全文获取类型
收费全文 | 9418篇 |
免费 | 640篇 |
国内免费 | 331篇 |
专业分类
电工技术 | 390篇 |
综合类 | 412篇 |
化学工业 | 1686篇 |
金属工艺 | 450篇 |
机械仪表 | 439篇 |
建筑科学 | 627篇 |
矿业工程 | 172篇 |
能源动力 | 309篇 |
轻工业 | 589篇 |
水利工程 | 119篇 |
石油天然气 | 288篇 |
武器工业 | 37篇 |
无线电 | 1506篇 |
一般工业技术 | 1322篇 |
冶金工业 | 730篇 |
原子能技术 | 90篇 |
自动化技术 | 1223篇 |
出版年
2024年 | 24篇 |
2023年 | 126篇 |
2022年 | 232篇 |
2021年 | 321篇 |
2020年 | 201篇 |
2019年 | 202篇 |
2018年 | 259篇 |
2017年 | 266篇 |
2016年 | 269篇 |
2015年 | 263篇 |
2014年 | 395篇 |
2013年 | 568篇 |
2012年 | 523篇 |
2011年 | 650篇 |
2010年 | 565篇 |
2009年 | 540篇 |
2008年 | 587篇 |
2007年 | 473篇 |
2006年 | 475篇 |
2005年 | 356篇 |
2004年 | 315篇 |
2003年 | 309篇 |
2002年 | 276篇 |
2001年 | 229篇 |
2000年 | 217篇 |
1999年 | 228篇 |
1998年 | 290篇 |
1997年 | 218篇 |
1996年 | 210篇 |
1995年 | 157篇 |
1994年 | 132篇 |
1993年 | 98篇 |
1992年 | 64篇 |
1991年 | 52篇 |
1990年 | 42篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A Saccharomyces cerevisiae sequence cloned by serendipity was found to encode a protein that is a new member of the Ypt/Rab monomeric G-protein family. This sequence shows high homology to the yeast genes SEC4 and YPT1 and, like SEC4 and YPT1, is essential for viability. The sequence was localized to chromosome V based upon hybridization to pulse-field gel-separated yeast chromosomes. The sequence has been deposited in the GenBank data library under Accession Number L17070. 相似文献
32.
33.
An analytical expression for both band-to-band and band-trap-band indirect tunnelings is used to study the gate-induced drain leakage (GIDL) current of MOSFETs measured before and after hot-carrier stress. The voltage and temperature dependence of GIDL are characterized. Both results show that interface traps situated near the midgap participate in the conduction of GIDL, and band-trap-band indirect tunneling could be the major mechanism. This is further supported by the fact that the percentage increase in GIDL induced by hot-carrier stress is about the same as the corresponding increase in interface-trap density. On the other hand, under low-field conditions, trap-assisted Poole–Frenkle emission dominates over tunneling for temperatures even well below room temperature. 相似文献
34.
Tests of univariate and bivariate stochastic ageing 总被引:1,自引:0,他引:1
Concepts of ageing describe how a population of units or systems improves or deteriorates with age. Many classes of life distributions are categorized and defined in the literature according to their ageing properties. An important aspect of such classifications is that the exponential distribution is nearly always a member of each class. The notion of stochastic ageing is important in any reliability analysis, and many test statistics have been developed for testing exponentiality against various ageing alternatives. This paper is an overview of these developments. The author begins with a table of ageing classes together with key references, followed by a brief discussion on the characterization of exponentiality. Test procedures are summarized, and followed by the main review. Tests of exponentiality against other alternatives are explained for randomly censored data. Finally, tests of multivariate ageing properties are listed. Some of the life classes have been derived more recently and, as far as is known, no test statistics have been proposed. On the other hand, several tests are available for some classes. Relative efficiency of a test is discussed whenever appropriate 相似文献
35.
36.
Negative resistance field-effect transistor (NERFET) devices using either strained InGaAs or unstrained GaAs channel layers have been fabricated. The strained InGaAs channel NERFET's show strong negative differential resistance and large drain current peak-to-valley ratio. The peak-to-valley ratio of the InGaAs channel NERFET is more than 3000 at room temperature and larger than one million (106) at 77 K. The peak-to-valley ratio is controllable by adjusting the collector voltage 相似文献
37.
大规模高含硫原油的炼制工艺必须配套设置脱硫和硫磺回收装置。笔者针对硫磺回收装置的特点,为确保装置的安全平稳运行,提出了该装置自动控制设计中需要严格监控的工艺参数及重点部位,叙述了仪表选型原则和精确测量与控制的原理和方法。 相似文献
38.
39.
40.
The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献