全文获取类型
收费全文 | 424646篇 |
免费 | 4752篇 |
国内免费 | 1356篇 |
专业分类
电工技术 | 7778篇 |
综合类 | 323篇 |
化学工业 | 63031篇 |
金属工艺 | 18261篇 |
机械仪表 | 13392篇 |
建筑科学 | 9535篇 |
矿业工程 | 2803篇 |
能源动力 | 10884篇 |
轻工业 | 31703篇 |
水利工程 | 4785篇 |
石油天然气 | 9932篇 |
武器工业 | 35篇 |
无线电 | 51376篇 |
一般工业技术 | 87645篇 |
冶金工业 | 76563篇 |
原子能技术 | 10560篇 |
自动化技术 | 32148篇 |
出版年
2021年 | 3895篇 |
2020年 | 2911篇 |
2019年 | 3639篇 |
2018年 | 6364篇 |
2017年 | 6426篇 |
2016年 | 6807篇 |
2015年 | 4100篇 |
2014年 | 7086篇 |
2013年 | 18720篇 |
2012年 | 10927篇 |
2011年 | 14643篇 |
2010年 | 11801篇 |
2009年 | 13334篇 |
2008年 | 13920篇 |
2007年 | 13673篇 |
2006年 | 11911篇 |
2005年 | 10685篇 |
2004年 | 10109篇 |
2003年 | 10246篇 |
2002年 | 9652篇 |
2001年 | 10155篇 |
2000年 | 9426篇 |
1999年 | 9794篇 |
1998年 | 24391篇 |
1997年 | 17074篇 |
1996年 | 13215篇 |
1995年 | 9975篇 |
1994年 | 8831篇 |
1993年 | 8928篇 |
1992年 | 6590篇 |
1991年 | 6458篇 |
1990年 | 6247篇 |
1989年 | 6010篇 |
1988年 | 5953篇 |
1987年 | 5137篇 |
1986年 | 5129篇 |
1985年 | 5607篇 |
1984年 | 5235篇 |
1983年 | 5011篇 |
1982年 | 4580篇 |
1981年 | 4500篇 |
1980年 | 4471篇 |
1979年 | 4346篇 |
1978年 | 4148篇 |
1977年 | 4750篇 |
1976年 | 6053篇 |
1975年 | 3681篇 |
1974年 | 3520篇 |
1973年 | 3581篇 |
1972年 | 3190篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
LJ Huang K Durick JA Weiner J Chun SS Taylor 《Canadian Metallurgical Quarterly》1997,94(21):11184-11189
Subcellular localization directed by specific A kinase anchoring proteins (AKAPs) is a mechanism for compartmentalization of cAMP-dependent protein kinase (PKA). Using a two-hybrid screen, a novel AKAP was isolated. Because it interacts with both the type I and type II regulatory subunits, it was defined as a dual specific AKAP or D-AKAP1. Here we report the cloning and characterization of another novel cDNA isolated from that screen. This new member of the D-AKAP family, D-AKAP2, also binds both types of regulatory subunits. A message of 5 kb pairs was detected for D-AKAP2 in all embryonic stages and in all adult tissues tested. In brain, skeletal muscle, kidney, and testis, a 10-kb mRNA was identified. In testis, several small mRNAs were observed. Therefore, D-AKAP2 represents a novel family of proteins. cDNA cloning from a mouse testis library identified the full length D-AKAP2. It is composed of 372 amino acids which includes the R binding fragment, residues 333-372, at its C-terminus. Based on coprecipitation assays, the R binding domain interacts with the N-terminal dimerization domain of RIalpha and RIIalpha. A putative RGS domain was identified near the N-terminal region of D-AKAP2. The presence of this domain raises the intriguing possibility that D-AKAP2 may interact with a Galpha protein thus providing a link between the signaling machinery at the plasma membrane and the downstream kinase. 相似文献
92.
Based on a variational analysis, the authors demonstrate that the noise-induced Gordon-Haus timing jitter in a dispersion-managed soliton transmission system can be substantially reduced by appropriate placement of the amplifiers 相似文献
93.
94.
Pigmented vulvar lesions were observed in a child during a sexual abuse evaluation. Gross examination of the lesions appeared most consistent with bowenoid papulosis; however, biopsy confirmed the lesions to be pigmented apocrine hamartomas. To our knowledge, these rare and benign tumors have never been described as pigmented, but should be added to the differential diagnosis of pigmented vulvar lesions. 相似文献
95.
A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed. 相似文献
96.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
97.
The introduction of high spatial and spectral resolution sensors on-board remote-sensing spacecraft has increased, by orders of magnitude, the data rates which need to be sustained on the down-link or cross-link transmission channels. Since these channels are severely limited in capacity, the need arises to perform on-board compression to reduce the volume of data which would need to be down-linked. This paper discusses the development and refinement of a low complexity lossy spectral/spatial compression method which provides high compression ratios at low levels of distortion. The developed techniques uses pixels in adjacent bands to predict the intensity of pixels in the band being compressed via a simple linear prediction model. This prediction method when combined with a low-distortion discrete cosine transform (DCT) block coding method yields performance comparable to block-adaptive Karhunen-Loeve Transform (KLT)-DCT methods without incurring the complexity penalty of the KLT. The methods' performance suffers under misregistration. A fractional-pixel interpolation enhancement to the basic technique significantly improves the performance in the case of misregistered bands 相似文献
98.
Known examples of the positive influence of electrohydroimpulse treatment on the quality of weld joints of various steels, particularly including an increase in their long-term and cyclic strength and also corrosion resistance, are analyzed. It is shown that in this case there is a reduction in residual macro- and micro-stresses and also a change in the parameters of the dislocation structure of the joint metal in the direction of stabilization of it.Translated from Problemy Prochnosti, No. 4, pp. 119–123, April, 1996. 相似文献
99.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
100.
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling
theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon
interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting
transition temperature (T
c) is then evaluated by using these coupling parameters and obtainedT
c = 95(92)K for Y(Yb)Ba2Cu3O7−δ
superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory.
The result deduced on the variation ofT
c withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed. 相似文献