全文获取类型
收费全文 | 8859篇 |
免费 | 39篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 35篇 |
综合类 | 3篇 |
化学工业 | 614篇 |
金属工艺 | 71篇 |
机械仪表 | 57篇 |
建筑科学 | 131篇 |
矿业工程 | 11篇 |
能源动力 | 46篇 |
轻工业 | 223篇 |
水利工程 | 15篇 |
石油天然气 | 28篇 |
无线电 | 208篇 |
一般工业技术 | 498篇 |
冶金工业 | 6402篇 |
原子能技术 | 43篇 |
自动化技术 | 525篇 |
出版年
2022年 | 22篇 |
2021年 | 28篇 |
2019年 | 31篇 |
2018年 | 26篇 |
2017年 | 43篇 |
2016年 | 39篇 |
2015年 | 27篇 |
2014年 | 39篇 |
2013年 | 198篇 |
2012年 | 101篇 |
2011年 | 125篇 |
2010年 | 82篇 |
2009年 | 103篇 |
2008年 | 125篇 |
2007年 | 118篇 |
2006年 | 127篇 |
2005年 | 125篇 |
2004年 | 114篇 |
2003年 | 95篇 |
2002年 | 77篇 |
2001年 | 82篇 |
2000年 | 62篇 |
1999年 | 251篇 |
1998年 | 1815篇 |
1997年 | 999篇 |
1996年 | 653篇 |
1995年 | 419篇 |
1994年 | 360篇 |
1993年 | 385篇 |
1992年 | 82篇 |
1991年 | 94篇 |
1990年 | 124篇 |
1989年 | 114篇 |
1988年 | 114篇 |
1987年 | 127篇 |
1986年 | 102篇 |
1985年 | 123篇 |
1984年 | 54篇 |
1983年 | 62篇 |
1982年 | 70篇 |
1981年 | 85篇 |
1980年 | 91篇 |
1979年 | 61篇 |
1978年 | 67篇 |
1977年 | 205篇 |
1976年 | 377篇 |
1975年 | 41篇 |
1974年 | 43篇 |
1973年 | 28篇 |
1972年 | 21篇 |
排序方式: 共有8910条查询结果,搜索用时 15 毫秒
1.
2.
David J. Lawrence Brianna L. Smith Cameron D. Collard Keyton A. Elliott Kyle L. Fakhoury Jeffery D. Mangold Anna N. Soyka 《International Journal of Hydrogen Energy》2021,46(2):1642-1655
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices. 相似文献
3.
4.
RA Culbertson 《Canadian Metallurgical Quarterly》1997,22(6):1359-1383
This study compares the perspectives of eighteen managed care executives and twenty-four faculty practice executives on critical policy issues related to the managed care marketplace. Market sites studied in 1994 included four major metropolitan areas: Minneapolis-St. Paul, Los Angeles, Philadelphia, and Atlanta. These markets were selected as being representative of communities with descending degrees of managed care involvement, but with significant market activity. Study participants from both managed care systems and faculty practices examined five policy issues: (1) the importance of including academic medical centers in current and future health care plans for marketing purposes; (2) the provision of clinical services that are unique to the academic medical center, that is, unavailable elsewhere in the community; (3) the degree of financial supplement that employers might pay for including an academic medical center; (4) future restructuring of organizations to sustain the educational mission of academic faculty within a viable delivery system; (5) satisfaction of managed care providers with graduates of academic medical centers, as measured by the clinical skills of graduate physicians. The study findings showed little support among managed care plans for paying supplements to include faculty practices in a health care network. Most study participants from managed care systems and academic faculty practices identified limited competencies that are unique to academic centers. Moreover, managed care organizations were only willing to undertake limited restructuring at best to include faculty practices within their networks. General concern about the preparation of resident physicians (especially those in primary care disciplines) for practice within contemporary managed care organizations existed among managed care informants. The results of the study indicate that as traditional funding sources for medical education are reduced, schools require greater integration with managed care plans to enable academic medical centers and their faculties to continue promoting clinical enterprise. 相似文献
5.
IS Grewal P Borrow EG Pamer MB Oldstone RA Flavell 《Canadian Metallurgical Quarterly》1997,9(4):491-497
Research in the past few years has documented significant advances in our understanding of the CD40-CD40 ligand (CD154) system in diverse immune functions. This system influences many T cell mediated inflammatory immune responses and effector functions, unmasking a previously unexpected role for CD40-CD154 in cell mediated immunity. Manipulation of CD154 in animal models of infection by the use of CD154-deficient mice or anti-CD154 antibodies has shown the importance of this system in the initiation of the inflammatory response, in the activation of antigen-presenting cells and in resistance to infections. 相似文献
6.
7.
Cells in the dorsal division of the medial superior temporal area (MSTd) have large receptive fields and respond to expansion/contraction, rotation, and translation motions. These same motions are generated as we move through the environment, leading investigators to suggest that area MSTd analyzes the optical flow. One influential idea suggests that navigation is achieved by decomposing the optical flow into the separate and discrete channels mentioned above, that is, expansion/contraction, rotation, and translation. We directly tested whether MSTd neurons perform such a decomposition by examining whether there are cells that are preferentially tuned to intermediate spiral motions, which combine both expansion/contraction and rotation components. The finding that many cells in MSTd are preferentially selective for spiral motions indicates that this simple three-channel decomposition hypothesis for MSTd does not appear to be correct. Instead, there is a continuum of patterns to which MSTd cells are selective. In addition, we find that MSTd cells maintain their selectivity when stimuli are moved to different locations in their large receptive fields. This position invariance indicates that MSTd cells selective for expansion cannot give precise information about the retinal location of the focus of expansion. Thus, individual MSTd neurons cannot code, in a precise fashion, the direction of heading by using the location of the focus of expansion. The only way this navigational information could be accurately derived from MSTd is through the use of a coarse, population encoding. Positional invariance and selectivity for a wide array of stimuli suggest that MSTd neurons encode patterns of motion per se, regardless of whether these motions are generated by moving objects or by motion induced by observer locomotion. 相似文献
8.
Free and bound non-sulphonated aromatic amines (NSAA) are determined in the food colours tartrazine, sunset yellow FCF and allura red. After reduction of the bound amines with sodium dithionite, the NSAA are extracted into chloroform, then transferred to aqueous acid solution, diazotized with sodium nitrite and coupled with 2-naphthol-3,6-disulphonic acid, disodium salt (R-salt). Reversed-phase ion-pair liquid chromatography and an absorbance detector at 512 nm are used to analyse the coloured derivatives. Samples of dyes were spiked with known amounts of aniline, 1-naphthylamine, 2- and 4-aminobiphenyl, 4-aminoazobenzene, benzidine, p-cresidine or 4-nitro-p-cresidine bound to R-salt. Recoveries averaged 90% in tartrazine, 65% in sunset yellow FCF and 71% in allura red. Detection limits ranged between 2 and 32 ng/g. A survey of 24 commercial samples revealed levels up to 520 micrograms/g total NSAA. The majority of NSAA are bound to the coupling compound during the manufacturing process and less than 7% remain as free amines in the dye. 相似文献
9.
10.
Lawrence K. Forbes Graeme C. Hocking Simon Wotherspoon 《Journal of Engineering Mathematics》2004,48(1):69-91
Rainwater can collect in a lens-shaped region within the rock of a tropical island, and may be separated from the underlying salt water by a sharp interface. This paper presents a nonlinear theory for determining the shape of this interface. The island is assumed to be saturated with rain, and provision is made for the outflow of rain-water through the sides of the island. The effect of a bore well on the shape of the interface is investigated, and the problem is solved using a spectral method. An integral-equation method is also presented for the case when the island has infinite width. 相似文献