全文获取类型
收费全文 | 5551篇 |
免费 | 229篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 139篇 |
综合类 | 13篇 |
化学工业 | 1425篇 |
金属工艺 | 117篇 |
机械仪表 | 104篇 |
建筑科学 | 431篇 |
矿业工程 | 10篇 |
能源动力 | 122篇 |
轻工业 | 764篇 |
水利工程 | 36篇 |
石油天然气 | 13篇 |
无线电 | 287篇 |
一般工业技术 | 919篇 |
冶金工业 | 638篇 |
原子能技术 | 58篇 |
自动化技术 | 711篇 |
出版年
2022年 | 44篇 |
2021年 | 69篇 |
2020年 | 55篇 |
2019年 | 58篇 |
2018年 | 66篇 |
2017年 | 85篇 |
2016年 | 114篇 |
2015年 | 137篇 |
2014年 | 149篇 |
2013年 | 249篇 |
2012年 | 227篇 |
2011年 | 243篇 |
2010年 | 209篇 |
2009年 | 224篇 |
2008年 | 217篇 |
2007年 | 250篇 |
2006年 | 202篇 |
2005年 | 203篇 |
2004年 | 184篇 |
2003年 | 125篇 |
2002年 | 136篇 |
2001年 | 111篇 |
2000年 | 99篇 |
1999年 | 77篇 |
1998年 | 87篇 |
1997年 | 85篇 |
1996年 | 83篇 |
1995年 | 76篇 |
1994年 | 55篇 |
1993年 | 78篇 |
1992年 | 80篇 |
1991年 | 53篇 |
1990年 | 62篇 |
1989年 | 62篇 |
1987年 | 71篇 |
1986年 | 58篇 |
1985年 | 72篇 |
1984年 | 65篇 |
1983年 | 64篇 |
1982年 | 63篇 |
1981年 | 69篇 |
1980年 | 68篇 |
1979年 | 68篇 |
1978年 | 53篇 |
1977年 | 54篇 |
1976年 | 57篇 |
1975年 | 56篇 |
1974年 | 67篇 |
1973年 | 49篇 |
1970年 | 41篇 |
排序方式: 共有5787条查询结果,搜索用时 15 毫秒
991.
Addition of lithiated methoxyallene 5 to literature‐known amino aldehyde 3 followed by ozonolysis provided syn‐configurated α‐hydroxy‐β‐amino ester 6 in moderate overall yield and with an ee of 90%. The predominant formation of syn‐compounds may be due to a chelate controlled addition step. 相似文献
992.
Aromatic aldehyde derivatives of N-phenyl-aza-15-crown-5 ( 2 ), N-phenyl-aza-18-crown-6 ( 8 ), and benzo-15-crown-5 ( 10 ) are condensed with malononitrile and 2-amino-1,1,3-tricyano-1-propene to give light yellow to orange colored crown ether derivatives 4 , 5a , 9a , 11 , and 12 . 5a and 9a were acylated with ethyl chloroformate to give the magenta colored dyes 5b and 9b , respectively. By condensation of N-(4-nitrosophenyl)-aza-15-crown-5 3 with 2-amino-1,1,3-tricyano-1-propene the magenta dye 6a is obtained. Acylation of 6a with ethyl chloroformate leads to the deep blue colored dye 6b . In these derivatives the nitrogen or oxygen atoms of the crown ethers are part of the chromophoric system, and binding properties are affected. Further chromophoric derivatives of aza-crown ethers are studied in which these are separated from the chromophoric moiety by a spacer. N-(ω-chloroalkyl)-N-alkylanilines 14a-c were attached to aza-15-crown-5 13a-c and aza-18-crown-6 13b-c to yield the spacer crown ether derivatives 15a-c and 16a-c , respectively. The formylated spacer crown ether derivatives 17a-c and 18b were condensed with 2-amino-1,1,3-tricyano-1-propene to give the orange spacer-chromoionophores 19a-c and 20 . In these crown ether derivatives the extended conjugation is interrupted by the spacer, and good binding properties are obtained. The complex formation constants of the crown ether derivatives with Na+ and K+ are determined using 1H NMR spectroscopy. 相似文献
993.
Secret of Timbre When the engineer talks to professional bassoonist about the secret of timbre of a real good bocal, also called crook, which is the second element after the double reed mouth piece leading into the first downwards leading wooden wing joint of a bassoon, then it is obvious that objective interpretations are rare in this discussion. It is said that pitch is the sum of fundamental and over tones whereas timbre is the transient behavior of pitches. The interpretation of timbre is … 相似文献
994.
Christian Kennes Huub H. J. Cox Hans J. Doddema Wim Harder 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1996,66(3):300-304
Three identical biofilters, run under the same conditions but inoculated with different mixed cultures, were fed a mixture of toluene, ethylbenzene, and o-xylene (TEX) gases. Inert porous perlite was used as support material, in contrast to the more conventional biofiltration systems where natural supports are used. Biodegradation started in all three biofilters a few hours after inoculation, without previous adaptation of the inocula to the toxic mixture. Despite acidification of the systems to pH values below 4·5, the elimination capacities reached were fully satisfactory. The best performing biofilter, in which bacteria were dominant, showed an elimination capacity of 70 g TEX m−3 h−1 with a near complete removal of the mixture up to an influent concentration of 1200 mg TEX m−3 at a gas residence time of 57 s. Most of the ingoing carbon was recovered as carbon dioxide in the outgoing gas. In the other biofilters fungi dominated and performance was slightly worse. With single substrates, the elimination capacity was higher for toluene and ethylbenzene than for the TEX mixture, whereas o-xylene removal was slowest in all cases. Also when feeding the mixture to the biofilters, o-xylene was removed most slowly. 相似文献
995.
996.
The nucleotide sequence of a 26·7 kb DNA segment from the left arm of Saccharomyces cerevisiae chromosome IV is presented. An analysis of this segment revealed 11 open reading frames (ORFs) longer than 300 bp and one split gene. These ORFs include the genes encoding the large subunit of RNA polymerase II, the biotin apo-protein ligase, an ADP-ribosylation factor (ARF 2), the ‘L35’-ribosomal protein, a rho GDP dissociation factor, and the sequence encoding the protein phosphatase 2A. Further sequence analysis revealed a short ORF encoding the ribosomal protein YL41B, an intron in a 5′ untranslated region and an extended homology with another cosmid (X83276) located on the same chromosome. The potential biological relevance of these findings is discussed. The sequence was submitted to the EMBL database under Accession Number X96876. 相似文献
997.
Roua Hassoun Heidi Budde Hans Georg Mannherz Mria Ldi Setsuko Fujita-Becker Kai Thorsten Laser Anna Grtner Karin Klingel Desire Mhner Robert Stehle Innas Sultana Thomas Schaaf Mario Majchrzak Verena Krause Christian Herrmann Marc M. Nowaczyk Andreas Mügge Gabriele Pfitzer Rasmus R. Schrder Nazha Hamdani Hendrik Milting Kornelia Jaquet Diana Cimiotti 《International journal of molecular sciences》2021,22(17)
Rare pediatric non-compaction and restrictive cardiomyopathy are usually associated with a rapid and severe disease progression. While the non-compaction phenotype is characterized by structural defects and is correlated with systolic dysfunction, the restrictive phenotype exhibits diastolic dysfunction. The molecular mechanisms are poorly understood. Target genes encode among others, the cardiac troponin subunits forming the main regulatory protein complex of the thin filament for muscle contraction. Here, we compare the molecular effects of two infantile de novo point mutations in TNNC1 (p.cTnC-G34S) and TNNI3 (p.cTnI-D127Y) leading to severe non-compaction and restrictive phenotypes, respectively. We used skinned cardiomyocytes, skinned fibers, and reconstituted thin filaments to measure the impact of the mutations on contractile function. We investigated the interaction of these troponin variants with actin and their inter-subunit interactions, as well as the structural integrity of reconstituted thin filaments. Both mutations exhibited similar functional and structural impairments, though the patients developed different phenotypes. Furthermore, the protein quality control system was affected, as shown for TnC-G34S using patient’s myocardial tissue samples. The two troponin targeting agents levosimendan and green tea extract (-)-epigallocatechin-3-gallate (EGCg) stabilized the structural integrity of reconstituted thin filaments and ameliorated contractile function in vitro in some, but not all, aspects to a similar degree for both mutations. 相似文献
998.
999.
Reichardt N Gniechwitz D Steinhart H Bunzel M Blaut M 《Molecular nutrition & food research》2009,53(2):287-299
To investigate the structure and fermentability of high M(r) components of coffee brews by human gut bacteria Arabica coffee samples of three different degrees of roast (light, medium, and dark) were used for drip brew preparations and fractionation by ultrafiltration with different M(r) cut-offs. Total carbohydrates of the fractions ranged from 28.6 g/100 g to 56.7 g/100 g. Galactomannans and arabinogalactans were the main polysaccharides and made up between one-fourth and one-half of the respective coffee fraction. After 24 h of incubation with a human fecal suspension the polysaccharides of all fractions were extensively degraded. A decrease in the absorbance values at 405 and 280 nm, respectively, indicated that also chemically noncharacterized UV-active components such as Maillard reaction products, had been partially degraded or modified by the human gut bacteria. The remainder after 24 h of fermentation still showed antioxidant activity. Bacterial cells belonging to the Bacteroides-Prevotella group increased 2- to 40-fold during fermentation depending on the M(r) range of the fraction and the degree of roast. The production of high amounts of acetate and propionate is in accordance with a role of these bacteria in the degradation of high M(r) components from coffee. 相似文献
1000.
Nico Stehr Hans von Storch 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2009,55(3):56-60
The voice of the social sciences in climate research and in climate policy discussions, except for interventions from economists
mainly about the costs associated with policy options driven by climate science research, has been muted if not altogether
absent. The absence of the social sciences from climate research and policy not surprisingly has coloured climate discourse
in peculiar ways. We are making the case for a greater involvement and importance of the social sciences in interdisciplinary
climate research.
It is not space but the structuring that comes from the soul that has social significance. Georg Simmel ([1908] 1992)
Soil and climate together determine the natural fertility of a country and of its people who are led either to indolence or to activity. Werner Sombart (1938)相似文献