全文获取类型
收费全文 | 4502篇 |
免费 | 144篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 68篇 |
综合类 | 29篇 |
化学工业 | 1350篇 |
金属工艺 | 109篇 |
机械仪表 | 85篇 |
建筑科学 | 272篇 |
矿业工程 | 14篇 |
能源动力 | 89篇 |
轻工业 | 352篇 |
水利工程 | 25篇 |
石油天然气 | 2篇 |
无线电 | 260篇 |
一般工业技术 | 832篇 |
冶金工业 | 628篇 |
原子能技术 | 39篇 |
自动化技术 | 502篇 |
出版年
2022年 | 49篇 |
2021年 | 61篇 |
2020年 | 48篇 |
2019年 | 60篇 |
2018年 | 65篇 |
2017年 | 55篇 |
2016年 | 99篇 |
2015年 | 85篇 |
2014年 | 114篇 |
2013年 | 214篇 |
2012年 | 177篇 |
2011年 | 258篇 |
2010年 | 192篇 |
2009年 | 171篇 |
2008年 | 204篇 |
2007年 | 187篇 |
2006年 | 138篇 |
2005年 | 160篇 |
2004年 | 137篇 |
2003年 | 107篇 |
2002年 | 88篇 |
2001年 | 86篇 |
2000年 | 86篇 |
1999年 | 88篇 |
1998年 | 119篇 |
1997年 | 92篇 |
1996年 | 74篇 |
1995年 | 80篇 |
1994年 | 71篇 |
1993年 | 75篇 |
1992年 | 70篇 |
1991年 | 49篇 |
1990年 | 74篇 |
1989年 | 47篇 |
1988年 | 45篇 |
1987年 | 56篇 |
1986年 | 42篇 |
1985年 | 60篇 |
1984年 | 54篇 |
1983年 | 47篇 |
1982年 | 53篇 |
1981年 | 45篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 66篇 |
1976年 | 44篇 |
1975年 | 42篇 |
1974年 | 56篇 |
1972年 | 41篇 |
1970年 | 40篇 |
排序方式: 共有4656条查询结果,搜索用时 0 毫秒
1.
Leibetseder Andreas Schoeffmann Klaus Keckstein Jörg Keckstein Simon 《Multimedia Tools and Applications》2022,81(5):6191-6215
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized... 相似文献
2.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
3.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
4.
Separation tests using hollow-fibre modules were performed for the difficult selective extraction of trivalent actinides over fission lanthanides from acidic media. This article shows that with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant, up to 94% americium could be extracted from 1.0 kmol/m3 HNO3, with minimal lanthanide co-extraction. Using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tri-n-octyl phosphine oxide, tests were performed on extraction, lanthanide scrubbing and stripping. In the extraction test, up to 99.99% americium could be extracted from 0.5 kmol/m3 HNO3, with approximately one third of the lanthanides being co-extracted. Mass transfer calculations using a consistent set of input data showed good agreement with the experiments. 相似文献
5.
6.
Pyrolysis experiments were performed in high vacuum and under reduced air pressure (100 Pa). The volatile products of pure cellulose and cellulose containing various amounts of flame retardant 2,2′-oxybis (5,5-dimethyl-1,3,2-dioxaphosphorinane-2,2′-disulfide), i.e., Sandoflam 5060 of Sandoz AG, were studied by means of gas chromatography in combination with mass spectroscopy. The volatile products were characterized with infrared spectroscopy. The studied revealed that the incorporation of the flame retardant enhanced the water release and shifted the onset of this reaction to lower temperature. On the basis of these findings an explanation for the mechanism of flame retardancy in generated cellulose fibers modified with this particular flame retardant is attempted. From experiments with different residual air pressure the influence of oxygen on the primary processes of the pyrolytic degradation of cellulose is being discussed. 相似文献
7.
The multi-homogeneous Bezout number is a bound for the number of solutions of a system of multi-homogeneous polynomial equations,
in a suitable product of projective spaces. Given an arbitrary, not necessarily multi-homogeneous, system, one can ask for
the optimal multi-homogenization that would minimize the Bezout number. In this paper it is proved that the problem of computing,
or even estimating, the optimal multi-homogeneous Bezout number is actually NP-hard. In terms of approximation theory for
combinatorial optimization, the problem of computing the best multi-homogeneous structure does not belong to APX, unless P
= NP. Moreover, polynomial-time algorithms for estimating the minimal multi-homogeneous Bezout number up to a fixed factor
cannot exist even in a randomized setting, unless BPP ⫆ NP. 相似文献
8.
The price of SO2 permits and the volume of trading under the US Acid Rain Program have been lower than expected. This can be explained by the creation and distribution of more permits than were initially authorized, by the sale of permits by high cost abaters who are subject to more stringent local emission constraints or who have irreversibly invested in high cost abatement technologies and by the deregulation of the natural gas and railroad industries which, in combination with incentives for cost-cutting under the new market approach to SO2 control, has lowered marginal costs of abatement curves and made them more uniform across powerplants. The low price of permits and low trading volume are evidence that market approaches to pollution control can be more cost-effective than command and control regulations. The effect of public policies and technological changes on the allowance market are usefully examined in the context of an ideal market, in which the equilibrium price of allowances equals the marginal cost of abatement of individual powerplants. Using recent data from Coggins and Swinton (1996), we are able to explain the current price of permits with some accuracy. 相似文献
9.
The authors present the construction, operation, and test results of a new type of electrostatic filter of very low pressure drop at usual flow-through velocities while providing excellent filtration for micron-size particles. The filter is constructed in the form of a thick mesh of dual wire fibers, electrically energized at approximately 200 V DC, and reversing the polarity at a very low frequency in the order of 5 mHz. While, in general, mechanical filters trap the particles on the air incoming surface, with subsequent rapid “blinding,” the new filter collects the particles inside the mesh volume thus offering a considerably longer life 相似文献
10.
Klaus Bauckhage 《化学,工程师,技术》1993,65(10):1200-1205
Utilisation of Different Components of Scattered Light for Particle Size Determination in Dispersed Systems . Light scattered by finely and coarsely dispersed particles can be used in variety of ways for characterization of sprays, emulsions, or suspensions. The characteristic of greatest interest is the particle size or the particle size distribution. While homogeneous, coarsely dispersed particles at sufficient dilutions and randomly distributed in a transparent continuous phase are generally amenable to particle size analysis, finely dispersed particles at higher concentrations or coarsely dispersed particles containing finely dispersed components are often difficult to measure. This article discusses ways of overcoming such difficulties on the basis of examples taken mainly from phase Doppler anemometry. 相似文献