全文获取类型
收费全文 | 288039篇 |
免费 | 3076篇 |
国内免费 | 817篇 |
专业分类
电工技术 | 5034篇 |
综合类 | 162篇 |
化学工业 | 45512篇 |
金属工艺 | 11903篇 |
机械仪表 | 8610篇 |
建筑科学 | 6867篇 |
矿业工程 | 1840篇 |
能源动力 | 6746篇 |
轻工业 | 25992篇 |
水利工程 | 3197篇 |
石油天然气 | 7088篇 |
武器工业 | 16篇 |
无线电 | 31462篇 |
一般工业技术 | 56983篇 |
冶金工业 | 51466篇 |
原子能技术 | 7532篇 |
自动化技术 | 21522篇 |
出版年
2021年 | 2109篇 |
2018年 | 3684篇 |
2017年 | 3628篇 |
2016年 | 3914篇 |
2015年 | 2479篇 |
2014年 | 4246篇 |
2013年 | 12046篇 |
2012年 | 6844篇 |
2011年 | 9225篇 |
2010年 | 7585篇 |
2009年 | 8656篇 |
2008年 | 8946篇 |
2007年 | 8826篇 |
2006年 | 7837篇 |
2005年 | 7316篇 |
2004年 | 6809篇 |
2003年 | 6559篇 |
2002年 | 6631篇 |
2001年 | 6502篇 |
2000年 | 6183篇 |
1999年 | 6234篇 |
1998年 | 14789篇 |
1997年 | 11046篇 |
1996年 | 8580篇 |
1995年 | 6529篇 |
1994年 | 5922篇 |
1993年 | 5797篇 |
1992年 | 4483篇 |
1991年 | 4446篇 |
1990年 | 4287篇 |
1989年 | 4302篇 |
1988年 | 4258篇 |
1987年 | 3600篇 |
1986年 | 3599篇 |
1985年 | 4165篇 |
1984年 | 3965篇 |
1983年 | 3625篇 |
1982年 | 3425篇 |
1981年 | 3560篇 |
1980年 | 3428篇 |
1979年 | 3369篇 |
1978年 | 3448篇 |
1977年 | 3930篇 |
1976年 | 5044篇 |
1975年 | 3168篇 |
1974年 | 3009篇 |
1973年 | 3030篇 |
1972年 | 2652篇 |
1971年 | 2476篇 |
1970年 | 2107篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
G Sperner P Seewald A Hamberger A Koller P Wanitschek K Golser 《Canadian Metallurgical Quarterly》1996,99(11):869-874
At the university hospital of emergency surgery in Innsburck and at the emergency services department of the hospital in Schwaz, anterior cruciate ligament reconstruction was performed in 467 patients between January 1992 and September 1993. In 117 cases, a double semitendinous tendon was used as an autograft. A total of 60 of these patients were followed up at an average of 20 months (13-33) after reconstruction. The results were rated according to the OAK and the Tegner scores. Objective measurements of instability were carried out by a KT 1000 arthrometer. In addition, 21 patients underwent computer-interfaced dynamometer testing using a Cybex 6000. Standardized loading of the thigh muscles was performed at angular velocities of 60 degrees/s (3 repetitions) and 240 degrees/s (30 repetitions): peak torques and total work were analyzed. The mean age was 23.5 years (17-55): 48 were male, 21 female. The main reasons for the ACL ruptures were sports injuries (51 cases). The patients were classified into three groups according to the data of the repair (group 1 reconstruction up to 1 week after trauma-28 patients: group 2: reconstruction between the 2nd and 6th week after trauma-15 patients: group 3: reconstruction 6 and more weeks after trauma-26 patients). In group 1. additional ruptures of the menisci. lesions of the MCL. and chondromalacia were seen in 71.4%. in group 2 in 73.3% and in group 3 in 80.8%. The average rating in the OAK score was 90.16 points: 38 patients (55.70%) had excellent results. 18(26.09%) were good. 9(13.04%) were fair and 4(5.80%) were poor. The Tegner activity score showed a reduction of 0.36 points on average. The largest amount of anterior translation was performed with the KT 1000 manual drawer test (2.29 mm on average compared with the contralateral side). Dynamometer testing showed a statistically significant difference in flexor and extensor mechanism (compared with the non-involved side) in both peak torques and total work. A repeat arthroscopy became necessary in five cases: arthrofibrosis in three and incipient joint infection in two cases. 相似文献
992.
993.
994.
Analysis of a novel semiconductor laser structure designed for obtaining wide tuning range along with high speed modulation response is presented. The laser consists of a composite cavity structure with two active (gain) sections. One of the sections has a grating corrugation while the other is flat. A detailed round-trip analysis is combined with the rate equations, which include sublinear gain/carrier relation, to perform steady-state and small-signal analysis. It is shown that the biasing (dc) condition of the different sections plays a critical role in the determination of the dynamic response of the device. In addition, we show that the gain-lever effect can be utilized for a considerable enhancement of the frequency modulation (FM) response. Other critical structural parameters such as the grating coupling coefficient and device geometry are discussed 相似文献
995.
J. G. Zheng Xiaoqing Pan M. Schweizer U. Weimar W. Göpel M. Rühle 《Journal of Materials Science》1996,31(9):2317-2324
Atomic structures of crystallographic shear planes (CSPs) in nanocrystalline thin films of semiconductor SnO2 were investigated by high-resolution electron microscopy. The films were prepared by electron beam evaporation in high vacuum (10–6 torr) and followed by annealing in synthetic air at 700 °C for 1–2 H. CSPs with the displacement vector of [1/2 0 1/2] were observed in the planes parallel to (¯101), (110) and (¯3¯21). Most of the CPSs were found to terminate or interact with each other within SnO2 crystallites. Partial dislocations exist at terminal places of CSPs or along intersecting lines of CSPs. CSP steps were also observed. Structural models of these defects have been proposed. Based on analysis of experimental data, it has been suggested that the Sn/O ratio at CSPs which are not parallel to their displacement vector, at cores of partial dislocations and at CSP steps, is higher than that of the perfect structure, that is, these defects are able to provide extra free electrons with the films. 相似文献
996.
G. B. Kainer 《Measurement Techniques》1996,39(4):366-368
This article presents a fundamentally new method for controlling the position of an object in three-dimensional space by using
a microinterferometer. This method assures high accuracy and efficiency. The method can be used for verifying accuracy of
contact gauges in position-measuring machinery.
Translated from Izmeritel'naya Tekhnika, No. 4, pp. 17–18, April, 1996. 相似文献
997.
A.K. Bhaduri S. Venkadesan P. Rodriguez P.G. Mukunda 《International Journal of Pressure Vessels and Piping》1994,58(3):251-265
The transition metal joint (TMJ) between an austenitic stainless steel and a chromium-molybdenum (Cr-Mo) ferritic steel used widely in steam generators of power plants has for a long time presented problems relating to premature failures in service. The direct (bimetallic) TMJ presently in use is designed for a service life of about 200,000 h; but such TMJs with iron-base weld metals have been failing in service within about one-third of their design lifetime, while their counterparts with nickel-base weld metals fail within about one-half of their design lifetime. The causes for such premature service failures of these TMJs are discussed in detail, leading to the development of improved TMJs. One of the improved TMJs with a trimetallic configuration of austenitic stainless steel/Alloy 800/Cr-Mo ferritic steel is discussed in detail, covering its development, characterisation and evaluation. Accelerated performance tests in the laboratory have indicated a four-fold improvement in the service life of the TMJ with this trimetallic configuration compared to the bimetallic configuration. The metallurgical details of these studies are also discussed in this paper. 相似文献
998.
Flexion-extension moments acting at the L5/S1 level and hip joints were calculated using three different techniques; a pure static analysis, a static analysis including the inertial force of the load, and a dynamic analysis. Ten subjects participated in the study and were asked to lift a box weighing either 50 N or 150 N, using a freestyle technique. The lifts were performed at normal and fast speed. The intra-subject lifting techniques were consistent when lifting the same loads. The moments predicted by the dynamic analysis and the static analysis were the same when holding weights in static postures. When performing the lifts, differences in the peak moments occurred between static and dynamic analyses. These differences were influenced by external load and by lifting speed. Taking the effect of the inertia of load into account in the static analysis resulted in an increase in the moment magnitude, but the predicted moment was still much less than in the dynamic analysis which yielded the largest moment magnitudes. The difference between dynamic and static analysis was greatest when lifting 50 N at fast speed; an 87% increase in L5/S1 moment and a 95% increase in hip moment was observed when replacing the pure static with a dynamic analysis. 相似文献
999.
G. A. Chukwu 《Journal of Petroleum Geology》1991,14(S1):211-220
The Agbada Formation is the major oil-producing formation in the Niger Delta Complex Basin, and overlies the Eocene Akata Formation, which is the principal hydrocarbon source rock. The Basin is deformed by large synsedimentaty faults, roll-over anticlines and diapirs; hydrocarbon accumulations are largely controlled by growth faults. A review of the influence of the stratigraphic and structural features on the migration and accumulation of hydrocarbons is given in this paper. 相似文献
1000.
Memory reallocation is used to construct a run-time data structure for fast/efficient storage of information during collection and analysis. The data structure presented uses dynamic memory but does not require the use of pointers to link nodes of information together. It allows for simple and efficient access to data via array indexing rather than through the use of lists or tree structures and it provides flexibility for competing storage requirements that are determined dynamically. The data structure is developed in the C programming language and a suite of ANSI standard C subroutines that make up a run-time data structure management system is provided. 相似文献