全文获取类型
收费全文 | 9566篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 11篇 |
综合类 | 5篇 |
化学工业 | 92篇 |
金属工艺 | 14篇 |
机械仪表 | 26篇 |
建筑科学 | 27篇 |
能源动力 | 63篇 |
轻工业 | 39篇 |
水利工程 | 1篇 |
石油天然气 | 3篇 |
武器工业 | 1篇 |
无线电 | 114篇 |
一般工业技术 | 133篇 |
冶金工业 | 8967篇 |
原子能技术 | 6篇 |
自动化技术 | 75篇 |
出版年
2022年 | 7篇 |
2018年 | 6篇 |
2016年 | 8篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 17篇 |
2011年 | 8篇 |
2010年 | 21篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 24篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 25篇 |
1999年 | 309篇 |
1998年 | 2817篇 |
1997年 | 1551篇 |
1996年 | 1008篇 |
1995年 | 584篇 |
1994年 | 454篇 |
1993年 | 570篇 |
1992年 | 80篇 |
1991年 | 117篇 |
1990年 | 117篇 |
1989年 | 110篇 |
1988年 | 107篇 |
1987年 | 108篇 |
1986年 | 110篇 |
1985年 | 91篇 |
1984年 | 14篇 |
1983年 | 25篇 |
1982年 | 54篇 |
1981年 | 53篇 |
1980年 | 89篇 |
1979年 | 12篇 |
1978年 | 31篇 |
1977年 | 213篇 |
1976年 | 477篇 |
1975年 | 25篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 9篇 |
1971年 | 15篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1955年 | 7篇 |
排序方式: 共有9577条查询结果,搜索用时 31 毫秒
21.
Histological and histochemical techniques have been employed to determine the structure and autonomic innervation of paraganglia located in the human pelvis. In foetal and early postnatal tissues, paraganglia formed rounded cellular masses which were frequently in company with the autonomic nerves and ganglia of the urinary bladder and other pelvic viscera. The constituent cells contained only small amounts of cholinesterase and were unrelated to enzyme positive autonomic nerves; acetylcholinesterase containing nerves were occasionally observed in the capsule and the fibrous septa of the pelvic paraganglia. In early postnatal specimens, pelvic paraganglia frequently contained single or multiple "pacinian-like" corpuscles, each possessing a central region which was rich in both acetyl and pseudocholinesterase. These structures were rarely observed within autonomic ganglia and were absent 4 1/2 years post partum. By means of a histochemical technique, pelvic paraganglia were found to contain catecholamine which was attributed to the presence of relatively large quantities of noradrenaline. These observations have been discussed with particular reference to the results of other studies on the autonomic innervation of paraganglia. 相似文献
22.
A technique is described for using the advantages of a social systems approach when working with elderly persons in psychiatric distress. The technique is based on the assumption that the solution to a variety of human predicaments lies within the collective instrumental and affective resources of the client's social network. The vehicle for accomplishing this objective is the "Network Session" during which a mental health professional meets with the elderly person and members of his/her social network to help resolve the difficulty. A case report demonstrating use of the technique is included. 相似文献
23.
D J Goldstein 《Journal of microscopy》1975,105(1):33-56
Microdensitometric errors can result from various factors associated with the monochromator system, including imperfect monochromaticity of the light, incorrect setting of the wavelength, and non-uniform illumination of either the microscopic field or the objective aperture. Certain types of potential error are characteristic of particular instruments. Thus in the Vickers M85 microdensitometer, where the flying spot is the reduced image of a hole situated at the monochromator exit aperture, the interpretation of results obtained with different spot sizes is complicated by the fact that the hole size affects both the spatial resolution and the spectral bandwidth of the system. Similarly, in instruments in which the monochromator exit slit lies in an aperture plane the numerical aperture of the whole system may be affected by the spectral bandwidth and vice versa. Overall instrumental sensitivity is mainly limited at the blue and red ends of the spectrum respectively by the lamp output and the photomultiplier tube sensitivity. Quartz-iodine lamps are slightly brighter than conventional tungsten sources, especially at short wavelengths, but tend to be less stable photometrically and are more expensive. Simple refracting monochromators and graded-spectrum interference filters in general pass more light, in the visible spectrum, than do grating monochromators of similar bandwidth. Most errors of wavelength setting can be avoided by routinely measuring at that wavelength, lambda(max), found empirically to give the maximum absorbance or integrated absorbance. Off-peak wavelengths can be set reproducibly with the aid of an eyepiece spectroscope, or by adjusting the wavelength so that the absorbance of a given specimen is some precise fraction of that at lambda(max). 相似文献
24.
Muhammed Iraqi Avishay Edri Yariv Greenshpan Oron Goldstein Noa Ofir Priyanka Bolel Muhammad Abu Ahmad Miri Zektser Kerry S. Campbell Ory Rouvio Roi Gazit Angel Porgador 《International journal of molecular sciences》2022,23(9)
Simple SummaryMembrane-associated PCNA is expressed on the surface of human MM cell lines and primary MM cells. Mab 14-25-9 interacts with membrane-associated PCNA and blocks its binding to NK-expressed NKp44, thus activating NK function. We showed that mAb 14-25-9 can serve as an immune checkpoint blocker, enhancing the function of NK cells on target human MM cell lines and primary cells.AbstractMultiple Myeloma (MM) is a devastating malignancy that evades immune destruction using multiple mechanisms. The NKp44 receptor interacts with PCNA (Proliferating Cell Nuclear Antigen) and may inhibit NK cells’ functions. Here we studied in vitro the expression and function of PCNA on MM cells. First, we show that PCNA is present on the cell membrane of five out of six MM cell lines, using novel anti-PCNA mAb developed to recognize membrane-associated PCNA. Next, we stained primary bone marrow (BM) mononuclear cells from MM patients and showed significant staining of membrane-associated PCNA in the fraction of CD38+CD138+ BM cells that contain the MM cells. Importantly, blocking of the membrane PCNA on MM cells enhanced the activity of NK cells, including IFN-γ-secretion and degranulation. Our results highlight the possible blocking of the NKp44-PCNA immune checkpoint by the mAb 14-25-9 antibody to enhance NK cell responses against MM, providing a novel treatment option. 相似文献
25.
This paper assesses the frequency detection capabilities of a new signal-dependent reduced-rank linear predictor applied to autoregressive spectrum estimation. The new technique is called reduced-order correlation kernel estimation technique (ROCKET). Its detection performance is examined by comparison to a full-rank autoregressive (FR-AR) estimator and two reduced-rank principal component autoregressive (PC-AR) estimators based on both the standard signal-independent version and a modified signal-dependent method. The performance of the new autoregressive estimator is also compared as a function of rank to the popular pseudo-spectrum estimator MUSIC. The performance metrics examined are the probability of detection (P/sub D/) and the false alarm rate (FAR) of detecting the spatial frequencies of plane waves impinging on a uniform line array in additive white Gaussian noise. These metrics are studied as a function of subspace rank, sample support, and signal-to-noise ratio (SNR). Simulations show that the signal-dependent reduced-rank estimators significantly outperform both the signal-independent version of PC-AR and the FR-AR estimator for low sample support and low SNR environments. One notable characteristic of ROCKET that highlights its distinct subspace selection is its performance as a function of subspace rank. It is observed that for equal powered signals, its peak performance is nearly invariant to signal rank and that at almost any subspace rank ROCKET meets or exceeds FR-AR performance. This provides an extra degree of robustness when the signal rank is unknown. 相似文献
26.
Eskildsen L. Goldstein E. da Silva V. Andrejco M. Silberberg Y. 《Photonics Technology Letters, IEEE》1993,5(10):1188-1190
Inhomogeneously broadened fiber amplifiers inserted periodically in an amplifier cascade are shown to provide significant interchannel power equalization in wavelength-multiplexed systems. Interchannel power variations in a six-amplifier cascade are reduced from 16 dB in a conventional system to about 5 dB when power equalizers are inserted 相似文献
27.
Broadband dispersion compensation is demonstrated at 2.5 and 10 Gbit/s using an optical-fibre equaliser in combination with pulse compression. At 2.5 Gbit/s, simultaneous penalty-free dispersion compensation is achieved in a four-wavelength system operating at 1550 nm through 67 km of 1310 nm-optimised singlemode fibre. Low penalties are obtained over the full 20 nm gain bandwidth of the erbium-doped fibre amplifier, with the receiver sensitivity slightly enhanced at the short-wavelength end.<> 相似文献
28.
Goldstein EA Heaton JT Kobler JB Stanley GB Hillman RE 《IEEE transactions on bio-medical engineering》2004,51(2):325-332
The electrolarynx (EL) voice prosthesis is widely used, but suffers from the inconvenience of requiring manual control. Therefore, a hands-free EL triggered by neck muscle electromyographic (EMG) activity was developed (EMG-EL). Signal processing circuitry in a belt-mounted control unit transforms EMG activity into control signals for initiation and termination of voicing. These control signals are then fed to an EL held against the neck by an inconspicuous brace. Performance of the EMG-EL was evaluated by comparison to normal voice, manual EL voice, and tracheo-esophageal (TE) voice in a series of reaction time experiments in seven normal subjects and one laryngectomy patient. The normal subjects produced voice initiation with the EMG-EL that was as fast as both normal voice and the manual EL. The laryngectomy subject produced voice initiation that was slower than with the manual EL, but faster than with TE voice. Voice termination with the EMG-EL was slower than normal voice for the normal subjects, but not significantly different than with the manual EL. The laryngectomy subject produced voice termination with the EMG-EL that was slower than with TE or manual EL. The EMG-EL threshold was set at 10% of the range of vocal-related EMG activity above baseline. Simulations of EMG-EL behavior showed that the 10% threshold was not significantly different from the optimum threshold produced through the process of error minimization. The EMG-EL voice reaction time appears to be adequate for use in a day-to-day conversation. 相似文献
29.
Lin L.Y. Goldstein E.L. Simmons J.M. Tkach R.W. 《Photonics Technology Letters, IEEE》1998,10(10):1425-1427
Optical-layer crossconnects with high port count appear to be emerging as key elements for provisioning and restoration in future wavelength-division-multiplexed networks. We demonstrate here a means of achieving high-density optical crossconnects utilizing free-space micromachined optical switches that exploit connection-symmetry in core-transport networks. The micromachined polygon switches proposed here are strictly nonblocking. Measured insertion losses of 3.1-3.5 dB for a 16×16 (8×8 bidirectional) switch suggest the promise of scaling to large port count 相似文献
30.
K. A. Valiev R. V. Goldstein Yu. V. Zhitnikov T. M. Makhviladze M. E. Sarychev 《Russian Microelectronics》2010,39(3):145-157
The degradation and bulk failure of a polycrystalline interconnect line caused by vacancy electromigration along grain boundaries
and vacancy-cluster nucleation at triple points in the bulk conductor are investigated within the general theory of the electromigration-induced
degradation and failure of thin-film on-chip interconnect lines, presented in Part 1 [1]. The general equations are tailored
to deal with vacancy electromigration, mechanical-stress generation, and void nucleation at triple points. Appropriate boundaryvalue
problems are formulated, and numerical methods and procedures to solve them are developed and implemented in software. Computer
simulations are performed to identify a pattern of electromigration failure at triple points. On this basis, (1) interconnect
lifetime is investigated over wide ranges of variation of material, structural, geometric, and operating parameters, and (2)
the current-density and temperature dependence—of the mechanical stress, vacancy concentration, and level of vacancy supersaturation
at a triple point, and of void radius and time to nucleation-is examined and explained. The simulation results are found to
agree well with previous experiments. This investigation could be seen as a natural continuation of our study of electromigration
failures developed by multilevel-metallization systems as a result of interconnect failure near via junctions or at open ends
[1]. Together they cover most mechanisms of electromigration failure suffered by metallization systems. 相似文献