全文获取类型
收费全文 | 2973篇 |
免费 | 73篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 24篇 |
化学工业 | 422篇 |
金属工艺 | 66篇 |
机械仪表 | 43篇 |
建筑科学 | 112篇 |
矿业工程 | 36篇 |
能源动力 | 57篇 |
轻工业 | 237篇 |
水利工程 | 22篇 |
石油天然气 | 13篇 |
无线电 | 263篇 |
一般工业技术 | 343篇 |
冶金工业 | 1032篇 |
原子能技术 | 31篇 |
自动化技术 | 349篇 |
出版年
2022年 | 20篇 |
2021年 | 37篇 |
2020年 | 37篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 50篇 |
2016年 | 35篇 |
2015年 | 37篇 |
2014年 | 47篇 |
2013年 | 156篇 |
2012年 | 66篇 |
2011年 | 101篇 |
2010年 | 69篇 |
2009年 | 76篇 |
2008年 | 100篇 |
2007年 | 86篇 |
2006年 | 75篇 |
2005年 | 84篇 |
2004年 | 61篇 |
2003年 | 78篇 |
2002年 | 61篇 |
2001年 | 57篇 |
2000年 | 57篇 |
1999年 | 83篇 |
1998年 | 217篇 |
1997年 | 144篇 |
1996年 | 118篇 |
1995年 | 81篇 |
1994年 | 78篇 |
1993年 | 88篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 51篇 |
1989年 | 49篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 35篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 59篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 21篇 |
排序方式: 共有3050条查询结果,搜索用时 31 毫秒
51.
52.
53.
P.J. Poole S. Charbonneau M. Dion G.C. Aers M. Buchanan R.D. Goldberg I.V. Mitchell 《Photonics Technology Letters, IEEE》1996,8(1):16-18
A technique for fabricating many different wavelength lasers on the same wafer has been developed. High energy ion implantation was used to selectively blue shift the emission wavelength of an InP-based quantum well laser structure. This structure was then processed into fully functional broad-area lasers whose current threshold was unaffected by the implantation process, indicating extremely high material quality after bandgap-shifting. This process has the potential for the integration of not only different wavelength lasers, but also other devices, such as waveguides, detectors, modulators, etc., on a single wafer. 相似文献
54.
Array pattern nulling by operating on the roots of the array polynomial in the complex plane using a genetic algorithm (GA) is demonstrated. A pattern envelope constraint and an array efficiency criterion are applied. The algorithm is much faster than a similar GA operating on the complex weights of the array factor 相似文献
55.
A method for constructing decodable de Bruijn sequences 总被引:1,自引:0,他引:1
Mitchell C.J. Etzion T. Paterson K.G. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1996,42(5):1472-1478
We present two related methods of construction for de Bruijn (1946) sequences, both based on interleaving “smaller” de Bruijn sequences. Sequences obtained using these construction methods have the advantage that they can be “decoded” very efficiently, i.e., the position within the sequence of any particular “window” can be found very simply. Sequences with simple decoding algorithms are of considerable practical importance in position location applications 相似文献
56.
57.
Philippe Meunier Robert Bruce Findler Paul Steckler Mitchell Wand 《Higher-Order and Symbolic Computation》2005,18(3-4):245-269
A set-based program analysis establishes constraints between sets of abstract values for all expressions in a program. Solving
the system of constraints produces a conservative approximation to the program's runtime flow of values.
Some practical set-based analyses use explicit selectors to extract the relevant values from an approximation set. For example,
if the analysis needs to determine the possible return values of a procedure, it uses the appropriate selector to extract
the relevant component from the abstract representation of the procedure.
In this paper, we show that this selector-based approach complicates the constraint solving phase of the analysis too much
and thus fails to scale up to realistic programming languages. We demonstrate this claim with a full-fledged value flow analysis
for case-lambda, a multi-branched version of lambda. We show how both the theoretical underpinnings and the practical implementation become
too complex. In response, we present a variant of set-based closure analysis that computes equivalent results in a much more
efficient manner. 相似文献
58.
PURPOSE: Corticosteroids are known to cause cataracts, but the effects of other medications on the lens are unclear. The aim of this study was to investigate the relationships between cataracts and a range of medications, including allopurinol, aspirin, chloroquine, diuretics, phenothiazines, and simvastatin. DESIGN: Population-based cross-sectional study. PARTICIPANTS: 3654 individuals 49 to 97 years of age (response rate, 82%) from an urban community near Sydney, Australia, were included. TESTING: Lens photography. PRIMARY OUTCOME MEASURE: Lens photographs were graded for the presence and severity of cortical, nuclear, and posterior subcapsular cataract. RESULTS: After adjusting for numerous potential confounders in ordinal regression models, use of phenothiazines was associated with nuclear cataract (adjusted odds ratio [OR], 2.18; 95% confidence interval [CI], 1.01-4.74); long-term aspirin users (> or = 10 years) had higher prevalence of posterior subcapsular cataract than did nonusers and short-term users (test for trend, P = 0.02); and the antimalarial drug mepacrine was associated with posterior subcapsular cataract (adjusted OR, 3.56; 95% CI, 1.56-8.13). There was a suggestion that use of chloroquine-like drugs for more than 1 year (test for trend, P = 0.12) might also be associated with posterior subcapsular cataract. Antihypertensive medications, cholesterol-lowering drugs, and allopurinol were not associated with any type of cataract. Potassium-sparing diuretics were the only diuretic to show any evidence of an association with cataract (test for trend for posterior subcapsular cataract, P = 0.14). Amiodarone was associated with cortical cataract (age- and gender-adjusted OR, 3.84; 95% CI, 1.01-14.81), but there were too few users to do analyses adjusted for multiple confounders. CONCLUSIONS: Most drugs commonly used in the community do not appear to be associated with cataract. The findings of this study do not support the hypothesis that aspirin protects against cataract. 相似文献
59.
JS Plummer KA Berryman C Cai WL Cody J DiMaio AM Doherty JJ Edmunds JX He DR Holland S Levesque DR Kent LS Narasimhan JR Rubin ST Rapundalo MA Siddiqui AJ Susser Y St-Denis PD Winocour 《Canadian Metallurgical Quarterly》1998,8(23):3409-3414
The synthesis and antithrombotic activity of a series of nonpeptide bicyclic thrombin inhibitors is described. We have explored the SAR with modifications to the P1 site. The introduction of arginine mimetics at the P1 site led to potent and selective thrombin inhibitors. 相似文献
60.
MH Mullerworth P Angelopoulos MA Couyant AM Horton SM Robinson OU Petring PJ Mitchell JJ Presneill 《Canadian Metallurgical Quarterly》1998,66(4):1242-1245
The use of PCR to amplify a specific virA gene fragment serves as a highly specific and sensitive method to detect virulent bacteria of the genus Shigella and enteroinvasive Escherichia coli. Amplification of a 215-bp DNA band was obtained by using isolated genomic DNA of Shigella, individual cells of Shigella dysenteriae, and mayonnaise contaminated with S. dysenteriae. Moreover, a multiplex PCR with specific (virA) and bacterium-restricted (16S ribosomal DNA) primers generated an amplification product of approximately 755 bp for all bacteria tested and an additional 215-bp product for Shigella and enteroinvasive E. coli. 相似文献