全文获取类型
收费全文 | 252740篇 |
免费 | 3043篇 |
国内免费 | 869篇 |
专业分类
电工技术 | 4809篇 |
综合类 | 193篇 |
化学工业 | 36153篇 |
金属工艺 | 9512篇 |
机械仪表 | 7545篇 |
建筑科学 | 6074篇 |
矿业工程 | 880篇 |
能源动力 | 7227篇 |
轻工业 | 21092篇 |
水利工程 | 2202篇 |
石油天然气 | 3230篇 |
武器工业 | 15篇 |
无线电 | 34289篇 |
一般工业技术 | 49999篇 |
冶金工业 | 48583篇 |
原子能技术 | 5077篇 |
自动化技术 | 19772篇 |
出版年
2021年 | 2173篇 |
2020年 | 1563篇 |
2019年 | 1918篇 |
2018年 | 3277篇 |
2017年 | 3310篇 |
2016年 | 3400篇 |
2015年 | 2220篇 |
2014年 | 3961篇 |
2013年 | 11479篇 |
2012年 | 6239篇 |
2011年 | 8579篇 |
2010年 | 6907篇 |
2009年 | 7893篇 |
2008年 | 8409篇 |
2007年 | 8299篇 |
2006年 | 7367篇 |
2005年 | 6505篇 |
2004年 | 6284篇 |
2003年 | 6559篇 |
2002年 | 6039篇 |
2001年 | 6514篇 |
2000年 | 5975篇 |
1999年 | 6392篇 |
1998年 | 16488篇 |
1997年 | 11418篇 |
1996年 | 8798篇 |
1995年 | 6610篇 |
1994年 | 5904篇 |
1993年 | 5846篇 |
1992年 | 4132篇 |
1991年 | 4020篇 |
1990年 | 3857篇 |
1989年 | 3648篇 |
1988年 | 3560篇 |
1987年 | 3017篇 |
1986年 | 2941篇 |
1985年 | 3210篇 |
1984年 | 2928篇 |
1983年 | 2829篇 |
1982年 | 2636篇 |
1981年 | 2542篇 |
1980年 | 2462篇 |
1979年 | 2305篇 |
1978年 | 2108篇 |
1977年 | 2606篇 |
1976年 | 3565篇 |
1975年 | 1764篇 |
1974年 | 1729篇 |
1973年 | 1665篇 |
1972年 | 1465篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
ABSTRACT: In a screening of South African indigenous food plants for antioxidant activity by testing for inhibition of lipid peroxidation, the "potherbs" Amaranthus sp., Sisymbrium thellungii , and Urtica dioica had very high activity. This activity was greatest in the boiled extract of Amaranthus sp. and the boilet and aqueous extracts of Sisymbrium thellungii and Urtica dioica. The activity in the aqueous extract of Nasturtium aquatica was lost by boiling. High activity was also obtained with the teas Galium aparine and Aspalathus linearis (Rooibos) and with the tuber Colocasia esculenta. 相似文献
972.
973.
Narayanaswami C. Kamijoh N. Raghunath M. Inoue T. Cipolla T. Sanford J. Schlig E. Venkiteswaran S. Guniguntala D. Kulkarni V. Yamazaki K. 《Computer》2002,35(1):33-41
Nearly four years in development, the IBM Linux watch contains a complete computer system that runs Linux, displays X11 graphics, and has wireless connectivity. The system fits in a case that could pass as a slightly unusual analog timepiece with a somewhat odd shape and an extraordinarily brilliant face. The developers have created two versions of the watch, one with an organic light-emitting diode display and the other with a liquid crystal display. Still considered a research prototype, the watch already runs some personal information management applications, and it can communicate with PCs, PDAs, and other wireless-enabled devices, viewing condensed e-mail and directly receiving pager-like messages. Eventually, users will be able to access various Internet-based services, such as up-to-the-minute information about weather, traffic conditions, the stock market, and sports 相似文献
974.
975.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 421–423, June, 1989. 相似文献
976.
977.
During a core melt accident, a pressurization of the containment has to be expected, which could lead to a failure of the containment due to overpressurization. This failure mode is expected to be the most likely one for large dry containments under accident conditions. Also during a core melt accident, a large quantity of hydrogen may be generated, giving the potential of a loss of containment integrity due to violent hydrogen combustion. Timely venting of the containment atmosphere can prevent overpressurization and may perhaps make the hydrogen situation in the containment less severe. This paper discusses the thermodynamic consequences of different vent strategies for a large German PWR during core melt accidents. 相似文献
978.
WC-(Fe, Ni, C) cemented carbides can be successfully transformation-toughened by careful control of binder composition and
taking into consideration the effect of thermal residual stress on the transformation characteristics of the binder. An additional
degree of control on the metastability of the binder phase can be achievedvia thermomechanical treatments. These treatments consist of transforming an austenitic binder to martensite by cooling in liquid
nitrogen followed by a suitable high temperature heat treatment to reaustenitize it. Thein situ deformation of the binder caused by the large shape and volume changes that accompany its transformation to martensite thus
provides the mechanical component of the thermomechanical treatment. Subsequent heat treatments not only reaustenitize the
binder but also modify its susceptibility to undergo stress-induced transformation. It is shown that the hardness/fracture
toughness behavior of WC-(Fe, Ni, C) cemented carbides can be significantly improved by the application of such treatments.
A qualitative explanation for the enhancements in fracture toughness provided by thermomechanical treatments is offered based
on a careful examination of the changes in phase constitution of the binder that occur during these treatments.
Formerly Manager, Research-Development, Reed Tool Company, Houston, TX. 相似文献
979.
New mesogenic homologous series having an azo central linkage was synthesized by fixing a rigid 4-methyl phenyl azo group
to resorcinol moiety. The terminal and lateral phenolic -OH groups were esterified, one by one, with 4-n-alkoxybenzoyl and acetyl group, respectively. All the twelve homologues synthesized exhibit mesomorphism. The methoxy ton-decyloxy andn-hexadecyloxy derivatives exhibit monotropic nematic mesophase whereas,n-dodecyloxy andn-tetradecyloxy derivatives exhibit enantiotropic nematic mesophase. The mesogenic properties of the present series was compared
with those of other structurally related mesogenic series.
Paper presented at the 5th National Seminar on Liquid Crystals, University of Jammu, Jammu, December 1997. 相似文献
980.
A. T. Mamadalimov B. L. Oksegendler Sh. O. Otazhonov B. É. Turaev T. A. Usmanov N. K. Khakimova Zh. A. Kadirov 《Technical Physics Letters》2002,28(7):581-583
The photoelectric properties of cotton fibers treated with iodine were studied in the fundamental absorption range. The samples exhibit a sublinear illumination-current characteristic and a long-term relaxation of photoconductivity (PC) after UV irradiation (hν=5 eV) of the iodine-doped fibers. A PC mechanism is proposed which explains both the nonlinear variation of photocurrent with illumination intensity and the PC decay according to a bimolecular recombination law after UV irradiation of the iodine-doped fiber in the fundamental absorption range. 相似文献