全文获取类型
收费全文 | 20257篇 |
免费 | 1842篇 |
国内免费 | 251篇 |
专业分类
电工技术 | 24篇 |
综合类 | 614篇 |
化学工业 | 5888篇 |
金属工艺 | 111篇 |
机械仪表 | 286篇 |
建筑科学 | 92篇 |
矿业工程 | 4篇 |
能源动力 | 24篇 |
轻工业 | 13682篇 |
水利工程 | 12篇 |
石油天然气 | 36篇 |
无线电 | 238篇 |
一般工业技术 | 763篇 |
冶金工业 | 70篇 |
原子能技术 | 49篇 |
自动化技术 | 457篇 |
出版年
2024年 | 215篇 |
2023年 | 496篇 |
2022年 | 1346篇 |
2021年 | 1457篇 |
2020年 | 813篇 |
2019年 | 884篇 |
2018年 | 732篇 |
2017年 | 824篇 |
2016年 | 712篇 |
2015年 | 850篇 |
2014年 | 967篇 |
2013年 | 1170篇 |
2012年 | 1282篇 |
2011年 | 1298篇 |
2010年 | 927篇 |
2009年 | 819篇 |
2008年 | 777篇 |
2007年 | 1008篇 |
2006年 | 928篇 |
2005年 | 802篇 |
2004年 | 678篇 |
2003年 | 506篇 |
2002年 | 443篇 |
2001年 | 291篇 |
2000年 | 238篇 |
1999年 | 265篇 |
1998年 | 173篇 |
1997年 | 140篇 |
1996年 | 184篇 |
1995年 | 169篇 |
1994年 | 179篇 |
1993年 | 152篇 |
1992年 | 140篇 |
1991年 | 97篇 |
1990年 | 68篇 |
1989年 | 72篇 |
1988年 | 50篇 |
1987年 | 53篇 |
1986年 | 35篇 |
1985年 | 33篇 |
1984年 | 24篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 28篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Markland William; Pollock Daniel; Livingston David J. 《Protein engineering, design & selection : PEDS》1989,3(2):111-116
The interactions between tPA domains that are important forcatalysis are poorly understood. We have probed the functionof interdomain interactions by generating tPA variants in whichdomains are duplicated or rearranged. The proteins were expressedin a transient mammalian expression system and tested in vitrofor their ability to activate plasminogen, induce fibrinolysisand bind to a forming fibrin clot. Duplication of the heavychain domains of tPA produced enzymatically active tPA variants,many of which demonstrated similar in vitro amidolytic and fibrinolyticactivity and similar fibrin affinity to the parent molecule.Zymographic analysis of the domain duplication tPA variantsshowed one major active species for each variant. Selectionof the residues duplicated and the interdomain spacing werefound to be critical considerations in the design of tPA variantswith duplicated domains. We also rearranged the domains of tPAsuch that kringle 1 replaced the second kringle domain and viceversa. An analysis of these variants indicates that the firstkringle domain can confer fibrin affinity to a tPA variant andfunction in place of kringle 2. Therefore, in wild-type tPA,the functions of kringle 1 and kringle 2 must be dependent partiallyon their orientation within the heavy chain of the protein.The functional autonomy of the heavy and light chains of tPAis demonstrated by the activity of a tPA variant in which theorder of the heavy and light chains was reversed. 相似文献
82.
83.
D. L. Purcell B. T. McClure J. McDonald Hemendra N. Basu 《Journal of the American Oil Chemists' Society》1996,73(3):381-388
An evaluation of the exhaust emissions from a compression ignition engine for fuels composed of 100 and 30% methyl esters
of soy oil (SME) is described. These fuels were compared with a low-sulfur, petroleum #2 diesel fuel in a Caterpillar 3304,
prechamber, 75 kW diesel engine, operated over heavy- and light-duty transient test cycles developed by the United States
Bureau of Mines. More than 60 h of testing was performed on each fuel. The objective was to determine the influence of the
fuels upon diesel particulate matter (DPM) and gaseous emissions. The effect of a modern diesel oxidation catalyst (DOC) also
was determined in an effort to minimize emissions. Neat SME produced a higher volatile fraction of the DPM, but much less
carbon soot fraction, leading to overall DPM reductions of 23 to 30% for the light- and heavy-duty transients. The DOC further
reduced the volatile fraction and the total DPM. The SME fuel reduced gaseous emissions of CO by 23% and hydrocarbons by over
30% without increasing NOx. The DOC further reduced CO and hydrocarbon levels. Mutagenicity of the SME exhaust was low. Results indicate that SME fuel,
used with a proper DOC, may be a feasible emission reduction technology for underground mines.
References to specific products do not imply endorsement by the U.S. Bureau of Mines, a now defunct agency. 相似文献
84.
85.
目的获得高质量的中国流行株HIV-1B/C重组亚型包膜蛋白抗原。方法改造表达载体,以构建中国流行株HIV-1B/C重组亚型包膜蛋白基因带有筛选标记的真核细胞表达质粒,将所构建质粒转染真核细胞,用含有抗性的培养基筛选出能够高效、持续表达包膜蛋白的稳定表达细胞株。结果所构建的表达载体pVRPEnv转染细胞后可表达目的蛋白,并建立了稳定表达细胞系。结论获得了可以高效、持续稳定表达中国流行株HIV-1B/C重组亚型包膜蛋白的细胞株。 相似文献
86.
Nielsen Per F.; Roepstorff Peter; Clausen Ib G.; Jensen Ejner B.; Jonassen Ib; Svendsen Allan; Balschmidt Per; Hansen Finn B. 《Protein engineering, design & selection : PEDS》1989,2(6):449-457
Californium-252 plasma desorption mass spectrometry (PDMS) hasbeen employed for the characterization of a series of humaninsulin derivatives in order to evaluate the performance ofthis technique as an analytical tool in protein engineering.Several of the characterized modifications result in a 1 a.m.u.mass change. The precision in mass determination obtainableby PDMS analysis is not sufficient for unambiguous verificationof such modifications based on the molecular weight alone. Itis, however, possible to carry out in situ enzymatic digestionof the sample. Subsequent PDMS analysis will in most cases revealif the modification has been introduced as intended. 相似文献
87.
Bates Paul A.; McGregor Malcolm J.; Islam Suhail A.; Sattentau Quentin J.; Sternberg Michael J.E. 《Protein engineering, design & selection : PEDS》1989,3(1):13-21
A predicted three-dimensional structure of the two N-terminalextracellular domains of human CD4 antigen, a cell surface glycoprotein,is reported. This region of CD4, particularly the first domain,has been identified as containing the binding region for theenvelope gp120 protein of the human immuno-deficiency virus.The model was predicted based on the sequence homology of eachdomain with the variable light chain of immunoglobulins. Theframework ß-sheet regions were taken from the crystalcoordinates of REI. For one region in the first domain of CD4there was an ambiguity in the alignment with REI and two alternatemodels are presented. Loops connecting the framework were modeledfrom fragments selected from a database of main chain coordinatesfrom all known protein structures. Residues identified as involvedin binding gp120 have been located in several other studieswithin the first domain of CD4. Epitopes from eight monoclonalantibodies have been mapped onto residues in both domains. Competitionof these antibodies with each other and with gp120 can be interpretedfrom the structural model. 相似文献
88.
Flaking and extrusion as mechanical treatments for enzyme-assisted aqueous extraction of oil from soybeans 总被引:6,自引:7,他引:6
B. P. Lamsal P. A. Murphy L. A. Johnson 《Journal of the American Oil Chemists' Society》2006,83(11):973-979
Flaking and extruding dehulled soybeans were evaluated as a means of enhancing oil extraction efficiency during enzyme-assisted
aqueous processing of soybeans. Cellulase, protease, and their combination were evaluated for effectiveness in achieving high
oil extraction recovery from extruded flakes. Aqueous extraction of extruded full-fat soy flakes gave 68% recovery of the
total available oil without using enzymes. A 0.5% wt/wt protease treatment after flaking and extruding dehulled soybeans increased
oil extraction recovery to 88% of the total available oil. Flaking and extruding enhanced protease hydrolysis of proteins
freeing more oil. Treating extruded flakes with cellulase, however, did not enhance oil extraction either alone or in combination
with protease. Discrepancies in oil extraction recoveries were encountered when merely considering crude free fat because
some oil became bound to denatured protein during extrusion and/or sample drying. Bound fat was unavailable for determination
by using the hexane extraction method, but was accounted for by using the acid hydrolysis method for total oil determination.
Oil extraction recovery from extruded soybean flakes was affected by oil determination methods, which was not the case for
unextruded full-fat soy flour. 相似文献
89.
Germplasm with shorter duration than that of the currently grown varieties is being generated to maximize productivity of irrigated rice. However, short-duration varieties often produce yields lower than the medium- and long-duration varieties. Experiments were conducted during the 1980–82 dry and wet seasons to increase productivity through the use of very early-maturing rices and the improved management of nitrogen (N) fertilizers.Results over three years showed that IR58 and IR9729-67-3 (growth duration 100 ± 5 days) yield as well as or higher than IR36 although earlier maturing. They generally had a higher productivity (kg ha–1 day–1) than IR36 (110 ± 5 days).Three years' data suggest that the improved timing of broadcast applications of urea in split doses increased grain yield comparable with the basal incorporation of slow-release sulfur-coated urea (SCU) or deep point-placement of urea supergranules (USG).Results on elite breeding lines showed that the early-maturing IR9729-67-3 produced higher protein yield ha–1 than longer duration varieties such as IR8 and IR42 in the dry season. Furthermore, contrary to earlier results, single basal incorporation of slow-release SCU increased the protein yield of rice by 53 kg ha–1 and deep point-placement of USG by 43 kg ha–1 over split application of prilled urea. 相似文献
90.
A series of novel hydrogel polysucrose microspheres with the mean size ranging from 200 to 500 μm were prepared via two‐step method. First, soluble polysucrose was synthesized by solution polymerization between sucrose and epichlorohydrin; second, a reversed phase suspension crosslinking reaction was performed to prepare polysucrose microspheres. The SEM images indicated that these spherical beads had smooth surface and hydrogel interior structure. FTIR was used to characterize the chemical structure of the beads. The hydrated and dry densities, equilibrium water content, and hydroxyl content of polysucrose microspheres were also investigated. The characteristic of high hydroxyl content (15.48–19.04 mmol/g) make these microspheres suitable for protein adsorption. Meanwhile, bovine serum albumin was used to examine the adsorption capacity of the microspheres. These microspheres had a capacity as high as 49.28 mg/g. The adsorption kinetics and recycling of the beads were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5934–5940, 2006 相似文献