全文获取类型
收费全文 | 264100篇 |
免费 | 3824篇 |
国内免费 | 857篇 |
专业分类
电工技术 | 5223篇 |
综合类 | 349篇 |
化学工业 | 37030篇 |
金属工艺 | 10345篇 |
机械仪表 | 8610篇 |
建筑科学 | 6378篇 |
矿业工程 | 1078篇 |
能源动力 | 6524篇 |
轻工业 | 22853篇 |
水利工程 | 2579篇 |
石油天然气 | 3906篇 |
武器工业 | 71篇 |
无线电 | 35961篇 |
一般工业技术 | 50972篇 |
冶金工业 | 47560篇 |
原子能技术 | 5444篇 |
自动化技术 | 23898篇 |
出版年
2021年 | 2096篇 |
2019年 | 2098篇 |
2018年 | 3565篇 |
2017年 | 3609篇 |
2016年 | 3852篇 |
2015年 | 2427篇 |
2014年 | 4173篇 |
2013年 | 11587篇 |
2012年 | 6849篇 |
2011年 | 9176篇 |
2010年 | 7207篇 |
2009年 | 8132篇 |
2008年 | 8976篇 |
2007年 | 8899篇 |
2006年 | 8084篇 |
2005年 | 7372篇 |
2004年 | 7063篇 |
2003年 | 6916篇 |
2002年 | 6515篇 |
2001年 | 6616篇 |
2000年 | 6313篇 |
1999年 | 6423篇 |
1998年 | 14668篇 |
1997年 | 10518篇 |
1996年 | 8297篇 |
1995年 | 6512篇 |
1994年 | 5754篇 |
1993年 | 5652篇 |
1992年 | 4552篇 |
1991年 | 4207篇 |
1990年 | 4061篇 |
1989年 | 3775篇 |
1988年 | 3617篇 |
1987年 | 3161篇 |
1986年 | 3063篇 |
1985年 | 3616篇 |
1984年 | 3362篇 |
1983年 | 2999篇 |
1982年 | 2844篇 |
1981年 | 2938篇 |
1980年 | 2755篇 |
1979年 | 2639篇 |
1978年 | 2490篇 |
1977年 | 2930篇 |
1976年 | 3561篇 |
1975年 | 2315篇 |
1974年 | 2307篇 |
1973年 | 2300篇 |
1972年 | 1851篇 |
1971年 | 1722篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
991.
992.
We first performed autogenous bone grafting for lesions of the hallux sesamoid in 1984. During the next 9 years, 21 patients (11 men and 10 women with an average age of 34 and 32 years, respectively) underwent this surgical procedure for symptomatic tibial hallux sesamoid non-unions. Successful bony union was achieved in all but two patients. The majority of patients obtained concomitant relief of preoperative symptomatology and returned to their preinjury level of activity. We believe that this procedure serves as an alternative to hallux sesamoid excision in selected cases. 相似文献
993.
Emulsifiers are an uncommon cause of allergic contact dermatitis. Five cases of allergic contact dermatitis to cetostearyl alcohol are presented. In all five cases, multiple positive reactions to other allergens were present, usually topical corticosteroid creams. 相似文献
994.
A genetic algorithm for multiple molecular sequence alignment 总被引:1,自引:0,他引:1
MOTIVATION: Multiple molecular sequence alignment is among the most important and most challenging tasks in computational biology. The currently used alignment techniques are characterized by great computational complexity, which prevents their wider use. This research is aimed at developing a new technique for efficient multiple sequence alignment. APPROACH: The new method is based on genetic algorithms. Genetic algorithms are stochastic approaches for efficient and robust searching. By converting biomolecular sequence alignment into a problem of searching for optimal or near-optimal points in an 'alignment space', a genetic algorithm can be used to find good alignments very efficiently. RESULTS: Experiments on real data sets have shown that the average computing time of this technique may be two or three orders lower than that of a technique based on pairwise dynamic programming, while the alignment qualities are very similar. AVAILABILITY: A C program on UNIX has been written to implement the technique. It is available on request from the authors. 相似文献
995.
996.
Bez R. Cantarelli D. Moioli L. Ortolani G. Servalli G. Villa C. Dallabora M. 《Electron Device Letters, IEEE》1998,19(2):37-39
A new method to erase a standard (double-poly, stacked-gate NOR-type) flash cell is proposed. The method, still using the tunneling mechanism to extract electrons from the floating gate, is based on the concept of keeping the electric field constant during the whole erasing operation. The new method has two main advantages with respect to the conventional one: (1) it does not depend on the supply voltage variation and (2) it allows a better reliability in terms of endurance-induced stress. Results have shown that flash device performances are greatly improved in terms of stability and endurance reliability up to one million cycles 相似文献
997.
Kang W.P. Wisitsora-at A. Davidson J.L. Kerns D.V. 《Electron Device Letters, IEEE》1998,19(10):379-381
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters 相似文献
998.
D. Dietrich ÖVE H. Reiter Th. Sauter H. -J. Schweinzer 《e & i Elektrotechnik und Informationstechnik》1997,114(5):225-230
The past decade may be regarded as the phase of the fundamental developments in fieldbus systems that were based on the OSI model. Today we are entering a second stage. It is the objective of this issue to present the current state and where the further developments will lead to. This introductory article is intended to give an overview on the subject. 相似文献
999.
The admixture test (A-test) is a popular method for the analysis of linkage data when locus heterogeneity is suspected. It can be applied on pairwise linkage data, multipoint data and even for the simultaneous analysis of data from multiple dispersed candidate regions. However, very little is known about the conditions for the use of the method under these divergent circumstances. By performing analytical evaluations, we demonstrate that the A-test is inconsistent if there is a relationship between the phenotype and the probability of being linked. Biased estimates of the recombination fraction (theta) and the proportion of linked families (alpha) may occur if the actual frequency of linked families is not identical among small and large families. We conclude that the A-test should be used with caution if the phenotype and the probability of developing the phenotype at a certain age cannot be shown to be equal for family members of linked and unlinked families. If dissimilarities in family size cannot be ruled out, the extent of bias should be considered and size specific alpha-values should be used in risk calculations. 相似文献
1000.
D Cullinan F Johnson AP Grollman M Eisenberg C de los Santos 《Canadian Metallurgical Quarterly》1997,36(39):11933-11943
Vinyl chloride reacts with cellular DNA producing 3,N4-etheno-2'-deoxycytidine (epsilonC) along with other exocyclic adducts. The solution structure of an oligodeoxynucleotide duplex containing an epsilonC.dG base pair was determined by high-resolution NMR spectroscopy and molecular dynamics simulations. NMR data indicated that the duplex adopts a right-handed helical structure having all residues in anti orientation around the glycosylic torsion angle. The epsilonC adduct has a sugar pucker in the C3'-endo/C4'-exo region while the rest of the residues are in the C2'-endo/C3'-exo range. NOE interactions established Watson-Crick alignments for canonical base pairs of the duplex. The imino proton of the lesion-containing base pair resonated as a sharp signal that was resistant to water exchange, suggesting hydrogen bonding. Restrained molecular dynamics simulations generated three-dimensional models in excellent agreement with the spectroscopic data. The refined structures are slightly bent at the lesion site without major perturbations of the sugar-phosphate backbone. The adduct is displaced and shifted toward the major groove of the helix while its partner on the complementary strand remains stacked. The epsilonC(anti).dG(anti) base pair alignment is sheared and stabilized by the formation of hydrogen bonds. The biological implications of structures of epsilonC-containing DNA duplexes are discussed. 相似文献