全文获取类型
收费全文 | 171242篇 |
免费 | 1535篇 |
国内免费 | 199篇 |
专业分类
电工技术 | 2610篇 |
综合类 | 121篇 |
化学工业 | 27418篇 |
金属工艺 | 9544篇 |
机械仪表 | 5805篇 |
建筑科学 | 3085篇 |
矿业工程 | 1890篇 |
能源动力 | 2817篇 |
轻工业 | 9355篇 |
水利工程 | 2748篇 |
石油天然气 | 8710篇 |
武器工业 | 12篇 |
无线电 | 14673篇 |
一般工业技术 | 38779篇 |
冶金工业 | 28088篇 |
原子能技术 | 6950篇 |
自动化技术 | 10371篇 |
出版年
2019年 | 1683篇 |
2018年 | 3087篇 |
2017年 | 3213篇 |
2016年 | 3460篇 |
2015年 | 1757篇 |
2014年 | 3098篇 |
2013年 | 6540篇 |
2012年 | 4492篇 |
2011年 | 5591篇 |
2010年 | 4571篇 |
2009年 | 5071篇 |
2008年 | 5081篇 |
2007年 | 5017篇 |
2006年 | 4244篇 |
2005年 | 3895篇 |
2004年 | 3695篇 |
2003年 | 3585篇 |
2002年 | 3490篇 |
2001年 | 3506篇 |
2000年 | 3391篇 |
1999年 | 3250篇 |
1998年 | 7103篇 |
1997年 | 5216篇 |
1996年 | 3859篇 |
1995年 | 2948篇 |
1994年 | 2621篇 |
1993年 | 2749篇 |
1992年 | 2266篇 |
1991年 | 2317篇 |
1990年 | 2428篇 |
1989年 | 2328篇 |
1988年 | 2339篇 |
1987年 | 2198篇 |
1986年 | 2256篇 |
1985年 | 2299篇 |
1984年 | 2209篇 |
1983年 | 2137篇 |
1982年 | 1980篇 |
1981年 | 2195篇 |
1980年 | 2056篇 |
1979年 | 2271篇 |
1978年 | 2431篇 |
1977年 | 2434篇 |
1976年 | 3102篇 |
1975年 | 2244篇 |
1974年 | 2310篇 |
1973年 | 2343篇 |
1972年 | 2157篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
992.
Event-related brain potentials (ERPs) were recorded during the test phases of two experiments. In experiment 1, subjects first studied two consecutively presented word lists. At test, they were presented with pairs of words, and were required to judge which word had been presented most recently. The test pairs were composed of two previously studied words, one drawn from each list, (Old+Old pairs), one previously studied and one new word (Old+New pairs), or two unstudied words (New+New pairs). At temporo-parietal electrodes, ERPs to Old+Old and Old+New pairs were both reliably more positive-going than those to New+New pairs. At electrode sites overlying prefrontal cortex, ERPs to Old+Old pairs attracting correct recency judgements were more positive, from around 300 ms onwards, than those elicited by the other classes of item, which did not differ from one another. In experiment 2, the test task was changed to one that required discrimination between Old+New items on the one hand, and Old+Old and New+New pairs on the other. ERPs to Old+Old and Old+New pairs once again differed from those to New+New pairs at temporo-parietal sites, but no differences were evident between the ERPs from frontal electrode sites. In line with the evidence from lesion studies, these findings suggest that judgements of relative recency depend upon processes, supported by the prefrontal cortex, additional to those that are necessary for recognition memory. They further suggest that these processes are activated rapidly and selectively in response to pairs of studied items when these must be discriminated on the basis of their relative recency of occurrence. 相似文献
993.
The beta recombinase, in the presence of a chromatin-associated protein such as Hbsu, catalyzes DNA resolution or DNA inversion on supercoiled substrates containing two directly or inversely oriented six sites. Hbsu stabilizes the formation of the recombination complex (Alonso, J. C., Weise, F., and Rojo, F. (1995) J. Biol. Chem. 270, 2938-2945). In this study we show that resolution by beta recombinase strictly requires supercoiled DNA, but inversion does not. On a substrate with two inversely oriented six sites, beta recombinase catalyzed both resolution and inversion if the DNA was supercoiled but only inversion if the substrate was relaxed or linear. Hbsu was critical for the formation of synaptic complexes; its concentration relative to that of the supercoiled DNA substrate determined whether resolution or inversion products were preferentially formed. The results suggest that the beta recombinase forms unproductive short-lived synaptic complexes between two juxtaposed inversely oriented six sites; the presence of 3 to 13 Hbsu dimers per supercoiled DNA molecule would stabilize a synaptic complex with a relative geometry of the six sites allowing beta recombinase preferentially to achieve resolution. Supercoiling probably helps to overcome an energetic barrier, since resolution does not occur in relaxed DNA. The presence of >30 Hbsu dimers per DNA molecule probably favors the formation of a recombination complex with a different geometry since the reaction is directed preferentially toward DNA inversion. 相似文献
994.
995.
RD Wegner I Henrichs H Joenje T Schroeder-Kurth 《Canadian Metallurgical Quarterly》1996,50(6):479-482
The clinical and cytogenetic data of the first patient proven to belong to the fifth Fanconi anemia complementation group are described. The Turkish boy presented with psychomotoric retardation, growth retardation, retarded bone age, brachycephaly, hypotelorism, epicanthus, syndactyly, brachydactyly, renal dystopia, and cryptorchism. In addition, an asymmetrical skeletal anomaly was seen with a double distal phalanx of the left thumb and hypoplasia of the right thumb. Typical hematological features of the disorder developed, at the age of 2.5 years, about 1 year after diagnosis. Cytogenetic studies confirmed the clinical diagnosis and revealed a spontaneous chromosomal instability and hypersensitivity to the cross-linking agents diepoxybutane and Trenimon. The findings in the patient, who is considered to be the standard for the fifth Fanconi anemia complementation group, are compared with data reported for other patients affected with Fanconi anemia. 相似文献
996.
B Liedman H Andersson B Berglund I Bosaeus I Hugosson L Olbe L Lundell 《Canadian Metallurgical Quarterly》1996,83(8):1138-1143
Patients with carcinoma of the stomach who underwent curative resection were randomized to total gastrectomy (n = 49), total gastrectomy and an S-shaped gastric substitute (n = 28) or subtotal gastrectomy (n = 12); all had a Roux-en-Y reconstruction. The gastric substitute and gastric remnant allowed a volume of 400-500 ml to be installed without increments in basal pressures. The corresponding volume in the Roux limb was 100 ml. Energy intake was approximately 120 kJ/kg preoperative weight per day 3 months after operation, and then remained constant. Patients who had subtotal gastrectomy ate less (91.7 kJ/kg preoperative weight) 3 months after operation, but thereafter increased their intake. Patients allocated to have a gastric pouch or subtotal gastrectomy complained more frequently of adverse postprandial symptoms (P < 0.03) as a major cause of reduced calorie intake. The construction of a gastric reservoir did not improve nutritional adaptation after surgery for gastric carcinoma. 相似文献
997.
S. M. Logvinkov G. D. Semchenko S. V. Tishchenko V. I. Toshinskii V. A. Borovaya I. N. Opryshko 《Glass and Ceramics》1996,53(1-2):33-34
Compositions and technologies are suggested for preparing highly efficient catalyst blocks with a honeycomb structure to be used for reducing nitrogen oxides with ammonia in flue gases from thermal power plants. The blocks have high structural strength and catalytic activity. 相似文献
998.
Conclusions The calculations for the different levels of volume heat release showed that the integral heat fluxes at the lateral and top
surfaces are virtually independent of the scenario of convective flow. However, the maximum of the heat flux on the lateral
surface in the homogeneous case is 1.5–1.6 times higher than the maximum heat flux in the stratified case. This could result
in larger mechanical loads on the reactor vessel and therefore more stringent requirements on the cooling of the outer surface
of the reactor vessel.
Institute of Fast Reactors, Russian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 76, No. 5, pp. 406–411, May,
1994. 相似文献
999.
1000.
All-Union Scientific-Research Institute of Nuclear Power Plants NIIP. Translated from Atomnaya énergiya, Vol. 77, No. 5, pp.
392–402, November, 1994. 相似文献