全文获取类型
收费全文 | 150530篇 |
免费 | 20772篇 |
国内免费 | 15586篇 |
学科分类
工业技术 | 186888篇 |
出版年
2024年 | 894篇 |
2023年 | 2428篇 |
2022年 | 4565篇 |
2021年 | 5230篇 |
2020年 | 5621篇 |
2019年 | 4958篇 |
2018年 | 4732篇 |
2017年 | 5946篇 |
2016年 | 6726篇 |
2015年 | 6989篇 |
2014年 | 9322篇 |
2013年 | 10085篇 |
2012年 | 10927篇 |
2011年 | 11894篇 |
2010年 | 9335篇 |
2009年 | 9647篇 |
2008年 | 9780篇 |
2007年 | 10995篇 |
2006年 | 9354篇 |
2005年 | 8257篇 |
2004年 | 6611篇 |
2003年 | 5803篇 |
2002年 | 4587篇 |
2001年 | 3805篇 |
2000年 | 3263篇 |
1999年 | 2558篇 |
1998年 | 2149篇 |
1997年 | 1814篇 |
1996年 | 1654篇 |
1995年 | 1476篇 |
1994年 | 1200篇 |
1993年 | 850篇 |
1992年 | 731篇 |
1991年 | 563篇 |
1990年 | 464篇 |
1989年 | 373篇 |
1988年 | 241篇 |
1987年 | 160篇 |
1986年 | 121篇 |
1985年 | 129篇 |
1984年 | 144篇 |
1983年 | 67篇 |
1982年 | 103篇 |
1981年 | 68篇 |
1980年 | 70篇 |
1979年 | 60篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1959年 | 19篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
Common sense sometimes predicts events to be likely or unlikely rather than merely possible. We extend methods of qualitative reasoning to predict the relative likelihoods of possible qualitative behaviors by viewing the dynamics of a system as a Markov chain over its transition graph. This involves adding qualitative or quantitative estimates of transition probabilities to each of the transitions and applying the standard theory of Markov chains to distinguish persistent states from transient states and to calculate recurrence times, settling times, and probabilities for ending up in each state. Much of the analysis depends solely on qualitative estimates of transition probabilities, which follow directly from theoretical considerations and which lead to qualitative predictions about entire classes of systems. Quantitative estimates for specific systems are derived empirically and lead to qualitative and quantitative conclusions, most of which are insensitive to small perturbations in the estimated transition probabilities. The algorithms are straightforward and efficient. 相似文献
73.
74.
R. LUNDÉN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(10):905-914
Propagation of small subsurface cracks subjected to shear under repeated rolling contact load is studied. An analytical crack model (Dugdale) with plastic strips at the two crack tips is employed. Compressive stresses promoting crack closure and friction between crack faces are considered. The triaxial stress state is used in the yield criterion. A damage criterion is suggested based on experimental LCF data. In a numerical study, critical crack lengths are found below which propagation of an existing crack should be effectively suppressed. 相似文献
75.
腐败是与政府行政权力相伴生的痼疾,既是一个历史现象又是一个国际现象。贪污腐败和寻租腐败是委托一代理模型中最典型的腐败方式,文章在此基础上对贪污腐败和寻租腐败进行成本一收益分析和市场均衡分析,并探讨治理行政权力腐败的有效途径。 相似文献
76.
B. P. PEHRSON J. D. LANDES 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):73-86
The purpose of this study is to examine the current standard fracture toughness test procedure to determine if there could be an easier method to get a JIc value from the test record. The current method for determining JIc involves a detailed computational and construction procedure. The objective in this study is to simplify the analysis for the determination of JIc. The results of this study show that the load and displacement record for a fracture toughness test can be used to directly estimate a JQ value, a provisional value for fracture toughness, JIc. The J value taken at the maximum load point can be used along with an adjustment factor to estimate a JQ value. This JQ estimate is close to the one obtained from the construction procedure of ASTM Standard E 1820. When a unit‐sized specimen is tested, that is, a specimen with a width of 50 mm and a thickness of 25 mm the maximum load point provides a direct estimate of JQ. Other sizes require a size adjustment factor, which is simply a square root relationship between the width of the test specimen and a unit width. The proposed new method of estimating JQ is simple in concept and requires a minimum number of calculations. It appears to produce values of JQ which are comparable to those obtained from the ASTM E1820 construction procedure and may produce less scatter. 相似文献
77.
Comments on the original article "A New Big Five: Fundamental Principles for an Integrative Science of Personality," by Dan P. McAdams and Jennifer L. Pals (see record 2006-03947-002). McAdams and Pals (April 2006) presented a new model to integrate the field of personality psychology. Cultural and evolutionary factors interact with an individual's basic traits, characteristic adaptations, and life narratives, which in turn are linked to roles, demands, and behaviors. The current authors welcome McAdams and Pals's (2006) model for providing a way to integrate much of the previously disparate empirical findings in personality psychology. However, the current authors also think that McAdams and Pals (2006) overstated the inclusiveness of the model, and more generally, the current authors dispute their assertion that the grand theories of personality can be integrated within a single model. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
This study tested a partial version of R. W. Lent, S. D. Brown, and G. Hackett's (1994) social-cognitive career theory model. Among 204 high school girls who attended science, math, and engineering (SME) career conferences, the authors used a 4-year longitudinal design to predict the choice of an SME college major and SME self-efficacy and outcome expectations in college. In addition, among students who had declared SME majors, variables assessed in high school and college were used to predict aspirations to become leaders in SME fields. The results generally provided empirical validation of the model. Regression analyses revealed that college SME outcome expectations were associated with plans to become a leader in an SME field. Implications for research and interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
80.
反拍卖采购:一种新的采购模式 总被引:6,自引:0,他引:6
反拍卖采购技术以其新的理念和对信息技术的融合,能够使企业采购成本大幅度降低。通过对我国传统采购模式与反拍卖采购模式的对比分析,可以了解到反拍卖采购技术的应用前景。 相似文献