全文获取类型
收费全文 | 118205篇 |
免费 | 2412篇 |
国内免费 | 464篇 |
专业分类
电工技术 | 1108篇 |
综合类 | 2346篇 |
化学工业 | 18233篇 |
金属工艺 | 5426篇 |
机械仪表 | 3724篇 |
建筑科学 | 4069篇 |
矿业工程 | 671篇 |
能源动力 | 2137篇 |
轻工业 | 6421篇 |
水利工程 | 1678篇 |
石油天然气 | 457篇 |
武器工业 | 5篇 |
无线电 | 11578篇 |
一般工业技术 | 22147篇 |
冶金工业 | 9234篇 |
原子能技术 | 521篇 |
自动化技术 | 31326篇 |
出版年
2023年 | 201篇 |
2022年 | 308篇 |
2021年 | 681篇 |
2020年 | 464篇 |
2019年 | 622篇 |
2018年 | 15033篇 |
2017年 | 13882篇 |
2016年 | 10625篇 |
2015年 | 1345篇 |
2014年 | 1250篇 |
2013年 | 2544篇 |
2012年 | 4752篇 |
2011年 | 11303篇 |
2010年 | 9755篇 |
2009年 | 6998篇 |
2008年 | 8436篇 |
2007年 | 9371篇 |
2006年 | 1698篇 |
2005年 | 2605篇 |
2004年 | 2273篇 |
2003年 | 2263篇 |
2002年 | 1574篇 |
2001年 | 800篇 |
2000年 | 728篇 |
1999年 | 654篇 |
1998年 | 651篇 |
1997年 | 611篇 |
1996年 | 594篇 |
1995年 | 586篇 |
1994年 | 538篇 |
1993年 | 524篇 |
1992年 | 514篇 |
1991年 | 317篇 |
1990年 | 423篇 |
1989年 | 391篇 |
1988年 | 330篇 |
1987年 | 355篇 |
1986年 | 313篇 |
1985年 | 423篇 |
1984年 | 421篇 |
1983年 | 319篇 |
1982年 | 297篇 |
1981年 | 286篇 |
1980年 | 272篇 |
1979年 | 273篇 |
1978年 | 249篇 |
1977年 | 226篇 |
1976年 | 213篇 |
1975年 | 197篇 |
1974年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Assessed the efficiency of the peer review system during 3 National Science Foundation panel meetings held in 1982 and 1983. During these meetings, nearly 200 proposals received almost 1,400 reviews from "insiders" (panel members) and "outsiders" (ad hoc reviewers). Although the ratio of ad hoc time to panelist time was about 2:1, ad hoc reviewers' quantitative ratings had scant independent influence on final proposal ratings. Nevertheless, it may be that ad hoc reviewers provided crucial qualitative information, acting more as expert witnesses than as judges. The outcome of about a third of the proposals (the very good and the very poor) could be reliably predicted by independent panelist assessments that occurred before the panel meetings. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
104.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed. 相似文献
105.
Jacob Hooker David Hinks Gerardo Montero Christopher Conlee 《Coloration Technology》2002,118(6):273-276
The synthesis of azo dyes via a conventional aqueous-based diazotisation and coupling reaction requires the use of relatively high concentrations of mineral acids, which leads to high electrolyte concentrations in wastewater. Reported in this paper is an environmentally benign one-pot method for the synthesis of a nonionic azo dye, N,N -diethyl- N -{4-[( E )-(4-nitrophenyl)diazenyl]phenyl}amine, in supercritical carbon dioxide without using a mineral acid. The product yield increased significantly with temperature, with 91% theoretical yield afforded at 80 °C. The pressure of the system had little influence on product yield. 相似文献
106.
William W. Bowerman Amy S. Roe Michael J. Gilbertson David A. Best James G. Sikarskie Rachel S. Mitchell Cheryl L. Summer 《Lakes & Reservoirs: Research and Management》2002,7(3):183-187
The bald eagle (Haliaeetus leucocephalus) is one of the most studied birds of North America, and a great amount of natural life‐history information, including the response of various stressors on the eagles' ability to reproduce, are well known. In Michigan, the eagle has been chosen to track the trends of bioaccumulative compounds of concern across watersheds in the state. The state has been divided into major watersheds, and 20% of these are surveyed each year. A control area in northern Minnesota, Voyageurs National Park, is also sampled annually. We report here on the methods used, the preliminary results of the 1999 field season, and how differences in mercury concentrations varied over a 10‐year period. Mercury in feathers of nestling eagles declined over time only in Lakes Michigan and Huron, but have not decreased among other subpopulations in Michigan. Concentrations of polychlorinated biphenyls (PCBs) and 4,4′‐DDE in blood plasma from nestling eagles have declined over time for most subpopulations; however, they remain greater for breeding areas associated with the Great Lakes' food web. Sea eagles of the genus Haliaeetus are a good sentinel species to track trends in bioaccumulative compounds in aquatic systems. 相似文献
107.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
108.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献
109.
The physical gestures that operate music instruments are responsible for the qualities of the sound being produced in a performance.
Gestural information is thereby crucial for a model of music performance, paired with a model of sound synthesis where this
information is applied. The highly constrained nature of performers gestures makes this task suitable to be modeled via a
constraint-based approach, coupled with a strategy aimed at maximizing the gestural comfort of performers. We illustrate the
problem representation, the search strategy and a validation of the model against human performance. 相似文献
110.
Approximately 80% of the international transport of goods is carried on by means of ships. A large portion of the transport
capacity is represented by Roll-on-Roll-off (RoRo) ships. Especially in Europe this is a relevant potential for the RoRo segment.
Consequently, the design and construction of RoRo ships plays an increasing role for German shipyards and their suppliers.
In order to make the loading and unloading procedure of trailer economically more competitive, ship owners would like to improve
the lashing of trailers on the ship. On the basis of a multibody system formalism, a software tool has been developed which
allows for an optimization of the loading of trailers on RoRo ships.
Commemorative Contribution. 相似文献