全文获取类型
收费全文 | 49691篇 |
免费 | 1641篇 |
国内免费 | 355篇 |
专业分类
电工技术 | 825篇 |
综合类 | 558篇 |
化学工业 | 10211篇 |
金属工艺 | 1074篇 |
机械仪表 | 1249篇 |
建筑科学 | 2097篇 |
矿业工程 | 513篇 |
能源动力 | 1287篇 |
轻工业 | 4019篇 |
水利工程 | 485篇 |
石油天然气 | 425篇 |
武器工业 | 27篇 |
无线电 | 4271篇 |
一般工业技术 | 7190篇 |
冶金工业 | 9873篇 |
原子能技术 | 450篇 |
自动化技术 | 7133篇 |
出版年
2023年 | 257篇 |
2022年 | 692篇 |
2021年 | 1004篇 |
2020年 | 600篇 |
2019年 | 749篇 |
2018年 | 902篇 |
2017年 | 792篇 |
2016年 | 999篇 |
2015年 | 814篇 |
2014年 | 1246篇 |
2013年 | 2850篇 |
2012年 | 1879篇 |
2011年 | 2363篇 |
2010年 | 1789篇 |
2009年 | 1913篇 |
2008年 | 2069篇 |
2007年 | 1981篇 |
2006年 | 1763篇 |
2005年 | 1552篇 |
2004年 | 1471篇 |
2003年 | 1655篇 |
2002年 | 1927篇 |
2001年 | 1516篇 |
2000年 | 997篇 |
1999年 | 999篇 |
1998年 | 1785篇 |
1997年 | 1293篇 |
1996年 | 1117篇 |
1995年 | 879篇 |
1994年 | 777篇 |
1993年 | 788篇 |
1992年 | 630篇 |
1991年 | 423篇 |
1990年 | 553篇 |
1989年 | 522篇 |
1988年 | 468篇 |
1987年 | 512篇 |
1986年 | 458篇 |
1985年 | 590篇 |
1984年 | 549篇 |
1983年 | 490篇 |
1982年 | 457篇 |
1981年 | 400篇 |
1980年 | 399篇 |
1979年 | 419篇 |
1978年 | 345篇 |
1977年 | 336篇 |
1976年 | 409篇 |
1975年 | 296篇 |
1973年 | 275篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
L De Petrocellis P Orlando M Gavagnin M Ventriglia G Cimino V Di Marzo 《Canadian Metallurgical Quarterly》1996,52(9):874-877
Five novel 1,2-sn-diacylglycerols with diterpenoid acyl moieties in the sn-1 position were isolated and characterized, together with the corresponding 1,3-sn-diacylglycerols, from three species of dorid nudibranchs molluscs. Their potent activity as morphogens in vivo in the Hydra tentacle regeneration assay and their parallel activity as activators of rat brain protein kinase C (PKC) in vitro are reported here. Our findings promote the use of these compounds as useful molecular probes for both in vivo and in vitro studies on the participation of PKC in cell development. 相似文献
52.
The price of SO2 permits and the volume of trading under the US Acid Rain Program have been lower than expected. This can be explained by the creation and distribution of more permits than were initially authorized, by the sale of permits by high cost abaters who are subject to more stringent local emission constraints or who have irreversibly invested in high cost abatement technologies and by the deregulation of the natural gas and railroad industries which, in combination with incentives for cost-cutting under the new market approach to SO2 control, has lowered marginal costs of abatement curves and made them more uniform across powerplants. The low price of permits and low trading volume are evidence that market approaches to pollution control can be more cost-effective than command and control regulations. The effect of public policies and technological changes on the allowance market are usefully examined in the context of an ideal market, in which the equilibrium price of allowances equals the marginal cost of abatement of individual powerplants. Using recent data from Coggins and Swinton (1996), we are able to explain the current price of permits with some accuracy. 相似文献
53.
Luginbuhl P. Collins S.D. Racine G.-A. Gretillat M.-A. De Rooij N.F. Brooks K.G. Setter N. 《Journal of microelectromechanical systems》1997,6(4):337-346
The fabrication using silicon micromachining and characterization of an acoustic Lamb wave actuator is presented. The intended use of the device is for mass transport and sensor applications. The device consists of dual interdigitated transducers patterned on a thin-film composite membrane of silicon nitride, platinum, and a sol-gel-derived piezoelectric ceramic (PZT) thin film. The acoustic properties of the device are presented along with preliminary applications to mechanical transport and liquid delivery systems. Improved acoustic signals and improved mass transport are achieved with PZT over present Lamb wave devices utilizing ZnO or AlN as the piezoelectric transducer 相似文献
54.
A Nu?ez C De la Roza ML Rodrigo-Angulo W Bu?o F Reinoso-Suárez 《Canadian Metallurgical Quarterly》1997,754(1-2):1-11
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters. 相似文献
55.
Analysis of Combined Systems of Two Endoreversible Engines 总被引:3,自引:0,他引:3
A single endoreversible engine can operate as a cooler, a true heat engine, a heat pump, or a refrigerator. We investigate how many different modes of operation a combined system of two endoreversible engines may display. Special attention is paid to the independent combined system which neither consumes nor supplies power. 相似文献
56.
Robert Hummel Larry M. Manevitz 《Annals of Mathematics and Artificial Intelligence》1997,20(1-4):69-109
There are many different methods for incorporating notions of uncertainty in evidential reasoning. A common component to these
methods is the use of additional values, other than conditional probabilities, to assert current degrees of belief and certainties
in propositions. Beginning with the viewpoint that these values can be associated with statistics of multiple opinions in
an evidential reasoning system, we categorize the choices that are available in updating and tracking these multiple opinions.
In this way, we develop a matrix of different uncertainty calculi, some of which are standard, and others are new. The main
contribution is to formalize a framework under which different methods for reasoning with uncertainty can be evaluated. As
examples, we see that both the “Kalman filtering” approach and the “Dempster–Shafer” approach to reasoning with uncertainty
can be interpreted within this framework of representing uncertainty by the statistics of multiple opinions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
57.
JA Alaejos Fuentes T López-Alburquerque J De Portugal Alvarez 《Canadian Metallurgical Quarterly》1997,14(5):239-240
We report a 20-year-old man affected by glycogenosis type III with distal muscle weakness, more severe in distal leg muscles. The electromyogram showed myopathic features. Nerve conduction studies and central motor conduction after magnetic stimulation of the brain were normal. Our results suggest that there is no involvement of central motor pathways in this disease. 相似文献
58.
Based on a contemporary cognitive-psychoanalytic theory (control-mastery theory; J. Weiss, H. Sampson, & Mount Zion Psychotherapy Research Group, 1986), this study proposed that college students have plans for college that consist of conscious and unconscious goals and obstructions to be overcome in meeting those goals. The construct of unconscious guilt was used to mediate the dual goals of autonomy and attachment. The idiographic plan-formulation method was adapted to derive plans for 12 sophomore women. Acceptable interjudge reliabilities and criterion validity were demonstrated, and several themes in the goals and obstructions were illustrated. Students worried more about mothers than about fathers, particularly when they perceived the mother as weak or needy. The potential of the method for generating inferences about unconscious process for normative development is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
59.
60.