全文获取类型
收费全文 | 4322篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 44篇 |
综合类 | 2篇 |
化学工业 | 402篇 |
金属工艺 | 82篇 |
机械仪表 | 168篇 |
建筑科学 | 56篇 |
矿业工程 | 3篇 |
能源动力 | 112篇 |
轻工业 | 83篇 |
水利工程 | 26篇 |
石油天然气 | 8篇 |
无线电 | 511篇 |
一般工业技术 | 485篇 |
冶金工业 | 1860篇 |
原子能技术 | 19篇 |
自动化技术 | 525篇 |
出版年
2023年 | 26篇 |
2022年 | 57篇 |
2021年 | 57篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 66篇 |
2017年 | 57篇 |
2016年 | 81篇 |
2015年 | 54篇 |
2014年 | 65篇 |
2013年 | 171篇 |
2012年 | 88篇 |
2011年 | 129篇 |
2010年 | 106篇 |
2009年 | 99篇 |
2008年 | 102篇 |
2007年 | 96篇 |
2006年 | 90篇 |
2005年 | 80篇 |
2004年 | 59篇 |
2003年 | 60篇 |
2002年 | 66篇 |
2001年 | 55篇 |
2000年 | 63篇 |
1999年 | 107篇 |
1998年 | 632篇 |
1997年 | 344篇 |
1996年 | 255篇 |
1995年 | 139篇 |
1994年 | 125篇 |
1993年 | 155篇 |
1992年 | 60篇 |
1991年 | 54篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 48篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 46篇 |
1984年 | 23篇 |
1983年 | 34篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 34篇 |
1978年 | 17篇 |
1977年 | 53篇 |
1976年 | 74篇 |
1975年 | 14篇 |
1973年 | 11篇 |
排序方式: 共有4386条查询结果,搜索用时 15 毫秒
861.
D. Patidar R. Sharma N. Jain T. P. Sharma N. S. Saxena 《Bulletin of Materials Science》2006,29(1):21-24
Chemical method has been used to prepare cadmium sulphide by using cadmium, hydrochloric acid and H2S. The reflection spectra of covered and uncovered sintered films of CdS have been recorded by ‘Hitachi spectrophotometer’
over the wavelength range 300–700 nm. The energy band gaps of these films have been calculated from reflection spectra. It
is found that the energy band gap of both films is same as 2.41 eV. It is indicated that energy band gap of these films does
not change. This value of band gap is in good agreement with the value reported by other workers. The measurement of photocurrent
has also been carried out using Keithley High Resistance meter/ Electrometer. This film shows the high photosensitivity and
high photocurrent decay. Thus so obtained films are suitable for fabrication of photo detectors and solar cells. 相似文献
862.
P K Khare S K Paliwal R Kuraria H L Vishwakarma Ashish Verma S K Jain 《Bulletin of Materials Science》1998,21(2):139-147
A detailed study of electrical conduction mechanism in bimetallized ferrocene-doped polyvinyl pyrrolidone films was carried
out. The measurements were carried out on films of about 20 μm thick, in the field range of (2.0–8.0) x 104 V/cm at temperatures ranging from 363 to 423 K. An investigation of the effect of impurity such as ferrocene in the polymer
matrix was undertaken. Lowering of activation energy and increase in current due to doping were observed. The results showed
that the charge carriers were generated by field-assisted lowering of coulombic barriers at the traps and were conducted through
the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari modified Poole-Frenkel mechanism.
The dependence of current and activation energy on the ferrocene concentration is explained on the basis of charge transfer
type of interaction between dopant and polymeric material. 相似文献
863.
Thermally-stimulated spontaneous currents from metal-iodine doped polyvinyl pyrrolidone-metal system
A study of the spontaneous response currents from the metal-iodine doped polyvinyl pyrrolidone-metal (MPM) systems, on thermal
stimulation at a constant rate, has been made with similar (Al-Al, Ag-Ag and Au-Au) and dissimilar (Al-Cu/Ag/Ni/PbZn) electrode
systems. Thermograms of spontaneous current emission of iodine-doped PVP films exhibit two maxima around 90 ± 10°C and 130–160°C
in the first heating run, whereas with the second heating run a single peak is found around 140–170°C. The magnitude and direction
of current depend on the choice and combination of electrode materials. The position of the current peak in the thermal spectrum
shifts with different heating run. A temperature dependence of open-circuit voltage (OCV) is also reported and it was found
that OCV varied linearly with the difference in electrode work functions. The active centres of PVP are the carbonyl group
of double-bond tertiary nitrogen atom (> N-C=O), and thus the charge transfer complexes are formed with iodine in PVP. The
spontaneously-generated current is discussed in terms of weak complex formation with the water molecules and the liberation
of different types of charges. 相似文献
864.
M. Jain 《Journal of Materials Science》1992,27(2):399-407
The evolution of dislocation structure during room-temperature, uniaxial, low-cycle fatigue of an overaged Al-Mg-Si alloy is studied. Ageing at 450°C produces a fine dispersion of Mg2Si precipitate particles. During fully reversed strain-controlled cyclic tests, these fine particles restrict deformation to local regions and a stable dislocation substructure is developed early in fatigue life. Substructural observations of hardening and saturation by transmission electron microscopy reveal extensive dislocation band formation on Mg2Si precipitate rods. Various microstructural features such as configuration of tangled dislocations, dislocation cells, precipitate morphologies, sizes, precipitate-free zones, etc., have been examined during cyclic hardening and saturation. The results have been analysed in terms of kinematic and isotropictype microstructural mechanisms. 相似文献
865.
L. H. Greene M. Aprili M. Covington E. Badica D. E. Pugel H. Aubin Y.-M. Xia M. B. Salamon Sha Jain D. G. Hinks 《Journal of Superconductivity》2000,13(5):703-708
An emphasis on reliable materials growth and development of new fabrication techniques has allowed us to investigate the electronic structure of high-temperature superconductors by planar quasiparticle tunneling and electron paramagnetic resonance (EPR) spectroscopies. The quasiparticle (QP) density of states (DoS) is investigated by tunneling into oriented thin films of Y1Ba2Cu3O7 (YBCO) and single crystals of Ba2Sr2Ca1Cu2O8 (BSCCO). Data are obtained as a function of crystallographic orientation, temperature, doping, damage, and applied magnetic field. These data demonstrate that the observed zero-bias conductance peak (ZBCP) is composed of Andreev bound states (ABS) which intrinsically form at a symmetry-breaking interface of an unconventional superconductor, for example, a (110)-surface of d-wave YBCO. Tunneling into doped or ion-damaged YBCO provides a measure of the QP scattering rate below T
c. An applied field causes Doppler shift of the ABS, arising from the scalar product between the QP velocity and the superfluid momentum, v
F·P
s, observed as a splitting in the ZBCP. Magnetic hysteresis of the splitting is consistent with the effects of strong vortex pinning near the interface. The directional field dependence shows that the ABS is highly anisotropic in its transport. These results, plus in-plane crystallographic orientational dependence on single-crystal BSCCO, demonstrate the d-wave symmetry of this superconductor. Below 8 K and in zero applied field, the ZBCP splits, indicating a transition into a superconducting state with spontaneously broken time-reversal symmetry (BTRS). EPR experiments are used to detect directly the spontaneous formation of the magnetic moments in the BTRS state. 相似文献
866.
Development of a Liposome Based Contraceptive System for Intravaginal Administration of Progesterone 总被引:2,自引:0,他引:2
Sanjay K. Jain Ranjit Singh Balram Sahu 《Drug development and industrial pharmacy》1997,23(8):827-830
Progesterone bearing liposomes were prepared by the cast film method and characterized for various physical attributes. The liposomes could encapsulate nearly 98% of the drug. The progesterone bearing liposomes were incorporated into polyacrylamide gel and the drug content was determined. The in vitro drug dqfusion across she-goat vaginal membrane from the liposomal formulation was found to follow near zero order kinetics. The progestational activity of liposomal and control gel was assessed by monitoring the effect on the formation of corpora lutea. It was observed that both the formulations inhibit the formation of corpora lutea and thus, exhibited progestationul activity but the efsect of liposomal preparation was found to be greater and prolonged as compare to control gel. 相似文献
867.
868.
BH Mulsant CF Reynolds MK Shear RA Sweet M Miller 《Canadian Metallurgical Quarterly》1996,2(5):242-247
We examined the prevalence and correlates of comorbid anxiety disorders in two groups of older depressed patients assessed at the University of Pittsburgh. A total of 336 older outpatients and inpatients with major depression were comprehensively evaluated with several instruments including the Hamilton Depression Rating Scale, and either the SADS-L or the SCID for DSM-III-R. These patients presented with major depression, associated with a wide range of functional, cognitive, and medical impairment. One-third to one-half of them also presented with severe symptomatic anxiety. However, only a small proportion (less than 5%) met diagnostic criteria for lifetime or current panic, obsessive-compulsive, or phobic disorders. At baseline, lifetime comorbid anxiety disorders were associated with a higher rate of alcoholism and higher symptomatic anxiety. Lifetime comorbid anxiety disorders did not affect the rate of response of depression, but they were associated with a higher use of benzodiazepines and a 50% increase in the time outpatients needed to respond. These findings suggest that, even in psychiatric patients with major depression, the lifetime prevalence of anxiety disorders is lower in late life, but that it has important clinical and therapeutic implications. 相似文献
869.
870.
JL Larson MK Covey CA Vitalo CG Alex M Patel MJ Kim 《Canadian Metallurgical Quarterly》1996,45(4):203-210
Validity and test-retest liability of the 12-minute distance (12MD) walk, a measure of functional status, were examined in patients with chronic obstructive pulmonary disease. Four tests were administered at weekly intervals. Performance increased (p < .01) over the first three tests. Test-retest reliability was r34 = .98 (df = 46) for tests 3 and 4. The 12MD walk correlated with the Sickness Impact Profile, Physical Dimension (r = -.45); forced expiratory volume in 1 second % predicted ( r = .40); maximal inspiratory pressure (PImax) (r = .52); and exercise-related breathlessness (r = -.49). Exercise-related breathlessness and PImax accounted for 42% of the variance. The validity and reliability of the 12MD walk were supported. 相似文献