全文获取类型
收费全文 | 4176篇 |
免费 | 238篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 33篇 |
综合类 | 4篇 |
化学工业 | 836篇 |
金属工艺 | 52篇 |
机械仪表 | 48篇 |
建筑科学 | 318篇 |
矿业工程 | 9篇 |
能源动力 | 154篇 |
轻工业 | 786篇 |
水利工程 | 31篇 |
石油天然气 | 8篇 |
无线电 | 193篇 |
一般工业技术 | 782篇 |
冶金工业 | 457篇 |
原子能技术 | 14篇 |
自动化技术 | 694篇 |
出版年
2023年 | 41篇 |
2022年 | 24篇 |
2021年 | 61篇 |
2020年 | 55篇 |
2019年 | 79篇 |
2018年 | 157篇 |
2017年 | 158篇 |
2016年 | 157篇 |
2015年 | 147篇 |
2014年 | 164篇 |
2013年 | 299篇 |
2012年 | 230篇 |
2011年 | 282篇 |
2010年 | 205篇 |
2009年 | 159篇 |
2008年 | 208篇 |
2007年 | 212篇 |
2006年 | 206篇 |
2005年 | 127篇 |
2004年 | 114篇 |
2003年 | 133篇 |
2002年 | 111篇 |
2001年 | 86篇 |
2000年 | 73篇 |
1999年 | 72篇 |
1998年 | 151篇 |
1997年 | 98篇 |
1996年 | 76篇 |
1995年 | 55篇 |
1994年 | 45篇 |
1993年 | 41篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 22篇 |
1980年 | 25篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 15篇 |
排序方式: 共有4419条查询结果,搜索用时 15 毫秒
1.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
2.
Björn Täljsten 《International Journal of Fracture》1996,82(3):253-266
This paper presents the use of fracture mechanics for the plate bonding technique. Plates of steel or carbon-fibre reinforced
plastic are bonded with an epoxy adhesive to rectangular concrete prisms and loaded in shear up to failure, what is normally
known in fracture mechanics as mode II failure. In this special application a linear and a nonlinear approach are presented.
The nonlinear equation derived for a realistic shear-deformation curve can only be used for numerical calculations. However,
for simplified shear-deformation curves, the derived formula can be solved analytically. Results from tests, which are compared
with the theory, are also presented. 相似文献
3.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
4.
Summary Small oscillations of a rotating elasticum with a mass at the free end are investigated with Poincaré-Lindstedt series. It is shown that the mass moves on a figure-eight shaped curve in a direction determined by the sign of the angular velocity and hence that the Coriolis force influences the motion. 相似文献
5.
C Held P Hjemdahl N Rehnqvist NH Wallén I Bj?rkander SV Eriksson L Forslund B Wiman 《Canadian Metallurgical Quarterly》1997,95(10):2380-2386
BACKGROUND: Disturbed fibrinolytic function may influence the progression of coronary atherosclerosis and contribute to thrombotic cardiovascular (CV) events. METHODS AND RESULTS: In the Angina Prognosis Study in Stockholm (APSIS), patients with stable angina pectoris were studied prospectively during double-blind treatment with metoprolol or verapamil. Various measures of fibrinolytic function were studied in 631 (of 809) patients. During a median follow-up time of 3.2 years (2132 patient-years), 32 patients suffered a CV death, 21 had a nonfatal myocardial infarction (MI), and 77 underwent revascularization. Plasma levels of tissue plasminogen activator (TPA) activity and antigen (ag), plasminogen activator inhibitor (PAI-1) activity at test, and TPA responses to exercise were determined at baseline and after 1 month's treatment and were related to subsequent fatal and nonfatal CV events. Univariate Cox regression analysis revealed that elevated levels of TPA-ag at rest (P < .05), high PAI-1 activity (P < .05), and low TPA-ag responses to exercise (P < .05) were associated with increased risk of subsequent CV death. After adjustment for baseline risk factors, TPA-ag independently predicted CV death or MI. In addition, PAI-1 activity independently predicted CV death or MI in male patients. Verapamil treatment was associated with a 10% decrease of TPA-ag levels and metoprolol treatment with a 2% increase (P < .001 for treatment difference). CONCLUSIONS: Plasma TPA-ag levels at rest, and among male patients PAI-1 activity as well, independently predict subsequent CV death or MI in patients with stable angina pectoris. 相似文献
6.
7.
K Bj?ro JP Blomhoff E Schrumpf F Brosstad A Bergan T Egge 《Canadian Metallurgical Quarterly》1997,117(9):1274-1276
Budd Chiari syndrome (liver vein thrombosis) may be a diagnostic and therapeutic problem. On the basis of four different cases we review the major diagnostic and therapeutic principles involved. Imaging techniques are necessary in order to establish the diagnosis. Ultrasound examination with Duplex doppler is usually sufficient, but MR angiography is also useful. Treatment options are thrombolysis, surgery or liver transplantation. What treatment is selected will depend on the clinical situation and the prognosis. 相似文献
8.
The paper describes a new boundary-layer wind tunnel at the Danish Maritime Institute in Lyngby. The wind tunnel is of the open-circuit type and is integrated into a building raised for the purpose. The design was constrained by the need to provide a simulation of the atmospheric boundary layer (without thermal stratification) and alternatively a uniform flow without excessive turbulence.The wind tunnel has a working section of principal dimensions: length 20.8 m, width 2.6 m and height 1.8 m (adjustable from 1.8 to 2.3 m). The maximum wind speed in the working section when empty is about 26 m s?1.Data acquisition, analysis and instrumentation in relation to the new wind tunnel are discussed and, finally, an example of a simulated natural wind is presented. 相似文献
9.
K. Lefmann B. Lake G. Aeppli S.-W. Cheong N. B. Christensen K. N. Clausen S. Hayden T. E. Mason D.F. McMorrow H. A. Mook H. M. Rønnow H. Takagi 《Journal of Low Temperature Physics》2004,135(5-6):621-664
One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La2?xSrxCuO4, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx. 相似文献
10.
Cardiodilatin (CDD)/atrial natriuretic peptide (ANP) is a 28-amino acid peptide hormone known to be synthesized in the heart of a large number of different vertebrates. It plays an important role in the regulation of blood pressure and natriuresis/diuresis. Since the cardiovascular system of the horse has to meet the highest requirements concerning its physiological performance, we intended to characterize the cardiodilatin/atrial natriuretic peptide system of this species. By means of immunohistochemistry and immunoelectron microscopy, we precisely identified auricular cardiocytes as the loci of CDD/ANP synthesis. Using aortic smooth muscle relaxation assay and CDD/ANP-ELISA, we succeeded in isolating the biologically active prohormone. We subsequently cloned the equine cDNA of the CDD/ANP precursor protein and deduced its primary sequence. The entire precursor protein is in good agreement with the CDD/ANP prohormones of other mammals. The deduced theoretical average Mr of equine CDD/ANP-1-126 is 13,764, corresponding to the molecular weight of purified peptide determined by ESI-MS. Our findings suggest that equine CDD/ANP is produced in auricular cardiocytes and the predominant storage form of CDD/ANP in the auricle is the prohormone CDD/ANP-1-126. 相似文献