全文获取类型
收费全文 | 5877篇 |
免费 | 135篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 86篇 |
综合类 | 22篇 |
化学工业 | 1250篇 |
金属工艺 | 163篇 |
机械仪表 | 118篇 |
建筑科学 | 248篇 |
矿业工程 | 30篇 |
能源动力 | 79篇 |
轻工业 | 816篇 |
水利工程 | 27篇 |
石油天然气 | 9篇 |
无线电 | 412篇 |
一般工业技术 | 884篇 |
冶金工业 | 1251篇 |
原子能技术 | 50篇 |
自动化技术 | 569篇 |
出版年
2022年 | 54篇 |
2021年 | 76篇 |
2020年 | 78篇 |
2019年 | 63篇 |
2018年 | 80篇 |
2017年 | 54篇 |
2016年 | 106篇 |
2015年 | 84篇 |
2014年 | 114篇 |
2013年 | 139篇 |
2012年 | 174篇 |
2011年 | 220篇 |
2010年 | 179篇 |
2009年 | 174篇 |
2008年 | 183篇 |
2007年 | 179篇 |
2006年 | 162篇 |
2005年 | 201篇 |
2004年 | 137篇 |
2003年 | 113篇 |
2002年 | 128篇 |
2001年 | 120篇 |
2000年 | 118篇 |
1999年 | 119篇 |
1998年 | 390篇 |
1997年 | 240篇 |
1996年 | 171篇 |
1995年 | 162篇 |
1994年 | 125篇 |
1993年 | 128篇 |
1992年 | 88篇 |
1991年 | 72篇 |
1990年 | 79篇 |
1989年 | 66篇 |
1988年 | 59篇 |
1987年 | 60篇 |
1986年 | 68篇 |
1985年 | 81篇 |
1984年 | 65篇 |
1983年 | 44篇 |
1982年 | 50篇 |
1981年 | 59篇 |
1980年 | 54篇 |
1979年 | 71篇 |
1978年 | 48篇 |
1977年 | 80篇 |
1976年 | 118篇 |
1975年 | 39篇 |
1974年 | 54篇 |
1972年 | 36篇 |
排序方式: 共有6014条查询结果,搜索用时 11 毫秒
21.
Schneider P 《Computers in healthcare》1990,11(1):26-7, 30
Community outreach programs like health screenings will face increasing scrutiny as attempts to reconcile expenses and revenues intensify. If you cannot supply evidence that a screening program can generate new revenue, that program might be written off as a loser. Providing the evidence is not as difficult as you might think; it requires planning and the resourceful use of software you may already have available. 相似文献
22.
Friedrich Otto 《Theory of Computing Systems》1987,20(1):253-260
WhenC is a concurrency relation on alphabet , then */=
C
is a free partially commutative monoid. Here we show that it is decidable in polynomial time whether or not there exists a finite canonical rewriting systemR on such that the congruences
R
*
generated byR and =
C
induced byC coincide. Further, in case such a systemR exists, one such system can be determined in polynomial time. 相似文献
23.
Two different methods of producing bi‐ and trimodal latices of a mixture of methyl methacrylate, butyl acrylate, and small amounts of acrylic acid were tested. It is shown that a combination of concentrating blends of seed particles by semibatch reaction, followed by a nucleation of small particles plus a second semibatch phase allowed us to obtain stable latices with solids contents over 65% and viscosities of below 2500 mPa s?1 with little coagulum formation. The key parameter in determining latex stability, coagulum formation, and viscosity appears to be the the particle size distribution, and especially its modification attributed to secondary nucleation. Because it is not possible to eliminate water‐soluble monomers from the polymerization recipe, secondary (homogeneous) nucleation must be minimized by careful addition of the free‐radical initiator and choice of monomer feed flow rates. The nucleation of the third population in the trimodal latices is best accomplished with a mixed surfactant system because renucleation by anionic surfactant alone leads to detrimental changes in the particle size distribution (PSD) resulting from excessive flocculation of particles. In addition, it was found that the viscosity of the final products was not sensitive to small changes in the ionic strength of the latex, although neutralization to a pH of 6 effectively doubles the final latex viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1916–1934, 2002; DOI 10.1002/app.10513 相似文献
24.
Summary Dynamic mechanical measurements on polystyrene — poly(vinylmethylether) blends are demonstrating that the relaxation processes in the blends are mainly connected with the motions of the poly(vinylmethylether) chain.Concerning the effect of mixing on topological properties of the blends, an increase of the polydispersity of the relaxation processes is detected in blends with high molecular weight polystyrene while low molecular weight polystyrene exerts an effect of dilution upon the relaxation of the high molecular poly(vinylmethylether) chains.From these measurements as well as from thermoanalytical data it results that the energetic interaction is more pronounced in the blends with oligomeric than with high molecular weight polystyrene. The glass transition temperature shows a larger deviation from additivity for blends with high molecular polystyrene than for those with oligomeric polystyrene.Herrn Prof. Dr. M. Kryszewski zum 60. Geburtstag herzlichst gewidmet 相似文献
25.
Communication is a key success factor of distributed software projects. Poor communication has been identified as a main obstacle to successful collaboration. Global projects are especially endangered by information gaps between collaborating sites. Different communication styles, technical equipment, and missing awareness of each other can cause severe problems. Knowledge about actual and desired channels, paths, and modes of communication is required for improving communication in a globally distributed project. However, many project participants know little about communication and information flow in their projects. In this contribution, we focus on knowledge about communication and information flow. It is acquired by modelling on‐going and desired flows of information, including documented and non‐documented channels of information flow. We analyzed a distributed software project from the information flow perspective. Based on the findings, we developed specific techniques to improve information flow in distributed software development according to the FLOW Method. In a second distributed project, we evaluated one of the techniques. We found the FLOW mapping technique to be suitable for effectively spreading knowledge about communication and information flow in global software projects. 相似文献
26.
We present formal definitions of anonymity properties for voting protocols using the process algebra CSP. We analyse a number of anonymity definitions, and give formal definitions for strong and weak anonymity, highlighting the difference between these definitions. We show that the strong anonymity definition is too strong for practical purposes; the weak anonymity definition, however, turns out to be ideal for analysing voting systems. Two case studies are presented to demonstrate the usefulness of the formal definitions: a conventional voting system, and Prêt à Voter, a paper-based, voter-verifiable scheme. In each case, we give a CSP model of the system, and analyse it against our anonymity definitions by specification checks using the Failures-Divergences Refinement (FDR2) model checker. We give a detailed discussion on the results from the analysis, emphasizing the assumptions that we made in our model as well as the challenges in modelling electronic voting systems using CSP. 相似文献
27.
Effect of moisture and particle size on the extractability of oils from seeds with supercritical CO2
J. M. Snyder J. P. Friedrich D. D. Christianson 《Journal of the American Oil Chemists' Society》1984,61(12):1851-1856
Moisture level and particle size of soybeans, peanuts and cottonseed were correlated with the extraction rate and yield of
oil when extracted with supercritical carbon dioxide (SC-CO2) at a constant temperature (50 C) and pressure (8000 psig). The rate of extraction and ultimate oil yields were quite low
with cracked soybeans. However, good extraction rates and nearly theoretical oil yields were obtained from ground or thinly
flaked (<0.010″) seeds. Moisture levels between 3% and 12% had little effect on extracability. Oil composition was not influenced
by either parameter. Scanning electron microscopy was used to study seed structure before and after extraction with SC-CO2. Micrographs of SC-CO2-extracted seeds were similar to hexane-extracted seeds.
Presented at the AOCS Meeting, May 1983, Chicago. 相似文献
28.
Monoalkyl esters of linseed-oil-derived C18-saturated cyclic acids (HCal), described in earlier work, showed promise as lubricant base stocks for turbine aircraft as
set forth in the military specification MIL-L-7808E. These esters, however, did not exhibit the increased oxidative stability
and higher viscosity required by the more recent specification MIL-L-23699.
Six diol esters of HCal have now been prepared. Both hindered and unhindered dihydric alcohols were used, including ethylene
glycol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, 2,3-dimethyl-1,3-propanediol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol
(I). The viscosities of these esters at 210F ranged from 10.1 to 19.6 centistokes and the pour points, from −35 to −62F. Oxidative
stabilities at 400F were determined with 0.5% each of phenyl-a-napthylamine (PANA) andp,p’-dioctyldiphenylamine as inhibitors. The esters of the unhindered diols had poor stability, whereas esters of the hindered
diols, in particular I, exhibited excellent resistance to the formation of acidic decomposition products and sludge. Although
the HCal ester of I by itself is too viscous to meet specification MIL-L-23699, its ASTM slope (0.650) is excellent. Blends
of this material with less viscous hindered esters, commercially available, may find application as lubricants for high-performance
turbine engines used in various aircraft.
Presented at the AOCS Meeting in Los Angeles, 1966.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
29.
E. N. Frankel R. A. Awl J. P. Friedrich 《Journal of the American Oil Chemists' Society》1979,56(12):965-969
The use of Cr(CO)6 was investigated to convert polyunsaturated fats intocis unsaturated products. With methyl sorbate, the same order of selectivity for the formation ofcis-3-hexenoate was demonstrated for Cr(CO)6 as for the arene-Cr(CO)3 complexes. With conjugated fatty esters, the stereoselectivity of Cr(CO)6 toward thetrans, trans diene system was particularly high in acetone. However, this solvent was not suitable at elevated temperatures required to
hydrogenatecis, trans- andcis, cis-conjugated dienes (175 C) and nonconjugated soybean oil (200 C). Reaction parameters were analyzed statistically to optimize
hydrogenation of methyl sorbate and soybean oil. To achieve acceptable oxidative stability, it is necessary to reduce the
linolenate constituent of soybean oil below 1–3%. When this is done commercially with conventional heterogenous catalysts,
the hydrogenated products contain more than 15%trans unsaturation. By hydrogenating soybean oil with Cr(CO)6 (200 C, 500 psi H2, 1% catalyst in hexane solution), the product contains less than 3% each of linolenate andtrans unsaturation. Recycling of Cr(CO)6 catalyst by sublimation was carried through three hydrogenations of soybean oil, but, about 10% of the chromium was lost
in each cycle by decomposition. The hydrogenation mechanism of Cr(CO)6 is compared with that of arene-Cr(CO)3 complexes.
Presented in part at Seventh Conference on Catalysis in Organic Syntheses, Chicago, Illinois, June 5–7, 1978. 相似文献
30.
Polymer Bulletin - Solutions of syndiotactic (s) poly (methyl methacrylate) (PMMA) and samples of solid s-PMMA prepared from these solutions were studied by NMR and infrared (IR) spectroscopy and... 相似文献