全文获取类型
收费全文 | 2700篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 15篇 |
综合类 | 1篇 |
化学工业 | 244篇 |
金属工艺 | 42篇 |
机械仪表 | 36篇 |
建筑科学 | 43篇 |
能源动力 | 28篇 |
轻工业 | 92篇 |
水利工程 | 16篇 |
石油天然气 | 5篇 |
无线电 | 112篇 |
一般工业技术 | 155篇 |
冶金工业 | 1821篇 |
原子能技术 | 11篇 |
自动化技术 | 113篇 |
出版年
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 29篇 |
2013年 | 71篇 |
2012年 | 35篇 |
2011年 | 59篇 |
2010年 | 55篇 |
2009年 | 38篇 |
2008年 | 40篇 |
2007年 | 49篇 |
2006年 | 38篇 |
2005年 | 39篇 |
2004年 | 24篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 71篇 |
1998年 | 534篇 |
1997年 | 320篇 |
1996年 | 193篇 |
1995年 | 106篇 |
1994年 | 114篇 |
1993年 | 119篇 |
1992年 | 20篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 35篇 |
1988年 | 24篇 |
1987年 | 44篇 |
1986年 | 37篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 30篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 54篇 |
1976年 | 100篇 |
1975年 | 15篇 |
1974年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有2734条查询结果,搜索用时 0 毫秒
21.
Flory's equation-of-state theory has been used to predict the lower critical solution temperature behaviour of polymer—polymer mixtures. The spinodal phase boundary of numbers of high molecular weight polymer mixtures have been previously simulated using this theory. In this paper a procedure for simultaneous predictions of the binodal and the spinodal curves by equating the chemical potential of each component in the mixture is presented. The method is tested for five different mixtures. The effects of the binary and pure component state parameters on the simulated curves are discussed and the simulated phase diagrams are compared with the experimental cloud point curves. It is found that in most cases the results are more consistent with the cloud point curve being closer to the spinodal curve than the binodal. 相似文献
22.
F. D. McDaniel B. L. Doyle C. H. Seager D. S. Walsh G. Vizkelethy D. K. Brice C. Yang P. Rossi M. Nigam M. El Bouanani G. V. Ravi Prasad J. C. Schwartz L. T. Mitchell J. L. Duggan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):1-10
A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino. 相似文献
23.
24.
Using ion exchange chromatography and an ATP-dependent actin precipitation step, we have isolated three myosin-I isozymes that, together, account for most of the K+EDTA-ATPase activity recovered from extracts of Dictyostelium. The two major myosin-I isozymes, present in approximately equal amounts, had apparent molecular masses of 125 kDa on SDS gels and have been identified by amino acid sequence analysis as the products of the Dictyostelium myosin-IB (DMIB) and myosin-ID (DMID) genes. DMIB, with a specific K+EDTA-ATPase activity 10-fold higher than DMID, was responsible for most of the activity in cell extracts. The third isozyme, present in low amounts, had an apparent molecular mass of 137 kDa on SDS gels and is too large to be the product of any of the known myosin-I genes. DMIB eluted from DE53 cellulose columns as two distinct peaks (II and III). Addition of the phosphatase inhibitor okadaic acid to the extraction buffer increased the fraction of DMIB recovered from growth phase cells in peak III from 35 to 70%. DMIB isolated from peak III, but not from peak II, displayed a significant level of actin-activated MgATPase activity. These results indicate that peak III represents a phosphorylated, actin-activatable form of DMIB. 相似文献
25.
AIMS: This study was designed to assess the efficacy of low dose methotrexate, 15 mg weekly, as a steroid-sparing agent in asthmatic patients requiring long-term oral prednisone treatment. METHODS: The study was a randomised, double blind, placebo controlled, cross over study of 48 weeks duration. Eleven patients with severe steroid-dependent asthma were included. A successful outcome was defined as a reduction in mean prednisone requirements of 7 mg daily compared to baseline requirements, during active treatment. RESULTS: Two patients were required to be withdrawn owing to methotrexate-related adverse effects. The mean prednisone dose for patients who completed the study was 14.4 mg per day (95% CI; 13.6, 15.1) during active treatment, and 12.9 mg per day (95% CI: 12.2, 13.6) during placebo treatment (NS). Only one patient reduced his individual dose requirements by more than 7 mg per day, whereas in three patients prednisone requirements actually increased during active treatment. There were no significant differences in symptom scores, pulmonary function data, and exacerbations between active and placebo treatments. CONCLUSION: No significant steroid-sparing effect was obtained using low dose methotrexate in this study. This negative outcome may be attributable to the small population of patients studied, low baseline FEV1, and the omission of a steroid minimisation run-in period. Our results highlight the importance of careful patient selection and a painstaking approach in the management of patients with steroid-dependent asthma. 相似文献
26.
27.
28.
29.
30.
Burns G. Leonard; Gomez Rapson; Walsh James A.; de Moura Marcela Alves 《Canadian Metallurgical Quarterly》2003,15(1):118
G. J. DuPaul (see record 2003-02033-012) offered two suggestions for additional research to understand the strong source effects reported by R. Gomez, G. L Burns, J. A. Walsh, and M. A. de Moura (see record 2003-02033-001) in attention-deficit/ hyperactivity disorder (ADHD) rating scales. The first suggestion was to determine whether the source effects represent mostly bias or accuracy. The second suggestion was to minimize source effects through the development of better ADHD rating scales. Because source effects can represent bias or accuracy, it is important to minimize the bias aspect through content validation procedures prior to attempts to determine whether source effects better reflect bias or accuracy. This comment offers various suggestions to reduce the bias in ADHD rating scales. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献