全文获取类型
收费全文 | 4732篇 |
免费 | 87篇 |
国内免费 | 9篇 |
学科分类
工业技术 | 4828篇 |
出版年
2023年 | 16篇 |
2021年 | 83篇 |
2020年 | 36篇 |
2019年 | 42篇 |
2018年 | 42篇 |
2017年 | 37篇 |
2016年 | 74篇 |
2015年 | 40篇 |
2014年 | 98篇 |
2013年 | 177篇 |
2012年 | 135篇 |
2011年 | 182篇 |
2010年 | 137篇 |
2009年 | 150篇 |
2008年 | 150篇 |
2007年 | 131篇 |
2006年 | 130篇 |
2005年 | 119篇 |
2004年 | 120篇 |
2003年 | 119篇 |
2002年 | 100篇 |
2001年 | 128篇 |
2000年 | 96篇 |
1999年 | 136篇 |
1998年 | 554篇 |
1997年 | 340篇 |
1996年 | 247篇 |
1995年 | 133篇 |
1994年 | 140篇 |
1993年 | 113篇 |
1992年 | 65篇 |
1991年 | 57篇 |
1990年 | 53篇 |
1989年 | 53篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 46篇 |
1985年 | 45篇 |
1984年 | 36篇 |
1983年 | 39篇 |
1982年 | 41篇 |
1981年 | 47篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 20篇 |
1977年 | 27篇 |
1976年 | 54篇 |
1974年 | 11篇 |
1973年 | 15篇 |
1972年 | 11篇 |
排序方式: 共有4828条查询结果,搜索用时 15 毫秒
81.
Time-series primitive static states for detailing work state and flow of human-operated work machine
This paper proposes a quantification method for a comprehensive work flow in construction work for describing work states in more detail on the basis of analyzing state transitions of primitive static states (PSS), which consist of 16 symbolic work states defined by using on-off state of the lever operations and joint loads for the manipulator and end-effector. On the basis of the state transition rules derived from a transition-condition analysis, practical state transitions (PST), which are common and frequent transitions in arbitrary construction work, are defined. PST can be classified into essential state transition (EST) or nonessential state transitions (NST). EST extracts common phases of work progress and estimates positional relations between a manipulator and an object. NST reveals wasted movements that degrade the efficiency and quality of work. To evaluate comprehensive work flows modeled by combining EST and NST, work-analysis experiments using our instrumented setup were conducted. Results indicate that all the PSS definitely changes on the basis of PST under various work conditions, and work analysis using EST and NST easily reveals work characteristics and untrained tasks related to wasted movements. 相似文献
82.
Atsushi Takahashi Isao Nakamura Masaaki Haneda Tadahiro Fujitani Hideaki Hamada 《Catalysis Letters》2006,106(3-4):133-138
Catalytic hydrogenation of naphthalene to decalin was studied over a carbon-supported rhodium catalyst in supercritical carbon
dioxide solvent at 333 K, and the results were compared with those in an organic solvent. cis-, trans-Decalin and tetralin were formed from the beginning of the reaction in supercritical carbon dioxide. Higher concentration
of hydrogen in carbon dioxide solvent and on the active site, and also the suppression of desorption of partially hydrogenated
tetralin molecules from the active site would be responsible for higher selectivity to cis-decalin in supercritical carbon dioxide than that in an organic solvent. 相似文献
83.
Hitoshi Masuda Chiyoshi Kamizawa Kunio Hata Kingo Yokota Tomoo Sakai Mitsuhiro Sato 《Desalination》1978,25(1):89-97
The evaporation drain of sulfite pulp spent liquor contains few volatile fatty acids, most of which is acetic acid. The main objective of this study is to recover acetic acid as the concentrated solution (about 4%), which could be used as a culture medium of the yeast. As acetic acid can easily pass through the cellulose acetate membrane, SP drains neutralized by NaOH, NH4OH and Ca(OH)2 were used as the feed solutions. In all cases, concentration by reverse osmosis was successfully carried out provided the appropriate pretreatment was employed. The recovery of acetic acid was 95.6, 90.5 and 98.2% for Na-, NH4-, and Ca-drain, respectively. In addition, the recovered (permeated) water may be used as an industrial one. 相似文献
84.
Takashi Nakamura 《Lipids》1986,21(9):553-557
Prostaglandin-like substances other than 3-(2-ethyl-5-hydroxy-3-oxo)-cyclopentanyl-2-propenal (compound I), which upon reacting
with amino acids form reddish pigments, were purified, and their chemical structures were determined. Three red pigment-forming
substances (RPS) in autoxidized methyl linolenate were purified successively by gel chromatography on Sephadex LH-20, column
chromatography and thin layer chromatography on Silica Gel 60, and by high performance liquid chromatography on μ-Porasil.
IR spectra of the RPS showed the absorption of an ester group (νC=O 1730 cm−1 in CHCl3) and of a longer branched chain (νC-H 2800–3100 cm−1), in addition to the absorption bands observed in compound I. Electron impact mass spectra of the trimethylsilyl ethers obtained
after reduction with NaBH4 and NaBD4 were analyzed in detail and compared with those of compound I. The structures of the RPS were identified as stereoisomeric
methyl 8-[2-(2-formylvinyl)-3-hydroxy-5-oxo-cyclopentanyl]-octanoates derived from methyl 12-hydroperoxy-linolenate.
Presented at the general meeting of the Japanese Society of Scientific Fisheries, held at Tohoku University, Sendai, Japan,
October 1984. 相似文献
85.
Dimethylsiloxane-tetramethyl-p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D3). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D3 initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D3 by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D3 to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×104 to 19.4×104 and were close to the predicted values calculated from the of the TMPS prepolymer and the amount of D3 added. In the case of method 2, weight-average molecular weights ranged from 19.5×104 to 24.2×104. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers. 相似文献
86.
A technique for separating similar and diverse ionogenic mixtures into their individual homologs was studied by high performance
liquid chromatography on an octadecyl-silica (TSK Gel LS-410) column. Conditions used for the separation were: column size,
6 mm id×200 mm; mobile phase, water/methanol (15:85, v/v) containing (a) 1.0 M sodium perchlorate and adjsting to pH 2.5 with
phosphoric acid, (b) 0.1 M and pH 3.5; column temp., 50 C. By using 2 mobile phase conditions, various surfactant mixtures
were separated into their individual homologs and simultaneously distinguished from each other, regardless of their ionogenic
properties. 相似文献
87.
Poly(4-acetoxystyrene) (PAS) and poly(4-acetoxy-3-methoxystyrene) (PAMS), poly(4-hydroxystyrene) (PHS) and poly(4-hydroxy-3-methoxystyrene) (PHMS) have been prepared. The effects of hydrogen bonding on the glass transition temperatures (Tg) of these polymers have been studied by differential scanning calorimetry. The Tg′s of partially hydrolyzed PAS and PAMS increased with the degree of hydrolysis. Partially hydrolyzed PAS and PAMS are estimated to be random copolymers, judging from the correspondence between the calculated and observed Tg′s of these polymers. The effect of water on the glass transition was also studied, and it was clarified how water adsorbed on the polymers acts as a hydrogen-bond breaker. The ‘critical water content’ is calculated from the decrease of Tg by water absorption, and the relation between hydrogen bonding and Tg is discussed. 相似文献
88.
Vertical pneumatic conveying was studied in a 3-inch diameter riser 30 feet in length using solids ranging in particle Reynolds number from 100 to 3500. Particle to gas mass flow ratios varied from 0 to 8 and pipeline conditions extended from dilute flow down into the choking region. Average particle hold-up was determined by means of a series of quick-closing valves and particle slip velocity was often found to be greater than the calculated terminal velocity. The reasons for this are examined. Frictional pressure losses in the riser were also determined and compared with literature data. The phenomenon of choking is considered briefly. 相似文献
89.
Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells 总被引:2,自引:0,他引:2
T. Matsumoto T. Komatsu H. Nakano K. Arai Y. Nagashima E. Yoo T. Yamazaki M. Kijima H. Shimizu Y. Takasawa J. Nakamura 《Catalysis Today》2004,90(3-4):277-281
A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm2. K2PtCl4 and H2PtCl6·6(H2O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs. 相似文献
90.
Individual action and synergistic effect in the combination of 6-anilino-1,3,5-triazine-2,4-dithiol (AF), zinc stearate, and barium stearate on the color stabilization of PVC were investigated. In this system, AF selectively reacts with allylic chlorine atoms in PVC. Consequently, unstable allylic chlorine units were converted to thermally stable allylic structures, thus retarding the development of polyene sequences. Zinc stearate accelerated the reaction of AF with allylic chlorine atoms in PVC, forming the zinc salts of AF (AFZnSt, St?C1–H35COO? ) by reacting with AF. Barium stearate reacted with ZnCl2 which is formed in the above reaction to give St2Zn and BaCl2. Consequently, barium stearate led to the selective reaction of AF with allylic chlorine atoms in PVC and the remarkable retarding effect of discoloration of PVC. 相似文献