全文获取类型
收费全文 | 14138篇 |
免费 | 33篇 |
国内免费 | 66篇 |
专业分类
系统科学 | 76篇 |
丛书文集 | 82篇 |
教育与普及 | 41篇 |
理论与方法论 | 78篇 |
现状及发展 | 5398篇 |
研究方法 | 832篇 |
综合类 | 7482篇 |
自然研究 | 248篇 |
出版年
2013年 | 138篇 |
2012年 | 344篇 |
2011年 | 625篇 |
2010年 | 151篇 |
2009年 | 69篇 |
2008年 | 389篇 |
2007年 | 427篇 |
2006年 | 393篇 |
2005年 | 440篇 |
2004年 | 433篇 |
2003年 | 384篇 |
2002年 | 423篇 |
2001年 | 383篇 |
2000年 | 379篇 |
1999年 | 274篇 |
1992年 | 237篇 |
1991年 | 182篇 |
1990年 | 208篇 |
1989年 | 196篇 |
1988年 | 201篇 |
1987年 | 206篇 |
1986年 | 163篇 |
1985年 | 251篇 |
1984年 | 173篇 |
1983年 | 158篇 |
1982年 | 176篇 |
1981年 | 145篇 |
1980年 | 174篇 |
1979年 | 398篇 |
1978年 | 301篇 |
1977年 | 295篇 |
1976年 | 251篇 |
1975年 | 289篇 |
1974年 | 314篇 |
1973年 | 315篇 |
1972年 | 346篇 |
1971年 | 349篇 |
1970年 | 432篇 |
1969年 | 363篇 |
1968年 | 383篇 |
1967年 | 356篇 |
1966年 | 319篇 |
1965年 | 205篇 |
1959年 | 107篇 |
1958年 | 204篇 |
1957年 | 137篇 |
1956年 | 122篇 |
1955年 | 105篇 |
1954年 | 82篇 |
1948年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
K K Leong K M Yu W B Lee 《厦门大学学报(自然科学版)》2002,(Z1)
Product data management (PDM) has been accepted as an important tool for the manufacturing industries. In recent years, more and mor e researches have been conducted in the development of PDM. Their research area s include system design, integration of object-oriented technology, data distri bution, collaborative and distributed manufacturing working environment, secur ity, and web-based integration. However, there are limitations on their rese arches. In particular, they cannot cater for PDM in dis... 相似文献
22.
Chromosomal effects of adeno-associated virus vector integration. 总被引:17,自引:0,他引:17
Adeno-associated virus (AAV) vectors are currently being used in several clinical gene-therapy trials (see the NIH OBA Human Gene Transfer Clinical Trials Database); however, little is known about the chromosomal effects of vector integration. Here we report that integrated vector proviruses are associated with chromosomal deletions and other rearrangements and are frequently located on chromosome 19 (although not at the wildtype AAV integration site). 相似文献
23.
During the evolution of proteins the pressure to optimize biological activity is moderated by a need for efficient folding. For most proteins, this is accomplished through spontaneous folding to a thermodynamically stable and active native state. However, in the extracellular bacterial alpha-lytic protease (alphaLP) these two processes have become decoupled. The native state of alphaLP is thermodynamically unstable, and when denatured, requires millennia (t1/2 approximately 1,800 years) to refold. Folding is made possible by an attached folding catalyst, the pro-region, which is degraded on completion of folding, leaving alphaLP trapped in its native state by a large kinetic unfolding barrier (t1/2 approximately 1.2 years). alphaLP faces two very different folding landscapes: one in the presence of the pro-region controlling folding, and one in its absence restricting unfolding. Here we demonstrate that this separation of folding and unfolding pathways has removed constraints placed on the folding of thermodynamically stable proteins, and allowed the evolution of a native state having markedly reduced dynamic fluctuations. This, in turn, has led to a significant extension of the functional lifetime of alphaLP by the optimal suppression of proteolytic sensitivity. 相似文献
24.
D Ashall B Parkinson 《厦门大学学报(自然科学版)》2002,(Z1)
Background: During the last fifteen years there ha s been an increased drive for organisations to reduce costs. From a production po int, this has often centred on lean manufacturing and JIT waste elimination proc esses. However, in 1991, the Iaccocca Institute Bethlehem P.A commissioned a re port specifically to analyse the changing nature of the marketplace. As a result , in the following year, the Agile Manufacturing Forum was initiated and the ter m ‘agile or responsive manufacturing‘ was first intr... 相似文献
25.
26.
Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition 总被引:2,自引:0,他引:2
K. Brune W. S. Beck G. Geisslinger S. Menzel-Soglowek B. M. Peskar B. A. Peskar 《Cellular and molecular life sciences : CMLS》1991,47(3):257-261
Summary Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics. 相似文献
27.
28.
FROM MANUFACTURING SCHEDULING TO SUPPLY CHAIN COORDINATION:THE CONTROL OF COMPLEXITY AND UNCERTAINTY
Peter B.LUH 《系统科学与系统工程学报(英文版)》2003,12(3):279-297
With time-based competition and rapid technology advancements, effective manufacturingscheduling and supply chain coordination are critical to quickly respond to changing marketconditions. These problems, however, are difficult in view of inherent complexity and variousuncertainties involved. Based on a series of results by the authors, decomposition and coordination byusing Lagrangian relaxation is identified in this paper as an effective way to control complexity anduncertainty.A manufacturing scheduling problem is first formulated within the job shop context withuncertain order arrivals, processing times, due dates, and part priorities as a separable optimizationproblem. A solution methodology that combines Lagrangian relaxation, stochastic dynamicprogramming, and heuristics is developed. Method improvements to effectively solve large problemsare also highlighted. To extend manufacturing scheduling within a factory to coordinate autonomicmembers across chains of suppliers, a decentralized supply chai 相似文献
29.
M E MacDonald A Novelletto C Lin D Tagle G Barnes G Bates S Taylor B Allitto M Altherr R Myers 《Nature genetics》1992,1(2):99-103
Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180. 相似文献