全文获取类型
收费全文 | 191925篇 |
免费 | 3205篇 |
国内免费 | 728篇 |
专业分类
电工技术 | 3449篇 |
综合类 | 117篇 |
化学工业 | 31519篇 |
金属工艺 | 8058篇 |
机械仪表 | 5401篇 |
建筑科学 | 4993篇 |
矿业工程 | 907篇 |
能源动力 | 5159篇 |
轻工业 | 18709篇 |
水利工程 | 1828篇 |
石油天然气 | 3166篇 |
武器工业 | 2篇 |
无线电 | 20656篇 |
一般工业技术 | 35789篇 |
冶金工业 | 35346篇 |
原子能技术 | 4365篇 |
自动化技术 | 16394篇 |
出版年
2021年 | 1857篇 |
2019年 | 1613篇 |
2018年 | 2693篇 |
2017年 | 2639篇 |
2016年 | 2776篇 |
2015年 | 1976篇 |
2014年 | 3303篇 |
2013年 | 8792篇 |
2012年 | 5478篇 |
2011年 | 7446篇 |
2010年 | 5786篇 |
2009年 | 6589篇 |
2008年 | 6582篇 |
2007年 | 6455篇 |
2006年 | 5538篇 |
2005年 | 5138篇 |
2004年 | 4826篇 |
2003年 | 4474篇 |
2002年 | 4388篇 |
2001年 | 4322篇 |
2000年 | 4131篇 |
1999年 | 4249篇 |
1998年 | 11168篇 |
1997年 | 7875篇 |
1996年 | 5985篇 |
1995年 | 4484篇 |
1994年 | 3789篇 |
1993年 | 3736篇 |
1992年 | 2672篇 |
1991年 | 2614篇 |
1990年 | 2476篇 |
1989年 | 2496篇 |
1988年 | 2429篇 |
1987年 | 2177篇 |
1986年 | 2107篇 |
1985年 | 2424篇 |
1984年 | 2229篇 |
1983年 | 2054篇 |
1982年 | 1932篇 |
1981年 | 2001篇 |
1980年 | 1843篇 |
1979年 | 1841篇 |
1978年 | 1806篇 |
1977年 | 2164篇 |
1976年 | 2766篇 |
1975年 | 1578篇 |
1974年 | 1562篇 |
1973年 | 1631篇 |
1972年 | 1362篇 |
1971年 | 1275篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
951.
G. C. Coelho J. A. Golczewski H. F. Fischmeister 《Metallurgical and Materials Transactions A》2003,34(9):1749-1758
Thermodynamical equilibria have been calculated for a wide variety of high-speed steel compositions belonging to the multicomponent
system Fe-C-W-Mo-V-Cr-Nb as well as for two series of white-cast-iron alloys containing niobium. Some temperature-concentration
diagrams for both classes of alloys are presented and calculated quantities (melting and transformation temperatures, amounts
and compositions of phases) are compared with experimental data. Good agreement between calculated and experimental information
has been obtained, with the exception of the MC phase compositions and transformation temperatures for white-cast-iron alloys
with high carbon and chromium contents. These differences can, however, be satisfactorily explained by plausible kinetic effects. 相似文献
952.
The effect of a gas dissolved in a liquid on the variation of the refractive index of the compressed mixture was studied.
The compression process was monitored with the aid of a holographic interferometer. The sensitivity of this method allows
the compressibility of water and the solubility of helium and nitrogen to be studied at pressures below 4 atm. A procedure
for obtaining qualitative and quantitative data on the solubility of gases in liquids is proposed. 相似文献
953.
X. X. Xi X. H. Zeng A. V. Pogrebnyakov A. Soukiassian S. Y. Xu Y. F. Hu E. Wertz Q. Li Y. Zhong C. O. Brubaker Z.-K. Liu E. M. Lysczek J. M. Redwing J. Lettieri D. G. Schlom W. Tian H. P. Sun X. Q. Pan 《Journal of Superconductivity and Novel Magnetism》2003,16(5):801-806
The recently discovered superconductor MgB2 with T c at 39 K has great potential in superconducting electronics. In this paper, we review the deposition techniques used for MgB2 thin films in the light of a thermodynamic study of the Mg-B system with the calculation of phase diagrams (CALPHAD) modeling technique. This thermodynamic study identifies a growth window in the pressure–temperature phase diagram, in which the magnesium pressure is very high for likely in situ growth temperatures. A Hybrid Physical–Chemical Vapor Deposition (HPCVD) technique that successfully achieves such a high Mg pressure is shown to produce in situ epitaxial MgB2 thin films with bulk superconducting properties. 相似文献
954.
Koenen Karestan C.; Stellman Jeanne Mager; Stellman Steven D.; Sommer John F. Jr. 《Canadian Metallurgical Quarterly》2003,71(6):980
Risk factors affecting the course of posttraumatic stress disorder (PTSD) are poorly understood. As part of a larger study on characterizing exposure to herbicides in Vietnam, the authors investigated this issue in a random sample of 1,377 American Legionnaires who had served in Southeast Asia during the Vietnam War and were followed over a 14-year period. High combat exposure, perceived negative community attitudes at homecoming, minority race, depression symptoms at Time 1, and more anger at Time 1 predicted a more chronic course. Community involvement at Time 1 was protective and associated with decreased risk at Time 2. Discomfort in disclosing Vietnam experiences was associated with an increased risk for developing PTSD but did not predict its course. Combat exposure predicted PTSD course more strongly than any other risk factor. Findings suggest recovery from PTSD is significantly influenced by perceived social support. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
955.
F Wimmer J Lanschützer H Resch A Andretsch H Lempradl H Thöne K Mörwald J Kieweg H P Narzt CFürst 《钢铁》2004,39(Z1):590-592
1前言及历史背景
为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析. 相似文献
956.
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
957.
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
958.
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
959.
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
960.
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