全文获取类型
收费全文 | 38362篇 |
免费 | 3167篇 |
国内免费 | 3144篇 |
学科分类
工业技术 | 44673篇 |
出版年
2024年 | 90篇 |
2023年 | 590篇 |
2022年 | 417篇 |
2021年 | 731篇 |
2020年 | 1018篇 |
2019年 | 1089篇 |
2018年 | 1013篇 |
2017年 | 1369篇 |
2016年 | 1476篇 |
2015年 | 1328篇 |
2014年 | 2271篇 |
2013年 | 3497篇 |
2012年 | 1834篇 |
2011年 | 2356篇 |
2010年 | 1693篇 |
2009年 | 2223篇 |
2008年 | 2206篇 |
2007年 | 2191篇 |
2006年 | 1928篇 |
2005年 | 1728篇 |
2004年 | 1447篇 |
2003年 | 1376篇 |
2002年 | 1254篇 |
2001年 | 989篇 |
2000年 | 994篇 |
1999年 | 907篇 |
1998年 | 807篇 |
1997年 | 729篇 |
1996年 | 658篇 |
1995年 | 563篇 |
1994年 | 514篇 |
1993年 | 494篇 |
1992年 | 372篇 |
1991年 | 362篇 |
1990年 | 283篇 |
1989年 | 222篇 |
1988年 | 190篇 |
1987年 | 168篇 |
1986年 | 139篇 |
1985年 | 183篇 |
1984年 | 188篇 |
1983年 | 169篇 |
1982年 | 148篇 |
1981年 | 97篇 |
1980年 | 72篇 |
1979年 | 85篇 |
1978年 | 61篇 |
1977年 | 67篇 |
1976年 | 19篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
41.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
42.
This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests. 相似文献
43.
MAX1773/MAX1773A是用于双电池系统的电源选择器,它允许外部控制器去管理双电池组、适配器输入、电池充电器和系统负载所需的电源连接。文中介绍了MAX1773/1773A的特点、引脚功能、内部结构和工作原理,给出了MAX1773/MAX1773A的典型工作电路。 相似文献
44.
Many media processing applications create a load that varies significantly over time. Hence, if such an application is assigned a lower processing-time budget than needed in its worst-case load situation, deadline misses are likely to occur. This problem can be dealt with by designing media processing applications in a scalable fashion. A scalable media processing application can run in multiple qualities, leading to correspondingly different resource demands. The problem we consider is to find an accompanying quality control strategy, which minimizes both the number of deadline misses and the number of quality changes, while maximizing the quality of processing. We present an initial approach to the above problem by modeling it as a Markov decision process (MDP). Our model is based on measuring relative progress at milestones. Solving the MDP results in a quality control strategy that can be applied during runtime with only little overhead. We evaluate our approach by means of a practical example, which concerns a scalable MPEG-2 decoder. 相似文献
45.
46.
47.
48.
Accidents in different complex sociotechnical systems are rarely compared using the same theoretical framework for risk management. We conducted a comparative analysis of two Canadian public health disasters involving drinking water distribution systems, the North Battleford Cryptosporidium parvum outbreak in April 2001 and the Walkerton E. coli outbreak in May 2000. Both accidents resulted from a complex interaction between all levels of a complex sociotechnical system. However, the low-level physical and individual factors differed in the two cases, whereas, the high-level governmental and regulatory factors tended to be the same. These findings may have implications for the design of public policies to minimize risk in complex sociotechnical systems. 相似文献
49.
Despite the universal and understandable distress associated with the death of a child from pediatric illness, do psychologists help surviving families in ways that match their need for assistance? Many families do not seek psychological help and cope adaptively with their loss. Indications for psychotherapy with bereaved families are based largely on experience with families who engage in treatment and who have greater distress. Other families may not receive sufficient services but are at risk for ongoing difficulties and unlikely to engage in treatment. Suggestions for intervention are made, with attention to the fit of therapeutic approaches with family needs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.
Rossato Janine I.; Bonini Juliana S.; Coitinho Adriana S.; Vianna Monica R. M.; Medina Jorge H.; Cammarota Martín; Izquierdo Iván 《Canadian Metallurgical Quarterly》2004,118(3):563
The gamma aminobutyric acid-A (GABAA) agonist, muscimol, the glutamate N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonopentanoic acid (AP5), and the inhibitor of the extracellularly regulated kinases (ERKs), UO 126, cause retrograde amnesia when administered to the hippocampus. In the present study, the authors found that they all cause retrograde amnesia for 1-trial inhibitory avoidance, not only when infused into the dorsal CA1 region of the hippocampus, but also when infused into the basolateral amygdala or the entorhinal, parietal, and posterior cingulate cortices. The posttraining time course of the effect of each drug was, however, quite different across brain structures. Thus, in all of them, NMDA receptors and the ERK pathway are indispensable for memory consolidation, and GABAA receptor activation inhibits memory consolidation: but in each case, their influence is interwoven differently. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献