全文获取类型
收费全文 | 12478篇 |
免费 | 975篇 |
国内免费 | 691篇 |
专业分类
电工技术 | 253篇 |
综合类 | 753篇 |
化学工业 | 1652篇 |
金属工艺 | 250篇 |
机械仪表 | 143篇 |
建筑科学 | 1767篇 |
矿业工程 | 929篇 |
能源动力 | 389篇 |
轻工业 | 956篇 |
水利工程 | 581篇 |
石油天然气 | 3608篇 |
武器工业 | 15篇 |
无线电 | 151篇 |
一般工业技术 | 823篇 |
冶金工业 | 861篇 |
原子能技术 | 144篇 |
自动化技术 | 869篇 |
出版年
2024年 | 37篇 |
2023年 | 129篇 |
2022年 | 284篇 |
2021年 | 387篇 |
2020年 | 376篇 |
2019年 | 313篇 |
2018年 | 309篇 |
2017年 | 406篇 |
2016年 | 446篇 |
2015年 | 417篇 |
2014年 | 651篇 |
2013年 | 823篇 |
2012年 | 794篇 |
2011年 | 1014篇 |
2010年 | 719篇 |
2009年 | 775篇 |
2008年 | 678篇 |
2007年 | 801篇 |
2006年 | 845篇 |
2005年 | 698篇 |
2004年 | 582篇 |
2003年 | 516篇 |
2002年 | 378篇 |
2001年 | 324篇 |
2000年 | 258篇 |
1999年 | 199篇 |
1998年 | 188篇 |
1997年 | 146篇 |
1996年 | 124篇 |
1995年 | 101篇 |
1994年 | 99篇 |
1993年 | 70篇 |
1992年 | 51篇 |
1991年 | 55篇 |
1990年 | 35篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 33篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
全国土壤中天然放射性核素含量调查研究(1983—1990年) 总被引:19,自引:5,他引:14
The Writing Group for the Summary Report on Nationwide Survey of Environmental Radioactivity Level in China 《辐射防护》1992,12(2):122-142
中国土壤中天然放射性核素含量调查(1983—1990年)是中国环境天然放射性水平调查研究的一部分。本文作为分报告之一,系根据全国29个省、市、自治区(不包括台湾省,海南省包括在广东省内)的调查结果整理编写而成,主要报告这项调查的方法和结果。本调查在全国按均匀网格布点,并区分不同成土母岩母质、土壤类型进行加密布点,在天然γ辐射剂量率局部异常地区以及部分核企业和放射性伴生矿等对环境可能产生放射性污染的地区,也作了加密布点。本调查布点区域复盖面积约占全国总面积的80%。采样点基本与陆地γ辐射剂量率测点同位布设,土壤采样与陆地γ辐射剂量率测量同步进行。全国共采集土壤样品13866份;分析测量了11216份,其中网格点样品9114个,加密点样品2102个。本报告主要结果由7777个25×25和50×50 km 的基本网格点分析数据统计得到。本调查主要结果如下:(1)全国土壤中天然放射性核素~(238)U、~(226)Ra、~(232)Th、~(40)K 含量按面积加权平均值(±单次测量标准差)分别为39.5(±34.4)、36.5(±22.0)、49.1(±27.6)、580.0(±202.0)Bq·kg~(-1),范围值分别为1.8—520.0、2.4—425.8、1.0—437.8、11.5—2185.2 Bq·kg~(-1)。(2)土壤中天然放射性核素含量与成土母岩母质类型明显相关。由1552个不同成土母岩 相似文献
82.
83.
Geotechnical characterization of potential lunar sites will be a critical part of the planning and design process. The strategies used to conduct a geotechnical investigation will be dictated by the specific needs of the lunar base, the unique environment of the lunar surface, and general character of the lunar soils and rocks. This paper outlines some of the types of geotechnical information that will be important and identifies some of the more promising strategies which might be used to obtain such information in the lunar environment. Some of the most important geotechnical information for planning and site development will be related to construction in the lunar soil. In addition to construction concerns, geotechnical data for foundation design (or verification of predesigned foundations) will be needed. The geotechnical site‐characterization work should include geophysical techniques, supplemented by conventional mechanical boring and testing only to the degree necessary to correlate geophysical measurements with conventional soil properties and to investigate anomalies. Equipment used for geotechnical site characterization will also serve for mineralogical exploration. Several techniques for geotechnical investigation that may provide very useful information in an expedient manner are described. Geophysical methods include seismic and electromagnetic methods, including seismic surveys that utilize surface waves. Electromagnetic methods such as ground‐penetrating radar are fast, efficient methods for mapping the subsurface, although these techniques do not measure soil characteristics that can readily be correlated with engineering properties. Seismic methods provide information that may correlate with soil strength, compressibility, and excavatability. In‐situ physical testing will likely include penetration testing for direct physical measurement of lunar soil behavior. 相似文献
84.
川中磨溪气田是一个含边水、低渗、含硫的视孔隙性的整装气田,强腐蚀性一直以来制约着天然气的生产;而油藏具有特低孔渗、裂缝性和强烈非均质性,一般采用衰竭式开采,压力降低较快,采出难度增加,采用挤凝析油解堵、小泵深抽、玻璃钢油管防腐、渗吸注水二次采油、化学清防蜡等一系列配套的新工艺、新技术和工具后,较大地提高了原油采收率,增产效果显著. 相似文献
85.
克拉2气田储层岩石的应力敏感性及其对生产动态的影响 总被引:9,自引:2,他引:7
克拉2气田是一个异常高压气藏,压力系数在2.0以上。在衰竭式开采条件下,其地层压力降幅可为普通气藏地层压力降幅的3倍以上,因此研究储层岩石应力敏感性及其对生产动态的影响意义重大。研究得出,岩石的应力敏感性特征主要有:岩石物性对应力的敏感性总体上不大,其中以孔隙度最小,渗透率次之,压缩系数最大;岩石物性随地层压力的下降而下降;在同一地层压降下.岩石物性下降幅度不是渗透率的连续函数,而是与渗透率分布范围有关,高渗透率范围,岩石物性下降幅度小,低渗透率范围,岩石物性下降幅度大。研究得出,克拉2气田岩石的应力敏感性对其生产动态的影响较小。 相似文献
86.
渗透率是反映储层渗流能力的重要参数,目前对于单一储层的渗透率表征方法,通常是在岩心分析渗透率或测井解释渗透率的基础上进行厚度加权算术平均。这种方法对于均质的储层来说是适用的,但对于非均质严重的储层,不能准确反映该储层的实际渗流能力。本文提出一种应用可动流体体积权衡表征渗透率的方法,经实际资料验证,能较好地反映储层的实际渗透能力。 相似文献
87.
L. Rutigliano D. Fino G. Saracco V. Specchia P. Spinelli 《Journal of Applied Electrochemistry》2008,38(7):1035-1041
This paper describes the results obtained from an electrokinetic treatment of a real soil polluted by lead acetate. Powdered
soil samples were pressed with a consolidometer till 100 kPa to obtain cylindrical specimens with the same characteristics
as a subsoil. Tests were carried out in a Perspex electrochemical cell where soil specimens were introduced with a hollow
punch. A low intensity direct current was applied in order to remove contaminants, due to electrophoresis and electroosmosis
phenomena. The water flow, conductivity, apparent electroosmotic coefficient, as well as other characteristic parameters,
were measured throughout the test. The water content and degree of pore saturation were estimated at the beginning and end
of the test. The soil slab was divided into four slices and the Pb concentration profile determined. The main factor governing
the extraction of contaminant was found to be the pH in the acidic range. Indeed, under these conditions high removal efficiencies
could be reached. These results could lead to the design of a new electrochemical treatment cell equipped with a cationic
membrane to expand the region of favourable pH within the soil. 相似文献
88.
A. Mounir EL Sayed A. Yamauchi N. A. Darwish A. A. Abd EL‐Mageed S. F. Halim 《应用聚合物科学杂志》2008,109(5):2988-2993
The charged mosaic polymer membrane (CMM) without reinforcement and the composite charged mosaic polymer membrane (CCMM) with reinforcement were investigated in terms of salt and water transport (permeability). The composite charged mosaic polymer membrane (CCMM) with reinforcement showed a unique transport behavior such as preferential material transport Lp and ω. Water permeability coefficient, Lp and salt permeability coefficient, ω were estimated by taking account of active layer thickness of composite polymer gel. The Lp and ω values of CCMM with reinforcement were larger than those of CMM without reinforcement. On the other hand, the reflection coefficient of CCMM, σ, showed negative value, which suggested preferential material transport to solvent transport. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
89.
This paper presents the results of an experimental investigation undertaken to evaluate different purging solutions to enhance the removal of multiple heavy metals, particularly chromium, nickel, and cadmium, from a low buffering clay, specifically kaolin, during electrokinetic remediation. Experiments were conducted on kaolin spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, which simulate typical electroplating waste contamination. A total of five different tests were performed to investigate the effect of different electrode purging solutions on the electrokinetic remedial efficiency. A constant DC voltage gradient of 1 V/cm was applied for all the tests. The removal of heavy metals from the soil using tap water as the purging solution was very low. When 1 M acetic acid was used as the purging solution in the cathode, the removal of chromium, nickel, and cadmium was increased to 20, 19, and 13%, respectively. Using 0.1 M ethylene diamine tetraacetic acid as the purging solution in the cathode, 83% of the initial Cr was removed; however, the nickel and cadmium removal was very low. A sequentially enhanced electrokinetic remediation approach involving the use of water as a purging solution at both the anode and cathode initially, followed by the use of acetic acid as the cathode purging solution and a NaOH alkaline solution as the anode purging solution was tested. This sequential approach resulted in a maximum removal of chromium, nickel, and cadmium of 68–71, 71–73, and 87–94%, respectively. This study shows that the sequential use of appropriate electrode purging solutions, rather than a single electrode purging solution, is necessary to remediate multiple heavy metals in soils using electrokinetics. 相似文献
90.
B. S. Seplyarskii S. V. Kostin G. B. Brauer 《International Journal of Self-Propagating High-Temperature Synthesis》2008,17(2):121-124
Explored is the filtration combustion in Ti-(Ti + 0.5C) layered powder systems in a coflow of nitrogen gas. The presence/absence
of nitrogen coflow through the layered system was found to drastically affect the character of wave propagation and structure/properties
of product. The obtained data can be regarded as a basis for fabrication of new layered and composite materials in the mode
of dynamic filtration combustion.
相似文献