系统作了较详细的介绍,供有关人员参考。 相似文献
59.
M. Zandian J. G. Pasko J. M. Arias R. E. De Wames S. H. Shin 《Journal of Electronic Materials》1995,24(5):681-684
Measurements of 77K RoA and 300K reverse bias dynamic impedance (RdA) products at one volt reverse bias has been carried out to assess the degree of correlation of this figure of merit. Planar
P-on-n heterostructures were grown on near lattice-matched CdZnTe substrates with Hg1-xCdxTe (0.20< x <0.30) by molecular beam epitaxy. These devices were passivated with CdTe and doped with indium and arsenic as
n- and p-type dopants, respectively. Current-voltage characteristic of these devices exhibit thermally generated dark currents
at small and modest reverse bias. We have observed that RoA values of these long wavelength infrared P-on-n heterostructure photodiodes at 77K correlate with room temperature RdA values. Diode arrays with high room temperature RdA values at one volt reverse bias also have high RoA values at 77K. Similarly, low RdA values at room temperature indicate poor performance at 77K where deviation from diffusion current occurs at reverse bias
of 0.2 to 1 volt at room temperature. The results presented here, for a small samples of devices, demonstrate that room temperature
measurements of current-voltage characteristics to evaluate Hg1-xCdxTe (0.22< x <0.28) diode performance and array uniformity at lower temperatures can be used. This provides an acceptable criteria
for further study at lower temperatures. 相似文献
60.
单层球面网壳地震反应特征分析 总被引:29,自引:0,他引:29
考虑不同矢跨比、荷载、跨度和支座刚度等多种因素的影响,对单层球面网壳在地震作用下的反应进行了较全面的研究,给出了其随各参数变化的规律,得出了在单层球面网壳抗震设计中起控制作用的是水平地震作用而不是竖向地震作用等有益的结论.此外本文还给出了由于阻尼比不同而需对引用现行抗震规范反应谱分析的网壳地震作用进行修正的建议. 相似文献