全文获取类型
收费全文 | 2047篇 |
免费 | 4篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 169篇 |
金属工艺 | 3篇 |
机械仪表 | 14篇 |
建筑科学 | 18篇 |
能源动力 | 6篇 |
轻工业 | 41篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 18篇 |
一般工业技术 | 50篇 |
冶金工业 | 1683篇 |
原子能技术 | 3篇 |
自动化技术 | 34篇 |
出版年
2018年 | 3篇 |
2017年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 29篇 |
2012年 | 12篇 |
2011年 | 7篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 6篇 |
2007年 | 15篇 |
2006年 | 18篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 74篇 |
1998年 | 509篇 |
1997年 | 280篇 |
1996年 | 200篇 |
1995年 | 106篇 |
1994年 | 92篇 |
1993年 | 118篇 |
1992年 | 16篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 35篇 |
1988年 | 28篇 |
1987年 | 31篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 46篇 |
1976年 | 129篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有2051条查询结果,搜索用时 31 毫秒
51.
A Nighorn NJ Gibson DM Rivers JG Hildebrand DB Morton 《Canadian Metallurgical Quarterly》1998,18(18):7244-7255
The nitric oxide (NO)-cGMP signaling system is thought to play important roles in the function of the olfactory system in both vertebrates and invertebrates. One way of studying the role of NO in the nervous system is to study the distribution and properties of NO synthase (NOS), as well as the soluble guanylyl cyclases (sGCs), which are the best characterized targets of NO. We study NOS and sGC in the relatively simple and well characterized insect olfactory system of the hawkmoth, Manduca sexta. We have cloned Manduca sexta nitric oxide synthase (MsNOS) and two sGCs (MsGCalpha1 and MsGCbeta1), characterized their basic biochemical properties, and studied their expression in the olfactory system. The sequences of the Manduca genes are highly similar to their mammalian homologs and show similar biochemical properties when expressed in COS-7 cells. In particular, we find that MsGC functions as an obligate heterodimer that is stimulated significantly by NO. We also find that MsNOS has a Ca2+-sensitive NO-producing activity similar to that of mammalian neuronal NOS. Northern and in situ hybridization analyses show that MsNOS and the MsGCs are expressed in a complementary pattern, with MsNOS expressed at high levels in the antennae and the MsGCs expressed at high levels in a subset of antennal lobe neurons. The expression patterns of these genes suggest that the NO-sGC signaling system may play a role in mediating communication between olfactory receptor neurons and projection neurons in the glomeruli of the antennal lobe. 相似文献
52.
MS McNeill DB Griffin TR Dockerty JP Walter HK Johnson JW Savell 《Canadian Metallurgical Quarterly》1998,76(6):1613-1620
Twenty-nine selected styles of subprimals or sections of veal were obtained from a commercial facility to assist in the development of a support program for retailers. They were fabricated into bone-in or boneless retail cuts and associated components by trained meat cutters. Each style selected (n = 6) was used to generate mean retail yields and labor requirements, which were calculated from wholesale and retail weights and processing times. Means and standard errors for veal ribs consisting of five different styles (n = 30) concluded that style #2, 7-rib 4 (10 cm) x 4 (10 cm), had the lowest percentage of total retail yield (P < .05) owing to the greatest percentage of bone. Furthermore, rib style #2 required the longest total processing time (P < .05). Rib styles #3, 7-rib chop-ready, and #5, 6-rib chop ready, yielded the greatest percentage of total retail yield and also had the shortest total processing time (P < .05). Within veal loins, style #2, 4 (10 cm) x 4 (10 cm) loin kidney fat in, had the greatest percentage fat (P < .05). Loin styles #2 and #3, 4 (10 cm) x 4 (10 cm) loin special trimmed, generated more lean and fat trimmings and bone, resulting in lower percentage of total retail yields than loin style #1, 0 (0 cm) x 1 (2.5 cm) loin special trimmed (P < .05). Results indicated that bone-in subprimals and sections required more processing time if fabricated into a boneless end point. In addition, as the number of different retail cuts increased, processing times also increased. 相似文献
53.
TH Kim WC Bowen DB Stolz D Runge WM Mars GK Michalopoulos 《Canadian Metallurgical Quarterly》1998,244(1):93-104
The present study has examined the distribution of axons of differing sizes in the optic pathway of the ground squirrel. Axon diameters were measured from electron micrographs at various locations across sections of the optic nerve and tract, and total distributions and numbers were estimated. In both the nerve and tract, roughly 1.2 million optic axons were present. The population of optic axons had a unimodal size distribution, peaking at 0.9 microm in diameter and having an extended tail toward larger diameters. Local axon diameter distributions in the optic tract indicated distinct (though partially overlapping) axon diameter classes, including one of fine sizes peaking at 0.8-0.9 microm, a second of medium sizes peaking around 1.7-1.8 microm, and a third composed of the larger fibers with diameters up to 4.8 microm. The fine-caliber axons were found at all locations in the tract, and were the only axons present immediately adjacent to the pia, while the medium- and coarse-caliber axons were found at deeper locations. Curiously, the larger axons were found primarily in the medial parts of the tract, where axons from the dorsal retina normally course. A similarly restricted distribution of the larger axons was observed in the dorsotemporal parts of the optic nerve, suggesting that this difference in the tract may relate to an asymmetric distribution of ganglion cells on the retina giving rise to these axons. Measurements of axonal size taken within the optic fiber layer in dorsal and ventral parts of the retina confirmed this asymmetry, consistent with previous demonstrations of soma size differences in the dorsal versus ventral retina. The partial segregation of axons by size in the optic tract of the ground squirrel then reflects both the asymmetric distribution of retinal ganglion cell classes and the chronotopic reordering of optic axons that occurs within the chiasmatic region. 相似文献
54.
On the recognition of printed characters of any font and size 总被引:2,自引:0,他引:2
Kahan S Pavlidis T Baird HS 《IEEE transactions on pattern analysis and machine intelligence》1987,(2):274-288
We describe the current state of a system that recognizes printed text of various fonts and sizes for the Roman alphabet. The system combines several techniques in order to improve the overall recognition rate. Thinning and shape extraction are performed directly on a graph of the run-length encoding of a binary image. The resulting strokes and other shapes are mapped, using a shape-clustering approach, into binary features which are then fed into a statistical Bayesian classifier. Large-scale trials have shown better than 97 percent top choice correct performance on mixtures of six dissimilar fonts, and over 99 percent on most single fonts, over a range of point sizes. Certain remaining confusion classes are disambiguated through contour analysis, and characters suspected of being merged are broken and reclassified. Finally, layout and linguistic context are applied. The results are illustrated by sample pages. 相似文献
55.
56.
Vortex rings have been formed in water by impulsive flow through an orifice, and mixing effects due to the lings have been measured. Laboratory tests on the mixing of stratified layers of salt solution by vortex rings formed at a 6.35 cm diameter orifice have indicated that Froude number is an important factor in determining the energy efficiency of mixing. Field tests using a 25.4 cm orifice in Hamilton Harbour (18 m depth of water) have shown a small mixing effect. Further experiments with a 25.4 cm orifice in a test tank have shown that the vortex rings have a range of at least 30 m. 相似文献
57.
58.
The influence of dyebath pH, dyeing time, levelling agents, dyestuff and anti-setting agent on hygral expansion has been investigated. The incorporation of an anti-setting agent in the dyebath minimised increases in hygral expansion resulting from the dyeing process. 相似文献
59.
This paper is concerned with the flow behavior of isotropic solutions of the rod-like polymer, poly(p-phenyleneterephthalamide) (PPT), in 100 percent sulfuric acid. Studies include entry flow visualization in a slit die and solution fracture, and die swell in capillaries and a slit die. It was observed that solutions of PPT exhibit nearly negligible die swell, a slip-stick type of fracture that disappears at high shear rates, and radial entry flow patterns similar to Newtonian fluids. Fracture was associated with the plateau in the shear stress vs shear rate curve. Because values of the wall shear stress (τw.) obtained from capillary measurements were in good agreement with those obtained from a cone-and-plate rheometer and values of the loss modulus (G″) obtained from small-strain dynamic oscillatory measurements, it is believed that the rheological properties lead to the flow instability. These results are in agreement with the predictions of a recent theory by Doi and Edwards for concentrated solutions of rod-like molecules. Data are also presented for a flexible chain polyamide, nylon 6,6, in 100 percent H2SO4 for the purpose of comparing the flow characteristics of rigid and flexible chain polymers. 相似文献
60.
An apparatus for investigating pulsed turbulent liquid flow in a 2 in. diameter, 80 ft. pipeline is described. The pulsation unit was powered by compressed air with a consumption of up to 2.7 std. cu.ft./min. at 35 lb/in2 gauge. The pressure drop for water flowing at mean velocities of 7.66 to 12.28 ft./sec. has been measured, both for steady flow and for pulsed flow, at frequencies between 0.48 and 0.82 Hz. The experimentally measured pressure versus time curves for pulsed flow can be matched fairly closely by a solution of Euler's equation employing the friction factors measured under steady flow conditions. 相似文献