全文获取类型
收费全文 | 705篇 |
免费 | 16篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 7篇 |
综合类 | 1篇 |
化学工业 | 138篇 |
金属工艺 | 23篇 |
机械仪表 | 7篇 |
建筑科学 | 17篇 |
矿业工程 | 2篇 |
能源动力 | 26篇 |
轻工业 | 36篇 |
水利工程 | 6篇 |
石油天然气 | 2篇 |
无线电 | 115篇 |
一般工业技术 | 157篇 |
冶金工业 | 91篇 |
原子能技术 | 26篇 |
自动化技术 | 70篇 |
出版年
2023年 | 5篇 |
2022年 | 24篇 |
2021年 | 21篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 17篇 |
2017年 | 29篇 |
2016年 | 24篇 |
2015年 | 11篇 |
2014年 | 27篇 |
2013年 | 50篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 31篇 |
2007年 | 30篇 |
2006年 | 27篇 |
2005年 | 16篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1957年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有724条查询结果,搜索用时 15 毫秒
621.
Precursors to MFe2O4 [spinels ferrites; where M = Ni(II), Co(II) and Zn(II)] have been prepared by the evaporation of polyvinyl alcohol added
mixed metal nitratesolution, in presence and absence of urea. Theprecursor materials have low ignition temperature and are spontaneously combustible at low temperatures (250°C to 400°C). The heat liberated
through the process is sufficient for the crystallization of the desired ferrite phase. The urea added process resulted in
finer, superparamagnetic particles (12–17 nm) compared to the process without urea (particle size 25–30 nm). The ultrafine
ferrite powders obtained have been characterized by X-ray powder diffraction (XRD), thermal gravimetry (TG), differential
scanning calorimetry (DSC), infrared spectroscopy (IR), transmission electron microscopy (TEM) and room temperature magnetic
measurement studies. 相似文献
622.
GL James JL Goldstein RK Pathak RG Anderson MS Brown 《Canadian Metallurgical Quarterly》1994,269(19):14182-14190
CAAX farnesyltransferase attaches a farnesyl group to proteins that terminate in the sequence CAAX, where C is cysteine, A is an aliphatic amino acid, and X is typically methionine or serine. A limited number of substrates for the CAAX farnesyltransferase have been identified in cultured cells. These include p21ras proteins and the nuclear lamins A and B. We describe here the use of a CAAX farnesyltransferase inhibitor, together with a hamster cell line that exhibits efficient uptake of [3H]mevalonate, as a means of identifying novel farnesylated proteins. One candidate protein was purified and its attached prenyl group identified as farnesyl. The predicted amino acid sequence of this protein, deduced from a cloned cDNA, terminates with the tetrapeptide Cys-Leu-Ile-Met, which conforms to the consensus sequence for recognition by farnesyltransferase. This farnesylated protein, designated PxF, is localized to the outer surface of peroxisomes as determined by indirect immunofluorescence and electron microscopy. 相似文献
623.
Androgen-repressed phenotype in human prostate cancer 总被引:1,自引:0,他引:1
HY Zhau SM Chang BQ Chen Y Wang H Zhang C Kao QA Sang SJ Pathak LW Chung 《Canadian Metallurgical Quarterly》1996,93(26):15152-15157
An androgen-repressed human prostate cancer cell line, ARCaP, was established and characterized. This cell line was derived from the ascites fluid of a patient with advanced metastatic disease. In contrast to the behavior of androgen-dependent LNCaP and its androgen-independent C4-2 subline, androgen and estrogen suppress the growth of ARCaP cells in a dose-dependent manner in vivo and in vitro. ARCaP is tumorigenic and highly metastatic. It metastasizes to the lymph node, lung, pancreas, liver, kidney, and bone, and forms ascites fluid in athymic hosts. ARCaP cells express low levels of androgen receptor mRNA and prostate-specific antigen mRNA and protein. Immunohistochemical staining shows that ARCaP cells stain intensely for epidermal growth factor receptor, c-erb B2/neu, and c-erb B3. Staining is negative for chromogranin A and positive for bombesin, serotonin, neuron-specific enolase, and the c-met protooncogene (a hepatic growth factor/scatter factor receptor). ARCaP cells also secrete high levels of gelatinase A and B and some stromelysin, which suggests that this cell line may contain markers representing invasive adenocarcinoma with selective neuronendocrine phenotypes. Along with its repression of growth, androgen is also found to repress the expression of prostate-specific antigen in ARCaP cells as detected by a prostate-specific antigen promoter-beta-galactosidase reporter assay. Our results suggest that the androgen-repressed state may be central to prostate cancer progression and that advanced prostate cancer can progress from an androgen-independent to an androgen-repressed state. 相似文献
624.
Yogesh Rathi Namrata Vaswani Allen Tannenbaum 《IEEE transactions on image processing》2007,16(5):1370-1382
Tracking deforming objects involves estimating the global motion of the object and its local deformations as functions of time. Tracking algorithms using Kalman filters or particle filters (PFs) have been proposed for tracking such objects, but these have limitations due to the lack of dynamic shape information. In this paper, we propose a novel method based on employing a locally linear embedding in order to incorporate dynamic shape information into the particle filtering framework for tracking highly deformable objects in the presence of noise and clutter. The PF also models image statistics such as mean and variance of the given data which can be useful in obtaining proper separation of object and background. 相似文献
625.
Multifunctional ligand 5-cyano-6-(-4-pyridyl)-2-thiouracil (L) was prepared and allowed to react withtrans [Co(en)2Cl2]+Cl‡ resulting into [Co(en)2LCl]2+.2Cl- which upon further reaction with equimolar ratio of ligand [L] gave the complex [Co(en)2L2]3+.3Cl−. These metal complexes were then separately reacted with thymine and adenine bases. Complexes thus prepared after characterization
by their elemental analysis, FAB mass and spectral (IR,1 HNMR, UV-visible) data were studied for their powder X-ray diffraction and optical microscopic characteristics. 相似文献
626.
The existence of array guided surface waves (AGSWs) on partially finite (finite /spl times/ infinite) array of dipoles in air have been demonstrated earlier; the work in this paper extends this study to fully finite (finite /spl times/ finite) planar arrays both in air and on a grounded material slab of infinite extent. Effects of AGSWs on scattering characteristics are examined and a ray interpretation is provided for the edge/corner excitation of AGSWs and conventional substrate surface waves. 相似文献
627.
J. Boucart R. Pathak Dongxu Zhang M. Beaudoin P. Kner Decai Sun R.J. Stone R.F. Nabiev W. Yuen 《Photonics Technology Letters, IEEE》2003,15(9):1186-1188
In this letter, we present the first demonstration of a long wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) using an InP-InAlGaAs distributed Bragg reflector (DBR). The use of such a DBR improves the thermal resistance of the VCSEL while keeping the growth process simple. The devices show operation to temperatures greater than 75/spl deg/C, and single-mode devices emit powers as high as 0.9 mW at room temperature. The tuning range is as high as 17 nm. 相似文献
628.
Two compositions of conventional aluminium base alloys were selected and equal amounts of tin and lead as a soft phase were
incorporated separately. Impeller mixing and chill casting technique were employed for the preparation of the alloys. Mechanical
properties of as cast alloys were evaluated at room temperature. Frictional behaviour of the alloys was studied in detail
under lubrication while creating different frictional states by imposing 5–60 kg of normal load on the bearing (bush) mating
surface. It was found that aluminium tin and leaded aluminium alloys slightly differ in mechanical properties. Frictional
states created during sliding against steel shaft (hardness 55–60 Rc) under oil lubrication were not much different. Leaded
aluminium alloy bushes show marginally lower friction than the conventional ones. 相似文献
629.
Ajay K. Srivastava Ashutosh Bhardwaj Kirti Ranjan Namrata Sudeep Chatterji R. K. Shivpuri 《Materials Science in Semiconductor Processing》2003,6(5-6):555-559
The influence of crystal damage on the electrical properties and the doping profile of the implanted p+–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 1015 BF2+ ions/cm2 at an energy of 80 keV and other with 1015 B+ ions/cm2 at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N2 ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF2+-implanted devices, whereas, boron diffusion depth increases continuously for B+-implanted devices. In BF2+-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF2+-implanted devices is similar to that obtained in B+-implanted devices. 相似文献
630.
The extraction behavior of U(VI), Pu(IV), and Np(IV) from nitric acid medium has been studied using branched chain di(2-ethylhexyl)isobutyramide (D2EHiBA) dissolved in different room temperature ionic liquids (RTILs) [Cnmim][NTf2] (where n = 4, 6, or 8). Uranium extraction (DU) increased gradually with aqueous phase acidity for the three RTILs used in this study suggesting solvation mechanism. There was a reversal in the extraction behavior of Pu(IV) and Np(IV) from nitric acid medium using D2EHiBA dissolved in RTILs as solvents as compared to the behavior reported in the molecular diluent, n-dodecane, which shows negligible extraction of these metal ions. The extraction of Pu(IV) increased with aqueous phase acidity in different RTILs in the order: [C8mim][NTf2] > [C6mim][NTf2] > [C4mim][NTf2]. The distribution ratio values of these metal ions followed the order: DPu(IV) ≥ DNp(IV) > DU(VI) using D2EHiBA as extractant suggesting that RTILs can modify the extraction behavior of extractants. 相似文献