全文获取类型
收费全文 | 24616篇 |
免费 | 1035篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 329篇 |
综合类 | 38篇 |
化学工业 | 5655篇 |
金属工艺 | 380篇 |
机械仪表 | 476篇 |
建筑科学 | 1307篇 |
矿业工程 | 100篇 |
能源动力 | 621篇 |
轻工业 | 1888篇 |
水利工程 | 233篇 |
石油天然气 | 71篇 |
无线电 | 1817篇 |
一般工业技术 | 4503篇 |
冶金工业 | 4531篇 |
原子能技术 | 196篇 |
自动化技术 | 3539篇 |
出版年
2023年 | 214篇 |
2022年 | 359篇 |
2021年 | 566篇 |
2020年 | 338篇 |
2019年 | 431篇 |
2018年 | 535篇 |
2017年 | 463篇 |
2016年 | 632篇 |
2015年 | 558篇 |
2014年 | 749篇 |
2013年 | 1419篇 |
2012年 | 1161篇 |
2011年 | 1510篇 |
2010年 | 1075篇 |
2009年 | 1014篇 |
2008年 | 1147篇 |
2007年 | 1085篇 |
2006年 | 944篇 |
2005年 | 761篇 |
2004年 | 745篇 |
2003年 | 659篇 |
2002年 | 563篇 |
2001年 | 428篇 |
2000年 | 362篇 |
1999年 | 402篇 |
1998年 | 752篇 |
1997年 | 553篇 |
1996年 | 442篇 |
1995年 | 411篇 |
1994年 | 377篇 |
1993年 | 362篇 |
1992年 | 269篇 |
1991年 | 195篇 |
1990年 | 268篇 |
1989年 | 260篇 |
1988年 | 215篇 |
1987年 | 224篇 |
1986年 | 226篇 |
1985年 | 265篇 |
1984年 | 224篇 |
1983年 | 223篇 |
1982年 | 207篇 |
1981年 | 194篇 |
1980年 | 168篇 |
1979年 | 193篇 |
1978年 | 164篇 |
1977年 | 185篇 |
1976年 | 231篇 |
1975年 | 160篇 |
1974年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
41.
42.
The expression patterns of laminin A, B1, B2, and nidogen genes were identified by in situ hybridization in postimplantation mouse extraembryonic tissues and maternal decidua during the period when the chorioallantoic placenta is established. Laminin and nidogen genes were not coordinately expressed either in the decidua or in trophoblast cells, indicating that these genes are regulated independently in these cell types during the establishment of the placenta. Laminin A mRNA was absent from the decidua except in the outer layer of cells adjacent to the myometrium and in the central decidual zone adjacent to the remnant of the uterine epithelium on Day 9. At this stage laminin B1, B2, and nidogen genes were strongly expressed in these cells and also in other regions of the decidua. Laminin B1 mRNA was present at higher levels in the decidua capsularis than in the decidua basalis, while nidogen mRNA showed highest expression in the decidua basalis. Laminin B2 mRNA was produced uniformly throughout the decidua at very high levels, suggesting that laminin B2 chains may be an important component of the decidual matrix. By Day 11, the nidogen gene was expressed only in endothelial cells lining the maternal blood spaces within the decidua. Laminin B1 and nidogen mRNAs were found at high levels within trophoblast giant cells at all stages, while laminin A mRNA was detected in trophoblast giant cells at later stages and laminin B2 mRNA was not produced in high levels by these cells. The patterns of gene expression show a very high degree of regional specialization, suggesting that the extracellular matrices in different regions of the decidua and extraembryonic membranes are likely to be composed of quite different ratios of laminin and nidogen polypeptides.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
43.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
44.
45.
Mass transport in pulsating flow devices using either moving boundaries or oscillating imposed pressure drops are compared with each other by means of a calculation using a simple model. We conclude that there is no difference between the two configurations as long as one is interested only in the power required to move the fluid for the convective mass transport achieved. However, the boundary driven configuration is more efficient if the power is divided by the total mass transport where both the diffusive and convective parts are taken into account, the boundary driven configuration is more efficient. The amplitude of the piston stroke in the pressure driven configuration and the amplitude in the boundary driven case are assumed to be the same, and the inertia of the moving devices themselves are ignored in this calculation. 相似文献
46.
47.
Thomas Amend Hans-Dieter Belitz 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1989,189(2):103-109
Summary Wheat flour particles sprinkled on a water surface form strands which are visible in the light microscope. These strands form aggregates by means of mechanical forces which show viscoelastic behaviour. Amino acid analysis of both the protein strands and the aggregates formed shows that they consist of gluten protein. The formation of the protein strands occurs at the air/water interface and results from the action of a protein film which spreads around the flour particles.
Mikroskopische Untersuchungen von Mehl/Wasser-Systemen
Zusammenfassung Weizenmehlpartikel, die auf Wasser gestreut werden, bilden lichtmikroskopisch sichtbare Stränge aus. Durch mechanische Beanspruchung lassen sich these Stränge zu Aggregaten zusammenfassen, die visco-elastisches Verhalten zeigen. Die Aminosäureanalyse sowohl der Proteinstrange wie auch der daraus gebildeten Aggregate zeigt, daß es sich dabei um Kleberprotein handelt. Die Proteinfäden entstehen an der Wasser-Luft-Grenzflache als Folge eines spreitenden Proteinfilms, der sich um die Mehlpartikel herum ausbreitet.相似文献
48.
Dr. jur. Thomas Sassenberg Assessor Niclas Bamberg 《Datenschutz und Datensicherheit - DuD》2006,30(4):226-229
Ob Betriebsvereinbarungen im Sinne des § 4 Abs. 1 BDSG eine „andere Rechtsvorschrift” sind und damit die Regelungen des BDSG
einschr?nken dürfen, geh?rt zu den Standardfragen des praktischen Arbeitnehmerdatenschutzes. Die Autoren befürworten eine
weite betriebliche Regelungskompetenz, beschr?nken diese aber zum Schutz der Arbeitnehmer durch eine Reihe datenschutzrechtlicher
Mindestanforderungen, die Betriebsvereinbarungen einzuhalten haben. 相似文献
49.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
50.