全文获取类型
收费全文 | 4852篇 |
免费 | 232篇 |
国内免费 | 128篇 |
专业分类
电工技术 | 176篇 |
综合类 | 844篇 |
化学工业 | 297篇 |
金属工艺 | 97篇 |
机械仪表 | 151篇 |
建筑科学 | 723篇 |
矿业工程 | 164篇 |
能源动力 | 68篇 |
轻工业 | 147篇 |
水利工程 | 428篇 |
石油天然气 | 209篇 |
武器工业 | 13篇 |
无线电 | 169篇 |
一般工业技术 | 121篇 |
冶金工业 | 948篇 |
原子能技术 | 10篇 |
自动化技术 | 647篇 |
出版年
2023年 | 24篇 |
2022年 | 66篇 |
2021年 | 114篇 |
2020年 | 95篇 |
2019年 | 70篇 |
2018年 | 52篇 |
2017年 | 98篇 |
2016年 | 119篇 |
2015年 | 111篇 |
2014年 | 286篇 |
2013年 | 196篇 |
2012年 | 310篇 |
2011年 | 362篇 |
2010年 | 304篇 |
2009年 | 312篇 |
2008年 | 304篇 |
2007年 | 357篇 |
2006年 | 286篇 |
2005年 | 282篇 |
2004年 | 278篇 |
2003年 | 260篇 |
2002年 | 193篇 |
2001年 | 143篇 |
2000年 | 97篇 |
1999年 | 69篇 |
1998年 | 40篇 |
1997年 | 37篇 |
1996年 | 18篇 |
1995年 | 19篇 |
1994年 | 25篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1990年 | 9篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1984年 | 8篇 |
1981年 | 8篇 |
1965年 | 8篇 |
1964年 | 11篇 |
1963年 | 9篇 |
1962年 | 9篇 |
1961年 | 10篇 |
1960年 | 9篇 |
1959年 | 8篇 |
1957年 | 13篇 |
1956年 | 13篇 |
1955年 | 15篇 |
1954年 | 8篇 |
排序方式: 共有5212条查询结果,搜索用时 0 毫秒
1.
通过对档案管理中存在的问题进行分析,提出了提高学籍档案管理效率的对策,以期能为中职学籍档案的管理工作提供有益的参考和借鉴。 相似文献
2.
As the development of cloud computing and the convenience of wireless sensor netowrks, smart devices are widely used in daily life, but the security issues of the smart devices have not been well resolved. In this paper, we present a new NTRU-type public-key cryptosystem over the binary field. Specifically, the security of our scheme relies on the computational intractability of an unbalanced sparse polynomial ratio problem (DUSPR). Through theoretical analysis, we prove the correctness of our proposed cryptosystem. Furthermore, we implement our scheme using the NTL library, and conduct a group of experiments to evaluate the capabilities and consuming time of encryption and decryption. Our experiments result demonstrates that the NTRU-type public-key cryptosystem over the binary field is relatively practical and effective. 相似文献
3.
Beebe-Frankenberger Margaret; Bocian Kathleen M.; MacMillan Donald L.; Gresham Frank M. 《Canadian Metallurgical Quarterly》2004,96(2):204
A cohort of 2nd-grade students provided comparisons of academic and social competence based on school retention/promotion decisions. Sample groups were (a) retained, (b) at risk for retention, (c) special education, and (d) promoted. Findings suggested most children with academic deficiencies are identified by schools early and are sorted into educational treatments differing in intensity that represent a continuum of competence. The authors provide empirical evidence counter to the assumptions that retained students have the requisite ability to catch up and have more problem behaviors than other low-achieving students. The relevance of high-stakes test scores for promotion/retention decisions and the parallels between schools' implementation of retention policy and implementation of regulations for identifying children with disabilities are included in the discussion. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
金瞰昆 《河北工程大学学报(自然科学版)》1993,(1)
对于碳酸盐岩中由生物及生物化学作用形成的具有同心或放射结构的异化颗粒(生物包粒),已为人们所熟悉,但目前还没有统一的分类与命名。本文在研究徐州大北望中下寒武统生物包粒特征的基础上,结合已有研究成果,对由生物及生物化学作用形成的具有同心或放射状内部结构的碳酸盐颗粒,按其粒度和形成颗粒的生物类型不同进行分类命名,提出分类命名的原则。 相似文献
5.
6.
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
7.
通过金相、硬度、耐磨性等测试分析表明,在“603”液体渗碳基础上研制出的新型中温低氰液体碳氮共渗剂对薄片件进行薄层碳氮共渗.能完全满足技术要求,并且取得了良好经济和社会效益. 相似文献
8.
9.
坨五站中间乳化层快速增长原因及治理方案 总被引:1,自引:0,他引:1
胜利采油厂坨五站高含水(95%)原油化学预脱水中,二级沉降罐内油水相之间的中间乳化层增长迅速,引起了一系列问题。现场调查和大量室内测试结果表明,产生这一现象的原因有:油溶性破乳剂WD-1加入点不合理。有2/3的含水原油在通过油水分离器之后才与破乳剂混合;二级沉降罐进油口伸入油相内,油流的冲击达不到中间层;WD-1对坨五站混合原油中的稠油破乳脱水性能欠佳,不能适应坨五站混合原油组成和含水的变化。针对上述各种原因筛选出了性能更好的一种破乳剂1916。根据确定的几种原因采取了相应的措施:将破乳剂加入点改在3个并联油水分离器之前;将二级沉降罐的进油口移到水相内;改用筛选出的破乳剂1916,结果使中间乳化层的增长受到了抑制。图2表4参2。 相似文献
10.
A motivational model of rural students' intentions to persist in, versus drop out of, high school. 总被引:1,自引:0,他引:1
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献