全文获取类型
收费全文 | 42261篇 |
免费 | 2399篇 |
国内免费 | 60篇 |
专业分类
电工技术 | 304篇 |
综合类 | 44篇 |
化学工业 | 7603篇 |
金属工艺 | 762篇 |
机械仪表 | 804篇 |
建筑科学 | 1299篇 |
矿业工程 | 89篇 |
能源动力 | 829篇 |
轻工业 | 6003篇 |
水利工程 | 382篇 |
石油天然气 | 177篇 |
武器工业 | 4篇 |
无线电 | 2397篇 |
一般工业技术 | 7405篇 |
冶金工业 | 10679篇 |
原子能技术 | 203篇 |
自动化技术 | 5736篇 |
出版年
2023年 | 359篇 |
2022年 | 351篇 |
2021年 | 903篇 |
2020年 | 757篇 |
2019年 | 694篇 |
2018年 | 1546篇 |
2017年 | 1547篇 |
2016年 | 1601篇 |
2015年 | 1130篇 |
2014年 | 1460篇 |
2013年 | 2801篇 |
2012年 | 2456篇 |
2011年 | 2245篇 |
2010年 | 1784篇 |
2009年 | 1584篇 |
2008年 | 1849篇 |
2007年 | 1638篇 |
2006年 | 1218篇 |
2005年 | 1019篇 |
2004年 | 953篇 |
2003年 | 834篇 |
2002年 | 751篇 |
2001年 | 487篇 |
2000年 | 483篇 |
1999年 | 642篇 |
1998年 | 3432篇 |
1997年 | 2062篇 |
1996年 | 1340篇 |
1995年 | 780篇 |
1994年 | 662篇 |
1993年 | 653篇 |
1992年 | 213篇 |
1991年 | 230篇 |
1990年 | 227篇 |
1989年 | 220篇 |
1988年 | 198篇 |
1987年 | 175篇 |
1986年 | 192篇 |
1985年 | 222篇 |
1984年 | 192篇 |
1983年 | 137篇 |
1982年 | 169篇 |
1981年 | 184篇 |
1980年 | 165篇 |
1979年 | 132篇 |
1978年 | 122篇 |
1977年 | 209篇 |
1976年 | 439篇 |
1975年 | 96篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
941.
S. N. Fisher A. M. Guénault R. P. Haley G. R. Pickett G. N. Plenderleith P. Skyba 《Journal of Low Temperature Physics》1998,113(5-6):651-659
We present preliminary measurements of the dynamics of a moving A-B phase interface in superfluid
3
He at temperatures below 0.2T
c
We initially stabilise the interface at low temperatures with a shaped magnetic field. We can then move the interface in a controlled manner by applying small additional time-dependent fields. The interface is created inside a quasiparticle radiator consisting of a cylindrical chamber in weak thermal contact with the refrigerant. Vibrating wire resonators inside the radiator allow us to monitor the temperature of the superfluid and to infer the heat generated by the interface motion. When we oscillate the interface at low frequencies, we measure spectacular oscillatory swings of the liquid temperature arising from the enormous change in the low lying density of states as the volume of the A-phase superfluid is alternately compressed and expanded. We have also observed hysteresis in the transition as a function of magnetic field. In particular, we observe a small history-dependent super-magnetisation of the B-phase prior to A-phase nucleation in the experimental chamber. When the system is in the metastable super-magnetised state we are able to observe a higher nucleation probability of the A-phase when the cryostat is exposed to neutrons. 相似文献
942.
We report preliminary results of the first heat capacity measurements on atomically layered
3
He –
4
He mixture films adsorbed on the surface of graphite. The
4
He film consists of two solid and two superfluid atomic layers. The heat capacity has been investigated over the range 1 – 70mK as a function of the surface density of
3
He atoms added to the film. At coveragesn3
< 4nm
–2
, the
3He forms a uniform two dimensional Fermi system. The coverage dependence of the linear coefficient of the heat capacity, , allows a determination of the hydrodynamic effective mass and
. At higher coverages a step-like increase in is observed, interpreted as the formation of a second two dimensional Fermi system. 相似文献
943.
R.M. Bowley A.D. Armour J. Nyéki B.P. Cowan J. Saunders 《Journal of Low Temperature Physics》1998,113(3-4):399-404
We analyse recent observations, using a torsional oscillator, of the superfluid transition of a fluid
4
He bilayer, within the framework of a modified dynamic theory of the Kosterlitz-Thouless transition. A parametric plot of the real and imaginary parts of the complex superfluid density, determined from the measured period shift and dissipation, achieves a high degree of collapse of the experimental data at different coverages onto a universal curve. This is compared with the result of the recent theory. 相似文献
944.
945.
Holmér AK 《Applied optics》1996,35(15):2614-2618
A kinoform is used to split the beam of a Nd:YAG laser into six beams. The laser beams are, by means of optical fibers and collimating-focusing optics, transferred to the surface to be machined. Thus multiple grooves can be machined simultaneously. For demonstration, 100-μm-wide grooves are simultaneously machined into a SnO(2) thin film deposited on a glass substrate. The resulting grooves are well isolated. This result shows that the technique could be used, for example, in solar cell manufacturing to increase the efficiency of laser scribing. 相似文献
946.
947.
M. -H. Julien M. Horvatić C. Berthier P. Ségransan 《Journal of Low Temperature Physics》1996,105(3-4):371-376
We present a63Cu NMR study of HgBa2Ca2Cu3O8+ underdoped single crystals with Tc 115 K. While the uniform spin susceptibility decreases below To 370 K, relaxation rate measurements demonstrate the opening of a spingap at Q = (, ) below T* 230 K, the highest temperature reported so far. The characteristic energy of spin fluctuations is shown to be higher than in underdoped YBa2Cu3O7–, and the analysis of the quadrupole and hyperfine couplings suggests that the in-plane Cu-O hybridization is also stronger. The T-dependence of T1 is the same in the three CuO2 planes which seems hardly compatible with the pure interlayer spin-pairing picture. 相似文献
948.
Burestedt E Narvaez A Ruzgas T Gorton L Emnéus J Domínguez E Marko-Varga G 《Analytical chemistry》1996,68(9):1605-1611
The response currents obtained for tyrosinase-modified Teflon/graphite, carbon paste, and solid graphite electrodes in the presence of catechol are analyzed primarily using rotating disk electrode experiments. The rate-limiting steps, such as the electrochemical reduction of o-quinones and the enzymatic reduction of oxygen as well as the enzymatic oxidation of catechol, are theoretically considered and experimentally demonstrated for the different electrode configurations. 相似文献
949.
JA Ortu?o-Cortés L Quintana-Tomás A García-García 《Canadian Metallurgical Quarterly》1996,19(2):47-51
1.5% Capsaicin (Cap) or Vehicle was respectively used to treat the right or left sciatic nerve in 20 Sprague-Dawley rats. On the seventh day, the 20 rats were at random divided into electroacupuncture (EA) group and non-EA group, the spinal cord corresponding to the afferent segments of sciatic nerve was taken out for observing the changes of acetylcholinesterase (AChE) activity and [3H]-quinuelidinylbenzylate (QNB) binding sites in the spinal dorsal horn (SDH). The results were as follows: (1) EA "Huantiao" could enhance AChE activity in the SDH and decrease [3H]-QNB binding sites; (2) Cap treating sciatice nerve could weaken AChE activity in the SDH and merease [3H]-QNB binding sites; (3) Cap treatment could inhibit or partially inhibit the actions of EA as above. The results indicated that ACh participated in the primary afferent of acupuncture information and might exist in Cap-sensitive neurons. 相似文献
950.
B Frennby G Sterner T Almén CM Chai BA J?nsson S M?nsson 《Canadian Metallurgical Quarterly》1996,3(8):651-659
RATIONALE AND OBJECTIVES: We wanted to improve determination of the glomerular filtration rate (GFR) with plasma clearance techniques because the alternative-renal clearance techniques-may involve inaccurate urine sampling or risk of urinary tract infection when bladder catheterization becomes necessary. Therefore, we compared the renal and plasma clearances of iohexol and chromium-51-ethylenediaminetetraacetic acid (51Cr-EDTA), as well as endogenous creatinine clearance, in 19 normal pigs using different techniques. METHODS: After an intravenous bolus injection of the GFR markers, 16 plasma samples were used to plot the marker concentrations versus time for 4.5 hr. Urine was collected during nine 30-min periods. Plasma clearance was calculated by dividing the dose of marker with the area under the plasma concentration curve (AUC) from the time of injection to infinity using one-compartment (ClAUC-slope) and three-compartment (ClAUC-3comp) models. The renal clearance was calculated by dividing the amount of marker excreted in the urine in a period with the AUC in the same period. This AUC was determined by integrating the total area in the period (Clren adv)--our reference method representing the "true" GFR--or by using the arithmetic mean of the plasma concentrations of the marker at the beginning and end of the urine collection period (Clren simple). Creatinine clearance was determined according to Clren simple. RESULTS: Renal clearances of iohexol and 51Cr-EDTA were significantly higher than creatinine clearance (P = .0002). There was no significant difference between the renal clearances of iohexol and 51Cr-EDTA or between their plasma clearances. The two mathematical methods of calculating the renal clearance of iohexol were highly correlated (rs = .99), as were the two methods of calculating its plasma clearance (rs = .95). Because of the extrarenal clearance of the markers, the plasma clearance methods for iohexol and 51Cr-EDTA always overestimated the true GFR. ClAUC-3comp was the method closest to the true GFR. For iohexol, the median overestimation of the GFR was higher with ClAUC-slope when early plasma samples (30-120 min) after injection of the marker were used (5.5 ml.min-1.10 kg-1) than when late samples (180-270 min) were used (4.0 ml.min-1.10 kg-1). After subtracting the median extrarenal clearances of iohexol and 51Cr-EDTA (previously determined in nephrectomized pigs) from their plasma clearances (ClAUC-3comp), the median overestimation of the true GFR was reduced from 2.0 to 1.1 ml.min-1.10 kg-1 with iohexol and from 2.1 to 1.3 ml.min-1.10 kg-1 with 51Cr-EDTA. CONCLUSION: GFR determination with plasma clearance techniques can be improved in three- and one-compartment models by taking late plasma samples and by subtracting the extrarenal plasma clearance of the species. One-compartment models can be improved by determining a correction formula in the species for the early parts of the decay curve of the plasma concentration of the marker. 相似文献