全文获取类型
收费全文 | 36366篇 |
免费 | 1915篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 317篇 |
综合类 | 17篇 |
化学工业 | 7235篇 |
金属工艺 | 702篇 |
机械仪表 | 851篇 |
建筑科学 | 1002篇 |
矿业工程 | 120篇 |
能源动力 | 618篇 |
轻工业 | 5884篇 |
水利工程 | 346篇 |
石油天然气 | 153篇 |
武器工业 | 5篇 |
无线电 | 1460篇 |
一般工业技术 | 6349篇 |
冶金工业 | 8159篇 |
原子能技术 | 153篇 |
自动化技术 | 4944篇 |
出版年
2024年 | 83篇 |
2023年 | 329篇 |
2022年 | 360篇 |
2021年 | 885篇 |
2020年 | 756篇 |
2019年 | 839篇 |
2018年 | 1508篇 |
2017年 | 1483篇 |
2016年 | 1558篇 |
2015年 | 1156篇 |
2014年 | 1369篇 |
2013年 | 2891篇 |
2012年 | 2098篇 |
2011年 | 1927篇 |
2010年 | 1588篇 |
2009年 | 1435篇 |
2008年 | 1366篇 |
2007年 | 1259篇 |
2006年 | 854篇 |
2005年 | 719篇 |
2004年 | 675篇 |
2003年 | 593篇 |
2002年 | 586篇 |
2001年 | 441篇 |
2000年 | 427篇 |
1999年 | 466篇 |
1998年 | 2430篇 |
1997年 | 1659篇 |
1996年 | 1059篇 |
1995年 | 638篇 |
1994年 | 498篇 |
1993年 | 582篇 |
1992年 | 218篇 |
1991年 | 221篇 |
1990年 | 169篇 |
1989年 | 167篇 |
1988年 | 170篇 |
1987年 | 150篇 |
1986年 | 134篇 |
1985年 | 164篇 |
1984年 | 150篇 |
1983年 | 114篇 |
1982年 | 148篇 |
1981年 | 165篇 |
1980年 | 168篇 |
1979年 | 97篇 |
1978年 | 98篇 |
1977年 | 297篇 |
1976年 | 647篇 |
1973年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Characterisation of greywater was conducted in two different greywater streams in the Netherlands (Groningen and Sneek). The concentrations of macropollutants and nutrients measured were very different in both streams; in particular the COD was 425 mg/L in Groningen's water whereas in Sneek it was 1,583 mg/L. The aerobic treatment of greywater in a fed-batch reactor led to a 90% removal of COD at different organic loading rates. Anaerobically, the removal reached 40% COD removal on average, the possible reason being the high amount of surfactants present in the influent. 相似文献
54.
MJ González-Corbella MC López-Sabater AI Castellote-Bargalló C Campoy-Folgoso M Rivero-Urgell 《Canadian Metallurgical Quarterly》1998,52(11):813-818
OBJECTIVE: To assess the effect of long-chain polyunsaturated fatty acids (LCPUFA)- and vitamin E-supplemented formula feeding on erythrocyte and plasma alpha-tocopherol (VE), and plasma retinol (VA) concentrations in neonates and to compare these values with those found in infants feeding on infant formula without LCPUFA or breast milk SETTING: University Hospital of Granada, Spain. SUBJECTS: 49 full-term infants. DESIGN AND INTERVENTION: Subjects who chose not to breast feed were fed either (i) unsupplemented infant formula (F) or (ii) infant formula supplemented with LCPUFA and vitamin E (FL). Alpha-tocopherol and retinol were measured at 7 days, 1 month and 3 months. RESULTS: Plasma and erythrocyte VE concentrations and plasma VE/total lipids ratio increased significantly in all groups at 1 month of life (P < 0.05), but did not change significantly between 1 month and 3 months in any group (P > 0.05). Erythrocyte VE and VA retinol concentrations were higher in infants fed an infant formula than in breast milk-fed infants at 1 month of life (P < 0.05). Finally, there were no significant differences in plasma or erythrocyte VE levels, plasma VA or plasma VE/total lipid ratio between any groups at 3 months of life (P > 0.05). CONCLUSION: Infants fed on LCPUFA- and vitamin E-supplemented infant formula for 3 months have similar vitamin E and A status to infants fed on breast milk or infant formula without LCPUFA supplementation. 相似文献
55.
B Cukrowska I Trebichavsky P Rossmann Z Reháková J Sinkora K Haverson R Lodinová-Zádníková H Tlaskalová-Hogenová 《Canadian Metallurgical Quarterly》1998,6(3-4):171-178
We have recently reported that thymic B lymphocytes (TBL) are the first B-cell subpopulation undergoing isotype switching to IgG and IgA during embryonic life. The aim of this study is to analyze the influence of antigenic stimulation on TBL location and activity using a germ-free (GF) newborn pig model, in which maternal antibodies and antigens do not affect B-cell development. Immunohistological analysis showed that TBL were disseminated mainly in the thymic medulla. There were no differences in the distribution of TBL, both in GF newborn piglets before and after colonization with Escherichia coli and in older conventionally reared (CONV) piglets. The number of immunoglobulin (Ig)-secreting cells measured by the ELISPOT method was not influenced by microflora and food antigens. IgM-positive cells secreting IgM and CD45RC-positive cells spontaneously producing IgM, IgG, and IgA were detected in newborn thymus. Our findings suggest that TBL differentiation and Ig switching to IgG and IgA-secreting cells is not influenced by external antigens and that the thymic microenvironment plays an important role in this process. 相似文献
56.
J. L. Huertas A. Rueda D. Vázquez 《Analog Integrated Circuits and Signal Processing》1993,4(3):199-213
A design-for-test methodology for SC filters is presented, based on an architecture using some additional circuitry and providing extra capabilities for both off- and on-line tests. The approach uses a comparison (voting) mechanism to indicate whether or not two copies of a filter element (a biquad, for instance) have a similar response during their actual operation. The design and implementation of a few filter examples are included to assess the potential usefulness of this new approach. 相似文献
57.
It is shown that the Caenorhabditis elegans genome contains several distantly related members of the gene family of saposin-like proteins. The putative products of genes T07C4.4, T08A9.7A, T08A9.7B, T08A9.8, T08A9.9, T08A9.10 are similar to the amoebapores of Entamoeba histolytica, granulysin of cytotoxic T lymphocytes and a putative amoebapore-related protein of the liver fluke Fasciola hepatica inasmuch as they consist of only a single saposin-like domain and a secretory signal peptide. The saposin-like domain of protein T07C4.4, which is most closely related to NK-lysin and granulysin, has been expressed in Escherichia coli and the recombinant protein was shown to have a circular dichroism spectrum consistent with the helix bundle structure characteristic of saposin-like domains. Recombinant T07C4.4 protein was found to have antibacterial activity, suggesting that these amoebapore homologs may play a role in antibacterial mechanisms of C. elegans. 相似文献
58.
Pena Julio Nápoles Gonzalo Salgueiro Yamisleydi 《Artificial Intelligence Review》2021,54(5):3817-3847
Artificial Intelligence Review - Attribute weighting is a task of paramount relevance in multi-attribute decision-making (MADM). Over the years, different approaches have been developed to face... 相似文献
59.
Tomá? Kroupa 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2012,16(11):1851-1861
We generalise belief functions to many-valued events which are represented by elements of Lindenbaum algebra of infinite-valued ?ukasiewicz propositional logic. Our approach is based on mass assignments used in the Dempster–Shafer theory of evidence. A generalised belief function is totally monotone and it has Choquet integral representation with respect to a unique belief measure on Boolean events. 相似文献
60.
The conditions for current oscillations in austenitic stainless steel (AISI Type 303) in 1M H2SO4 containing Cl? ions are given. The periodic oscillations are produced in a close potential range determined at the active-passive transition region. It requires a non-homogeneous distribution of inclusions and carbides at the metal surface and a concentration range of Cl? ion where active and passive areas coexist on the metal surface. The constraints at the surface determining these two regions are related to the Cl? ion competitive adsorption and the local accumulation of corrosion products. Electrochemical data and SEM observations are correlated. 相似文献