全文获取类型
收费全文 | 5469篇 |
免费 | 195篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 64篇 |
综合类 | 25篇 |
化学工业 | 1050篇 |
金属工艺 | 166篇 |
机械仪表 | 95篇 |
建筑科学 | 292篇 |
矿业工程 | 80篇 |
能源动力 | 63篇 |
轻工业 | 616篇 |
水利工程 | 95篇 |
石油天然气 | 2篇 |
无线电 | 324篇 |
一般工业技术 | 855篇 |
冶金工业 | 1222篇 |
原子能技术 | 26篇 |
自动化技术 | 695篇 |
出版年
2023年 | 37篇 |
2021年 | 64篇 |
2020年 | 45篇 |
2019年 | 42篇 |
2018年 | 85篇 |
2017年 | 84篇 |
2016年 | 145篇 |
2015年 | 120篇 |
2014年 | 142篇 |
2013年 | 201篇 |
2012年 | 264篇 |
2011年 | 267篇 |
2010年 | 167篇 |
2009年 | 166篇 |
2008年 | 213篇 |
2007年 | 179篇 |
2006年 | 219篇 |
2005年 | 115篇 |
2004年 | 103篇 |
2003年 | 104篇 |
2002年 | 114篇 |
2001年 | 77篇 |
2000年 | 69篇 |
1999年 | 97篇 |
1998年 | 383篇 |
1997年 | 213篇 |
1996年 | 178篇 |
1995年 | 107篇 |
1994年 | 124篇 |
1993年 | 110篇 |
1992年 | 44篇 |
1991年 | 65篇 |
1990年 | 51篇 |
1989年 | 68篇 |
1988年 | 37篇 |
1987年 | 52篇 |
1986年 | 44篇 |
1985年 | 58篇 |
1984年 | 55篇 |
1983年 | 50篇 |
1982年 | 64篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 55篇 |
1978年 | 40篇 |
1977年 | 56篇 |
1976年 | 102篇 |
1975年 | 45篇 |
1974年 | 39篇 |
1970年 | 32篇 |
排序方式: 共有5670条查询结果,搜索用时 31 毫秒
61.
S. Salar Behzadi Silvester Ölzant Reinhard Länger Christian Koban Frank M. Unger Helmut Viernstein 《European Food Research and Technology》2006,223(2):238-245
Inversion of sucrose is a stability problem particularly of candies with acidic taste that contain sucrose and small amounts of organic acids such as citric acid, since the free d-fructose produced by hydrolysis is hygroscopic. The following possibilities were investigated for preventing the hydrolysis of sucrose in tablets containing sucrose and citric acid: Adding various amounts of tri-sodium citrate to the formulation to neutralize the citric acid, (Hot) melt coating of citric acid and tri-sodium citrate with a vegetable fat at different coating ratios, variation of the ratio of coated citric acid and tri-sodium citrate in formulations, and compressing the formulations with different compression forces. After tablet processing and storage of tablets, the concentration of d-fructose was determined on the basis of enzymatic reactions. A response surface central composite design was used. The above-mentioned variations were chosen as independent variables and the amount of d-fructose was chosen as response variable. The lowest rates of inversion could be achieved by increasing the content of tri-sodium citrate and the ratio of coating material and decreasing the ratio of coated citric acid and tri-sodium citrate in the tablet formulations. The compression force had no significant effect on the inversion of sucrose. 相似文献
62.
The ionic conductivity of pressed pellets of dehydrated synthetic offretite, cancrinite and zeolite A, with various alkali metal ions, was determined by low-frequency impedance spectroscopy. Experiments were carried out in the frequency range 10 Hz–10 MHz at temperatures from 100–600°C. The conduction activation energies range between 55 kJ mol?1 (Na-zeolite A) and 108 kJ mol?1 (Li-cancrinite). The best conductivity value obtained was that of Na-zeolite A with 2.9×10?3Ω?1cm?1 at 600°C. 相似文献
63.
W Sch?nzer 《Canadian Metallurgical Quarterly》1996,42(7):1001-1020
Anabolic androgenic steroids (AAS) are misused to a high extent in sports by athletes to improve their physical performance. Sports federations consider the use of these drugs in sports as doping. The misuse of AAS is controlled by detection of the parent AAS (when excreted into urine) and (or) their metabolites in urine of athletes. I present a review of the metabolism of AAS. Testosterone is the principal androgenic steroid and its metabolism is compared with that of AAS. The review is divided into two parts: the general metabolism of AAS, which is separated into phase I and phase II metabolism and includes a systematic discussion of metabolic changes in the steroid molecule according to the regions (A-D rings), and the specific metabolism of AAS, which presents the metabolism of 26 AAS in humans. 相似文献
64.
65.
T Forst A Pfützner P Kann B Schehler R Lobmann H Sch?fer J Andreas A Bockisch J Beyer 《Canadian Metallurgical Quarterly》1995,12(10):874-879
Alterations in bone metabolism in diabetes mellitus is a topic of special interest. Bone blood flow is increased in the distal limb of diabetic patients, which is believed to increase osteoclastic activity. We measure bone mineral density using dual-photon absorptiometry in the distal lower limb, the femoral neck, and the lumbar spine in 41 IDDM patients and in 30 control persons. In the diabetic group there was a 10% reduction of bone mineral density in the femoral neck (p < 0.01) and a 12% reduction in the distal limb (p < 0.001) compared with the control group. No significant difference was found in the lumbar spine (p = 0.22). Our data yield incidence for peripheral osteopenia in IDDM-patients, independent of any systemic bone disease such as osteoporosis. A link between decreased bone mineral density and diabetic neuropathy has been observed for the femoral neck (p < 0.001), but not for the distal limb or axial skeleton. Whether there is a common aetiological link or a casual connection between diabetic neuropathy and bone mineral density has still to be determined. 相似文献
66.
Prof. Dr. rer. nat. Helmut F. Bauer 《Forschung im Ingenieurwesen》1985,51(5):133-140
The response due to time-fluctuating temperature distribution applied at the free surface of a viscoelastic cylindrical liquid
column with no axial dependency has been determined analytically. The amplitude of the radial- and angular velocity as well
as the free liquid surface elevation has been presented as a function of the “reduced” forcing frequency of the oscillatory
temperature and has numerically been evaluated for an angular temperature field proportional to sin 2φ. It was found, that
visco-elasticity as described by the Maxwell model has quite some influence upon the liquid behavior. It shows for larger
relaxation times besides the enlarged resonance peak additional peaks below and above resonance. This is particularly evident
inside the liquid column, indicating a more pronounced elastic behavior of the liquid. 相似文献
67.
68.
M Peschen H Grenz B Brand-Saberi M Bunaes JC Simon E Sch?pf W Vanscheidt 《Canadian Metallurgical Quarterly》1998,290(6):291-297
Growth factors produced by a variety of cells act as signalling peptides through specific cell surface receptor pathways. Functions such as cell proliferation, migration and differentiation have been assigned to each of them. Here, we report alterations of platelet-derived growth factor receptor alpha (PDGFR-alpha) and beta (PDGFR-beta) and vascular endothelial growth factor (VEGF) expression patterns in the progressive clinical stages of chronic venous insufficiency (CVI). A total of 30 punch biopsies were taken from patients with CVI, and VEGF and PDGFR were detected by indirect immunofluorescence and immunoperoxidase techniques. PDGFR-alpha and PDGFR-beta expression was strongly increased in endothelial cells of capillaries, pericapillary cells and connective tissue cells in the stroma of the skin of venous eczema and venous leg ulcer patients, and to a smaller extend in the dermis of those with lipodermatosclerosis. VEGF staining showed a similar expression pattern in the progressive CVI stages. However, staining of vessels in particular might simply reflect binding of VEGF, secreted by keratinocytes or fibroblasts, to its receptors. Growth factor and receptor expression in specimens from telangiectases and reticular veins, and from pigmented areas, resembled that of normal skin. We conclude that PDGFR-alpha, PDGFR-beta and VEGF play an important role in mediating inflammation and epithelial hyperproliferation in venous eczema, inducing connective tissue sclerosis in lipodermatosclerosis, and causing the reduced reepithelialization tendency in venous ulcers. We speculate that endothelial proliferation with chronic venous hypertension might be mediated by these growth factors. 相似文献
69.
70.
Light touch contact of a fingertip to a stationary surface provides orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip lead to sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, the coupling of postural sway to a moving contact surface was investigated in detail. Head, center of mass, and center of pressure displacement were measured as the contact surface moved rhythmically at 0.1, 0.2, 0.4, 0.6, and 0.8 Hz. Stimulus amplitude decreased with frequency to maintain peak velocity constant across frequency. Head and body sway were highly coherent with contact surface motion at all frequencies except 0.8 Hz, where a drop-off in coherence was observed. Mean frequency of head and body sway matched the driving frequency =0.4 Hz. At higher frequencies, non-1:1 coupling was evident. The phase of body sway relative to the touch plate averaged 20-30 degrees at 0.1-Hz drive and decreased approximately linearly to -130 degrees at 0.8-Hz drive. System gain was approximately 1 across frequency. The large phase lags observed cannot be accounted for with velocity coupling alone but indicate that body sway also was coupled to the position of the touch plate. Fitting of a linear second-order model to the data suggests that postural control parameters are not fixed but adapt to the moving frame of reference. Moreover, coupling to both position and velocity suggest that a spatial reference frame is defined by the somatosensory system. 相似文献