全文获取类型
收费全文 | 14527篇 |
免费 | 1100篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 202篇 |
综合类 | 24篇 |
化学工业 | 3155篇 |
金属工艺 | 537篇 |
机械仪表 | 733篇 |
建筑科学 | 255篇 |
矿业工程 | 5篇 |
能源动力 | 628篇 |
轻工业 | 1420篇 |
水利工程 | 53篇 |
石油天然气 | 18篇 |
武器工业 | 2篇 |
无线电 | 2472篇 |
一般工业技术 | 3302篇 |
冶金工业 | 1057篇 |
原子能技术 | 138篇 |
自动化技术 | 1653篇 |
出版年
2023年 | 187篇 |
2022年 | 120篇 |
2021年 | 506篇 |
2020年 | 366篇 |
2019年 | 367篇 |
2018年 | 481篇 |
2017年 | 500篇 |
2016年 | 593篇 |
2015年 | 519篇 |
2014年 | 741篇 |
2013年 | 1024篇 |
2012年 | 1040篇 |
2011年 | 1271篇 |
2010年 | 907篇 |
2009年 | 866篇 |
2008年 | 790篇 |
2007年 | 653篇 |
2006年 | 540篇 |
2005年 | 465篇 |
2004年 | 439篇 |
2003年 | 375篇 |
2002年 | 311篇 |
2001年 | 267篇 |
2000年 | 268篇 |
1999年 | 242篇 |
1998年 | 426篇 |
1997年 | 261篇 |
1996年 | 219篇 |
1995年 | 133篇 |
1994年 | 118篇 |
1993年 | 109篇 |
1992年 | 67篇 |
1991年 | 47篇 |
1990年 | 44篇 |
1989年 | 45篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1974年 | 13篇 |
1972年 | 11篇 |
1970年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
Eunseok Song Yido Koo Yeon-Jae Jung Deok-Hee Lee Sangyoung Chu Soo-Ik Chae 《Solid-State Circuits, IEEE Journal of》2005,40(5):1094-1106
This paper describes a single-chip CMOS quad-band (850/900/1800/1900 MHz) RF transceiver for GSM/GPRS applications. It is the most important design issue to maximize resource sharing and reuse in designing the multiband transceivers. In particular, reducing the number of voltage-controlled oscillators (VCOs) required for local oscillator (LO) frequency generation is very important because the VCO and phase-locked loop (PLL) circuits occupy a relatively large area. We propose a quad-band GSM transceiver architecture that employs a direct conversion receiver and an offset PLL transmitter, which requires only one VCO/PLL to generate LO signals by using an efficient LO frequency plan. In the receive path, four separate LNAs are used for each band, and two down-conversion mixers are used, one for the low bands (850/900 MHz) and the other for the high bands (1800/1900 MHz). A receiver baseband circuit is shared for all four bands because all of their channel spaces are the same. In the transmit path, most of the building blocks of the offset PLL, including a TX VCO and IF filters, are integrated. The quad-band GSM transceiver that was implemented in 0.25-/spl mu/m CMOS technology has a size of 3.3/spl times/3.2 mm/sup 2/, including its pad area. From the experimental results, we found that the receiver provides a maximum noise figure of 2.9 dB and a minimum IIP3 of -13.2dBm for the EGSM 900 band. The transmitter shows an rms phase error of 1.4/spl deg/ and meets the GSM spectral mask specification. The prototype chip consumes 56 and 58 mA at 2.8 V in the RX and TX modes, respectively. 相似文献
52.
JM Bach H Otto GT Nepom G Jung H Cohen J Timsit C Boitard PM van Endert 《Canadian Metallurgical Quarterly》1997,10(4):375-386
Tissue composition and the distribution of body mass are described for four genera of East African Bovidae (Madoqua, Gazella, Damaliscus, Hippotragus) with supporting data from four others (Neotragus, Oryx, Tragelaphus, Connochaetes). These species are high in muscle mass, an adaptation convergent with other high-speed terrestrial cursors, bounders, and saltators. The segments below the elbow/cubitus and knee/stifle/genu joints in small bovids are both lighter in percent of total body mass (8.6% TBM) and less heavily muscled (10-15% of total limb musculature) than those segments in macaques (13.6% TBM, 20-25% of the limb musculature). Bovid species differ from one another in the regional distribution of muscle mass. Madoqua kirkii (4-5 kg) concentrates muscle in the lumbar extensors and hindlimbs; large species such as Damaliscus doreas (50-60 kg) and Hippotragus niger (160-220 kg) distribute it more evenly between the lumbar and cervical regions and between the hindlimbs and forelimbs. Gazella dorcas (10-20 kg) is quantitatively intermediate in those characteristics. The redistribution of muscle mass with increasing size correlates with the loss of axial bending of the vertebral column: in small, hindlimb dominant, 'dorsomobile' species such as Madoqua sagittal mobility increases stride length through 'extended' suspension; in large 'dorsostable' species such as Damaliscus and Hippotragus the vertebral column resists bending, consequently abbreviating or omitting this non-contact phase of the gait cycle. Locomotor adaptation as it is reflected in size, shape, and musculoskeletal structure is the key to habitat choice, dietary specialization, social structure, and male agonistic behavior and, therefore, central to the fabric of behavioral ecology. 相似文献
53.
Joonho Lim Kipaek Kwon Soo-Ik Chae 《Electronics letters》1998,34(4):344-346
The authors propose a reversible energy recovery logic (RERL) circuit for ultra-low-energy consumption, which consumes only adiabatic energy loss and leakage current loss by completely eliminating non-adiabatic energy loss. It is a dual-rail adiabatic circuit using the concept of reversible logic with a new eight-phase clocking scheme. Simulation results show that at low-speed operation, the RERL consumes much less energy than the complementary static CMOS circuit and other adiabatic logic circuits 相似文献
54.
DI Rodenhiser JD Andrews DN Mancini JH Jung SM Singh 《Canadian Metallurgical Quarterly》1997,373(2):185-195
Glutamatergic synaptic potentials induced by micromolar concentrations of the potassium conductance blocker 4-aminopyridine (4-AP) were recorded intracellularly from rat neostriatal neurons in the presence of 10 microM bicuculline (BIC). These synaptic potentials originate from neostriatal cortical and thalamic afferents and were completely blocked by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 100 microM D-2-amino-5-phosphonovaleric acid (2-APV). Their inter-event time intervals could be fitted to exponential distributions, suggesting that they are induced randomly. Their amplitude distributions had most counts around 1 mV and fewer counts with values up to 5 mV. Since input resistance of the recorded neurons is about 40 M omega, the amplitudes agree to quantal size measurements in mammalian central neurons. The action of a D2 agonist, quinpirole, was studied on the frequency of these events. Mean amplitude of synaptic potentials was preserved in the presence of 2-10 microM quinpirole, but the frequency of 4-AP-induced glutamatergic synaptic potentials was reduced in 35% of cases. The effect was blocked by the D2 antagonist sulpiride (10 microM). Input resistance, membrane potential, or firing threshold did not change during quinpirole effect, suggesting a presynaptic site of action for quinpirole in some but not all glutamatergic afferents that make contact on a single cell. The present experiments show that dopaminergic presynaptic modulation of glutamatergic transmission in the neostriatum does not affect all stimulated afferents, suggesting that it is selective towards some of them. This may control the quality and quantity of afferent flow upon neostriatal neurons. 相似文献
55.
Lossless subband coding system based on rounding transform 总被引:1,自引:0,他引:1
We propose a new rounding transform called the overlapping rounding transform (ORT). It is defined as a two-port input/two-port output FIR filtering system with a pair of rounding operations. The ORT is applied to develop lossless subband coding systems. The ORT approach has both a simpler representation and more possibilities for lossless subband implementation than the lifting scheme 相似文献
56.
We describe in this report a sensitive and direct method for the analysis of tamoxifen (TAM) in microsamples of plasma. The drug and internal standard (quinine bisulfate, I.S.) were separated on a 10-microm particle, 10 cm X 8 mm CN cartridge in conjunction with a radial compression system. The mobile phase was a mixture of 0.1 M sodium acetate in 0.001 M tetrabutylammonium phosphate solution (pH 6) and methanol (30:70, v/v) at a flow-rate of 4 ml/min. After addition of I.S. and o-phosphoric acid in acetonitrile (0.6 M) to the plasma (30 microl), the mixture was placed in an ultraviolet shortwave transluminator for 2 min prior to injection into the chromatograph. The compounds were detected in the effluent fluorometrically at excitation and emission wavelengths of 258 and 378 nm, respectively. Under these conditions, no interference in the assay from any endogenous substance or other concurrently used drugs was observed and the retention times of I.S. and TAM were 4.4 and 10.15 min, respectively. The concentration of TAM in plasma was linearly (r>0.9983) related to the peak height ratio (TAM/I.S.) in the range 0.01-2.0 microg ml(-1) and C.V. at 0.075, 0.4 and 1.2 microg ml(-1) was < or = 4.96%. We are currently using this assay for monitoring TAM in plasma and investigating its pharmacokinetics in cancer patients receiving cytotoxic drugs in addition to TAM as a multi-drug resistance modifier. 相似文献
57.
58.
The incidence of stress fractures is increasing among competitive and recreational athletes as well as among children and the elderly. By understanding the continuum of bone's response to stress and maintaining an appropriate index of suspicion, the health care provider can diagnose these injuries appropriately. An accurate history and examination is essential and will differentiate stress fractures from other stress reactions. The more common stress fractures are discussed. 相似文献
59.
60.
Analysis of composite laminates with transverse cracks 总被引:1,自引:0,他引:1
The analysis of the behaviour of composite laminates with general balanced lay-up sequences and containing distributed transverse cracks is discussed and demonstrated in this paper. It is shown that a constitutive model of damage for composites, which has been successfully used to analyse the effects of uniformly distributed transverse cracks in cross-ply laminates, can be readily extended to the analysis of uniformly distributed transverse cracks in more general symmetric laminates. The further extension of the theory to non-uniformly distributed damage can be achieved by finite element analysis. It is shown that the finite element implementation of the theory is particularly simple since the contribution of the damage to the overall behaviour can be incorporated into the force vectors. 相似文献