全文获取类型
收费全文 | 6927篇 |
免费 | 177篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 63篇 |
综合类 | 2篇 |
化学工业 | 1246篇 |
金属工艺 | 76篇 |
机械仪表 | 113篇 |
建筑科学 | 231篇 |
矿业工程 | 7篇 |
能源动力 | 178篇 |
轻工业 | 368篇 |
水利工程 | 28篇 |
石油天然气 | 11篇 |
无线电 | 578篇 |
一般工业技术 | 858篇 |
冶金工业 | 2466篇 |
原子能技术 | 61篇 |
自动化技术 | 824篇 |
出版年
2022年 | 55篇 |
2021年 | 81篇 |
2020年 | 47篇 |
2019年 | 62篇 |
2018年 | 87篇 |
2017年 | 102篇 |
2016年 | 125篇 |
2015年 | 88篇 |
2014年 | 113篇 |
2013年 | 256篇 |
2012年 | 213篇 |
2011年 | 259篇 |
2010年 | 212篇 |
2009年 | 222篇 |
2008年 | 212篇 |
2007年 | 219篇 |
2006年 | 223篇 |
2005年 | 163篇 |
2004年 | 175篇 |
2003年 | 143篇 |
2002年 | 147篇 |
2001年 | 111篇 |
2000年 | 103篇 |
1999年 | 135篇 |
1998年 | 774篇 |
1997年 | 447篇 |
1996年 | 305篇 |
1995年 | 239篇 |
1994年 | 220篇 |
1993年 | 211篇 |
1992年 | 79篇 |
1991年 | 65篇 |
1990年 | 65篇 |
1989年 | 64篇 |
1988年 | 67篇 |
1987年 | 64篇 |
1986年 | 45篇 |
1985年 | 99篇 |
1984年 | 58篇 |
1983年 | 58篇 |
1982年 | 55篇 |
1981年 | 88篇 |
1980年 | 74篇 |
1979年 | 52篇 |
1978年 | 23篇 |
1977年 | 79篇 |
1976年 | 143篇 |
1975年 | 46篇 |
1974年 | 30篇 |
1973年 | 26篇 |
排序方式: 共有7110条查询结果,搜索用时 15 毫秒
31.
NV Zheleznova SL Mukomolov AB Zhebrun FS Noskov II Malkova EP Shargorodskaia AD Al'tshte?n VA Pliutnikova IN Lavrent'eva NN Ptichnikova 《Canadian Metallurgical Quarterly》1996,(5):49-53
The use of a recombinant poxvirus (RPV) strain, expressing HBsAg in the process of reproduction in different bioreactor systems under stationary and bioreactor conditions of cultivation, made it possible to obtain highly purified HBsAg. The identity and purity of HBsAg was confirmed by the analysis of its amino acid composition, SDS electrophoresis in polyacrylamide gel, electron microscopy and high-performance liquid chromatography. Good prospects of the use of RPV-expressed gene engineering HBsAg as the basis vaccines against hepatitis B was demonstrated in 10 experimental batches of vaccine. All batches of the preparation had pronounced immunogenicity and were safe and nontoxic in animal experiments. The ID50 of experimental batches did not exceed 211 ng/ml, which, according to the data of comparative experiments, was lower than, or equal to, corresponding values of analogous foreign commercial preparations, based on plasma or yeast HBsAg. 相似文献
32.
33.
M Belkin MS Conte MC Donaldson JA Mannick AD Whittemore 《Canadian Metallurgical Quarterly》1995,21(2):282-93; discussion 293-5
PURPOSE: To determine the optimal surgical strategies in reoperative infrainguinal bypass, we reviewed our results in 300 consecutive secondary bypasses in 251 patients operated on between Jan. 1, 1975, and Nov. 1, 1993. METHODS: There were 168 men (67%) and 83 women (33%), with a mean age of 64.8 years and a typical distribution of risk factors including smoking (76.4%), diabetes (33.7%), and coronary artery disease (47.1%). The indications for surgery were limb-threatening ischemia in 83.5% and severe claudication in 16.5% of patients. The majority of conduits (n = 213) were autogenous vein and were composed of a single segment of greater saphenous vein in 121 bypasses (57%) and various alternative veins including composite, arm, and lesser saphenous vein in 92 bypasses (43%). Prosthetic conduits included 69 polytetrafluoroethylene, 16 umbilical vein, and two Dacron grafts. RESULTS: There was one perioperative death (0.3%) and a 25% total morbidity rate including a 1.7% myocardial infarction rate. There was a 28.6% early (< 30 days) graft failure and 10.7% early amputation rate for prosthetic bypass grafts compared with 13.6% early graft failure and 5.6% early amputation rates for vein grafts. Autogenous vein bypasses had higher 5-year secondary patency rates than had prosthetic grafts (51.5% +/- 4.6% vs 27.4% +/- 6.1%, p < 0.001). Results with autogenous vein bypass improved significantly from the 1975 to 1984 to the 1985 to 1993 interval with 5-year secondary patency rates increasing from 38.3% +/- 6.9% to 59.1% +/- 5.8% (p = 0.017) and 5-year limb-salvage rates increasing from 40.4% +/- 7.6% to 72.4% +/- 6.6% (p < 0.001). Vein grafts to the popliteal and tibial outflow levels had equivalent long-term results. Vein grafts completed for claudication demonstrated results superior to those for limb salvage, with a 5-year secondary patency rate of 75.8% +/- 8.1% versus 52.3% +/- 7.9% (p = 0.048). Secondary autogenous vein bypass grafting performed after early primary graft failure (< 3 months) did particularly poorly, with only a 27.2% +/- 7.7% 4-year secondary patency rate. Greater saphenous veins tended to perform better than alternative vein bypasses, with a 5-year secondary patency rate of 68.5% +/- 6.0% compared with 48.3% +/- 10.5% (p = 0.09) and a 5-year limb-salvage rate of 77.8% +/- 7.4% versus 54.2% +/- 11.8% (p = 0.046). CONCLUSIONS: When patients suffer a recurrence of limb-threatening ischemia at the time of infrainguinal graft failure, aggressive attempts at secondary revascularization with autogenous vein are warranted based on the low surgical morbidity and mortality rates and the improved patency and limb salvage rates that are currently attainable. 相似文献
34.
Ferdinand P. Ferragu O. Lechien J.L. Lescop B. Magne S. Marty V. Rougeault S. Kotrotsios G. Neuman V. Depeursinge Y. Michel J.B. Van Uffelen M. Varelas D. Berthou H. Pierre G. Renouf C. Jarret B. Verbandt Y. Stevens W. Voet M.R.H. Toscano D. 《Lightwave Technology, Journal of》1995,13(7):1303-1313
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging 相似文献
35.
This article is primarily concerned with standards seen as a means for collective appropriation of technological information. It begins with an attempt to throw light on the relationships between standards, patents and licenses. Then we develop a two-stage duopolistic model whereby each firm must decide on a programme of standardization before choosing its level of production. The risks of multiple or inefficient equilibria are strong enough to justify the intervention of standardization organizations to inform and coordinate individual firms. But the paper also explains why some organizations likeetsi try to play a new role by promoting open access to master patents when used in the definition of a standard. 相似文献
36.
37.
38.
Prof. Dr.-Ing. M. Michel Dr.-Ing. Th. Schütze 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(6):419-426
Übersicht Mit Hinblick auf die zunehmend Verbreitung findende Pulsmusterberechnung in Echtzeit werden in dem Aufsatz Gesichtspunkte diskutiert, die sich aus den Eigenschaften des leistungselektronischen Stellgliedes, des Pulswechselrichters, ergeben. Die bei Abtastregelungen für die Dauer einer Abtastperiode konstante Stellgröße muß bei ihm durch Pulsweitenmodulation in ein Pulsmuster mit konstanter Amplitude und Pulsen variabler Breite umgesetzt werden. Durch ein neues Verfahren mit versetzter Abtastung haben dabei Rechentotzeiten bis zur Dauer einer halben Abtastperiode keinen Einfluß mehr auf das Pulsmuster.
Herrn Prof. Dr.-Ing. Klemens Heumann zum 60. Geburtstag gewidmet 相似文献
Algorithms for pulswidth modulation of inverters with online calculated pulse patterns
Contents Online calculation of pulse patterns will be employed more intensively in the future. Aspects concerning the powereleotronic circuit, the pulsewidth-modulated inverter, are to be discussed. The set value being constant for the duration of a sampling interval, has to be converted by a modulation algorithm into a pulse pattern with constant amplitude and pulses of variable width. Calculation dead-times up to half of sampling interval have no influence on the pulse pattern when using a new algorthm with shifted sampling instants.
Herrn Prof. Dr.-Ing. Klemens Heumann zum 60. Geburtstag gewidmet 相似文献
39.
40.
M Prade A Spatz P Duvillard C Bognel G Michel MA Belda N Mourra C Lagorce 《Canadian Metallurgical Quarterly》1993,13(5):317-323
From 4 cases recently seen at the Institut Gustave-Roussy, this report describes the pathological and evolutive features of benign glandular inclusions in inguinal, pelvic or abdominal lymph nodes. These lesions are defined by the presence of tubular formations in lymph nodes, lined by a single layer of epithelium which is cuboidal or columnar and resembled that of tubal epithelium with ciliated, secretory and intercalary cells. In most cases, benign glandular inclusions in lymph nodes still quiescent. In rare instances, they may proliferate and become papillary. The association of proliferating glandular inclusions in lymph nodes with borderline tumor of the ovary raises the problem of their primary or metastatic origin. However, their pathological features argues for a primary origin in lymph nodes. Thus, we think that a metastatic potential of borderline tumors of the ovary is not supported by any convincing argument. 相似文献