全文获取类型
收费全文 | 2652篇 |
免费 | 104篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 62篇 |
综合类 | 12篇 |
化学工业 | 404篇 |
金属工艺 | 121篇 |
机械仪表 | 80篇 |
建筑科学 | 123篇 |
矿业工程 | 13篇 |
能源动力 | 57篇 |
轻工业 | 193篇 |
水利工程 | 26篇 |
石油天然气 | 29篇 |
无线电 | 249篇 |
一般工业技术 | 353篇 |
冶金工业 | 709篇 |
原子能技术 | 82篇 |
自动化技术 | 260篇 |
出版年
2022年 | 20篇 |
2021年 | 38篇 |
2020年 | 17篇 |
2019年 | 32篇 |
2018年 | 42篇 |
2017年 | 37篇 |
2016年 | 38篇 |
2015年 | 49篇 |
2014年 | 43篇 |
2013年 | 130篇 |
2012年 | 69篇 |
2011年 | 119篇 |
2010年 | 76篇 |
2009年 | 84篇 |
2008年 | 106篇 |
2007年 | 110篇 |
2006年 | 115篇 |
2005年 | 78篇 |
2004年 | 80篇 |
2003年 | 71篇 |
2002年 | 57篇 |
2001年 | 38篇 |
2000年 | 44篇 |
1999年 | 54篇 |
1998年 | 205篇 |
1997年 | 115篇 |
1996年 | 71篇 |
1995年 | 55篇 |
1994年 | 62篇 |
1993年 | 53篇 |
1992年 | 43篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 33篇 |
1988年 | 38篇 |
1987年 | 41篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 27篇 |
1978年 | 22篇 |
1977年 | 37篇 |
1976年 | 44篇 |
1975年 | 14篇 |
1974年 | 18篇 |
1973年 | 13篇 |
排序方式: 共有2773条查询结果,搜索用时 31 毫秒
21.
This paper presents the results of an experimental study of semiintegral bridge abutments. Primary interests were to investigate (1) potential problems with the particular detail tested; (2) rotational characteristics of the semiintegral abutments; and (3) ability of the specimens to withstand cyclic loading induced by temperature variations during the expected life of the bridge. Sixteen experiments were conducted on three large-scale specimens. The results of the tests have shown that semiintegral abutments can significantly reduce the moments transferred from the superstructure to the foundation piles. Test results have also shown that semiintegral abutments can tolerate the number of displacement cycles that a bridge will experience during the course of its economic life. 相似文献
22.
The elderly may be considered a group at risk with regard to mental health and the mental health system. Aging women experience a double jeopardy arising from social, economic, and psychological conditions surrounding age and gender—in particular, poverty, widowhood, and the dynamics of family caregiving. This double jeopardy translates into a vulnerability within the mental health system that is seen in issues of service utilization, therapist–client interactions, and diagnosis, most notably in diagnoses of Alzheimer's disease, alcohol and drug misuse, and depression. The failure of the mental health system to consider elderly individuals as psychological survivors further suggests an implicit assumption that mental decline is a normative part of the aging process. Recommendations for change include addressing gender and age interactions in mental health policy and in psychological research, training, and practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
23.
Markham B.L. Thome K.J. Barsi J.A. Kaita E. Helder D.L. Barker J.L. Scaramuzza P.L. 《Geoscience and Remote Sensing, IEEE Transactions on》2004,42(12):2810-2820
Launched in April 1999, the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument is in its sixth year of operation. The ETM+ instrument has been the most stable of any of the Landsat instruments. To date, the best onboard calibration source for the reflective bands has been the Full Aperture Solar Calibrator, a solar-diffuser-based system, which has indicated changes of between 1% to 2% per year in the ETM+ gain for bands 1-4 and 8 and less than 0.5%/year for bands 5 and 7. However, most of this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on vicarious calibrations and observations of "invariant sites", hyperarid sites of the Sahara and Arabia. Weighted average slopes determined from these datasets suggest changes of 0.0% to 0.4% per year for bands 1-4 and 8 and 0.4% to 0.5% per year for bands 5 and 7. Absolute calibration of the reflective bands of the ETM+ is consistent with vicarious observations and other sensors generally at the 5% level, though there appear to be some systematic differences. 相似文献
24.
John R. Barker 《Journal of Computational Electronics》2003,2(2-4):153-161
The breakdown of the Kohn-Luttinger ansatz for self-averaging of impurity scattering is shown to occur in small finite semiconductor device structures when less than 1000 impurities are in the device volume. As a consequence the standard non-equilibrium Green function formalism for quantum transport is invalid. Instead, a non-self-averaged propagator formalism is proposed based on a T-matrix model for non-asymptotic finite-cluster scattering. The formalism is illustrated by a study of the charge density and current density profiles resulting from coherent flow through a finite atomistic device containing a small number of impurities. The flow typically separates into open streamlines and a set of blocking vortices. 相似文献
25.
SL Barker MJ McNicholas D Kader P Abdon T Adalberth D McGurty DI Rowley CM Walker 《Canadian Metallurgical Quarterly》1998,43(6):400-403
A cohort of 39 patients (28 male, 11 female) that had undergone total meniscectomy as adolescents (mean age 16 years) underwent FISP 3D Magnetic Resonance Imaging at a mean follow up of 30 years. The presence of meniscal tissue was assessed by two independent observers blinded to the operation details. The volume of any meniscal tissue present was calculated. A posterior horn remnant was seen in 57% of medial and 45% of lateral meniscectomy cases. The mean volume of an operated medial meniscal remnant was 0.29 mL compared with a mean volume of 1.15 mL for an intact medial meniscus. The mean volume of an operated lateral meniscal remnant was 0.30 mL compared with 1.07 mL for an intact lateral meniscus. We have shown that the incidence of incomplete excision of the posterior horn is more common after total medial meniscectomy, and that at a mean follow up of 30 years there is no convincing in vivo MRI evidence of long-term meniscal regeneration. 相似文献
26.
The IRDA IrLAP protocol is analytically modelled. Throughput performance is examined with bit error rate, window size, and turnaround times. It is shown that for the proposed 16 Mbit/s and 127 frame maximum window size extension the link BER quality becomes critical if maximum throughput is to be achieved. A window size of 60 is less sensitive to bit error rate variations. Reducing the minimum turnaround time is always beneficial 相似文献
27.
MH Edwards S Pierangeli X Liu JH Barker G Anderson EN Harris 《Canadian Metallurgical Quarterly》1997,96(12):4380-4384
BACKGROUND: Previous studies have demonstrated that human monoclonal and polyclonal anticardiolipin antibodies have thrombogenic properties in vivo. Using such a model in which these antibodies have been shown to increase both the size of an induced thrombus and the duration of time in which such a clot lasts, we investigated whether hydroxychloroquine alters the dynamics of such thrombus formation. METHODS AND RESULTS: Three groups of nine mice were injected with purified immunoglobulin G (IgG) from a patient with the antiphospholipid syndrome (IgG-APS) and then fed with hydroxychloroquine at various doses (100, 6, and 3 mg/kg body wt). Three control groups of mice were also studied, including mice injected with IgG-APS and then fed with placebo, as well as two other groups injected with IgG from normal human serum and fed either hydroxychloroquine or placebo. A standardized thrombogenic injury was subsequently induced in the femoral vein of each mouse and the area (size) of thrombus measured as well as the total period of time that thrombus was present. Mice treated with hydroxychloroquine and IgG-APS showed significantly smaller thrombi that persisted for a shorter period of time compared with animals treated with IgG-APS and placebo. CONCLUSIONS: Hydroxychloroquine significantly diminished both thrombus size and total time of thrombus formation in mice previously injected with IgG-APS. 相似文献
28.
S.A. Brindhaban P.H. Barker M.J. Keeling W.B. Wood 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1994,340(3):436-441
The energies of resonances in the 27Al(p, γ) reaction at 992 and 1317 keV and of the threshold of the 27Al(p, n) reaction at 5804 keV have been measured accurately with respect to a 1 V standard. Both calibration energies and energies suitable for Q-value calculations are given. Corrections are made for the effects of the energy distribution of the proton beam, of nonuniform energy loss of the protons in the target and of ionisation of the target atoms. 相似文献
29.
A multiparameter wearable physiologic monitoring system for space and terrestrial applications. 总被引:4,自引:0,他引:4
Carsten W Mundt Kevin N Montgomery Usen E Udoh Valerie N Barker Guillaume C Thonier Arnaud M Tellier Robert D Ricks Robert B Darling Yvonne D Cagle Nathalie A Cabrol Stephen J Ruoss Judith L Swain John W Hines Gregory T A Kovacs 《IEEE transactions on information technology in biomedicine》2005,9(3):382-391
A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described. 相似文献
30.
Impacts of spectral band difference effects on radiometric cross-calibration between satellite sensors in the solar-reflective spectral domain 总被引:2,自引:0,他引:2
In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on an investigation of radiometric calibration errors due to differences in spectral response functions between satellite sensors when attempting cross-calibration based on near-simultaneous imaging of common ground targets in analogous spectral bands, a commonly used post-launch calibration methodology. Twenty Earth observation imaging sensors (including coarser and higher spatial resolution sensors) were considered, using the Landsat solar reflective spectral domain as a framework. Scene content was simulated using spectra for four ground target types (Railroad Valley Playa, snow, sand and rangeland), together with various combinations of atmospheric states and illumination geometries. Results were obtained as a function of ground target type, satellite sensor comparison, spectral region, and scene content. Overall, if spectral band difference effects (SBDEs) are not taken into account, the Railroad Valley Playa site is a “good” ground target for cross calibration between most but not all satellite sensors in most but not all spectral regions investigated. “Good” is defined as SBDEs within ± 3%. The other three ground target types considered (snow, sand and rangeland) proved to be more sensitive to uncorrected SBDEs than the RVPN site overall. The spectral characteristics of the scene content (solar irradiance, surface reflectance and atmosphere) are examined in detail to clarify why spectral difference effects arise and why they can be significant when comparing different imaging sensor systems. Atmospheric gas absorption features are identified as being the main source of spectral variability in most spectral regions. The paper concludes with recommendations on spectral data and tools that would facilitate cross-calibration between multiple satellite sensors. 相似文献