全文获取类型
收费全文 | 252604篇 |
免费 | 3029篇 |
国内免费 | 867篇 |
专业分类
电工技术 | 4807篇 |
综合类 | 193篇 |
化学工业 | 36126篇 |
金属工艺 | 9505篇 |
机械仪表 | 7543篇 |
建筑科学 | 6072篇 |
矿业工程 | 880篇 |
能源动力 | 7225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 | 34279篇 |
一般工业技术 | 49968篇 |
冶金工业 | 48536篇 |
原子能技术 | 5075篇 |
自动化技术 | 19752篇 |
出版年
2021年 | 2167篇 |
2020年 | 1560篇 |
2019年 | 1916篇 |
2018年 | 3270篇 |
2017年 | 3308篇 |
2016年 | 3398篇 |
2015年 | 2217篇 |
2014年 | 3955篇 |
2013年 | 11473篇 |
2012年 | 6233篇 |
2011年 | 8574篇 |
2010年 | 6906篇 |
2009年 | 7883篇 |
2008年 | 8404篇 |
2007年 | 8295篇 |
2006年 | 7362篇 |
2005年 | 6497篇 |
2004年 | 6282篇 |
2003年 | 6555篇 |
2002年 | 6035篇 |
2001年 | 6513篇 |
2000年 | 5974篇 |
1999年 | 6389篇 |
1998年 | 16480篇 |
1997年 | 11409篇 |
1996年 | 8792篇 |
1995年 | 6606篇 |
1994年 | 5901篇 |
1993年 | 5843篇 |
1992年 | 4131篇 |
1991年 | 4020篇 |
1990年 | 3857篇 |
1989年 | 3648篇 |
1988年 | 3559篇 |
1987年 | 3017篇 |
1986年 | 2941篇 |
1985年 | 3206篇 |
1984年 | 2927篇 |
1983年 | 2828篇 |
1982年 | 2637篇 |
1981年 | 2542篇 |
1980年 | 2462篇 |
1979年 | 2305篇 |
1978年 | 2109篇 |
1977年 | 2604篇 |
1976年 | 3562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
961.
962.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 421–423, June, 1989. 相似文献
963.
964.
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
965.
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
966.
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
967.
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
968.
969.
An Si bipolar monolithic decision circuit for practical use is developed using an improved circuit technique and super self-aligned process technology with the reliable 1.25 ?m rule. The circuit consists of a slice amplifier, a master-slave D flip-flop and an output buffer. This circuit is capable of operating up to 2.1 Gbit/s with a decision threshold ambiguity width of less than 10 mV. In addition, a clock phase margin of 250 degrees and power dissipation of 640 mW at VEE=?6 V can be achieved. 相似文献
970.
Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting. 相似文献