全文获取类型
收费全文 | 6059篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 3篇 |
化学工业 | 88篇 |
金属工艺 | 28篇 |
机械仪表 | 17篇 |
建筑科学 | 22篇 |
矿业工程 | 8篇 |
能源动力 | 5篇 |
轻工业 | 38篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 55篇 |
一般工业技术 | 179篇 |
冶金工业 | 5553篇 |
原子能技术 | 13篇 |
自动化技术 | 62篇 |
出版年
2021年 | 10篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 39篇 |
2012年 | 13篇 |
2011年 | 20篇 |
2010年 | 11篇 |
2009年 | 21篇 |
2008年 | 17篇 |
2007年 | 15篇 |
2006年 | 26篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 15篇 |
2000年 | 23篇 |
1999年 | 174篇 |
1998年 | 1719篇 |
1997年 | 961篇 |
1996年 | 602篇 |
1995年 | 346篇 |
1994年 | 303篇 |
1993年 | 338篇 |
1992年 | 51篇 |
1991年 | 70篇 |
1990年 | 78篇 |
1989年 | 72篇 |
1988年 | 74篇 |
1987年 | 77篇 |
1986年 | 59篇 |
1985年 | 68篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1981年 | 37篇 |
1980年 | 58篇 |
1979年 | 8篇 |
1978年 | 22篇 |
1977年 | 168篇 |
1976年 | 353篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1970年 | 5篇 |
1955年 | 4篇 |
排序方式: 共有6079条查询结果,搜索用时 15 毫秒
1.
2.
Locke Davenport Huyer Serena Mandla Yufeng Wang Scott B. Campbell Bess Yee Christian Euler Benjamin F. Lai A. Dawn Bannerman Dawn S. Y. Lin Miles Montgomery Kayla Nemr Timothy Bender Slava Epelman Radhakrishnan Mahadevan Milica Radisic 《Advanced functional materials》2021,31(6):2003341
Itaconate (ITA) is an emerging powerhouse of innate immunity with therapeutic potential that is limited in its ability to be administered in a soluble form. A library of polyester materials that incorporate ITA into polymer backbones resulting in materials with inherent immunoregulatory behavior is developed. Harnessing hydrolytic degradation release from polyester backbones, ITA polymers result in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released ITA inhibits bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrate a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of ITA. 相似文献
3.
4.
5.
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
6.
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
7.
8.
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
9.
Calum MacNeil Jaimie T A Dick Ewan Bigsby Robert W Elwood W Ian Montgomery Chris N Gibbins David W Kelly 《Water research》2002,36(1):75-84
In freshwaters. Gammarus spp. are more sensitive to organic pollution than Asellus spp. and the relative abundance of the two taxa has been proposed as a pollution index. We tested the validity of this by examining the relationship between the Gammarus: Asellus (G : A) ratio and (1) a suite of physico-chemical variables. (2) established biotic (average score per taxon, ASPT) and richness (species richness (S) and Ephemeroptera, Plecoptera and Trichoptera families richness (EPT family richness)) indices generated from the macroinvertebrate community. In addition, we investigated a suspected biotic interaction, predation, between Gammarus and Asellus. Both univariate and multivariate analyses showed that the G: A ratio was sometimes responsive to changes in parameters linked to organic pollution, such as BOD5 and nitrate levels. However, the G : A ratio also appeared responsive to variables not directly linked to organic pollution, such as conductivity and distance from source. There were significant positive correlations among the G : A ratio and the ASPT, S and EPT, indicating that changes in the relative abundances of Gammarus and Asellus were reflected in changes in the pollution sensitivity and richness of the wider macroinvertebrate community. A laboratory experiment revealed significant predation of Asellus aquaticus juveniles by Gammarus duebeni celticus adults, but no reciprocal predation. We propose that the G: A ratio may be useful as a crude measure of organic pollution that could supplement more complex indices in a multimetric approach to pollution monitoring or be used for monitoring individual sites, where a simple technique is required for monitoring purposes over a period of time. Also, we urge recognition of the possible role of biotic interactions among taxa used in the generation of pollution indices. 相似文献
10.