全文获取类型
收费全文 | 10500篇 |
免费 | 261篇 |
国内免费 | 14篇 |
学科分类
工业技术 | 10775篇 |
出版年
2022年 | 93篇 |
2021年 | 122篇 |
2020年 | 90篇 |
2019年 | 123篇 |
2018年 | 153篇 |
2017年 | 134篇 |
2016年 | 175篇 |
2015年 | 151篇 |
2014年 | 205篇 |
2013年 | 523篇 |
2012年 | 319篇 |
2011年 | 420篇 |
2010年 | 396篇 |
2009年 | 337篇 |
2008年 | 384篇 |
2007年 | 362篇 |
2006年 | 327篇 |
2005年 | 336篇 |
2004年 | 248篇 |
2003年 | 270篇 |
2002年 | 244篇 |
2001年 | 201篇 |
2000年 | 205篇 |
1999年 | 176篇 |
1998年 | 696篇 |
1997年 | 508篇 |
1996年 | 374篇 |
1995年 | 298篇 |
1994年 | 252篇 |
1993年 | 257篇 |
1992年 | 123篇 |
1991年 | 115篇 |
1990年 | 124篇 |
1989年 | 135篇 |
1988年 | 124篇 |
1987年 | 90篇 |
1986年 | 81篇 |
1985年 | 110篇 |
1984年 | 116篇 |
1983年 | 88篇 |
1982年 | 75篇 |
1981年 | 71篇 |
1980年 | 86篇 |
1979年 | 79篇 |
1978年 | 91篇 |
1977年 | 124篇 |
1976年 | 207篇 |
1975年 | 61篇 |
1974年 | 64篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 6 毫秒
101.
Time-of-flight secondary ion mass spectrometry has been used to study the interaction of -amino propyl triethoxysilane with an E-glass surface. The fragmentation pattern has been interpreted by assigning a series of mass peaks to the structural unit of the poly(aminosiloxane). The composition of the coating is complicated by the presence of polydimethylsiloxane and its copolymers. The highest mass fragment was obtained from the coating exposed by extraction with warm water (697 AMU). The largest molecular fragments would appear to have degrees of polymerization of 6 with differing numbers of silanol groups. On re-extraction with hot water the fragment size decreased. It is postulated that the network chain length of the three-dimensional polymer decreased as the interface was approached. At the glass surface a chemically bound molecular layer could be identified. The full chemical nature of the deposit is complicated by the incorporation of aluminium from the substrate into the coating. It was also possible to confirm that a layer of warm-water soluble oligomers existed at the air interface. 相似文献
102.
A Further Comparison of Splitting Rules for Decision-Tree Induction 总被引:10,自引:0,他引:10
One approach to learning classification rules from examples is to build decision trees. A review and comparison paper by Mingers (Mingers, 1989) looked at the first stage of tree building, which uses a splitting rule to grow trees with a greedy recursive partitioning algorithm. That paper considered a number of different measures and experimentally examined their behavior on four domains. The main conclusion was that a random splitting rule does not significantly decrease classificational accuracy. This note suggests an alternative experimental method and presents additional results on further domains. Our results indicate that random splitting leads to increased error. These results are at variance with those presented by Mingers. 相似文献
103.
Jones AD Homan AC Favell DJ Hitchcock CH Berryman PM Griffiths NM Billington MJ 《Meat science》1985,15(3):137-147
Protein-bound N(τ)-methylhistidine (N-MeHis) has been suggested as an index for the estimation of muscle (meat) protein in meat and meat products. This paper examines the levels of N-MeHis in a range of six prime beef cuts together with beef flank, cheek, mechanically recovered meat (MRM) and offals. The study was undertaken by two separate laboratories using a previously reported HPLC procedure involving the conversion of N-MeHis to a fluorescent derivative. It is shown that, whilst similar N-MeHis levels are present in the prime cuts, there is considerable variation in those found in the other cuts and offals. The average N-MeHis level in six prime cuts observed at both laboratories is 122 μg/g fat-free connective tissue-free (FFCF) meat; however, flank exhibits apparently high N-MeHis levels, whilst cheek and MRM contain only approximately 70% of the level found in the prime cuts. The offals contain between 0 and 65% of the N-MeHis level found in prime cuts. The greater variability and the often lower value of the N-MeHis content of these legitimate meat materials preclude the establishment of a single realistic index for FFCF beef, and present fundamental problems for the assessment of the lean meat content of manufactured beef products by N-MeHis determination. 相似文献
104.
105.
A time variant, roundness based adaptive size and roundness control system is presented for the plunge grinding process which avoids the need for a large data processing capacity and compares favourably in performance with the large and expensive control system previously developed and therefore improves the prospect of industrial use. The non-linear control functions and adaptive model are presented and analysed. The hardware of the integrated, low cost system and the software algorithms used to reduce the computational power requirements are discussed and the results of grinding experiments are presented. 相似文献
106.
Jones Robert M. Webster John G. Keesey Ulker Tulunay 《IEEE transactions on bio-medical engineering》1972,(1):29-33
In normal vision, eye movements cause the image to move on the retina. Special apparatus can stabilize the image on the retina so it cannot move, and vision fades away. Previous methods for stabilizing the image were either optical systems or complex computer-controlled feedback systems. A simpler feedback system is presented which detects eye motion and rotates a mirror through which the target is viewed, to exactly compensate for eye motion. Unlike previous optical systems, this new system has no lenses in either the viewing or the image-forming path to limit the spatial resolution. 相似文献
107.
57Fe Mössbauer spectroscopy has been used to characterize the iron-bearing minerals present in some British Columbia coals. The minerals observed in a range of samples include pyrite/marcasite, siderite, jarosite, rozenite or melanterite, and Fe2+ -bearing clay minerals such as illite. The presence of jarosite is confirmed through the magnetic hyperfine interaction observed at 4.2 K. The absence of magnetic ordering at 4.2 K for the ferrous sulphate component indicates the presence of rozenite, FeS04 · 4H20, or melanterite, FeS04 · 7H20, rather than szomolnokite, FeS04 · H20 or FeS04. The effects of ashing on two of the coals is also studied. 相似文献
108.
G. T. Jones L. A. Glasgow L. E. Erickson S. A. Patel C. H. Lee 《Chemical Engineering Communications》1990,97(1):181-196
Understanding the dynamic phenomena of viability loss of shear sensitive cells and bubble breakage and coalescence within airlift reactors requires knowledge of local, liquid-phase hydrodynamics. The laser-Doppler velocimeter (LDV) is a non-invasive instrument which may be used to obtain this information. Experimental procedures and software were developed to detect and measure Doppler bursts in two-phase flow in a split-cylinder airlift reactor. Off-line analysis of the data indicated a detection rate approximately one order of magnitude greater than that observed using an available commercial frequency tracker. Approximately 400 to 500 observations are needed for the ensemble mean to characterize the local mean velocity to within ±5% for a superficial gas velocity of 10.4 cm/s, the highest superficial gas velocity used in these studies. The limitations, prospects, and signal-processing options for LDV in this application are also discussed 相似文献
109.
Analysis of the carbon disulphide extracts of nine samples of UK coal-maceral concentrates by 1H highresolution n.m.r. spectroscopy, gas-liquid chromatography and field-desorption mass spectrometry indicates the presence of components with a wide molecular weight range extending up to 1200 amu; these are attributed to n-alkanes up to ≈C50 and highly condensed polynuclear aromatic compounds. 相似文献
110.
Tjokorde W. Samadhi Linda E. Jones Alexis G. Clare 《Journal of the American Ceramic Society》2003,86(12):2044-2049
Carbon reacts with Na2 SO4 in glass batches, influencing SO x emissions. To study the role of carbon active surface area (ASA) in the decomposition phenomena, Na2 SO4 is reacted with three carbons with a wide ASA range. The decomposition behavior was evaluated by thermogravimetric analysis (TGA) and evolved gas analysis via mass spectrometry and Fourier transform infrared spectrometry. Higher carbon ASA yields lower decomposition temperatures. SO x emissions are realized at temperatures as low as 773 K. Isothermal Na2 SO4 –C decomposition initiates via the nucleation of Na2 S. The rate constants for the nucleation regime are normalized against ASA, yielding an activation energy of 275 kJ/mol for nucleation. 相似文献