全文获取类型
收费全文 | 2313篇 |
免费 | 85篇 |
国内免费 | 21篇 |
学科分类
工业技术 | 2419篇 |
出版年
2023年 | 12篇 |
2022年 | 35篇 |
2021年 | 58篇 |
2020年 | 55篇 |
2019年 | 55篇 |
2018年 | 58篇 |
2017年 | 39篇 |
2016年 | 46篇 |
2015年 | 53篇 |
2014年 | 68篇 |
2013年 | 154篇 |
2012年 | 109篇 |
2011年 | 104篇 |
2010年 | 95篇 |
2009年 | 75篇 |
2008年 | 93篇 |
2007年 | 85篇 |
2006年 | 100篇 |
2005年 | 84篇 |
2004年 | 57篇 |
2003年 | 74篇 |
2002年 | 52篇 |
2001年 | 41篇 |
2000年 | 36篇 |
1999年 | 44篇 |
1998年 | 103篇 |
1997年 | 70篇 |
1996年 | 49篇 |
1995年 | 37篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 25篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 20篇 |
1976年 | 30篇 |
1975年 | 13篇 |
1973年 | 10篇 |
排序方式: 共有2419条查询结果,搜索用时 15 毫秒
21.
The geochemical behavior of U, Th series nuclides in surface marine sediments collected fromthe Red Sea coastal environment of Sudan was examined using daughter/parent and nonisotopic activity ratios. Pronounced anomalous behavior of several series of nuclides has been observed, particularly at shallower depths. On the average, the 234U/238U ratio is fairly constant and close to 1.13, suggesting scavenging of 234U from the overlying water column. In shallow-water sediments collected from the biologically productive area of the fringing reef and from the tidal-flat of Sanganeb atoll, compared to harbor and deep-sea sediments, 238U was found in large excess relative to 232Th. The 228Th/232Th disequilibrium indicates rapid sedimentation at shallower sites, which agrees well with data reported in the literature for similar environments. Depletion was observed of precursor thorium isotopes (230Th, 232Th) with respect to their mobile daughter isotopes of radium (226Ra, 228Ra). On the other hand, there is surface enrichment of 228Th and 210Po with respect to their progenitors 228Ra and 226Ra, as demonstrated by the 228Th : 228Ra and 210Po : 226Ra activity ratio, which is greater than unity in all the sediments analyzed. The 210Po/226Ra ratio is fairly constant (average 3.2). 相似文献
22.
The rate of filtration and the water content of cake are influenced by the existence of a dense skin in a highly compressible
cake. The phenomenon of the dense skin has been rarely studied, and its existence has not been verified experimentally. In
this study, the porosity variation in a very compressible cake is measured by using a new experimental apparatus, and with
this the existence of dense skin has been established experimentally. ‘Unified theory on solid-liquid separation’, a recently
developed theory, is utilized for calculating the porosity variation in a very compressible cake. 相似文献
23.
Solomon Sundar Manoharan Swati Sigamani John Prasanna Manju Lata Rao Ranjan Kumar Sahu 《Journal of the American Ceramic Society》2002,85(10):2469-2471
Interaction of electromagnetic radiation with a physical mixture of metal nitrates and amides/hydrazides is observed to initiate high-temperature reactions, useful for realizing several high-temperature ceramic materials. A judicious choice of such redox mixtures undergoes exothermic reactions when they couple with microwave radiation. The coupling of electromagnetic radiation with metal salts and amides/hydrazides depends on the dielectric properties of the individual components in the reaction mixture. The approach has been used to prepare γ-Fe2 O3 , Fe3 O4 , MgCr2 O4 , α-CaCr2 O4 , and La0.7 Ba0.3 MnO3 . 相似文献
24.
F. H. Sam Froes 《Powder Metallurgy and Metal Ceramics》2007,46(5-6):303-310
The approaches to production of titanium powder injection molded parts are reviewed. Historically, oxygen levels have been
too high for structural use (particularly with the Ti-6Al-4V alloy). However, recent advances in starting powders, binders
and sintering facilities now allow oxygen levels in the Ti-6Al-4V alloy to be controlled to about 0.2 wt.% oxygen. This should
result in significant expansion of the titanium PIM market place into aerospace, automobiles, surgical instruments, dentistry,
communication devices (such as computers and cell phones), knives and guns.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 118–125, 2007. 相似文献
25.
Barry D. Solomon 《Energy Policy》1985,13(1):97-101
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing. 相似文献
26.
BM King JT Cook KN Rossiter LM Theobold H Sam 《Canadian Metallurgical Quarterly》1996,60(6):1569-1571
Bilateral lesions in the most posterodorsal aspects of the amygdala in female rats resulted in immediate and dramatic weight gains on a standard lab chow diet. The rate of weight gain returned to normal by Day 20, but the difference in body weight between animals with amygdaloid lesions and those with sham lesions was maintained for the duration of the study (60 days). Because rats with posterodorsal amygdaloid lesions have also been found to be hyperinsulinemic, it is hypothesized that the lesions result in a similar, though smaller, version of the syndrome that follows lesions of the ventromedial hypothalamus. 相似文献
27.
The ERM proteins--ezrin, radixin, and moesin--occur in particular cortical cytoskeletal structures. Several lines of evidence suggest that they interact with both cytoskeletal elements and plasma membrane components. Here we described the properties of full-length and truncated radixin polypeptides expressed in transfected cells. In stable transfectants, exogenous full-length radixin behaves much like endogenous ERM proteins, localizing to the same cortical structures. However, the presence of full-length radixin or its carboxy-terminal domain in cortical structures correlates with greatly diminished staining of endogenous moesin in those structures, suggesting that radixin and moesin compete for a limiting factor required for normal associations in the cell. The results also reveal distinct roles for the amino- and carboxy-terminal domains. At low levels relative to endogenous radixin, the carboxy-terminal polypeptide is associated with most of the correct cortical targets except cleavage furrows. In contrast, the amino-terminal polypeptide is diffusely localized throughout the cell. Low level expression of full-length radixin or either of the truncated polypeptides has no detectable effect on cell physiology. However, high level expression of the carboxy-terminal domain dramatically disrupts normal cytoskeletal structures and functions. At these high levels, the amino-terminal polypeptide does localize to cortical structures, but does not affect the cells. We conclude that the behavior of radixin in cells depends upon activities contributed by separate domains of the protein, but also requires modulating interactions between those domains. 相似文献
28.
R Kneen NG Pham T Solomon TM Tran TT Nguyen BL Tran J Wain NP Day TH Tran CM Parry NJ White 《Canadian Metallurgical Quarterly》1998,27(4):845-850
PURPOSE: To review the University of Florida experience in treating ependymomas, analyze prognostic factors, and provide treatment recommendations. METHODS AND MATERIALS: Forty-one patients with ependymoma and no metastases outside the central nervous system received postoperative radiotherapy with curative intent between 1966 and 1989. Ten patients had supratentorial lesions, 22 had infratentorial lesions, and 9 had spinal cord lesions. All patients had surgery (stereotactic biopsy, subtotal resection, or gross total resection). Most patients with high-grade lesions received radiotherapy to the craniospinal axis. Low-grade intracranial lesions received more limited treatment. Spinal cord lesions were treated using either partial spine or whole spine fields. RESULTS: Of 32 intracranial tumors, 21 recurred, all at the primary site; no spinal cord tumors recurred. Overall 10-year survival rates were 51% (absolute) and 46% (relapse-free); by tumor site: spinal cord, 100%; infratentorial, 45%; supratentorial, 20% (p = 0.002). On multivariate analysis, tumor site was the only factor that influenced absolute survival (p = 0.0004); other factors evaluated included grade, gender, age, duration of symptoms, resection extent, primary tumor dose, treatment field extent, surgery-to-radiotherapy interval, and days under radiotherapy treatment. CONCLUSIONS: Patients with supratentorial or infratentorial tumors receive irradiation, regardless of grade. Craniospinal-axis fields are used when spinal seeding is radiographically or pathologically evident. Spinal cord tumors are treated using localized fields to the primary site if not completely resected. Failure to control disease at the primary site remains the main impediment to cure. 相似文献
29.
R. Sam Williams Steve Lacher Corey Halpin Christopher White 《Materials and Structures》1988,21(4):313-320
RILEM Bulletin
Fourth International Conference on Durability of Building Materials and Components 相似文献30.
Railway Engineering Science - Electrified railways are becoming a popular transport medium and these consume a large amount of electrical energy. Environmental concerns demand reduction in energy... 相似文献