全文获取类型
收费全文 | 200910篇 |
免费 | 4845篇 |
国内免费 | 1904篇 |
专业分类
电工技术 | 4700篇 |
技术理论 | 5篇 |
综合类 | 1942篇 |
化学工业 | 31770篇 |
金属工艺 | 9199篇 |
机械仪表 | 6585篇 |
建筑科学 | 6319篇 |
矿业工程 | 1595篇 |
能源动力 | 5295篇 |
轻工业 | 18902篇 |
水利工程 | 2103篇 |
石油天然气 | 4442篇 |
武器工业 | 174篇 |
无线电 | 22836篇 |
一般工业技术 | 36100篇 |
冶金工业 | 34166篇 |
原子能技术 | 4516篇 |
自动化技术 | 17010篇 |
出版年
2022年 | 1408篇 |
2021年 | 2508篇 |
2020年 | 1787篇 |
2019年 | 2057篇 |
2018年 | 2980篇 |
2017年 | 2938篇 |
2016年 | 2971篇 |
2015年 | 2647篇 |
2014年 | 4055篇 |
2013年 | 9278篇 |
2012年 | 6239篇 |
2011年 | 7957篇 |
2010年 | 6478篇 |
2009年 | 7272篇 |
2008年 | 7173篇 |
2007年 | 7055篇 |
2006年 | 6207篇 |
2005年 | 5641篇 |
2004年 | 5209篇 |
2003年 | 5062篇 |
2002年 | 5264篇 |
2001年 | 5072篇 |
2000年 | 4582篇 |
1999年 | 4632篇 |
1998年 | 10717篇 |
1997年 | 7690篇 |
1996年 | 5931篇 |
1995年 | 4503篇 |
1994年 | 3788篇 |
1993年 | 3699篇 |
1992年 | 2699篇 |
1991年 | 2614篇 |
1990年 | 2486篇 |
1989年 | 2476篇 |
1988年 | 2410篇 |
1987年 | 2142篇 |
1986年 | 2086篇 |
1985年 | 2375篇 |
1984年 | 2190篇 |
1983年 | 2017篇 |
1982年 | 1861篇 |
1981年 | 1930篇 |
1980年 | 1783篇 |
1979年 | 1795篇 |
1978年 | 1754篇 |
1977年 | 2086篇 |
1976年 | 2660篇 |
1975年 | 1542篇 |
1974年 | 1535篇 |
1973年 | 1591篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The following modes of isotope exchange of azidothymidine (3'-azido-3'-deoxythymidine) with tritium were studied: solid- and liquid-phase isotope exchange with gaseous tritium and isotope exchange in solution with tritium water. Catalytic reactions of azidothymidine with gaseous tritium in solution result in virtually complete reduction of the azido group to amino group. This reduction also occurs in the course of solid-phase catalytic hydrogenation; the yield of 3'-amino-3'-deoxythymidine ranges from 20 to 70%. The molar radioactivity of tritium-labeled azidothymidine prepared by solid-phase catalytic isotope exchange with gaseous tritium and by isotope exchange in solution with tritium water does not exceed 0.5 Ci mmol-
1. 相似文献
992.
利用范氏力将单壁碳纳米管样品组装到钨针尖上 ,用FEM/FIM对同一碳纳米管样品用热处理方法和场脱附方法进行了研究。场离子显微镜是具有原子级分辨能力的尖端表面分析工具 ,由场离子像推测这次组装的样品是由三根单壁碳纳米管突起组成的碳纳米管束。清洁碳纳米管束样品的场发射像和场离子像有极好的对应关系。场脱附后的碳纳米管束的场发射特性较好地符合Fowler Nordheim场发射模型。通过比较碳纳米管束吸附态和热处理后以及场脱附后的Fowler Nordheim曲线的斜率变化 ,得出碳纳米管束样品逸出功的变化 ,再结合场发射像的变化推断出场脱附与热处理结合是一种较理想的获得清洁碳纳米管表面的方法 相似文献
993.
Richard F. D.; Bond Charles F. Jr.; Stokes-Zoota Juli J. 《Canadian Metallurgical Quarterly》2003,7(4):331
This article compiles results from a century of social psychological research, more than 25,000 studies of 8 million people. A large number of social psychological conclusions are listed alongside meta-analytic information about the magnitude and variability of the corresponding effects. References to 322 meta-analyses of social psychological phenomena are presented, as well as statistical effect-size summaries. Analyses reveal that social psychological effects typically yield a value of r equal to .21 and that, in the typical research literature, effects vary from study to study in ways that produce a standard deviation in r of .15. Uses, limitations, and implications of this large-scale compilation are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
对传统的钼酸铵溶液净化工艺及文献介绍工艺进行了较为详细的分析 ,并与实验数据对比分析 ,找到了较为合理的工艺方案 相似文献
995.
A new superfluid specific additive integral of motion is found. This facilitates investigation of the general thermodynamic equilibrium conditions of a superfluid. The analysis is performed in an extended space of thermodynamic variables containing (along with the usual thermodynamic coordinates such as pressure and temperature) superfluid velocity and momentum density. The equilibrium stability conditions lead to thermodynamic inequalities which replace the Landau superfluidity criterion at finite temperatures. 相似文献
996.
K. Lefmann B. Lake G. Aeppli S.-W. Cheong N. B. Christensen K. N. Clausen S. Hayden T. E. Mason D.F. McMorrow H. A. Mook H. M. Rønnow H. Takagi 《Journal of Low Temperature Physics》2004,135(5-6):621-664
One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La2?xSrxCuO4, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx. 相似文献
997.
Shackelford Todd K.; Goetz Aaron T.; McKibbin William F.; Starratt Valerie G. 《Canadian Metallurgical Quarterly》2007,121(2):214
Sperm competition occurs when the sperm of multiple males concurrently occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 237 men in committed, sexual relationships. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) greater sexual interest in his partner, (b) greater distress in response to his partner's sexual rejection, and (c) greater sexual persistence in response to his partner's sexual rejection. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses limitations of the current research and situates the current results within the broader comparative literature on adaptation to sperm competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
以构造层序、层序地层分析和基准面分析原理为手段,利用高分辨率地震剖面、测井、岩相等资料,重点研究了东营凹陷胜北断裂带深断陷型湖盆层序中的低位体系域砂体沉积特征、发育规律及其石油地质意义.研究表明,沙三期胜北断裂带的活动形成了断裂坡折带,该坡折带控制沙三段层序低位体系域冲积扇、扇三角洲、浊积扇和小型三角洲等砂体的发育及时空展布.断裂坡折带控制的低位体系域砂体位于层序底部、最大湖泛面之下,成藏条件优良,是隐蔽油气藏勘探的主要方向. 相似文献
999.
The behavior of hydrogen in solids under the action of intense ionizing radiation is of importance in solving numerous problems of materials science for the nuclear and thermonuclear power industry, spacecraft engineering, hydrogen energetics, and microelectronics. Experimental results are presented that provide evidence of the radiation-induced yield of hydrogen from single crystal silicon bombarded with 710-MeV bismuth ions. 相似文献
1000.
S. Danto P. Houizot C. Boussard‐Pledel X.‐H. Zhang F. Smektala J. Lucas 《Advanced functional materials》2006,16(14):1847-1852
Conditions of formation of bulk tellurium chalcogenide glasses, containing 70–80 at % Te associated to Ga and Ge are described. The characteristic temperatures are measured: the glass‐transition temperature, Tg, is situated in the range 140–185 °C and the difference Tx – Tg, where Tx is the onset crystallization temperature, is in the range 76–113 °C. Moreover, the optical transmission window is exceptional, ranging from 1.99 μm in the bandgap up to 28 μm in the phonon region. Developed within the framework of requirements for the Darwin mission (a search for and study of extrasolar planets), feasibility of infrared optical fibers formed from these glasses is studied. Drawing experiments are conducted with the glass Ga2‐Ge3Te15, which possesses the maximum Tx – Tg, and a first optical fiber is presented. 相似文献